Soft Starters for Air Conditioners

svetz

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The label on the side of the AC condenser should state LRA (Locked Rotor Amps), for example a 3 ton AC might be 77, a 5 ton 145.

If LRA is the inrush, than 77A x 240V = 18.5 kVA would be needed. If the power factor is 1, that's 18.5 kW. For sizing a generator, this ref says:
The case is that nameplate LRA is given for full voltage starting. In reality, when you start a motor from a generator, the current surge causes voltage dip. When voltage drops, the current is reduced proportionally. Most residential appliances can start with 30% voltage sag, that is at 30% lower currents. As the result, starting volt-amps could be 0.7*0.7=0.49 of nominal.

For example, a typical 5-ton (5HP) a/c has 145 LR amps at 240VAC. At 30% voltage dip it would require (145*0.7)*(240*0.7)=17,052 VA to start. Note that commercial applications normally allow only 15% drop, in which case you would need to deal with 0.85*0.85=.72 of nominal starting kVA.

So, for the generator it's probably taking 77 x .7 x (240x.7) = 13VA. I wonder at what appliance voltage sag the inverter resets at? A 30% dip is 168V, a 15% dip 204V. Possibly this can be calculated or deduced/calculated from the surge information?

Soft Start Candidate?
I've "heard" a soft starter can reduce the start up load by as much as 40%. How much of that is real and how do you pick a soft starter?
 
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svetz

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Types of compressors
AFAIK, there are a few types of compressors common in HVAC units. One is a variable speed motor driven by an inverter...these are typically what you find in a mini-split and a soft starter won't work with them so we'll ignore them.

The other is a motor that has a start and run winding. Capacitors in an AC circuit shift the phase,
so a start capacitor can have the run winding and the start winding out of phase which servers to
do the initial push/pull to get the rotor turning. Once turning, the start capacitor is cut from the circuit
via a centrifugal switch. These are easily identified by the two big capacitors in the condensor
(or a dual capacitor).

Another common type of motor is the Permanent Split Capacitor (PSC). They are reversible so
common in heat pumps. They are efficient, have only once capacitor, and therefore do not need a centrifugal switch.
CSCR_diagram.jpg

How does a single-phase soft starer work?
Soft starters limit the starting voltage, this reduces the rotor torque. But, reduced torque for an air conditioner is acceptable because when it turns the Phigh = Plow in the compressor. This also means you need a delay between the compressor starting/stopping to allow the pressure to equalize.

How low can the voltage go? The reference in post #1 suggests 30% for residential appliances. "Smart" soft starters do more then lower the voltage, they do it based on algorithms. By altering the voltage ramp up while monitoring the current during the first few startups, they can optimize the power flow for future startups.
 
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svetz

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...Think you meant 18.5kVA in the first post. :)...
Sure did! Thanks!

The EasyStart and HyperEngineering seem to be the two best known brands. Schneider and Siemens have them too, although they look more general purpose. WEG and Stellar make them for very large (commercial) air conditioners.
 

snoobler

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Nice! I hadn't heard of Hyper before. I wonder if that would be a good candidate for a deep well pump as well.
 

mapguy525

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Sure did! Thanks!

The EasyStart and HyperEngineering seem to be the two best known brands. Schneider and Siemens have them too, although they look more general purpose. WEG and Stellar make them for very large (commercial) air conditioners.

Do you have any experience with the HyperEngineering products?

I have been impressed so far with performance of the Microair EasyStart used for 13.5/15 K btu AC units on RV's. It is not cheap.
 

svetz

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...Do you have any experience with the HyperEngineering products?...
No, just started looking into them....hopefully folks that have them can give us reliability reports. Only saw one comment on it on Amazon:

It takes a number of on cycles until the the compressor inrush current is sufficiently reduced. An emergency generator has to be able to supply the initially higher starting current. In our case the first startup current was 49 A. This reduced to 25 A after several cycles. The LRA our compressor is about 75 A without soft start.

