John T - resistor followup and battery question

Hey John T -

Your advice that 3 ohms is the correct resistance for a cutout system "low charge" resistor for my Minnie Mo U was right on!

I found a 3 ohm, 20 watt resistor in my electrical junk box, temporarily wired it to the charge switch and it worked great. Found it limited the "low" charge rate to about 4 amps at governed RPM - exactly what I wanted.

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However I ran into another problem: I started the tractor early Sat morning then left it to warm up. While warming the charge switch was set to "high" and the ammeter indicated about 10 amps. After warming 15 minutes or so, I reset the charge control switch to "low" and put the tractor to work.

I ran the tractor for perhaps an hour before noticing all (3) battery caps were missing. (They'd been in place when I first started it up.) Upon closer inspection I discovered the battery top was cracked around its entire perimeter. Also one end of the battery was split all the way to the bottom (photo) and there was no electrolyte visible in the end cell.

It appeared the battery had suffered an internal explosion while the tractor was warming up unattended. (I'm sure I'd have seen/heard if it let go while I was aboard!)

The battery is just over one year old. On "high charge" the charging system is only good for about 15 amps cold (it tapers to around 12 amps as the generator warms up). So it's not like the battery had been grossly overcharged.

Any ideas what might have caused the failure???

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More curiousity: The Minnie ran fine all day with the split battery - I didn't dare shut it off. All day the ammeter indicated a 3 - 4 amp charge at governed RPM. Then despite overnite temps in the low teens, the tractor started unassisted and ran fine another 8 hours the following day with the split battery. Go figure(!)

...Bob M

Bob, Back in the early '70's I had a battery in my '63 Buick run all winter with a crack down one corner from top to bottom. That cell was empty for months, yet it never failed to start for me. I tried epoxy glue on it, but it wouldn't stick.

Can't explain how it kept working, but I was going to school and was broke, so I just ran it.

You MAY NOT have had an actual battery explosion. The caps MAY have been frozen in place and covered in ice so their vents were plugged, and the battery may have been simply pushed apart by gases generated by charging it. As the battery top warmed a bit and the internal pressure increased in each cell, the caps may have been simply popped off.

(quoted from post at 12:55:12 12/18/08) You MAY NOT have had an actual battery explosion. The caps MAY have been frozen in place and covered in ice so their vents were plugged, and the battery may have been simply pushed apart by gases generated by charging it. As the battery top warmed a bit and the internal pressure increased in each cell, the caps may have been simply popped off.

Click to expand...

Makes sense, except for one detail. How could the end cell split and lose electrolyte and THEN be able to have gas pressure sufficient to pop the cap? You would think gas pressure could split the case OR pop the cap, but I am curious as to how it could do BOTH things on the same cell. Thanks..[Freezing could do it, but that doesn't fit the facts.]

Bob/TheDurk -

Freezing - while a possibility - I believe is unlikely here for several reasons:

1 - The battery in my Super H (an "identical twin" battery purchased the same day as the battery that failed) was parked alongside overnight. It worked uneventfully all weekend.

2 - The cell caps are the push-in type (not threaded). They slipped out and back in easily when I checked the water level a couple days earlier.

3 - Whatever it was that caused the failure it was VIOLENT! Could locate not a single cap in the fresh snow anywhere around the tractor.

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Right now I'm kinda leaning toward a momentary interal fault (short or something) inside the battery. Then whatever it was that that blew it apart also cleared the fault.

I don't know...

What may have happened is the gas pressure may have SIMULTANEOUSLY split the case and blown the caps out. Probably the end split first and the stress/shock broke the plugs out so the gas could pop them free as well. That makes sense to me. I just didn't think you could do one, and THEN the other on the same cell.

You mechanical types are kinda hazardous to be around blowin up this tricity stuff. Ima thinkin a short developed in one cell from "stuff" flakin off a plate n momentary high current caused excess hydrogen gas n the rest,,,,,,Well youre a mechanic you gotta figure out that part lol........ I DO NOT see any chance of overcharing causing it with the charging system were dealin with and those low charge rates, maybe with an alternator but not that genny......

I guess they make more vibration resistance (truck/tractor/dozer etc) batterys but they are more expensive and then you have to sacrifice something in capacity.

Each battery cell is 2.1 volts, with no acid in one cell seems like she would only have been a 4 volt battery, dont sound like she should have been good at cranking an engine, but given the correct "short" I guess she could still draw charging current to keep it running...

Such a thing dont ever happen on John Deeres ya know ..............

John T

Yeah John T - your theory makes sense.

And it serves me (a mechanical type) right for fooling with a tractor that uses this "tricity" stuff. (Perhaps instead I shoulda got one of those *#&@~& noisy green tractors you start by wrestling a very large wheel on the side....!)

Anyway I just got a call from the guy at the tree farm where my tractors are used. He reported the old Minnie cranked right up on the split battery this afternoon.

All I can figure is while there's no acid visible covering the plates in that busted cell there must still be enough left near the bottom of cell so the battery can still work.

A new battery goes in Sat morning BTW. ...Bob M

MAYBE.....the "split" still seals, but there was a volume expansion sufficient to drop the acid below the level where it is visible. This would explain further how it could "split" and still have pressure to blow the cap. As you can see, this point has bothered me.

Very interesting development. I agree it is an internal open or short with attendant spark KKAAboom. (batteries are wierd machines) I'm glad the resistor worked well. Jim