Battery Faults on AC Compressor

[TurbineTester]

I have 6 100 Ah Lifepower4 batteries connected to 4 inverters running split phase, 2 in each phase. Up until this last week I was running the same setup but on only 2 inverters. I could Tun my whole house on those two inverters with mostly no problem if we were careful about running high appliances at the same time. Dryer and water heater and coffee pot was big No. The house AC would run in this configuration but it would constantly trip the GFCI outlet in our bathroom. Occasionally either a dryer or microwave or AC starting would overload the inverters and the power would shut off until they auto restarted 5-10 seconds. We got tired of dealing with trying to balance loads so I got the two additional inverters. Now, however, when the AC comes on it’s about a 50/50 shot as to whether or not we actually fault out the batteries. This is super frustrating because then the entire system has to be completely manually shut down and restarted in order. Every AC in/out breaker and every single battery breaker and then whole system has to be restarted in order. These batteries should be able to handle the inrush of this compressor turning on right? I mean if I have a hard start installed on the ac ( which we do) and 6 freaking batteries with surge capacity of over 1,000 amps in total, I don’t understand why they are shutting down. Now we can be at a moderate load of around 5000w and the AC kicks in and the house is dark for dozens of minutes while a restart everything. Used to be it would just kick over to grid power and the lights would flicker. Now we are dark and grumbly in our house. Super frustrating. Please help me stop tripping the batteries and any suggestions welcome.

Thanks in advance.
Chris

 

[sunshine_eggo]

LRA of A/C compressors is ungodly. I'm impressed you got it to start at all with only two. Have you considered a soft start? Contrary to the specifications, those lightweight inverters really don't have much surge capability.

Wiring parallel inverters sharing phases can be critical. Your AC and DC wiring need to be identical.

 

[shopman]

A hard start kit and a soft start like the Microair unit are two different things. The hard start won't help you at all but the Microair Easy Start will solve your problem. The Microair will drastically reduce the startup current draw of your A/C compressor and its that startup current surge that's killing your system. As an example, our unit would draw over 70 amps on startup. After installing the Microair unit it reduced that startup current to just 18 amps.

 

[timselectric]

Seems odd that it's tripping 6 batteries.
How are they wired?

 

[DIYrich]

What inverter? How are you charging the battery? Do you charge them to 100% on a regular basis?

 

[timselectric]

The house AC would run in this configuration but it would constantly trip the GFCI outlet in our bathroom.

I think that you have some wiring issues.

 

[Nobodybusiness]

I have 6 100 Ah Lifepower4 batteries connected to 4 inverters running split phase, 2 in each phase. Up until this last week I was running the same setup but on only 2 inverters. I could Tun my whole house on those two inverters with mostly no problem if we were careful about running high appliances at the same time. Dryer and water heater and coffee pot was big No. The house AC would run in this configuration but it would constantly trip the GFCI outlet in our bathroom. Occasionally either a dryer or microwave or AC starting would overload the inverters and the power would shut off until they auto restarted 5-10 seconds. We got tired of dealing with trying to balance loads so I got the two additional inverters. Now, however, when the AC comes on it’s about a 50/50 shot as to whether or not we actually fault out the batteries. This is super frustrating because then the entire system has to be completely manually shut down and restarted in order. Every AC in/out breaker and every single battery breaker and then whole system has to be restarted in order. These batteries should be able to handle the inrush of this compressor turning on right? I mean if I have a hard start installed on the ac ( which we do) and 6 freaking batteries with surge capacity of over 1,000 amps in total, I don’t understand why they are shutting down. Now we can be at a moderate load of around 5000w and the AC kicks in and the house is dark for dozens of minutes while a restart everything. Used to be it would just kick over to grid power and the lights would flicker. Now we are dark and grumbly in our house. Super frustrating. Please help me stop tripping the batteries and any suggestions welcome.

Thanks in advance.
Chris

Regardless of what the AC does you shouldn’t have GFCI tripping.

Take a look at your wiring.

 

[TurbineTester]

A hard start kit and a soft start like the Microair unit are two different things. The hard start won't help you at all but the Microair Easy Start will solve your problem. The Microair will drastically reduce the startup current draw of your A/C compressor and its that startup current surge that's killing your system. As an example, our unit would draw over 70 amps on startup. After installing the Microair unit it reduced that startup current to just 18 amps.

