Camping tactics can get confused with electrical efficiency I suppose.
eg, with solar it is smarter (for RV battery charging reasons) to run your laptop on its own battery in the morning and then charge it from solar in the afternoon, when the battery amps have tapered so there is "free" solar to run loads. That has nothing to do with PWM vs MPPT though.
Cost comparisons PWM vs MPPT are very difficult because panel prices are all over the map and then besides that there may be shipping costs for some who cannot pick up their own.
Some places have much lower cost per watt 24v panels than 12v panels; some places they cost the same. MPPT controllers remain very expensive, but that may be changing. Thinner wire is less expensive, but how much saving you can realize with that depends on how much wire you need- sort of a minor aspect anyway.
My PWM 200w set cost $1.08/W for panel and $39 for the 20a controller, and the set gets 12.6amps (Isc) I am over sized a bit on controller amps. a 15a would be ok. So 216 plus 39 =$255.
So 600w worth of that would cost three times at $765 and get me 38 amps. about $20/amp
If you can get 24v panels to make up 600w at $ 0.75/W, that would be $450 plus the controller. to get 45a What does that MS45 amper cost? No idea $400? if so that is $850 for 45amps. about $19/amp
So somewhere close in cost per amp at the 600w level between MPPT and PWM?
I don't understand worrying about electrical efficiency if that didn't get you more amps per dollar as the true measure of efficiency
My batteries (and so the same for me) only care about amps. MPPT is just a hard way to get more amps. "Efficiency" should be measured in amps per dollar. If MPPT got you more amps per dollar, that would be the way to go.
At some bigger array size there is a cross-over price point when MPPT gets more amps per dollar, but that would be a bigger (in watts and panel area) array than most Rvers would have based on some recent posts on that topic where costs were worked out.
I only care about amps. (12v-PWM guy) When I buy a panel I look at its Isc. Don't care about its watts, except as a marker for what Isc to expect.
In operation, I check the Isc on the panel aimed in full sun and then look at the amps going to the battery. Should be the same. If not, I fix what's wrong and now I'm good.
Thanks again for taking the time to explain it, even if I need a two by four over the head first.
I also forgot we are talking controllers that do 24v panels but do the amps out to a 12v battery, so the Voc limit and the amps limit are for different things.
Yes, I will stick to my 12v PWM set-up. Less brainwork! :) Thanks again!
"but you want to stay inside the 45amps limit.
You want to stay within the WATT limit on th einput side for the operational voltage 12, 24, 36, or 48"
Argggh! But you said if you go close to the 45 the controller will heat up and you want to stay well below that limit. Now you don't care if you go over the 45?
I meant just use bigger panels at the same Voc to get more wattage as one choice.
I have got myself all confused again. :(What question are you trying to ask here? :@
I am trying to figure out how you can stay inside the 45a limit, the 150 Voc limit, and double the array wattage all at the same time by going from 12v to 24v batteries.
I haven't got a grasp on the ratio of controller size in amps and its Voc input limit if there is one, that the clever design allows all this, or if you hit one limit "too early" or what.
Don't controllers also have a wattage limit rating? ISTR some do.
150 Voc limit using panels with 35v Vmp and 42v Voc means 150/42 = 3 panels in series is the limit?
So to double the array wattage to 1200w and stay inside the 150 Voc you need to double the length and width of the three panels, because you can't use six of those others in series, but that doubles the amps, but you want to stay inside the 45amps limit
Or run another three-panel string in parallel but that doubles the amps, but you want to stay inside the 45amps limit.
I have got myself all confused again. :( They said 600w and 45a was the limit.
Your 6v batts will get you more AH (220 say) than the two 12s (160?) so that is not the problem
You have a draw somewhere. That 13.4v does not means your batteries are charged. That means they are just getting charged on the way from 12.x in the morning to 14.x in the afternoon. Whether they ever get fully charged (12.7 resting) depends on how much daylight is left after they get to 14.x and can do the absorption stage before dropping to float voltage of 13.8 whatever the set point is for that.
You need to watch the Trimetric amps and see if amps are negative net when they should be positive. Say your solar is adding 10amps, you have a 5amp draw, you will see 5 amps charging showing. If you have more draw than incoming, down it goes.
I might have just seen it there for a minute!
I am using the same size battery bank in each case, but you are increasing it each time so it can still take the same amps at the higher voltage.
When you say 24v bank, you just forgot to say you need more batteries :) to keep accepting that 45amps. No, you said never mind battery acceptance rates, you are powering loads.
