thinking about a 200 amp 12v pwm controller

I"ve started looking into putting together around a 200-250 amp 12v pwm controller for a DC drive i have. I've got the pwm driving aspect of this down aside from the mosfet selection and dealing with the heatsinks that i'll be stuck using. Anyone ever put something along these lines together before? The cycle time will be low around 1 min on and very long time off.

30min+ range, this should help with heat issues. Any input is welcome.

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Reply to
izzi
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No, but you can easily get mosfets within that range(I think anyways).. You are looking for a very low rdson and I think it means your going to have to parallel mosfets. (theres an article on the net on how to safely do this)

I have some 40V 80A 2.5mOhm 300W power fets that if you paralleled n of them you could have

n*80 Amps,

2.5/n mOhms.

Hence the power dissipation per fet is

(I/n)^2*2.5/n = 0.0025*I^2/n^3

With I = 200, n = 4, you have only 1.5W per mosfet.

and total amperage is 4*80 = 320A so you have a little headroom to spare(might need to up it to 5)

Basically 5 of these mosfets in parallel act like one 50V 400A 0.5mOhm mosfet.

Of course this doesn't take into account switching losses which make the results invalid. (But formula would be similar)

Point being that paralleling mosfets is like paralleling resistors... it reduces the current on each one but allows you to increase the total current. Of course if one goes out then you end up increasing the current through the remaining which could end up putting to much through them. you'll need to search for paralleling mosfets to see how to do it properly and probably need some sort of saftey mechanisms(maybe somehow use a multiple relay for each branch that will cut all branches if one isn't conducting due to a bad mosfet).

In any case I'd probably try to find properly rated mosfets first ;)

Reply to
Jon Slaughter

Concerning the heatsink, you may want to look into heat pipes:

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basically these are "super heat sinks". A bit of googling will find you various suppliers. In the past I have heard of custom ones being used for cost-no-object apps - but there may well be some standard ones around you can get fairly cheaply. There are restrictions on orientation and, I think, ambient temperature.

Of course the best option is to avoid generating heat in the first place, you want every last % of efficiency, which can be helped by things not normally relevant to modern micro designs like using larger-than-minimum-size inductors (lower losses).

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Nemo
Reply to
Nemo

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