Can I upgrade a cheaper motor controller to handle more current?

I know the answer to "Can I do [blank]?" is always "Yes!... with enough time and effort."  I'm looking more for the economical breakdown of how to figure if it's worth the time and effort to do a mod, or if it's "better" to just buy off-the-shelf.

I have a 250W motor controller for a 250W motor on a small scooter.  I have recently come upon a 500W motor, same voltage and also PMDC just like the 250W.  Now, I'm assuming that the main difference between the two is probably the number/quality of the transistors being used to control current.  So I'm thinking it's reasonable that if I were to just "double" the transistors, I could get "double" the current.  (P=V*I and all)  

Of course, make sure heatsink can handle dissipations, might run into current limiting if there's some current sensing happening, etc... but in short, is my train of thought correct or at least headed in the right direction?  I find there's a bit of a gap between "Introduction to PWM/ESCs 101!" and "DIY Motor Controllers from SCRATCH!" that isn't very well documented.  I think I'm fitting in right there.

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I had similar thoughts when I upgraded my old scooter.

Of course you can buy properly rated controllers for good money but I did not want to have useless controller collecting dust.

On my controller everything was sealed in resin only the heatsink mounted to it was not covered in black.

After a lot of scratching and burning my fingers with the heat gun I was able to remove most of the resin so I could take the electronics out of the plastic cover and gain access to what is on the heatsink.

No markings on the transistor so I had to use my trusted tester to figure out it was a power mosfet.

Getting something in the 25A range was next to impossible so I used 3 TIP142 in parallel on a slightly bigger heatsink.

To get more cooling than inside the scooter I cut a square hole in the front for the heat sink to get fresh air.

Worked like a charm for several years until I finally sold the scooter.

Three TIP142 NPN Darlington will give you 30A at a slightly higher voltage drop BUT these bipolar transistors are not good at sharing a current load equally..

Usually paralleling power resistors we pot a small value emitter resistor what did you do ?

Good one!

Thanks for the reminder.

Original circuit had a 2Ohm shunt on the emitter, I had nothing of that value in a pack of three so I opted for three hand wound resistors made from Nichrome wire.

If I remember correctly I used a value of 3Ohms each.

They were made by winding the wire on a small glass stirring rod and left outside the original electronics with a small cover.

I know at highe amps transistors in parallel like to heat up quite uneven but I did not notice any problems during use.

That was all many years ago and today I would simply order a controller like this:

http://www.ebay.com.au/itm/Neu-30A-Max-40A-50V-150...

and rewire the potentiometer into the handle on the scooter.

If you look around you often find new things cheaper than the price for upgrading somthing old.

jongscx (author)  Downunder35m2 years ago

That's true, this would also apply to buying something new cheap then upgrading it to a more expensive "version". Effectively, a controller is a sandwich of Control and Power circuitry, to save money, manufacturers will just reuse the Control portion. Often, they'll also just reuse the Power and leave components unpopulated.

Yeaa China is sucking us in (then one day we will pay)

I got ten UV lasers for $ 29

BTW you mean 2_Ohm and 3 Ohms not 20 or 30, Yes ? :)