Bridge rectifier

Wed Oct 24, 2012 11:37 am

Quick question: Will an encapsulated/potted bridge rectifier rated at 1000 volts function properly at just 6 volts?
No need to read further unless you wish to do so.
I have a Dayton (Grainger) battery charger that did not work yesterday. Never an indication of problems before. The transformer hums, no indication of overheating, no unusual noises. I opened the case and all looks well. The circuit breaker shows continuity. Further testing will follow.
Grainger offers no diagrams or parts for this charger. Appears to be made by Century from other photos I found online of the interior working parts. No diagram or parts for the Century either.
Two diodes on the heat sink, not yet tested. So the transformer must be center-tapped if the DC output is full wave.
My electronics knowledge is from the days of vacuum tubes. If the original diodes, either or both, should prove to be faulty, the bridge is my cheapest and quickest repair.
If the bridge rectifier I found (of adequate amperage rating) rated at 1000 volts will work OK at 6 and 12 volts, it will be mounted on the heat sink plate with compound and just the positive output terminal should be used for my purposes. Does that sound right?

Re: Bridge rectifier

Wed Oct 24, 2012 12:26 pm

Short answer: yes. Long answer: maybe or maybe not. It takes 0.6 volts to activate a diode, if for some reason the bridge is really many diodes in series to get the 1000 volt rating then it may not work. Can't think of a reason they would make a bridge like that but possible. I made a few like that over the years to get to the 25K volt range. You likely have a standard 4 diode bridge and it should work on 12 volts. Radio shack and others sell a 30 A? bridge that I have used in the past with good results.

Re: Bridge rectifier

Wed Oct 24, 2012 1:12 pm

Check for output voltage from the transformer, prior to the diodes.

Small, individual diodes are available from sources such as Radio Shack. Larger individual diodes are available from industrial supply stores. If the diodes are pressed into the heat sink, individual diode may be the way to go.

Check your capacitor(s), providing the battery charger has a capacitor(s).

Re: Bridge rectifier

Wed Oct 24, 2012 3:51 pm

Hectic day. Little time for any particular project. The transformer output is 14.9 VAC with no load. Looks good to me.
I want a 50 amp rectifier minimum and all I find from convenient, low-priced sources, are rated 1000volts. Apparently Radio Shack has pared back their offerings and no longer offers anything near 30 amps, per the results of my search. No capacitors or other smoothing filters in this charger.

Re: Bridge rectifier

Wed Oct 24, 2012 6:13 pm

Diodes for a car alternator. If you can't find any, I can probably find something.

Re: Bridge rectifier

Wed Oct 24, 2012 6:37 pm

Bus Driver if you can post how you’re going to repair your charger .I have a Century charger that quit working a few weeks ago and I’m trying to figure out what to do. I’m getting A/C voltage to the rectifier. The rectifier has no markings on it and nobody has any info.

Thanks Jack

Re: Bridge rectifier

Wed Oct 24, 2012 6:45 pm

Jim stated:
Diodes for a car alternator. If you can't find any, I can probably find something

Jim and Landreo; I wonder if you can wire in a rectifier from a Delco-Remy type 10Si Series alternator?

Re: Bridge rectifier

Wed Oct 24, 2012 8:05 pm

JackF wrote:I wonder if you can wire in a rectifier from a Delco-Remy type 10Si Series alternator?
Don't see why it wouldn't work. You will only need to use two of the three input terminals, leaving one blank/empty.

Might see if you can find the bridge from a non functioning alternator. Lot of times one pair of diodes ceases to function, leaving two functioning pairs.

Re: Bridge rectifier

Wed Oct 24, 2012 8:51 pm ... arger-881/

This link shows one that looks like mine inside. The second photo item "what is this" is the circuit breaker. I think that the nut on the circuit breaker is the only thing that holds the heat sink/diode assembly in the charger. The charger is in the shop building some distance away. I think the heat sink plate is also the conductor from the diodes to the circuit breaker. Don't short it to the charger housing. For JackF, if you can wait a couple of weeks or so, I will try to post the latest on my attempts to get this one repaired. The 50 amp bridge costs less, part plus postage, shipped directly from Hong Kong than the cost of the gas for me to drive to Radio Shack. So I am going to try that. They may take 2-3 weeks to arrive.
More questions: Using just three of the terminals on the bridge means that just two of the internal diodes will be in use but the center-tapped transformer will give full-wave rectification. Does that mean that the bridge will heat less than if all 4 diodes were being used? And if a failure occurs, is it likely that the other two diodes would still be useful by switching a few leads to get the output polarity correct?
My charger is 6 volts, 12 volts 2 amps, 12 volts 10 amps/50 amp boost. I do not recall using the boost feature.
Thanks for the help. Interesting thread.

