Lawn Tractor Battery/charging issue (longish)


HI,
20 HP B&S engine, 42" deck, 12V Exide Battery abt 1 1/2 years old. I thought about taking this to a battery forum/group but IME you get a lot better reality check here.
I accidentally left my lawn tractor key in the ON position and then got sick so it sat that way for almost three weeks. The battery of course went stone-cold dead over that time as it was also sitting out in the sun on top of the key not being turned off. No, lights were not turned on; key was just in the RUN position, not RUN/LIGHTS.
I tossed an 8A battery charger on it and it drew no current. No spark, nothing as if the battery were an open ckt. Shorting the clamps caused sparks and a current meter jump so power was on and the charger was working. I gave it a few minutes and noticed it was starting to take a charge; for an hour or so it sat around one amp. I cycled the charger on and off a few times, turned the key and let the starter whirr (wouldn't engage of course), and the charge rate moved up to around 3 amps and stayed there. It was mid afternoon by then. Around 5 it was still charging at 3 amps so I took the charger off and tried to start it. It's a good starting tractor so it started on the first spark; the starter didn't even run enough to know whether it sounded like the battery was almost up or nearly down. The charge rate then was still around 3 amps by then, so I figured the battery was still pretty low. I let it sit there for a half hour running, figuring I'd charge the battery. It sat at about 6A charging when I started the tractor and the battery was being charged from the tractor's charging cktry. But about a half hour later I went back to check, and it was showing a 15 Amp charge!
So, I took it out and mowed in the big side field for awhile, figuring that would let the battery charge and the bouncing around might help any deposits in the battery drop off, etc.. But the meter was at 15A and stayed there throughout. Sound-wise, the battery seems fully charged when the starter starts it even when it's nearly cold. I haven't let it set over a couple days yet though, because this only happened yesterday, but I plan to, to see if the battery is a battery or a capacitor<g>. Capacitors self-discharge.
Nothing wrong with the meter: idle drops current to low value, 1/3 speed or more puts it up to the 15A. Charger OK, worked fine on the generator battery to top it off. That only leaves the battery itself and/or the charging cktry in the tractor. Since 18A is 100% of meter deflection (an actual meter, not just a coil of wire looped around studs), I'm assuming the charging rate might actually go higher if it were possible to draw more current from the charging ckt on the tractor. In other words, it's maxxed out. I did see it approach 17A for a short time out in the field, but it quickly settled back to 15A again. NO change after mowing for a whole hour! Still at 15 Amps. Engine was hot, but it started like ASAP and as though the battery were brand new! I haven't had a chance to let it sit for a couple days to see if the battery loses its charge quickly.
I forgot to mention: It's a standard lead-acid battery, a little larger that normally found in lawn tractors because it's a 2-cylinder 20 HP B&S engine. IIRC the CCA (Cold Cranking Amps) on it was something like 120 Amps and it had a 5 year warranty for what that's worth<g> and the brand is Exide. What really bugs me is, I just replaced the battery in the spring a year ago! And I've probably ruined it now. If I can't get my volt-meter back quickly I'll go to RS and buy a cheapie for use here. As long as it'll handle over ten amps AC and DC I should be able to use it to TS this.
Q; Is it likely the battery is shot and can't be recovered? I wasn't thinking quickly enough to check to see if the battery had reversed its voltage; it was probably past even that point though, IMO. Q; Is it likely the charging cktry (just recifiers, but 4 of them instead of the usual 2) was damaged and could be the reason for the permanently high charging rate? Any reasonable way to explain the apparently permanent high rate of charge? It's not logical to me that the charge rate would increase with time like that.
Thanks for any relevent, knowledgeable feedback,
Twayne`
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Hi there, battery is prolly toast. It is not able to charge to full voltage. Never never charge battery with your vehicle. This makes the charger in the mower run full out. I would get a new battery and toss the old one. The charger in the mower is MUCH more expensive than the battery. BTW, HF has some multimeters also. As for voltages, a good battery will be about 12.5 volts just sitting. A regulated charger (mower, auto) will charge around 14.2 to 14.8 volts. Less than 13.6 volts won't completely charge battery. More than 14.8 will over charge battery and boil the electrolyte away. Modern batterys don't have pure lead plates. The plates are a sponge; this enables a large current pulse to start vehicle. It also destroys the battery is discharged below about 50% charge. I'm so old, I remember when batteries had pure lead plates. You could run a hot butter knife around the top, melt the tar, remove the plates, wash all the lead sulfate off, reassemble, and refill with acid. Good as new battery. Not now-a-days. lol

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Good advice. A charging system going at an uncontrolled full blast will eventually self distruct.

