Refurbishment of 3 old battery chargers, from flea market... 

We have found that plain epoxy glue works well as an insulator. Can simply be applied onto open terminals, and allowed to dry. The self-mixing 5-minute works well, but heat it up to make in fluid. then it runs into cracks and holes. Been using this for pond heaters for decades.

Good job brother! I’ve been waiting for someone that actually explains wtf we’re looking at and how to diagnose these little buggers. I have a stack of these in my shop to repair now. 😊

Another difference between selenium diodes and silicon (FWB) is the voltage drop across the diodes. Selenium is usually about 3 volts and silicon is about 0.7 so the output voltage with the silicon will be a little higher.

As it happens, I rebuilt my old 10 amp charger based entirely on your video. And it's working great. I had no idea what that old selenium diode arrangement was. But your testing proved that my "diode" is ok for now. All it was was a rotted cable. But, Now I have learned how to fix old (but good) battery chargers. Thanks a lot! Awesome vid, by the way.

The reason the thermal fuse was buried in the windings is to sense the temperature of the windings in case something was to happen. This is common in alot of devices to protect from fire due to transformer overheating. It is also done on motors for the same reason.

I really appreciate this video. I’ve recently come to appreciate manual chargers, and still have a lot to learn about recognizing the different types of transformers and rectifiers inside them, but this helps a lot.

this is one of the best youtube uses i've ever seen!! Thanks for sharing your expertise.

One thing to be mindful of is that the selenium rectifier has a considerably higher forward voltage drop than does the silicon one. This means that the transformer output is higher to compensate, and the design would be such that it'll output rated current into a heavily discharged battery, and taper off as the charge level (and thus voltage) comes up. It'll work fine with the silicon unit, but you wouldn't want to leave it on too long as it will not taper off like it should. It will still output charging current, even when the battery voltage is well up.

I wish someone around Columbus Mississippi could fix these chargers. I have 2 that need fixing

Really enjoyed your video and was impressed with your thorough approach and understanding of the properties of electricity and battery charging. It's pleasing and informative to watch someone who has a hands-on technical grasp of what they're doing. You've obviously have had serious training in this arena. Thanks for taking the time to share.

Thanks for sharing your knowledge and craftsmanship. I have Schumacher that died unexpectedly recently. I do believe and support repair if possible, that which is broken. Your video helps on many levels. Your electric knowledge is quite extensive, by the types of repairs you do. Thanks again.

Thanks for showing us this. I have my Father's Woodward-Schumacher 4 amp charger from the 60's, Model WS84, still working, but a little crusty. It is very similar to your Schumacher 6 amp, but the cord does not have a grounded plug, so it must be from the late sixties. For more info on a 1 amp version of these search for "An Old Technician's Work Bench: One Amp Charger." He posts lots of details about it, such as a simplified schematic, info about selenium rectifiers, and shows a scope trace of the voltage from this half wave rectifier. His friend asked him about making his own charger, and there are tips on that too. Be sure to read the comments too.

Bridges vs. Diodes: If your charger only has only two diodes, look up center tap configuration transformers for use with rectifiers. For the Schumacher 6 amp charger in this video, the center tap goes to the ammeter, then to the positive clamp to the positive post on the battery, and the "outer" taps go to the two diodes, then to the negative clamp.

Very hypnotic listening to your voice, I grew up watching Mr. Rodgers and listening to you brought me back in time to then. I'm curious what you do for a living. Your unintimidated manor would make you a wonderful educator.

I found a vintage sears one at recycling center that had its wires cut off. Rewired it and it works pretty good except gauge doesn't work, but it checks out with meter.

Я всегда говорил и буду говорить, что трансформаторное зарядное устройство самое надежное! Спасибо автору канала за то, что подарили этим работягам новую жизнь!

Its gotta be a great feeling to be able to repair something that others have given up on...Good going..

