Efficiency of using higher voltage systems, 60, 72, 84, 96

[Carguy7555]

Is there a chart that may show how much more efficient say using the exact same amount of 18650 batteries configured into an ever increasing larger voltage pack and how that increases efficiency? We know as the voltage increases there's less resistance through the electrical path. Higher voltage, smaller wires needed to transfer the same amperage. So if I have say 100 18650 batteries and configure the 100 batteries into 48v packs and take the same 100 batteries and configure them into 72v packs. Yes we would have less 72 volt packs compared to the more 48v packs with the 100 batteries. Now you take both packs and run them both at 20mph till both packs hit their low limit (taking into account identical wind conditions, etc). The 72v pack running through the circuitry more efficiently should give you a greater overall ride distance due to the higher voltage efficiency then the less efficient 48v pack. Have there been any % figures posted or chart for this question? If you move from a 48v system to a 72v or 96v system using the same amount of batteries there is a 5% gain? 10% gain? 25% gain? Rich

 

[Jon NCal]

There could be a loss of energy due to heat, but if you size the wires/connectors correctly you will get the same efficiency at the different voltages. It's only around 400w to do 20mph. You can do a simulation on the Motor Simulator tool on the Grin Tech site.

 

[Sunder]

No point going a 96v motor to gain efficiencies at the wire and connectors, if you have a motor that has the wrong kv for the voltage and it is always in the inefficient zone Gain 5% and lose 30% doesn't sound like a good deal to me.

Buy the right motor for your application, choose the right voltage then use the right wire and connectors. For a run of less than 1.5m, which is probably the longest power conducting cable I can think of on a bike, even awg0000 and a few pairs of SB225s is pretty cheap.

 

[Ykick]

If using ample wire size for either system along with a sensible motor winding for desired road performance there’s really no measurable or practical difference IME.

I tend to choose series cell counts and thus operating voltage more for packaging and size considerations than anything else.

 

[Carguy7555]

Not the answer I wanted to hear. Now I'm going to have to test it on a bike stand over the winter. Monitor all specifics till they both hit single cell 3.0v. I guess I'll let you know in a month. Looking at the 3 responses I guess I already may know the answer. If what you say is the case it will change the direction I go with builds.Rich

 

[Ohbse]

There is no difference, assuming the motor wind is altered proportionally with system voltage.

It may in fact be worse re configuring to higher voltage as switching losses with higher volt rated power electronics tend to go up. It's also more dangerous, makes battery management more difficult (lots more wires/BMS complexity)

Conductor losses for running higher amps at lower voltage are easily dealt with just by upsizing the conductor. In an intelligently designed vehicle these conductors should all be pretty short. A length of slightly larger copper is significantly cheaper than a BMS that can deal with twice the cell count!

 

[motomech]

High Volts are for Hot Rodders who want to go fast.
Greater gains in efficiency can be had without the expense and hazards of high Volts by focusing on aerodynamics(recumbents), or, as a member here(dogman)has pointed out, eating a lighter lunch or wearing a tighter fitting jacket.

 

[amberwolf]

If you have a fair bit of spare time for reading, there are quite a few discussions about volts vs amps that may shed more light on the subject. I get yelled at when I post links to searches so I leave that to you to look up if you're interested.

But they may just make it more confusing. :/

 

[Carguy7555]

Motomech, When you say "hazards of high Volts", what are some examples of high volt hazards. Rich

 

[liveforphysics]

We know as the voltage increases there's less resistance through the electrical path. Higher voltage, smaller wires needed to transfer the same amperage.

This is a common misconception.

None of those two statements is true.

No intrinsic efficiency advantage to be 5v, 50v, 500v, or 5,000v.

Harnessing and controller FET stage gets impractical at 5v for more than a few kW, but still never has to be an efficiency hit if you were willing to run the extra pound or two of copper and controller FET mass.

 

[KarlJ]

Mr Spinning magnets,
I do apologise i've had a few beers

can you explain?
Harnessing and controller FET stage gets impractical at 5v for more than a few kW.

Regards Karl

 

[Voltron]

I think what hes saying is that you can make an efficient 5v system as long as you size the wires and FETS to handle 1000 amps but it gets impractical, just like a 5000v 1 amp system would prob be.

 

[dogman dan]

You might instead look at the efficiency of the getting what you need to do what you want to do. Lets assume its a bike, and will be somewhat close to legal in the USA at least, and that you don't weigh 400 pounds.

What I mean is,, the sweet spot for "bike" is 36v or 48v. Lots of shit on the market that is easy to find that optimize the whole system at those voltages.

Motors, both mid drive and hub, in the right wind for bicycles are out there. Bms's easy to get and affordable, chargers same. Easy to make a quite efficient system at those voltages, for a Sub 350 pound total weight.

The low hanging fruit should be picked first, for efficiency, that's wind drag. It's just like if you want to live off grid, start with insulating the dang house.

Now,, if you aren't building a bike, then things change. Maybe what's out there for what you want to do is built for 100v. We have no idea what you want at this point.

Like Luke says, it could be 5v, or 12v, but what's out there easy to get kind of pushes you to certain voltages to do certain things. 20 mph 36v , 30 mph 48v, 40 mph 72v,, just kind of gets to be the easy way to do things. And none of them stupidly inefficient, if under 300 pounds vehicle.

And at some point,, it gets real easy to just buy a gas motorcycle. The cheapest e bike I've ever owned came in at 25 cents a mile. My 90 mph scooter, used of course, is coming in at 12 cents a mile. That's for purchase, insurance, maintenance, and damn little gas.