I used to take the 6 volt radios from junked cars, the filament transformer from junked TVs and eliminate the vibrator, feeding the 6 volt AC to the radio. Wonderful radios with amazing static supression. The OZ4 gas rectifier was the weak link. And most of the radios were AM only. Made a great shop radio, especially if fluorescent lights were in use.

Re: Bridge rectifier

Thu Oct 25, 2012 6:09 am

After I posted I started confusing myself how I could make this work. What two terminals on the rectifier would I attach and how do I incorporate the diode trio and do I need the diode trio? One side of the rectifier is the positive side and the other is the negative. I’m looking for some old books on how this thing works… I just can’t remember this stuff anymore.
Thanks for your help!


Re: Bridge rectifier

Thu Oct 25, 2012 8:57 am

Using the diagram of the Delco 10SI. Alternating current from the stator is supplied to the 3 terminals on the bottom of the bridge. Direct current out put is the single terminal at the top in the photo, positive voltage.

Check the forward bias with a multimeter, Ohms setting. You should get a reading in one direction. Reverse the leads and no reading. This check will also disclose an open pair of diodes. No current flow in either direction.

Depending on how the output side of the transformer is wired, you may only need one or perhaps two of the terminals on the bottom of the bridge for your battery charger.

Re: Bridge rectifier

Thu Oct 25, 2012 9:49 am

I just added then deleted a post that was mostly wrong. If you saw it, forget it. Here is my second try. I hope it makes sense this time.

The AC produced by the alternator is 3-phase. The output from your transformer is single phase. You should be able to turn your single phase into DC using the connections as shown in the schematic for 2 of the 3 connections from the stator. You will end up using 2 of the 3 portions of both the diode trio and the rectifier bridge.

Re: Bridge rectifier

Thu Oct 25, 2012 11:32 am

To avoid embarrassing myself, I could have just let this thread play out. My charger is working again. This morning I tested everything about the charger- eventually. The 9 volt battery died in my tester during the process, so that introduced a delay.
The diodes tested good. The heat sink plate does mount to the circuit breaker as I assumed earlier. Could find no problem inside the charger housing.
So I tested the DC leads for continuity and the Positive tested open. When I pulled back the red sleeve on the battery clamp, the solder had pulled loose allowing the conductor to just float touching nothing. The clamp around the insulation was holding well. The soldering on the negative clamp was holding but did not look to be well done. Resoldered both of them, put it all back together and it works fine.
So I was too hasty to buy the bridge rectifiers.

Re: Bridge rectifier

Thu Oct 25, 2012 3:29 pm

Since the problem is solved just a few comments that may help others.

The 10 si diode trio is for the field current and likely would not survive in a battery charger due to the higher current. The rectifier bridge should work. A center tapped transformer is actually 2 phase current and needs only 2 diodes for full wave, if you use a bridge then do not use the center tap.

Some of the old auto radios used rectifier tubes such as the OZ4 but others used a mechanical rectifier in the form of a sychronous vibrator. The primary side vibrator was linked mechanically to a second set of points on the secondary which switch the polarity of the current on the secondary in synch with the primary. Mechanically rectified the current and no other rectifier needed. Interesting solution.

When checking a diode use an analog multimeter or a digital with a diode setting. Modern digital meters may not put out .6 volts and the diode will measure open both ways. An analog meter or digital with a diode setting will put out enough volts to activate the diode.

Re: Bridge rectifier

Thu Oct 25, 2012 4:29 pm

This was a worthwhile discussion anyway. I large percentage of charger failures are probably diode failures. I had a charger fail in a way very similar to what you finally found. The solder at the clip was holding, but the wire broke just off the end of the clip and inside the insulation. All the handling those leads get is eventually going to take a toll somewhere.