wwhitney
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Re: First DC Station capable of charging at a rate of up to 350 kW, operational by 6/17?

Sun Dec 18, 2016 10:12 am

arnis wrote:Incorrect. Both of you.

Perhaps.

I spent ten minutes trying to the find the heating rate of charging a lithium ion battery at 1C or 2C, and didn't find any good answers. Battery university (http://batteryuniversity.com/learn/arti ... _batteries) seems to claim that charging cobalt blended lithium ion at rates of 0.5C to 1.0C is 99% efficient, but I'd prefer a primary source. I doubled the 1% inefficiency for my computation for good measure.

So I'd be interested in any references you have for the charging efficiency being only 90%, heating-wise.

Cheers, Wayne

arnis
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Re: First DC Station capable of charging at a rate of up to 350 kW, operational by 6/17?

Sun Dec 18, 2016 1:58 pm

That's the thing. It is not a fixed number. It depends on charge state and chemistry and
charging speed and temperature and how old the battery is (degraded Leaf vs new).

90% is a number easy to understand. It is not that bad with Leaf. I believe.
I will check DC charging station DC output and LeafSpy charge data next time.
But I'm not sure that station calculates independently.
Short range EVs <30kWh -- Medium range: 30-60kWh -- Long range: >60kWh
Charging: Trickle <3kW -- Normal 3-22kW -- Fast 50-100kW -- Supercharging >100kW

wwhitney
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Re: First DC Station capable of charging at a rate of up to 350 kW, operational by 6/17?

Sun Dec 18, 2016 2:29 pm

arnis wrote:That's the thing. It is not a fixed number. It depends on charge state and chemistry and
charging speed and temperature and how old the battery is (degraded Leaf vs new).

Sure, I agree, but for a first approximation we just need an average figure. I'm surprised I couldn't locate even an approximate answer to the question: what fraction of the DC energy put into charging a large format lithium battery ends up as heat? There's a big difference between 1% and 10%.

BTW, the Enphase AC battery claims a round trip efficiency of 96%. Of course, that's a small battery (1.2 kWh) and I don't know what charge/discharge rate that was measured at. But it does make it seem like DC charging loss of only 1% to 2% is plausible.

Cheers, Wayne

arnis
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Re: First DC Station capable of charging at a rate of up to 350 kW, operational by 6/17?

Sun Dec 18, 2016 3:38 pm

For now, lets just estimate whats going on with the best example we have.
Tesla. With bigger battery. It charges at speed up to 120kW.
Let's assume 98% one way efficiency. That is only 2.4kW of heat.
I know that Tesla uses 6kW resistive heater for battery heating (Tesla has excellent battery thermal management).
I don't have exact number but I've heard it takes half an hour to heat it up from cold to acceptable, guess that is 10-15
degrees (international!). Tesla pushes 6kW of heat and it takes a lot of time.

We can clearly state that at 120kW speed Tesla battery gets much more than 2.4kW of heat.
To be more exact Tesla is not able to charge at maximum speed in some scenarios because of thermal throttling.

http://insideevs.com/tesla-ups-supercha ... 90d-video/
Image

Do we agree that Tesla can extract heat at minimum 6kW rate?
Short range EVs <30kWh -- Medium range: 30-60kWh -- Long range: >60kWh
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wwhitney
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Re: First DC Station capable of charging at a rate of up to 350 kW, operational by 6/17?

Sun Dec 18, 2016 4:49 pm

arnis wrote:We can clearly state that at 120kW speed Tesla battery gets much more than 2.4kW of heat.
To be more exact Tesla is not able to charge at maximum speed in some scenarios because of thermal throttling.

That's a non-sequitur. Is thermal throttling only based on pack temperature, or could it be based on the temperature of other electrical components, like the big relay that Tesla uses to switch the power input pins between the charger and the battery?

To determine the heating inefficiency of charging, we'd need the following data on a charging session:

Starting pack temperature
Ending pack temperature
Pack thermal coefficient
Pack heat lost to cooling
Energy delivered in kWh

The computation would be a lot simpler if any forced pack cooling is temporarily disabled for this data gathering. Depending on how well the pack is thermally isolated, we might also need to know the passive cooling rate when the pack is above ambient temperature. If the temperature decay rate is low enough, and the charge session is short enough, we can ignore the passive cooling.

arnis wrote:Do we agree that Tesla can extract heat at minimum 6kW rate?