Good that you kept the integrity of the function in a safe engineering process, great news thx for sharing. 🇬🇧

The most thorough well made and executed video I've seen. Excellent work good sir

Those internal thermal fuses are a time bomb waiting to destroy your charger. It's put there deliberately so you'll come buy a new one and help fill the landfills, and keep good jobs with people making new ones that weren't really needed. Insanity.

Nice explanation of the transformer fix.

Nicely done and great video! Another disadvantage to those gimmicky new 'smart' chargers is that they only charge a battery that's low. If it's completely dead they just cycle off and consider the battery "unchargable". Those old transformer type chargers don't care, they'll keep trying even if it boils the cells dry. So they can be used to bring back a dead battery, the new ones will not. This video should be some help to me too, I have an old Western Auto charger that doesn't function, you've given me some ideas what to look for. Thanks!

I picked up the same Electromite 6 amp charger on CL for $5. The selenium rectifiers are weak and output is around 2 amps, just like in this video. Now I know exactly what to do to upgrade it back to 6 amp output.

Thank you for sharing your time and vast knowledge you are so thorough .I have an old charger missing the guage on the front but when I put both leads on both wires for the guage I get 12.5 volts do I need a guage

My grandpa had a Schumacher a lot like, if not the same as, the the gray one you have there. It was always plugged in, I found it still plugged in after I bought the place. Now I’m curious if it still works. I’ll have to go check it out, it’s still where he had it, just unplugged.

I have my dad's old Sears 6V/12V charger. The cords were shot and I wanted to use the info from your video to rework it. I replaced the A/C power cord and put temporary jumpers in for the output. I got 12.1 volts and 6.0 volts with no load and a negative output from the diodes. When I hooked up to a 50W, 12V lamp the lamp works but the voltage drops to 9.4 volts. Time to rebuild. I mounted a 25A/400V bridge rectifier on a heatsink, mounted it on a side wall, and moved the diode wires to the ac terminals on the bridge, connected my positive output cable to the meter and the negative cable to the negative terminal on the rectifier bridge. I set the voltage selector switch to 12V and plugged it in. I got 12.4 volts. I then moved the voltage selector switch to the 6V setting and VOILA! I got 18.3V What in the world??? Any ideas?

I found this video after I lost track of the neutral on an old sears similar to the one featured . It helped me figure out what was going on and saved me $50 at harbour freight Thanks

The glass bulb breaker; how do you reset that, after it has “worked?”

Excellent video! Thanks for posting! You are extremely knowledgeable and do a great job explaining things! Please keep posting!

very detailed repair process, this video earned yourself another subscription, thanks for the effort that must go into these

Great info, now I have to find some MIA (Made In America) chargers!

I own the 10 amp Schumacher SE-40M and it stopped working recently and I switched to using solar w/charge controller on my car batteries, but sometimes plug-in is still useful. It was my Dad's and is in a little better condition outwardly--less rust. So thanks for this. I think my diodes might be the problem as I took it apart and cleaned it and messed with the diodes not knowing what part of that assemply need replacement. It went from pumping 6 volt instead of 12 volt to 0 volts (which is odd--nothing is zero volts!). One of the clamps had rust at the wire connection and had been heating up before it went down so I fixed that. Now I just need to source the diodes. Only place I found has parts for a similar model (SE-40MAP) and I suspect that is the not same. Any help on where to source diodes for the SE-40M would be appreciated.

I have the exact same relic battery charger you have there it’s the one with the Mickey Mouse plastic cover over the meter bought brand new in 1970 and it works perfect still charging today and I mean today 👍🇺🇸⚡️

When replacing the selium with modern silicon rectifiers, it would be wise to put a few of them in series on each leg to drop the voltage and electrically mimic the old selenium so the output voltage isnt too high.

Interesting layman approach…. Troubling shooting 101!

