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Old 10-29-2021, 10:01 AM   #8
Dannyx
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Join Date: Aug 2016
City & State: Constanta
My Country: Romania
Line Voltage: 230VAC 50Hz
I'm a: Hardcore Geek
Posts: 3,248
Default Re: Master power switch for E-bike ideas

I considered a mechanical switch of some description initially but it became apparent there aren't any rated for such high DC amps (at least not at a reasonable price !) although I'm not entirely sure what the maximum current draw during normal operation IS (not counting capacitor charge inrush), since I have no way of measuring it, at least not easily.

I could measure the draw with my clamp meter on the battery leads by lifting the wheel off the ground and letting it rip, but that would only give me a no-load reading which is sure to double upon riding, especially during take-off and hills. I'd have to somehow secure the meter to the bike to measure while riding and the worst part is it doesn't have a MAX feature to freeze the maximum instantaneous reading, so I'd have no way to read it, other than to maybe ask a buddy to run behind me

Taking the maximum rating of the controller as a (loose) reference, 40A, I expect it to be 20-30A tops, which is STILL higher than what most contactors I found can tolerate, which is why I switched to a FET.

I was hoping the "slow-ish" turn-on time wouldn't be destructive because the charge-up time of the caps SHOULD be brief enough to "escape" the linear region before it overheats, plus I'd use a heatsink...I guess I should just try it. Worse-case scenario I kill the FET...
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