Beef up my board?

[bobleecnc]

Hi I bought one of Daves 4 axis unipolar boards It was a breeze to assemble .But now I find out that my motors are to puny I'm trying to turn some 5/8 -8 acme screws in delrin with some old triple stack nema 23 vexta motors they weren't quite enough torque. so I got some old vexta ph299-01 nema 34's off ebay .the thing is that they draw 4 amps per phase at 3 volts Dave's board is only supposed to be good for 3 amp is there any way to beef up my board so that I can run these bigger steppers on it?
and by the way how big a power supply do I need really to run these (amperage wise) ? and as for voltage am I better of to go with 42 volts or 30 volts as Dave recommends? will I lose torque at the higher votage?
One last question does anybody have any data on these old 299 motors like
the holding torque both unipolar and bipolar maybe I'll have to go to a bipolar board to drive them. sorry for the ranting But I'm kinda in a quandry
Thanks Bob

[paulC]

No Daves board can't supply more current than the maximum rated.
The chopper curcuit will take care of it all for you.
If you set your reference voltages to the setting required for 3 amps and hook on the steppers you will have a working solution, you just won't get the maximum torque of the motors. I would use the maximum voltage Dave recommends, no more.
Paul

[WilliamD]

What is it about these chips that rate them 3 amps? Is it that they'll get too hot and cook? Or are they literally capped at 3 amps programming wise? I would think someone could come up with a "super cooling" solution to get more out of them, if that is indeed the limitation. Just a thought.

[pminmo]

cooling won't do it, its the max rating of the mosfets inside the part. How big or a machine are you moving? A decent triple stack nema 23 is pretty powerfull.

[bobleecnc]

well the machine is 40x60 I guess it doesn't matter now anyway I smoked something on my board I set the voltage resistors for 3 amps (.54vdc) as per instructions turned it off let the caps bleed down then hooked up the stepper to my a phase the parallel cable was hooked up and I think windows was booting .the stepper was just hissing as the smaller ones used to do then there was some snapping and popping and then the board started smoking I killed the power but I'm afraid its too late . Iguess it must have been the charge pump problem that I forgot about .Well I guess that does it for unipolars guess I'm going to have to go to a 4axis bipolar board or 4 single axis boards and a breakout board .Does anybody know of a reliable board cheaper than gecko's
Bob

[tintruder]

Bob,

Looks like "cheap" isn't your best option. Once you junk this thing and buy another, you'd already have been half way to Geckos. I'd say save up for a couple months if needed. Marius uses 30A mosfets in many designs...you won't be blowing up Gecko drives!!!

Funny how the cheerleaders say the boards have no problems and if they blow up, the owner is an idiot who can't solder.... here's one more user who had a WORKING board
blow up because the board was being tasked to work at a higher but within alleged design specs level. Just like 3/4 of the rest of the people who are buying new SLA7062s every week.

www.kelinginc.com has 450 oz-in NEMA23 steppers for $54, 280 oz-in for $39. Same chinese factory as HCNC uses.

See cncresource.com for replacement SLA7062 chips far cheaper then HCNC scalps you for.

See the input a competent designer posted in the Yahoo groups aboout using power supplies near the max voltage the board is supposed to handle. Basically, if your PS puts out 32vdc+ and your motors were turning a load then decelerated quickly, it probably isn't your fault the chip blew up, and all the solder re-flowing in the world wouldn't have saved you.

[bobleecnc]

Yes I see what you mean and the good part was there was only 24 volts going to the board and I hadn'T given it any commands yet thanks for the supplier info I'll check that out Bob

[bobleecnc]

I went to the link for the steppers but didn't see them listed anywhere

[tintruder]

OOPS www.kelinginc.net

[pminmo]

You can "blow up" any drive, but obviously Gecko's will "take a licking and keep on ticking". The problem with all of the debate is they are systems, bad designs implemented in correct conditions can work, great designs can not work in bad systems. Motor characteristics will make some drives look good, same motor may make other drives look bad.
The same applies to motor/driver power supply as part of a system. Back EMF can be handled in some systems so that the power supply can run with less margin vs some systems that don't manage the back emf.

[ger21]

Originally Posted by pminmo You can "blow up" any drive, but obviously Gecko's will "take a licking and keep on ticking".

Also remember that some Geckos (G202, G212) will take more licking than others (G201, G210).

[bobleecnc]

what constitutes a good reliable design? it for me needs to be forgiving to some degree as you can see I'm probably not the most careful person its just my nature I try to follow the rules but I don't always suceed.what else should I look for?