I hear you that the Softsrart will solve the problem and I will likely order that today. However, even if the LRA on the AC were 100 amps that’s still only a surge of 240 Amps at the batteries. Even considering losses if it were a surge of 300 amps it’s across 6 batteries and each battery would only see a 50A surge for a brief second. I don’t understand why that would trip the batteries into an alarm state?

 

[TurbineTester]

What inverter? How are you charging the battery? Do you charge them to 100% on a regular basis?

They are charged through 16kw of solar panels on a daily basis or as the sun provides.

 

[Quattrohead]

Don't assume all the batteries will provide an equal amount of load, one may be reacting quicker possibly due to it a slightly lower internal resistance or maybe it is the closest to the inverters in your wiring scheme. Then when that one trips the next one picks up the task, cannot complete it trips and so on.
It sounds like you may have some less than ideal wiring going on and I know it hurts to criticize your great work but please share more about how your batteries and AC outputs are connected.

 

[TurbineTester]

What inverter? How are you charging the battery? Do you charge them to 100% on a regular basis?

Also they are EG4 6500EX

 

[TurbineTester]

Don't assume all the batteries will provide an equal amount of load, one may be reacting quicker possibly due to it a slightly lower internal resistance or maybe it is the closest to the inverters in your wiring scheme. Then when that one trips the next one picks up the task, cannot complete it trips and so on.
It sounds like you may have some less than ideal wiring going on and I know it hurts to criticize your great work but please share more about how your batteries and AC outputs are connected.

My four inverters are fed AC from the main service entrance wire after the meter, before the breaker using ILSCO tapping lugs. When I am on inverters for the whole house I turn of the 200A main breaker at the main panel. My four inverters receive the grid though a sub panel in my garage. Two of the inverters (both input on 2P2) get solar power, the other two are grid/battery only. The only reason I did that was because I started with two inverters and ran all the solar to them. Plan was to include the 2P1 inverters on solar when I have the physical space cleared out to add more PV. All 4 inverters are fed battery power through 1/0 AWG welding wire and 100AMP DC breakers. The AC output from the inverters is 6ga THHN wire (for L and N, ground is slightly smaller per Will’s videos) run into a load center that feeds the garage (lights, garage door, router, fridge and freezer) and has breaker output going back to the house main load center. So at that panel there are 4x60A breakers feeding the load center and 2x20 amp circuits for the garage loads and 4x60A breakers connected to the 4x6ga THHN feeding the L leg of split phase back to the house main load center. N-G are bonded at the garage load center panel and ground rod driven at garage. At the main house load center the breakers feed the panel through 4x60A breakers. Main panel grounded with 2x8’ ground rods. Keep in mind the 200a breaker is physically off when I want the inverters to power the whole house. Since I connected the two new inverters (total 4) the GFCI has not tripped a single time. Instead the batteries fault, but not every time. The GFCI would often trip when the 2 inverters would transfer from solar/battery over to grid power for the AC compressor start. I also think I had the split phase configured incorrectly when I had only two inverters. When I was running 2 I had them at split phase 120* out of phase (because it was the default). When I wired up the two new ones and actually remembered how to do the 120/240 math and measure with voltmeter I realized they they should be 180* out of phase to get the full 240 volts I had with grid (instead of 208). So that’s the basic gist of the full configuration. I can post some pictures shortly.

 

[TomC4306]

I hear you that the Softsrart will solve the problem and I will likely order that today. However, even if the LRA on the AC were 100 amps that’s still only a surge of 240 Amps at the batteries. Even considering losses if it were a surge of 300 amps it’s across 6 batteries and each battery would only see a 50A surge for a brief second. I don’t understand why that would trip the batteries into an alarm state?

Did you forget about the "moderate load" already running?

Now we can be at a moderate load of around 5000w and the AC kicks in and the house is dark

 

[TurbineTester]

Did you forget about the "moderate load" already running?

