Heat Sink for VNH2SP30

Support Motor controllers/drivers and motors
1

A friend of mine recently picked up two high-current motor controllers with the VNH2SP30 chips on them. The motors are 12V and no-load idle somewhere around 5-6A. They haven’t been stall tested yet, but from the data sheet my friend is figuring around 14A, possibly a little more. Power is being supplied from a pair of 12V 13Ah NiMH batteries, so the supply can keep up.

So here’s the question: How do you heat sink the VNH2SP30 chip so it doesn’t turn into a black hole?

FWIW this is only my second exposure to DC motors this size. The other ones were spindle motors for some small machine tools running off of KBIC-120 speed controllers, which turn 110VAC into 90VDC and involve large blocks of aluminum as heat sinks.

More or less we were planning on doing something similar: Mount the headers for the high current motor controller on the back side of the board, apply heat sink compound to the VNH2SP30 chip, and use the board’s mounting holes to bolt it to the aluminum frame, using the frame as a heat sink.

Would we do better using a finned heat sink? It’s possible to add fans for forced cooling, but the device is going to be exposed to a lot of dirt and grit, so a fan may not last long.

Could we get something like a Bud or Hammond die cast box and mount the motor controller inside, using the box itself as a heat sink? It’d be nice to protect the boards from the elements. They’ll be used outdoors.

My friend is doing all the design work on the project. I’m tagging along to do some of the mechanical fabrication, and to be someone he can bounce ideas off of. The last thing either one of us wants is to let the magic smoke out of either of these. But it’s doubly bad for me since they’re not mine. I’d hate to fry his hardware because of my ignorance.

Thanks,

Tom

2

Hi.

A no-load current of 5A makes me a bit nervous since the stall current can easily be more than ten times that. If the current is high, there’s only so much the heat sink can do. The VNH2SP30 has thermal pads on the bottom that are soldered to the PCB, which has many vias under those pads to get the heat to the other side of the board. Therefore, a good spot for a heat sink is the bottom side, but you will need an electrical insulator between the PCB and the heat sink since there are different electrical nodes present under the chip. A heat sink thermal epoxied to the IC also helps.

- Jan

3

Man, you’re not the only one who’s nervous! That the thing starts at 5A doesn’t make me entirely happy.

Before hooking anything up to the motor controller, though, we’re both pretty insistent on stall-testing the thing. Real numbers before we let out any real smoke.

So a heat sink on either or both sides of the board would work, provided there’s no chance of electrical contact? Good to know. That gives us a starting point.

Thanks!

Tom

4

I just remembered that we have a dual discrete H-bridge in the works that might be helpful to you. There’s no current sense, but it’s based on D2PAK MOSFETs that can do 50 A for at least several seconds. Email or call me if you’re interested.

- Jan