DC charging, how fast?

[jasleinstein]

It seems we will not get public DC charging for the i3 in the state of Washington, but since I paid for the option, I am curious, what are your charging times for DC? How fast will it charge?

thanks

 

[jadnashuanh]

BMW specs with a 50Kw capable CCS unit (they are not all that big) at 80% in less than 30-minutes. Because of the heat generated, once it reaches that level, it slows down the charging rate. Now, you may not be starting from near zero charge, so that magic 80% could be achieved sooner and may have more than 80% at the end of a 30-minute period.

FWIW, BMW is promoting a lower-powered, less expensive and cheaper to install 25Kw CCS unit. It is still lots faster than the EVSE, but not as fast as a 50Kw unit. Because of the ramping down, if you wanted to get to 100%, they both would be close, but the 50Kw one would still beat it.

 

[stumbledotcom]

I've charged at both the ABB 50Kw units that NRG has deployed and the BMW i. 25Kw variety multiple times. Haven't kept records but there doesn't seem to be that much of a real world difference. They seem to work faster than advertised, if anything. But that's because my BEV never starts from zero. I typically get to 80% in 15 minutes or less. The final bit estimates around an hour but I've never bothered letting it go to 100%. The BMW-NRG promo provides a free 30-minute session. Most of their units shut off automatically so to keep the charge going you have to stand there and swipe your card. The few times I've used the entire 30 minutes while shopping, the car winds up in the 85 to 95% range before the cut off.

 

[jasleinstein]

Thanks guys

 

[Jeffj]

From what I've read, once you get to 80%, the DCFC ramps down and its no faster (and may even be slower) than a standard L2 charger. There are good reasons why some of the units shut off after 30 minutes, as you are getting zero benefit from DCFC vs L2 after 30 minutes, and likely (if you are starting from more than zero charge) in less than 30 minutes.

It would be nice to test this, but as in the OP's case, DCFC here in Colorado is virtually non-existant.

 

[janner]

When I charge at a CCS facility it normally starts at 125A and I normally stop when it drops below 20A: this is normally around 25-30 mins and I have around a 90% charge by then.

 

[i3Alan]

BMW specs with a 50Kw capable CCS unit (they are not all that big) at 80% in less than 30-minutes. Because of the heat generated, once it reaches that level, it slows down the charging rate. Now, you may not be starting from near zero charge, so that magic 80% could be achieved sooner and may have more than 80% at the end of a 30-minute period.

FWIW, BMW is promoting a lower-powered, less expensive and cheaper to install 25Kw CCS unit. It is still lots faster than the EVSE, but not as fast as a 50Kw unit. Because of the ramping down, if you wanted to get to 100%, they both would be close, but the 50Kw one would still beat it.

The charge slowdown has nothing to do with heat generated (normally). As the battery gets closer to full charge, it simply cannot safely accept as high of charge current. You will always get to the point where the max safe charge is equal or less than 25 Kw faster with a 50 Kw charger than with a 25 Kw charger, but the charge rate thereafter will be the same with either charger. Once the max safe charge rate is 7.2 Kw, then a 7.2 Kw L2 EVSE will complete the charge as quickly as a 50 Kw or 25 Kw (or any other) DCFC.

 

[jadnashuanh]

Not only do you have to worry about heat in the vehicle, that huge power supply in the CCS unit gets hot as well. The i3's cooling is geared more around using its own internal 7.4Kw dc power supply than an external 50Kw one, but recharging batteries does raise their internal temperature as the current is forced in and the chemical changes occur. The internal resistance of the battery changes as it is charged...trying to force higher current into it creates more heat.

One of the things newer battery tech seems to find is that nano technology can improve the power density and current carrying capacity of a battery, making them higher density storage devices. Newer cells will likely use that technique, along with other things to give us more capacity in the same space, or just smaller batteries to save weight and increase range.

FWIW, even the EVSE ramps down, and it is only using a max of 7400W, or nominally 30/32A at the maximum - the current being applied is not constant over the charging cycle.

 

[RJSATLBA]

From what I've read, once you get to 80%, the DCFC ramps down and its no faster (and may even be slower) than a standard L2 charger. There are good reasons why some of the units shut off after 30 minutes, as you are getting zero benefit from DCFC vs L2 after 30 minutes, and likely (if you are starting from more than zero charge) in less than 30 minutes.

It would be nice to test this, but as in the OP's case, DCFC here in Colorado is virtually non-existant.

I monitored the volts and amps on a 50kW charger on an occasion when my next charge was going to have to be a short top up from a 7kW unit to get me to the next rapid. Clearly it made sense for me to stay on the first rapid until the charge rate dropped below 7kW, provided I wasn't blocking the charger. That didn't happen until 93%.

 

[i3atl]

From what I've read, once you get to 80%, the DCFC ramps down and its no faster (and may even be slower) than a standard L2 charger. There are good reasons why some of the units shut off after 30 minutes, as you are getting zero benefit from DCFC vs L2 after 30 minutes, and likely (if you are starting from more than zero charge) in less than 30 minutes.

