charging system on a Craftsman lawn tractor

[Molerj]

Mosey has good advice if this had an alternator like a car. By his handle I assume that he
works on automobiles. Lawn tractor alternators are a little different. Also the solenoid wouldn't
have anything to do with charging the battery. It just aids in starting the tractor. Make
sure you have a good battery. Lawn tractor batteries, on average, last about 3 yrs. I've seen some
not last that long & some longer. I always buy the stronger battery, the one with more Cold Cranking Amps
It usually is the 29.00 one compared to the 19.00 one at auto parts stores.

 

[BrokerBob]

molerj

Although I generally agree with your post, I think that a clarification is in order. Yes, the starter solenoid has nothing to do charging the battery; however, neither I nor anyone else has ever made that claim!

The potential issue with a "bad" starter or ignition solenoid involves when the engine is NOT running. I can only draw on my personal experience. Several years ago I discovered that I was having to charge up the battery on a regular basis. A new battery helped, but did not cure the problem. There was nothing different going on in terms of the way I was operating the machine. I checked the alternator/generator output and it seemed to be putting out sufficient voltage to charge the battery during normal operation.

All I could think of was the possibility that some systemic "short" was slowly discharging the battery while the tractor was not in use. I replaced the starter/ignition solenoid and the problem disappeared. I spoke with a Sears Parts employee and he claimed that they sold a large number of this part. Hence, my conclusion and sharing of this experience.

 

[Mosey]

Thanks everyone for your input on this. I have done some testing and here's what I found out.

First, the original Sears Diehard is dead. I put it on my bench and charged it with my battery charger for 2 days. I measured the voltage right after charging it and it was 10.5V. A few hours later it was 7V. So, it just won't take a charge anymore. I have talked to a couple places that sell batteries, including Sears, and they all say a lawn tractor battery usually only lasts about 4 years, maybe longer if you keep it in the house in the winter. I've had mine for 4 years and left it out in the cold every winter.

Next, I charged the old battery (Bravo brand) for 2 days. I measured the voltage and it was 12.75V right after charging. I left it on the bench unhooked to anything and it stayed at 12.75V for 2 days. I put it in the mower and it started it right up. I mowed for about a half hour. I measured it while it was still running and it was about 13.8V at full throttle and about 12.8V at idle. It measured 12.8V right after I shut it off. It's been another 2 days now with it sitting in the mower hooked up, and it still measures 12.75V. Based on how this battery acted the first time I put it in, it will probably hold for about a week, but not much longer.

If I jump start the mower with the Sears battery in it, it only shows about 12.5V at full throttle and about 7V at idle, so it must be charging OK and the bad battery is loading down the charging system.

So, I plan to keep using the old Bravo battery for the rest of this year, since I won't need the mower much until next spring. Then, next spring I'll buy a new battery ($22) and see what happens. If the new battery doesn't stay charged, I'll buy one of those solenoids ($14). I can see the possibility of the solenoid have some sort of short in it and grounding the hot side of the battery and draining the battery. Based on how my luck runs, I'll probably be buying both a battery and a solenoid!

Thanks again for your help! I'll try to remember to update this again next year to help anyone else who might have this type of problem.

 

[Molerj]

Funny thing about lawn mowers, they sure keep you guessing. Sometimes the simplest
things can keep them from running. A tiny ground wire not making good contact, even
tho it is wrapped around the bolt & the bolt is tight. Or a plug that is a tad corroded &
won't let it start. Sometimes I'll work on something for hrs. till I find the problem.

 

[karmakanic]

Glad to see the problem got resolved.

I apologize for any confusion my post caused, I should of added some more information to the following statement.

<font color=blue>The voltage you read will be dependent upon the state of charge and condition of the battery, along with the condition of the alternator.</font color=blue> I should of added:
You must have a battery in good condition and fully charged to diagnose a charging system using a voltmeter. And even then, you can cannot completely diagnose the problem using just a voltmeter.

As neil pointed out, the charging system works in terms of amps. It sends current (amps) into the battery, which raises the potential energy of the battery (volts). The voltage regulator caps this voltage at 13.7 or so to keep the battery from boiling dry and to protect the electrical consumers. The battery acts as a storage chamber for potential energy, much like a water tower does in a water supply system. Starting your tractor is kinda like flushing your toilet in that sense. /w3tcompact/icons/smile.gif

If the battery is bad, it will completely confuse any voltage reading you get. How it affects the voltage depends upon what type of failure has occured in the battery. (sulfated plates, dry cells, open circuit, ect)

You need to be able to measure the current flowing out of the alternator to pin down whether you have an alternator or battery problem. You also need an amp meter to measure key-off draw, the other problem that can occur which would discharge the battery. Of course, you can also use a process of elimination, like Danny used. But, the combination of voltage and amperage reading, in conjunction with a method of placing a artificial load on the system, can give you a matrix that will diagnose any charging/battery problem very quickly. That's how modern computerized charging system testers work.

You don't need a fancy computerized machine to diagnose the system. And you can get away without a load machine, since you can place a load on the system by starting the tractor or turning the lights on. But you do need a way of measuring those amps, since they are the things that actually do the work.

FWIW, the nominal voltage of a six cell lead-acid battery at room temperature is 12.54. I would be suspicious of a battery that measures 12.75 (assuming accurate meter, and no surface charge) This is often times a sign of sulfated plates.

And another FWIW, there is no difference between a lawn tractor charging system and an automobile charging system, other then size and maxium amperage output.

Dave

 

[Soundguy]

<font color=blue>got a meter that can measure amps. I'm not exactly sure what those little alternators put out, but it should be at least 15+ amps. The max amperage output will occur right after starting the tractor and will decrease as

<font color=black>I would be highly surprised if a lawnmower charging system had a 15+ amp output. Both of my ford farm tractors, and my Yanmar tractor are in the teen range. I would be surprised if it was over 6 amps.

I've seen kholer regulators in the 4-6 amp range for some of the larger engines.

Mileage may vary, but even on a dc generator setup... like my 8n.. 11 amps or 20 amps if you have the big generator.

Otherwise, everthing said is good advice. I hope the guy gets his problem fixed.

Soundguy