So much more fun than a paint by number craft kit... THANKS

Super Cool video, Thanks for posting. I have a really old Sears similar to one you have here on vid but I'm fairly sure it's older. I want to use it for Electrolysis now so I'll look into this thing after watching your vid....Thanks Again!

I have my dad's old charger that is like your $1:00 unit. Still works great.

Excellent information. Fixed my old Sears Battery Charger with no problem. Thanks David!

Very Good Job ! Excellent Job of Deciphering ! And Repairing and Explaining ! Thanks ! 👍

Thanks so much for this very informative, and helpful video! I’ve definitely learned a few things from you in this video. Hopefully you may have a couple minutes to answer a question here.. I have basically the same 10 Amp, dual rate, Schumacher charger as the last one you worked on in the video. But mine is an SE-40MA. The internal set up in mine only differs in that the circuit board is mounted horizontally (opposed to vertically), and the transformer is the same way. The one in your video has it mounted laying on its side. My charger was working perfectly until the other day, when I accidentally touched the two battery clamps together with the unit plugged in with it set on Manual, and on the 12V setting. Which did cause a nasty little spark. After this happened, I could hear a slight humming coming from the unit. So I tested it with a multimeter, and the 12V circuit setting was only showing 1.04 V. Switched to the 6V setting, the hum goes away, and it shows 6.56V, which is normal. Any advice on what your first thoughts are as to what may have gone south would be sincerely, and gratefully appreciated! Based on your video, I’m thinking it may be either the selector switch itself, or something on the board for the 12V side. Seems unlikely to me that it’s the winding fuse you pointed out, since the 6V side still works... Anyway, thanks for any reply. Totally understand if you don’t. Liked and subbed anyway. Great video! 👍

Do the two white wires go on the AC on the bridge rectifier and the black wire on the - on the bridge rectifier

Can you do another telling how to hook up the bridge rectifiers? I couldn't follow the wiring for those. Thanks.

I needed to see how you got the grommet back in the black on for the power cord. I have the same issue and cant get the grommet back in.

I have a relatively new Schumacher that I think got left on the start mode. What would you guess would be the point of failure? I'm hoping it's just the diodes... Thanks, and nice work!

It is a great feeling repairing somthing , really enjoyed watching this video while having my breakfast in the uk 👍

I did this change and now my charger is putting out 8 amps instead of 6...and after an hour...the battery acid is bubbling heavily. Do I need a resistor or something?

Excellent video. Very clear and informative. Thank you very much for doing this. DVD:)

I appreciate this wow 7 years ago! Ive got a question at the 14:26 point when you wired up the bridge diode. I've got the exact same machine and I've got the new bridge diodes, but I'm not 100% sure of wiring it There are three fins/tabs in the same orientation. One is labeled as '+' ...I think you leave that unoccupied, One is labeled a/c, the other 2 are labeled '~'. You've got the a/c fin attached to the negative wire clip, and the 2 selenium wires attached to each of the '~'. Am I right to conclude it doesn't matter which winding attaches to the '~'? It's alternating current going into the bridge diode, and comes out as direct current.. Does that sound right? Thank you for this video!

At 23:34 the way to safely insulate the connection I recommend Plasti Dip rubberized peelable coating.

Will a 8 amp 400V full wave bridge rectifier work? I have exactly the one you fixed with the internal fuse that caused so much trouble. Mine only needs diodes I think. I don't know how to wire the bridge into the charger.

How can one test a multi-amp battery charger transformer, itself? Mine is a approx. 25 -30 year old, 2/10/50 amp Schumacher 12 volt battery charger. Mine is not making any humming noise, anymore, like it used to, when plugged in, and is not putting out any voltage at the battery clamps end. The transformer, itself, looks fine - no discoloration, no burnt smell. It just went out, today, while using it. I heard a bit of a strange noise, maybe even a pop or some sort, right before it shut down. It is the type charger without any electronic "board" in it - it's of a very simple design. And now it won't turn back on, and is non functional. Thanks.