No, i didn't. 5000w AC output is only 113.12A/6 batteries is less than 20A per battery. Even if one of the batteries is seeing double that current draw, and the batteries are loaded unequally so we get 100A surge we would only have 140A total current from a worst case battery for 1-2 seconds. The spec, if i'm reading it correctly, states that over current protection has to exceed 150A for 3 seconds or 100A for 10 seconds to trigger BMS fault. Now, just because i didn't forget about the moderate load already on the system, doesn't mean that my assumptions are right or that my math is good Obviously, the next logical step is to see what the actual battery fault is when the AC compressor starts. It could be overcurrent, or under voltage and could be limited to a single cell. I just got the computer hooked up to read the batteries last night. Today i'm going to try it again and see what the actual fault is at the battery. After that i obviously need to get a soft start installed and see how it behaves then.

 

[solarhombre]

No, i didn't. 5000w AC output is only 113.12A/6 batteries is less than 20A per battery. Even if one of the batteries is seeing double that current draw, and the batteries are loaded unequally so we get 100A surge we would only have 140A total current from a worst case battery for 1-2 seconds. The spec, if i'm reading it correctly, states that over current protection has to exceed 150A for 3 seconds or 100A for 10 seconds to trigger BMS fault. Now, just because i didn't forget about the moderate load already on the system, doesn't mean that my assumptions are right or that my math is good Obviously, the next logical step is to see what the actual battery fault is when the AC compressor starts. It could be overcurrent, or under voltage and could be limited to a single cell. I just got the computer hooked up to read the batteries last night. Today i'm going to try it again and see what the actual fault is at the battery. After that i obviously need to get a soft start installed and see how it behaves then.

Do the 4 inverters display 120V output when running? I made a wiring mistake (I used the current sharing cable when I shouldn't) and initially one was showing 111V and the other 118V. This issue tripped my AFCI and sometimes a GFCI when transferring from grid to batteries and vice versa.

The slow start kit will definitely help. I replaced a 13yo 5 ton AC this year and through the Emporia Vue2 I noticed that the new compressor starts slowly (200-300W) and then ramps up over a minute or so instead of a loud bang and 3500W+ instantly.

Lastly, when it's time for a new water heater, get a heat pump one. I run mine in heat pump mode only and it uses between 300W and 420W when running, and also cools and dehumidifies the garage.

 

[TurbineTester]

Do the 4 inverters display 120V output when running? I made a wiring mistake (I used the current sharing cable when I shouldn't) and initially one was showing 111V and the other 118V. This issue tripped my AFCI and sometimes a GFCI when transferring from grid to batteries and vice versa.

The slow start kit will definitely help. I replaced a 13yo 5 ton AC this year and through the Emporia Vue2 I noticed that the new compressor starts slowly (200-300W) and then ramps up over a minute or so instead of a loud bang and 3500W+ instantly.

Lastly, when it's time for a new water heater, get a heat pump one. I run mine in heat pump mode only and it uses between 300W and 420W when running, and also cools and dehumidifies the garage.

Yes all four show 120v. Hmm, my water heater is basically in the center of my house, moving it to a new location and installing a heat pump seems like it would be very expensive.

 

[rcrracer]

2 in each phase

What keeps these two inverters in perfect phase with each other?

 

[DIYrich]

When I was running 2 I had them at split phase 120* out of phase (because it was the default). When I wired up the two new ones and actually remembered how to do the 120/240 math and measure with voltmeter I realized they they should be 180* out of phase to get the full 240 volts I had with grid (instead of 208). So that’s the basic gist of the full configuration. I can post some pictures shortly.

My first thought was whether you commissioned them properly. Did you measure the voltage across l1 and l2 with a volt meter?

My guess is that one of your batteries is bad. Can you connect to the BMS's? You may need to test each battery individually. Each one alone should be able to support 5kW load for a short period of time.

What charge rate are you using for the batteries? Do one slow charge cycle (30 amps, .05c) on an occasional basis. Otherwise, 60 amps (0.1c) on a regular basis. If you have net metering, let the rest of the PV go the grid. If you don't have net metering, then let solar charge to 80%, and slow charge from there.

 

[Hedges]

As mentioned by others, balance of current draw between batteries is important. How about a sketch and/or photo of battery & inverter DC connections?

I think your batteries will be in a rack with cables or busbars between them. One inverter you would connect diagonally. Second inverter you might connect opposite diagonal. Four, could copy the first two.

Starting surge of course is an issue, and you can't measure fast enough to see it. But with a heavy steady-state load you could compare current draw among the batteries. DMM, debug voltage drop across connections.

