charging system on a Craftsman lawn tractor

[Mosey]

How much voltage should I expect the charging system to produce on a Craftsman lawn tractor with a 15HP gas engine? I know a car should produce around 14 Volts, but I'm wondering if a small engine like this only produces a small trickle charge? What should I expect to see if I put a voltmeter on it while it's running?

 

[DarinRay]

Well after reading your question I was going to wait to see what the others thought but I was real curious so I just went out to the barn and started my 98 craftsman 20 HP and I am reading 14.24 VDC. I am not sure if this is the right reading but that's what I'm getting and thought I would let you know.

Darin

 

[Mosey]

DarinRay - Thanks. I measured mine and it read 12.6V at full throttle. At idle it read only 7V.

This all started about 6 weeks ago. I went to start the mower and the battery was dead. So, I jump started it and mowed the grass. After I shut it off, it restarted with no problem. Just in case though, I charged up another battery that I had in an old mower that I got rid of 3 years ago. This other battery has been sitting around unused all that time, but it took a charge. A week later, the same thing, dead battery. I always take the key out so the kids won't mess with it and leave it on. This time, I swapped batteries and mowed the grass. I put the original (Sears Diehard) battery on the charger. The old battery seemed to hold a charge better though, and the mower restarted the next time I needed it, which was about 2 weeks. But, then the last time I tried to start it, it was dead. So, I put the Sears Diehard back in, which had been charged for about 24 hours, and it seemed OK. But, I made the mistake of leaving the key in it and the kids played with it and left it on. So, I charged the Sears Diehard again, but this time it didn't take a charge and only read about 10V after being charged overnight. So, I don't know what's going on.

 

[BrokerBob]

Mosey:

Up until last year I owned a Craftsman with an 18 hp B&S. Like you, I encountered a problem with the battery becomming discharged. At the time, it seemed to me that the battery was losing its charge just from sitting rather than through regular operation. At first, I assumed the battery had become "tired" and replaced it. The problem persisted.

Although I should have checked the generator output, I never did. Instead it seemed more likely to me that the battery was discharging due to a ground somewhere in the system. I replaced what I believe is called the starter solenoid terminal block. It seems to be a very common Sears part as it is included in the parts display in the Sears store in my area. Once this part was replaced, the problem ceased to exist.

I can't say for certain that this is your problem. The voltage output that you are reporting seems a bit marginal, however, I would not rule out the need to replace the starter solenoid terminal block.

Good luck.

BrokerBob

 

[Mosey]

BrokerBob, Thanks. I was wondering about the possibility of something draining it. I'll see what one of those costs, and if it's not too much I may just swap it out and see what happens.

 

[njrqs]

Mosey

From my knowledge of auto electrics, 12 volts is 12 volts no matter whether it is put out my your mower or a Mack Truck.

It is all about the amperage that the alternator/generator puts out.

Alternator on my truck is 80amp but maybe a mower is 1 amp for example. The bigger alternator will charge things quicker (Discounting surface charge issues)

My mower does similar. When sitting for a while it goes flat. I think maybe the alternator doesn't put out much amperage and the battery being so small must not be 100% charged. Probably due me starting it to run the young fella around the yard and not getting time to charge !!

Cheers

 

[Mosey]

BrokerBob - Is what you are calling the "starter solenoid terminal block" the starter solenoid itself? I couldn't find anything called a terminal block, but they have "solenoid kit" for $12 which is the starter solenoid itself. Thanks.

 

[DarinRay]

I actually had to have my starter solenoid changed too after being only about 1.5 yrs old. I think mine was just because the poor girl wouldn't start for me sometimes or it idled down after turning the key off. ?????

Darin

 

[karmakanic]

Danny,
There's a problem with your charging system if you're only reading 7 V at idle and 12.6 V max. A fully charged battery will read 12.5 or so, depending upon temperature, and needs 13+ volts to be adequately recharged after starting the tractor. The voltage you read will be dependent upon the state of charge and condition of the battery, along with the condition of the alternator. You can get a better idea of what's happening if you've 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 the battery is recharged. If the battery continues to pull high amperage, then the battery is bad, and will burn out the alternator over time. This is a common reason for alternator failure.

You might try cleaning all your positive and negative connections in the circuit between battery, starter, and alternator. If that doesn't fix it, pull the alternator and take it to your local rebuilder. I'm assuming it has an internal voltage regulator, if it has an external regulator, pull it also and take it with the alternator.

The rebuilder can bench test, and determine if it's a regulator or alternator problem. Kinda sounds like you've got a bad diode in the alternator. With a bad diode, the alternator will charge, but it's output will be 30% below normal.

HTH,
Dave

 

[BrokerBob]

One of the dangers of offering advice is that someone may actually have the nerve to ask for a further explanation. I will give it my best.

I used the description "starter solenoid terminal block". If my memory serves me, the part I am referring to is bolted to the tractor in or very near the battery compartment. It has no visble moving parts and appears to be made of plastic or some insulating material. It has several terminals for connecting a battery cable, starter cables, etc.. I presume that there is some type of solenoid-operated switching device inside the plastic housing.

I suggested changing this part because I have the personal experience in which the part seemed to be responsible for the battering draining down over time. No doubt due to some kind of internal short.

Hope this helps and that I sound like I may actually know what I'm talking about.

BrokerBob