Transformer comments

I'm about 8 digests behind, so forgive me if these things have already been
covered in later issues.

>Message: 3
> Date: Sat, 07 Dec 2002 22:49:37 -0600
> From: Chris L <datac@...>
>Subject: Toroid Transformer update
>
>Well, Thanks to you guys in the group, I was able to run one of my
>Toroids loaded on the bench for about two hours today. I conclude that
>it is rated for 44v 4.5amps.I fused the transformer with a 10 amp fuse.
>The first load I connected, A calrod, was about 4 amps according to my
>clamp-on Amp meter. After about a half hour, I could not detect any heat
>by hand in the transformer, but I noticed the Amp load dropped now that
>the Calrod was hot, to just over two amps. So, I added another 1500 watt
>heater in parallel. This jumped the amp load to just under 9 amps.
>Nothing started to smoke, so I left it run. After about 15 minutes, the
>amp meter showed 4.9amps. The Transformer was showing 85 degrees. After
>an hour of this running, the temp was just a tweak over 80 degrees which
>I assume dropped because the load was lessened as things warmed up. At
>this point, I recall the AC load on the primary was just over 2 amps.

Do you mean 85 degrees Fahrenheit? I suspect you may. If the transformer
was cool at 2 A, it makes sense for it to be moderatly warm at 85 F at 4 A.
However, at that temperature the transformer is just loafing. The safe
transformer temperature suggested by several others is 80 degrees Celsius
(centigrade), which is 176 degrees Fahrenheit. You won't be able to touch
the transformer for more than a fraction of a second at that temperature,
yet it's still operating safely.

It also makes sense that it would be cool, because you're only half loading
the transformer - one of the secondary windings is not doing anything, and
the primary is big enough to drive both of them.

>Now, Bob Thomas indicated that I could "parallel" these three
>transformers ?? Or should I just use one per axis ?? If I did parallel
>them, I assume I could take one half of each transformers secondary, and
>simply parallel them. Not sure. I see fuses blowing already !!
>
> If you remember, these were "dual" secondarys. I guess each leg could
>put out 4.5 amps 44v, but I threw a 2 amp fuse between the two hot legs
>and it popped. Obviously I can not combine the "dual" secondarys on one
>transformer to get 9 amps, but I could run two drives off of one
>transformer....

You just got the phasing of the secondary windings wrong. You need to
connect the two ends that become positive at the same time together, and the
two ends that become negative at the same time together, to use the windings
in parallel. If you swap the connections to one winding, you get the effect
of a big short circuit and it blows your fuse.

Sometimes the "positive" end of each winding is marked by a dot, either on
the transformer or the circuit diagram. You need to connect those two leads
together. If you don't have that information, there's an easy way to
determine how to connect the secondaries: Select one wire from each
secondary winding, and connect them together. Leave the remaining two
secondary wires unconnected. Apply power to the primary of the transformer.
Now measure the voltage between the two open secondary leads.

If you measure 88 V between the two leads, you have the two secondary
windings connected in series. If you want 88 V 4.5 A out, use the two leads
you just measured as outputs. If you measure essentially zero volts between
the two secondary leads, you have the secondary windings connected in
parallel. If you want 44 V at 9 A, connect these two leads to each other
for parallel use. If what you got isn't what you wanted, just interchange
the leads from one secondary.

Sounds like your transformers were last used as 88V with center tap.

Dave