[casey]

I have an electric Civic with most of a Leaf pack set up as 330v. I do not have a charger or BMS currently and am looking into options.

The motor is a Kostov 11" rated at 144v however the guy I bought it from said it ran fine at 330v. This would lead me to believe it would be ok to run any voltage in between those?

I live about 20 miles from town. My starting goal for this car would just be to get to town where I could plug in. I am in the process of removing and inspecting all the batteries. When I reinstall them I am considering putting in just 20 modules for the nominal 144v. At ~10kwh storage this should get me to town and then some. In theory. Luckily the car has a tow bar installed.

If the motor will work at least up to 330v it seems like I could then add modules until I got the range I wanted while keeping the weight down as much as possible. As long as I had a variable voltage charger (considering the Manzanita PFC20)

Then comes cell balancing. This is where I feel the most unclear. A computer taps voltage and temp of each module and takes control of charger on/off? But how a high voltage charger connected to the pack mains would give attention to an individual module eludes me. Or can the BMS actually dissipate power through the tap wires to let lower voltage cells "catch up" ?

For the 20 module idea it looks like an option would be 2x Manzanita MK3x12 Digital Lithium Regulator

Any info or advice would be appreciated!

 

[casey]

After more reading it seems that yes the BMS dissipates power as heat when modules reach their max voltage. Which is of course a waste of watts. Wouldn't it be more efficient, if you are bothering to run wires to every module anyway, to charge them individually and stop when they are full?

 

[remy_martian]

Ok. Do that. Then pull the plug to go get a pack of cigarettes....what are your cell voltages? Some may not have been charged yet.

There are ways to not dissipate as much power when charge balancing - it costs money.

 

[casey]

Ok. Do that. Then pull the plug to go get a pack of cigarettes....what are your cell voltages? Some may not have been charged yet.

There are ways to not dissipate as much power when charge balancing - it costs money.

Can you explain further? I was thinking of a small charger for each module. Would avoid the need for the high voltage charger and monitoring is built in instead of a separate system. And they could turn off when they are done instead of dissipating. I'm sure there's good reasons it's not done this way! I am new to this type of battery pack and just trying to understand.

 

[cricketo]

I dislike what most hobby (and some "professional") BMSes do for balancing. I like the idea of using BMS strictly for monitoring, and using the Chinese inductive balancing modules. I am trying that out on the small scale now, but would be interesting to read if anyone has looked into it on a larger scale like here.

casey, this is the one example of the thing I am talking about :

3S 4S 6S 10S ~12S Li-ion Lifepo4 LFP Battery Active Equalizer BMS 1.2A Balancer | eBay

Find many great new & used options and get the best deals for 3S 4S 6S 10S ~12S Li-ion Lifepo4 LFP Battery Active Equalizer BMS 1.2A Balancer at the best online prices at eBay! Free shipping for many products!

www.ebay.com

I think the biggest unit I've seen was 17s, they're stackable though.

 

[remy_martian]

^ anyone got a schematic for these? The docs that come with them on how they're applied?

 

[cricketo]

^ anyone got a schematic for these? The docs that come with them on how they're applied?

They're quite straighforward. Here is a wiring diagram from a listing on Ali :

 

[remy_martian]

That part I get, lol

 

[cricketo]

That part I get, lol

What is your question then ? The thing is analog, has no voltage thresholds on anything like that - if the two adjacent cells have different voltages, it bleeds one into the other. Has a very small "standby" current.

 

[remy_martian]

It's got inductors, so it has to be a switched current source, doesn't it? An analog bleeder would dissipate power in the pass transistor.

