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Topic: Voltage drop for AC whats acceptable?

Posted By: Our Place on 07/18/12 05:16pm

Plugged into 30amp post and getting a voltage of 120.7 on digital voltmeter. Voltage inside camper is at 118.2 with nothing running but the converter. When i turn on the AC and the compressor kicks on the voltage drops to 105.8 and floats between 105.8 and 106.5. I have been telling my dealer that the AC unit has been acting up but they keep blaiming the campgroung for low voltage. I get simalar results at home but there i'm using a 30 to 15 adaptor but i'm on a single 20amp branch and not using any extension cords. Is this the campground or the compressor going bad?? Its a Dometic 15000btu roof top unit and the camper is a 2011 running on 30 amps.


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Posted By: ktmrfs on 07/18/12 05:32pm

Most appliances designed for U.S./canadian markets are designed to operate reliably from 105VAC to 130V AC. Nominal voltage is usually considered 115V. West Coast grid line voltage tends to be higher than the east coast grid line voltage.

your reading 106V under load, question is how accurate is the meter. a cheap digital meter may not even be RMS responding but peak responding RMS calibrated so a distorted sine wave will give erroneous results. And most inexpensive AC meters are not real accurate, +/-10% is common, even quality ones are in the 1-2% range unless your into an industrial quality meter. And where are you reading the voltage?? at a wall outlet or directly at the compressor input (unlikely) If it's 106 at a wall outlet, it may be down even a few more volts at the compressor and your likely under the 105V lower limit at which point the motor can get hot from excessive current draw.

my conclusion is your voltage is marginal, but can't say that is the cause of the AC problems or not.


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Posted By: Ivylog on 07/18/12 05:53pm

My coach shuts down the power when it gets below 109 volts to protect itself. Someone smarter than me felt that was as low as the voltage should go. Campground has a problem.


This post is my opinion (free advice). It is not intended to influence anyone's judgment nor do I advocate anyone do what I propose.
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Posted By: Our Place on 07/18/12 05:56pm

Looks like the problem IS the campground! I went and got my 3500 genset and I know it works so i tried it and guess what, it does! I'm getting 121.2 running with only the converter using power and when the AC kicks on the voltage actualy goes up to 122.7. I'm using a Fluke 29 sries meter and the camper has a analog meter inside. I got a AMP probe meter comming tomarrow and i'm going to see exactly how many amps the AC is pulling. I would think that if it was pulling alot it would trip breakers in the camper? Still testing.....


Posted By: enblethen on 07/18/12 06:02pm

That is a lot of voltage drop. I would be concerned about a loose connection within the system. 10 per cent is within range but you are outside that.
Where are you reading the 105.8 volts? If this is inside the rig then it would be lower at the AC unit.
It could be a loose connection between the 120 volt AC distribution panel and the air conditioner. It could be one of the internal power connectors in the ac units lower control unit on the ceiling in the rig.
If the rig is under warranty I would try to get it looked at by the dealer.


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Posted By: Big Katuna on 07/18/12 06:09pm

108 is the MINIMUM allowable voltage. I would turn off the AC before I would run anything lower than that. The voltage at the ac is probably a little lower than at the wall due to copper losses. Also, measure at the the pedestal at the 15A recep; the problem may be YOUR 30A plug. They get hot and wear out. I recommend getting a 50A to 30SA adapter. You will usually puick up a few volts and a more robust recep by doing so.


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Posted By: Wayne Dohnal on 07/18/12 06:43pm

The manufacturer specs are 115 volts +/- 10%, allowing operation down to 103.5 . The rub is that it's 103.5 at the air conditioner, where it's not very easy to measure. With an accurate meter I'd call the bottom limit as 105 measured on a different circuit inside the RV, allowing for the air conditioner circuit to drop another 1.5 volts. As you can see, everybody seems to have a different opinion on this.


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Posted By: time2roll on 07/18/12 07:31pm

You are a good cadidate for a voltage booster

http://www.powermasterrv.com/products.html

www.autoformersdirect.com

www.voltagebooster.com

http://www.trci.net/products/surge-guard/voltage-regulator


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Posted By: Ex-Tech on 07/18/12 07:34pm

I have the Dometic 15K unit and store the RV at work where I spend a few nights a week.
My supply line is about 150' of 12 gauge wire and by the time my AC kicks on with the converter operating as well, my volt meter (analog) reads between 103-107 volts. It has operated this way for 5 years and is still going strong. It is possible that the hard-start kit with the potential relay helps with this low voltage issue.


Posted By: SidKaye on 07/18/12 07:48pm



X2

We bought an autoformer about 15 years ago to prevent problems from LOW voltage which occurs in too many parks when electricity demand is HIGH. Rigs with 2 and 3 AC units and some are all electric. Many parks were built before those kinds of electrical demands existed and most never upgraded.

Sidney


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2002 Excel,Ltd,30RGW,Hughes Autoformer,Honda Eu1000i, ClearSpot 4G+,

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Posted By: Chuck&Gail on 07/18/12 08:11pm

We love our Hughes autoformer. End up needing it at about 20% of the CG's we stop at.

