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Onan LT II Transfer Switch JB 7.5


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Old 06-04-2017, 12:13:44 AM
JohnnyC JohnnyC is offline
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Default Onan LT II Transfer Switch JB 7.5

I hooked up an Onan LT II transfer switch to my JB and seem to have a slight issue. I could write it up in several paragraphs and screw it up, so I made a 7 minute video detailing the problem. The video can be seen by clicking on the following link.

https://www.youtube.com/watch?v=8eVV...ature=youtu.be

If you have any experience with these transfer switches or have any idea what may be the cause of the problem shown in the video. please let me know.

Thanks in advance,

JohnnyC
New Jersey
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Old 06-04-2017, 01:44:42 AM
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EricWood EricWood is offline
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Default Re: Onan LT II Transfer Switch / JB 7.5

Johnny,

Do you have another 120 VAC cube relay handy? I see some of the other modules have been replaced with regular relays.

Stick another 120 VAC relay in the K6 position, the black sensor in the lower left of the relay board. K6 has a full time duty, as it is normally energized as long as utility is present, and has to be energized to, among other things, energize K3 Start Relay, which is also a normally energized relay (Cube relay all the way to the right side of the pack). K3 has to be energized to keep genset from cranking in Auto position.

If you stick a good relay in the K6 position, and it, and the K3 relays pick up, that might be all there is to that particular issue. Retest to confirm at that point. If that cures it, you could find a "reasonably" priced voltage sensor relay to plug in to the K6 position. Also, perhaps consider a time delay relay for the K4 retransfer relay position, if you find out through further testing that the orange one doesn't work.

LT II was never one of my favorites. Used to carry all the time delay relays and sensors on the truck, but they are being obsoleted.
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Old 06-04-2017, 05:08:44 AM
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Billy J Shafer Billy J Shafer is offline
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Default Re: Onan LT II Transfer Switch / JB 7.5

I agree with Eric. Problem will be K6 or K3. K6 is the line side sensor. Which feeds power to the control system. K3 is the start relay. I have seen them fail allot. I always put a cube relay in it's place. I have also seen the main board burn the tracts off the back.

LTII was not a very good switch. I carried a box of spare parts on my truck. I would also pull the shields off of the transformers. They had a bad habit of starting fires. Check them over for proper voltage.

Just be glad you don't have the LT26K. A real nightmare.
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Old 06-04-2017, 07:20:24 AM
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Default Re: Onan LT II Transfer Switch / JB 7.5

Eric and Billy, thanks for the information. I too targeted the K6 relay after reading the Service Manual the other day. The manual says K6 is an adjustable voltage sensor relay. The relay that was in the switch was a cube and I believe it was either factory or replaced professionally since there was a factory plastic wire tie properly in place to hold the relay from coming out. None the less, I had an extra adjustable voltage sensor relay that I saved from another Onan transfer switch that I junked last year and plugged it into K6 relay socket. The results are the same....... In both cases (cube and adjustable relays in the K6 socket) they made a strong click sound when utility power was applied which appropriate. I did not focus on the K3 relay which I will do today. I may have another cube relay laying around somewhere, but I will have to look into the deep dark corners of my workshop.

One observation that I noticed with the clear cube relays is what appears to be slight moisture build up on the clear shell walls inside the cubes after I played with the transfer switch for a while. I can't be 100% sure, but it was enough to catch my attention. So, my mission is to attempt to unbury any cube relays that I may have saved and focus on K3 and try a third relay in K6.

I like these challenges. If the LT II transfer switch worked the first time there would be little to learn. By resolving problems, you get to know how these things work in detail.

JohnnyC
New Jersey
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Old 06-04-2017, 10:07:22 AM
akirkland akirkland is offline
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Default Re: Onan LT II Transfer Switch / JB 7.5

The most common failure points on an LTII are the time delay retransfer relay and the time delay stop relay. So common , in fact, that there are dip switches to bypass them. Look in upper right hand corner of printed circuit board. Push retransfer dip switch to on position, then try testing switch. Try same test with stop bypass switch.
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Old 06-04-2017, 11:27:26 AM
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Default Re: Onan LT II Transfer Switch / JB 7.5

On K6 make sure it is a single phase relay. Because there is a 3 phase also both look the same.
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