Alan wrote:

So, looking at RS, I have a choice of "Schottky Barrier Rectifiers",
"Rectifier diodes" and "Standard recovery diodes". The main difference
being that the Schottkys have a lower voltage drop, about 0.70v vs 1.4v of
the rectifier ones. The Schottkys are also higher frequency rated.

For my application I'm passing DC through these, not AC. Is there a reason
*not* to use the Schottky diode, as the lower voltage drop would be
advantageous.
Differences in physical package type etc are irrelevant for my
application.


Without commenting on the overall design, as I haven't had time to digest it
yet, so to directly answer this query:

Use Schottky - no disadvantages and one very important advantage that you've
half alluded to: the forward voltage drop is half that for a simple silicon
rectifier. That's half the heat to get rid off.

Here's a part that might be suitable:

http://www.chipcatalog.com/IR/300CNQ035.htm

I have no idea where you'd buy it.

Now, at 300A continuous, you need to get rid of 210W of heat (as opposed to
420W)! That'll need a moderately efficient heatsink, maybe with a fan.

If however, as the application is jump starting, you'll presumably have a
low duty cycle, so if you can bolt the diode to a lump of metal with enough
thermal mass to absorb the energy output for the maximum single shot run
time. Unless you're starting a row of knackered cars in sequence, I would
have thought your max run time at 300A would be a couple of minutes and
even then, not at 100% duty cycle, then a long rest period, plenty for it
to cool down.

Anything else I should consider?

I'll have another read of the whole thing after tea if that's OK - I'll be
back if I think of anything.

Tim