Old timer-based charger: Diode(s) blown?

[rlw]

Looks like my old-school charger has one (or two!) shorted diodes. This is a pre control board charger with just a timer. The only identification on the front of the charger is "E-Z-GO TEXTRON - 36V BATTERY CHARGER - UL Listed 20L4", Manufacture date: 10/2/84, S/N 1067 (pix below).

Last night, I hooked up all my batteries (on the garage floor) with the new 4 gauge cables I built. I also connected the newly-cabled charger socket to them. By the way, I put DE-OX on the lugs and bolts, so I can report how well that works to reduce corrosion.

Before connecting AC power, I plugged in the DC to the charger socket, and was greeted with a big spark. It also popped the 50A breaker on the charger. Resetting the breaker resulted in an immediate pop. I double-checked the battery connections, and checked the full pack voltage with a V-O-M across BL+ and BL-, that was at 36.5 V (That's why I wanted to charge the batteries!). As soon as I reset the breaker, I saw the meter deflect down to the 20V range for a zillisecond before it popped again.

My guess is that one or both of the diodes are blown (probably shorted). I haven't gotten around to disconnecting the wires from the diodes to check them, but it doesn't look like there's much else that could go wrong on that side of the transformer that would pop the breaker.

What are the specs on the diodes so I can replace them if need be?

I found a wiring diagram for a newer control board charger in the stickies (it was close), but couldn't find anything for this one. I drew out a schematic as best I could for this charger, and there seemed to be a couple of oddities:

1. It looks like the timer switches the neutral on the AC-in. Any reason why it's not switching hot?
2. I'm not sure what the big capacitor on the secondary does - any ideas?

I'm hoping JohnnieB or ScottyB will jump in here, as they seem to be the go-to guys for charger/battery/electrical answers. I'm charging the batteries two-at-a-time right now with a 12V charger so I don't kill 'em.

Thanks,

RLW

[rlw]

I pulled both diodes, both were shorted. Called the local EZ-GO dealer, and they had 'em in stock. Turns out they're 1N1188 diodes. I bought 2 of 'em for about $12 each.

The fellow who owns the dealership said there's a possibility the transformer is bad. He said I should verify the secondary (the legs of the xfrmr that connect to the diodes) should be around 6 ohms. Does anyone else have any suggestions on that?

Thanks,

RLW

[Bowslayer]

I would assume if the transformer is bad you will trash the charger anyway so why not just put the diodes in it and see if it works?

[rlw]

It'd be a d4mn shame to kill a couple of perfectly good diodes - ;^)

Actually, that's what I'll probably do anyway.

[JohnnieB]

You've got a totally manual charger, so checking transformer is easy.

Disconnect the wires going to the diodes and measure the AC voltage.

Should be about 83 to 97 VAC if transformer and capacitor is good and about 55 to 65 Vac if Capacitor is bad.

[rlw]

JohnnieB,

Thanks for the info. I'll check that to avoid sacrificing my new diodes.

I found some schematics for what seem to be the next generation of that charger (timer + control board). I also drew a diagram as best I could (although I'm pretty sure I got the transformer wrong). Do you know of any schematic for this particular charger?

Also, I was wondering what the purpose of the capacitor is on the leads coming out of the primary side of the transformer. My oldest brother, a former DEC principal software engineer and now a licensed electrician in his old age, said he's seen that kind of arrangement in SOLA constant voltage transformers, but never in a "dumb" half-wave charger. Any idea on that?

Thanks again,

RLW

[rlw]

JohnnieB,

I found the answer to my question about the capacitor - the transformer/cap is a constant-voltage setup - here's a link to a very good discussion on how that works: http://www.fieldlines.com/index.php?topic=136150.0 (reply #6).