"According to ANSI C84.1-1995 (R2001) any voltage below 110 volts for long term, or 106 volts for short term, may very well damage things in your RV (most commonly air conditioners, but anything could be damaged)."


Chuck
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Posted By: sum1 on 07/19/12 12:00am

Light bulbs aren't affected, but motors can be adversely impacted by low AC voltage. Don't think of it as a certain voltage below which there will be damage. The lower it gets, the risk of damage seems to increase exponentially. 120 is great, 110 is OK, but you're likely to reduce the lifespan of a given motor significantly at 105 and below. I go into amber alert below 110 and seriously consider the risk/benefit at 108, deciding if I'm willing to accept the risk. Unless I'm out of fuel, I'll usually light up the genny at that point.


Posted By: wa8yxm on 07/19/12 07:26am

105 is considered to be "The floor" however that is excessive drop. IF there is a 20 amp and a 30 amp outlet in the park box monitor the voltage on the 20 amp, Depending on the age of the box and who wired it it MAY be wired in parallel with the 30 amp outlet, IF there is a 50 amp outlet in the box it is not.

See if the voltage drop is "park side" or "Client side" (YOURS).


Home was where I park it. but alas the.
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Posted By: Our Place on 07/19/12 08:41am

Had an electrican look at it this morning and its not the AC, he said the AC is only pulling 10.4 amps when running but pulls 22 upon startup. We now believe that the campground is the problem and we are ordering a voltage regulator today so we'll have one for future problem, or to prevent them!


Posted By: MrWizard on 07/19/12 09:08am

by voltage regular i assume you mean 'auto transformer'

regulation is what it does, in steps thru relays selecting the windings to be used

it is by defination/name an Auto Transformer

around here the more specfic the terms used the less ambiguos and the less arguments produced


I can explain it to you.
But I Can Not understand it for you !

....

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Posted By: Learjet on 07/19/12 04:18pm

is it every month this discussion comes up?

From my MachIII information:

"Tested under the following conditions: Cooling A.R.I. Standard Conditioning 95° F. DB/71° F. WB Indoor, 115° F. DB Outdoor at 103.5 VAC."

My unit and every AC or home frig I have seen is rated at 115 volts, hence the +/- 10% or a min of 103.5 volts, and yes....at the unit.

Now please....go camping [emoticon]


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Posted By: Shadow_Grey on 07/19/12 04:23pm

Learjet wrote:

is it every month this discussion comes up?

From my MachIII information:

"Tested under the following conditions: Cooling A.R.I. Standard Conditioning 95° F. DB/71° F. WB Indoor, 115° F. DB Outdoor at 103.5 VAC."

My unit and every AC or home frig I have seen is rated at 115 volts, hence the +/- 10% or a min of 103.5 volts, and yes....at the unit.

Now please....go camping [emoticon]


Amen brother! Let's go camping!


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Posted By: wittmeba on 07/19/12 08:24pm

The differences you may be seeing are the differences between "Published" or "Designed" voltages vs. "Utilization" voltages.

110/115/120 are intended to be the same voltage. They will be dependent on where you are in the chain of production. The closer the substation the more likely you are to seeing 120V. At the end of a country road you may see only 110 V - but they are meant to be the same.

As mentioned above different devices will survive varying voltages with different results. Electronics do not handle over-voltage very well at all. Motors suffer overheating from under-voltage conditions. Resistors (toasters, heaters, etc) and some lighting wont care.

As MrWizard states low voltage does (indirectly) cause damage.

P=IE this expression from OHM's law states that Power(Watts)=Current X Voltage. If the voltage drops, current must increase to maintain the power demanded by the load. That means a 1HP, 115V/60HZ motor will attempt to main 1HP regardless of the voltage you provide.

There are tables that show how the life of a motor decreases with each volt of drop.


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Posted By: DryCamper11 on 07/20/12 08:11am

wittmeba wrote:

If the voltage drops, current must increase to maintain the power demanded by the load. That means a 1HP, 115V/60HZ motor will attempt to main 1HP regardless of the voltage you provide.


As you said, resistors don't care. They don't maintain power. They maintain resistance and the power drops with voltage.

Many electronics run on 5 volts and the first thing they do is convert the voltage down. There may be less heat at lower voltage for some designs. Many are perfectly happy to run on low voltages, although you can't be sure. I don't worry about 106 volts for my electronics.

The real problem is motors, because they are closer to constant power devices. The trouble occurs with motors that are running near their maximum load. Heat is function of current, so at maximum load, they are using maximum power, and as voltage drops, they draw more current than they were designed to handle. Sometimes, it's lots more. Your electric drill will be OK drilling 1/16" holes through wood with low voltage, but will be in trouble if you try going through steel with a 1/2" bit. The one problem in most RVs is the motor in the air conditioning unit. It runs near the maximum load for the motor. The other real problem is home-type compressor refrigerators. Not many RVs use them, but they also use motors running near their design limit. I worry about my AC motor below 108 volts.


