Voltage drop in homemade transformer, not sure why!!

[wildbill hickup]

The microwave transformer I rewound, http://www.fieldlines.com/story/2005/11/7/135321/710 wound up being used as a homemade battery charger and has work fine until this morning. Let me back up some and explain the event since above post.

As discribed in previous post I wound up with two legs each producing about 13.5 volts DC after being rectified. For Identification I'll call the white pair Leg 1 and the black Leg 2. I mounted the transformer and to each leg attached a 25A bridge rectifier. Leg 1 I completed by running to short leads to + and - stainless steel studs compleate with wing nuts. To these I added to longer lead with battery clamps on the ends. While I did hook up a rectifier to Leg 2 that was all, it went unused til now. I also connected a small cooling fan from a computer PS 12V .15A to Leg 1. All is well and I have been using this to charge batteries with, with very good results the last time being last night.

This morning I had the bright idea to fixup my little charger and make it a really fancy dual output so I could either parallel the two legs for more amperage or charge two batteries at once. Enter Murphy's Law (If it works don't $%&^ with it) I should know better. I soldered on + and - outputs from Leg 2 to their own repective SS studs allowing me to hook another set of leads (for bat #2) if needed. I also ran jumpers to studs from Leg 1 (-) straight accross (+) thought a switch that could be switched on to parallel the two legs. Weeeelllll he we go. After completing all my fancy upgrades I decided to take some readings. Whooaaa what happened? Switch off (not paralleled) Leg 1 reads 10.13VDC Leg 2 reads 9.95VDC parallel them by turning switch on and the output is 9.99VDC. I disconnected all  jumpers between Legs 1 and 2 voltage came up to about 11 on Leg one and 10 something on Leg 2. After puzzling for a moment I decided OK I'll just unhook everything and get back to where I was 13.5 Approx on Leg one. No such luck, I unhooked everything I did clear back to DC output on the rectifier on Leg 2, still get only 11.01 VDC from Leg 1 the same Leg I was getting 13.5 from earlier this AM.

What did I do :-( ? Now I can't even use the thing to charge a 12v battery.

By the way now that it doesn't work at all I intend on rewinding the whole thing with regular winding wire instead of Romex, but I still would love to know what the hell happened?  Can someone explain!!!!

Wildbill

[Flux]

Your dc open circuit voltages will be mean. The peak will still be high enough to charge a battery.

Probably the mains volts are a little lower than when you last checked it.

Charging batteries from such a crude thing with no ballast to limit current will make it desperately sensitive to supply volts.

You should have wound for a few more volts and used some resistive ballast. Better still wind for an even higher voltage and use a large choke on the dc side of the rectifier to maintain conduction over a reasonable angle.

Ill designed single phase battery chargers are common place even in professional circles. Cost is everything for manufacturers but for your own use it would be worth winding for the higher voltage and use the core of a second microwave transformer to make a decent choke.

Try it on a battery, 11 v mean open circuit will still give about 17v peak.

Flux

[stephent]

Bad rectifier(s) in #2 leg? (even unhooked they will drag the voltage of the other leg down while still hooked to rectifier).

Unhook #2 rectifier and check #1 leg again---or vica versa..It could be #1 rectifier bad, too or also.