BMS to control battery charger?

[simicrintz]

Holy crap-that went right over my head, Sergio! I never considered that and will follow up with Lester (I still have it-for good or bad!).

A million thanks for your reply (and unending envy of your knowledge)!

[simicrintz]

Talking to Summit (Bill S. again) and he is asking for the chemistry of my batteries, which I am obviously not telling him (other than "lithium")......

So the next question is if I could use this charger (assuming the setting capability exists), why couldn't we use any 36V charger and not have to look for a Lithium specific charger?

[Sergio]

That charger does not have the proper algorithm CC/CV to properly charge a lithium battery.

Your particular setup uses 14 cells and has a max charge of 50.4v.

A lead acid charger typically charges to a max voltage of 2.70vpc or 48.6v for a 36v FLA pack (18 cells * 2.7v) which would work well for your pack.

If you had a 14 cell Leaf pack or a 16 cell LifePO4 it would not work since a 48v FLA charger goes up to 64.8v (24 cells * 2.7v).

This suggestion is very specific to your setup and the charger needs a profile with a max of 2.7vpc (volts per cell) and cannot try to do an equalization cycle.

[Murby]

Originally Posted by simicrintz

Have the Lester Summit II charger (some of you know this already) and even though it states that it is compatible with Lithium, it is not compatible with my Lithium. While I may still bite the bullet and buy the Schauer, I really would like to use the Lester if I can, since I already have it.

Read this on the site where I got the batteries and wondering what you smarter-than-me folks think. I'll reach out to the seller also, but would love to hear thoughts from those not tied so tightly to the sales pitch.

"BMS has charging control that connects to charger negative to provide a shutoff of the charger when the battery is fully charged at 4.2v per cell. This will allow the use of a charger that is not designed for lithium that would normally charge over the allowed 50.4vdc The Installation requires installing the orange plug into battery receptacle, connecting negative lead with eye ring to battery negative post and the BMS charger negative to the charger negative".

I'll attach a few pics of the batteries with the BMS attached (if you look closely at the one pic you will see the black wire that needs to go to the charger negative).

Thanks guys. Yes, I am ready to be done with this and be able to run this thing. While I am looking for input, if this really will work it may be helpful to others as well.

Never NEVER use a BMS as a control element in any lithium ion system. The BMS is to a battery what a seat belt is to a car.. its an emergency catch all in case one of your other system's components misbehaves.

Your charger should never allow the battery to go beyond its rated high voltage limits, the BMS is there to stop the charger if it malfunctions.

You should never allow your cart to discharge past its rated lower limit, the BMS is there in case you mess up.

Violating these rules increases your chance of catastrophic failure with severe consequences.

[Volt_Ampere]

I agree 100% that the BMS should not be used to terminate charge on a charger that will overcharge if not terminated. It is important to have a proper charger that does CI / CV charge at the proper profile for the batteries you have. Terminating early during the CI charge will work for a while but it's not good for the long term health of your battery. Also, you want redundancy. Normal operation is that the charger does CI/CV charging to the proper final voltage. The BMS monitors every cell and terminates the charge if ANY cell exceeds the maximum voltage.
The BMS should also balance the cells and protect the cells from low voltage during discharge.

[simicrintz]

Originally Posted by Sergio

That charger does not have the proper algorithm CC/CV to properly charge a lithium battery.

Your particular setup uses 14 cells and has a max charge of 50.4v.

A lead acid charger typically charges to a max voltage of 2.70vpc or 48.6v for a 36v FLA pack (18 cells * 2.7v) which would work well for your pack.

If you had a 14 cell Leaf pack or a 16 cell LifePO4 it would not work since a 48v FLA charger goes up to 64.8v (24 cells * 2.7v).

This suggestion is very specific to your setup and the charger needs a profile with a max of 2.7vpc (volts per cell) and cannot try to do an equalization cycle.

Now I need to ask a dumb question: if the Lester can be set at 36V and no equalization, will it work for my application? Initially I read that I could use the Lester if I could set those parameters, but now I am questioning that ("That charger does not have the proper algorithm CC/CV to properly charge a lithium battery.); what am I missing here?

At the end of the day I just want to do this right, and not try to butcher something. I can eat a $350 charger if I have to and am not hell bent on using it if it is marginal or unsafe. I'll order whatever charger will fit this application (I have looked at the Schauer and understand it will work fine and others have used it, but if there is something else that works as well and I can save a few bucks I am open to it).

Thanks to all of you guys for hanging in there with me! I would rather ask ten stupid questions and appear a fool than do something dangerous because I was too embarrassed or prideful to ask at all!

[Sergio]

I think in more than one thread everyone mentioned it is not an ideal solution but since you kept asking I thought you really want to use it.

I meant to say "to properly charge all lithium batteries", but since the voltage can not get higher than 48.8v the current would taper and should allow the cells to saturate.

If you not really determined to use that charger, the proper lithium charger adjusted for your specific pack voltage is the best solution.

Aside from the BMS really being a safety device rather than a charge controller, if the charger were to stay at full current until the BMS triggered a shut down, the batteries would not fully charge regardless of how high the cut off voltage, here is more information:

https://batteryuniversity.com/learn/...0lithium%2Dion

[simicrintz]

"If you not really determined to use that charger, the proper lithium charger adjusted for your specific pack voltage is the best solution".

Done and no more talk about the Lester from me ever again, Sergio-I promise! I will find the correct charger and never look back at the Lester again!!

Thank you for the link-I am off to learn something there now.

I did not mean to be confusing and apologize.

[simicrintz]

Quick update: I ordered the correct charger last night (I went with the Schauer with a custom profile). I want to thank everyone again who offered advice and help (and put up with all my stupid questions!) as I worked through this.

I am excited to get this up and running (hopefully after the first) and want to do it all right. Much appreciation to you all for the continued support; Merry Christmas!