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Johnl wrote:

... That's what the voltage regulator is for...
And, there's not much point in having a charging system if you're not going to use it...
Paranoia, not advice...
--
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Thanks for the response. Got a pleasant surprise today; my buddy brought back my multi-meter! That means I have more info now and hopefully you'll continue to bear with me.
-- Since I had my multi-meter, I went out and started the engine: -- Voltage on the battery terminals is 14.4 V with the enginer running, 12.6 VDC with the engine off. That should say the regulator is working, right?
-- Being cold, the battery "sounded" good; fast starter spin, good start, etc.. I purposely left the choke off so it'd start harder & give me a chance to evaluate the battery state under starting load. Surprisingly enough it still seems to be OK but I'm going to replace it anyway soon's I can get to the store. I've never had a totally dead battery last long afterwards anyway.
Using the meter on the V ac range though: -- It reads 29 Vac across the battery terminals. Of course it's not 60 Hz so who knows what the actual voltge is, but ... that sounds high to me with a nice big battery for a smoothing agent. No?
-- And it still reads a 15A charge rate. I'm fairly sure, not positive, that the meter is oK. It's one of the sealed types, not just a loop of wire, and as the engine gets down to low rpm the meter does drop as the rpm drops. Engine Power seems to be fine, although one cylinder sounds like it might be stronger than the other. I can hear the difference at low idle and it's running rougher than it did.
I have another automotive battery I can temporarily put on it and topped off the charge on it today. The Vac component on that was only around a volt or so and DC of course was around 14.5, neglecting calibration of the meter. I think it's in reasonable shape though. Do you see any problems putting a charged car battery on it for testing? I'm considering putting a small power resistor in there too and calculating the current thru it, if I can find my old rheostats. I've got one that's half an ohm ot 4 ohms; it should work for what I need. Funny thing; I didn't run it near long enough to get the engine hot and when I turned the key off, it still did a backwards run for a second or so and quit running on the change in direction back to the right way. It's never done that before either until this whatever-I-did-to-it. The top screen of the flywheel is visible tru the hood vents is how I can see the direction changes.
I'm going to see if I can dig out the rectifiers tomorrow and get a meter on them. I have a feeling they're the cause of everything strange that's going on. I wish I had a scope so I could look at the voltage/current; it'd make things a lot easier<g>.
Not sure what you meant by never charging the battery "with" the vehicle, but I assume you mean in the vehicle and connected? Would that be hard on the rectifiers somehow? Hmm, might it explain why the charge rate INCREASED over time instead of decreased? e.g. it was 3A constant from the charger and I left it on for over an hour.
O well, I bet this is going to be expensive! I never did do anything in a small way<g>!
Cheers,
Twayne`

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Let me get this straight, Your battery is good, your charging system is charging and you are going to "modify" it. You obviously have more time and money than common sense.
Let it alone, there is nothing wrong with the mower.
Hank
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Twayne wrote:

If you shut the engine off and there is no load on the battery, and it's fully charged, it should take hours to settle to 12.6V, in my experience. I wonder if there's a drain of more than a few milliamps.

Charging current or engine vibration could cause material to flake off the plates of a discharged battery. I would have used a charger with series resistance such as a light bulb.

29VAC would correspond to a peak-to-peak of 82V.

You mentioned permanent magnets. I don't know how a PM alternator is regulated, but it sounds as if it's putting out surges that are perhaps more than 100 amps. That could cause a rough idle. If it were mine, I'd want to see a schematic.
If your mower has magneto ignition, I wonder if leaving the key on should drain the battery. Maybe a preexisting problem in the charging system is what drained it.
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Twayne wrote:

You might want to check the ignition timing settings. Maybe the flywheel key is sheared. Or the engine could be carboned up really bad and dieseling.
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Whats the water level? Are you sure the ampmeter is working correctly? Since it starts and runs and apparently charges, what's the problem? Is it boiling out the battery? If you're worried about the battery, and it has a five year warranty, take it back and have them test it. If it is bad, they will exchange at a pro-rated basis.
Hank
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Twayne wrote:

A lead acid battery will act strange if it becomes completely discharged. Basically the sulfuric acid turns into water as it is discharged. Then when charging, the water doesn't draw too many amps, but as it turns the water into sulfuric acid again, the charge amperage will go up. I would put my charger/maintainer on the battery and leave it sit a few days then see how it starts and charges. It's probably fine.
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