So what kind of work do you do? Intrested in how you can take time off when you want like that.

So you didn't say what you hooked up the the bridge rectifier or I missed it so its 2 ac from the transformer and the 1 dc out ?

David, I have the 6 amp 6/12 volt Schumacher from the 70's in its original box. Made in USA. I also have the 10 amp Schumacher from 1999 made in Mexico also in pristine shape. Never thought much about these chargers as they always worked well. I used the 6 amp to charge my aircraft gell cell battery at my hanger. Interesting to see the internals.

Gimmiky applies to modern motor cars too. So much you can easily do without.

Question. The alligator clamps both came off loose. It’s an obvious question. But I need your professional opinion. Now that they are loose. How do you know which one is positive and negative. What I did Opens up the charger and trace the wire to the transformer assuming that the positive. And the other wire attacked to the chassis is the negative. Mi neighbor used to charge a battery and said the wires got extremely hot. Any ideas? Thanks Nice vid by the way. Thanks for sharing

where you located. I got a 12v-72v old charger Id like to save. Maybe could send it to you? Found a blown fuse in it once... but now its not working again.

Where can I get a new rectifier? I have an older 6 amp Century battery charger that needs one

I have one that puts 12 volts out, but the amps are very low. your thoughts?

Can you explain how you hooked the rectifier bridge up to the transformer I have the 10/2 amp sears I used 2 bigger rectifiers and put one of the ac output to each ac input positive an put a negative wire on the negative side of one of them and I got it to put out the output voltage of 10vdc at 2 amps and 12 dc at 10 amps but as soon as I hook it up to an amp meter or a batter the meter will go to 15 amps and it sounds really quite on 2 amps no load then it sounds really deep when you put a load on it an the transformer gets warm after a few seconds it was an automatic charger but I couldn't figure it out so I just removed the board

I have a old Schumacher ,and old Sears,the sears was hooked up backwards ,once,how do I check it . and they both have been dropped. any suggestions . I wish I was as smart as you , so I could fix them,or least know if they working right. Thanks,I really like your video

where do you get the little button diodes. I have looked for them on ebay, amazon other sites not sure if what I find are right. Looks like I need to small ones with red circle around.

The old charger is from the later 60s to early 70s. It has a 3 prong cord that came into use in the late 60s.

great video. solid explanations. thank you

Have you ever worked on a schumacher se-2151ma? i want to try and replace the rectifier with a diode bridge but there are 4 wires from the transformer and then a circuit board that is soldered to the rectifier...wasnt sure how i would go about replacing this. Any help is appreciated

First off very informative video. I also have a Electromite charger. However mine works on 6amp but does not work when switched to 12amp. Am I over thinking probability being it may just be a faulty switch? Look forward to your response. Thanks, Cory.

Great video. You obviousely get as much enjoyment out of fixing things as I do.

Old video I know, but I have an old AEC battery charger that looks similar to the black Schumacher 10 Amp charger in this video. It will not produce over 11.5 volts or so. If that is caused by the diodes, where can I find some replacement diodes for it? Thanks. EDIT: Nevermind, I found some on Amazon.

Can you post how to check my charger. Its only putting out 8-10v if i just hook up too the leads. Im confused how to test

So the selenium rectifier is basically a primitive, 2-piece version of a 4-diode bridge rectifier?

Nt sure how I can send a pic to you but I have a question about an old Napa 85-179

Great video! I enjoy repairing and restoration of old stuff. I just finished a 1930s companion scroll saw, and a 1960s(?) Israeli made ac/DC low amp converter, which has a selenium rectifier. I would have never known what the heck that thing was! So thanks for the in depth and very helpful information and diagnostic methods. I'm currently going back together with a Schumacher 6/2 model that looks like the 10 amp model you showcased last. Well, it's the same shape, but it's got a different volt meter and look to the faceplate. I came looking for a good shot of the switch and wires to and from the transformer. I cannot locate the pictures I had taken of everything, months ago. Ugh!! Per chance, do you happen to have a good clean shot of the switch and diode side of the transformer? I almost forgot, my charger isn't automatic, so it might be too different looking to help, but anything would potentially help. Thanks for anything you could do!

