Battleborn Voltage Drop Problem

[jakegw2]

So here is a bit of a mystery for the smart minds on this forum...

A few days ago I was sitting waiting in our camper in a parking lot while my wife ran an errand. It was a bit hot and I only expected to be there for an hour or two so I turned on the AC running off my two 100A Battleborn LiFEPO4 batteries through my Xantrex XC2000. It started up fine and ran for a minute or two and then stopped. This surprised me as my Victron 712 monitor showed fully charged and all the other electrical 12v items were still working. I tried to start the AC again and it wouldn't start.

I'll cut the story down and get to the conclusion. When put under heavy load (~110-130A) the voltage on the batteries was dropping below 11.5v and the inverter was cutting off. I have never seen this type of voltage drop on the Battleborns. Normally they drop at most to something around 12.9V under a very large load, but not below 12v.

I ran the generator to see if perhaps my BMS was miscalibrated. The charge rate maxed out at about 30A and they did take a charge for a bit beyond the 100% point, but not that much beyond it.

The next day I went to lower the loft bed that is powered by twin 12v motors and the lights began to flicker. This type the load is only about 20A and the voltage was dropping down to 10.7V during bed movement. This was after having been plugged into shore power for most of the day.

Thinking this might be a loose connection issue I went under the camper and removed and then reattached several of the connection points from the battery. I also tried running off of just the converter (disconnecting the house battery) and everything works fine. If I do the same from the alternator everything works fine as well. The problem appears to be isolated to the two batteries.

The following day the batteries stopped working entirely. They show no voltage when disconnected and when provided with a voltage the BMS does not 'wake up' and begin accepting a charge. Just minutes before they died I had gone under the van and measured the voltage on them when they were physically disconnected from camper. The multimeter read 13.6v (which should be full charge).

I am waiting to here back from Battleborn about what the issue might be. In my internet searches I have found several other people on different forums describing this exact same problem with their fairly new and lightly used Battleborns. Discouragingly, none of them posted a resolution to their problem so I am still in the dark as to the cause or solution.

So my questions for this group are the following:

1. How could two batteries operating in parallel fail simultaneously? For those not familiar with Battleborn they have an internal BMS that protects against most failure modes.

2. Is this a BMS issue or a lithium cell issue? The battleborns are made up of four modules, each with a whole bunch of basically D-Cell sized cylindrical cells in parallel, and then the four modules are connected in series. For the battery to completely fail you would need failure of all of the cells in a single module, and this would have to happen on both of the batteries. This seems extremely suspicious.

3. What could have caused this failure? As far as I know I have never operated the batteries outside of the Battleborn specs, except for a small handfull of time when I charged them at about 0.55C during testing of my system (the spec limit is 0.5C). 130A load is well within the 200A continuous rating for the parallel batteries. The inverter can't even make use of the over 400A surge capacity of the batteries even on AC startup.

4. Is there a way this could still be a loose connection issue (e.g. connection passes voltage but cannot support high-current draw)? If so, why does everything work when the van is running? I tested the connections I can access (all but the ones attaching to the battery posts and the parallel wire connections between batteries).

Other thoughts on the situation are also appreciated.

 

[markopolo-ClassB]

You need to see individual cell voltages to know if the cells (or groups of parallel cells) are way out of balance. Unfortunately, your BMS doesn't show individual cell voltages.

My first guess would be that the cell groups are no longer balanced.

Example:

2.6V + 3.9V + 3.7V + 3.4v = 13.6V

vs

3.4V + 3.4V + 3.4V + 3.4V = 13.6V

 

[rowiebowie]

I agree. Fully charge the battleborns through a complete balancing cycle. Try a call to Battleborn support if you still have questions.

But another concern is trying to run your roof ac on only 2 x 100Ah batteries. I would suggest 400Ah's as a minimum for such an appliance.

I run a 700W microwave on my 2 x 100Ah Renogy lithiums (the actuall draw from the microwave is actually around 1100 watts as the result of inefficiencies), but never considered running the rooftop ac.

