555C Alternator Charging

[Tommy Picklesimer]

The 555C backhoe Alternator charge light is on dim when engine is at full throttle and bright when at idle . I have had it checked and they said it was charging . But by the service manual their should be 12 volts on the charge indicator wire,but mine lights a test light dim with switch on and main output terminal is hot with switch on or off . I know you need 12 volts to start alternator charging. I was thinking that their shouldn't be any power at alternator when switch is off or am I wrong? I checked at battery and it shows about 13.5 when running full throttle. Im thinking battery might be weak,had on charge all night before I checked system.

Oh Yea this is a GREAT site for info

[TrevorJ]

OK, it could be many things.

Checking all you wire connections for good contact, is usually the first place to start.

Often steel washers are placed on alternators, which after time will rust to an extent and less power can get through. (Copper and aluminium don't sit well together, nor does aluminium and some stainless steels, however the posts should be insulated and no part of the washer is against the alternator housing except the earth.) I often find these washers aren't flat, ie no one has bothered to file them for good contact. Tinning and coating them with a thin layer of solder helps them stop weathering as bad.

After that, there's many other things which can cause your issue.

It may be just easier to take it to someone who's got a test bench to test the alternator and trouble shot any issues with it.

[Tommy Picklesimer]

The alternator has been bench tested and said was good . I was wondering about the power at main post alternator HOT all the time or just when switch is on and should there be 12 volts at indictor light wire?

[TrevorJ]

That's a good start. I don't know if your alternator has a built in regulator or a separate one, so there may be still an issue with the regulator if you have the older style of alternator still.

Regardless of that, generally most tractors and equipment, the power at that post is generally on the all the time, either direct to battery or through an amp meter.

The light you see on the dash, runs the field circuit. It is off /on per the key. Once the alternator spins up and is creating it's own power, and the field circuit does not draw power through the dash bulb as much, and appears to go out. I've had sick regulators before and as a result the draw through the dash bulb is higher, so the light will dimly glow even though it's still charging a bit.

However if the field wire has an issue, (bad contact somewhere) sometimes there's not quite enough power from scratch to let the alternator archive sufficient power generation, so the alternator generally has to spin much faster till it's able to help power the field.

Providing it's not a faulty separate regulator, I think you're going to have to check the wires back to the bulb in the dash and there to the switch and check it out for bad contact or even a hidden break in the wire. A multimeter comes in handy for those sort of things.