# Volt Battery to 48v, and a Good BMS recomendation



## brian_ (Feb 7, 2017)

You might have more luck leaving out "volt" and including "chev" (because people use "Chevrolet", "Chevy", or just "Chev" in the name). Still, it's a challenge. 

I would suggest using the standard term "module" for a group of cells; "pack" is usually the whole battery, or the entire portion contained within one outer housing.

Also, the first-generation Chevrolet Volt modules have 6 or 12 cells in series, for a nominal 22.5 V or 45 V... not quite 24 V and 48 V.


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## mrarmyant (Jun 19, 2008)

Hmm those voltages are different from what I've read.


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## brian_ (Feb 7, 2017)

mrarmyant said:


> Hmm those voltages are different from what I've read.


Where did you read these very convenient and lead-acid style voltages of 24 V and 48 V?

From General Motors:
2016 CHEVROLET VOLT
BATTERY SYSTEM

*First Generation Volt*


> Cell Chemistry NMC-LMO Pouch
> Cell Configuration 96S 3P (288 cells)
> Discharge Power (10 s) 110 kW
> Charge Power (10 sec) 60 kW
> ...



nominal voltage per cell = 360/96 = 3.75 volts
18 or 36 cells, 3 in parallel, so 6 or 12 in series
or 22.5 or 45 volts (nominal)

*Second Generation Volt*


> Cell Chemistry NMC-LMO Pouch
> Cell Configuration 96S 2P (192 cells)
> Discharge Power (10s) 120 kW (+9%)
> Charge Power (10s) 60 kW
> ...



nominal voltage per cell = 360/96 = 3.75 volts
24 or 32 cells, 2 in parallel, so 12 or 16 in series
or 45 or 60 volts (nominal)

I assume that the "24 V" and "48 V" refer to Gen 1 modules. The actual nominal voltages are lower, but of course fully-charged voltages will be higher. Similarly, 12-cell and 24-cell lead-acid systems are only nominally 24 V and 48 V - they can go lower and are much higher when fully charged. That's what I meant by:


> ... *nominal *22.5 V or 45 V... *not quite* 24 V and 48 V


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## brian_ (Feb 7, 2017)

mrarmyant said:


> I would run the 2 24v packs in series then in parallel with the 2 48v packs.


For 18-cell and 36-cell modules to add up to 288 cells, in a total of 9 modules, there must be only two 18-cell and seven 36-cell modules in a complete Gen 1 Volt battery. So if you used the entire battery, you would have more than two of the larger modules; if you wanted to simplify the setup, you could use just the larger modules, all in parallel.

This all assumes that the operating voltage of 12 of these cells in series is sufficient. If you need 13 cells, you can't use intact Volt modules, and reconfiguring them might not be worth the effort (especially if you want to use the BMS).


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## john61ct (Feb 25, 2017)

Go to Electric Vehicle forums for very knowledgeable reverse-engineering types figuring this stuff out for DIY EV conversions, doubt you'll find many in boating forums. 

Definitely hugely expensive R&D and prototyping will be required to make this sort of Science Project safe for real life boating, open-hardware projects are nowhere near ready yet. 

And you'd never get insurance, those car lithium chemistries are very much subject to thermal runaway risk (boom bad!) unlike LFP.


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## brian_ (Feb 7, 2017)

mrarmyant said:


> I would run the 2 24v packs in series then in parallel with the 2 48v packs.





brian_ said:


> For 18-cell and 36-cell modules to add up to 288 cells, in a total of 9 modules, there must be only two 18-cell and seven 36-cell modules in a complete Gen 1 Volt battery. So if you used the entire battery, you would have more than two of the larger modules; if you wanted to simplify the setup, you could use just the larger modules, all in parallel.


I just posted that response, but I see in another thread that you have already come to this conclusion:


mrarmyant said:


> ... am going to use the 12 cell modules (7 of them) from a Chevy Volt Pack.


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## brian_ (Feb 7, 2017)

john61ct said:


> Go to Electric Vehicle forums for very knowledgeable reverse-engineering types figuring this stuff out for DIY EV conversions, doubt you'll find many in boating forums.



This *is* an electric vehicle forum, not a boating forum.


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## john61ct (Feb 25, 2017)

brian_ said:


> This *is* an electric vehicle forum, not a boating forum.


Sorry crossed wires. 

Since many people express an interest in this, and here's where the expertise is, I'd hope you could accommodate that bit of variation. 

