[pminmo]

extreme,
You do have the chopper wired similar to the above picture on the single axis board above? i.e. no direct wiring to the stepper from the plus side of the power supply. Any way you can take some oscope pictures of the waveforms off the gate, source and drain waveforms?

Phil

[extreme]

I'll try to. One end of coil (or resistor) goes to center tap and another goes to boards negative.

[extreme]

Here are two pics , gate and the source-drain. Division is 10 volts, zero set to -30 volts ( to see better) , so as I can see amplitude on gate is 12 vots. Drain and source "visuals" are almoast the same. Yesterday I got nicer pics with low currents. Measurments with motor coil @ 1.7 amps.
Measurments with motor coil @ 1.7 amps.

[pminmo]

Ok if the gate has a 12v swing that is good. I'm assuming that the top of the gate swing is around 35V? putting the bottom at 23V?

Phil

[extreme]

Atleast that is what the scope shows. Drain and source graphic is not as nice as gates, i think it should look like gates but with amplitude from 0-35 volts. Maybe I fried my fet ? I still can hear how stepper sing. Will see what scope will show on other channels tomorow.

[pminmo]

You should see corresponding pulse trains on both the source and drain. Source should be power supply to 2V or so lower depending on load. The drop accross the current limiting resistors. Drain side should swing 0ish to 33v or so.

Phil

[extreme]

I looked at other channels and they are similar to the first one. Something's not right here. If i get that swing on the gate, why would'nt it open ? What else can I do to help solve this mystery ?

Thanks,
Robert

[pminmo]

Robert,
Using the scope look at the timing of the gate, set the time base so you only get two or three pulses. Use the gate signal as the trigger, don't change the time base and look at the drain side. Post a picture. Tell me the time base per division, volts per division and what the top and bottom voltage reading are.

Phil

[pminmo]

Finally,
I finished building my 3 axis (expandable to 4) 3397tssop board. Here is some pictures. I wish the tssop's were easier to solder! I've ran each stepper axis, but haven't finished c/o.

Phil

[extreme]

Hey pminmo, nice soldering. Mystery solved, I scoped the drain and found it's amplitude was about 70 volts ( before it got out of bounds) and realised it was the induction of the coils. After that I put a diode between - and center tap and it is cool. amplitude now is smaller and fets run cool.

Thanks for your help and effort.
Robert

[pminmo]

Extreme,
Glad to hear you found the problem. Which direction +/- was the 70V? I assume it was associated with the edge the FET turns off?

Phil

[extreme]

Pminmo, it was -35 to + 35 volts. The diode removes about 30 volts from the bottom and now everything runs fine, but when I measure current with my multimeter i get 1.5 amp reading instead of 2.5 amps. Is that the way it should be ?

What does the JP1 do ? I thought it is to connect outputs from interface boards when stacking them, but there are 8 seperate pins and one common when I need 12 seperate pins for 3 axises, right ? so how do I use it ?

One more question. You mentioned that with discrete board with specified fets can't go more than 30 V. Is it because the same coil back induction ? I think we can solve this problem by adding a fast switching diode between each fets drain and the "-". O did that without modding anything, just soldered them on the copper side. Will see what happens.

Thanks

[pminmo]

You won't get a reading with a multimeter that is the same as your max current setting. It will be less.

The 30V is the combination of the FET rating and the back emf, as well as the open coil field surges.

Phil

[extreme]

Anyway, what does jp1 on chopper driver do ?

[pminmo]

I believe it's intent was to be able to plug into the 3 axis board and carry limit and home switches to the db25 connector.

Phil

[pminmo]

I just uploaded a second version of the one axis discrete board. This version allows a person to use more of a variety of MOSFETS, not just the logic level ones. Plus it incorporates motor drive enable logic, and uses a different 3 terminal voltage regultor. By using the LM317HVT and IFR640N MOSFET's the board should be able to be run with power supply voltages of up tp 60VDC.

Phil

[pminmo]

If anyone is interested I had a few extra 3397 boards that are up for sale in the classified here:http://www.cnczone.com/classifieds/s...hp?product=425

Phil

[extreme]

Pminmo, I still have some trouble. When I connect the motors, my multimeter shows only 0.7 amps instead of 2.5 A rated. It cant fall that much one wires. They are 1 or 1.5 mm^2 and about 1.5 meters long. Is that the way it should be ?

[pminmo]

What kind of multimeter, and how are you hooking it up? Do your steppersseem to work properly?

Phil

[extreme]

I hook it up between chopper's center tap and motor. It's a simple multimeter which measures voltage, current, resistance, capasity etc. Well, steppers do spin but there is not much torque