mosfet control box for warn

Expensive, I'll bet. Why not make one then you could include PWM speed control too? How much current does a winch pull under max load - 100A... 150A?? Might need to do a bit of load sharing on the MOSFETS but it wouldn't be too difficult.
otoh semiconductors do have a habbit of blowing up rather more readily than relays and would be more difficult to do a field repair on...?

Mike Harding

shreek, I probably could with your help :) but that sounds like work :)

"...otoh semiconductors do have a habbit of blowing up rather more readily than relays and would be more difficult to do a field repair on...? "

Not necessarily so...Which is more reliable and hassle free, a external solenoid type alternator regulator, or an internal electronic one?

Semiconductors blowing up is more likely to be because of poor design/poor environment (cooling)/"cost cutting" (specifying components that will only "just" do the job), than by any inherent defect in the semiconductor itself.

You are already using Mosfets in the output stages of your electronic ignitions, more often than not in your fuel injection drivers, and many other electronic bits in your car, and you "trust" them....

The failures will follow the usual "bathtub" curve (quite a few (relaively) initially, reducing to an insignificant number for a looong time, then a slow increase in failures) , but with a considerably longer time between failures (bottom of the bathtub curve) than would be the case with a solenoid type regulator.

As for doing a field repair, all that would be needed would be a soldering iron ($20 butane one would be fine), a multimeter,screwdrivers/spanners as appropriate, a spare Mosfet or two, and the knowledge to work out which one is dud. In other words, apart from the Mosfet, nothing over and above what you would normally have on hand in your tool box.

Hi Gary

>Semiconductors blowing up is more likely to be because
>of poor design/poor environment (cooling)/"cost cutting"
>(specifying components that will only "just" do the job),
>than by any inherent defect in the semiconductor itself.

Welcome to the world of commercial electronic product design.

>As for doing a field repair…
>In other words, apart from the Mosfet, nothing over and
>above what you would normally have on hand in your tool box

An anti-static handling station?

I have a lot of kit out there right now in military situations using my MOSFET designs for high current 12V DC motors and they work pretty well, very few field failures over the past 6 years but they are well over-rated for the application and I could do that because the margins on military equipment are considerable - consumer stuff is a whole different ball game. If I had an electric winch I would stay with the relays, carry an extra one and be pretty sure I could, somehow, repair the contacts enough to work another time or two - I don't fancy my chances with repairing a shorted MOSFET.

Mike Harding

PS. I'm currently working on automotive electronics - I am surprised how often relays are still being used in new designs.

What does mosfet stand for?

Metal Oxide Semiconductor Field Effect Transistor.

It's a modern-ish transistor used mainly for switching purposes - they can handle very high currents and are very fast in their switching which means they dissipate low power when switching high currents.

Mike Harding

Thanks Mike, as you may have gathered I know nothing about electronics/trickery but find stuff it can do intersesting.

"...Welcome to the world of commercial electronic product design...."

More or less what I implied - "cost cutting" = bad design using parts that are sailing a bit too close to the wind ("under" or "at" rated). No argument there...

"...An anti-static handling station? ..."

Not needed, with adequate preparation. Most high current mosfets have (Gate - Source - Drain) internal protection diodes. If you are that worried, punch the Mosfet leads through aluminium foil before you store them or loop a strand of wire between all the terminals. During the installation, solder the leads with the aluminium foil in situ or leave the loop of wire intact untill all the connections are made, and remove the foil/wire when finished.

"... I don't fancy my chances with repairing a shorted MOSFET...."

As long as the intenals are not potted (unlikely due to req for free air circulation), there would be no reason why this could not be attempted. If you were really , really worried connect a bare wire round your wrist, looped around the butane torch or spanner (more likely given the currents concerned), and clipped to the metal casing of the Mosfet.

Could it be any worse than trying to repair a burn out contact or open cct coil? They are both going to leave you high and dry if you don't have spares. No difference in difficulty really, pretty much a choice of what you want to fix and how often/likely it is going to need a fix.

------------
If you wanted to make a true antistatic station you could improvise one with an aluminium frying pan (workstation), a couple of tent pegs into wet earth (earth point) and a length of wire connecting them (and also to you and you tools as described above). Still nothing out of the ordinary extra you would have to take....

One other thought is with the Mosfets you could just leave the offending one out of the cct assuming they were using >3-4 to do the switching per "contact". The switching cct would still work but would have less current capacity. The idea then would be to try to beeconomical with current drain/load on the winch by using the 1st or 2nd layer of winch cable rather than the 4th or5th layer, and use a snatch block at all times.

Hi Gary

"...An anti-static handling station? ..."

>Not needed, with adequate preparation.

Don’t you let a production engineer hear you say that! They’d confiscate your soldering iron :)

"... I don't fancy my chances with repairing a shorted MOSFET...."

>As long as the intenals are not potted (unlikely due to req for free
>air circulation), there would be no reason why this could not be
>attempted.

I actually meant the MOSFET itself rather than replacing it. With a relay you’re in with a fighting chance of repairing burned contacts – the most likely fault in this application.

In essence I agree with you that providing you have the skill, knowledge and tools to fault find electronic circuits it could be done at the roadside providing it was simply a MOSFET failure. The trouble is that the MOSFETs will be surrounded by a fair number of other components to handle gate drive, load sharing, overload protection etc and all these components will, almost certainly, be surface mount and if they’re 0603 you’ll be damn lucky to _see_ them let alone repair them with a gas soldering iron – not to mention you’d probably stuff the PCB tracks/pads in the process, in fact I note IR are now doing a surface mount MOSFET to handle 110A so even the MOSFETs may be surface mount. In fact in a paralleled MOSFET H bridge configuration finding which one had blown without de-soldering a number of them or cutting tracks would probably not be possible. Far easier to plug in or resolder 4 wires to a relay I reckon.

Mike Harding

PS. Dave, thanks for the 400A info, I didn’t know it was that much but I’m not surprised.