Single Cell PEVs with Boost Converter?

[Username1]

In theory would it be possible to run a PEV using a single large LFP cell with a boost converter? I'm talking all the way up to powerful PEVs like high-end escooters.

For example using a single 1000 ah LFP cell (3200 wh). Let's say you used a fairly reasonable 2c discharge. That's around 3v/2000a which would need to be converted to around 100v/60a. That's around 30x voltage boost.

I'm guessing no such boost converter exists but if you designed it from scratch, could it be made small and efficient enough for use in PEVs? Obviously it would need to be placed very close to the cell terminals due to the massive cables.

 

[amberwolf]

How much power do you mind losing to the inefficiency of the DC-DC? Typically these can be as low as 75%, I don't know the highest possible but the best I've seen test results for that I'd believe was maybe 85%. (so 15-25% of your battery lost as waste heat in the converter, for those cases). It might be possible to design it with higher efficiency because of the narrower conversion range it has to do, so eaiser to tune all the circuits better.

Depending on the motor controller design you might be able to integrate the DC-DC into it. Solcar here on ES used to run a newsgroup (on Yahoo?) dedicated to this kind of system; he designed at least one that he used for his bike(s). I dont' think there's a thread here about the system, but there was info on the NG, if there is an archive of it anywhere (like archive.org).

Another thread about this kind of thing from several years ago
https://endless-sphere.com/forums/viewtopic.php?f=2&t=73895
but the OP never came back so I dunno if he ever worked it out.

 

[Username1]

I think 95%+ efficiency would be the goal, with anything under 90% being unacceptable.

Quick google searches show DC converters in this efficiency range, but I just have no idea if that's possible with these power levels (≤10kW) and space constraints (a reasonably sized controller box). Like you said it would probably be best integrate this into the controller, then place it next to the cell.

Would converting 1000+ amps even be physically possible in a small space? Aren't DC converters just transformers with more steps involved, meaning you'd need to coil a massive wire?

 

[john61ct]

Boost conversion going up in voltage is **much** less efficient than buck, going down.

And high amp levels gets not only bigger and bulky, but **very** expensive and hard to find.

Even between common voltages, say 12V up to 48V nominal, I've never seen anyone even try to get 1S range up past single digits.

And why? what is the motivation behind such a goal?

 

[Username1]

I'm not attempting this myself, just curious if it's possible.

The benefits would be greatly reduced complexity and increased reliability. You'd only have a single cell without multiple connections, BMS. No worries about individual cells going bad, or out of balance. You'd also have a 100% cell-to-pack ratio.

Unlike nickel based chemistry, LFP allows large cells to be produced. Production LFP cells happen to align almost perfectly with the capacity needed for PEVs. They range in size from tiny to around 1000ah (3200wh), which is roughly the maximum capacity used in PEVs.

 

[john61ct]

Yes, bigger cells are common these days. Personally I would not go higher than 180Ah in mobile applications with shock / vibration issues.

However you need much higher voltages, and series connections to create a battery bank is how you get that IRL.

Note when you see a DC-DC converter advertising a certain efficiency rate, that is always very "optimistic", cherry picked Voltages / Current where efficiencies are high.

Even 70-80% would I think be unobtainable from 1S up to say 48V and higher.

Go looking for units that do what you want, mouser, digikey, allied, newark, arrow, element14, avnet etc

Pull the data sheet and let us know if you think you found something practical.

IMO if it were feasible we would have heard of working examples by now.

Of course future technology developments can change everything...