Hello ,
On my latest build I am down to sourcing a battery.
The question is 60 or 72v. I am looking for 400 battery amps.
I do not need top speed but rather acceleration. I am thinking either 20s 8p or 16s 10p. Wisdom says that 72v is more efficient but something in my brain says the extra 2p of the 16s will have better more consistent current flow. The controllers are makerx g300 and I have two 12000w hubs.
Any thoughts.
thanks
Maurice.
Same number of cells same energy output, but the 20s pack will do better as less amps. If your controller supports the higher voltage, which it does, use it.
10char
Neither as far as I’m concerned. Less amps going through wires less heat generated.
Same thing esc side.
10char
nah. same number of cells, same amount of energy you can theoretically pull from a pack. Just less losses along the way with higher voltage. i.e power lines going to your house are at a very high voltage and low amperage.
10char
What gave me pause was the calculator at Falcon Pev. According to their formula, amps seem to affect speed at least as much as volts.
Battery current has basically no effect on your top speed, as long as you have enough power to overcome the wind and rolling resistance at that top speed.
It will affect your acceleration, and how long it takes you to get to that top speed though.
Motor current has a more significant effect on your acceleration at low speed. Battery current affects acceleration at high speed.
Voltage, gearing, motor KV and wheel size are the only factors to calculating top speed.
Plug all your relevant numbers into the esk8 calculator (upper left corner, blue bar) and see what your calculated top speeds under load are. Choose the battery configuration that gives you the number you like more.
That’s either 40 or 50 amps per cell. Molicel P42A are good for up to 40, and even that is pushing it a bit so you wouldn’t want to try and get 400A from an 8P.
Theoretically this is probably true, but in reality i’ve seen the opposite… why have available amps if you’re not going to use them!?
Mo powah baby
More amps you run on a single cell = more heat = more IR = more heat = more energy lost due to energy conversion = worse efficiency = less range
I think 20s and 16s is pretty similar though, and the difference is gonna be barely recognisable. But if it goes between 20s and 10s I believe the story’s gonna be a lot different.
Only if you make absolutely zero changes to the rest of the system.
The whole point of higher voltage is to go with a higher gear ratio and motor KV (better thermals on higher KV motors)
Pretty much. Higher gear ratio, better torque, same or higher speed.
I think you will be surprised when you test this on the dyno
Forgot to specify that these are DD hub motors. 13 inch tires.
On hub motors you’re stuck at a 1:1 ratio and I don’t know how to optimize for that.
Likely your hubs were made targeting 10s
If you’re using hub motors and want acceleration then the 16s10p is almost certainly better. With other setups, you can mess with motor KV or gearing ratio to get around the lower current and higher top speed with the 20s8p. With hubs you don’t have that option. Are these hubs intended for Vespas or something though? You’re giving a really high power rating and a really large tire compared to most hubs I’ve seen.
NVM, I was tired and not thinking correctly Evwan corrected me.
Can you explain why you think this? I don’t believe this is correct.
Because you can’t change the gearing or kv. At a certain voltage, you will be going a specific unchangeable speed. To get more acceleration at that speed you will need more current. For example at let’s say 10 mph you may be at 30 V. The available power will be 30 V times your battery amps.
Maybe there is something I’m misunderstanding, but I’m pretty sure that is how it works.
16s10p p42a. 67.2v @ 350 amps = 23520w
20s8p p42a. 84v @ 280 amps = 23520w
Both are 35 amps per cell.
the 20s pack will have less voltage drop (as a result of the lower current) and it will raise the top speed (max rpm)
Other characteristics should be identical between them.
It’s not this simple. If phase amps are high enough and it’s battery amp limited, the 16s pack will have more amps going in at a lower voltage, but an identical wattage.