Bad rectifier

SweeperForce

Chief Petty Officer
Joined
Feb 7, 2010
Messages
487
After noticing my main tach wasn't running right I suspected the rectifier. I check the leads with and ohm meter in one direction and got resistance. When I reserves the leads it should read open. Mine read resistance going both ways. So I ordered a new one, I just got a message from the vendor thet they are on back order til late Sept to early Oct. Can I harm or ruin anything by running the engine without a rectifier? To my knowledge the only thing it does is run the tach and recharge the batteries. Thanks, Tom
 

pnwboat

Rear Admiral
Joined
Oct 8, 2007
Messages
4,251
If it is indeed just a Rectifier and not a Regulator/Rectifier, then it probably won't hurt anything but make sure you tape up the wires so that they don't touch ground.

Radio Shack sells a rectifier that is rated higher than the factory Force unit for about $5. P/N 276-1185. It's rated at 25 amps and 50 volts. Your battery charging stator winding is about 16 volts at about 9 amps.

http://www.radioshack.com/product/in...ductId=2062584

Only issue may be that if your wire leads have crimped on eyelets for a post and nut, you may have to change them because the Radio Shack version has flat lugs for a slip on connector. Shouldn't be a show stopper.

http://www.youtube.com/watch?v=pAV14aj_DT0

http://www.youtube.com/watch?v=ThX0_E9x1mc

http://www.youtube.com/watch?v=R2ngCNezp8Q
 
Last edited:

Jiggz

Captain
Joined
Oct 23, 2009
Messages
3,817
Diode resistance testing calls for hi/low resistance readings usually with a ratio of 10 or more. It does not necessarily mean one reading will have resistance while the reverse should read infinity, instead it should be hi and low or low and hi. And sometimes, unless you have a comparable readings from another working unit or known resistance stated in the manual it is quite hard to have a definite diagnosis.

The sure best way to test a diode rectifier is through "hot checks". This means with the engine in fast idle (approx 2K rpm), read Vac from the two input wires (usually yellow or yellow/grn) and you should read AC voltages in the range 14~18 volts. Next is to read the output wires (Vdc)which should read above battery voltage, usually 13.5~16 volt DC. You will need to read the battery voltage before starting the motor and the test itself. In this way, you have a reference for the output voltage. If output voltage is equal to or less than initial battery voltage, then the rectifier is faulty. Worse yet, if there is no voltage AC from the two input wires, meaning the stator is faulty or maybe a loose connection.

I believe you have the 150 HP A model with Prestolite system thus your stator has the 7 amp output non-regulated. The radioshack replacement should be a good replacement which costs less than $5. Of course, as PNW mentioned you will need to do slight modifications with the connectors.
 

SweeperForce

Chief Petty Officer
Joined
Feb 7, 2010
Messages
487
Ok, here's the scoop. My batteries are sitting at 11.5vdc before starting. While running I got just under 12vdc. With the input green wires I got 7.12vac and 7.03vac while running. According to the other posts my numbers are low. Is there anything else I should check?
 

Jiggz

Captain
Joined
Oct 23, 2009
Messages
3,817
Make sure you are reading between wires and not a wire to ground both on the input and output wires. And then you also need to fast idle the motor to about 2K rpm so the stator can generate enough voltage to check the integrity of the rectifier. The video link is missing.
 

pnwboat

Rear Admiral
Joined
Oct 8, 2007
Messages
4,251
If your AC output on the Green wires is still low after checking per Jiggz suggestions, try disconnecting the two Green wires and check the voltage across them with the engine at fast idle. If the rectifier is bad, it may be pulling the AC input voltage down. If you see 14 - 16 volts AC with the wires disconnected, then I would say that the rectifier is bad.

You can also check the battery charging winding in the stator with your OHM meter. It should read about .6 OHMs across the two Green wires. Almost a short but not quite.
 
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