In the Boonies!


Posted By: Wayne Dohnal on 07/20/12 10:15am

It's interesting that on some subjects one gets trounced by the crowd for NOT following manufacturer specs, but on this subject you get voted off the island if you DO advocate following the manufacturer specs. Besides everyone's intuition, is there any real data available? Things like the temperature specs of the motors, actual failure statistics, etc. I personally know of a couple of air conditioner failures from driving under low obstacles, but none from burned out motors. There's general agreement that the motor runs hotter with lower voltage, but what if it's still within the motor's temperature specs? Maybe running at a higher voltage lengthens the life. Does it really matter a lot if the unit lasts 30 years instead of 28, for instance? Is there any real data with actual life expectancy numbers out there for anybody to share?


Posted By: wittmeba on 07/20/12 11:53am

Hi Wayne,

Quote:

There's general agreement that the motor runs hotter with lower voltage, but what if it's still within the motor's temperature specs?


My background is from GE with Industrial Motor Controls but I believe the rules are the same. If you dig deeper into the Warranty of the unit, usage, etc you will find that even within the specs of the designer the results will be that you will see reduced life from under voltage of motors.

Motors are "dumb" animals. They only know to work at their designed level of output. With reduced voltage they attempt to maintain the same output, but run hot and the heat breaks down the insulation of the motor windings. The results are pretty consistent across the board from all motor manufacturers - burnout.

Quote:

Does it really matter a lot if the unit lasts 30 years instead of 28, for instance?

I think this is a key question. I believe every motor mfg will state the life expectancy of their motors. Im not sure that running at over voltage will extend that life. We expect motors to live somewhere between the 1 year warranty and 30 years we may own the motor.

I searched for a table that would support motor life at under voltage but didnt find anything. My recollection is for every 3% under voltage would reduce the life by 1/2. Perhaps some motor expert will chime in with supporting data.


Posted By: MEXICOWANDERER on 07/20/12 12:05pm

I can merely go by what I see. What I see when I post mortem a motor on an AC with chronic under-voltage operation is not the entire winding discolored or burned. (burnt for you Canadians).

What I see is a coil or two that gets overheated and shorts. And like a chain, a broken link in a motor renders it rather useless. A few dozen times drooping the voltage during a high head startup to 95 is going to make one person very unhappy and another smile as they key the register.


Posted By: DryCamper11 on 07/20/12 12:46pm

Wayne Dohnal wrote:

It's interesting that on some subjects one gets trounced by the crowd for NOT following manufacturer specs, but on this subject you get voted off the island if you DO advocate following the manufacturer specs.

I truly appreciate the link to the white paper you posted. I was surprised that it indicated voltage as low as 103.5 was acceptable. After reading it, I've modified my opinion. My AC is 40 years old. It's still going strong and who knows if the voltage numbers in that white paper apply to mine, so I'll probably keep on sticking to my 108 volt minimum, but manufacturer's recommendations carry a lot of weight with me. There's no point in just guessing, so I hope you don't think anything I posted was "voting you off the island" [emoticon]

I'll be the first to admit - I've got limited data to act on.

I have some concern about the comments in that paper. They tell us to compare calculated amperage to measured, then point out that they haven't corrected for voltage. The difference between 103.5 and 126.5 VAC is going to produce a comparable 22% variation of current.

Quote:

Besides everyone's intuition, is there any real data available? Things like the temperature specs of the motors, actual failure statistics, etc. I personally know of a couple of air conditioner failures from driving under low obstacles, but none from burned out motors. There's general agreement that the motor runs hotter with lower voltage, but what if it's still within the motor's temperature specs? Maybe running at a higher voltage lengthens the life. Does it really matter a lot if the unit lasts 30 years instead of 28, for instance? Is there any real data with actual life expectancy numbers out there for anybody to share?


I'll add my voice to the request for any solid information.

I'm pretty sure that the compressor has a reasonably constant mechanical load so the motor current draw will increase as voltage decreases to hold the power constant. If current increases by 22% (that's comparing 126.5 volts to 103.5, which isn't really fair, but still ...) , the power dissipated in winding resistance as heat will go up by the current squared, i.e., by 48% If we compare 103.5 to 117 volts, a more reasonable design number, it's still a power dissipated as heat difference of 28%.

I suspect it will be hard to get solid numbers on how much longer an AC compressor motor will last when it's dissipating more heat in the motor windings, but low voltage is so common, if they died quickly, there would be many warranty replacements [emoticon]

I'm trying to decide if $100 for a buck boost is worth the cost to bump up my AC voltage to the range I'm comfortable with.


Posted By: DryCamper11 on 07/20/12 12:56pm

mexbungalows wrote:

What I see when I post mortem a motor on an AC with chronic under-voltage operation is not the entire winding discolored or burned. (burnt for you Canadians).

What I see is a coil or two that gets overheated and shorts.

