Lestronic II repair attempt

[JohnnieB]

Here is a drawing showing how to connect.

The leads from the transformer that when to the two diodes connect to the terminals with "~" signs.

The "+" terminal connects to the charger positive output (white wire and red wire)

The transformer center tap, fuse and ammeter are left as is.

The "-" terminal on the bridge rectifier is not connected to anything.

That thermal paste will work just fine.


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What we are doing is using 1/2 of the diodes in the bridge rectifier package.

Other chargers use heatsink that is electrically isolated from the charger chassis, so you can just drill holes in it and used stud type rectifiers (power diodes), but Lestronic II and PW II use the grounded back panel and electrically isolate the diodes from it while thermally coupling them to it. The diodes in bridge rectifier we're using are electrically isolated from the mounting bracket, so it is more or less the same arrangement electrically and thermally.

[coosa]

Thanks again Johnnie, I believe that I understand it. I will order the rectifier and compound, but after I hook it up I will probably post a picture and get you to check my work before I plug it in. :)

You are a great teacher, and I really appreciate your willingness to take the time to explain something like this.

[JohnnieB]

I used to teach troubleshooting in the USAF back in the '70s. Still have the bug I guess.

Found a picture of the bridge and labeled the terminals and a oblique side view also.

This same mod ought to work on all the Powerwise-II and Lestronic-II chargers and the other labels that use the same diode assemblies.

I just might post a thread in the various forums (CC, EZGO Yamaha, etc.) and use your photos to show how easy it is.

[coosa]

That is truly great info that would help a lot of people if they could read it. There are probably lots of cart owners like me who really are not qualified to try to repair a charger, but could do it with a set of directions like this.

The hardest part for me in this job was trying to figure out what diode would work for this charger. I lack the skill and knowledge to make a substitute like you have recommended here. And yours will be a $12 part and probably superior to the $150 it would have cost to use 2 of the OEM boards.

It will feel good if I can get this old charger to work again. It weighs over 50 pounds and is much superior to the junk chargers you get with a cart now.

[JohnnieB]

Originally Posted by coosa

That is truly great info that would help a lot of people if they could read it. There are probably lots of cart owners like me who really are not qualified to try to repair a charger, but could do it with a set of directions like this.

The hardest part for me in this job was trying to figure out what diode would work for this charger. I lack the skill and knowledge to make a substitute like you have recommended here. And yours will be a $12 part and probably superior to the $150 it would have cost to use 2 of the OEM boards.

It will feel good if I can get this old charger to work again. It weighs over 50 pounds and is much superior to the junk chargers you get with a cart now.

I tend to agree about the junk chargers of today. There are a couple that are marginally okay (like the Lester Summit-II family), but IMHO, the best charger ever made was the DPI Gen-3 Accusense. It had a transformer to step the line voltage down and SCRs to regulate the output with a mix of constant current and constant voltage charging phases that ending up in a float charge mode. Too bad they stopped making it, thanks to the tree huggers in the Republik of Kalafornia.

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I used the bridge rectifier trick before. A friend had inherited a tube type stereo preamp and power amp from his audiophile dad along with a bunch of 6L6 power output tubes and some others. Anyway the rectifier tube went out and he didn't want to spend the $100 or so for a replacement, so we wired in a couple of the diodes in a bridge rectifier out of sight on the tube socket and left bad tube in place, so it looked the same unless you flipped it over and took the bottom cover off. Still sounded the same since it was only in the power supply.

[coosa]

The rectifier assembly and the compound came in over the weekend, so I installed it this morning. I followed the instructions on applying the paste, drilled an extra hole for the rectifier to attach to the rear of the charger, and it looked like this:



That is correct, isn't it? So I took it to the shed, hooked it up, and same results. :(

When I plugged in the AC cord, nothing happens. Then when the DC cord is plugged into the cart, it immediately starts humming, but the ammeter doesn't register and the battery pack still shows 38.0 volts, so there is no output at all. Not only does the charger hum, but I can put my hand on the cover and feel it vibrating like it's working correctly. I tried plugging in the DC cord first, but results were the same.

I'm thinking that it must be something simple that is preventing any output, but I don't have the background to figure it out without help. It picks up the signal from the pack the instant I plug it in, so I don't think it can be an issue with the DC cord. The fact that it hums, vibrates, and heats up the AC cord makes me think the transformer is working, but somehow the output isn't reaching the battery pack.

Could something in the ammeter be stopping the flow of current through it? I don't think so, but thought it worth asking. The ammeter on my DPI charger stopped registering years ago, but the charger still works fine.