"..... everything is the same except the battery voltage is 48 as compared to 12 allowing the array max power (45 amp controller) to be (45 amps X 48 Volts = 2,160 watts) with the same max inout voltage limitation of 150 VDC – the controller will then be able to put 45 amps (it's 45 amp rating) into the 48 volt battery bank."
I am still stuck here. You jacked up the size of the array so it has more total Voc? so how can that 150v input limit still work?
" A 45 amp controller could have up to a (45amps X 24 volts = 1080 watt array) and then supply 45 amps to the 24 volt battery. "
But the 24v "battery" is half the AH of the 12v battery as when you have two 12s in series vs parallel, so it can only take half the amps.
which is where I got lost, but now I am found. :) You just need to double the number of 100AH batteries :)
I don't even understand what my question is! Anyway, still in a muddle.
Two 100AH 12v batteries. As a 24v get 100AH As a 12v get 200AH
Acceptance rate for charging the 200AH/12v is say 40a, what is it for the 100AH/24v?
So do you need the same size controller in amps whether 12 or 24 battery, or what?
How long does it take to charge each bank? Same time? half the time, twice the time?
Now you have a 40amp controller at 12v. Is it still a "40amp controller" at 24v? So its 40amp limit is the same? What about its input voltage limit? Same?
Last year we got into another muddle over the limits for the MS 15L, ISTR, which turned on it having a 200w or a 400w limit depending on system voltage?
So do these controllers have different limits for different situations or not?
I am unclear on sensing wire importance in all of this but mentioned since that is the real topic :) Sorry, OP! :(
Thanks for explaining all that in detail. Sadly, I (and maybe others, but not as badly most likely :( ) am still in a muddle on some of it--
" A 45 amp controller could have up to a (45amps X 24 volts = 1080 watt array) and then supply 45 amps to the 24 volt battery."
But what about the battery acceptance rate for a 24v battery? We know the charging profile for a 12v battery and the rates, so eg, with a smart charger starting at 20% charging rate on a 200AH bank of two 100AH in parallel, it would be at 40 amps.
How do you do the AH "size" for the same two batts in series? What is the appropriate charging rate? (comparable to 20% with 12v)
Now what happens with appropriate amps sizes for controllers between 12v and 24v with the same 600w array when on
A. 12v battery bank
B. 24v bank
I also got lost how the "150v input limit" stays the same whether the array is in series or parallel where its voltage and amps changes.
I am getting confused. Some points-
-The PWM "12v" "600w" system would produce 38a at Isc, not 50a but who's counting? :) that "600w" is defined as Vmp x Imp and Vmp is approx. 17.5v (not 12) so that leaves 600/17.5 = 34.3 amps. Isc is higher than Imp for the "working part" of the IV curve so you get that 38amps max.
1. The panel instructions warn that it can go over its ratings at times (such as cloud effect or cold temps, etc) and advises choosing the components (controller size, fuses, etc) to account for that by 20% (at least Sharp does)
2. The US NEC requires a 20% margin above panel amps rating for homes and (not sure if required or advised) RVs
3. Some (all?) PWM controllers will allow amps higher than their amps ratings to go through to the battery. The word is that the controller can then overheat and eventually fry but is ok for short times like cloud effect.
4. Some(all?) MPPT controllers limit their amps output to their ratings. Either:
a. That allows for panels going over their ratings so the controller won't overheat, or
b. It will run warm at rating which will shorten its lifespan, or
c. It will overheat if you strap it to too much panel so the incoming is way over its built-in overhead allowance
5. incoming voltage rating not to be exceeded at all or controller will fry instantly. "Overhead" here is to allow for incoming voltage to be above the panel rating Voc taken at 25C such as in cold temps. Total array Voc (series or parallel )is what counts to the controller when figuring that.
6. Expected max voltage or amps depends on the "voltage" of the system 12/24/36/48
I can't follow what happens to the ratings and their max limits when going from 12 to 24 to 48 and series parallel unless it is spelt out slowly not using any big words.
The MS 15L controller clips the amps to 15 even if it is getting more in. Now the 45 amp controller "limits" (clips) the amps to 45.
I am just still on about how the PWM 12v can get 15.1a Isc on 240w and so to meet the 20% overhead you need a 20a controller.
600w on PWM would do 38 amps at Isc. 20% headroom would mean you need a 45.6a controller
The MS45 says with 600w you max at 45a with no headroom and limits the amps to 45. So it sounds like they are saying the MPPT will do
45-38 = 7/38= 18% better
The thing is if the controller limits/clips the amps then you can max out the controller's amps rating because it won't go over that and overheat the controller or blow the fuse on the pos line to the battery
So you can load the clipping controller right up with panel wattage at 12v, but you have to get a higher amp controller for PWM, non-clipping type
The voltage input max rating is another thing. Not sure how they match up the v max and amps max for various voltages 12/24 etc.