That makes sense. The coil will have spots of narrower wire - higher resistance there, which heats slightly more. Copper gets more resistive with heat, so it gets worse at that localized spot. The hotter it gets, the higher the resistance. Over time the insulation breaks down at that spot and we get a short. I'm surprised you see it at all, unless you unwind the windings in the post mortem. The core of the winding, hidden from view by the other wires, where heat can't escape, is usually where the problem short circuit happens.


Posted By: sum1 on 07/20/12 01:30pm

This doesn't make me an expert, but decades of experience running hundreds, if not thousands, of AC motors and tools on various lengths of building wiring and extension cords has taugh me a few things. Long runs are bad. Skinny wire makes it worse. Voltage under load is low at the end of a long skinny run. We have several times justified the risk of using these motors with low voltage for physical or financial reasons and that's where we've smoked them.


Posted By: enblethen on 07/20/12 05:57pm

A lot of the discussion has turned to "low voltage" and got off the OP's concern about voltage drop.
The OP reported a major drop in voltage from the pedestal 120.7(?) to the AC unit 105.8(?).
Depending on where he is taking the measurements, this is excessive voltage drop.
Yes, low voltage can damage motor driven items. Talk is about fan, but the compressor drive throws much more load into the system especially to get it started.
There is a problem somewhere in the system whether it is in his rig or the campground. A new rig possibly under warranty needs to get investigated so it can be taken care before the warranty expires.


Posted By: M GO BLUE on 07/19/12 09:23am

If not an auto transformer then get yoourself a multi-function Surge Guard to fullt protect your RV...




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Posted By: Klueck on 07/19/12 09:28am

Get one of these and don't worry about it.

If your voltage gets too high or low it will shut off power to the Rv and prevent any damage to your expensive electronics.

It will also tell you before you plug in if there is a problem with the pedestal.


Posted By: Wayne Dohnal on 07/19/12 11:29am

Quote:


"According to ANSI C84.1-1995 (R2001) any voltage below 110 volts for long term, or 106 volts for short term, may very well damage things in your RV (most commonly air conditioners, but anything could be damaged)."
Another technical document that has multiple interpretations. I actually interpret it as saying it should be perfectly safe to operate an air conditioner down to 104 volts. What did I miss?

In Table 1, the bottom of Voltage Range B is shown as 106, unless no lighting loads are supplied, in which case the bottom is 104 volts. Paragraph 2.4.3, defining Voltage Range B, says "Insofar as practicable, utilization equipment shall be designed to give acceptable performance in the extremes of the range of utilization voltages". It also says that outside of Voltage Range B "utilization equipment may not operate satisfactorily". The notes for Table C3 mention that motor designs include a -10% voltage tolerance. I can't find anything in the document discussing damage, only unsatisfactory performance. The 2006 version of the document has the identical information although the paragraph numbers have changed.


Posted By: MrWizard on 07/19/12 11:42am

the problem
is low voltage is most likely to occur when temps are the hottest and the A/c has too work the hardest

those kinds of situations are NOT specifically spelled out in Documents like above

a a blender or washing machine in the house at 70* will operate quite nicely at 105vac
but NOT your roof top A/C with 105* outside temps and 105vac supply


Posted By: Wayne Dohnal on 07/19/12 01:18pm

Quote:


a a blender or washing machine in the house at 70* will operate quite nicely at 105vac
but NOT your roof top A/C with 105* outside temps and 105vac supply
Maybe the performance at 105 volts is lower, I don't know. I was specifically addressing the damage issue.


Posted By: DryCamper11 on 07/19/12 01:31pm

Klueck wrote:

Get one of these and don't worry about it.

That device will happily let you run on 104VAC. That's way too low for me, but only for some devices. I'd worry a lot if my AC was running at 104VAC. I'd be happy to make coffee at that voltage, or try to run my charger. I have lots of devices that will run fine below or above the limits it sets. I think I'd rather just know what the power is, not have it kill the whole system (well, I'd want it powered off if it sees 240 VAC). I suppose each of us has different limits.


Posted By: MrWizard on 07/19/12 01:39pm

yes damage
what causes the damage ?? heat
the motor is NOT damaged just because there is lower voltage applied

lower voltage forces the internal current load to be abnormally high in order to maintain the magnetic field and keep rotation at the correct speed,
the more work that needs to be done the more heat
your washing machine will do the same work
but you a/c has to work harder to compress the hot freon that it has too keep moving, and it is working outside in the hot air and the compressor can not be keep cool enough, fan slows down compressor is hotter, the air is hotter the chances for damage increase exponentially

its a matter of environment , low voltage is only one factor of the environment


Posted By: Wayne Dohnal on 07/19/12 02:13pm

Let me try to be extremely specific. I'm not making any claim that's based on anything other than reading comprehension. There's a post that says ANSI such-and-such says damage will occur below 110 and/or 106 volts. I read the document and found it to say the opposite. I read the info from the air conditioner manufacturers that say their units are good down to 103.5, with no mention of temperature, such as on page 2 of this document suburbanmfg.com/rvp/pdf_documents/SKMBT_C35308100910420.pdf . If I'm reading incorrectly the issue is with me and I'd like to know how I'm misinterpreting. Otherwise the disagreement is with ANSI and the air conditioner manufacturers.