Finally, I have a battery monitor but have found that I cannot fully trust it. I can fully charge and balance my lithium's and months later (with 0 draw showing on the monitor) the monitor will show 95%. However, the Voltage will show 13.0 to 13.1. At 13.0 volts, my batteries should be closer to 50% state of charge.

When traveling and charging daily at camp sites or while driving, I consider the monitor to be accurate. But for extended periods when my van is parked, I must have some low parasitic drain that the monitor is showing.

 

[booster]

I agree. Fully charge the battleborns through a complete balancing cycle. Try a call to Battleborn support if you still have questions.

But another concern is trying to run your roof ac on only 2 x 100Ah batteries. I would suggest 400Ah's as a minimum for such an appliance.

I run a 700W microwave on my 2 x 100Ah Renogy lithiums (the actuall draw from the microwave is actually around 1100 watts as the result of inefficiencies), but never considered running the rooftop ac.

Finally, I have a battery monitor but have found that I cannot fully trust it. I can fully charge and balance my lithium's and months later (with 0 draw showing on the monitor) the monitor will show 95%. However, the Voltage will show 13.0 to 13.1. At 13.0 volts, my batteries should be closer to 50% state of charge.

When traveling and charging daily at camp sites or while driving, I consider the monitor to be accurate. But for extended periods when my van is parked, I must have some low parasitic drain that the monitor is showing.

I don't think the monitor is the issue, as it appears you have an internal battery draw it doesn't even see. Probably the BMS but that amount is very high for that, so something is not right somewhere. The monitor didn't see it but they are down 54% from sitting, but monitor is OK in daily use would indicate inside the battery leakage or use.

 

[rowiebowie]

I don't think the monitor is the issue, as it appears you have an internal battery draw it doesn't even see. Probably the BMS but that amount is very high for that, so something is not right somewhere. The monitor didn't see it but they are down 54% from sitting, but monitor is OK in daily use would indicate inside the battery leakage or use.

Perhaps you are right, but my point is that the OP might also be thinking his batteries are full, when actually they need a charge and balancing as suggested by Marcopolo.

 

[booster]

Perhaps you are right, but my point is that the OP might also be thinking his batteries are full, when actually they need a charge and balancing as suggested by Marcopolo.

Very possible, of course.

 

[HarryN]

As noted by others, the start up load and power demand is too much for only 2 batteries.

System designs with BB and honestly most batteries really need to be based around the idea of 50 amps / 600 watts per battery in order to work well consistently.

In addition to the running power draw, each time the compressor goes through an on cycle, the locked rotor amps demand is passed through the inverter and onto the battery pack. This is much higher than the average demand, but is contributing to the BMS heating up.

Essentially what has happened is that your air conditioner has placed a load on the batteries / internal BMS that exceeds the design and specs. First hand experience for better or worse.

In the very early versions of BB, a BMS trip like that would end the battery's life.

In the versions made later, the BMS will reset if given the chance. This requires complete removal of all power to EACH battery for a few seconds / maybe 10 - don't remember.

It is possible that the BMS of one battery has turned back on, and the other is still tripped. The only way to reset it is to completely isolate it from the circuit.

The same situation can come up on system startup, because the current needed to initially charge up the capacitors in an inverter can (often will) draw current fast enough to trip the BMS. This is why the normal suggestion is to have a pre-charge circuit or some way to charge these up, but few people do it.

This is why I suggest to people that when they are building a power system, each parallel battery string has it's own breaker between it and the main bus bar.

So for a 12 volt / 4 battery system, this would need 4 breakers for the batteries since there are 4 parallel strings.

Similarly, for a 24 volt / 2 battery system, this would only need 2 breakers, since there are only 2 parallel strings.

The BB's are a good LiFe battery with fairly solid protections.

The mistake that many people make is trying to run a power system at the max spec of the components instead of closer to 50% of the max spec.

