WD45 D alternator rebuild

Alternator wasn't original. Single wire needs to be spun fast to start charging. Once it starts it will charge at low speed. There might not be enough engine speed possible if it has the original generator large diameter pulley. Good auto electric shops can supply a smaller diameter pulley to get it spun fast enough to start charging. On my gas 4020 the small pulley takes about 1650 engine RPM to start charging and that's with a 5 or 6" crankshaft pulley.

Most 1 wire alternators charge without spinning fast with an added wire from the gas ignition switch through a lamp, resistor, or diode. On a diesel a convenient technique is with an oil pressure switch that closes on pressure rise, available from NAPA. Requires a T at the oil pressure sensor.

Gerald J.

I don't have a tach and had to guess on the rpm. Put a multimeter on it and didn't get any change no matter the rpm. Would it be best to do a conversion from single to 3 wire alternator?

Not really. Never done much electrical work. About what size do I need?

Not on a diesel. You need the impulse from the ignition to run an electronic tach

Have a 210 and a 175D that the tach is driven from the alt. Would take some rigging but is possible.

Some Perkins engines connect a mechanical tach to the cam shaft end. I looked at a MF-135 set up that way today and the tach pointer rotation is opposite from my NF-135 with a Continental engine where the tach drive is by a rotation reversing and speed changing gear box on the back of the  generator. My 4020 uses a gear drive under the distributor.

Modern pickup diesel engines use crankshaft or cam shaft position sensors to indicate speed.

A classic electric tachometer uses a permanent magnet generator. Its decently precise that the voltage from the armature is exactly proportional to the generator's shaft speed.

An alternator generates alternating current and rectifies it (usually internally, but vintage Leece-Neville alternators used external rectifiers). Some tapped the AC for a tachometer because the frequency of the AC is exactly proportional to the alternator shaft speed. The frequency is predicted by counting the rotor poles. Two rotor poles passing one field pole makes one cycle of AC, so a 16 pole alternator rotor makes 8 cycles of AC per revolution. Frequency is not hard to read with many PIC chips having a built in counter and they can drive a display. I'm sure something like that is in use on many a modern tractor and semi.

Then there are optical tachometers that shine a light on a shaft with a bit of reflective tape on the shaft that light hits and display the shaft speed directly on the display.

Then there are mechanical tachometers that are nothing more than a high ratio work gear drive from the input shaft to a dial pointer. Time the dial pointer revolutions or count them for a minute, multiply by the gear ratio. Not handy when the end of the shaft isn't handy and its working hard. There are also mechanical tachometers that drive from the end of a shaft usually with a rubber button and move the pointer to show the shaft speed.

A shaft position sensor can put out pulses usable by an ignition triggered electronic tachometer too, but may need amplification to have enough voltage.

And there are sensors specifically made for shaft speed, a lot like the speedometer sensor in my '98 F150.

Gerald J.

Most one wire Alternators need 1200-1400 rpm in order for them to excite the regulator to start charging. I wouldn't recommend a one wire Alternator for a Tractor. Most one wire Alternators though can be changed to a three wire by simply wiring in the VR. Pop the plug out of the top of the one wire and plug in the three wire pigtail. We offer the conversion in a kit to change your one wire to a three wire. To read more about the conversion and learn a little about the system, drop by our website. I have some good information and articles on our site. 
Steve@B&B
bb-customcircuits.com

Got it too full throttle, and the needle went crazy. Looks like the alternator is good.

I had a 7000 with an electrical tach that ran off the alternator. It might be easier than running a cable.