They do warn to make sure you pick your max input voltage ( Voc --not the Vmp) ) at the coldest temp you will have the panels operating in and not at 25C.
"So a 45 amp controller should never be designed with more than a 600 watt array"
I know you guys are talking about MPPT and 24v or higher systems, but please clarify.
with 12v panels and PWM, a 20a controller can do approx. 250w of panels and still have the desired 20% margin the US NEC wants for when amps are higher, such as cloud effect.
This means 40 amps of controller can do 500w of panels safely. But MPPT controllers clip the amps so they can go to the rated amp limit safely
Going with a 235w MPPT 24panel doing 15a max (not clipped) as some have reported, that would mean 40/15 x 235 = 626w of panels.
So is it confirmed by using that 600w for 45a, that MPPT and 24v gets nearly the same amps as 12v and PWM? :) :)
AFAIK (not far, I don't have a MH) that little panel is for the engine battery and is not for the house batteries,
You can see if it is working by the voltage on your engine battery. With the engine off, voltage is likely 12.4ish with no solar. There are draws like the clock etc dragging it down all the time) With solar (and the sun is up) it could be 13 something volts or at least higher than 12.4ish.
With inverter on using the switch, leave the microwave off. Tell us the battery voltage before and after. If there is another load on the inverter not yet identified, the battery voltage will be lower due to the "loaded voltage" of whatever might be on. Battery voltage should stay nearly the same when the inverter is turned on but with no load.
Say it is 12.5 before, it will drop to say 12.2 or whatever--depends on the size of the load (if any)
Still no word whether the rest of the receptacles are live besides the Entertainment Centre ones when on inverter. And if they are, what might be plugged into them that is on.
The TV etc will be on on standby, but this should be a very small load. You need to unplug the TV to have no draw at all from it when on inverter
Also does the converter have its own breaker and is it off, or does it share the breaker with the receptacles and the entertainment centre, so it could be on, knocking out the inverter or microwave?
The inverter staying on while the MW shuts off is odd. My theory cannot account for that. Maybe it happens so fast, the microwave quits faster and then the inverter doesn't need to, no idea.
"The battery is brand new." You know the converter works (you get 12v on shore power---but confirm it is at 13.6v, not 12.x volts)
So suspect the new battery is not connected properly or its fuse blew.
First suspect is the last thing anybody touched :(
We use our MW all the time with Heart 1000W MSW inverter and 2 6V batteries.
Best of luck
Heart inverters (no longer) were considered to be of a very robust design.
There is also that MSW inverters do not draw all the power from a MW that a PSW inverter does (so it runs slower etc. )
A 1000w MSW inverter may be able run a MW that would require a higher wattage PSW inverter demanding full power, and so draw fewer amps from the battery bank as well.
"He put a 3 way switch in the camper (shore power/inverter/battery)."
-(My theory remains that there are other loads besides the MW.)
-How can a three way switch can have two 120v inputs and one 12v input (battery) and one output? Is it a transfer switch and sub-panel or a pass-through with internal transfer switch or just what?
-IMO, OP should take the time to run each circuit one at a time on each input and diagram it all so he is up to speed before dealing with the installer again.
-Several cases posted where the OEM 120v circuit breakers were labelled wrong. You have to confirm those as the owner anyway. "Know your rig."
You are good controller-battery for sure. The array end with #4 should be ok, but let others advise on details where you have a combiner and series or parallel and all that.
Perhaps a new thread for that specific question, naming your controller model, specs, panels, array configuration (with options?)
Solar homes people say "go big - or go home". You can't go big with RV - there is no space. If you want to keep the same lifestyle in RV as in your shore home - then generator is your destiny. Even if max up your solar wattage and battery bank size.
BFL, how often did you have to rotate your tripod to achieve 28% boost compared to fixed tilt?
As stated, three times a day. RJ has found that is sufficient too. At sunset to SE, 1145 to S, 1445 to SW (where 1315 is high noon)
The dips in amps between moves are small so you don't lose much in AH. Just not worth it to be rotating it more often.
If one of those spotty days for when the sun is out, then you might play with it more to grab the sun when it is available--if you have nothing better to do with your time! :)
I can see the attraction of having a roof-full of flat panels and then forget about it for the next several years. You get what you get and there is nothing you can do, so just enjoy your day. :)