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Discussion Starter · #1 ·
So, I feel like an idiot asking this question, but my searches has been coming up empty for a while.

I have 8 Chevy volt batteries I have for my ev conversion. These batteries have been on my garage floor sitting for 2 years.

I recently took a volt meter and to test their voltage, and I see they are each at 47.5 v (i was afraid they were depleted to useless bricks they way my 12v car batter would have been)

Now that I see they are OK for the time being, I want to make sure I keep them healthy as I figure out the other aspects of this conversion.

How can I charge these batteries to keep them healthy (or when I start testing my ev set up on a bench)

Also, once I have them in the car, what in-car charger and/or BMS do you recommend?

Thanks
 

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The charger you use for 390V or whatever the full-pack target is

like Elcon Brusa or DeltaQ

will not be suitable for the voltage of those sub-pack units - 390V ÷ 8 =12S? just guessing

Also you do not want to store LI chemistry packs at Full, so you need adjustability, best to get to 3.7-3.8V per cell / group.

Grin Satiator is a great little adjustable charger, very safe and reliable, limited to 360W

model # 4808 "24V-52V" output range 24-63V @8A (manual states 12-63V).

Or get an adjustable lab - style power supply, but then you need to be very careful to be the "human regulator" to stop charge at the right voltage

a proper automatic charger like the Grin is much safer, boom bad!
 

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Too late for OP, but for others, do not spend big money on batteries just to let them sit.

Calendar life is finite, separate from cycling lifespan.

And not only should they be kept cool and isolated from BMS or any other circuitry that can fail or draw vampire loads

but also maintain at proper storage voltage, anywhere near Full will accelerate EoL, check on their voltage level pretty often, at least monthly.

For long term projects, maybe use a cheap worn set, borrow or whatever,

buy the "production" pack after the vehicle is all ready to go.

Of course always be looking, and if you see packs in good shape going super cheap - very rare these days! then seize the opportunity and grab them quick
 

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Discussion Starter · #4 ·
The charger you use for 390V or whatever the full-pack target is

like Elcon Brusa or DeltaQ

will not be suitable for the voltage of those sub-pack units - 390V ÷ 8 =12S? just guessing

Also you do not want to store LI chemistry packs at Full, so you need adjustability, best to get to 3.7-3.8V per cell / group.

Grin Satiator is a great little adjustable charger, very safe and reliable, limited to 360W

model # 4808 "24V-52V" output range 24-63V @8A (manual states 12-63V).

Or get an adjustable lab - style power supply, but then you need to be very careful to be the "human regulator" to stop charge at the right voltage

a proper automatic charger like the Grin is much safer, boom bad!
thank you for this information!

Looks like I can go with the Grin Satiator (72v version) and use this until the batteries are used in the car.

So, with this charger, i can safely charge 1 or 2 batteries at a time, correct?

The in-car charger can be something like the Elcon PFC4000 Charger, right?

Just having brand names to look up has been a big help
 

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Discussion Starter · #5 ·
Too late for OP, but for others, do not spend big money on batteries just to let them sit.

Calendar life is finite, separate from cycling lifespan.

And not only should they be kept cool and isolated from BMS or any other circuitry that can fail or draw vampire loads

but also maintain at proper storage voltage, anywhere near Full will accelerate EoL, check on their voltage level pretty often, at least monthly.

For long term projects, maybe use a cheap worn set, borrow or whatever,

buy the "production" pack after the vehicle is all ready to go.

Of course always be looking, and if you see packs in good shape going super cheap - very rare these days! then seize the opportunity and grab them quick
tell me about it, lol! lesson learned!

I did feel like i was getting a deal, and I did plan on having this conversion done around the time I got the batteries, but life happens.

More importantly, im still a fish out of water when it comes to this stuff. So while Ive been wrenching on cars for a long time, the EV stuff is still confusing...but Im starting to understand all this stuff slowly.
 

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The "72V" model #7205 "36V-84V" outputs 36-103V (manual states 20-103V)

will be slower, only 4-5A, IMO better to get the lower voltage thus higher current model unless you have a specific reason to get the 72V one.

The problem of imbalance should not arise since you are only charging to 40-60% SoC for storage purposes.

At some point you will need to deal with it, before assembling into the full 390V ? 96S pack ?

