Running 14.4 V on 7.2V ESC

[fregon45]

What do I need to worry about when driving a 7.2V ESC at 14.4V? (besides damaging the FETs with high current) Is it just an issue of overloading the FETs? or is the big concern in frying the BEC?

I've built my own PIC based ESC and I used a beefy 7805 regulator for BEC, so I could run it at pretty high voltages. But now I have a commercial built ESC that is rated at 7.2V, but I want to drive it at 14.4V. This is for a boat, with water cooling. If I use an external BEC that can handle the higher voltage, do I have to worry about overdriving anything else in the ESC (again, other than the FETs). Thanks.

[mjsas]

Without a schematic it is impossible to say. There quite a few other circuits besides the BEC that could go up in smoke. It may use op amps to drive the FETs, it could have a very small 5 volt regulator, etc.

[pentium]

Some of the electrolytic capacitors are maybe only rated for 10v. They would blow up at a higher voltage.

[Martin_G]

Hi!

(besides damaging the FETs with high current)
I'm wondering why you are limiting possible FET-damages to overcurrent...

serus,
Martin

[vintage1]

its a very complex question.

Normally there would be an onboard regulator for the digital bits: that might not be able to withstand 14v.

Then there are the electrolytics. Or electroltytic.Not toop hard to replace that.

Then the FETS themselves. Probably rated for at least 25v, but will the drive circuitry work? Will the whole thing go unstable? what about the extra energy to drive teh parasitic capacitance? will that melt the FETS?

too many unknowns mate.

Its a 50/50 chance.

[Martin_G]

Hi!

Even 12V FETs exist... with 12V max Vgate
e.g. IRF7475 or IRF7476

servus,
Martin

[Bruce Abbott]

Bidirectional ESCs often use a voltage booster to fed the high-side FET Gate drivers. There is a good chance that the booster will generate too much output voltage, which could burn out the driver circuit and/or FETs.

[fregon45]

Hi everyone, that's for the info and replies. I guess what I'll have to do is power-up the ESC at 7.2 V, and probe around to see what's going on.

I'm guessing that in most cases the limiting factor is the BEC. If you're running at 15V, but the BEC regulates at, say 5V, then that's a 10V drop, and at say 1A running the servos (maybe more) you're BEC has to be dissipating 10Watts, which can get hot really fast.

So that's where I'm guessing the voltage limit rating comes from. I was unaware that some FETs were rated as low as 12V. I'll have to check into that.