Re: 10 amps to drive steppers

Any of you guys integrating hi power stepper drive units such as Dans or
others with custom power supplies, should consider 2 areas of disconnection
which will cause problems,
1 Driver board driving the phases without a motor connected - can happen
inadvertantly - I've been there
2 Reconnecting a driver board with the motor voltage present - the high
value smoothing capacitor(s) on your power supply is charged to the full
supply voltage and carries a serious amount of charge - unless you take
action to get rid of it it will stay charged for a very long time.

Both of these situations seriously endanger your valuable boards.
To protect against the driver driving without a motor connected, a good idea
is to use a plug and socket connection for the motor with a couple of pins
more than you need - so if you need 4 pins for your 4 wire motor get a 6pin
plug and socket. Use the 2 unused pins as a loopback - shorting them
together in the plug which is connected to the motor and the socket which is
mounted on the case can then use this short to enable the board. You could
have your DC supply voltage going into the socket via one pin, looping back
in thro the plug when it is connected and then taken from the second pin of
the socket and sent to your board, no motor connected = no DC voltage to
board....the boards I use have an output inhibit pin which must be held low
0v for the board to drive the motors - a high or no connection will disable
the boaard from driving.
I use the above method to feed a ground wire into the socket that then loops
back via the motor plug and then back onto that pin.

With the other issue of main motor suopply capacitors remaining charged
after switch off, you should use a bleed resistor connected across the motor
supply voltage - eg across the capacitor (s).
The trick here is to get a value of resistor which is low enough to allow
the capacitor to discharge quickly thro it but without drawing too much
current from the capacitors and getting too hot.

I use a 70v supply and a 2.2k resistor gives me about a 30 second disharge
time - 2 in series (4.4k) gives about a minute. The amount of current tro
the 2.2k = 70/2200 = 30mA which i can afford to waste. But when we calculate
the wattage of the resistor it shows
70v x 0.03A = 2.1W that is a big ceramic covered resistor and 2w is hot -
very hot, it will burn you if you touch it. Also if you shed 2w you need the
resistor to be double that for reliablity e.g a 4watt.
So I use 2 2.2k 2watt resistors in series to give 4.4k and it takes a minute
to disharge the cap, the current tro is halved to 0.015A therfor the total
power dissipation is also halved to 1W. Now I have less heat, more
reliability and less current waste and a minute is enough.
Be warned, these reistors still get hot so should be kept away from heat
sensitive stuff and in the cooling path.

Mo