Question about capacity vs drain voltage

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buzztiaan   1 W

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Question about capacity vs drain voltage

Post by buzztiaan » May 29 2015 4:17pm

Little thing has been bugging me and i cant seem to be able to google my way out of it :/

So, say a 2500mAh 3S cell gets me 5 km range.
Now i want to increase the range. So i grab a 5000mAh 3S cell to get 10km.

Thus far i still get it.

Then what if instead, i take a 5000mAh 6S cell, i still get ~10km (probably a little less) but a much higher max speed.

But, if i limit the throttle to ~50% max, wont a 5000mAh 6S get me ~20km range by only having ~12v drain on it?

I am missing some piece of the puzzle here, but i am sure someone here has it ;)
HK150 - 5055 SK3 280kv - 6S 5000mAh - 90mm bigfoots
https://nurdspace.nl/RobertLongboard

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buzztiaan   1 W

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Re: Question about capacity vs drain voltage

Post by buzztiaan » May 29 2015 5:36pm

Of course, the battery would still output 22V and it would be the ESC that turns it into the right voltage hmm.

My gut says this;

If i run my ESC at 50% throttle and my motor takes 60A power, the voltage will be halved (lets say 11 for easy maff), but amperage stays the same.
Thus, 11/22*60 = 30A load on the battery. While, with a 3S (or 11V for maff reasons) battery, the higher throttle wont mean a higher voltage, so ; max throttle 11/11*60 = 60A load on the battery.

So, same mAh rated battery with higher cell count, should be able to provide a similar throttle level as a lower cell count, for a longer time (close to double, i assume)

Am i right? :)
HK150 - 5055 SK3 280kv - 6S 5000mAh - 90mm bigfoots
https://nurdspace.nl/RobertLongboard

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Marcin   1 W

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Re: Question about capacity vs drain voltage

Post by Marcin » May 29 2015 5:57pm

You are correct: On the same setup a 6S 5000mAh would have double the range of a 3S 5000mAh while riding at the same speeds.

A motor running at 6S might require 10A to go 10km/h but it will require double that current at half the voltage (3S) to achieve the same speed.

Look at Amps as if they are the amount of water flowing through a pipe and voltage as how fast water flows through a pipe
If you halve the amount of water that is flowing, but double it's speed you still move the same amount of water.
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buzztiaan   1 W

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Re: Question about capacity vs drain voltage

Post by buzztiaan » May 29 2015 6:24pm

Thanks a lot for confirming :)
HK150 - 5055 SK3 280kv - 6S 5000mAh - 90mm bigfoots
https://nurdspace.nl/RobertLongboard

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mateusleo   1 kW

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Re: Question about capacity vs drain voltage

Post by mateusleo » May 29 2015 6:36pm

Always think on the power you are consuming: lets say you have a pack which holds 1 kWh of energy, if you drain it at 1 kW power, at, lets say, 30 km/h, you'll get 30km range. Ideally, the same pack at 2 kW drain, at ideally 60 km/h will also give you 30 km range, but with half the time. But thats ideally, what actually happens is that the whole system is usually less efficient at higher power, mainly if its higher power by increasing amps, due to resistance; but higher voltage will also be sometimes less efficient in an ebike. That happens because higher voltage implies in higher speeds. higher speed implies in more friction, more wind resistance, more stops and starts, and that will reduce the range too. But thats all according to the way you throttle and if you drive in a hilly or flat area.
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buzztiaan   1 W

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Re: Question about capacity vs drain voltage

Post by buzztiaan » May 30 2015 5:53am

superclear, thanks a lot!

Soon i'll get one of those watt meters and jam it on my board, should help my awareness a bit :D
HK150 - 5055 SK3 280kv - 6S 5000mAh - 90mm bigfoots
https://nurdspace.nl/RobertLongboard

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