How to find capacitance value of ebike controller?

[brownj24]

I am trying to design a pre-charge circuit to eliminate arcing from my 72v battery to my Grin Phaserunner controller when plugging in. Does anyone know how to find the capacitance (uf) of the Grin Phaserunner so I can determine what size resistor I need? I can't find anything in the manual or on their website.

Maybe it's a common value across mid-power ebike controllers?

Thanks!!

 

[harrisonpatm]

If you have different resistors laying around, you could trial and error it the way I did until I found a resistor value I liked. Place a multimeter on the + and - of the controller terminals to read capacitor voltage, should be 0V. Use a jumper to connect B- to controller -. Then use a jumper to connect B+ in series with a resistor to controller +. Time how long it takes for the multimeter to get to battery voltage. Start with a nice high value, like 1k or 2k which could take anywhere from 10 seconds to 2 minutes to charge the caps (depending on capacitance, which is what you are trying to find). I don't know the formulas off the top of my head, but you could then use the time to charge the caps, resistance, and voltage to calculate capacitance. Or, if you don't want to do math, just keep swapping out resistors until you it takes as long to charge the caps as you like.

 

[nicobie]

Any resistor 100-300 Ohms will work Watts don't really matter as is all happens in a split second. Which is why you need the pre-charge circuit in the first place.

 

[amberwolf]

. Does anyone know how to find the capacitance (uf) of the Grin Phaserunner so I can determine what size resistor I need?

If you have a multimeter with capacitance testing, you can discharge the controller's caps (resistor across the battery input) with it disconnected from everything else completely, and use the meter's test to get a guesstimate if it's within the tester's range.

My guess would be less than 2000uF, given the size of the PR and the typical size of 100v+ electrolytic capacitors.

 

[brownj24]

Thank you amberwolf. I found that it was just over 1000uF

 

[brownj24]

Any resistor 100-300 Ohms will work Watts don't really matter as is all happens in a split second. Which is why you need the pre-charge circuit in the first place.

When I plugged the number (1000uF) into the equation, I got 30 ohms. Is my math wrong?

 

[E-HP]

When I plugged the number (1000uF) into the equation, I got 30 ohms. Is my math wrong?

That would probably work. I use 50 ohms and a push button to precharge. I can see the voltage rising on the CA, and flip the main switch when it gets near 72V, which takes around a second.

 

[brownj24]

Excellent, thank you for sharing your real world experience!