Battery voltage affects how much current drawn by inverter. Lithium discharge curve is relatively flat, but I could imagine different SoC leaving a couple more full trying to carry the entire load. Balanced resistance over some charge/discharge cycles might help get them balanced.

Since you have heavy resistive loads as well, a kludge would be temporarily load-shed. When A/C cycles on, a relay could disconnect something like oven, dryer, water heater momentarily, reconnect after a few seconds. All power to a dryer interrupted would end its cycle, but just one leg would simply turn off heating element while keeping timer and motor running.

 

[TurbineTester]

Quick pic of the system

 

[sunshine_eggo]

All DC cables the same length?

All AC cables on each phase the same length?

If not, see link #5 in my signature.

 

[Hedges]

Looks like each battery has short cable to busbar.
Where do inverters connect to busbar? (I think that is hidden by wire loom/guard).

 

[Browse]

I experienced something similar with my HVAC with soft starter and my 4 Lifepower4 batteries. Had to change my inverter setting to run off voltage levels instead of % SoC. Batteries were sagging too low and the inverter would fault. Set a low battery shutoff voltage to 46VDC and everything worked after that.

 

[ksmithaz1]

I'm picking this back up, because I'm going to try and solve the brown-out I'm getting with A/C startup. RLA/LRA (Run Load/Locked Rotor) amperage numbers may not even tell the whole story. For example, the 4T on my roof is the 2nd to the last column:



So 19.9 amps nominal running, 109 amps when the rotor won't spin. Based on monitoring, I've found my actual RLA to be about 18+ amps with everything running, so better than spec. A soft-start kit will improve your in-rush by pushing the start winding a little harder, ie getting it spinning sooner to increase impedance, but in-rush is an inverse curve, and can be 15x nominal at time 0+. That puts you in the 300A range, for a fraction of a fraction. A really good recording meter will let you catch a reasonable chunk the tail end of the current fall-off, but keep in mind the curve is much steeper than the ability of a decent meter to sample and display.

To simplify, the capacitor in a compressor motor breaks out some electricity for an offset winding to continually nudge the armature in the right direction, which is kind of critical when you first apply power to get it to spin. A soft-start kit simply increases the initial nudge, then drops out once the motor is actually spinning. 3-Phase motors do not require a start winding, and have a somewhat lower in-rush. I the DC world, when you apply power to a capacitor, there is a huge in-rush while it 'fills' the capacitor. As the capacitor fills up the resistance increases lowering in current. In the AC world the windings in the motor create resistance based on impedance, which is determined by a number of factors (frequency, resistance of the winding, ...), but "LRA" represents a worst case lowest impedance if you energize the windings and nothing can spin (once spinning you increase impedance. so more resistance, less current). Similar to a capacitor, when you first energize windings they want to build up a magnetic field and create an in-rush of current as the field grows, and the armature is not spinning. So until an ac electric motor is spinning, it really tries to eat electricity, then falls off rapidly once it starts spinning.

I'm going to be playing with some current limiting devices, but that big jolt, also gets the train moving, so you need enough juice to get it spinning, without allowing it to cause a current over-draw that drops out your voltage below a reasonable threshold and gives you a brown out.

 

[wheisenburg]

I have a small 2 ton AC. The surge current even on this unit was 65 amps AC. Many meters are fast enough to capture the full surge current. This maps to 312 amps DC. If you have a large 4-5 ton AC it could have a 120-130 amp surge current. This could trip those batteries if you have other loads running. What likely happened here is that your increased inverter capacity, simply allowed the AC to draw more current on start up and overload the batteries. I have three batteries and two Schneider inverters. I was getting battery faults when my AC started up if I had any other large loads running. Lucky that they just reset themselves and came back up after a minute or so.

I know these inverters are smaller than mine, but I am running 4/0 to each inverter. They surge to 12,000 watts or 240 amps DC each. I plan to add 3 more batteries. That should allow the batteries to handle the surges, but right now the batteries are the weakest link. Do you have a common DC bus for the inverters or do you just run 8 1/0 wires back to the battery bus?

Microair Easy Start solved the issue for me. My surge current is now 25 amps. Running current is around 5. When an AC first starts up, it is basically a short circuit for a short period of time. These huge surges can also cause nuisance trips in other circuits. I would be through you panels and double check all the connections. Make sure nothing is loose. I did this and found some loose neutral and ground wires.