Battery Upgrade

nickdearing88 · July 2017

I finally took the plunge and purchased 2 - 12v 100Ah LiFePO4 batteries from Battleborn (via our hosts).

Per the manufacturer's recommendations, I wired the batteries in parallel (12v 200Ah) and charged to ~14.4v with a 30 minute absorb. I set the CC to 14.3 because the meter usually reads the battery voltage a few tenths of a volt lower than actual.

The balancing system is passive (using resistors) and top-balances between 14.2v and 14.6v (max). Battleborn has had really good luck with cell balancing using only the passive system and it saves costs, lowers self-consumption, and complexity.

I then switched to series configuration for 24v 100Ah. I've only played around for the past two days but I'm watching charge and discharge voltages very closely. It's amazing how flat the discharge curve is compared to LA. The OC resting voltage when full is about 13.6v so I set my float voltage at 13.5. Therefore no real charging should occur during float unless a large load turns on. It even took several amp-hours of use after completing absorb before the batteries dropped from absorb voltage to my float setting!

I plan to cycle between 20% - 90% SOC but I figured a full absorb was important for balance purposes during commissioning.

I'll update with my experience as I go, but so far -- I'm happy.

karrak · July 2017

I had a look at the documentation on your battery, looks like a nice battery. I really liked to see the spec saying the battery lifespan in Ah cycled through it rather than in number of cycles!

It is a shame that the battery doesn't have a way that you can measure the individual cell voltages.

I agree with your strategy of charging to 14.4 during the commissioning. On a regular basis I would charge a battery like yours to 27.6V (3.45V/cell) and terminate the charge at C/20-C/50 or set the absorb time at 15 minutes and set the float to 26.8V (3.35V/cell), slightly less than your setting.

Once a month I would do a charge and absorb at 28.8V (3.6V/cell) to balance the battery. If you wanted to automate this process and if your charge controller will allow it you could set the charge controller to do an equilise cycle at 28.8V (14.4V/cell)

Simon

mcgivor · July 2017

Is there any information regarding ambient temperature verses life expectancy? Can't seem to find any on the Battle Born site.

mike95490 · July 2017

Warning. If you are going to top balance this battery, you better keep the EQ amps BELOW the amps the BMS / balance vampire boards can handle, or you will overvoltage some cells
And same theory about Absorb and Float, don't push more into the cells, than the balancer boards / BMS can handle

nickdearing88 · July 2017

karrak said:

I had a look at the documentation on your battery, looks like a nice battery. I really liked to see the spec saying the battery lifespan in Ah cycled through it rather than in number of cycles!

It is a shame that the battery doesn't have a way that you can measure the individual cell voltages.

I agree with your strategy of charging to 14.4 during the commissioning. On a regular basis I would charge a battery like yours to 27.6V (3.45V/cell) and terminate the charge at C/20-C/50 or set the absorb time at 15 minutes and set the float to 26.8V (3.35V/cell), slightly less than your setting.

Once a month I would do a charge and absorb at 28.8V (3.6V/cell) to balance the battery. If you wanted to automate this process and if your charge controller will allow it you could set the charge controller to do an equilise cycle at 28.8V (14.4V/cell)

Simon

@karrak Thanks for the great suggestions. I agree and was thinking along the same line with your suggested voltages and absorb time. Once of the reasons I went this route is to test and experiment. Once I'm more comfortable with the LI characteristics, I would likely make my own "pack" with prismatic cells and a custom BMS/active balancer. But these are very practical for a drop-in LA replacement and perfect for users who don't have a detailed battery background.

Great idea about the equalization voltage for balancing, I never thought of that but it's perfect!

nickdearing88 · July 2017

mcgivor said:

Is there any information regarding ambient temperature verses life expectancy? Can't seem to find any on the Battle Born site.

I didn't see it on their website either but they might if you email them. Mine will be in a temperature controlled environment in a few weeks but are currently wired up in the garage. I'm targeting to keep them between 60F - 75F, which should keep them very happy.

nickdearing88 · July 2017

Update: I did run into a BMS issue but as soon as I mentioned it to Battleborn, they knew exactly what it was. Apparently they discovered a small number of BMS units had an issue and I just happened to get one of them. They are promptly sending me two new batteries with correct BMS system and pre-paid return labels. The customer support seems to be awesome.

