Isolation xformer ? - Printable Version
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Isolation xformer ? - Eric - 09-15-2014
Finally got a isolation xformer. Currently I have the power going to the xformer and then going to my variac or should I feed the variac first or does it matter?
Eric
RE: Isolation xformer ? - Eric Adams - 09-15-2014
Eric, I'm sure everyone has an opinion but I have the Variac before the isolation Transformer. It has worked for me.
RE: Isolation xformer ? - morzh - 09-15-2014
Either way will work.
I use Variac after the isolation simply cause I need it closer to me to regulate.
RE: Isolation xformer ? - Eric - 09-15-2014
I really didn't think it would matter I guess I will go with what works best with my bench layout which is xformer then variac. Thanks
Eric
RE: Isolation xformer ? - Joe Rossi - 09-15-2014
Do you have a recommended brand?
RE: Isolation xformer ? - morzh - 09-15-2014
Any transformer that meets your power requirements is fine.
I have Dale medical, which is Fluke, bought it inexpensively on eBay as used equipment from remodelled hospitals.
Whatever you buy, check first.
RE: Isolation xformer ? - Arran - 09-16-2014
A Hammond, or any other North American made isolation transformer would be fine, and cheaper if they are second hand. I have at least one isolation transformer someplace but have never used it, most of the radios I work on are AC sets, which are already isolated from the power line, unless they have a leaky line capacitor going from the hot side of the line to chassis. In the case of AC/DC sets most of the ones I have are not hot chassis sets, and I really have no reason to work on them whilst they are plugged in unless I am aligning them or performing a voltage check.
Even with the AC sets I usually do most of the work whilst the set is unplugged, most of the checks can be performed with an ohm meter if there are doubts, paper and electrolytic caps always get changed, unless they are obviously new.
Regards
Arran
RE: Isolation xformer ? - morzh - 09-16-2014
Well, extra safety does not hurt, but of course an IT does not give you a guarantee of not being fried. One could die from an AA battery. If he swallows it.
This said, I always start with IT, and then if it is an AA5, hot chassis or not, I keep it on IT, id it is a transformer set and I know it works and the transformer does not leak/short, then I could use it directly.
BTW. Speaking of AA5 that are not "Hot chassis" - the chassis and the electrical common are linked with a capacitor which in case of Philco 46-250 I just worked on is 0.2uF.
0.2 uF will give you a touch current of 9mA.
Now according to the safety tables, AC touch current is like this:
Startle - 0.5mA (hand-hand, hand-feet, hand-seat)
Strong muscular reaction
- 5mA (Hand-hand)
- 10mA (both hand - feet)
- 5mA (hand - seat)
Which is non-lethal for most people. (the least deadly current is 40mA both hand to feet).
But then what if you wear pace maker, have a weak heart etc.
I say, IT is a good thing, especially with non-transformer radios.
RE: Isolation xformer ? - codefox1 - 09-20-2014
Whatever, an ammewter, or milliiampmeter and hands off will let you know what is going on. 1:1 isolation transformer is great for AC/DC sets and associated vintage test equipment. Hands off keeps you lifing.
RE: Isolation xformer ? - K7Sparky - 01-31-2015
If you have a scrap yard around you have a good place to frequent to find one. They don't like to bust up the transformer to get the copper around here. I'm guessing the old burn out ovens are also a thing of the past.
Transformers windings are current limited. If you find a 440 / 220 to 220 / 110 CPT (Control Power Transformer), hook it 220 to 220 and it is good for 1/2 the KVA rating on 120.
A transformer doesn't care which side is primary. You can take 2ea. 120 / 12 and hook them back to back for a 120 / 120. Lowest current winding is your KVA limit. Use a fuse - what have you lost if you smoke one anyway.
I also like a GFCI on my test bench feed. May not help, but gives me a warm fuzzy feeling.
Don't expect your smoke detector to tell you if a transformer is smoking unless it is an opacity type. Burning insulating varnish does not polarize.