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FS2020

Coach Batteries Not Charging on Shore AC

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Frank, got to say that is strange, you mentioned removing the Body Builder fuse removed the parasitic load from the Coach batteries. Even thought the fuse is in a fuse box under the dash.

1.5 amps is going somewhere! The fact that it is loading the coach batteries, would make one think something related to the coach circuits..

Do you have power operated steps / and do the coach and chassis disconnect relays still work?

Rich.

Rich,

Good call. You are right, even though the fuse is in the chassis fuse box, it is causing a 1.5A drain on the coach batteries.

The Intellitec disconnect relay for the coach batteries is not working. I have ordered a new relay and new switch panel.

Helps to have a second set of eyes!

Thanks,

Frank

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Update:

I took apart the Power Distribution Panel and verified that the Intellitec Battery Disconnect Relays are working.

Inside the door of the RV are two rocker switches that open/close the Battery Disconnect Relays. The switch for the coach batteries was only receiving about 2 V. It needs 12V to open/close the disconnect relays. So I jumped the 12V feed from the chassis switch into the coach switch, and it now the coach disconnect relay works.

Also, the coach batteries are no longer being drained by a parasitic load.

Some progress, slowly.

Thanks,

Frank

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Frank,

From your information regarding the voltage dropping to 2 volts from the coach batteries. One would think there is a defective Counter EMF diode in the wiring between the relay actuation 12 volt supply and the switch? A resistance reading between the fuse and the 12 volt connection at the battery (12 volt wire removed at the battery post )might give you the same reading both ways and a resistance of between 30 and 40 K ohms. Didoes are nice devices, but when they fail and there is no information regarding their presents, it can become a hair pulling experience.

Do you measure 12+ volts at the rocker switch from the coach 12.5 volts?

If not then the culprit could be between the fuse and the switch. You could read the voltage at the fuse coming from the battery, think you mentioned it was low in a previous post? In that case its in the main wiring harness between the coach batteries and the coach builders fuse.

Thing is its working, but if the current solution causes some strange problems down the road you might consider adding a diode to the supply side of the switch. Needs to be installed in the proper orientation to work!

My instincts tell me one thing and the math says something else,regarding the resistance reading I think you would get; so I will need to ponder the thought a little more.

Rich.

A resistance of 7 ohms, with a current of 1.5 amps would drop the voltage to 2 volts. So a bad connection / splice or corroded connection could be the culprit. That would mean a power drop of 15 watts. Something should be a little on the warm side!

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Thanks to your expert advice, I have the battery disconnect relays working now. But power from the coach batteries is not being delivered to inside the RV. The chassis power works fine and the engine starts.

The power from the coach disconnect relay goes through a "short stop" breaker that is labeled "Short Stop 24V D33 4OA." (I tried to attach a photo, but it asks for a URL. When I tried a URL is gave an error?)

I jumped it with my multimeter and 1.5 A is flowing through it. That's only 18W at 12V. Is that too much for a normal drain from the coach with everything off?

In any case, I'm going to replace it and see what happens.

Thanks,

Frank

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Frank,

From your information regarding the voltage dropping to 2 volts from the coach batteries. One would think there is a defective Counter EMF diode in the wiring between the relay actuation 12 volt supply and the switch? A resistance reading between the fuse and the 12 volt connection at the battery (12 volt wire removed at the battery post )might give you the same reading both ways and a resistance of between 30 and 40 K ohms. Didoes are nice devices, but when they fail and there is no information regarding their presents, it can become a hair pulling experience.

Do you measure 12+ volts at the rocker switch from the coach 12.5 volts?

If not then the culprit could be between the fuse and the switch. You could read the voltage at the fuse coming from the battery, think you mentioned it was low in a previous post? In that case its in the main wiring harness between the coach batteries and the coach builders fuse.

Thing is its working, but if the current solution causes some strange problems down the road you might consider adding a diode to the supply side of the switch. Needs to be installed in the proper orientation to work!

My instincts tell me one thing and the math says something else,regarding the resistance reading I think you would get; so I will need to ponder the thought a little more.

Rich.

A resistance of 7 ohms, with a current of 1.5 amps would drop the voltage to 2 volts. So a bad connection / splice or corroded connection could be the culprit. That would mean a power drop of 15 watts. Something should be a little on the warm side!

Each rocker switch is supposed to receive 12V. Then the switch sends + or - 12V to the disconnect relays to open/close the relay. The chassis rocker switch is receiving 12V. The coach rocker switch is receiving only 2.5V. I just connected the 12V supply from the chassis switch to the coach switch, and the coach switch now works.

But I think you're right, I could have a short somewhere in the wiring to the coach rocker switch.

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I think I solved the problem of the coach batteries not charging when on shore AC:

The coach battery disconnect relay feeds into a ShortStop 40A circuit breaker. I just realized that there's a little black button that resets the Shortstop breaker. I pushed the reset and it started charging the coach batteries.

I feel kinda dense for not noticing the Shortstop reset, but it is not marked and there are no directions. I'm an engineer but I have no experience with RV electrical systems. I basically had to figure out the entire battery disconnect and charging system. I have spent at least 50 hours on this problem. I took the RV to two RV repair shops around Pittsburgh and neither one of them would even try to diagnose the problem. They said they repair RV's but electrical systems are too complicated for them. I must agree.

I tried to attach a photo of the Shortstop breaker for others, but it won't let me. A window pops up and asks for URL to the image. How do I attach a photo to my post?

To see if the problem of parasitic drain had been solved, I disconnected shore AC and measured 12.58 V on the coach batteries. 18 hours later the coach batteries were at 12.49 V. Now that the batteries are being charged by shore AC, the 40A AC-DC converter should easily cover the parasitic load when on shore AC.

We're going to sell this RV and buy a newer, smaller one -- and I'll be sure to buy a shop manual with it!!!

Thanks everyone!

Frank

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