I need some help. I just installed a 12 volt battery bank with 10 Lifepo4 batteries from Elfhub. They all run to bus bars and then to (2) Aims 5000 watt modified sine inverters. I charge with a 100 amp Lithium rated charger from Powermax, set at 14.4vdc. The batteries charge up fine but when we apply any load above 1700 watts, the inverters will fault and turn off. I've done plenty of these systems with golf cart batteries and they work fine. I thought the Lifepo batteries would be better but I'm afraid that the BMS in those batteries is somehow not liking my setup. My thinking was that even with 100 ah BMS, 10 batteries running in parallel to bus bars should be able to produce that much power with no trouble. Any thoughts?
Inverters cut out at half capacity
- Thread starter agrota21
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RCinFLA
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A 5000 watt 12v inverter is an unrealistic device due to DC current required. 12v system is reasonable for 1200-1500 watts. You cannot afford much battery line voltage drop on a 12v system.
You are likely dropping out due to inverter DC input voltage slump. Most cheapo 12v inverters shutdown at 10.5vdc.
1700 watts / 85% efficiency = 2000 watts DC input / 10.5vdc DC input = 190 amps.
You are likely dropping out due to inverter DC input voltage slump. Most cheapo 12v inverters shutdown at 10.5vdc.
1700 watts / 85% efficiency = 2000 watts DC input / 10.5vdc DC input = 190 amps.
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No doubt, these are cheap components but I've been using these inverters on golf cart batteries in dog grooming vans for years, with no problems. I have a meter connected to the bank and it says we are at 13.2 volts
Zwy
Solar Wizard
Open circuit voltage or under load? As was mentioned, under load is when the voltage reading needs to be taken. What size/length of cables from busbar to inverter?
McKravitts
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Check the battery voltage at the conection to the inverter(s). With that high amp draw it's probably much lower.
What gauge cable are you running from the batteries to the inverter(s)?
RCinFLA
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I highly doubt you have 13.2v DC at 190 amps load current at inverter DC input terminals.
10.5 low cutoff...running at 13.2 under load. I am wondering if it's current, not voltage. but you would think the voltage would drop if we exceeded the current capacity...I'm just not sure if the BMS behaves in such a way that it just shuts down the output when it maxes out. That said, I have 10 batteries...10!
I started at 13.7 after charging the batteries to float stage. I hear you, but that's what the voltmeter says and it's connected to the bus bars right near the inverter.
The whole bank is wired with 1/0. I was thinking about doubling up the leads from the bus bar to the inverter but it's really only about 18" away.
Yes, but what's dropping? The inverter or the battery output? Do Lifepos shut down in that circumstance? We just did a little test with the van engibe running, hoping the charge line would suppliment the bank enough but it still dropped out. Sometimes it will even blink on and off without crashing completely.
1/0 is only capable of feeding 125A, and it would do that with a voltage drop.
5000W should pull around 410A... so... yeah, dramatically too small wiring.
You would need a PAIR of 4/0 feeders to handle 5000W...
What brand LFP batteries are you using?
It is possible they have cheapo bms that is limiting output.
It is possible they have cheapo bms that is limiting output.
How are the 10 LFP batteries tied in parallel?
McKravitts
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1/0 is rated 100 amps. You are trying to push almost double that through it.
Yes...cheapo...Elfhub. Customer bought all the stuff and I am just installing it for her.
Each battery has it's own run to a 5 unit bus, both a negative one and a positive one...2 groups of 5 with a 1/0 jumper from bus to bus...
50ShadesOfDirt
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Now that the whole picture is uncovered (no proper design from the start), you could keep trying to thrash all the pieces into a solution, or, you could work with the customer to do the design work, and see what pops out at the other end. From that design, some or all of the current pieces then might fit (be reused) in the new design.
At the least, and just guessing because the design requirements aren't obvious, I'd say move to 24v or 48v inverter, being as someone thought they needed two 5kw 12v inverters. The good news is that you can assemble some beefy 24v or 48v battery-banks from the pile of 12v batteries.
Customer might complain, but that is a consequence of possible purchase before design ...
At the least, and just guessing because the design requirements aren't obvious, I'd say move to 24v or 48v inverter, being as someone thought they needed two 5kw 12v inverters. The good news is that you can assemble some beefy 24v or 48v battery-banks from the pile of 12v batteries.
Customer might complain, but that is a consequence of possible purchase before design ...
Partimewages
Solar Addict
Were all the batteries 100% charged with a known acceptable Lifepo4 charger? Lifepo4 is not very forgivable like lead acid. At 12 volts even your connections could be causing the issue.
Yes, they had been charged, but of course, by then they were at 70% or so. I.m thinking, at a minimum, I need to double up the cabling.