Those question marks are for you to answer!

I would avoid paralleling anything until you are at least reading voltages at the 1S group level - 12S per sub-pack?

What cells? mAh per? how many paralleled?

is that XpYs consistent across all your packs?

The in-car charger can be something like the Elcon PFC4000 Charger, right?
I'm not up on specific models, is that 4kW nominal? You have 240V available at home?

be sure to look for the CAN option for communication / control

you want to be able to user- adjust the voltage for sure, and likely the current drawn on a per charge session basis

and also select your BMS (one day) for CAN control compatibility with the charger, and

to be capable of controlling the normal-usage daily cycling, based on the per-cell/group 1S voltage
 

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Hi
At 47.5 volts your cells will be at 3.95 volts - or roughly 75% of capacity
The normal operational range is 3.5 volts to 4.1 volts
So that is not too bad a level to leave them at
If anything you may want to discharge them a bit
An old mains electric fire would do as a simple discharge device
When you have got your car completed then you will need a charger
I'm using a second hand BRUSA - works really well and can be set to the correct voltage

As far as a BMS is concerned - I don't use one!! - they (BMSs) kill at least 20 times as many batteries as they save
I use a very simple circuit that tells me if a cell is down by comparing the two halves of the battery pack

I'm very impressed with my Chevy Volt battery cells/modules - and I am CRUEL to them
 

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Discussion Starter · #8 ·
The "72V" model #7205 "36V-84V" outputs 36-103V (manual states 20-103V)

will be slower, only 4-5A, IMO better to get the lower voltage thus higher current model unless you have a specific reason to get the 72V one.
I selected that one because I saw it can do more volts and I figured i would select the charger that closely matched my voltage...I didnt even think to look at the amps 😣

At some point you will need to deal with it, before assembling into the full 390V ? 96S pack ?
my original plan was to wire the batteries in series to get 370 volts, and power a leaf motor with a motor controller that I would have to assemble. (the controller kit was pieced together by Arlin who has a leaf motor in his honda crx)

The car Im converting is my old 1987 acura integra that I turbo charged, so I wanted to match its current performance, hence the high voltage requirement (even if it didnt have a lot of range, this car is not my daily driver)

But since I may have jumped into the deep end with this conversion, I may try to go a simpler route at first.

I see some 144v EV kits on ebay that Im thinking about using instead of my "high performance" idea. The plan is to at least get this conversion going and to get a better understanding of EV components with some hands on experience and less guess work. But seeing as its an ebay kit, im a lil skeptical😅

I would avoid paralleling anything until you are at least reading voltages at the 1S group level - 12S per sub-pack?
What does the 'S' mean? Sorry for the noob question
I'm not up on specific models, is that 4kW nominal? You have 240V available at home?
I do have a 240v plug and charger here at home. My daily driver is a Toyota rav4 EV. As for the charger model, I just googled some of the brands you recommended and I tried to pick a model that seemed like it would fit my needs. Still kinda feeling my way in the dark with all this
 

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Discussion Starter · #9 ·
Hi
At 47.5 volts your cells will be at 3.95 volts - or roughly 75% of capacity
The normal operational range is 3.5 volts to 4.1 volts
So that is not too bad a level to leave them at
If anything you may want to discharge them a bit
An old mains electric fire would do as a simple discharge device
When you have got your car completed then you will need a charger
I'm using a second hand BRUSA - works really well and can be set to the correct voltage

As far as a BMS is concerned - I don't use one!! - they (BMSs) kill at least 20 times as many batteries as they save
I use a very simple circuit that tells me if a cell is down by comparing the two halves of the battery pack

I'm very impressed with my Chevy Volt battery cells/modules - and I am CRUEL to them
good to know! I heard good things about volt batteries, so when I saw some for sale on craigslist, i quickly bought them.
So far, they are handling my neglect!

Where did you get the components to piece together that simple circuit,? Also, did you have to build some sort of case to house that circuit?
 

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What does the 'S' mean? Sorry for the noob question
Wow yes, baby steps.

Start an intensive self-learning project on LI battery basics, reading past threads here and other forums,

develop in-depth Google Fu skills on any new terms, posting specific as possible questions when you really get stuck. . .

