My power supply voltage is too high - what can I do?

[revved_up]

Ok, so I goofed. Sometimes it gets confusing keeping it all straight and I was pretty sure of which power supply I wanted and still I bought the wrong one.

After an pm confirmation from Mike a couple of weeks ago in order to use the supply I bought (PS8N63R12) This power supply gives me 63 volts and can be used If I were to wire my motors (PK296A2A-SG7.2) full coil. I had wanted to wire half coil. I had purchased this supply on the reccomendation of John at antek and wish I still had copies of the emails because I did ask him if 63 was too high for half coil, but that is another matter.

My questions are:
1. is there anything I can add to this supply to bring the voltage to where it should be?
2. in anybodys opinion would I be better off buying a new powersupply or just wiring full coil?

It is only a $155 mistake but I really don't have use for this power supply for any other use if I do buy the correct one and I have probably waited too long to try and exchange it with Antek.

any input?

[Richards]

Craig,

Why not try full coil for the time being. You will still get good performance and good torque. You might lose a little high end speed, but things will work just fine.

After you've learned to run the machine, when you're tweaking things for maximum performance, you might try the half-coil winding to see whether there is much difference. (All of my testing is on the test bench where I can really spin those motors. In the "real world", other factors might intervene and you might actually find that full-coil connections work better.)

(To convert your present power supply to one giving 1/2 that voltage, you will have to change the toroidal transformer. If you can find a Variac transformer at a good price, you could dial in almost any output voltage, but a new Variac transformer will cost more than the power supply.)

[Gerald D]

Apparently those Variacs are also risky from a safety viewpoint. Something about them not being fully isolated?

[revved_up]

Thanks Mike, I have been stewing on this for a while trying to decide what to do an figured I would post it back in the open forum instead of PMing you again as the answer may benefit other who may have made the same mistake.

That being said I believe I have all the electronics to start building the control box so time to get busy!!

[Richards]

Gerald is totally correct. You MUST NOT use a Variac as a replacement for a transformer. You place the Variac before the transformer to vary the voltage that the transformer receives. (My Variac has a range of 0 to 140% of normal.)

So, for instance, if I have a 70VDC power supply that I want to test with 35V motors, I would reduce the voltage, with the Variac, going to the toroidal transformer by about 50% so that the toroidal transformer would give me 35VDC. As soon as I had verified the correct voltage for the motor, I would buy a toroidal transformer that gave me the desired voltage - so that the Variac would not be needed.

[Doug_Ford]

Craig,

I would go ahead and try it. My set up gives me lots of speed but now I wish I had more torque. I'm cutting 3/4 inch mdf at full depth and my speeds are between 3 and 4 inches per second with a 1/4 inch carbide endmill. Rapid transits are around 15.5 inches per second but often do you rapid? When I increased the cutting speed, I lost steps so I'm thinking more torque might actually allow me to cut faster.

I have 35 tooth pinions and a 7.2 ratio gear box.

[smreish]

Doug...your trying to cut 3/4" mdf in one pass? - is your tool life decent or are you burning up bits quickly? I try to follow the onsrud cutting guide which suggests that you don't exceed 3/8" depth for a 1/4" bit @ 90-180ipm. Just curious. When I had a spindle on my Multicam I didn't even run a full depth pass on 3/4 mdf....tell us more please.
Sean

[Doug_Ford]

Heh heh. I forgot about those tables on the Onsrud site. I just kept setting the speeds faster and faster until I lost steps. The router didn't seem to slow when I cut at 300 ipm full depth but I lost steps so I backed off.

With regards to bit life, I haven't cut that much yet Sean so I can't really answer your question. As soon as I had my dust collector up and running, I had a bunch of stuff pop up at work. In fact, that's where I am right now. Tonight or tomorrow, I'll try to calculate the total distance I've cut with my endmill so far but I can tell you that it won't be a good indicator because I dulled it some when I was cutting sheet aluminum. The endmills are cheap 1/4" carbide bits from Enco.

[Gerald D]

Folk are typically cutting 3/4" MDF in one pass with 3/8" cutters and spindles, not routers. Also with a very firm hold-down (vacuum).

[smreish]

3/8 bit in 3/4 Mdf makes sense if you follow the "not to exceed 2 diameters" rule for 1 pass. I surely wouldn't put the router bearings through that side load. Spindle yes. Router nope. Good feedback doug. Thanks.

[domino11]

Sean,
Are the router bearings really not up to that kind of work? How much can you expect a router to do then as far as depth of cut goes? Im just wondering cause due to cost, I will be using a router. Should you be changing the bearings on a regular basis when using a router in this kind of application then? :confused:

[smreish]

Heath.
The router bearings can handle the load without cause. I do find that the bearings do like to get hot when subject to significant side loading. I have used the portercable 7518 on the table for 2 years on the warthog machine without issues. I do have the routers rebrushed and bearings changed about every 400-500 hours of production time if I start to hear them sing on powerdown sequence. When you hear it, you'll know. My local tool shop charges about 60$ for a rebuild with brush and bearing. I like the router for ease and cost of replacement. I always have a spare on the shelf due to the table being a mission critical machine in the shop. I will switch to a spindle when $$ permits. I hope that answers you question. Don't worry. A lot of cnctables use routers dependably without issues.