A/C pulling from Batteries instead of Generator with GROWATT at High Temps and High Altitude

[Wildman13]

Hello all,
I have a GROWATT 24v 3000 all in one and 2 SoK 206ah lithium batteries. I installed this system back in October and everything has been working great, except for the A/C.

My test run failed after a few minutes as I tripped the BMS in one of the SoK's. I realized I had the settings in the GROWATT wrong. I changed them and the A/C then worked from the generator. I only needed it once over the winter in Arizona but now went to use it again (98 degrees in Utah at 4,500') and it keeps tripping the BMS.


I have a champion 2500 watt inverter generator which puts out 1850 watts continuos. The A/C is a 13.5k and runs at 1650 watts. My thoughts are the high temperatures and altitude combined are dropping the output of the generator below the 1650 needed to run the A/C. I've read its a 3% per 1,000' elevation. This would put the power drop around 13.5%. This puts the output at 1600watts which is almost what the A/C needs to run. I've read temperatures need to be over 104 F to start causing a power drop on the generator.

I would think this would only require a little power from the batteries and not trip the BMS but I'm not an expert in how the loads transfer in such situations.

Any input on what I can test or do to fix the problem would be great. My wife is currently NOT very happy.

 

[WYtreasure]

Try running the A/C on a low fan & higher temp setting. Some cool is better than no cool. ?‍

A swamp cooler may be a better idea, if you have water.

 

[Samsonite801]

A/C units can draw double or more amps at compressor startup with the surge inrush current until the motor coil builds up sufficient magnetic flux.

I had to install compressor motor soft starters on my motorhome for my two roof A/C units to they each wouldn't spike so much at startup with my Magnum 2800w inverter. Before, it would start about 1/3 of the time, but mostly would just trip my inverter with overload light and shutdown (in my case I have plenty of battery amps)...

SoftStartRV – The RV AC Soft Start For Any Air Conditioner - Guaranteed

RV AC soft start devices to run air conditioners - Guaranteed. All RV air-conditioning brands. Soft starters for single AC or entire RV.

www.softstartrv.com

Those guys at the above link focus more on RV A/C units, but several companies make soft starters for all kinds of residential A/C units as well. But the soft starter fixed the problem, both of my A/C units start right up every time now (I can only ever run one at a time with my 2800w inverter, trying second one when first one is running still trips the inverter).

But they even have generic one that can just plug into a power cord (called the SoftStartUp):

FAQ – SoftStartUP

softstartup.com

They say it works for other types of appliances as well like refrigerators and things.


I also bought a different brand soft starter (Hyper Engineering) for my big 14.5 hp upright shop air compressor...

Soft Start Single-Phase | Eltwin

www.hypereng.com

But this would also reduce the inrush on your batteries at startup... You might read into them more, and watch some You Tube videos on them.

Or another option could be to look into the 'inverter' style variable-speed A/C units (like mini-splits and window units) which have all DC motors for the fans and compressors as they natively soft start and tend to draw a lot less amps across the board.

Other than that, the only other option might be to add another battery bank in parallel so the inverter battery circuit draws less amps through each BMS on compressor motor startup (and normal running operation)...

But soft starters are considered a good thing to add anyways on motors which surge a lot on startup, as they make the motor come up to speed a bit slower and smoother. They will also smooth out the sudden load put onto the transistors in the inverter (they soften the blow on the circuit), could help to make the inverter last longer as well.


EDIT: I was not certain if you're having an issue with motor startup, or consistent running operation when I made this post. If the issue is with normal running only when the BMS shutting down, I would definitely consider adding another battery bank. Soft starters are still a good idea though for reasons I mentioned in the paragraph above.

 

[Wildman13]

A/C units can draw double or more amps at compressor startup with the surge inrush current until the motor coil builds up sufficient magnetic flux.

I had to install compressor motor soft starters on my motorhome for my two roof A/C units to they each wouldn't spike so much at startup with my Magnum 2800w inverter. Before, it would start about 1/3 of the time, but mostly would just trip my inverter with overload light and shutdown (in my case I have plenty of battery amps)...

SoftStartRV – The RV AC Soft Start For Any Air Conditioner - Guaranteed

RV AC soft start devices to run air conditioners - Guaranteed. All RV air-conditioning brands. Soft starters for single AC or entire RV.

www.softstartrv.com

Those guys at the above link focus more on RV A/C units, but several companies make soft starters for all kinds of residential A/C units as well. But the soft starter fixed the problem, both of my A/C units start right up every time now (I can only ever run one at a time with my 2800w inverter, trying second one when first one is running still trips the inverter).

But they even have generic one that can just plug into a power cord (called the SoftStartUp):

FAQ – SoftStartUP

softstartup.com

They say it works for other types of appliances as well like refrigerators and things.


I also bought a different brand soft starter (Hyper Engineering) for my big 14.5 hp upright shop air compressor...