Each cell is "nominal" 3.7V and let's say 2Ah (you need to find out the actual, might be 2200mAh whatever I've no idea about those packs)

So put 10 of those in parallel groups (10P) you get 20Ah

Put 12 of those cells in series (12S) you get 44Vnom, charge at ~49-50V and 36V at rest is drop-dead empty.

Same voltages if you string 12 of the groups together, aka build 10P12S sub-packs, but now 20Ah capacity.
 

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Nope.

Nominal for all the LI chemistries is 3.7V, except for LFP at 3.2V and LTO at 2.3V

It may vary a little between say LMO NMC NCA, technically it is the at rest 50% SoC point, nothing linear about that curve and not just done by averaging the simple numbers, actual mAh halfway point is carefully calculated for each chemistry

but all those used for consumer EV propulsion these days in the developed world, get rounded to single place 3.7V.

Some vendors do mess with the truth, you see some generic LFP advertised as "3.3V" but that's just BS marketeers scamming as usual

A 95% very sketchy industry
 

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Nope.

Nominal for all the LI chemistries is 3.7V, except for LFP at 3.2V and LTO at 2.3V

It may vary a little between say LMO NMC NCA, technically it is the at rest 50% SoC point, nothing linear about that curve and not just done by averaging the simple numbers, actual mAh halfway point is carefully calculated for each chemistry

but all those used for consumer EV propulsion these days in the developed world, get rounded to single place 3.7V.

Some vendors do mess with the truth, you see some generic LFP advertised as "3.3V" but that's just BS marketeers scamming as usual

A 95% very sketchy industry
You are talking about specifications
I am talking about actual real life measurements - there is a difference!!
And the mid point of the Chevy volt cells linear voltage portion is at 3.8 volts - as MEASURED
 

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Does not change the "nominal" voltage

means "a label only", why bother going on about it?

not used for anything real anyway.

3.5V is just an arbitrary usage cutoff

just like a stop-charge voltage lower than 4.2V

to improve longevity and reduce fire risk.

Nothing to do with the characteristics of the cell itself, the customer (GM) has nothing to say about the cell's objective prooerties

100% down to 0% SoC for the cells are defined by the spec sheet of the cell maker

which is what 50% SoC is based on, likely 2.5Vpc is the zero point for deriving nominal.
 

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Does not change the "nominal" voltage

means "a label only", why bother going on about it?

not used for anything real anyway.

3.5V is just an arbitrary usage cutoff

just like a stop-charge voltage lower than 4.2V

to improve longevity and reduce fire risk.

Nothing to do with the characteristics of the cell itself, the customer (GM) has nothing to say about the cell's objective prooerties

100% down to 0% SoC for the cells are defined by the spec sheet of the cell maker

which is what 50% SoC is based on, likely 2.5Vpc is the zero point for deriving nominal.
Nope all balls
the 3.5 volts is the MEASURED voltage where the cell is still on the linear part of the curve

And its very very useful - I use this as my "fuel" gauge - its at least as accurate as the fuel gauge in a dino burner
 

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That's great, and very useful.

However has nothing to do with what the nominal voltage actually is for the cells inside these packs.

Nor what the point of "nominal voltage" is more generally,

never meant to apply to anything useful

just a label.
 

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Too late for OP, but for others, do not spend big money on batteries just to let them sit.

Calendar life is finite, separate from cycling lifespan.

And not only should they be kept cool and isolated from BMS or any other circuitry that can fail or draw vampire loads

but also maintain at proper storage voltage, anywhere near Full will accelerate EoL, check on their voltage level pretty often, at least monthly.

For long term projects, maybe use a cheap worn set, borrow or whatever,

buy the "production" pack after the vehicle is all ready to go.

Of course always be looking, and if you see packs in good shape going super cheap - very rare these days! then seize the opportunity and grab them quick
Thanks John, buying the "production" batteries last of all is an important point I've often seen reiterated here on the forum. Here's a question though - while at the build /testing stage, can one purchase a rectifier that convert 240v a/c to 240v d/c to power the inverter in lieu of a full battery pack?
Cheers!
 

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Dunno. I'd use a small-Ah pack backed by a high C-rate charger both at around the target voltage working together.

Might be cheaper anyway, and useful for other purposes, easy to sell on. . .
 
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