looking for a power supply for an electronicly challenged person

[chevy]

I have been reading the post about building power supplies from everything from a microwave to a computer supply and I am CONFUSED lol is there a low cost power supply, or step by step directions (for dummies) or somebody out there that might build what I need to run 3 Geckodrive G201 running 3 1780 oz/in steppers?

Thanks everybody

[pen25]

i bought a nice powersupply on ebay.

http://cgi.ebay.com/ws/eBayISAPI.dll...tem=7559309703

[NC Cams]

It is imperative for you to specify the rated current, voltage level and type of voltage need by your steppers (IE: 10 amps at 80 volts DC or whatever per motor).

Simply providing the output torque is insufficient. Don't buy or build any power supply until/unless you have or can determine the above required specifications.

[chevy]

sorry Im kinda new at this part....the motor specs ar as follows:

operation bipolar
rated voltage 3.5
rated current per phase (amps per phase) 6.2
Resistance (Ohms) +/- 10% .56
Induction (mH) +/- 20% typical 6.4
the motor can be seen at:http://www.homeshopcnc.com/page3.html

[NC Cams]

Effectively you need a p/s that can supply about 20 watts per motor (3.7volts x 6.5 amps) or roughly 60 watts for all three, total.

This assumes you will have ALL three motors consuming peak power simultaneously - not probable but possible.

Finding a 3.7volt DC power supply off the shelf won't be easy but a 5vdc one should be easy to find. To prevent going overcurrent, you will need to put a dropping resistor in series with the p/s to drop the voltage going to each phase of the motor if you run it on 5vdc.

Using ohm's law (E=IR), simply solve for R as follows to find the resistor needed for 1.3v drop:

(5-3.7)=6.5 x R
R=0.2 ohm

Now, to figure resistor wattage:

Watts= IxIxR
W=6.5x6.5x0.2
W=8.85 watts (round up to 10 at least, bigger wattage won't hurt but it HAS to be 0.2 ohms)

Thus, you need at least a 10 watt resistor (be sure to mount it on a heat sinkg or else it will get HOT.

Thus, if you found a 5 volt p/s power supply capable of putting out 20 amps (100 watts), you should easily have the power needed to run the motors. You can go bigger but you shouldn't have to...

The ebay one could work providing it could put out 19-20 amps at the 5 volt setting.

I'm not an expert in motor sizing or establishing p/s specs but that's how I"d look at it and I'd be fairly confident it should work.

Then again, you could always contact the motor vendor and see what they recommend for a P/S but that would spoil the fun of experimenting by letting the smoke out of parts.....

[johnt]

Chevy,
If you are looking to buy motors from homeshopcnc, ask Rick if he still sells power supply parts. If so, he can sell you the parts specifically suited to your motors.
And read the article on campbelldesigns.com about building a PS.
I knew nothing when I built mine and it works good.

[fyffe555]

Chevy, you've got three 3.5v 6.5a steppers and three gecko 201's. have a look at the gecko web site - there's some very useful documentation there including how to size and select the power supply, as well as the G201 manual.

Simply put, you've got three very large motors there and you need a very large supply, 60-70vdc and 12.5amps +

Basically Steppers need somewhere between 10-20 x face voltage - in your case thats 35-70vdc. You'd need a supply somewhere between 60-70vdc, Geckos can handle up to 80vdc and 7amps per motor. Gecko suggest the total Powersupply amp requirement is usually calculated as 2/3rds the total so you'd need something like 12.4amps minimum @ 60-70vdc.

Simplest supply would be a transformer, probably a toroid rated at >12.5a and ~48vac, a recifier and a smoothing cap - thats it. Examples at Gecko, Cambell designs etc. Personally don't like using switching supples.

Gecko drivers are chopper drivers and limit the Motor current - do NOT use any resistors in the supply or motor wiring other than those specified in the Gecko manual or you will burn up the Gecko's.

Andrew

[H500]

Originally Posted by NC Cams Effectively you need a p/s that can supply about 20 watts per motor (3.7volts x 6.5 amps) or roughly 60 watts for all three, total.

NCCAM, the calculation cannot be used for chopper drives.

[NC Cams]

I stand corrected for chopper drives. Sorry for the misinformation.

This is how we sized a p/s for some steppers we implemented but we were not using a chopper drive.

Hopefully the math was correct. 8-))

[fyffe555]

For non chopper drives you would still want/need to run higher than name plate voltages and need to use power resistors to limit current to plate spec. For these large motors a chopper drive would probably be less than the non chopper drivers and resistors!