# Which parts to trade out of a PWM for higher HP

My neighbor owns a scrap metal yard which he lets me pick over as needed. I have an assortment of DC motors from 4 250W 24V motors to a 2.5HP 90VDC from a treadmill. I am looking at building a go kart for myself and my kids to play with but need some help with the PWM controller.

It would be great if I could find a single design that would work for all standard DC motors (not brushless of course) and just vary the input voltage from 12-90V. My understanding is that I can run a 0.25HP motor on a 5HP controller, but not the other way around. Assuming the cost isn't significant to trade out some MOFSETs it would be great to have a single design to replicate as needed.

I have seen several sets of plans such as http://www.instructables.com/id/How-to-Make-an-Universal-DC-Motor-Speed-Controller/ that use a 555 timer, one that uses a 556 timer and so on. Now my thinking that that there are many components in the plans that would stay the same such as the potentiometer and timer since those won't have tons of amps flowing through them, but if I get larger MOFSETs, do I need to get larger capacitors and resistors?

I am not an EE, but I would imagine there will be a couple things to consider when trading an IRFZ46 (https://www.digikey.com/product-detail/en/infineon-technologies/IRFZ46NPBF/IRFZ46NPBF-ND/811998) for a beefier MOFSET such as:

https://www.digikey.com/product-detail/en/texas-instruments/CSD19532KTTT/296-43211-1-ND/5764599

Now I am hoping to not be building a 100HP controller like this guy: http://www.instructables.com/id/Homemade-100-HP-Motor-Controller-for-an-Electric-C/ since it cost him a few hundred, but I figured that with the plentiful nature of DC motors in my life, buying them retail would really add up.

The first link for the universal controller looks pretty simple, what do I need to do to be able to power a large HP motor with it?

In other news, my neighbor just bought a bunch of electric trains from the city which are getting scrapped which have about 250 300 amp hour lithium batteries weighing 156lbs each. I thought I might just throw that in behind the seat of the go kart. I figure if it puts out enough amps, I could convert the voltage from 12V to anything needed for the controller without needing to wire them in series.

• While it might save me time and money the first time to just buy a PWM, if I were to need 5 of them, seems I should do my own. I have a laser engraver that can cut the circuit boards, and a reflow soldering oven for baking, so I have a little more at my disposal than the average Joe, I just need some advice. – Alan May 3 '18 at 23:00
• Thanks Tony, $11 is a great buy but can I really use something like that to power up a 1HP motor under heavy torque of a go kart use? – Alan May 3 '18 at 23:02 • Looking on Ebay, the 40A only go to 50V, so I would get great torque, but low top speed. – Alan May 3 '18 at 23:09 • aliexpress.com/item/… means 60V is only 2/3 max RPM what is the battery voltage? – Tony Stewart Sunnyskyguy EE75 May 3 '18 at 23:17 • "my neighbor just bought a bunch of electric trains" - for their sake I hope you live out in a rural area with lots of space. :P – user253751 May 4 '18 at 0:51 ## 2 Answers If I were doing this, I would be looking at off the shelf PWM boards like this one: https://smile.amazon.com/RioRand-7-80V-Motor-Controller-Switch/dp/B071NQ5G71 There are tons of variations available on amazon, ebay, and ali express. You can probably even swap the potentiometer out for a peddle without too much difficulty. If you really want to build something, or you can't find a controller with the right specs for your project. Here's the basic building blocks: • Mosfet switch circuit. Needs to handle your voltage and current requirements. Don't forget the freewheeling diode. You can hook up multiple mosfets in parallel to increase the current capability. • Gate driver circuit. This slams the mosfet off and on fast, which will drastically decrease the heat it generates. It's just 1 chip and some caps. • PWM generator. I would just use an arduino for this. The sketch will be very short, and you can easily change the limits and output frequency. Get a peddle and hook it to the arduino as an analog input. • I'd use a 555 for the PWM signal instead of the Arduino. It's cheaper (couple of$ for the components) and no programming required. – RJR May 4 '18 at 3:13

To drive a 48 to 90V motor from a heavy 12V battery requires a Boost regulator which is going to be current limited. These tend to cost about \$180/kW offshore, assuming single phase DC-DC adjustable boost regulator.

Complexity is too high for a non-EE.

High power motors tend to be 3 phase with hall sense feedback for commutation with soft start being V/RPM constant.

Torque is proportional to Vout/DCR - RPM/RPM(max)* V rated.

RPM is proportional to Vout/V_rated * RPM max (no load) * 80% at rated load power.

Heat loss may be 5% or more so cooling fans or very large e-insulated , thermally-conductive heatsink is needed.

( you dont need a mickey-mouse 555 PWM circuit but a scooter motor speed controller designed for your specified motor which is ?? 1 or 3 phase, brush or brushless rated for 20A at 90V or 160A @ 12V with lots of protection, OVP,OCP,OTP )

• Good to know, I had been thinking of using a camera flash charging type circuit to power up a bunch of salvaged HVAC capacitors. The power would then come directly from the capacitors, which would be replenished using the battery for something like this: web.mit.edu/first/kart – Alan May 4 '18 at 0:28
• Could you run this in parallel to get the needed amps? amazon.com/Yeeco-High-power-Regulator-Converter-Constant/dp/… – Alan May 4 '18 at 0:32
• If you can modify it share 10 units to get 160A from 12V , Maybe but I doubt it – Tony Stewart Sunnyskyguy EE75 May 4 '18 at 0:55