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Discussion Starter · #1 ·
Hi all,

This is a spec sheet for the battery pack in my 2011 Th!nk City. I'm hoping some of you could take a look at it and give me an idea of how much power this pack will support. I'm trying to determine if it's worth keeping this pack or selling it and going with a custom unit.

It appears to say the pack is capable of supporting 74kw "burst discharge" for 30s. That should be right at 100hp. Am I reading that correctly? Is that rating just based on the OEM motor and controller in the vehicle or a generic measurement of what the battery will support regardless of anything else down stream?

Thanks.
 

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Discussion Starter · #2 ·
Also, just noticed it says the vehicle can charge at 50A which would be 12kw... how is that possible? the on-board charger is only a 3.3kw unit. Are they just suggesting that the batteries could theoretically handle it but the on-board charger won't allow it? If so it would be amazing to upgrade that charger. I have a 10kw EVSE in my garage which could take advantage of that.
 

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DCFC EVSEs promise much higher rates, going direct DC to charge presumably bypassing the puny onboard charger

CHAdeMO, SAE Combo aka CCS and Tesla’s proprietary supercharger are the 3 "standards"
 

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Discussion Starter · #5 ·
DCFC EVSEs promise much higher rates, going direct DC to charge presumably bypassing the puny onboard charger

CHAdeMO, SAE Combo aka CCS and Tesla’s proprietary supercharger are the 3 "standards"
Ah, so you're saying if the car was set-up to accept DC fast charging it could support that. That makes sense. I don't need to invest any more time/money into upgrading charging but thought it would be nice to have if it was simple.
 

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Obviously the drivetrain will be limited by the pack, you're not adding more storage right?

But irrelevant anyway, the car software will limit the power to a point conducive to longevity.

They would not allow the user to burn the pack or drivetrain up in just a week or two of abuse.

Think like an old school carburetor limited by a "governor".
 

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Ah, so you're saying if the car was set-up to accept DC fast charging it could support that. That makes sense. I don't need to invest any more time/money into upgrading charging but thought it would be nice to have if it was simple.
Nah, the battery doesn't care if its DC fast charging or a faster AC charger. If you put in a 12kW charger, the battery would happily accept the charge.

That's only around a 0.5C rate, so that's not really that difficult. I suspect that the battery could take even more, the rating is probably just based on how high they tested it.
 

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After 0.5C the cells take a longevity hit, especially as temps go below T-shirt weather
Nah, most Li-ion cells are good for 2C continuous charging at 25C. As long as they don't get hot and don't get to the point of plating, there is no hit on longevity. This here is just an overly conservative rating, probably because they didn't do higher level testing.
 

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The longevity benefit may well get "lost in the noise" with high C-rate discharging keeping cycle lifetimes short anyway.

But with a usage pattern that normally gets 1000+ cycles you will see a definite impact between 0.5C and 2C.

Especially in cool temps, get below say 20°C I'd cut even low currents in half, and stick to maybe 0.1C at 10° or below.
 

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Discussion Starter · #12 ·
I'm pretty happy with it's current charging speed. I don't drive the car enough to need anything faster. I usually go 2-4 days without even plugging it in. I was just curious about the limits mentioned in that flyer.

I'm most concerned with the discharge rate. Longevity isn't a real concern of mine as long as we're not talking about weeks vs years! I don't need the car to last 100k miles. I was just curious as to what it could support without destroying itself quickly.
 

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But with a usage pattern that normally gets 1000+ cycles you will see a definite impact between 0.5C and 2C.
Research has shown that if temperature is controlled and the threshold for plating is not exceeded, it is better for cycle life to charge somewhat faster.
 

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For what chemistries and over what range?

I've only seen that sort of data on AGM lead deep cycling, never any kind of LI batteries.
 

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For the Think battery pack, they used Enerdel batteries and BMS. They're 12s2p Moxie Energy modules if I recall correctly (not the power modules). There were 2 modules in each battery box, 4 battery boxes in each string. 2 strings in each pack paralleled at the main contactor. They used their own BMS as well.

The biggest issue I see with trying to get more out, is that the connectors to the batteries, cables, contactor, fuse, bussbars, etc, are all made for the limits on that datasheet you've got. Also, the BMS (Their RLEC and MLEC) has a current sensor, so it would likely try to limit the output to the inverter.

If you're using as a standalone pack, you'll either need to replace the BMS, or integtrate the RLEC boards into a BMS master of your own.

Here's the module spec that I "THINK" are in the Th!nk:
https://enerdel.com/me350-049-rd-bo/

1.5kWh each
12S2P
43.2 nominal
70A max continuous current (2C)
105A pulse for 10 seconds (3C)
70A Max charge/regen current (2C)

Since there are 2 strings, it looks like it matches the image you attached (140A continuous = 70A string 1 + 70A string 2). Max would likely be 210A for 10s, but that's if the BMS allows it, or if the fuses are rated.
 

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For what chemistries and over what range?

I've only seen that sort of data on AGM lead deep cycling, never any kind of LI batteries.
For Lithium. I don't have the link any more but it was a rigorous study. The basic gist is that side reactions are more likely to happen during charging, so if you can prevent too much heat it is better to charge fast because the cell spends less time in the charging condition.
 

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"Lithium" is just an umbrella term for dozens of wildly differing specific chemistries.

No one statement is true for all of them, much less specific numbers.

Charge at a low rate and there is no heat produced.

Between 0.4C and 1C there is very little difference in heat generated, but a very well-established reduction in longevity.

Perhaps with a particular lithium chemistry like LCO, it is "safer" to charge at 5C than 4C, but neither rate would be good for longevity.
 
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