No, I don't know anything about how Tesla extracts heat from its packs, and you haven't presented any data on the topic.

Cheers, Wayne

arnis
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Re: First DC Station capable of charging at a rate of up to 350 kW, operational by 6/17?

Mon Dec 19, 2016 2:04 pm

What? :roll:

First of all:
https://www.youtube.com/watch?v=D18gsJgYfd4
This noise is Tesla running AC compressor and main fans. This is due to battery pack getting hot.
This same stuff occurs when Tesla makes a drag race but that is not because of pack. Motor/inverter are not used during SCing.

Secondly: Tesla calls "passive cooling" cooling with glycol without AC and fans. So it kinda means something else for Leaf guys.

Three: Yes, thermal throttling is MOSTLY due to pack getting hot. There were some instances due to plug getting too hot (needs service).
Contactors don't get even warm at 120kW rate.

Tesla has sophisticated thermal system. Research that:

http://c1cleantechnicacom-wpengine.netd ... 162710.jpg (passive cooling drivetrain, battery idle )
https://i.imgur.com/TOUXlWM.png (p
https://1.bp.blogspot.com/-djg9fnihcEA/ ... nsored.jpg (battery passive heating, using drivetrain heat, cabin cooling)
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TonyWilliams
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Re: First DC Station capable of charging at a rate of up to 350 kW, operational by 6/17?

Mon Dec 19, 2016 2:18 pm

We do thermal throttling with JdeMO for the 2012-2014 Toyota RAV4 EV and Tesla Roadster:

125 amps - max now, may go up to 200 amps in the future.

90 amps max - 45C / 113F degrees battery temp
60 amps max - 47C / 117F degrees battery temp
30 amps max - 49C / 121F degrees battery temp
OFF -------------- 51C / 125F degrees battery temp

arnis
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Re: First DC Station capable of charging at a rate of up to 350 kW, operational by 6/17?

Tue Dec 20, 2016 1:46 pm

Today I did a 10min DC charge with healthy 24kWh Leaf battery at exactly 1.4C - constantly - 32kW speed.
I got a result: 97% efficiency. This was in the low SOC part. And only 1/4 of all capacity was charged.
Unfortunatly I can not be sure that number on DC station and LeafSpy are very accurate.

For now (without additional information) I suppose 3% inefficiency is possible at "not that fast rate" and "low SOC".
I suppose Tesla has no worse than 95% efficiency at 120kW rate.
Therefore appr. max 120x0,05=6kW of heat generation in the pack.
This looks plausible. At the same time big question mark - why Tesla can not handle keeping the pack at constant temperature
at very warm weather scenario.
Short range EVs <30kWh -- Medium range: 30-60kWh -- Long range: >60kWh
Charging: Trickle <3kW -- Normal 3-22kW -- Fast 50-100kW -- Supercharging >100kW

wwhitney
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Re: First DC Station capable of charging at a rate of up to 350 kW, operational by 6/17?

Tue Dec 20, 2016 4:42 pm

Thanks for the data!

Cheers, Wayne

EVDrive
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Re: First DC Station capable of charging at a rate of up to 350 kW, operational by 6/17?

Wed Dec 21, 2016 12:46 am

TonyWilliams wrote:We do thermal throttling with JdeMO for the 2012-2014 Toyota RAV4 EV and Tesla Roadster:

125 amps - max now, may go up to 200 amps in the future.

90 amps max - 45C / 113F degrees battery temp
60 amps max - 47C / 117F degrees battery temp
30 amps max - 49C / 121F degrees battery temp
OFF -------------- 51C / 125F degrees battery temp


I'll buy an upgrade for my JdeMO. The current version you installed on my car works exceptionally well and of course, faster is always welcomed. Thanks for making my Rav4 great again!

For the 350 KWH charger, it is a welcome good sign of progress. I'm impressed with the Fast Charger rollout that EVGO is doing in California. I would have thought ChargePoint would be more aggressive, I hear they're working on it. As soon a Quick Charge station goes online near me, I pay to use it to support the rollout and expansion of the infrastructure, proving the use case. Bring on the EV, Lighting Fast Charger, connected cities.
- SF Bay Area
- 2011 Leaf traded in at 46,000 miles, 3 years, lost 1 bar
- Upgraded to 2014 Rav4EV with Quickchargepower.com CHAdeMO port, 53,000 miles
- Tesla Model 3 reserved

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