It would be nice to test this, but as in the OP's case, DCFC here in Colorado is virtually non-existant.

I monitored the volts and amps on a 50kW charger on an occasion when my next charge was going to have to be a short top up from a 7kW unit to get me to the next rapid. Clearly it made sense for me to stay on the first rapid until the charge rate dropped below 7kW, provided I wasn't blocking the charger. That didn't happen until 93%.

Yes, that's what we've found in our local testing as well - whether on a 50kW or 24kW unit, 92% is the magic point where there's no benefit over 7kW L2.

 

[Boatguy]

I've only used it half a dozen times, usually when I'm between 20% - 40% SOC. I get to 80% in 15-20minutes and then move on.

The existence of a network is what makes Tesla a viable long distance vehicle, and the lack of a network restricts BMW et al to "local" transportation for 90% of the owners. To break out of local and really replace an ICE, BMW et al need to actually install DC chargers rather than just issue press releases about them.

 

[jadnashuanh]

By the time BMW starts delivering an ICE replacement BEV, CCS units will be around. The i3 is not nor ever should be compared to something like a Tesla that starts out with 3-4x bigger battery and a much bigger price tag. Nor, is it reasonable to compare it to the Chevy Volt, which has a much larger fuel tank and nearly 3x bigger motor and a much shorter EV only range. The addition of the REx to the i3 was not made to make it go anywhere...it was to reduce range anxiety for those making the transition to a BEV with the range designed into it geared for commuting. You can use a pair of pliers to remove a nut, but a wrench often does the job better...same thing on the i3...the REx is the plier equivalent...you can use it for longer range travel, but it is not the best tool for the job. Now, if it HAD been designed for an ICE replacement capable of any travel anywhere anytime without undue delays or recharging, and sold as such, then, you'd have reason to complain. As it is, IMHO, it is what it is - an optimized city car.

The next I-series car is likely to be viable and sold as an ICE replacement, and the infrastructure is likely to be there to make it viable when that happens. In the interim, most BMW models will be getting a hybrid option, partly to boost their CAFE averages, and partly to gain experience, add volume, and boost demand for things like CCS units, leading up to a BEV. Inductive charging and other tools will also likely become readily available.

 

[cx650t]

Charge rate is dependent on the initial state of charge and temp. In 20 mins I’ve received anywhere from 8 to 13 KW. Chargenow limits the fast charge to 30 mins and then it shuts down. Level 2 chargers also ramp down the current as the battery approaches capacity. I've had the power go from a 7KW rate down to less than 1KW as the charge approached 100%.

 

[davesw1]

If you look on the dash when charging, you see the plugged in symbol and the word rapid and 2 arrows until it gets to 80 % then it goes back to just showing the plugged in symbol as it goes down to normal charge

 

[i3atl]

If you look on the dash when charging, you see the plugged in symbol and the word rapid and 2 arrows until it gets to 80 % then it goes back to just showing the plugged in symbol as it goes down to normal charge

It does not drop down to "normal charge" at 80%. See the chart at the bottom of this page - you can see that the charge rate remains above L2 speeds even after 90%.

http://electrifyatlanta.com/wp/?page_id=357

 

[jadnashuanh]

The charging rate is somewhat dependent on the ambient temperatures and the ability of the cooling system to keep things at a safe level, which is not a constant.

 

[RJSATLBA]

The charging rate is somewhat dependent on the ambient temperatures and the ability of the cooling system to keep things at a safe level, which is not a constant.

If so, a non-engineer like me would expect that the sensitivity of charging rate to ambient temperature would reduce once the rate of charge started to fall such that by the time it has fallen to L2 7kWh level, the cooling system would be able to cope fully with battery heating without having to constrain the charge rate, with the possible exception of the most extreme ambient temperatures.

The last time I monitored a DC rapid charge (with nobody else waiting) to see when the rate of charge fell to L2 7kWh level in order to minimise my overall charging time when the next charger en route was to be an L2, it occurred at 93% in an ambient temp of c 5C.

 

[janner]

I've monitored my last two DC Rapid Charges from Ecotricity up to 93%. Ambient air temperature about 15 degC.

The car charges at 110amps until about 70% Charge - this is about 4% charge per minute.

After 70% charge the rate of charging declines to about 2% charge per minute.

It's surprisingly two (almost) straight lines - I'll post the graph if I can find out how to.

 

[i3atl]

...the sensitivity of charging rate to ambient temperature would reduce once the rate of charge started to fall such that by the time it has fallen to L2 7kWh level, the cooling system would be able to cope fully with battery heating without having to constrain the charge rate, with the possible exception of the most extreme ambient temperatures.

Exactly. Extreme temperatures would have an effect on the peak charge rate, but from ~75% on the impact would be minimal.

This effect is more noticeable in EVs which lack batteries with proper thermal management.

 

[jadnashuanh]

Keep in mind that the CCS unit may have heat issues as well...it's got one huge power supply in it.