During specific discharge parameters (after 20 minutes, between 25-50 amps), the BMS would cut the voltage to 9.5v for a second, then back to normal. Under 25 amps or over 50 amps discharge, the issue doesn't occur.

nickdearing88 · July 2017

Here are is the discharge curve chart from Battle Born if anyone's interested.

nickdearing88 · July 2017

mike95490 said:

Warning. If you are going to top balance this battery, you better keep the EQ amps BELOW the amps the BMS / balance vampire boards can handle, or you will overvoltage some cells
And same theory about Absorb and Float, don't push more into the cells, than the balancer boards / BMS can handle

Shouldn't be a problem......so far they're down to only about .02C by the time they are anywhere near the Absorb voltage.

karrak · August 2017

nickdearing88 said:

Once I'm more comfortable with the LI characteristics, I would likely make my own "pack" with prismatic cells and a custom BMS/active balancer.

When you say active balancer, do you mean a balancer that shifts energy from one cell to another?

Personally, I can't see much point in doing this as the amount of energy that is lost in just passively balancing using resistors is negligible. In the last twelve months I haven't had to balance my battery at all, in the twelve months before that I would have wasted about ~10Wh to balance my battery. I also can't see much point in having automatic balancing unless you want a "set and forget" system or it is operated by someone who didn't have enough technical expertise to do the balancing manually.

Simon

karrak · August 2017

nickdearing88 said:

mike95490 said:

Warning. If you are going to top balance this battery, you better keep the EQ amps BELOW the amps the BMS / balance vampire boards can handle, or you will overvoltage some cells
And same theory about Absorb and Float, don't push more into the cells, than the balancer boards / BMS can handle

Shouldn't be a problem......so far they're down to only about .02C by the time they are anywhere near the Absorb voltage.

On top of this, if any cell did go outside the safe operating voltage zone the battery BMS would disconnect the battery from the rest of the world regardless of how much current was being taken from or put into the battery.

Simon

nickdearing88 · August 2017

karrak said:

nickdearing88 said:

Once I'm more comfortable with the LI characteristics, I would likely make my own "pack" with prismatic cells and a custom BMS/active balancer.

When you say active balancer, do you mean a balancer that shifts energy from one cell to another?

Personally, I can't see much point in doing this as the amount of energy that is lost in just passively balancing using resistors is negligible. In the last twelve months I haven't had to balance my battery at all, in the twelve months before that I would have wasted about ~10Wh to balance my battery. I also can't see much point in having automatic balancing unless you want a "set and forget" system or it is operated by someone who didn't have enough technical expertise to do the balancing manually.

Simon

Yes, I did mean moving current from one cell to another to balance.

Good to know. I'm still learning the nuances of various balancing. When I first looked at Battle Born's information, I read "Automatic Cell Balancing" and interpreted as "Active Cell Balancing". When he said it was a passive system with resistors, I figured it was a cost savings measure. By the sounds of it, your system is also using resistors for balancing? I just figured most of the systems people installed used active balancing to move the current between cells rather than eat it up via a resistor as heat. But, I was expecting large imbalances based on some posts here.

Another +1 on your lower Absorb rate and using Equalize monthly at 3.6v/cell for balancing. Really good idea and although it's only been a few days, seems to be working great!

nickdearing88 · August 2017

karrak said:

nickdearing88 said:

mike95490 said:

Warning. If you are going to top balance this battery, you better keep the EQ amps BELOW the amps the BMS / balance vampire boards can handle, or you will overvoltage some cells
And same theory about Absorb and Float, don't push more into the cells, than the balancer boards / BMS can handle

Shouldn't be a problem......so far they're down to only about .02C by the time they are anywhere near the Absorb voltage.

On top of this, if any cell did go outside the safe operating voltage zone the battery BMS would disconnect the battery from the rest of the world regardless of how much current was being taken from or put into the battery.

Simon

Absolutely, that's the purpose of the BMS, to protect the battery.

Battery Upgrade

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