I had a very old 160cc Honda that had a selenium rectifier to supply DC for the battery, lights etc. I believe it had 6 maybe 8 plates. I believe this was about 1966. I saw some in use later so I am not sure when they changed to Germanium or solid state. Oh, when they went bad, they stank REAL BAD. And, the Sears is now much better than new, IMO!

You really know you're stuff, quick question.... I have a Schauer Model B7612 which is a 6AMP , 6-volt and 12-volt charger....it's very old but always was very reliable. It didn't work when i attempted to charge the lawn-mower battery this last go with the bad lawn-mower battery, so I called Schauer tech support and he said it's just wore completely out (it's probably 25 year old). The AMP meter needle doesn't go up like it always did and then gradually go back down in amps as the battery charged, it just stays around the upper-middle (even when off). when i connect a volt/ohm meter to the charger Leads 6-volt mode shows about 8.2v and 12 volt mode shows about 14v , so i think the voltages look good (but this is not on a load)...but i also had a completely dead 12-volt lawn-mower battery i had the charger on so that could be why it seemed to not work....but the needle just might be broke and the unit might be fine. the needle is more than half way up (8-amp meter like most 6-amp chargers have on them) with the unit turned off! what's the best way to test this on a load, would i have to have two volt-ohm meters like you have? one on the voltage and one on the amp output during a load test (connected to a battery or a high wattage light like you were demonstrating)? sorry for such a long description, i'm not real good at explaining this situation.

Very good information! I have an Ever Start brand charger that looks exactly like the last charger. I almost threw it out because it was not charging one of my batteries, but I recently discovered that it was one of those "smart" chargers that won't charge a battery that was under a certain voltage. I checked it with a meter and it does put out a charge, so it does seem to still work. I'm going to check it on a relatively old car battery that is still good to see if it will charge it.

Great job on the repairs! I like how that bridge rectifier turned out mounted to the heat-sink! I happen to have a similar charger to the 1st one (6a Schumacher) however mine is 2amp with the same selenium rectifier in it and glass tube breaker. I'm thinking it's only half wave and wondering if I were to put the same bridge rectifier you used in the in the 10amp unit? Should I look for a lower amperage bridge rectifier or is it ok to use anything above 2? An interesting thing to note is that my rectifier is fed from the negative or common side and through the breaker to the negative lead. The 6 & 12 vac taps go through the selector switch then out to the positive lead.

What's the part number for the rectifier?

the selenium rectifier rectified half the ac wave, a bridge rectifier will recitify both halves of the ac wave,leading to a higher dc voltage and more bubbling of batter, overcharging. i did the same thing to an older selenium charger, i came back to find it had risen the battery to over 19v....simply just swap each of the selniums to single 10a diode in a heatsink, if charging a more dead battery 11v and lower you will exceed the 6a draw and push the transformer too hard, the peak is just that , for actual dead batterys, a battery near 12v unloaded is 50 percentcharged really

THANKS FOR THE VID, GOT MINE APART BUT SO LOST

Where can I buy replacement parts?

Measuring the output voltage is easy, but how about measuring the output current if the built-in meter isn't accurate?

I've got a newer Schumacher battery charger, one of the few good brands left, it does a good job of bringing dead batteries back to life, it can also start an old LS V8 with relative ease, which is something cheaper chargers have a hell of a time doing, I find it good to store batteries off the ground in a relatively warm room when not in a vehicle that's going to be driven regularly, in the case of our old Escort wagon, we park it a 40-45 degree garage with a battery tender maintaining the battery so that come spring it wakes right up so I can re-repair the ever troublesome wiring on our 300K mile Grand Caravan

THANK YOU.. 35:51 saved my day!! Mine is a schumacher 2/10/50 amp, using a rivet for an electrical connection failed on mine too! I bent the ear on the plate, drilled hole just like you did. its charging my battery! I'll buy you lunch!