 

[jakegw2]

Marcopolo - I don't think it is an internal balancing issue within the batteries for two reasons:
1. The BB batteries consist of 30 D-sized cylindrical cells in parallel stacked in a group of four sets in series. Unlike prismatic cells I would need all thirty cells in one group to be unbalanced for that to be my issue. It is also set up to auto-balance when charged with 14.6V to full charge.
2. The batteries are in parallel so both batteries would have to have the same problem for this to be the issue.

HarryN
You may be right that I blew a BMS. The specs show the batteries can support up to 600A per battery for <0.5 seconds, 200A for 30 seconds, and 100A continuous. This is far more than the inverter could use and more than the AC can draw even at locked rotor (which is rated at 63A @ 120V or 630A @ 12v = 315A per battery). As you said, while this is within specifications it is certainly a bit more than 50% and if one battery failed the remaining one would have it's current limit exceeded on the next cycle.

I spoke with BB today and they suggested that it was possible the BMS on one battery failed in such a way that it was providing some sort of short path (with resistance) to the other. This would explain why the other battery failed - it was drained below the cutoff voltage for its internal BMS.

It is difficult as I am on a trip but I will try to drop the battery tray today and test both batteries independently.

 

[markopolo-ClassB]

You're probably right about it being a greater issue than out of balance cells.

For Battle Born balancing, I'll post this copy & paste text from their site for anyone interested: (https://battlebornbatteries.com/und...ting-started-with-your-battle-born-batteries/ )

If you’re floating at 13.6V, there’s no balancing happening and you’re not going to balance the cells until you charge it up to around 14.4V, or at least 14.2V.

To rebalance your system, we recommend being able to charge it up to 14.4V once a month or even once a week.

........ you do want to have them stay in the absorption stage for the battery cells to balance. Typically, we recommend 20 to 30 minutes per battery string in parallel.

So, according to Battle Born, fully charge them then hold the pair of batteries at 14.4V for 1 hour weekly or monthly should keep them in balance.

If this turns out to be a warranty claim let us know how that works out.

 

[JML-ClassB]

You might consider getting a soft start system installed on your AC if you plan on using it with batteries in the future. I do not have one but have herd good things about them. My BIL may put one in his 2013 PW that has two, Lion 105 AmHr LiPos, though he has no intention of running the AC off the batteries - he wants to for the occasional use when he is plugged into a 20 Amp shore power plug and needs to run the AC. I'll see how it goes with his before I decide.

 

[jakegw2]

An update on my situation...

I called BB and they recommended removing power from each battery and then applying a charging voltage to them individually to wake up the BMS.

This was tricky as I am actually on a trip and do not have my normal hydraulic jack I use to drop the under-carriage mounted battery tray. Asking around I was able to borrow a jack from some neighboring campers and a bit of dumpster diving got me the remaining items I needed to access the batteries. The much lighter weight of lithium made this sort of makeshift tool setup a possibility - I could never have managed it with the weight of lead-acid batteries.

So i got the batteries down, connected them up one at a time and applied first the charge from my inverter/charger (which I confirmed the voltage using a multimeter) for ~15 minutes or so and retested each battery.

The first one took only a few amps in charge and then stopped charging. It reads 13.6V, but cannot support any load - even a small light drops the voltage to zero until it is removed.

The second one took no charge at all and read 0V before and after the charge attempt.

To ensure that the issue wasn't my charger I repeated this same sequence using the chassis power with the engine running. Identical results for each battery.

To make it though until the batteries arrived I installed a small deep-cycle battery from Wal-mart. My inverter/charger (Xantrex XC2000) does a terrible job providing power to the coach without a functional battery because it adjusts its current output only about once every 2 seconds. This causes any motor load to power down the coach for 2-6 seconds until the charger finally ramps up its output to match the new load. The temporary battery fixed this issue.

With this evidence in hand I called BB and they shipped me two new units overnight at their expense (great service!). I installed the new batteries and everything is working perfectly again, just as it did before the problem began.