 

[cricketo]

I don't see any transistors on it, but there is a tiny 8-pin IC (per cell pair). Here is a picture, but it is definitely difficult to make out any details even in person :

 

[remy_martian]

Not much to go on 😭

 

[casey]

I dislike what most hobby (and some "professional") BMSes do for balancing. I like the idea of using BMS strictly for monitoring, and using the Chinese inductive balancing modules. I am trying that out on the small scale now, but would be interesting to read if anyone has looked into it on a larger scale like here.

casey, this is the one example of the thing I am talking about :

3S 4S 6S 10S ~12S Li-ion Lifepo4 LFP Battery Active Equalizer BMS 1.2A Balancer | eBay

Find many great new & used options and get the best deals for 3S 4S 6S 10S ~12S Li-ion Lifepo4 LFP Battery Active Equalizer BMS 1.2A Balancer at the best online prices at eBay! Free shipping for many products!

www.ebay.com

I think the biggest unit I've seen was 17s, they're stackable though.

Thanks! Does seem like a better approach from a saving power perspective though I do not understand deeply enough to say for sure. I live off grid so those watts are sacred. If I paired those with the manzanita micro pfc20 I think I'd have a reasonably safe battery pack? I am about ready to pull the trigger on that charger, looks quality and versatile enough for whatever batteries I end up with.

If I charged the pack without the equalizers or BMS for balancing the danger is if one or more cells was not coming up to voltage the good cells would get overcharged and maybe explode? I am not planning to do this! Just want to understand.

 

[cricketo]

If I paired those with the manzanita micro pfc20 I think I'd have a reasonably safe battery pack?

No, you're still playing with fire. You need to have a way to stop charging if any of the cell groups reaches max voltage, and without a BMS you wouldn't know.

 

[casey]

No, you're still playing with fire. You need to have a way to stop charging if any of the cell groups reaches max voltage, and without a BMS you wouldn't know.

Ok gotcha. Would the manzanita regulator boards be the right move in that case? I don't love the idea that the safety of the pack is determined by software programs and an ethernet cable but it doesn't seem like there's an alternative.

 

[cricketo]

Ok gotcha. Would the manzanita regulator boards be the right move in that case? I don't love the idea that the safety of the pack is determined by software programs and an ethernet cable but it doesn't seem like there's an alternative.

That's probably what you'd want, but looking at the spec sheets they provide I can't quite tell the level of integration PFC20 has with their BMS. On the picture I see a connector labeled "reg bus", which I suspect is the hookup to the BMS, but it's not called out. I'd recommend reaching out to their support to clarify that question - overvoltage charger cutoff. And I mean this is to be totally safe. I don't believe there is never any room for shortcuts, but if you're planning to use that thing on a regular basis and want to leave it unattended doing its thing, you should build safeties into the design.

 

[casey]

That's probably what you'd want, but looking at the spec sheets they provide I can't quite tell the level of integration PFC20 has with their BMS. On the picture I see a connector labeled "reg bus", which I suspect is the hookup to the BMS, but it's not called out. I'd recommend reaching out to their support to clarify that question - overvoltage charger cutoff. And I mean this is to be totally safe. I don't believe there is never any room for shortcuts, but if you're planning to use that thing on a regular basis and want to leave it unattended doing its thing, you should build safeties into the design.

100% agreed, these are some scary batteries and my main complaint about the BMS solutions I'm finding is how much they seem like a duct tape solution rather than meaningfully integrated into the charging. Really appreciate your replies, I'm going to reach out to manzanita micro support before I go any further

 

[remy_martian]

Charging has multiple sources on an EV and the batteries need thermal and cell balance management.

The batteries aren't any scarier than a girlfriend making dinner with meat cleaver in her hand.

 

[casey]

Charging has multiple sources on an EV and the batteries need thermal and cell balance management.

The batteries aren't any scarier than a girlfriend making dinner with meat cleaver in her hand.

Ok multiple charging sources is a good point I didn't think of. Need the same protections no matter where the power is coming from.

And yeah I've many times said a similar thing about "dangerous" things.. a nail is a dangerous tool if you pound it into your hand. But I'm still new to Li-Ion charging and trying to avoid the analogous incident

 

[remy_martian]

I ordered one of the 4S units cricketo linked, above, off eBay.

I verified that the schematic is the one in the attached datasheet, except they use a couple of 10uF in place of the 22uF.