Posted By: lryrob9301 on 07/19/12 03:21pm

Well all I know is my Progressive Industries EMS-PT50C is set to cut off at 104 volts at the pedestal. It states it's set operating range is 104 volts to 132 volts.


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Posted By: LarryJM on 07/20/12 06:38pm

Big Katuna wrote:

108 is the MINIMUM allowable voltage.


ABSOLUTE GARBAGE and please show me a reference from and A/C manufacturer that specs that voltage. IIRC Dometic specs for "NORMAL" is around 103.5 at the contacts inside the A/C.

SHOW THIS MISSOURIAN your proof which I won't wait for since you will not be able to support your incorrect position.

Larry


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Posted By: enblethen on 07/20/12 07:02pm

I beleive reference is being made to 10 per cent voltage drop is allowed by the NEC for branch circuits which is calculated with 120 volts.
You are allowed 3 per cent voltage drop on a feeder circuit.
From the electrical panel feeding through the pedestal to the panel inside the rig, allowable voltage drop would be 3 per cent.
From the panel inside the rig to the AC unit could be an additional 10 per cent.
Not knowing how the system is wired it would be nearly impossible to calculate voltage drop.
OP has 120+ at pedestal. It then drops to 105+ at some location not specified.


Posted By: Wayne Dohnal on 07/20/12 07:50pm

I've got some air conditioner numbers from generator testing I did a few years ago. The load was a 13,500 btuh Dometic Brisk Air. The voltages were "hot switched" while the setup was running so there aren't any restart or head pressure issues to corrupt the data. For confidence, the voltage and current readings were taken with 2 meters, and I ran the test two times, on different days.

122.1 volts - 10.50 amps - PF=.93 - VA = 1283 - watts = 1193
116.9 volts - 10.65 amps - PF=.96 - VA = 1245 - watts = 1195
111.6 volts - 10.90 amps - PF=.98 - VA = 1216 - watts = 1192
102.5 volts - 11.50 amps - PF=.98 - VA = 1179 - watts = 1155
98.20 volts - 12.20 amps - PF=.98 - VA = 1198 - watts = 1174

My own conclusions:

1) The motor does in fact maintain about the same output power as the voltage varies (is it a reasonable assumption that the motor mechanical output is proportional to the watts?).
2) Assuming the watts measurement proportionately indicates how much heat is generated by the motor, that also stays approximately constant as the voltage varies.
3) With the higher current at the lower voltages, any weaker points in the motor will be disproportionately stressed.

A test sample of one doesn't prove anything but is a lot better than no sample at all. I also recorded that with the air conditioner, water heater, refrigerator, and power converter with 15 amp load all running the voltage at the air conditioner was 2.8 lower than at the pedestal. This of course varies with the rig but could be pretty typical.


Posted By: Airstreamer67 on 07/21/12 11:34am

Does anyone know why some protective devices (eg Surge Guard) will shut off at 102 volts instead of something higher?

Isn't 102 a bit low for protection of motors?


Posted By: enblethen on 07/21/12 11:54am

I would guess that the engineers have determined 102 is acceptable for an inrush could cause a system to drop below the deisgned level momentarily without causing any damage. This maybe OK in some cases but in many it is not good.
Yes, it is too low for many items other then motors.


Posted By: DryCamper11 on 07/23/12 08:50am

Wayne Dohnal wrote:

I've got some air conditioner numbers from generator testing ...
My own conclusions:

1) The motor does in fact maintain about the same output power as the voltage varies (is it a reasonable assumption that the motor mechanical output is proportional to the watts?).


Thanks for the numbers. Yes, the mechanical power is proportional to the electrical power. For constant speed motors, changing voltage won't change the speed, so the power output doesn't change and input current has to rise proportionally to balance the lower input voltage. There's some additional loss due to increased heating from increased current, etc., but it's reasonably close to constant power.


Posted By: RCMAN46 on 07/25/12 08:50am

mexbungalows wrote:

I can merely go by what I see. What I see when I post mortem a motor on an AC with chronic under-voltage operation is not the entire winding discolored or burned. (burnt for you Canadians).

What I see is a coil or two that gets overheated and shorts. And like a chain, a broken link in a motor renders it rather useless. A few dozen times drooping the voltage during a high head startup to 95 is going to make one person very unhappy and another smile as they key the register.

I suspect that the coils that you found (burnt for you Canadians) was the start winding. It is the start winding that gets the bad end of things from a weak system where the voltage will droop. The motor will try to draw more current as the voltage drops and this is the worst case when the motor is starting and the start winding sees high currents due to the low voltage. A typical induction motor will draw from 6-10 times normal full load current during start on a normal stiff power system. When the voltage droops then the motor is not able to produce the horsepower required to accelerate the load and the start time is extended and sometimes it even fails to start and trips breakers. During these extended start times the start winding is energized. Start windings are designed to be in the circuit for a very short time. When the start times are extended the start winding overheats and damages the winding insulation.


Posted By: wa8yxm on 07/25/12 04:04pm

Some comments on the auto-former.

