Voltage Drop on 320 MKS

[ChristopherBThomas]

Hi this is Chris, Last week I had the bedroom slide on my 320 MKs pull out the wires that power the over-bed lights. This is a common issue apparently. I sorted out the wiring on that, but when checking the voltage I noted the following:
1) no lights on have 12 V nominal although battery voltage is 13.9 V
2) one over-bed light 8.7 V
3) 2 over bed lights 8.5 V
4) only the outside light under the slide 5.4V
5) tank heater switch on 0.0 V

The indications are consistent with and without shore power. I checked the ground and have good ground at the lights and control panel by the door

I am concerned I have a hard ground somewhere when I turn on the tank heater...is there a fuse or control panel to disconnect?
Any advice on isolating?

[Jlawles2]

I'd start by checking your repair. Odd thing, but it's possible that the repair is high resistance not allowing full voltage through. Have you checked the voltage at the switch for the lights?

Tank heater ??? No clue, look for a blown fuse powering the tank heater.

If you mean the over bed light voltage drops to 0 volts when you turn the heater on, check the battery with the shore power disconnected as it sounds like you have a bad battery.

Don't forget to trace the wires back. When they pulled out, it's possible that there is damage where it passes through the floor.

[Jkwilson]

If you had a short significant enough for that kind of drop, fuses would be blown or something would be on fire. Where exactly are you measuring those voltages?

[ChristopherBThomas]

Measuring at the control panel (awning, tank levels, etc). The circuit in question powers:
1) bedroom over bed lights and under slide lights.
2) Tank heater (freeze protection) on off
3) Tank level indicator circuit board.

Note, I ran an independent chasse ground wire and I have a good ground. Tested voltage drops with both ground wires, and have a 2 ohm from my temp ground wire back through the installed ground so I think that is OK.

I disconnected the bedroom and under slide lights are fed from the same line. And got the same low ground indication when activating Tank Heaters. Then I connected the bedroom lights to a different circuit without issue. - no voltage drop. It is not my repair.

I re-connected the bedroom lights and disconnected the tank heaters, then turned on the lights and got the voltage drop again.

Did the same with the indicator circuit -

SOOOO - I think the circuit for the lights and tank heater, and indicators are OK, the problem seems to be whatever feeds power. If it is loaded it can't supply. No wetness or chaffing detected.

It is not at all clear what/where the power supply is or where the fuse is. I want to check for loose fittings/corrosion.

Thanks for the help!!!!!!

Chris

[Jlawles2]

not knowing where the convince center and power panel are in reference to each other i am going to guess the wires come out the back of the convience panel, go right into the bathroom wall then down to the basement. You will find a mass of wires coming down if you pull the front compartment back wall. From there they branch out all over the camper.

[ChristopherBThomas]

Troubleshooting update:

7.5-amp fuse was blown but not indicating blown. Replaced- All lights services work properly.

BUT:

I have an 11.5 V induction voltage on the DC bus: specifically on the 7.5-amp fuse, and on other unused/unfused ports I read 11.5 V on the PROTECTED side. It is enough to drive the overbed LEDs, but that is it.

This is why i was seeing what appeared to be a hard ground as I added loads

But concerned now that I have a ground issue on the DC bus.

Any recommendations on chasing this down??

[howson]

11.5 V induction voltage on the DC bus

???

Induction voltage means (to me) an Alternating Current (AC) voltage being induced (or produced) in a wire due to electromagnetic force (emf). (Yes, I got part of that statement from Wikipedia. I knew what I wanted to say but it said it better.)

Is it being stated that there's an 11.5vAC measurement on the DC circuit? Or am I misreading the stated symptom?

Howard

[Jlawles2]

You an get DC inductive voltage. That's how wireless charging works.

[Jkwilson]

You an get DC inductive voltage. That's how wireless charging works.

Wireless charging is high frequency AC rectified to DC. Inductive coupling only works with changing voltage or moving wires.

[ChristopherBThomas]

All, I have reached out to the manufacturer of the fuse panel. My thought is that there is an indicator light that should light up when there is a loss of power on the protected side (blown fuse). These lights must have power, and i suspect that since my lights don't work (they were possibly damaged as a result of cables being pulled out by the bed). In any case, I think the power for that blown fuse indicator was what was powering my lights with a blown fuse. Enough power for that light but not enough for anything else.

I will let you know what the manufacturer says.

Chris

[Country Campers]

I have had and seen blown fuses with no light indication. Not sure if there is an issue or just poor circuitry, hopefully you get some good information.

Brian

[TedS]

I think the circuit with the blown fuse must have a closed circuit in order for the indicator light to shine. Otherwise there is no path for current flow through the led to illuminate it. The led is wired in parallel with the fuse.

[ChristopherBThomas]

All, I corresponded with the Fuse Box manufacturer, and they indicated that the in a BLOWN FUSE or NO FUSE condition, there will be a voltage present that drives the Blown Fuse indicator and could light a low-power LED in blown fuse condition - specifically: Blown Fuse does NOT mean Zero volts on the protected side. As Ted mentions above, this is a result of the indicator light circuit in the PD60 Fuse box.

Thanks for all your thoughts on the subject...My system if up an operating.

Chris

[Jlawles2]

Note I have experience several (from old school glass to the new mini blade style) of fuses that appear to be good to only have a bad internal connection. In some cases it was enough to send voltage across the fuse but not enough to activate the circuit in question.

As a result of many many headaches in dealing with fuses and not trusting the little LED's on modern panels to indicate, I err on the side of test everything. I test BOTH sides of a fuse, any difference in voltage and it gets pulled and replaced (again headaches).