Undervolting.. how much topspeed would i loose?

samv76

100 mW
Joined
Jun 3, 2020
Messages
40
Hi all,
Since the battery in my govecs 3.4 is nearly dead. I am exploring new battery options.

One of thise ootions is a 18s 2p pack of lg chem 39AH pouches.

However, the motor in my govecs is rated for 72 V . So going 18S would be undervolting it.
I was windering if the loss of Max motor RPM is linear? So since i would be loosing 10% nominal voltage , would the max rpm also be reduced by 10%?
The current output of this LG chem oack would be way more thenna stajdard battery pack from govecs so total power output could be the same? However im not sure if undervolting leads to liwer efficiency ajd this more heat generatiin ajd higher consumption?

Hope you can help,

Regards,
Sander
 
Thx for the reply .
I had a go at the simulator but i cant seem to figure it out . I dont have all the data it needs for a custom motor .

Maybe its better to stick to a 2oS configuration as this is what the scooter was designed for. Saves me having to find a 18S charger as well.
 
larsb said:
It’s linear, you’ll lose 10% top speed. No other effects like poor efficiency. Why switch to lower voltage? I’d buy a new 20s battery.

The difference in real world top speed will be a little less than that, because the power required to maintain a certain speed diminishes faster than the speed does.

Unloaded RPM will be proportional to voltage, just as you say.
 
larsb said:
It’s linear, you’ll lose 10% top speed. No other effects like poor efficiency. Why switch to lower voltage? I’d buy a new 20s battery.

Mostly because a set of new 18s lg chem batterys was offered to me.
I like the idea of having 18 pouches vs 440 18650 cells that are in my battery now.
Spotwelding 400 plus cells is a pita 😂

Also for some reason i have in my head that lg puched would outlast any 18650 battery. But im not sure if that is just in my head
 
A downside might be the controllers LVC (Low Voltage Cutoff) that is at a higher voltage (for 20S) then required for a 18S pack. It could mean you can use less capacity then the pack can provide. Not sure if the controller is programmable/hackable for a lower LVC?
 
SlowCo said:
A downside might be the controllers LVC (Low Voltage Cutoff) that is at a higher voltage (for 20S) then required for a 18S pack. It could mean you can use less capacity then the pack can provide. Not sure if the controller is programmable/hackable for a lower LVC?

good point, i will have to check in the sevcon.
 
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