Had a weird thing happened with MH 12 volt

[GlennLever]

Had a weird thing happen, had no power in the MH (12v) motor cranked and headlights and stuff worked.

Used a test light and the coach batteries seemed dead.

Plugged the MH in and everything worked.

Unplugged it and everything still works, and the battery status say they are all good.

Tested the coach batteries with the test light and it was still very weak (went across two 6 volt batteries to get 12 Volts for the test light). Test light was bright across the chassis batteries.

The batteries are all new Delco batteries.

Thoughts?

[jesilvas]

My idea is you can't trust a test light. It just shows voltage or not. Not actual numbers. You need an actual volt meter for that.

[GlennLever]

Originally Posted by jesilvas

My idea is you can't trust a test light. It just shows voltage or not. Not actual numbers. You need an actual volt meter for that.

Actually I disagree with this, A volt meter uses no current and a dead battery can still read 12 v on a meter if there is no load on the battery, an incandescent bulb uses current and it it is dim indicates no current.

That really is not the point though, nothing worked inside the MH (v12), hooked up shore power and everything worked, removed the shore power and everything still worked and the battery status indicated the MH batteries were in good condition. The MH status checker would not even function before shore power was hooked up?????

[terry735001]

Originally Posted by GlennLever

Actually I disagree with this, A volt meter uses no current and a dead battery can still read 12 v on a meter if there is no load on the battery, an incandescent bulb uses current and it it is dim indicates no current.

That really is not the point though, nothing worked inside the MH (v12), hooked up shore power and everything worked, removed the shore power and everything still worked and the battery status indicated the MH batteries were in good condition. The MH status checker would not even function before shore power was hooked up?????

you are right ...there are some good videos showing how to test a motors ECM this way and well only show the err if a test light is used

[Old Bounder]

It sounds to me like you have a loose or corroded connecton in the house battery area. Firing up the converter with shore power probably temporarily bridged the gap, but it will be back.

[GlennLever]

Originally Posted by loulong

It sounds to me like you have a loose or corroded connecton in the house battery area. Firing up the converter with shore power probably temporarily bridged the gap, but it will be back.

New batteries were installed less than a year ago, all battery connections were cleaned at that time and all cables are in good condition.

[TeJay]

When you first had the problem the engine cranked and your headlights worked. That's because you were using current from the engine (cranking) battery). Stuff inside the MH didn't work because they were using the coach batteries. I think you understood that part.

There is switching that takes place when you charge from the coaches alternator and then switch to shore power. I have not seen the schematic for the switching that switching but I'd guess that's where the problem is.

It is my understanding that there are remotely operated switches called solenoids designed very much the same as a starter solenoids. They are a high current carrying switches that are operated by energizing (creating a magnetic) a coil of wire which in turn closes the switch and high current can then pass. These switches can and will over time deteriorate and become a high resistance connection which stops most if not all current flow.

When a starter solenoid fails in a cranking circuit we hear the solenoid click. Either the battery is weak and can't provide enough current or the current flow to crank the starter is blocked by the high resistance connection in the solenoid. Inside the solenoid is a copper clad washer that rotates. Over time the sparks created each time it is energized gradually wears the copper off the washer. Sometime it works and other times it won't because each time it's hitting a different spot to make a connection.

Since this is an intermittent electrical problem that's where I think I'd start my trouble shooting. You could locate the schematic and then the solenoids. They are not to expensive and could just be changed to see if that fixes your problem. They can be tested with a voltage drop test but that's another matter.

Please keep us advised as you get this issue resolved. We will all benefit.

Thanks,
TeJay

[GlennLever]

Originally Posted by TeJay

When you first had the problem the engine cranked and your headlights worked. That's because you were using current from the engine (cranking) battery). Stuff inside the MH didn't work because they were using the coach batteries. I think you understood that part.

There is switching that takes place when you charge from the coaches alternator and then switch to shore power. I have not seen the schematic for the switching that switching but I'd guess that's where the problem is.

It is my understanding that there are remotely operated switches called solenoids designed very much the same as a starter solenoids. They are a high current carrying switches that are operated by energizing (creating a magnetic) a coil of wire which in turn closes the switch and high current can then pass. These switches can and will over time deteriorate and become a high resistance connection which stops most if not all current flow.

When a starter solenoid fails in a cranking circuit we hear the solenoid click. Either the battery is weak and can't provide enough current or the current flow to crank the starter is blocked by the high resistance connection in the solenoid. Inside the solenoid is a copper clad washer that rotates. Over time the sparks created each time it is energized gradually wears the copper off the washer. Sometime it works and other times it won't because each time it's hitting a different spot to make a connection.

Since this is an intermittent electrical problem that's where I think I'd start my trouble shooting. You could locate the schematic and then the solenoids. They are not to expensive and could just be changed to see if that fixes your problem. They can be tested with a voltage drop test but that's another matter.

Please keep us advised as you get this issue resolved. We will all benefit.

Thanks,
TeJay

Thanks, next chance I get I will check the solenoids

[TeJay]

I'll also add this regarding what "loulong" referred to in his post. Any large gauge wire carrying a lot of current if corroded will also limit the amount of current it can carry. Removing each connection at those solenoids or any of those heavy wire connections and brushing them with a wire brush to clean the corrosion is a must do.

What ever you do don't forget the ground connections. Ground connections have to carry the same amount of current as the hot ones do. They are JUST as important as the hot connections but often forgotten when servicing.

TeJay

[wa8yxm]

Leave plugged in for 72 hours