Forum Discussion

pickjare's avatar
pickjare
Explorer
Mar 23, 2016

General wiring misunderstanding on Nash22H

Hi, I have a 2001 Nash 22h that is new to us. I just modified battery brackets to accept 2 new Trojan 6V T105 batteries. At same time I installed a Pico master disconnect switch rated for 300A continuous with the intention of using switch to disconnect batteries between trips. And at same time I installed the Charge Wizard for the Progressive Dynamics 9140A factory equipped converter. I spent all winter researching these topics, especially from this forum thank you, and thought I new what I was doing. After all the above was complete, I simulated 2 nights of camping by camping in my driveway and measured current draw from furnace (6 amps), lights, etc., and drained batteries down to 65% SOC (12.33V) as measured with a volt meter after 24 hrs at rest with disconnect switch turned to off to see if we can boondocks 2 relatively cold nights. Alright, next I turned the disconnect on and plugged in the trailer to try out the new Charge Wizard. Here's the strange part: at converter positive is red, negative is white--right? Disconnect switch is installed on negative Cable near converter--I thought that would be a nice place for the switch and assumed those cables went straight to battery anyway so why not. With switch on I measured voltage at converter terminals, 14.4 V and with clamp on amp meter, 21 Amps. I went to negative cable at battery terminal and have only 13.7V but still have exactly 21 amps right at battery. Puzzling. I thought I had too much voltage drop Somewhere and was afraid batteries will be undercharged and as I investigated further I found the cables do not appear to run from battery to converter, instead they go to a power panel. So what have I done by installing switch right at converter negative cable? Is that ok? Same as if it were at battery cable right at battery? As I pondered this, I realized the polarity of charging current was backwards. I am using a quality clamp on meter that shows direction to negative battery terminal and at the converter the negative cable shows current moving toward the converter. This is backwards in my mind as the converters job is to charge batteries. Now I'm real confused. I haven't turned on a single light or anything since I plugged in, and I'm leaving it plugged in for now because converter should have blown fuse if polarity is in fact wrong. Must be my way of thinking. Have I explained this ok? Does anyone know what I am seeing here? Thanks.
  • DrewE's avatar
    DrewE
    Explorer II
    Mar 23, 2016
    Usually the disconnect switch is placed in the positive battery lead, I suspect because the negative is often chassis ground and it's too easy to get unwanted sneak paths around the disconnect, especially when there are some things that must be powered all the time. (For example, the emergency breakaway switch circuit for trailer electric brakes should be powered regardless of the battery disconnect state.)

    The current sense doesn't sound backwards to me. The current that goes out the positive lead from the converter needs to go into the negative lead, and vice-versa for the battery. (Technically, of course, the current mostly consists of electrons flowing, and as they are negatively charged it physically flows out of the negative pole of the source and into the positive. Nevertheless, by convention the sign of measurements assumes positive charge carriers. Blame Benjamin Franklin, who had no way of knowing what polarity was correct and guessed wrong.)

    Wiring the converter to the DC power panel is not at all unusual, but by no means universal. It does mean that with the battery disconnected, you can use the converter to power the RV systems. The alternative (which seems a little more useful to me, and actually happens to be how my RV is wired up) is to connect the converter to the battery side of the battery disconnect, which means you can recharge with the disconnect switch open but not have live RV house circuits.

    I think the PD 9140 doesn't have red and white leads, but two screw terminals that the maker of the RV attaches wires to. If there are red and white wires, by convention the red almost always would be the positive and the white the negative.

    To track down your voltage drop, measure the voltage difference between the converter and the battery in the positive wire and in the negative wire, and scrutinize the side of the circuit that has excessive voltage. Even with a relatively long wire run and possibly marginally sized wires, I would not expect a 0.7 volt drop at 21A. My hunch is that you have a poor ground connection at either the converter output or the battery ground connection...but I could very well be all wrong.

About Technical Issues

Having RV issues? Connect with others who have been in your shoes.24,195 PostsLatest Activity: Feb 03, 2025