Re: Need help with a battery charger

Posted by KEB on February 24, 2006 at 19:38:08 from (209.108.192.162):

In Reply to: Re: Need help with a battery charger posted by '52 Farmall H on February 24, 2006 at 17:42:56:

Took another look, figured it out. Both lines from the transformer to the rectifier are fused, probably to protect the diodes. There apparently isn't a fuse on the AC input - BAAAAD design. The cutoff wire attached to the chassis is where the ground from the power cord connected.

I've been working almost every weekend for the past six weeks, & never seem to have any time to do things like draw schematics. Hopefully, tomorrow will be the last weekend workday for a while. Will try to draw up a wiring diagram this weekend & post it here.

There are three failure modes for a transformer; 1) an open winding, 2) a winding to winding short, and 3) a winding to frame short. A winding-to-winding short will generally result in an overheated transformer due to high current in the shorted windings. An open results in the transformer simply not working. A winding to frame short produces a safety hazard, since the frame can be at 120 volts without drawing enough current to trip a breaker.

A resistance check with a good ohmeter that can accuratly read down into the 10ths of an ohm range, and someone who knows how to use it, can tell whether the resistance on both sides of the center tap is equal, which would indicate no shorted windings, and verify which terminal is the center tap. In the higher resistance range, an ohmmeter can do a quick check for winding to frame short, although a megger (high voltage ohmmeter) is required to do an actual leakage check. An open winding will be obvious.

Diodes can also be checked with an ohmmeter. Most digital ones have a range designated by a diode symbol, and will show lower resistance with the leads connected in one direction than in the other. In your case, the measurements on the diodes should be made between the common point (the center wire) and each of the wires going to fuses. Checking from one fused wire to the other won't tell you anything unless one of them is open, as you're measuring two diodes in series pointing in opposite directions, and you'll get the same readings both ways.

Keith

Replies:

• Re: Need help with a battery charger '52 Farmall H 10:51:03 02/25/06 (0)

Add a Reply Name: E-Mail: Subject: Comments: Optional Link URL: Link Title: Optional Image URL: Email Notification: If you check this box, email will be sent to you whenever someone replies to this message. Your email address must be entered above to receive notification. This notification will be cancelled automatically after 2 weeks.

TRACTOR PARTS	TRACTOR MANUALS

We sell tractor parts!  We have the parts you need to repair your tractor - the right parts. Our low prices and years of research make us your best choice when you need parts. Shop Online Today. [ About Us ]