There are tons of comments on the EasyStart...the negative ones are about:
  • Poor installation instructions
  • Delayed time between restarts (if your AC cycles a lot, this isn't for you)
  • Takes 10 full power start ups before it "learns" how to reduce the power.

...I have been impressed so far with performance of the Microair EasyStart used for 13.5/15 K btu AC units on RV's. It is not cheap....
Do you know your before/after inrush?
 
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LanduytG

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I can vouch for the Easy Start. I have 2 of them on my 5th wheel and can run both units on a 3kw gen. I use to know the numbers for inrush but its been a couple of years. Start up surge is not much more than full run. From what I remember you have to start and stop the a/c 5 times so it can learn. I remember that after the third time it never made much of a difference.

Greg
 

HRTKD

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@Sojourner1 put a startup device on his RV A/C unit recently. As detailed as he is with his solar system, he may know the numbers for his A/C also.

I've run two A/C units on my trailer. One was the rooftop unit and the other was a portable. Both ran OK without modification, but my trailer has a 5500w generator. My circuit breakers will trip if I fire up two space heaters at the same time. I need to find an easy start device for those. :)
 

Sojourner1

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Here is my experience installing the micro-air 364 on my Carrier Air V 15k air conditioner (Locked Rotor Amps -- Low Profile, High Capacity 59.0 Amps) on my 5th wheel trailer.
20170715_110913_copy_1600x1200.jpg
When I was in a campground hooked up to 50a service, completed the 5 learning cycles. It was interesting to watch the Magnum Remote display in the AC input screen, the air conditioner fan would run for a couple minutes then I could see 3-4a load coming in for 60 +/- seconds then quickly climb to roughly 18a then settle at 14a.
Here are the test that I did. While still plugged into the pedestal I turned the load share down (Hybrid inverter) 15a, 10a, 5a and turning the air conditioner off for a couple minutes between each lowering and at no time did the ac unit stumble or did a red fault light show on the me-arc.

Then I disconnected the the power from the pedestal and connected it to the eu2200i generator setting the load support to 15a and 10a, same results no red fault light on the me-arc and no "overload" or stumble on the generator. Also I'm in tree cover/ overcast so little to no solar was helping.

Tried the 15k A/C unit from just batteries to see if the fault light would show on the Me-Arc display from the hybrid inverter. No fault light and no stumble in the A/C at anytime.

Initially turning it on the fan started and after 30 seconds the compressor started to spool up slowly, watching the displays I could see the amps slowly climbing and max somewhere in the 190a range before settling down to 94a. So if I just use my minimum loads and the sun is shinning the solar panels will cover roughly 60-75a of the A/C load, balance from batteries would be 30ah +/- (6% SoC be depleted per hour).
 

Ampster

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My circuit breakers will trip if I fire up two space heaters at the same time. I need to find an easy start device for those.
Are they resistive? I did not know resistive loads had surge current. Maybe that is why the smiley emoticon?
 

snoobler

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Since he said circuit breakers, I'm sure he's pulling too much on a given circuit breaker. 2 1000W space heaters on a single 15A breaker will pop it. I think the smiley indicated he was being silly.
 

HRTKD

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Yes, it was probably just too much load on a circuit. I need to label the outlets to be able to differentiate which outlets are on different circuits. It's a small trailer, so there can't be THAT many circuits. It's a learning experience. I've popped breakers at the distribution panel as well as at the generator. Connecting space heaters on the same circuit that the converter is on may also be what happened. I haven't spent much time examining the AC side of the trailer.
 

svetz

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I contacted MicroAir and told them about the Enphase Ensemble setup here to see if their EasyStart device would work. They weren't 100% sure with the frequency shifting (curtails power from the solar panels while off-grid), so they're sending me a "special" version that they can get diagnostics from and download updates to. They seemed sure they could get it to work, so fingers crossed! 🤞
 

