More than 400V systems, where do things go sour?

[wycolo]

Tesla's motors can still run at the same voltage which is around 75 volts ac. The 800 volt DC from chargeport must now be routed differently to the battery bank - you need to split the existing battery in half and then put the two halves in series. If you can still output the battery bank at 400v then you can use the existing Inverter as well. So its all about reconnecting the battery segments.
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[jkn]

Are you sure about 75 VDC? Of course it is possible, but I would guess over 200 VDC at full power.

400 V battery could be 80 cells connected parallel and then 100 of those groups in series. Breaking of one cell would reduce capacity of whole battery by 1/80 = 1.25%. 800 V battery would be 40*200 so failure of one cell would reduce capacity by 1/40=2.5%. Bigger cells would reduce costs, but failure on one cell would reduce capacity even more.

If car has two 400 V batteries in series for charging, then charging current is same for both. Balancing must be done while using energy.

 

[bestellen]

There has to be some downsides to it too or else why would virtually ervey EV is 400v? If not, why not make a kilovolt EV? Electric hyper car Rimac Concept One's pack is more than 600V I think.

 

[scaesare]

One comment that had been made some time back was that the IGBT selection availability for use in the inverter may not have been rated for higher voltage. Or that the C-rates of the batteries were such that even if HV IGBT's were available were, it may have not made sense to incur the additional expense to design for > 400V when there was no real practical advantage.

That having been said, it's believed that Tesla uses International Rectifier IGBT's. While the majority of the IGBT parts they list in their Product Selection Guide for motor drive usage are rated at 600V peak, they do indeed have 1200V parts as well, with similar current rating specs.

That may be a more recent product, not sure. In any case, they are available now, should there be an advantage in basing future designs on them.

 

[Peter Egan]

So as you might have heard Porsche announced they were working on a new charging system for their upcoming Mission E and Audi, VW EVs down the pipeline. They claim a 15 minute charge rate for 80% using a 800V system.

I don't know much about batteries or EVs other than what I research and try to learn but, to my understanding simple pros of a 800V hypothetical Tesla Model S would be;

• Lighter, thinner cables for both power electronics and Supercharging equipment. As you'd need less current for the same amount of power. No need to use space grade inconel at the fuse to support up to 1500 Amps. Same power can be achieved with only 650Amps. Or use the same thing and double the power.
• AFAIK charging a battery pack is limited at what the cells can get, not delivering the power. If so a 20 stall supercharger already has 1.3mW of power available spread across 10 banks, 20 stall. Be it an iPhone or a car lithium ion batteries can only charge up to 80% in a fast way (Depending on your cells' max. C rates) and the rest, afer the cells reach peak voltage is CV stage where current tapers off. Suppose Tesla changed the layout of their current pack to use same cell count but connecting 37 cell parallel making a 122Ah cell. Making 12 groups per module and having 16 modules. Result would be a 700V nominal, 122Ah cell. Still around 85kWh. With the current C rates Supercharger delivers it could start its depleted charge at 615V, 270A = >165kW. Faster charging?

There has to be some downsides to it too or else why would virtually ervey EV is 400v? If not, why not make a kilovolt EV? Electric hyper car Rimac Concept One's pack is more than 600V I think.

I am also guessing that the chargers' work would be more difficult too as they'd work as transformers? Also DC-DC inverter would have much more work too I guess.

Someone who knows this better than I do could explain.

Increasing the battery voltage is not an issue. It just requires half size current collector plates and flipping the direction of half the cells in a module. When charging, each module is presently 25 volts - each module is 6 in series. Halve the size of the plates will cell flipping gives a 50V max module - still well under the 60 volts limit for low-voltage. ((Note - OEMs are thinking of moving to 48V for a number of ICE vehicle systems.)) A minor issue is the number of cells to share the current if one cell in a sub-module fails is reduced by half - I expect not a critical issue.

We will likely see 690 V nominal systems on sports vehicles first.

While 96 or 192 cells in series offers lots of packaging options, it is a somewhat silly number when there are lots of small cells - 18658, 2170. Really, 100, 200 or 400 cells in series (360V, 720V, 1440V) is a better approach.

 

[arnis]

So the only real benefit going above 400V is having smaller conductors in wires and also plug pins?
If this is true then I can guess why Tesla (and many others) went with 400V.

 

[Ulmo]

So the only real benefit going above 400V is having smaller conductors in wires and also plug pins?

FWIK (I'm not an engineer) Yes. For charging faster than SuperCharger speeds or for high performance sports cars (similar issue), it can make the difference between unaffordable and too heavy to carry the cord to plug in (and increases weight of car for internals), vs. affordable and light enough to handle, so it's not a small difference. The new charging systems they're talking about charging faster than 350kW would probably require higher voltage unless the plug was a robot snake, in which case it could be pretty heavy but very expensive and same problem inside car, or superconductors, which would be lighter and less expensive (at economies of scale), but that would require automotive superconducting cabling as well, and that might have reliability and energy issues. Higher voltage seems easier for that.

If these types of batteries are what we're going to keep using in the future, then in decades I'm expecting superconducting cabling to be normal, reliable, and light weight, and for the voltages of the packs to be about double what they are now for most vehicles (by then the insulation and electronics will have evolved to handle that inexpensively and nicely), or whatever multiple gets the pack charged as fast as the standard fast chargers of the time will charge at. If the new battery types of the future (let's say they hold 5x as much) is 5x, or 3x, or whatever, that might be the multiple that holds the new volt standard together.

If this is true then I can guess why Tesla (and many others) went with 400V.

There are other reasons to have lower voltages: easier to get at those voltages in step down transformers for charging equipment, and 600V is a common wire max volt rating. It makes total sense that the first step we used was in the sub-600V range. And, it would make sense that the next range is 2x-4x that. First, we need to get these affordable, and I'm guessing that may still mean the sub-600V range.

 

[arnis]

If, in near future, there will be a battery pack that fits into normal sized car (Model S) AND can sustain charge rate
CONSIDERABLY above 120kW and I was Elon Musk, I would not switch to higher voltages.
I would add second socket to the passenger side tailgate.

But this is not something that will happen during next few years. Even if we make Model X with two 100kWh packs we
can still not cool the chemistry fast enough for it to charge considerably faster than 120kW. The end.