High Volts Vs Amps and controller options

[LI-ghtcycle]

Ok, I have used LiPo for years, and I just don't care for all the extra concerns/maintenance, so now that I am foraging into higher voltage Li-Ion, I have noticed a trend.

It would seem lots high powered builds go to about 20 - 24s and then make up the rest in amps.

Is it just not practical to go the other direction and make your watts with higher voltage?

I am looking to put around 7200w through a Cro-Motor (at that time I will start using a CA v3 & statorade to keep things from over-heating using 40s 4p using 2x this battery from Lunacycles: http://lunacycle.com/72v-panasonic-pf-11-6ah-with-luna-charger/ )

For example, I understand that one of the strengths of LiPo is that you can get extremely high amp output, so it makes sense if that is your main power source, in my case, I would like to see if there are controllers that would do something along the line of:

40s 4p Li-Ion, so roughly 160v hot off the charger, and limiting amps to 50?

The reason I ask is I'm not looking to make a record breaker necessarily, but I would like to have a couple of these batteries:

(72v Panasionic PF 11.6ah 20s 4p)

http://lunacycle.com/72v-panasonic-pf-11-6ah-with-luna-charger/

And have the option of running them in parallel (20s 8p) for every-day riding/pulling a trailer for work, and then when we want to goto EV Events, be able to run that same set-up with the batteries in series, (40s 4p) at a race track and push 50 MPH+.

Is this practical?

The other reason is the BMS on these batteries is rated at 50amp continuous, and IIRC, higher amp BMS generally drive the cost up dramatically, or is it the other way around where higher voltage for the controller becomes impractically expensive and thus people stay lower voltage (around 80 - 100v) and make the rest up with amps?

I am not looking to make a moped wheel/motorcycle tire burn-out machine (at least not with this bike! ) and I am wanting to test the limits of our very heavy built 24" bicycle wheels with Nuvinci hub, and since we are running a Cro-Motor as mid-drive, I might have to put a moped tire on the back for track days, but other than that, I am hoping to be able to keep our current heavy-built bicycle set-up as is.

I had a Eureka moment looking at this build:

https://www.electricbike.com/marks-cromotor-phatrod/

And realized motor and battery wise, we have a very close to the same set-up. (Ours would NEVER be in the same universe as far as Mark's amazing custom build however! Kudos!)

Thoughts?

Thanks!

 

[amberwolf]

Controller cost goes up quick with voltage, and *reliable* options get narrow fast. :/

You'd also need different controllers (or one with quite a wide input voltage range) for each voltage configuration.


Plus wiring care is more of a concern the higher voltage you go. Better insulation needed on anything that carries it.


Precharge of such a system is almost certainly necessary, and it's probably near the point that it's safer to use a contactor than to turn things on with a switch.


Another potential concern is that if the seriesed packs have individual BMS, and that BMS shuts one pack down for whatever reason, the FET that is now longer conducting has to be able to handle the entire seriesed pack voltage across it (not just the voltage of the pack it's attached to). So if it's a 100V FET, and the packs total up 150V or whatever, at that point, it's probably going to exceed the FET's actual capability by a large margin and may blow it up. The FET that is still conducting on the still-active pack doesn't have this issue, just the one on the pack that shuts down.

I think this issue can be mitigated with a diode in series with the packs, as long as you can find one that can handle both the current required and the total pack voltage. But it probably won't be small, or cheap.



There's probably other things, but those are some of the complications people have posted about in the past.

 

[LI-ghtcycle]

Thanks AW!

I am contacting Lyen about a controller, and I will mention to Luna the concern over one BMS being hit with the full pack voltage, maybe I will just have to use a second purpose built battery pack with a stouter BMS.

Either way, I hope to do this with the greatest of "over engineering for safety" as in a BMS and controller that won't be working too hard at these power lvl's.

Ideally, I would do this with a programmable controller so I wouldn't have to worry about the large voltage differences between 72v & 144v.

Anyone know what a typical Cycle Analyst V3's voltage limit is? I have been pouring through the info on Ebikes.ca, but I cannot seem to find a maximum voltage listed anywhere. :?

 

[liveforphysics]

Embrace current.

A couple feet of thicker wire is a pretty reliable thing.

 

[LI-ghtcycle]

Embrace current.

A couple feet of thicker wire is a pretty reliable thing.

Good point! LFP

Now that I think about it, maybe just for the demo pack I will put together a LiPo pack and save my current 72V pack for the street.

I can live with a LiPo pack that I only use for "track days" to take to the track at an EV event, that way it could be on the smaller side, say just 6ah of 24s Nanotechs or similar.

I am thinking running 24s LiPo at 80a to shoot for about 50 mph+ .

What controller would you all suggest?