Hey i have a old charger and it needs work. Where would I take it?? What would you charge

.I have two of those chargers. One I bought new and the sears one I found in someone's end of the driveway garbage about 15 years ago. They all work and do have what appears to be the metal oxide (selenium) rectifiers. I have recently acquired an old 3 amp 6 volt and 12 volt charge which has no output and I plan to use a silicon bridge rectifier (using just 2 of the 4 diodes in it) to replace the failed selenium rectifier. I have to make tests as to what series power resistor I will need to make sure the batteries don't get overcharged due to the fact that selenium has a greater forward voltage drop across it than the silicon does. I need to simulate that voltage drop so the batteries don't overcharge and boil out or warp.

some Á hole cut my power cord and the cord is solid black how do I know witch way to rewire a new power cord ??

you are the damn man.

Hi I have an avacus ac/dc converter charger and its giving up more volt as it use to, 15.8 volts that which is usually 13 volts. I've check its internal parts and the transformer has a plastic wraped around it showing that its burned. I hope you have an idea to whats making it giving a lot of volts and amps, its making my batteries pour out acids. Please help thanks.

Can you give us the part number of that rectifier you used to replace the old selenium one on the 6 amp charger? I have the same charger from my grandfather and i want to keep it going. Thanks

How do you use a bridge rect in place of the two? Where did you put the CT?

hello very good video. A question I ask myself. That it is the value of the diode bridge that you put on the 1° charger. Thank you for your response

I have battery chargers an they are not charging but if I touch the two cables I get a spark can they be fixed

Hi David...I have an old Schauer Charger we used for years and then it stopped working. I bought a new charger that had some fancy modes and it actually wrecked a new battery. I have tried to figure out what is wrong with the Schauer, but can't figure it out. The switch seems to be connected inside, but maybe it's supposed to be. I try to follow videos...yours is GREAT , but my charger is different . I don't have the heart to ditch it, so maybe I can send it to you ??

on the first charger you fixed are you only using 3 of the 4 terminals of the new rectifier?

He's right about the new battery chargers. They suck. The most frustrating part is THEY WONT CHARGE A DEAD BATTERY! Wtf??? They'll charge up a LOW battery but if a light was left on and forgotten and it runs down to zero volts it tells you the battery is bad. These new chargers cost us a fortune in batteries they refuse to even try to charge

Thank you for this video, very timely that RU-vid recommended it to me today as I just brought an old charger home to use for electrolysis and it smoked. looking inside I found the smoke to be coming from a mysterious component which I now know (thanks to you) is a Diode Bridge Rectifier. I understand the Bridge Rectifier changes AC to DC normally with two AC wires in and Plus and Minus DC wires out. I'm confused about how your Bridge Rectifier can work with only 3 wires connected. Mine also only has 3 wires. I don't know which to connect assuming I can find a replacement BR Diode. Since 2 of the 3 wires on our Diods are the same color i assume both DC inputs are used, I don't know if the 3rd wire used is positive or negative. Is the Diode grounded on the mounting bolt?

Hi David , I'm trying to do the same thing with an old 6/12 volt 6 amp battery charger . Mine has 3 wires off the output of the transformer (center tap ?) . I get 14 volts from either side to the center and 27 volts from the 2 outside leads . Each of the outside leads goes to one of the 2 old rectifiers and the center one goes to the output via the meter . I'm wondering if yours was the same and how you wired it through the bridge rectifier . Thanks , Barry

I have heard a lot of the new charges are not worth owning.

Can't you buy a new thermal fuse for the one that had a bad one,that a safety thing right.