I haven't yet tried to test the capacitor. Should that be the next test? Btw, when I ran the same test on the rectifier that I did on the diodes in the pictures I posted earlier, I got a reading of .356 on each. That is below the .450 minimum that Lester said their diodes should read, but I suppose it is irrelevant in this case?

JohnnieB, I guess I could PM you my questions, but someone else might benefit from my struggles if it stays on the forum. Thanks again for your help, and to anyone else who wants to join in.

[JohnnieB]

The bridge is wired correctly.

The fuse and ammeter appear to be wired correctly in the picture you posted earlier.

The fact the transformer hums, means 120VAC is being applied to the transformers primary windings, which in turn indicates the cart's battery is being sensed (Red wire on bridge's + terminal and black wire on ammeters output terminal) via the black and white wires in the output cable. Also means control board is working, or at least the turn on part of it.

Since there isn't any output at all (battery voltage doesn't increase), the problem ought to be between the ammeter's output terminal the one with the black output cable and black sensing wire and the point where the two legs of the two fuse links join. (Or having both secondaries open, but that isn't very likely)

Disconnect charger from AC outlet and from cart!!!!!!!

Break out an Ohmmeter and from the ammeter terminal with the black output cable on it to the other side of the ammeter. If it has continuity, measure from output cable terminal to the output of the fuse assembly. Then to the two inputs to the fuse links.

If all of that checks good. disconnect the two wires from the transformer to the fuses and the two wires to the diodes. The two transformer secondaries are now isolated from each other, so there should be continuity between one of the wire at the fuse to one of the wires at the diodes, as well as continuity between the other set of wires, but no continuity between the two set.

It's hard to explain inn words, so take a look at the attached schematic.

The four wires from the two secondaries are labeled 1, 2 , 3 & 4 at the transformer.

Should be continuity between 1 & 2 and between 3 & 4, but not between 1&2 and 3&4

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Once we get this sorted out, we'll check the voltage with and without the capacitor connected.

[coosa]

Johnnie, while you were typing that, I took the cover off with the charger under my shed and blew it out with the air compressor, then checked all the connections and sprayed a shot of electronic cleaner on them. Tried it again, had the same results.

So I followed the directions on how to do a capacitor test, and it tested good. Resistance started at 0.1, then steadily climbed to 1.3 and held there. I believe that indicates it is good.

Thanks for the additional instructions. I'm gonna go try all that now.

[coosa]

Johnnie, I ran all those tests and everything beeps. So what next?

This reminds me of long ago when I was the Principal of a HS. I had a Maintenance Supervisor who was really good and knew a lot about most any system. He saved us a lot of money by fixing things himself instead of calling on contractors.

But the school system would not allow him to hire his own helper. That was a plum job to be given to a school board relative, and he went through several over the years. One new helper was particularly frustrating to him, and after working with him a week or so the supervisor figured out that the guy would never be able to read fractions. He would ask him to get a 1/2" wrench and there was no telling what the helper would bring back.

But eventually the supervisor realized that the helper could recognize colors, so he bought a bunch of different colored tape and wrapped everything according to color. I remember that the 1/2" wrench was red, so he could tell the helper to get a red wrench and he could do it! :)

Ok, I guess everyone realizes I'm the helper who needs color-coded instructions here. :)

I thought I would add a little something interesting to this thread, since Johnnie is carrying it alone.

[JohnnieB]

Checking the capacitor with and Ohmmeter tells you if it is still acting like a capacitor, but not what the capacitance value (Farad is the unit of capacitance, but it is huge, so they typically are measured in µF or smaller values).

The ferroresonant transformer and boost capacitor are a matched pair and without the capacitor the voltage across the center-tapped secondary is about 60VAC, and with the capacitor connected it is about 90VAC. The µF value of the capacitor changes with age, and so does the latter voltage. If the µF value drifts too far, the charger won't put out a high enough DC voltage to charge the 36V battery pack.

Connect the two wires from the transform back to the fuse terminals, but not to the diodes.

Bypass the relay on the control board, or if the cart is handy, plug into cart. Just so the transformer hums when plugged into AC power.

Measure the VAC between the two wires that were originally connected to the diodes.

Be very careful when disconnecting and reconnecting the capacitor, there is about 500V on it.

Be sure AC power cord is unplugged and short across the capacitors terminals with the shaft of a screwdriver (or something similar) with an insulated handle. It'll arc, so don't ruin the tip of a good screwdriver.

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I've ran across a few that even color coding wouldn't work.