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Onan 7.5DKDFJ Low A/C Output


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  #11  
Old 04-12-2018, 06:03:31 PM
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Default Re: Onan 7.5DKDFJ Low A/C Output

HELP! OK put new rectifiers in, and the last jumper on the sx460 that was missing for the remote voltage trimmer option. Now I am getting 70 volts ac on the black and red output, should I have 110-120 per leg? Or is it 55-65 per leg. Very confused right now, this is a 110 only set up on my rv, but I thought it was 110 on the red, 110 on the black, 3.5kw each? It runs to a breaker that has two 3.5 running together. When I refer to red and black i'm referring to the four wires going out of the generator, red/black/green/white.
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Old 04-12-2018, 07:13:27 PM
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Default Re: Onan 7.5DKDFJ Low A/C Output

Pat I think you are close but I am somewhat confused by your terminology so lets get some information so we can sort through this. What AC voltage reading do you get when you check red to neutral and black to neutral. Which two leads connect to the terminals 7 and 8 on the SX460. I think that they may not be on connected correctly. Also there should be 3 jumpers on the SX460 board , the 50/60Hz one should be on the 60Hz side , the 110/220V one should be between terminals 3 and 4 and the Remote VR adjust should be on terminals 1 and 2. Get back to us and well go from there. Cheers Dan

Ps the fact that you changed over from transformer to SX460 regulation makes this a bit more complex.
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Old 04-12-2018, 07:29:54 PM
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Default Re: Onan 7.5DKDFJ Low A/C Output

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Originally Posted by BigBlockChev View Post
Pat I think you are close but I am somewhat confused by your terminology so lets get some information so we can sort through this. What AC voltage reading do you get when you check red to neutral and black to neutral. Which two leads connect to the terminals 7 and 8 on the SX460. I think that they may not be on connected correctly. Also there should be 3 jumpers on the SX460 board , the 50/60Hz one should be on the 60Hz side , the 110/220V one should be between terminals 3 and 4 and the Remote VR adjust should be on terminals 1 and 2. Get back to us and well go from there. Cheers Dan

Ps the fact that you changed over from transformer to SX460 regulation makes this a bit more complex.
Sorry, the ac voltage is with the built in adjuster from 45-75, on both red and black, to neutral. But if i flash the field (fused-diode) I get perfect 120? I have flashed, reversed f1- f2, rechecked the 3 jumpers, so aggravated, but at the same time elated to see 120, although forced!

---------- Post added at 07:25:12 PM ---------- Previous post was at 07:24:07 PM ----------

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Originally Posted by patsmobile1 View Post
Sorry, the ac voltage is with the built in adjuster from 45-75, on both red and black, to neutral. But if i flash the field (fused-diode) I get perfect 120? I have flashed, reversed f1- f2, rechecked the 3 jumpers, so aggravated, but at the same time elated to see 120, although forced!
Forgot the 7-8 leads, they are T-1, and T-4 from the gen head.

---------- Post added at 07:29:54 PM ---------- Previous post was at 07:25:12 PM ----------

Feel stupid for not marking the rectifiers before pulling them also, I assumed incorrectly that they were the same, of course now knowing one is + and one -. I was pretty confident in installing them from the corrosion marks from the old ones, but if they are in wrong would that account for the voltage issue? Sorry to go on, but man i'm excited that it may be salvageable, not to mention we have a trip planned for Sunday, and I need to reinstall this unit asap! Thank you for helping me!!
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Old 04-12-2018, 08:09:49 PM
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Default Re: Onan 7.5DKDFJ Low A/C Output

Don't worry about making mistakes. We all do that is how you learn. Except me I am perfect
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Old 04-12-2018, 08:15:44 PM
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Default Re: Onan 7.5DKDFJ Low A/C Output

It should not make a difference which rotating rectifier goes where, they just supply rectified DC to the rotor. It sounds like Terminals 7 and 8 should be supplied by T1 and T2 instead of T1 and T4. The most important question though is do you get significant voltage between the red and black, if you do then something is wrong. If this is supposed to be a 110V output unit then the AC voltage between the two internal windings of the stator is supposed to be in phase so that if they are combined/connected you get 110V at twice the current for a total of 7Kw. If it is connected as a 220V unit you will get twice the voltage at the same current , but you would not be able to connect the outputs together in the same breaker or it would result in a dead short. Roughly similar to connecting two 12V batteries in series to get 24V at the same current or connecting them in parallel to get 12V at twice the current. The reason I am getting into this is because when you changed from the transformer regulation system to the SX460 a lot of things changed. Did you completely remove the transformer so it could not be confusing the wiring connections? It is critical that we understand what you actually did without making any assumptions. Cheers Dan
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Old 04-12-2018, 08:35:24 PM
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Default Re: Onan 7.5DKDFJ Low A/C Output

The only wires used are t-1,t-4, f1 f2, with the 10ohm in the field wire, and using the still good onan push button circuit breaker in the ac side. Red and black have the same voltage, 110 when flashing it, and 75 when not flashing them. Looks like t2 t3 and nuetral and ground together, then t1 t4 going to 7-8. I will get some pics asap also, it's tough not seeing it!
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Old 04-12-2018, 09:02:22 PM
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Default Re: Onan 7.5DKDFJ Low A/C Output

It sounds like it is set up for 220v output. what happens when you pull the jumper off the 110/220 terminals? Pics would be great. Cheers Dan
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Old 04-12-2018, 09:06:32 PM
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Default Re: Onan 7.5DKDFJ Low A/C Output

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Old 04-12-2018, 09:19:07 PM
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Default Re: Onan 7.5DKDFJ Low A/C Output

Dan you are the MAN, but why with the jumper off, that is supposed to be for 110, did I get half that, and vice-a-versa. I pulled the jumper started it with meter hooked up, got 139, adjusted it to 120 even, same 120 on the red and black, as it should be!!!!

---------- Post added at 09:19:07 PM ---------- Previous post was at 09:14:16 PM ----------

Do you think I am running the wrong two T wires, does it matter now that the output is right? You folks have no idea how grateful I am, not to mention happy. I make under 2k a month being a disabled gimpy ass veteran, and should not own this rv, it means so much to be able to keep it going by replacing the bearing (original issue) and then diagnose the regulator, and rectifiers, could not have done it without your help!
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Old 04-12-2018, 10:46:04 PM
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Default Re: Onan 7.5DKDFJ Low A/C Output

We are getting closer to the answer. The 460 is trying to meet a voltage setpoint across T1 and T4, that setpoint is nominally 240V, now that you are in the ballpark it is able to regulate to that value. I was keying on your RV having a 120V supply but from what you have described you have a 50A 120/240V supply feeding your electrical panel. If that is correct then you are in business. I was concerned that you had changed the output of your generator from 120V to 240V in the course of checking components and wiring. This would be bad if the RV was expecting 120V and got 240v. I have a 6.5DKD RV unit set up for 240V so I was able to go look at the output connections to compare with yours. I like to be able to explain things so that anyone can understand them, I hope I have succeeded. Cheers Dan
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