Voltage drop through disconnect

[Redwood65]

HI everyone! I am a NB

This looks like a way cool site to bounce Q's and ideas around. Of which I have a question to post.

I am getting about a 50% voltage drop through my disconnect box. I have a 120v Pmax, Poly cell panel on the roof of my RV and the Voc rating is 21.5v. My panel is almost flat on the roof and 10awg solar wiring in the circuit, I am getting 18.5 to 19.4v with full direct sun at the panel, and just before the disconnect box "pull blades". After the blades it drops down to 9.2 to just under 10v.

I am stumped as to what is going on. Could it be just oxidation on the terminals?

Please help.

[inetdog]

HI everyone! I am a NB

This looks like a way cool site to bounce Q's and ideas around. Of which I have a question to post.

I am getting about a 50% voltage drop through my disconnect box. I have a 120v Pmax, Poly cell panel on the roof of my RV and the Voc rating is 21.5v. My panel is almost flat on the roof and 10awg solar wiring in the circuit, I am getting 18.5 to 19.4v with full direct sun at the panel, and just before the disconnect box "pull blades". After the blades it drops down to 9.2 to just under 10v.

I am stumped as to what is going on. Could it be just oxidation on the terminals?

Please help.

Hello Redwood65, and welcome to Solar Panel Talk!

Depending on how much current your load (a charge controller?) is drawing, the power lost in a voltage drop of 9 volts will be generating a lot of heat and something should be getting very noticeably warm.
Did you make both measurements with the switch closed? Otherwise you would be comparing Voc from the panels to whatever the voltage drops to with the load in place.
If you have no load(s) connected, then there is no way to drop voltage across the switch contacts.
Try measuring directly between the panel side of the disconnect and the load side of the disconnect with the switch closed. (Measure each pole separately). Tell us the result.

[Redwood65]

Hello Redwood65, and welcome to Solar Panel Talk!

Depending on how much current your load (a charge controller?) is drawing, the power lost in a voltage drop of 9 volts will be generating a lot of heat and something should be getting very noticeably warm.
Did you make both measurements with the switch closed? Otherwise you would be comparing Voc from the panels to whatever the voltage drops to with the load in place.
If you have no load(s) connected, then there is no way to drop voltage across the switch contacts.
Try measuring directly between the panel side of the disconnect and the load side of the disconnect with the switch closed. (Measure each pole separately). Tell us the result.

Thanks inetdog for the welcome.

Yes, I did take both measurements, before and right after the switch contacts, with the switch closed. I will take an amp. reading tomorrow on both sides to see what those readings are as well.

This is a simple circuit, PV Panels to disconnect and fuse (after the switch) box, then to a PWM charge controller, and to the 2, 12v batteries. The readings are the same going into the charge controller, ~9.3 to 9.9v. Needles to say, I am not charging my batteries very well right now.
I will take your suggestions and report later.

[inetdog]

Thanks inetdog for the welcome.

Yes, I did take both measurements, before and right after the switch contacts, with the switch closed. I will take an amp. reading tomorrow on both sides to see what those readings are as well.

This is a simple circuit, PV Panels to disconnect and fuse (after the switch) box, then to a PWM charge controller, and to the 2, 12v batteries. The readings are the same going into the charge controller, ~9.3 to 9.9v. Needles to say, I am not charging my batteries very well right now.
I will take your suggestions and report later.

While you are at it, measure your batter voltage at the same time.
I was not asking for the voltage before and after, I was asking you to put on voltmeter lead on one side of the contact and the other side on the other, then open and close the switch to see whether there is any change. If not, then the switch is just completely open (defective or burned out) and the voltage you are seeing is just the leakage back through the CC.
Is the switch in the disconnect rated for use with DC?

[SunEagle]

While you are at it, measure your batter voltage at the same time.
I was not asking for the voltage before and after, I was asking you to put on voltmeter lead on one side of the contact and the other side on the other, then open and close the switch to see whether there is any change. If not, then the switch is just completely open (defective or burned out) and the voltage you are seeing is just the leakage back through the CC.
Is the switch in the disconnect rated for use with DC?

Good direction to finding the issue.

I also think he has an open fuse and is measuring the battery voltage on the load side of the switch.

[Redwood65]

HI everyone! I am a NB

This looks like a way cool site to bounce Q's and ideas around. Of which I have a question to post.

I am getting about a 50% voltage drop through my disconnect box. I have a 120v Pmax, Poly cell panel on the roof of my RV and the Voc rating is 21.5v. My panel is almost flat on the roof and 10awg solar wiring in the circuit, I am getting 18.5 to 19.4v with full direct sun at the panel, and just before the disconnect box "pull blades". After the blades it drops down to 9.2 to just under 10v.

I am stumped as to what is going on. Could it be just oxidation on the terminals?

Please help.

Thanks for the responses and help guys.

I am new to almost all of this, and so I went back and did some more research on my charge controller on the net (no manual came with it), and found out my issue. I have a negative ground for my trailer / Batteries, so this is what is messing with my system. I do not understand the how or whys of it and how it works that way, but I need to find a PWM or MPPT that can handle a negative ground system and not cost me an arm and a leg. I'm open to any leads or suggestions. All of the controllers I have found so far are about $200.

Thanks again for your help and responses.

[Sunking]

No ground is needed.

[Redwood65]

No ground is needed.

Thanks Sunking

The ground is for the trailers circuit that the batteries are in. It is a 5th wheel so it has some load the need to be grounded, especially when I've got it hooked up.

I think I have isolated the issue to the charge controller. I had the charge controller connected to the battery and trailer circuit before i connected the solar panel circuit to it ( as was the instructions), so when i did all my tests at my switch, the charge controller was still connected and i think was messing with my voltage in the system, giving me the voltage drop. I am getting the voltage I should - 19.3 at the leads going to the controller - but not connected to the controller.

Thanks for the help