I have one and love it.

HOWEVER: they are portable, they only sell portable but they do sell an "Install kit" I will describe the kit since you can buy it's parts and make one up yourself.

Some parks have rules "NO AUTOFORMERS" Well, if the manager should happen by he will never see an autoformer on my rig, I plug in without one. WHY.

See "Install kit" above

The kit consists of some 50 amp power cord, a plug and a socket,

Here is what I did.

I cut a couple feet off my shore cord and installed a brand new POWER PULL type plug on the end.

I removed the leads (Shore power) from teh auto-transfer switch and ran them to a 50 amp outlet, in a proper box

I replaced the leads with the shore power cord in the ATS box.

The Atoformer sits in a hidden cabinet right in front of the ATS, The ATS is plugged into it and it's plugged into the outlet that replaced the ATS on teh shore power lead.

Out of sight, and I can't forget to put it "In line" either since it's there all the time.


Posted By: Star Gazer on 07/26/12 07:14am

I just recently started using a Buck Boost Transformer on my boat. The dock supplied voltage is around 112-115 but as soon as my AC load is put on it drops to around 103-105. Sometimes lower if a lot of other boats are there on a hot weekend. I can hear the difference when the compressors kick on.

With my gen running the voltage stays above 120 with full loads on. After several years of fighting with the marina to fix it, I got the buck boost. Wihs I done it years ago as I have less than $200 in it with a new shore power cord I attached it too.

The only thing I worry about is these do not have a voltage regulator. The transformer gives me 135 volts without a load, then drops to 124 with a load. The transformer is wired to boost 15% and I had thought about changing to 10%. My electrician says the higher volts will do no harm but if we ever get real voltage at the marina it could be a problem. I suppose a voltage regulator can be installed after the buck boost?


2008 Phaeton 36QSH
2015 Ford Transit 250
2006 17' Casita FD (mobile observatory)


Posted By: DryCamper11 on 07/26/12 07:36am

Star Gazer wrote:

The only thing I worry about is these do not have a voltage regulator. The transformer gives me 135 volts without a load, then drops to 124 with a load. The transformer is wired to boost 15% and I had thought about changing to 10%. My electrician says the higher volts will do no harm but if we ever get real voltage at the marina it could be a problem. I suppose a voltage regulator can be installed after the buck boost?


You can buy voltage regulators, but the cost will be far more than the transformer. Typical buck boost transformers have two primary windings and two secondary windings. I suspect you have a 12V/24V buck boost. You can wire those to give 5% boost (primaries in series, secondaries in parallel), 10% boost (primaries in parallel, secondaries in parallel)or 20% boost (primaries in parallel, secondaries in series). You need one with a high enough VA rating, but .75KVA at less than $100 will handle 30 amps. You can install manual switches to select the different wiring modes if you are tricky. You can also install a control system to throw a relay automatically to switch modes, but that requires building a circuit.

The Hughes Autoformer uses an autoswitching relay, although the price is a lot higher than just the transformer.

There was a link to a circuit posted in a thread here that could be adapted to autoswitch a relay.


Posted By: Learjet on 07/26/12 10:04am

thanks for the heads up on a buck boost transformer, that is exactly what I have been looking for. For less than $100 dollars I can set up a fixed 10% boost. Much cheaper than some of the other automatic options out there.

I just ordered on of these


Posted By: Star Gazer on 07/26/12 10:54am

Just make sure they give you the correct wiring drawing for the voltage you want. I was given the wrong one with too much boost and need to redo it. Not hard to do but requires an experienced person to wire nut all the connections properly.

Dean


Posted By: DryCamper11 on 07/26/12 11:28am

Learjet wrote:

thanks for the heads up on a buck boost transformer, that is exactly what I have been looking for. For less than $100 dollars I can set up a fixed 10% boost. Much cheaper than some of the other automatic options out there.

I just ordered on of these


Temco is a good supplier, but I had to call the manufacturer to get one question I had answered correctly. Temco told me I couldn't do something I was pretty sure was possible (run at 5% low boost) and the manufacturer said "No problem - we do that all the time."

The 500 watt unit you bought should be OK for only 10% boost, but I was thinking about buying the 750 watt unit so it could be run in any configuration at 30 amps.


Posted By: Wayne Dohnal on 07/26/12 12:02pm

Can you guys help me understand something about this buck/boot transformer? It's a 0.5 kVA transformer, yet can support somewhere between 2 and 5 kVA in a nominal 120 volt configuration. I can see the differences between the windings in series vs. parallel, so that part isn;t a mystery. Can somebody explain how the transformer can support a load much higher than its rating? The full current of the load has to pass through the windings.


Posted By: DryCamper11 on 07/26/12 01:06pm

Wayne Dohnal wrote:

Can you guys help me understand something about this buck/boot transformer? It's a 0.5 kVA transformer, yet can support somewhere between 2 and 5 kVA in a nominal 120 volt configuration. I can see the differences between the windings in series vs. parallel, so that part isn;t a mystery. Can somebody explain how the transformer can support a load much higher than its rating? The full current of the load has to pass through the windings.