BB included a return shipping kit and label (it has to be shipped back using freight service) and I dropped them off the next day. BB has assured me they will do a failure analysis on the old units and let me know what the cause of failure was. I will update this forum with the results when I get them.

 

[HarryN]

Sounds very typical of battle born. They take good care of their customers.

Just realize that if you do the same thing again with trying to run the air conditioner on 2 batteries, it will be your expense to replace the batteries the next time.

Consider to figure out where to put the additional 2 batteries that are necessary for pretty much any LiFe battery in that size range.

 

[jakegw2]

An Update with New Information

I think I may have discovered what killed my BB batteries.

A week or so after replacing my batteries I was visiting a friend who is an HVAC technician. I mentioned that my camper AC had a burning smell when I last turned it on a few weeks previously and he offered to look at it.

We tried to fire it up when connected to shore power and it just hummed (it didn't do that last time I used it, but it did now). The voltage on the shore power line dropped to the 90V range but no breakers tripped. Thinking that it might be due to the long extension cord I was using I started my generator and tried again. The generator died immediately after the AC was turned on.

So it looks like the problem with my AC results in an extremely high current draw that somehow does not trip my breakers (at least not very fast, I turned off the AC within 2 seconds of it failing to start).

He started poking around on the rooftop unit and quickly discovered that the extra starting capacitor I had installed a few years back was blackened - the source of the burning smell I had noticed several weeks before. Sure enough, the capacitor had failed and was acting as a short. He pulled it out and the AC worked perfectly again.

The AC wasn't strictly needed so I hadn't tried to use it since the time when it failed to run on battery. I more or less forgot about it for the rest of the trip since the weather was mostly cool. This might explain how they both batteries managed to fail at the same time. It still doesn't explain why the inverter passed the excess load through without any difficulty, why none of the breakers (on the AC or DC sides) tripped, nor why the internal BMS didn't protect the batteries, but at least it is a clue to what could have been the precipitating event.

It seems like this scenario is exactly what the over-current protection on the BMS is for - an event where some sort of low-resistance or short environment accidentally occurs. I wonder if the version of BB battery I got had a BMS with incorrectly functioning over current circuitry.

 

[HarryN]

Excellent questions:

- A good quality inverter can run in overload condition for a while.

If the overload is high - only a few seconds. If the overload is modest - sometimes for quite a while.

One of the ways that inverters deal with heavy overload is to distort the waveform, so it can go from smooth / sinusoidal to very choppy. Similar to heavy distortion in a sound system.

Depending on the device receiving this waveform , the distortion can either pass through, or cause a lot of heat.

- On the input side, as long as that inverter can make "some kind of wave without overheating, it will keep pulling more power from the battery pack, no matter what the label indicates.

- The breakers that you have - and most RVs have, are thermal breakers. They are designed to run at somewhat higher than the rating in order to deal with surges.

They also take "time" to trip - because they have to get hot first.

This is as opposed to a magnetic hydraulic breaker, which can be purchased in various specs of "nearly instant trip times vs delayed". An example are the breakers re-sold by blue sea as "C" breakers.

If you switch to either the magnetic hydraulic type, or a T fuse, it will break very fast, but the challenge is that nearly all air conditioners in the world are on time delay fuses or breakers because motors have this initial surge / locked rotor amps number.

Your system behaved exactly the way that the AC system behaved on my very first use of BBs in a 12 volt fed inverter - air conditioning unit did.

_________

- The capacitors that are part of the roof air conditioner are for soft starting the compressor motor. These are different from conventional capacitors, in that they are intended to only operate for a few seconds / then have time to cool down.

A few years ago there were quite a few counterfeit capacitors being sold where a chinese distributor was purchasing caps with "spec a" and putting them inside of a cap can marked with "spec b". It is possible that you caps were fake, or that they simply burned out from the waveform signal distortion.

It is hard to tell.

Unfortunately I know these things due to hands on experience, and digging / talking to some EE friends of mine - not because I am smart.

___

Can you make this setup work with just 2 batteries - maybe. I think the term is called "dancing on the edge of a dime."