Re: 10 amps to drive steppers

> know how it goes. The only modification to the board needed to allow

higher

> current is to parallel the existing .1ohm sense resistors with another

.1ohms

> which will double the adjustment scale to 10 amps.
>
> Wish Me Luck!

Matt,
I wish you luck!
It is far nicer to explore at the ends of the envelope when you have a
safety chute.
Getting the board to run at high Amps is one thing, getting it to run
reliably for years is another.
My advice is to analyse and improve your protection system to keep the
experimenting fun and painless.

Do the units have a temperature sensor on the heatsink for over temp
protection?(always a good idea when you are relying on forced cooling and
fan health) If not consider providing a thermistor or other type temp temp
sensor on the heatsink near to the trannys/fets this should be used to drive
the enable/disable pin.
You may have several of these in key positions. If you need simple circuitry
let me me know.

Use good quality heatsink compound and really go over the top with the
cooling design. The simple baffles in Tim Goldsteins setup caused a 40F
drop.
Many fans are better than one. If one goes then you still have forced
cooling from the other fan(s) On the subject of fans get the airflow specs
for the fans you intend to use and go for the highest you can find - I use
the Minebea Smartfan 4715ML-012P542-P1 12V 0.5A (commonly found in old
Compaq Servers this has an external thermistor which allows it to run as
fast as it needs to saving on life, you can replace this with a 5k pot for
manual setting or with a 1k resistor for an airflow that will have your
Bridgeport hovering around the shop!


Get the max operating temps for the mosfets from the manufacturers
datasheets or Dan. Run the units for extended periods measuring their temps
and gradually increase the current until you don't feel safe going further -
need more current then add more cooling and continue your tests.

With good cooling you will keep it going well and the attention paid to
sensing/shutdown areas will be a great security blanket. Dan may be able to
shed some light on these areas.

Mo