Chevy Volt Lithium

[simicrintz]

Thank you for posting that, molfpedal.

"Lester Electrical has chosen not to support Lithium Ion battery applications when much safer Lithium Iron Phosphate battery types are available".

Same guy (Bill) sent me something similar when he replied to me. Battery seller called BS when I showed it to him and said that was just an opinion and mostly based on the fact that their charger only worked on a limited scale for Lithium. "Two men say they're Jesus; one of them must be wrong"......

[Sergio]

I think the only relevant comment from Lester was this:

Our Lithium battery profiles are constant current profiles with no voltage limiting, so our chargers are not compatible with systems that require this feature.

Those "systems" that require this feature would be any Lithium battery and while LifePO4 do tolerate a certain amount of overcharge up to a lead acid level, they are not immune to overcharge either.

[simicrintz]

Crap. Sounds like I am going to be sending back (or selling) my Lester......

[Volt_Ampere]

Most Lithium chargers are simply current limited power supplies with the open circuit voltage set to the max charge voltage and the current limit set to the max charge current. This is really the same for FLA battery chargers.

[Sergio]

I think Lester comment about "no voltage limit" is the real issue, they must not have a profile that ends with a "constant voltage", their profiles appear to only use dv/dt so no reasonable upper limit on how high the voltage will get before the timer limit for the profile which is typically 20 hours.

They also only support "lead acid" nominal charging voltages of 36v or 48v with no adjustment possible which eliminates a lot of custom packs.

My concern with those Chevy packs would be how to safely charge two separate strings of batteries in parallel.

You should at least add a manual battery disconnect switch that "isolates" the two packs during charge.

You could also automate the process by adding a SW201 contactor.

The "C-" negative pig tails from each BMS would connect together in one pole of the NC contact.

The other pole of the NC contact would go to the charger negative output.

The pack negative cable from each battery set would go to a NO pole.

The SW201 would be powered by the key switch so when the key was OFF, the packs would be isolated and the charger would be connected to the BMSs.

That way if a single cell on an individual pack goes HV during charge, that pack BMS would stop the charge for that pack and the cell would be protected from overcharging since it could not be charged from the other pack without the pack negatives being connected together.

[simicrintz]

Probably a stupid question but I will ask anyway: how are the Volt packs different from the Leaf packs as it applies to charging? Are the Leaf packs just single or are they hooked in parallel also? If it makes sense to split them while charging (excellent explanation on that; thank you Sergio) then I will go that route. If the Lester is truly inadequate for this (and I am convinced now that it is and I will go a different route) I'll get the Schauer charger (unless someone tells me different). I want this to be as trouble free as possible and I prefer to only do it once!

[Sergio]

Most folks build a single pack (single BMS) with multiple cells in parallel if more capacity is needed.

Since the cells in the Chevy pack cannot be taken apart, You need two BMS, one for each pack to balance and provide cell monitoring for that pack.

When the packs are connected together, it creates a problem for a single pack to stop either charge or discharge.

My suggestion fixes the charge problem, but you need to be careful on the discharge side and don't run the packs too low.

[simicrintz]

How does Chevy do it with all the packs in the Volt? It just seems more complicated than it needs to be (this coming form a completely uneducated individual-me!)?

My goal is a functioning cart that has good range, is reliable and safe-not necessarily in that order! I do not want to cut corners and will work more/save more to do this right; I am not in a hurry!

[Sergio]

All the modules on a Chevy volt car are in series for a nominal 360v pack.

Separate packs in parallel present a technical challenge to build and operate safely.

[ACCLR8N]

Why can't the Volt batteries use the same inexpensive charger we use on the Leaf batteries?