Grex Do-it-yourself Conference

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Grex Do-it-yourself Item 30: Wanted - 110 to 220 transformer for shortwave radio
Entered by keesan on Sun Jul 25 00:10:29 UTC 1999:

Does anyone have a 220 to 110 transformer they are not using, large enough
to run a shortwave radio?  (A Grundig, owned by an Albanian immigrant who came
to Kiwanis looking for one when Radio Shack could not help him.  He speaks
no more than ten words of English.)

11 responses total.

#1 of 11 by n8nxf on Mon Jul 26 11:32:56 1999:

He wants to convert 110 to 220 or 220 to 110?  What frequency?  Radio
Shack use to sell converters.  Purchase radio would also be worth
trying.

#2 of 11 by keesan on Mon Jul 26 13:08:19 1999:

RS converters are $32.  Jim wanted to make one cheaper.  110 to 220, for a
Grundig shortwave radio that works in Albania or on batteries here.  Jim says
60 cycle, the transformer will not know.  (PHonographs sometimes have settings
for 55 or 60, it affects speed on some motors somehow).

#3 of 11 by rcurl on Mon Jul 26 14:01:46 1999:

(I responded on this somewhere else, but...) What power rating is really
needed? Presumably the radio is solid state, so it should not require
more than 5 watts or so. You can use just the primary of a 110 *or* 220
volt stepdown transformer as an autoformer to step up to 220, like Scott
did for the Grex power meter. 

(Good phono motors are synchronous, so the speed is determined by the
frequency: alternative frequencies are used by having transmissions.)

#4 of 11 by keesan on Mon Jul 26 16:01:52 1999:

Jim says 'yes, what sort of equipment do I get one out of?'.

#5 of 11 by rcurl on Mon Jul 26 18:44:08 1999:

Anything that has a little switch to choose between use on 110 or 220 (if it
uses a transformer with sufficient rating).

#6 of 11 by scott on Tue Jul 27 11:06:36 1999:

...but not a PC power supply, since those do their business in a totally
different way.

#7 of 11 by n8nxf on Tue Jul 27 11:46:02 1999:

I suspect that the shortwave you are trying to power with 110 can be
rewired from 220 to 110.  Generally there are two 110 volt windings
on the primary side.  For 220 volt operation you put them in series
and for 110 volt operation you put them in parallel.  You just have
to be sure you phase them right (Or one winding will buck the other.
Check it by applying power with only one winding connected.  Connect
one wire for the second winding and than measure the voltage between
the unconnected second wire and the point to which you want to attach
it.  If you see 220 volts, reverse the connections.  If you see close
to 0 volts you are all set to make the connection.)  Many times these
things a duel voltage capable but no switch is provided.  You have to
wire them according to where you want to sell them.

#8 of 11 by rcurl on Tue Jul 27 16:13:37 1999:

Be careful about trying putting them in parallel. For one thing, you
probably can't: it is usually one winding with leads to the ends and a
center tap. If there really are two separate windings - they won't be
absolutely identical electrically, so one will feed power to the other and
the whole thing could overheat (the difference between the windings
providing essentially a short).

#9 of 11 by keesan on Tue Jul 27 18:41:19 1999:

The owner may not feel comfortable about having Jim do surgery on his radio,
especially as we cannot explain what we are doing in Albanian.  
One option is to make a 6V (4 D cell) DC or even 9V black cube power adaptor
into something that will plug into the battery compartment.  Maybe solder the
wires into the battery thing.  He will bring in the radio next Saturday at
noon and we can plan the details out then.  Jim is thinking of trading this
help for some help recycling cardboard (and forcing him to learn some English
this way, he has not learned any in a year, that we can tell.  He used to come
in looking for a shortwave radio but could not figure out how to use the one
I sold him so returned it.)
        I will attempt to link this to diy.

#10 of 11 by n8nxf on Wed Jul 28 11:22:19 1999:

r.e. #9  Lots of transformers are made with dual primaries and are used
as I described.  Having a slight imbalance in the two windings does not
cause it to overheat as long as the magnetic fields created by the two
windings are in phase.  I've done this hundreds of times and have seen
it done in several medical instrument designs.  (If the windings had a
very low impedance there would be a problem, seems to me.)

r.e. #10  You could cut and old broomstick to a length that would be
equal to 4 D cells and put copper tabs on the ends to attach the wall
wart.  Beats soldering to the battery tabs.  You may have to cut the
broomstick in half to make insertion / extraction possible.

#11 of 11 by rcurl on Thu Jul 29 05:52:00 1999:

I finally looked at a Jameson catalog, and they sell both 110 -> 220 and
220 -> 110 x-formers for $5 each. These are 50 VA units with built in
plugs and sockets for European/US plugs/receptacles. You best order
a bunch, as they have a $5 fee for orders under $20. There is also a
shipping charge by weight. I need something from them that costs 3.50,
so I'd like to ride on the order (if you want to buy those x-formers). 
They are at www.jameco.com, if you want to look at their catalog
(slowly.....).

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