alternator not charging house batteries

Garyj · 07-12-2020, 03:11 PM

2015 Thor Four Winds 33SW Super C. On my most recent trip I noticed that the house batteries we not being charged by the alternator while driving down the road. This has always worked in the past. I went to troubleshoot it when I got home and it was working! After several attempts I caught it when it was not working and found there was no voltage at the isolation relay on the terminal that actuates the relay (12v signal comes from the isolation delay relay). Intermittent IDR, right? I replaced it and no change - it still works sometimes and not other times. The IDR is getting the 13.5 - 14.0 volts from the alternator at all times so it's not a wiring problem. I find it hard to believe I got a bad IDR but that's all I can think of at this point. Any ideas out there?

Oneilkeys · 07-12-2020, 03:46 PM

You’re right, it doesn’t seem likely that you would have two bad iDRs but the only possibilities that I see is another bad IDR or a problem in the wiring - either a connector or bad wire which intermittently makes a connection. I would try jumping the wire first.

Garyj · 07-12-2020, 04:00 PM

Thanks. I tried that and the wiring seems to be ok. I get alternator output voltage on the wire right at the input to the IDR whenever the engine is running. Sometimes the IDR supplies 12v to the isolator relay and sometimes not. The next thing I'll check more carefully is the actual alternator voltage at the IDR. The IDR spec says it activates after it sees 13.3v for 12 sec. Maybe I have some drop in alternator voltage from the engine compartment to the house.

Garyj · 07-12-2020, 05:31 PM

OK. I looked more carefully at the alternator voltage "signal" to the IDR. When I disconnect the IDR at the connector the voltage at the connector reads 14.2v, same as the alternator voltage. When I plug it back in to the connector the voltage drops to about 13.6v. That's technically enough to activate the IDR (13.3) but there's not much margin and that could be why my problem is intermittent. There's no way that little IDR can be drawing enough to drop the voltage by .5v unless there's some resistance somewhere in the line. Looks like I will have to run a new wire from the engine compartment. Anyone know where this wire would plug into the chassis electrical system? it doesn't show battery voltage when the engine is off so it must be a switched source.

Oneilkeys · 07-12-2020, 05:35 PM

Even if you had a temporary voltage drop from the alternator, It should kick right in again if the alternator gets back up above 13.3v. IDR sure seems like the culprit. Intermittent issues are the absolute worst to solve. Good luck.

Bob Denman · 07-12-2020, 05:39 PM

The IDR...

https://www.thorforums.com/forums/at...1&d=1594575547

willettj · 09-20-2023, 06:54 PM

Quote:

Originally Posted by Garyj

OK. I looked more carefully at the alternator voltage "signal" to the IDR. When I disconnect the IDR at the connector the voltage at the connector reads 14.2v, same as the alternator voltage. When I plug it back in to the connector the voltage drops to about 13.6v. That's technically enough to activate the IDR (13.3) but there's not much margin and that could be why my problem is intermittent. There's no way that little IDR can be drawing enough to drop the voltage by .5v unless there's some resistance somewhere in the line. Looks like I will have to run a new wire from the engine compartment. Anyone know where this wire would plug into the chassis electrical system? it doesn't show battery voltage when the engine is off so it must be a switched source.

Hi Garyj, I have a 33SW as well and just looking to get valuable feedback from other owners.

willettj · 12-09-2023, 06:00 PM

Where would I find the IDR on a Thor 33SW? I've looked at the Thor schematics and it doesn't even show one, only the emergency start solenoid. But I do get charge power from the alternator on the house batteries and that can't be coming thru the emergency start and I can't determine where they wired that in..

Dan-sr@perra-us.net · 12-09-2023, 06:41 PM

Quote:

Originally Posted by Garyj

2015 Thor Four Winds 33SW Super C. On my most recent trip I noticed that the house batteries we not being charged by the alternator while driving down the road. This has always worked in the past. I went to troubleshoot it when I got home and it was working! After several attempts I caught it when it was not working and found there was no voltage at the isolation relay on the terminal that actuates the relay (12v signal comes from the isolation delay relay). Intermittent IDR, right? I replaced it and no change - it still works sometimes and not other times. The IDR is getting the 13.5 - 14.0 volts from the alternator at all times so it's not a wiring problem. I find it hard to believe I got a bad IDR but that's all I can think of at this point. Any ideas out there?

Check the output from the alternator. On my 1996 Allegro P30 Chevy I had an issue with the instruments going crazy when the engine was running at high RPM. It turned out that the rectifier in the alternator was going bad. Under certain conditions AC bled over into the DC output from the alternator. I am not sure how to detect that or even if you can without using an oscilloscope.

Maybe just pull the alternator and have the alternator tested. Advance Auto parts will test it for free and I expect that many other Auto Parts store might also do so.

willettj · 12-09-2023, 07:20 PM

Quote:

Originally Posted by willettj

Where would I find the IDR on a Thor 33SW? I've looked at the Thor schematics and it doesn't even show one, only the emergency start solenoid. But I do get charge power from the alternator on the house batteries and that can't be coming thru the emergency start and I can't determine where they wired that in..

Disregard this post

After some further reading it appears what Thor has labeled Emergency Start Solenoid in the schematic is actually the BIRD / Trombetta, which is likely how I am getting alternator charge to the house batteries.. now I just have to climb under the RV and look around the batteries to find this thing!

Chateau_Nomad · 12-09-2023, 08:01 PM

Usually mounted on the driver side firewall area or fender well... because of closer proximity to the E-start switch on the lower driver side dash.

Wiring to ignition and the start switch disappear into a loom. There's another wire or two that run from that area to the chassis battery.

willettj · 12-10-2023, 02:29 PM

Quote:

Originally Posted by Chateau_Nomad

Usually mounted on the driver side firewall area or fender well... because of closer proximity to the E-start switch on the lower driver side dash.

Wiring to ignition and the start switch disappear into a loom. There's another wire or two that run from that area to the chassis battery.

Thanks for the tips!

willettj · 12-12-2023, 08:01 PM

So I found my BIRD and the Trombetta isolation relay and Thor could NOT have made these any harder to get to! I took this pic by holding my phone over the top of the hydraulic jacks motor etc.. I can only assume this went in prior to the jacks and has not been touched since. I was planning to re-work this a bit but may leave it alone until something actually fails and I'm forced to go in there. The diagram shows how my 33SW is wired.

simidrm · 12-18-2023, 03:09 AM

Same thing mine was doing, I used a volt meter on the trombetta and check coach and chassis batteries with engine running, checked signal wire to trombetta and it had power, the trombetta was clicking when I unhooked the signal wire, replaced trombetta and everything worked for about a week, sent it to dealer and they did the same thing and replaced trombetta again and it didn’t last the trip home, if I remember correctly that trombetta is a constant duty 200amp solenoid, I got another constant duty 900 amp and 2 years it is still working

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