power supplies form those 24v transformers

Some of my customers from the list have asked about
powers supplies for servos/amps. This concerns higher
voltage for the larger Bridgeport conversion type motors.

I want to help my customers on this, but I want to
do it on list so others can help or use the information.

Now, there was a thread about the economical 24v 10a
transformers. I have looked into a supply using four of
these for a nominal 66v 20a or six giving 66v 30a.

But I think there is a problem with these. You see,
line voltages are speced a little differently in various
countries.

The primary of these is listed as 110vac I think.

We want a higher voltage supply, but some margin
away from an amplifiers maximum input voltage must
be allowed. This give some latitude for things like
normal line voltage variations, surges from nearby
equipment, and servo regenerative braking.

So, considering using two of the 24v secondaries in series
we may get

48 vac

x 117/110 (our nominal US line voltage)

x1.1 (+10% normal line variation)

x1.414 (after rectification and filtering)

-1.4 (the forward voltage drops of the rectifiers)
= 78vdc

I think this is a little too close to the Gecko 80v max input.
I talked with Mariss about this some, and he needs to have
the last word on this as they are his amps.

If you are using something like Copley 412, 78v is fine.

I suspect these transformers give 24v at 110, but our line voltages
are often 120+. The power companies like to run high to sell more
power with less I^2R on their lines.

Didn't someone measure higher open circuit voltages on these things?

So I am not going to recommend using the transformers in this way.
But if someone has some in hand and can ACCURATELY measure the
transformer output and line using the 220v primary and 240v line I
would like to know. Tim?

Why 240? The KVA of a 30 amp supply is kind of pushing it for a
standard 120v 15a line considering surges.

If the 24v transformers put out 24 with 120 or 240 in that
would yield a much more reasonable 73.5vdc max, 66v nominal.
But I don't think they do. It would be nice ,though, as they are a bargain.

If they are to high, there are lots of other options. One
is Doug Fortune's Monster supply at
http://www.cncKITS.com

Another is the toroidal power transformer kit at
http://www.toroid.com
They supply a 1.5 KVA toroid core with a pre-wired primary,
and you wind your own custom secondary.

A further option is a snubber, higher current bleeder resistor,
or diodes.

But I would like to see exactly what these transformers put out.

Les


Leslie Watts
L M Watts Furniture
Tiger, Georgia USA
http://www.alltel.net/~leswatts/wattsfurniturewp.html
engineering page:
http://www.alltel.net/~leswatts/shop.html
Surplus cnc for sale:
http://www.alltel.net/~leswatts/forsale.html