Maybe a sub forum?


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## Duncan (Dec 8, 2008)

Hi
I'm using Volt modules in my car

I go from 3.5 V up to 4.1 V - Yarbert published a charge voltage curve - those two stay away from the extremes and still allow me to use about 75% of the capacity

So for the "2Kwhr" modules which are 12S-3P That gives

42 Volt - to - 49.2 Volt - 

a 48 volt Lead acid pack is actually 52 v to about 56 volts

The Volt modules are really really nice and well engineered!
Mine stay exactly balanced - I don't use a BMS - just check them every six months or so and I am abusing them! - drawing up to 1200 amps!

If I was using them in a boat I would put as many 2 Kwhr modules in paralel as I needed - no BMS - but I would use a "BattBridge" to tell me if I had any problems -http://www.evdl.org/pages/battbridge.html

In fact I would use a separate BattBridge with each module - and connect then with Alderson connectors so if one started failing I could simply disconnect it

Then it would simply be a case of charging them up to 49 volts and never discharging below 42 volts


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## mrarmyant (Jun 19, 2008)

brian_ said:


> This *is* an electric vehicle forum, not a boating forum.


Indeed. And a boat is a vehicle  :

Vehicle:
a means of carrying or transporting something such as motor vehicles or space vehicles


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## mrarmyant (Jun 19, 2008)

I dig this! Thanks! I'm actually going to use a an ardiuno micro-controller wit canbus to use the stock BMS for some extra control but will probably use this on top of it as a safety net. If I weren't worried about the plastic holding up to salt water and other odd aluminum corrosion I would 3d print adapters for the packs to use sea water to cool the batteries but I don't think Ill ever be asking too much of the batteries.



Duncan said:


> Hi
> I'm using Volt modules in my car
> 
> I go from 3.5 V up to 4.1 V - Yarbert published a charge voltage curve - those two stay away from the extremes and still allow me to use about 75% of the capacity
> ...


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## brian_ (Feb 7, 2017)

Duncan, your Volt modules appear in about the middle of your build thread, as replacements for a previous battery. They are nicely reconfigured and installed in the car without a description that I could find, but it looks like you have three large and one small module combined in series, then two of those sets in parallel - that would be 42s (and 3p on each side so 6p in total) for a nominal voltage of 157 V (at 3.75 V per cell, as per GM specs).

If I have this right, I suppose it could be described as 2p(42s3p)


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## brian_ (Feb 7, 2017)

mrarmyant said:


> If I weren't worried about the plastic holding up to salt water and other odd aluminum corrosion I would 3d print adapters for the packs to use sea water to cool the batteries but I don't think Ill ever be asking too much of the batteries.


It sounds like you're planning on no cooling. I understand the concern with running seawater through the battery, but you could circulate coolant through the battery and a heat exchanger, and seawater though the other side of the heat exchanger. Pressurize the coolant (as it enters the heat exchanger) to higher than the seawater pump outlet, and if the exchanger fails you only risk loosing coolant, rather than contaminating the battery. I believe that this setup (with a heat exchanger) is common practice for cooling marine engines, where it is described as a "closed" system.


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## Duncan (Dec 8, 2008)

Hi Brian

No I'm running them all in series - a total of 6 of the 2 Kwhr modules and the two 1 Kwhr modules

I just didn't quite have space for the last 2 Kwhr module!

So I'm running between 84S 3P - 340v full charge and 295v low charge 

As far as cooling is concerned I would not bother on a boat - the batteries really like about 35C - which is a bit hot anywhere on a boat

And with a relatively small motor - 10Kw? - you are not going to be able to draw enough current to warm them up

In my car I am using a coolant flow - but mainly to cool my controller down by transferring heat into the batteries

The only reasons that I can see to connect up the cooling is to avoid having some voids that "something" could live in - or to transfer coolant so that all of the batteries are at the same temperature


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## brian_ (Feb 7, 2017)

Duncan said:


> No I'm running them all in series - a total of 6 of the 2 Kwhr modules and the two 1 Kwhr modules
> 
> I just didn't quite have space for the last 2 Kwhr module!
> 
> So I'm running between 84S 3P - 340v full charge and 295v low charge


Hey, I was close: the right combination of modules, but with all in series rather than two strings in parallel. 

315 V nominal, using GM's 3.75 V/cell

Thanks Duncan.


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