On choosing a motor driver for 20A brush motor, and cooling

Hi. I’m considering buying a pair of motor drivers for a project and would like some advice.
Rigth now I’ve found two very interesting model:

• VNH2SP30 Motor Driver Carrier Pololu
• High-Power Motor Driver 24v12a

I use a 24V lead acid battery and 24V brush DC motor with a measured stall current of 17-18A at room temperature The application need some torque so I’d like to find something that can support near stall current for a prolonged period of time (let’s say 15 minutes).
Rigth now, I find the 24V12a the most interesting.

However to support the 18A, the documentation says it need an heatsink
My problem is that I’m not exactly sure how to cool that thing.

I can’t find an exposed thermal surface and I’m not even sure if I’m better to cool the top of the mosfet or the traces on the bottom.
Also by looking at the many design variation I find the design to be very interesting in its capacity to adapt in many products…

Would it be easy to just change the mosfet on the board for another model ?
If so what do I need to look for ? The gate charge Qg ?

Finally what about the 100uF capacitor across the alimentation ?
How do I size that capacitor value ?

In an ideal world for me there would be some variation of 24v20a with easy to cool To220 mosfet, or an add-your-own-mosfet-and-boostrap-capacitor variation…

Thank you very much in advance.


The VNH2SP30 definitely won’t work at 24V, so it’s not an option for you. We have a version of the discrete H-bridge with twice as many MOSFETs in the works, so if you can wait about two weeks, that might be able to handle your application without any heat sinking. Even the 24v12 might be fine since a decent motor has a stall current quite a bit higher than the normal running current, and running close to stall might melt the brushes or otherwise damage the motor.

You can epoxy a heat sink to the tops of the MOSFETs; you can also put something on the bottom side of the board, but you’ll have to make sure not to short any of the electrical connections. Changing the MOSFETs probably wouldn’t be that easy, and we’re already using MOSFETs that are quite good.

For the cap on the power supply, you generally want that to be as big as you can fit.

Thanks for the suggestion about the add-your-own-MOSFET version. We’re already planning on making some higher-current versions (with SMT parts), but we’ll think about a through-hole MOSFET version.

- Jan