This is a very common question. These are just wound as two side by side isolated 12 volt transformers and they are rated as that. Say I wanted 24 volts AC at 30 amps. The two secondary windings would be in series and all 30 amps would flow through them. I'd need 720 VA and I'd buy the 0.75 KVA unit. I could rewire that unit for only 12 volts by connecting the 12 volt windings in parallel and get 60 amps out.

If I take that same unit and connect it as a boost transformer to get a 20% volt boost (100 volts in plus 20 volts boost) I'd still only count the current in the secondaries.

The rating is based on the current through the secondary windings. When connected as a boost (or buck) transformer, most of the current doesn't flow through the primary windings and the voltage applied to them isn't counted in the rating.

The primary wires are quite small in diameter as compared to the secondary wires (as you would expect for a typical 12 volt transformer), and it seems strange when connecting them up as the input bringing in power to be boosted will be gauged for 120V 30 amps, while the primary wires you are connecting the input to are gauged for far less.

* This post was edited 07/26/12 01:25pm by DryCamper11 *


Posted By: Star Gazer on 07/26/12 01:08pm

I bought a .75 kva unit here is my model and cost.

FT2005

Federal Pacific SB12N.750F FT2005 -
Buck Boost Transformer - 120x240 Pri - 12/24 Sec - 0.75 kVA - 60Hz - 1
Phase - NEMA 3R Encapsulated
$113.67


Posted By: DryCamper11 on 07/26/12 01:13pm

Star Gazer wrote:

I bought a .75 kva unit here is my model and cost.
FT2005
Federal Pacific SB12N.750F FT2005 -
Buck Boost Transformer - 120x240 Pri - 12/24 Sec - 0.75 kVA - 60Hz - 1
Phase - NEMA 3R Encapsulated
$113.67

That's a good unit. It's what I would have chosen.


Posted By: Wayne Dohnal on 07/26/12 02:16pm

DryCamper11 wrote:

Look carefully at any of the wiring diagrams. The full current of the load only has to pass through the secondary windings.
OK, I get it, yet I till have trouble with it. If I think of it as the secondary being an isolated power source in series with the line voltage, things are perfectly clear. Yet when I look at that diagram showing the boosted voltage across all the windings, I have a hard time thinking all the current doesn't go through the primary. The current is of course branching in two different directions which I just have a hard time visualizing. Same principle as the neutral in a split-phase system, I believe.

I'm keeping my eye out for a 120-to-240 step up transformer, and at first thought I could use the primaries of this buck-boost transformer as an autoformer, except now I realize it would be good for only 0.5 kVA. Or would it handle a 1.0 kVA load because the windings would be carrying only half the load?


Posted By: DryCamper11 on 07/26/12 02:44pm

Wayne Dohnal wrote:

Same principle as the neutral in a split-phase system, I believe.

Yes.

Quote:

I'm keeping my eye out for a 120-to-240 step up transformer, and at first thought I could use the primaries of this buck-boost transformer as an autoformer, except now I realize it would be good for only 0.5 kVA. Or would it handle a 1.0 kVA load because the windings would be carrying only half the load?

As you know, it's not designed for that. Assuming it worked (and I note that auto transformers usually aren't used to increase voltage that much), one of the two primary windings would have to carry the entire current at 120V. The rating is for both windings working together, so I think you might have to halve the rating to 375 VA.

IOW, a 120X240 12/24 0.75KVA transformer is designed to handle about 30 amps in each 12V winding or only about 375 VA (half the rating). The primary for that secondary is handling one tenth of that 30A current (only 3A) at ten times the voltage (120), so it's got wires in it designed only to handle the 3A current it will normally see.

Doesn't seem very practical to me even if it worked.


Posted By: LScamper on 07/26/12 04:10pm

There is no reason it would not work. The total rating would be the total rating of the transformer, that is a 500VA transformer will handle 500VA in each case. Each primary will carry the same current as the load. A 500VA transformer running at 120VAC with the primaries in series adding will provide 240VAC at 2.08A to the load. The source current will be two time the 2.08A or 4.16A. VA = 120*4.16 = 500VA and 240 * 2.08 = 500VA. There will be a little more current from the source due to magnetizing inductance of the primaries.


Lou



Posted By: DryCamper11 on 07/27/12 07:27am

LScamper wrote:

The total rating would be the total rating of the transformer, that is a 500VA transformer will handle 500VA in each case.

LScamper is right - sorry for the mistake. Half the current flows through each primary winding, so you'd get the entire VA rating. Of course you wouldn't be using either of the secondary windings, which are the high current, large diameter windings, so that part of the buck boost transformer would wasted. If you can live with the limited VA rating (a few amps for 500VA), and the lack of isolation between input and output, it should work.

OTOH, there must be pure 1:2 autotransformers that would be cheaper, as they'd not have to include the heavy secondary windings.


