Yet another power supply question

[TarHeelTom]

Spirits are rising, as we've finally moved into the (re) assembly phase of rehabbing the Bridgeport. We've had all the basic functions working with the components spread all over the shop. Now it's time to start shoehorning them into the (former) electrical cabinet.

Have the power supply for the Gecko mounted, as well as the Gecko/bob assembly, and have saved a corner of the chassis for a 24 volt power supply for the limit switches, relays, and air solenoids. No 24 volt supply available yet, but might wire up a couple of 12 volt motorcycle batteries in series for interim testing.

Also need a power supply for several computer pancake cooling fans. Two of these will be mounted below the Geckos, and probably a couple more on the spindle motor, plus a couple more on the Z stepper, which seems to be the hottest running stepper (so far).

My original assumption was that the air solenoids would be the high current item, the fans would be a trivial load, and the relay loads would be somewhere in the middle.

The Kehliing power supply for the steppers has a (so far) unused 5 v regulated output. Called my local computer store to ask what voltage the fans require. None of them knew. Went down there and bought a sack full of used 80mm fans for $10. They are labeled 12 V, with varying amperages, up to 0.7 amps.

Did a google-fu on the air solenoids, they're rated at 0.32 inrush amps. The spindle speed solenoids will be run very rarely, so a very light duty load. The brake solenoid won't run often, but could be energized for longer periods of time, such as during (manual) tool changes.

There is no need for the 12 V supply for the cooling fans to be grounded, so the center tap on the transformer would be acceptable.

In another message, Al pointed out a source for a nice 12-0-12 10a transformer, but haven't yet found a source for a 9-0-9 10 amp. Anyone got any ideas?

I've got lots of diodes and bridges left over from the original Bp computer, plus lots of big caps, so that part will be easy.
So, it appears my initial assumption was fubar. Looks like a 9-0-9 volt transformer at 5 amps might be enough, but 10 amps should leave lots of headroom.

My assumption has been that about

[Al_The_Man]

Did you get the switching supply or Toroidal transformer version?
If Toroidal it is easy to add a small overwind.
Alternatively the 12-0-12 with a bridge with no capacitor is suitable to run the fans at 12v, as well as any other 12v solenoids or relays. These items do not necessarily require the smoothing cap on a 12 supply which would tend to raise the DC slightly too high to 16vdc.
At .32 a for the solenoids, I would take it these are 120vac?
Al.

[TarHeelTom]

Originally Posted by Al_The_Man Did you get the switching supply or Toroidal transformer version? If Toroidal it is easy to add a small overwind. Alternatively the 12-0-12 with a bridge with no capacitor is suitable to run the fans at 12v, as well as any other 12v solenoids or relays. These items do not necessarily require the smoothing cap on a 12 supply which would tend to raise the DC slightly too high to 16vdc.

Bought the KL-541 from Keling, which they no longer show in their catalog. Appears to be a Toroidal. Looks similar to the ones on this page: Page Title What size wire, 18 or 16 ? Suppose it'd be easy enough to add two separate windings, one for 12 and one for 24.

Originally Posted by Al_The_Man At .32 a for the solenoids, I would take it these are 120vac? Al.

They are marked 24vdc. According to their data sheet, the standard version is 0.32A, the special version is about 0.08A, IIRC. Here's a picture:

Tom Wade Machinist -- Tracing old wiring

Here's the pdf on the solenoids, current is on page 14.
http://www.versa-valves.com/LIT_K_USA.pdf

Thanks,

Tom

[Al_The_Man]

18g or 16g, 18 should be enough, you could put on one 12v and continue on with another 12v.
This way you could put a bridge on the first tap for 12v, and the same common and the 24v end for the 24v.
If you want to check the turn/volt put on 5 or 10 turns and see what the result is.
Probably ~1.5turns/volt.
A cap after the bridge will reduce the amount of turns needed by AC = x.707 DC.
Al.

[TarHeelTom]

Originally Posted by Al_The_Man 18g or 16g, 18 should be enough, you could put on one 12v and continue on with another 12v. This way you could put a bridge on the first tap for 12v, and the same common and the 24v end for the 24v. If you want to check the turn/volt put on 5 or 10 turns and see what the result is. Probably ~1.5turns/volt. A cap after the bridge will reduce the amount of turns needed by AC = x.707 DC. Al.

Things turned out better than I had hoped.

Went looking for a roll of wire, but didn't find it. But did find a small transformer marked 115 on one side, and 0-9-18 and 0-9-18 on the other side. It came out of the Bp, but I do NOT remember removing it.

Had both secondaries wired in parallel, and nothing on the two 9 taps. Still had wires going to and from a small bridge. I added a couple of wires to the 0 and 9 taps, and jumpered the two 9 taps in parallel, and fired it up. Added a couple of 60v caps from original computer (BOSS 5) and it measured (no load) 26 and 15. So all is well, and I expect that this particular transformer supplied 24 v for the first 40 years, it ought to be adequate, especially using a few more efficient relays.

Only identifying marks on the transformer are "36-1" on the top surface.

Spent the evening drilling and tapping holes and mounted the transformer, two monster bridges, and the two caps. Went to bed feeling that a lot got accomplished today.

Thanks again, Al

Tom