Onan rectifier source?

[kpinnc 12,017]

Mine is dead on my 520-H, and the aftermarket one I got last year died as well. 

 

Anybody got a trusted source on these? 

[rmaynard 15,451]

I think I have a good used one from a known-running 520. PM me if interested.

[Horse Newbie 7,069]

What does it look like… pic ?

[Ed Kennell 38,167]

I bought a couple $20 aftermarkets for a 520 about 10 years ago.  The one I used is still charging fine.    I may have the other new one in a 5 gallon bucket or someone may have picked it at one of the big shows.     I don't remember the supplier.

[lynnmor 7,305]

I have good luck with the cheap ones, try again.  Be sure that you have a good ground to the mounting bolt, perhaps run a wire to the battery ground.

[kpinnc 12,017]

8 hours ago, lynnmor said:

I have good luck with the cheap ones, try again.  Be sure that you have a good ground to the mounting bolt, perhaps run a wire to the battery ground.

 

Yep. Did that last year. 

 

I just keep getting weak ones I guess.

[Wayne0 457]

The one I found in the jungle has been working for 2 years so far.

[kpinnc 12,017]

I found another original this morning from my old 518, and it's dead too. 2 genuine Onan and one aftermarket. I'm at a loss. My engine stator is giving better than 35VAC at full throttle. All three used an external ground wire. 

 

Tires and rectifiers... It's getting to be an annual thing! Sheesh!

[lynnmor 7,305]

You need to check the wiring, perhaps you are running starter current thru the rectifier.  In other words, check the battery cables and connections to make sure that the starter is well connected and there isn't a possibility that the current isn't following an additional path. 

[kpinnc 12,017]

So I've now tried two "known good" rectifiers, and I'm even more confused.

 

If I leave the external ground off, I'm seeing 19-21 VDC from the rectifier. When I ground the mounting bolt (either rectifier), it drops to 3VDC.

 

And all of my DC readings are negative voltage. 

[kpinnc 12,017]

I also measured both stator leads, and I think there is the issue. One side to ground reads 14Vac, the other reads 19Vac. 

 

This might be nothing, but for grins and giggles I looked for DC volts on the stator, and saw -22VDC and -14VDC individually taking one side to ground. 

 

Any electrical gurus out there? 

Edited March 9, 2023 by kpinnc

[Handy Don 12,217]

1 hour ago, kpinnc said:

I also measured both stator leads, and I think there is the issue. One side to ground reads 14Vac, the other reads 19Vac. 

 

This might be nothing, but for grins and giggles I looked for DC volts on the stator, and saw -22VDC and -14VDC individually taking one side to ground. 

 

Any electrical gurus out there? 

I think you have a short in your stator.

Test resistance on the leads to ground. Pretty sure it should be infinite. Resistance through the stator (lead to lead) should be very small since it should be one wire all the way through.

 

[kpinnc 12,017]

17 minutes ago, Handy Don said:

I think you have a short in your stator.

Test resistance on the leads to ground. Pretty sure it should be infinite. Resistance through the stator (lead to lead) should be very small since it should be one wire all the way through.

 

 

I looked at that. .05 ohms across, and zero either side to ground.

[lynnmor 7,305]

[Handy Don 12,217]

1 hour ago, kpinnc said:

 

I looked at that. .05 ohms across, and zero either side to ground.

Ok. In that case, I’d suspect the short is not to ground but within the stator windings somewhere--effectively shortening the wiring and likely excluding one or more of the coils.

[NA73 70]

onan stator resistance

spec a 20 amp: 0.06 - 0.10 ohms

spec b 20 amp: 0.10 - 0.19 ohms

35 amp: 0.6 - 0.10 ohms

 

onan ac voltage: 1800/3600 rpm

spec a 20 amp: 21/41vc-ac

spec b 20 amp: 29/57v-ac

35 amp: 24/47v-ac 

 

uncertain on how to determine spec: A or B or 35-amp.

this from the pdf: 492-4006 Onan P216 P218 P220 P224 SM.pdf

 

seems to me, if the AC voltage is within spec with good grounds and the DC voltage is too high/low then the rectifier is the problem. 

 

In 2021 I bought a DB Electrical AKH6003 off amazon and it has been perfectly fine - voltage is damn-near perfect(14.3/14.5). but I seem to recall that the physical dimensions may have been a little off from the original rectifier. 

the problem I had at the time was that it (rectifier) was putting out 17-19v DC and cooked a battery.

 

 

[Handy Don 12,217]

Doubting that all of the voltage regulators (including one that works elsewhere?) are the problem.

The common item is the stator.

 

DC negative voltage? Switch the probes and it’ll become positive. Trying to measure DC in a circuit that is AC is rarely gonna end well. Too much depends on the frequency of the AC power and the design of the meter doing the reading.

 

First things first. What is the AC voltage across the two stator wires when disconnected from the regulator with the engine at 3600 (or thereabouts)? Is it around 40 or more volts? If not, then the stator is not giving spec output. 

[kpinnc 12,017]

19 hours ago, Handy Don said:

DC negative voltage? Switch the probes and it’ll become positive. Trying to measure DC in a circuit that is AC is rarely gonna end well. Too much depends on the frequency of the AC power and the design of the meter doing the reading.

 

First things first. What is the AC voltage across the two stator wires when disconnected from the regulator with the engine at 3600 (or thereabouts)? Is it around 40 or more volts? If not, then the stator is not giving spec output. 

 

That's something that didn't occur to me. On the rectifier, the B+ terminal is connected to one of the AC terminals- not something I can change, it's made that way. So I can see how that could make the meter read wonky. 

 

And yes, at full throttle I see 46 to 48 VAC across the stator.

 

The Onan manaual says the regulator is internally protected from resistive faults, and if something downstream exists, the rectifier will appear to have zero output. Just gonna have to check for shorts...

[lynnmor 7,305]

2 hours ago, kpinnc said:

 

On the rectifier, the B+ terminal is connected to one of the AC terminals- not something I can change, it's made that way. So I can see how that could make the meter read wonky. 

 

Photo please.

[kpinnc 12,017]

2 hours ago, lynnmor said:

Photo please.

 

The AC tabs are the outer ones, with the DC B+ in the middle. In the 2nd pic, you can see the left terminals (AC and B+) are bridged.

 

This is an OEM Onan rectifier. 

 

[Horse Newbie 7,069]

15 minutes ago, kpinnc said:

 

The AC tabs are the outer ones, with the DC B+ in the middle. In the 2nd pic, you can see the left terminals (AC and B+) are bridged.

 

This is an OEM Onan rectifier. 

 

I have never seen that… of course I’ve only looked at one Onan engine up close.

[kpinnc 12,017]

1 minute ago, Horse Newbie said:

looked at one Onan engine up close.

 

I'm hoping that is what's causing my Fluke to register negative DC output. 

[rmaynard 15,451]

Kevin, if you need a stator, I have one.

[kpinnc 12,017]

11 minutes ago, rmaynard said:

Kevin, if you need a stator, I have one.

 

Thanks Bob. I think I have a couple in a box somewhere, but I do appreciate it. I might still need one.

[peter lena 8,623]

@kpinnc  referring to your mower deck clean / preservation , doing this for years ,

 also on that rectifier , found a seperate ground 12 ga wire , from battery ground bolt , directly to rectifier , tin bolt , really helps , never count on original grounding areas . too many , connective spots are rust/ corrosion/ paint . test that with an alligator clip test wire  for reaction , pete