Soft Start Single-Phase | Eltwin

www.hypereng.com

But this would also reduce the inrush on your batteries at startup... You might read into them more, and watch some You Tube videos on them.

Or another option could be to look into the 'inverter' style variable-speed A/C units (like mini-splits and window units) which have all DC motors for the fans and compressors as they natively soft start and tend to draw a lot less amps across the board.

Other than that, the only other option might be to add another battery bank in parallel so the inverter battery circuit draws less amps through each BMS on compressor motor startup (and normal running operation)...

But soft starters are considered a good thing to add anyways on motors which surge a lot on startup, as they make the motor come up to speed a bit slower and smoother. They will also smooth out the sudden load put onto the transistors in the inverter (they soften the blow on the circuit), could help to make the inverter last longer as well.


EDIT: I was not certain if you're having an issue with motor startup, or consistent running operation when I made this post. If the issue is with normal running only when the BMS shutting down, I would definitely consider adding another battery bank. Soft starters are still a good idea though for reasons I mentioned in the paragraph above.

Thank you very much for your technical answer.

The inverter seems to trip in the first few minutes. We did get cool air one time for about 10 minutes before it tripped the others were within a minute so it sounds like your issue.

I had originally planned on installing a soft start but then crunched the number (that I could find) and it seemed I didn't. To clarify are you saying that the A/C will pull twice the published 1650 when the compressor kicks in? If so that would make perfect sense but also ver shady on the manufacturer to not publish such information. Our generator is a 2500 max watt so maybe if it doesn't pull twice when the compressor kicks in it might be handling it.

We don't normally go to campgrounds and haven't tested it since putting the whole system in there. If I went to a campground and it ran just fine do you think that would be a good test of proving that I need a soft start or bigger genny?

 

[Samsonite801]

Thank you very much for your technical answer.

The inverter seems to trip in the first few minutes. We did get cool air one time for about 10 minutes before it tripped the others were within a minute so it sounds like your issue.

I had originally planned on installing a soft start but then crunched the number (that I could find) and it seemed I didn't. To clarify are you saying that the A/C will pull twice the published 1650 when the compressor kicks in? If so that would make perfect sense but also ver shady on the manufacturer to not publish such information. Our generator is a 2500 max watt so maybe if it doesn't pull twice when the compressor kicks in it might be handling it.

We don't normally go to campgrounds and haven't tested it since putting the whole system in there. If I went to a campground and it ran just fine do you think that would be a good test of proving that I need a soft start or bigger genny?

Well, the 2500w generator isn't going to be affected by the surge as much as an inverter. The generator will just bog down the speed likely so the surge will be absorbed there, and it will eventually catch back up to full 60Hz RPM.

But the inverter is going to try all it might to keep the output voltage at spec and if it can't meet the load (due to input voltage sagging too low or something) or falls outside of sensor thresholds it will just trip and shut off so it doesn't damage itself. A physical generator armature can handle surge more naturally, as it just transfers as being more load physically on the generator shaft.

Yeah, there are a lot of factors that tie into what the surge will be. If the compressor has fully bled down its head pressure then surge might be less for a second and ramp up more gradually. If there is any residual head pressure (or any additional physical load on the motor), then surge can be a significant amount higher. Some motors I've seen may only surge up about a 1/3 over rated amps, while others can surge 2-3 times over their rated amps, for several seconds, until the inrush balances out.

The soft starter can be thought of in plumbing metaphor like a max flow regulator, to regulate the max inrush, so it flattens out the demand on the supply circuit, clipping it to a maximum possible flow as it spins up. The motor also doesn't start up as violently as before when a soft starter is in there.

Soft Starters also have some other trickery like ability to adjust the frequency of the waveform as the motor speed is increasing, so it can start it more efficiently (improved low RPM motor torque, and align the frequency with the shaft speed better as motor ramps up), basically like a VFR speed controller does...

BTW, they do make amp clamp meters that can record the maximum current flow to actually check what the surge current peaks at..

 

[Hagrid]

There are some excellent answers above, and all I'd like to say is that your issue is almost sure to be the inrush current on startup.

Larry Graves
Grand Design 295RL
1200W Solar, 24V/3000W GroWatt Inverter
4 SOK 12.8V/206AH LiFePO4 Batteries

 

[timselectric]

Just an example.
I have a 24k BTU window unit that draws 10a at 240v.
But the starting surge is 39a. The addition of a soft start brought it down to 12a. My inverter is much happier, now.

 

[Wildman13]

Thanks everyone. Guess I will be getting that softstart unit after all and putting in it. Does anyone have a recommendation? I'm off to the land of google.

 

[MichaelK]

Thanks everyone. Guess I will be getting that softstart unit after all and putting in it. Does anyone have a recommendation? I'm off to the land of google.

The other alternative would be a larger inverter, or one that handles starting surge better. Low-frequency, transformer-based inverters typically handle starting surges much better. That would also be better for starting other "big ticket" items, like large power tools.

