[SriRamJaiRam]

So I'm told that the internal charger on the i3 has a limitation on how fast the car will charge. Another words, if I install a 60 amp 240V charger at my house, the car will still charge at the same rate as if I was using a 30amp charger. Anyone with any thoughts about this or more information? Thanks!

[smorrissey]

That's correct; the car can only charge at a maximum of 7.4 kW, so anything larger than a 30A charger is overkill...unless you are planning for the future...

[m_thompson]

Technically the AC charger is in the i3, and the device in your house is a very fancy AC outlet. A bigger outlet will not result in faster charging.

If your i3 has the DC Fast Charger option then you can buy a wall mounted 24-kW DC fast charging unit. That will need a really big AC plug.

[jadnashuanh]

AN EVSE sends out a signal telling the vehicle how much power it can supply, then, the car adjusts how much it wants, up to that limit. Especially near the end of the charge, the vehicle will NOT be using the max available, and it may be using less all the time if you set the idrive menus to a lower value (possibly so that you didn't overload the house's max load, or other things that may be on that circuit).

[BrokenVert]

I have a 40 amp charger just to reduce heat loads.

Also if you have the original charge controller in your car youre limited to 5.5.

[jadnashuanh]

An EVSE is essentially just a big switch. Once it is closed, it is the car that is determining how much power it will take based on what the EVSE reported it had available. The only thing that would cause heat in the EVSE is the resistance of the output relay contactor contacts based on the power available...I seriously doubt you'd notice any difference in performance on the i3 with a 30, 40, 50, or even larger EVSE unit. Now, if they skimped on the cable to the J1772 plug, maybe, but most of the cables available can easily handle far more than the i3 can take. Even on a 30A unit, the contactor is probably rated for at least 40A, and maybe more, so resistance of them would not be an issue.

[BMWrules7]

Originally Posted by BrokenVert

I have a 40 amp charger just to reduce heat loads.

Also if you have the original charge controller in your car youre limited to 5.5.

I think heat is a byproduct of inefficiency in design.

I was always led to believe that this inefficiency is a relative constant.

Now, a larger unit may not release into ambient the same amount of heat because its larger size is sinking and dissipating heat on a larger scale, but the heat (in terms of inefficiency) remains constant.

[jadnashuanh]

The only heat in an EVSE might come from its small power supply that provides operating power to the control board, and that would be about the same regardless of how big your EVSE's power contactor is (and thus, the max output it can provide). The quality and load rating on the contacts (like a fancy switch) would determine how much resistance they may have and as a result, how much heat they'd generate, but I'd be really surprised if a 40A unit produced less heat while recharging than a 30A unit at the same output levels.

As an aside...I have the latest software that CAN limit the recharging rate on the i3, but in the last week or so since I put in a meter to monitor things it's been in the mid-40-degree range...my 30A EVSE and the car is drawing about 6.95Kw. The logic does NOT appear to restrict charging rate much until things heat up, and depending on the ambient conditions, it may NEVER slow it down. I didn't have the meter installed while it was still summer temps, so I do not know if on mine, it did drop the recharging rate much...I don't tend to watch the thing to find out as long as it is charged in the morning, I'm happy! Those living in sunny SoCal may notice the slowdown...those living elsewhere, may not. To say it affects all of them all of the time has been disproven by what I'm seeing with mine. I hope that by next summer, things have been restored to the full potential, and I have faith that they will.

[BrokenVert]

Originally Posted by BMWrules7

I think heat is a byproduct of inefficiency in design.

I was always led to believe that this inefficiency is a relative constant.

Now, a larger unit may not release into ambient the same amount of heat because its larger size is sinking and dissipating heat on a larger scale, but the heat (in terms of inefficiency) remains constant.

Yeah you're basically right. But a smaller gauge wire operating closer to its limit will naturally be hotter than a larger gauge wire operating with the same amount of current. Thats a combination of the larger wire heat sinking better, but also the efficiency of the electron motion. The smaller gauge wire is running less efficient than the larger gauge.

I also always feel a little safer having some overhead, especially when it comes to such high (for the home) current applications.

[jadnashuanh]

In the USA, an EVSE must be provided with a breaker and wiring rated at 125% of the steady state load...there's already a pretty big margin built in. A bigger one isn't a bad idea for future-proofing, should your next EV be able to accept more, but it won't make any difference on the i3 at least until they change it (and who knows when that will be).

The wire resistance of 8g, 20' long is about 0.013-ohms. same length 6g, 0.008-ohms. 30A along 8g, 30^2*0.013 ~ 12W, 30^2*0.008 ~ 8W...distributed along the full length of the wire...we're talking almost unmeasurable.