New 24v LiFePo4 drops to 5.5V

[OzSolar]

Hello,

Please redirect me if this isn't the right place for this post.

I have a brand new 24v 200 AH LiFePO4 battery that immediately drops from 26.3 v to 5.5 v when I close the system breaker to the new Victron Quatro inverter. This is a breaker I installed on the positive line for testing, not one built into the battery. When I open the breaker the battery immediately returns 26.3 v. During this test the inverter is in the "OFF" position and no noise (IE: high amp dead short) or smells of any kind are observed. In order to eliminate my wiring AND the inverter as the source of the problem I wheeled a different 24 v battery over to my test bench and the Victron starts right up. The only thing that was changed was the battery.

This battery does not have any sort of externally accessible switch, fuse or circuit breaker. It has a meter that gives A, AH, V and SOC. It continues to read 26.3 v when I'm measuring 5.5 at the terminals. Also during this time I'm not measuring any amps with my clamp on ammeter but course it's not very accurate under 2 or 3 amps.

The somewhat decent documentation that come with the battery does not address this in any fashion.

Of course I'll be calling my supplier tomorrow but I'd be curious what others think might be going on in the meantime.

Thank you,
Travis

 

[OzSolar]

I have heard back from the manufacturer and they suspect that the BMS is seeing the large start up current of the inverter as "too big in the millisecond". I interpret that to mean that the BMS sees the large inrush of the initial start up of the 5,000 watt inverter as short in the system and goes into protection mode.

In the last 20 years I've hooked up a lot of big inverters to big lead acid battery banks but this first foray in to LiFePO4 is a whole new learning curve. So now I have learned that pre-charging isn't just to prevent that annoying spark but it actually serves a purpose to protect the BMS. Hopefully others will read this and learn with me. No more Radio Shack in town so I'm now waiting for the mail to bring me 25 watt 30 Ohm resistor that Will suggest in his video about the subject. I will report back later.

 

[OzSolar]

My batteries are just fine. The 5000 w Victron Inverter just wants so many amps to charge up it's capacitors when initially turned it causes the battery's BMS to protect itself. Thankfully it self resets without issue. Paralleling two batteries work just fine to turn the inverter on. It unfortunate that none of the literature that comes with the batteries or Inverter mentions this phenomenon.

 

[Gazoo]

You might be interested in this thread. There is an easy way to pre-charge the inverter capacitors. I would follow the advice in that thread if you have to connect to your inverter again even though you have it working with two batteries in parallel.

 

[OzSolar]

You might be interested in this thread. There is an easy way to pre-charge the inverter capacitors. I would follow the advice in that thread if you have to connect to your inverter again even though you have it working with two batteries in parallel.

Thank you Gazoo. I had not seen that thread. To me it's worth mentioning that it wasn't until the 10th message (from Will in fact) before anyone mentioned that if you don't pre-charge you risk crashing the battery's BMS.

Previously when I searched for "pre-charging" I found only a few a other threads and didn't see any mention of any reason other than preventing the spark. Of course you have known about pre-charging for a awhile but it's new to me and I've installed 100's of grid systems in prior years. Of course, they were all FLA. I only mention this because I'm trying to help someone else in the future who finds themselves in the same predicament as me thinking they have a $2,200 brand new dead battery because none of the literature mentions pre-charging. I'm on a big learning curve all over again! Ha This forum has been helpful.

Has anyone talked about why manufacturer's don't have built in pre-charge circuit? Thanks again for sending that thread!