HRTKD

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I contacted MicroAir and told them about the Enphase Ensemble setup here to see if their EasyStart device would work. They weren't 100% sure with the frequency shifting (curtails power from the solar panels while off-grid), so they're sending me a "special" version that they can get diagnostics from and download updates to. They seemed sure they could get it to work, so fingers crossed! 🤞

That's pretty cool! A company that actually wants to work with customers. Amazing.
 

svetz

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...That's pretty cool! A company that actually wants to work with customers. Amazing.
I've exchanged a number of emails now (mostly logistics/data) with MicroAir now and they're very professional and responsive. I went from 86.4 to somewhere between 29 and 35 inrush amps; so that's way cool. Starting from the inverter is even lower, about 26.6 amps consistently. Posting all the nitty gritty details in the system's blog.
 

Samsonite801

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My application isn't for an A/C, but rather a Husky air compressor. I purchased the Hyper Engineering SureStart - SS1B08-16SN - 50/60Hz, 230v, 08-16 FLA.

My motor is a Marathon Electric 5KCR48UN2553Y non-reversible rotation (which I have a hard time finding exact documentation for).
1606503989934.png

I removed the supply cables off of the L1, L2 and Gnd so far, to get them out of the way for a minute...
1606504035900.png

Trying to figure out how to wire it in. I look at the diagram, and they seem to only show the 'run' cap in their circuit. Does this mean we omit the 'start' cap completely?

1606503863152.png

I think the diagram for the motor might be this one or close to it:
1606504157694.png

I guess I see the run cap in this diagram is sitting backwards in relation to the way Hyper Engineering has you put it in their circuit, toward the aux/start coil. Do I ditch the whole factory circuit and just wire it all exactly the way from the Hyper Engineering circuit, ditching the start cap altogether? That's what I'm assuming. And I don't know if mine has that 'EX START - When Specified' thing in there or not... And Hyper Engineering doesn't really show how the centrifugal start/run switch ties into the circuit. Is that omitted along with the start cap?

The manual says, 'make sure you uninstall any previously installed hard-start kits'... Wondering if that means the factory centrifugal switch and start cap circuit?

Most of this wiring in the factory circuit is not visible without taking the rear bearing housing of the motor off. I can only see two wires coming out of each capacitor mount when pulling those covers, and what you see inside the terminal power input panel (seen in picture above)...

I did send a message with my questions to Hyper Engineering, but don't imagine they'll get back to me until next week...

I think I'm gonna run over there in a bit to the storage unit where it is and pull off the caps, and ohm out all the leads and see if I can identify the windings and confirm the stock wiring matches what the above motor diagram seems to be indicating (it was not an exact p/n match for my motor).

Trying to make sense of it, hopefully I don't damage the gaskets that hold the smoke in...

Just thinking out loud here, maybe someone has some experience with this, or people could just cheer me on and cross your fingers for me and we'll see what happens.

BTW, Happy Thanksgiving holiday :)
 
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Samsonite801

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So I went over and checked out the motor with an ohmmeter, and confirmed it matches the diagram exactly, here are some edits:

1606525415309.png

I imagine the direction of the run cap doesn't matter since is AC... And it does have the 'EX START' winding in there as well, because I can measure both the START and EX START separately, and sum the ohms up across both.

1606525471402.png


So yeah, didn't really have enough guts to just try anything out yet... I might wait til next week and see if I can chat with Hyper Engineering support about it. The question for me is where exactly to tap the RUN CAPACITOR connection to, right on the START coil, or with it also going through the EX START coil too, and the other question about whether to ditch the factory start circuit (with the start cap and centrifugal switch).

I am excited to see this thing work, because I know before, I was not able to start this motor using my Prius UPS inverter before (has 3500w continuous, 5250w surge).

The manual says this Hyper SureStart is supposed to 'learn' after more starts and further optimize for smooth, low-surge startup. Can't wait to see how it works. If the motor still can't start it with the SureStart, I got another inverter coming for the Prius which is almost same but a bit bigger at 4200w continuous (not sure the surge rating as I couldn't find a published spec on it)...

1606527072282.png
1606527093739.png
 
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