Posted By: Wayne Dohnal on 07/27/12 10:49am

Thanks for the transformer brainstorming. I never had a need to understand how the buck/boost worked, but now I know. It's one of the few things where on the surface it looks like you're breaking the laws of physics.


Posted By: wa8yxm on 07/27/12 11:33am

Things I know....

It is possible, with a bit of electronics, to design a motor that would work and work well, at low voltages, say 90 or even less, and then with an electronic controller make them so they could survive an over voltage, say 150 or even 250 volts.

The cost of that controller is in the 10 dollar range.

SO WHY DO THEY NOT MAKE THEM LIKE THAT!


Posted By: DryCamper11 on 07/27/12 11:40am

Wayne Dohnal wrote:

Thanks for the transformer brainstorming.

If any of my posts helped, all I can say is that it's scant repayment for the useful information here, including some excellent information in your posts that I've read.

It's Friday - another weekend looms - this time we'll be in NH. [emoticon]


Posted By: LScamper on 07/27/12 06:04pm

wa8yxm wrote:
"It is possible, with a bit of electronics, to design a motor that would work and work well, at low voltages, say 90 or even less, and then with an electronic controller make them so they could survive an over voltage, say 150 or even 250 volts.

The cost of that controller is in the 10 dollar range."

I always like to learn. Could you elaborate on this some. $10 seems like they would do it if it was that easy.


Posted By: Learjet on 08/02/12 05:06pm

I got my Buck Boost Transfomer in and wired it for 10% boost and it works perfect. Just what I need at home for my emergency generator and might come in handy camping. I measured 0.8 amps with no load, so it uses some current just hooked up.

* This post was edited 08/02/12 05:26pm by Learjet *


Posted By: DryCamper11 on 08/03/12 07:35am

Big Katuna wrote:

Using a simple boost transformer will be just fine up to the time the power company starts delivering 129 VAC to your line. I'll stick with my Autoformer.


I've been monitoring my line voltage at home and have never seen it go up to anywhere near that level. For those who are handy with electronics, it's easy to install a cutoff that will cut the voltage if it exceeds a limit. Some may already have that built in as part of a full function power monitoring system. If the boost is too high, the PMS will cut power.

The next easiest is to add a circuit to autoswitch from 0% to 10%. That's what the patented autoformer design did. It switched the primary contacts. For those who really want to get fancy, a circuit can be added to automatically switch the boost from 0%-5%-10%-20%. That's more sophisticated than the autoformer and could be built for less (although I think it's overkill).

I agree that just buying an autoformer is easier, but where's the fun in that? [emoticon]


Posted By: Learjet on 08/03/12 08:48am

Big Katuna wrote:

Using a simple boost transformer will be just fine up to the time the power company starts delivering 129 VAC to your line. I'll stick with my Autoformer.


Let me be a little clearer what I'm using it for:


1. My camping generator (tri-fuel) is also my emergency generator at home connected to natural gas. Gas is on one side of house and main electrical connection is on other, I could have bought a long hose or plumb....But since my generator is only 120v I used 30 amp rv cords that I already had to connect to my main panel (with a lockout device). Even with 30 amp wires and running only a max of 19 amps through this 75 feet of wire the voltage in the house with the base (min) load was @ 115 volts under full load it dropped to 106-108 volts. So even with the min or max load and the booster connected my voltage is perfect now (116-125)under generator power. No worries, I have multipile voltage monitors with alarms.

2. As far as camping, very rarely do I expect to use it, but occasionaly at family events I hook up to a 20 amp rec...OMG [emoticon]...and yes run the AC. My amps measure at VENA AC meter are only about 13 with just the AC and converter on, yet due to extension cord the voltage can get low. I would use the booster in this case, only when closely monitored. My Vena AC/DC monitor has programable alarms for high or low voltage.

So clearly this is not for everyone, but the unique situations I will use it for and under my careful supervision, it will work for me. My cost under $100. [emoticon]

* This post was edited 08/03/12 05:58pm by Learjet *


Posted By: Learjet on 08/15/12 06:30pm

In reference to my above explanation....

Project is finished.

Inside...

[image]

carrying wrap that came with camco cord used as handle

[image]

Final project...

[image]


Posted By: Learjet on 08/29/12 02:34pm

well, thanks to hurricane Issac my booster transformer is working just as planned. The measured voltage inside my house is 117 to 120 on generator power. Lets hope my YamahaDog keeps running for the ???? days. Damn you Issac


Posted By: DryCamper11 on 07/26/12 06:46am

wa8yxm wrote:

Some parks have rules "NO AUTOFORMERS"

Do they say why? It should have no more effect than plugging in another device and pulling a bit more current. If you are paying for power you should be able to use it, I would think.


Posted By: DryCamper11 on 07/26/12 01:15pm

Wayne Dohnal wrote:

The full current of the load has to pass through the windings.

I might not have been clear. Look carefully at any of the wiring diagrams. The full current of the load only has to pass through the secondary windings.


Posted By: Big Katuna on 08/02/12 08:29pm

Using a simple boost transformer will be just fine up to the time the power company starts delivering 129 VAC to your line. I'll stick with my Autoformer.


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