As Samsonite mentions, you can get a clamp meter that can read "inrush current". I have a Uni-T 216C, which has proved very valuable for me to determine starting surges. My well-pump has a starting surge of 4X its running power. Your air-con may be the same, but you'd know once you get a meter. Every solar enthusiast should get one

 

[timselectric]

Thanks everyone. Guess I will be getting that softstart unit after all and putting in it. Does anyone have a recommendation? I'm off to the land of google.

EasyStart™ 368 Soft Starter

The EasyStart™ soft start motor starter supports 115 & 230V A/C motors & employs a 4-part start ramp sequence that offers the lowest possible start-up current.

www.microair.net

 

[HRTKD]

As linked to in the post above, the Microair is very popular within the RV community.

One thing to check, make sure your Growatt isn't trying to charge the battery bank at the same time it's trying to power the air conditioner. I have a friend that I talked down off of the ledge this weekend because his system kept tripping. It turned out that he was trying to run off of the dual Honda eu2000 generators (30 amp max) and the Victron inverter was set for 50 amps. The inverter was pulling way too many amps on the shore power line, thinking it could run the air conditioner and charge the batteries.

 

[WYtreasure]

EasyStart™ 368 Soft Starter

The EasyStart™ soft start motor starter supports 115 & 230V A/C motors & employs a 4-part start ramp sequence that offers the lowest possible start-up current.

www.microair.net

Great link, thanks.

I checked on the product hoping it would work for my hot tub. The answer is no.
I'm glad I read this page.

Using EasyStart in Applications Other Than Air Conditioning - Micro-Air, Inc.

www.micro-air.com

 

[Samcat]

One of best solutions if you are willing to spend money and use existing hardware on the RV will be variable compressor speed with inverter that control demand needed to run most efficiently. This roof top units still run 1990 technology and can easily require 3X inrush current to start and they will run single speeds irrelevant to the demand needed for your needs. Split style clima with inverter technology is what you should focus on in the future. This units can draw less than 400-900 watts when operating on variable speeds. And by doing this way you can remove roof top units and have more aerodynamic RV or use it for solar panels on the roof.
Good luck.

 

[timselectric]

Great link, thanks.

I checked on the product hoping it would work for my hot tub. The answer is no.

They didn't provide instructions for my 24k BTU window unit, either. But, I made it work. It just depends on how the existing motor is wired. If you can get to all of the wiring, you can make it work.

 

[Samsonite801]

Great link, thanks.

I checked on the product hoping it would work for my hot tub. The answer is no.
I'm glad I read this page.

Using EasyStart in Applications Other Than Air Conditioning - Micro-Air, Inc.

www.micro-air.com

Yeah, when I had purchased the soft start for my air compressor, their wiring diagram didn't line up with my motor wiring, so I had to ping an email to Hyper Engineering and they had me send a copy of my motor diagram, they up-edited it for me with revisions to their normal wiring, in order for it to work for my application.

Sometimes it doesn't hurt to ping their technical team prior to purchasing a soft starter, so they can make sure you're purchasing the best match soft starter device for your motor.

 

[WYtreasure]

It always helps to chat with someone smarter, that's why I am hanging out here.

The "Single Phase" & HP limitation will keep me from using it on our hot tub.
I'll keep looking for a soft start product for the 20 year old 240V 4HP motors. Our part$ $upplier is alway$ happy to take our call.

I'm in over my head chatting on the subject past this point. The document I linked to in post 12 is a good read though.

FYI:
I jumped in this thread because of the desire to operate my new SPF 6000T DVM MVP @4,800' MSL & high temps. High temps are not likely in this house BUT stranger things have happened. We just went through a couple days of tornado watches and to that I say WTH?

 

[Samsonite801]

It always helps to chat with someone smarter, that's why I am hanging out here.

The "Single Phase" & HP limitation will keep me from using it on our hot tub.
I'll keep looking for a soft start product for the 20 year old 240V 4HP motors. Our part$ $upplier is alway$ happy to take our call.

I'm in over my head chatting on the subject past this point. The document I linked to in post 12 is a good read though.

FYI:
I jumped in this thread because of the desire to operate my new SPF 6000T DVM MVP @4,800' MSL & high temps. High temps are not likely in this house BUT stranger things have happened. We just went through a couple days of tornado watches and to that I say WTH?

You can check with Hyper Engineering. The one I purchased for my single-phase 240v air compressor which is 14.5a rated load, it works good... The model I got says it supports starting amps up to 44a rms (32a rated motor load amps)

Soft Start Single-Phase | Eltwin

www.hypereng.com

Models​

• SS0B12-20SN (115V, 60/50Hz, 12-20 FLA)
• SS1B08-16SN (230V, 60/50Hz, 08-16 FLA)
• SS1B16-32SN (230V, 60/50Hz, 16-32 FLA)

Maybe a call to them and you could have them check which would be the best model to use with your hot tub pump motor... They had very good customer service, where the guy drew up a special diagram for it to work with my motor.