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3 tons
NV.
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theoldwizard1 wrote:3 tons wrote:
... my view is that the Autoformer is no substitute for a Micro-Air, because of it’s slower response time, a characteristic of it’s slower transformer based induction response time versus the MicroAir’s near light-speed response mosfets…
Here is the short electrical engineering of what is happening.
All electric motors that power heavy loads have a "starting capacitor" (there is a mechanical switch that cuts out the capacitor once the motor is "up to speed").
When a capacitor is fully discharged (before the motor starts), it "looks like" a short circuit when power is first applied. Additional/larger starting capacitors just make this worse. The MicroAir actually "limits" (slows down by a few hundred microseconds) how fast that capacitor charges up eliminating the current spike.
Rather than to modulate the starting capacitor, the MicroAir replaces it…
3 tons
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pianotuna
Regina, SK, Canada
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3 tons wrote:
... my view is that the Autoformer is no substitute for a Micro-Air, because of it’s slower response time, a characteristic of it’s slower transformer based induction response time versus the MicroAir’s near light-speed response mosfets…
My tests of the autoformer show these results.
The back yard experiment was at my brother's cottage with a 50 amp outlet. It is in a resort area fed by an ancient grid connection. The autoformer would cut in perhaps 1/4 second (or less), before the airconditioner motor even finished getting up to speed.
Once I added the MicroAir, the autoformer did not cut in any more but that meant the air conditioner ran at a barely acceptable 107 volts, rather than the 112 on the autoformer. The motor speed was lower as well.
I did find a work around by fudging the cut in voltage for the autoformer upwards from the factory setting to 113 volts.
The sequence now appears to be fan start, time delay, compressor start, autoformer cut in. Before it was fan & compressor start with almost instant autoformer cut in.
My view is the MicroAir is no substitute for an autoformer. It does NOTHING to raise the voltage.
Running from the generator the microair seems to make no difference. That is with the Magnum generator input throttled to 23 amps (which is the output from the generator).
* This post was
edited 04/18/23 01:21pm by pianotuna *
Regards, Don
My ride is a 28 foot Class C, 256 watts solar, 556 amp-hours of Telcom jars, 3000 watt Magnum hybrid inverter, Sola Basic Autoformer, Microair Easy Start.
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pianotuna
Regina, SK, Canada
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theoldwizard1 wrote:
Here is the short electrical engineering of what is happening.
All electric motors that power heavy loads have a "starting capacitor" (there is a mechanical switch that cuts out the capacitor once the motor is "up to speed").
When a capacitor is fully discharged (before the motor starts), it "looks like" a short circuit when power is first applied. Additional/larger starting capacitors just make this worse. The MicroAir actually "limits" (slows down by a few hundred microseconds) how fast that capacitor charges up eliminating the current spike.
What is in the MicroAir that limits the surge? I do know they had a replacement for the 'hard start' kit on the oem air conditoner.
Thanks for this information--it explains why the autoformer cuts in so fast without MicroAir, and why the autoformer doesn't with the MA in place.
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3 tons
NV.
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3 phase motors don’t require capacitors to get the rotor to spin, since multiple alternating phases do the trick - not so with single phase…Voltage sag is the result of the difficulty ‘single phase’ has to motivate the rotor to spin…Adding an autoformer may help to slightly boost the voltage (which may help preserve the windings), but doesn’t alter this hard single phase dynamic…Consider too that a quarter of a second response time still equates to about 15 full AC wave cycles, which is like running molasses compared to a fast acting capacitor or a MicroAir soft start device, which nowadays are a common upgrade in the HVAC industry, even including now capacitor free blower motors - check your blower motor…
Besides high cost, this is why we don’t see sluggish autoformers featured on single phase motors…JMO
3 tons
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K_and_I
North Central Ohio
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This is not directly related to rv's, but I had an Easy Start on my trailer and liked it so well, I put one on my residential 2.5 ton heat pump when Micro Air started making residential units. My heat pump compressor was rated at 73 amps lra. The Easy Start has blue tooth ability to be read by my phone. This is what it showed after the 5 training starts:
![[image]](https://i.imgur.com/9tWfaTwl.jpg)
From 73 lra to 23- not bad
K_and_I
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pianotuna
Regina, SK, Canada
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K_and_I,
Nice that they have a blue tooth app. Mine does not as I was an early adopter.
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3 tons
NV.
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Thanks, From 73 LRA (Locked Rotor Amps) down to 23 LRA (about a 2/3rds reduction!) is all that’s needed to know…Voltage sag is of little concern…
3 tons
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StirCrazy
Kamloops, BC, Canada
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K_and_I wrote:This is not directly related to rv's, but I had an Easy Start on my trailer and liked it so well, I put one on my residential 2.5 ton heat pump when Micro Air started making residential units. My heat pump compressor was rated at 73 amps lra. The Easy Start has blue tooth ability to be read by my phone. This is what it showed after the 5 training starts:
From 73 lra to 23- not bad
wow, I am going to have to check that out. would be a lot easier on the breaker over a longer period also
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ktmrfs
Portland, Oregon
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micro air vs. autotransformer:
the purpose of the micro air is to reduce PEAK starting current (locked rotor amps) so that non ideal voltage sources (typical small generator) that have limited max current output to START a AC unit. It does nothing to increase voltage once started.
Autotransformer:
bump up a low voltage source to a higher voltage to keep voltage within expected operating range.
So. If your using a "ideal" voltage source, most utility lines that can easily supply 3x or more the breaker rated current on a short term basis, the micro air really isn't needed.
But if your line voltage sags, then the autotransformer is solution.
Now I suspect, but can't verify, that what pianotuner is seeing with the micro air and autotransformer is this, The auto transformer probably has hysteresis, it will cut in at a low voltage and KEEP it in at a given level EVEN if the input voltage rises somewhat above the cut in voltage. So what may be happening is w/o the micro air, voltage sags enough to cut in the autotransformer but it doesn't rise enough to cut it out completely and continues to do it's intended job,
Now add the micro air, Now input voltage never drops enough to get the autotransformer to cut in, since the current draw is low enough to not cause a big enough sag in input voltage, so the voltage remains at the very low end,
so.... in this case the micro air (a) isn't needed to start the AC anyway and (b) then voltage remains low,
If one takes the autotransformer out of the circuit and starts the AC I suspect the line voltage then would be back to the 107 or whatever it is with the micro air, Micro air shouldn't reduce the input current draw once the compressor is running by any noticeable amount, it only reduces starting current,
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pianotuna
Regina, SK, Canada
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ktmrfs thanks for the excellent explanation.
I do have one location which I visit yearly where the unloaded line voltage is 100. The autoformer is a god send then to boost the voltage when running an electric heater.
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