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Mg451 · 17-09-2021, 09:04

Steve i have a temp sensor on my balmar. So ive ruled out overheating.

Tenedos · 17-09-2021, 09:41

Quote:

Originally Posted by SteveSails

Totally agree with the comments from witzgall, set your regulator properly and the BMS should never shut down.

I couldn’t fully follow this. How do you ensure this doesn’t happen?

Mg451 · 17-09-2021, 09:45

Set the reg to stop charging before your bms settings. There fore it never triggers an overcharge.

Tenedos · 17-09-2021, 09:58

Quote:

Originally Posted by Mg451

Set the reg to stop charging before your bms settings. There fore it never triggers an overcharge.

That’s actually what I am asking. With an internal BMs how does the regulator know battery is getting full?

witzgall · 17-09-2021, 10:34

If the charge voltages are below the BMS cutoff voltage, and the cells are balanced, then you won't get a shutoff. This issue to avoid is where cell imbalance takes one cell too high, and the bms shuts down, even with the pack voltage is under the bms pack voltage cutoff. This can be mitigated by NOT charging up to the upper charge voltage specified by the MFG. It is complicated by the fact that some BMS designs only balance at the top of the charge.

It is my opinion that this will happen at some point at the end of a pack's life. With a high quality pack, that is replaced when the total capacity is quite down, this may be avoided by preemptively replacing the pack. If a cell is bad, or mismatched, it can happen sooner. In either case you can end up with a BMS shutdown.

Chris

Quote:

Originally Posted by Tenedos

I couldn’t fully follow this. How do you ensure this doesn’t happen?

SteveSails · 17-09-2021, 12:09

The regulator "knows" the battery is near full by the amount of power the alternator field winding requires to maintain the alternator output voltage at the set level. When the battery is full it accepts very little current and the alternator field power requirement is also low. This true for any battery chemistry, BMS or not. Battle Born batteries shut down if the terminal voltage is greater than 14.7V, so if the alternator is set to produce no more than 14.4V the batteries won't shut down. BB batteries also top balance when the voltage is above 14.2V and they recommend holding that for at least 1/2hr before dropping back to a "float" voltage of about 13.6V. A properly set up Balmar 614 regulator will do just that.

As to what happens as the batteries age? That remains to be seen, at least for me. It will interesting to see if BB will offer a remanufacturing service for old batteries.

I'll offer another opinion... I believe drop in Li like Battle Born are fine for smaller house banks, say <400Ah, above that, and especially if charge currents are several hundred amps, an external communicating BMS should be used. Also larger banks should be designed as a power system, cells, BMS, charge sources, monitoring, protection devices, failsafe backups, and so on need to be integrated as a whole.

Tenedos · 17-09-2021, 12:11

Thank you folks, just wanted to say this is a very enlightening thread.

Mg451 · 17-09-2021, 12:11

If you have 4 batterys (4) bms. Id assume this is highly unlikely.

rgleason · 18-09-2021, 10:52

Quote:

Originally Posted by witzgall

Chris from Balmar here.
Some comments in-line:
People are making the BMS issue far too complicated.

1. If your battery switch fails, you will blow your alternator diodes. Has nothing to do with Lithium and has been happening for 50 years.

This was true 50 years ago, but not with a quality alternator, using either 400v diodes or avalanche diodes. A switch failing still may blow the diodes, but it not a given anymore.

...and other good points...

6. If your alternator is externally regulated and limited to 14.4v, then you don’t need a dc-dc charger. Just parallel the start and house banks with a VSR or relay. This will provide a buffer should the BMS shut down - which again, should never happen in a properly programmed system.

Here is where I disagree. In my experience (I cruised with lithium back in 2011+ and of course what I have learned in the industry since) a DC-to DC device to the start battery, such as our Digital Duo charge or another device, is the very best way to do this. Every battery is charged at their optimum voltage, the cabling is simpler and safer.

Chris

Chris,

Sorry, I guess I stand corrected on one point
https://balmar.net/products/digital-duo-charge/

I did not realize the Duo Charge was a DC-DC for the starter battery.
Looking at the Balmar Diagram, if his boat is wired that way with a switch between the House Battery and the Alternator then that surely was the problem.

I suppose the Duo Charge could have been wired from the alternator side of the switch and the alternator would have been protected, but then the switch would not be useful for working on the alternator.

It is instructive, with regard to what will happen when the BB shut off.

Maybe it is just better to know that you must disconnect the battery or pull a fuse to work on the alternator.

I guess that is why an even better Zap Stop would be useful. --That shows its condition.

rgleason · 18-09-2021, 11:04

SteveSails wrote:

Quote:

Battle Born batteries shut down if the terminal voltage is greater than 14.7V, so if the alternator is set to produce no more than 14.4V the batteries won't shut down. BB batteries also top balance when the voltage is above 14.2V and they recommend holding that for at least 1/2hr before dropping back to a "float" voltage of about 13.6V. A properly set up Balmar 614 regulator will do just that.

I assume your numbers are accurate for Battleborn, but most LiFePo are at the "knee" when at 13.8v so I think I would set the Balmar parameters lower than 14.4v, maybe 14.2 since you want to top charge occasionally (1 per month).

Also I am trying to understand why Battleborn has such high voltages....

I agree about this thread. Thanks to all for sharing.

SteveSails · 18-09-2021, 11:50

The Battle Born battery has a BMS between the battery terminals and the cell terminals, so a battery terminal voltage of 14.4V doesn't necessarily mean 14.4V at the cells. I did call BB and they confirmed the battery can sit for hours with 14.2V - 14.6V applied to the terminals with no ill affect.

I think each manufacturer of drop in Li batteries has their own take on the BMS so there could be differences in the charge voltage, balance voltage and max charge current. Best to check and set your system accordingly.

rgleason · 24-09-2021, 03:38

It would be interesting to see how bb actually is wired in a teardown.

SteveSails · 24-09-2021, 05:04

BB teardown.

https://www.youtube.com/watch?v=G5E30u-66VI

rgleason · 25-09-2021, 04:50

Thanks I had found that will prowse youtube. They are well built. Right after that video there is one where he interviews the bb pres about temperature sensing. At the end of that video he explains they wanr their batteries to be top balenced by charging to 14.4v.

For long term storage however he says it is best to be not charged or 13.8v at the most.