By the way, I called Lester tech support and spoke to George, who told me this charger was manufactured by EZ-GO. He put me in touch with Mark at EZ-GO, who referred to this charger as "the WHITE charger". Mark's looking for a schematic to scan and send to me. I asked him if it would be OK to post it on the forum, but he deferred that to higher-ups at EZ-GO. I won't post it without their permission.

UPDATE: Got an email from Mark @ EZ-GO - he sent me the 1983 Electric Marathon Service Manual as a PDF. It includes the wiring diagram and troubleshooting for the "White" charger. Still haven't heard if I can post it to the forum (it's a scan, 14.1 megabytes). If I get permission, I'll contact the board managers to see if they want to create a sticky.

Thanks again for the help - the knowledge available from this forum is pretty awesome!

RLW

[rlw]

Checked the secondary voltage w/capacitor connected - ~94VAC, cap disconnected - ~64VAC. Cleaned up the old grease on the heatsink, put new on, bolted up the diodes and I'm chargin' the whole pack now...

TNX again...

RLW

[JohnnieB]

Originally Posted by rlw

JohnnieB,

Thanks for the info. I'll check that to avoid sacrificing my new diodes.

I found some schematics for what seem to be the next generation of that charger (timer + control board). I also drew a diagram as best I could (although I'm pretty sure I got the transformer wrong). Do you know of any schematic for this particular charger?

Also, I was wondering what the purpose of the capacitor is on the leads coming out of the primary side of the transformer. My oldest brother, a former DEC principal software engineer and now a licensed electrician in his old age, said he's seen that kind of arrangement in SOLA constant voltage transformers, but never in a "dumb" half-wave charger. Any idea on that?

Thanks again,

RLW

A day late and a dollar short as usual, but I'm back.

Here is a generic drawing of a manual charger with timer.

The nice thing is that the same basic design is the heart and soul of all the ferroresonant transformer type chargers.
Replace the timer with a control board and you'll have an automatic charger akin to some that are being currently sold.

FWIW - I might have been exposed to some of your brothers software. I did some R:Base applications on a PDP-11.
My youngest boy is a software engineer.

Your brother is right about seeing ferroresonant transformers in power line conditioners (Sola and others), but the irony is that due to the ferroresonant transformer and associated capacitor, the "Dumb" chargers aren't dumb, however you do have to study them a bit to see their smarts.

A ferroresonant transformer circuit is typically viewed as a constant voltage device and its current limiting property is overlooked.
Regardless of how far the batteries are discharged, the maximum current is about 20 Amps (in the case of a 36V golf cart charger), which tapers off as the battery's terminal voltage increases.

Using just a transformer, a capacitor and a couple of diodes, somebody came up with a design that produces the charge curve show in the attached drawing.
I contend the design is elegant and the chargers using it aren't "Dumb".

Glad to hear you got the old workhorse working again.

[rlw]

JohnnieB,

Funny you should say "elegant" design, I thought the same thing as I was testing it last night, watching the voltage change as the current rose, then dropped soon after turning it on. All this with a slightly fancy xfrmr, a big capacitor, and a couple of diodes.

The diagram you supplied is pretty close to what I have, as is the diagram in the '83 cart manual I got from Mark @ EZ-GO. One difference - I've got a 50A "reset" breaker on the DC+ out (the wire coming from the heat sink), and no fuses between the center taps on the xfrmr and the ammeter on the DC- side. One other oddity with my charger - the timer switches the AC neutral (white wire) instead of AC hot (black wire). Not sure why they did it that way. I thought about swapping 'em when I had the cover off, but maybe it's some kind of safety issue to keep the hot out of the switch on the timer. I dunno.

BTW, my brother was the king of DEC's RT11 back in the day. Were you doing real-time coding, or running your stuff under RSX?

I never was much of a DEC guy, Unix/Linux was my forte'. I do mostly Window$ work now. I complain about Micro$oft all the time, but if their stuff worked right, I'd either be pickin' cans outta dumpsters, or trying to find a job fixing old electric golf carts. ;^)

RLW