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Discussion Starter · #1 ·
Hello all,

DC fast charge heat up batteries more than other (Levels 1 & 2 charging, driving, etc.).
Could someone recommend what kind of cooling your diy EV's use to keep them at good temps.? Planning CHAdeMO (CCS once available) implementation in my diy convertsion.

Thanks in advance.
 

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Better for the cells' lifespan, to keep C-rates lower than the point where internal temperature rise becomes significant, or even detectable.

That rise is a symptom of lifecycles-reducing stress, not a cause.

Artificially keeping them cool from the outside is a safety precaution, to prevent the pack exploding into flames

and to allow the vendor to cite higher performance figures by stretching the "safety envelope".

Liquid cooling systems are too much expensive complexity, IMO not worth it for most DIYers
 

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Sure go for it if you think you got the skillz

but if you then really rely on that DIY TMS, better be sure to build in active monitoring, redundancy etc

more points of failure
 

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DC charge is not in itself the problem.

Determining the right amps level and keeping the flow capped,

or actually limiting current based on a detected temp rise is the challenge

and these take pretty high level components and skillz to implement
 

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BMS watches all the cells and makes sure they don't get too high or too low (too high = boom, too low = die). Also some monitor temperature.

DC charge is pretty difficult but not impossible, I had it in my car until I did a rebuild (CHAdeMO), going back in once I get a new shunt.
I see you posted in this thread, Jack Bauer (Damien) is the one who made the CHAdeMO hardware I'm using, I rewrote the software to work with his hardware.
Temperature monitoring is coming next after CHAdeMO has been used some more. At that point it wouldn't be difficult to add temperature-based charging.
I'll be testing up to 100A into my pack and see how the temperatures behave, chances are the batteries will be fine.
 

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Hello all,

DC fast charge heat up batteries more than other (Levels 1 & 2 charging, driving, etc.).
* * * Planning CHAdeMO (CCS once available) implementation in my diy convertsion.
That is simply not true.

The car asks for a max current level for charging.

So, for example if you go to a public charger and don't ask for more than you charge Level 2 at home, there simply is no difference in DC charging a pack.
 

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Discussion Starter · #10 ·
So after watching the EV Bolt dismantle and reading other info there's a separate heating/cooling system to keep the batteries at the ultimate temp.

Having a dedicated heating/cooling line what makes me ask how the DIYers approach this side of things.
 

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OEM EVs have to be able to handle large temperature ranges without problems - 0 to 120 F or so. DIYers tend to ignore things like this, maybe adding a manual battery heater if necessary.
Tesla likes to condition their batteries a lot -- but they have a specific chemistry and charge/discharge very quickly.
 

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Yes of course manufacturers pay many millions to large teams of top engineers.

Does not translate to something a backyard DIYer must try to reproduce
 

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Discussion Starter · #13 ·
OEM EVs have to be able to handle large temperature ranges without problems - 0 to 120 F or so. DIYers tend to ignore things like this, maybe adding a manual battery heater if necessary.
Tesla likes to condition their batteries a lot -- but they have a specific chemistry and charge/discharge very quickly.
Yes of course manufacturers pay many millions to large teams of top engineers.

Does not translate to something a backyard DIYer must try to reproduce
Does that mean that DC charge will not damage the battery, even if not cooled/heated during charge? Or you're saying that BMS in communication with the charge station will let know to lower current if overtemp. threshold, i.e. have it charge slower?
 

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Does that mean that DC charge will not damage the battery, even if not cooled/heated during charge? Or you're saying that BMS in communication with the charge station will let know to lower current if overtemp. threshold, i.e. have it charge slower?
I don't really know, not having access to a laboratory and a year or so of full scale testing.

But my CHAdeMO system is going to have overtemperature limits at some point (translate: when I get around to adding it) and the same probably goes for any similar solution. I've got 2 temperature sensors in each battery module, so that should be plenty of monitoring. That will either cut back the charge current or shut it off altogether (probably going to have setpoints for both of those).
 

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The issue has nothing to do with DC charging, as such.

I am saying that you "should" keep the amps C-rate low enough that the cells do not get significantly hot.

My preference is simplicity, both for safety and reliability.

It may be possible for you to design a fancy circuit to lower the current as a response to temperature rising

never heard of that yet being done IRL.
 

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Usually a BMS can monitor pack temperatures. With the chargers and charger controllers that some of us DIYers use, it is trivial to add a backoff triggered by higher temperatures. Plenty safe and plenty reliable :)
But I agree that heating is a symptom of other problems -- you're probably charging too fast if the cells are getting too warm.
 

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Does that mean that DC charge will not damage the battery, even if not cooled/heated during charge?
You seem really freaked out over "DC charge"

This will totally wad your panties up...your AC charger (Level 1 or Level 2) charges the pack with, gasp, DC.

Determine that charge limit, which you or somebody, have deemed to work for the battery pack design you have and that's the current you limit your public charging at with the protocol of that charging method. For DIY, you likely won't get Tesla-levels of charge rate unless you have serious technical skills.

You ask for 500 amps, you'll get it and watch your home project likely go off in fireworks (don't ask how I know 18650's go off like Roman Candles), possibly being the drowning swimmer that sinks the public charger as well. Ask for 50 Amps and you wont get more.

My strong suggestion for what I sense to be your skills level -- stay away from DC charging or have someone competent set it up for you.
 

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Discussion Starter · #18 ·
Usually a BMS can monitor pack temperatures. With the chargers and charger controllers that some of us DIYers use, it is trivial to add a backoff triggered by higher temperatures. Plenty safe and plenty reliable :)
But I agree that heating is a symptom of other problems -- you're probably charging too fast if the cells are getting too warm.
So what I'm getting is that the ambient temperature could be hot which causes the batteries to heat and that's why in the video provided earlier EV Bolt (maybe Tesla too) has dedicated battery cooling/heating system?
And should the BMS be set to the appropriate charging rate specified by the battery datasheet, the fast or slow charge won't increase battery temperature significantly (unless there's a damaged cells or else)?
 

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First - I guess so? Tesla definitely actively heats the battery before supercharging Introducing V3 Supercharging and might cool it down if temps get too high.

Second - yes. Although the BMS doesn't usually control charging, it advises the charging device, whatever that may be. With enough charging power, the batteries will definitely heat -- but that's up to the individual to worry about.
 

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In my conversion I am implementing both active heating and active cooling for the batteries. These states are triggered / set by my BMS via either a heat or cool request (analog+over CAN). So all temperature "intelligence", setting and monitoring is done in the BMS. My own EV peripherals controller handles switching on the airconditioning compressor, battery heater, valves, pumps, etcetera. I also have a pre-heat for fastcharging feature and a stationary pre-heat mode.
Not on the road yet, so cannot say anything about actual temperatures.
 
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