How is an RV battery wired

  • Hello,

    the following problem has now appeared:

    According to the previous owner, the battery was never properly charged while driving. I wanted to get to the bottom of that now.
    It should be a German RV50 model from 1977. According to the circuit diagram for the German models on "schmudken.de", three cables should come out of the alternator: yellow; Red-white and black.

    For me, however, instead of the red and white cable, a green one comes from the LiMa. This runs via the ignition lock (like the resistor in the circuit diagram, so that voltage is applied to the rectifier for daytime switching, but not for nighttime switching. This means that no battery is charged as soon as it is switched to night, i.e. with lights on ....
    Do you want to just connect the green cable directly to the rectifier, as actually intended for the charging voltage in the circuit diagram (original white-red cable) - or is there something against it from your side?

    - How did you solve the problem with the "day" - "night" switch so that the battery is charged even when the lights are on?
    - And is the current wiring "original" at all? Or is it not a German model?

    Greetings Xaster

  • The first thing to do is look under the panel to see which cable colors come from the engine wiring harness.

    Greetings from the south of Germany,

    Sven &

  • I changed the post, had swapped something ... with the cable colors.

  • Try this circuit diagram

    And check whether the wiring fits:

    197cf8f3bb9e5a60253178598130c6cdcedf02d6.jpg

    Greetings from the south of Germany,

    Sven &

  • You probably just miss the bridge between yellow and yellow / red ...

    If the circuit diagram fits!

    The easiest way is to open the lamp pot and check whether everything is still wired originally and the cable colors are connected 1: 1 to the plug connection.

    Greetings from the south of Germany,

    Sven &

  • The red and white cable doesn't come out of the engine with mine either, only blue black yellow green, yellow or green not being used, which I don't know anymore. The red-and-white arises somewhere in the wiring harness and leads to the rectifier. It doesn't get you much further now.

    Greetings Heino

  • The red and white cable doesn't come out of the engine with mine either, only blue black yellow green, yellow or green not being used, which one I don't know anymore. The red-and-white arises somewhere in the wiring harness and leads to the rectifier. It doesn't get you much further now.

    Greetings Heino

    There are also alternators in which yellow and red / white come out of the engine.

    Greetings from the south of Germany,

    Sven &

  • You probably just miss the bridge between yellow and yellow / red ...

    If the circuit diagram fits!

    The easiest way is to open the lamp pot and check whether everything is still wired originally and the cable colors are connected 1: 1 to the plug connection.

    Unfortunately, not everything in the lamp pot is original anymore. Some cables have been re-soldered, some run into the void. But since all functions are given, that doesn't bother me. The question is actually how you solved the problem with charging the battery, since the RV is no longer diverted voltage to the battery via the rectifier when the ignition lock is switched on at night. Which inevitably leads to the battery being drained by the indicators and brake light, as I want to drive with the lights on during the day too.

    The solution would now be simple to clamp the green cable coming from the LiMa directly to the rectifier so that it always supplies the battery ...

  • So if your wiring harness has been tinkered with so much, I would try to restore it to its original condition, then troubleshooting will be easy for you. In addition, direct wiring from the green cable to the battery is not possible, as the light & charging coil is a coil with a center tap and the voltage regulation works according to the power adjustment principle.

    Greetings from the south of Germany,

    Sven &

  • Hello everyone, hello Sven,

    I think I got the circuit diagram shown above from you too. It fits quite well, although I had a lot of tinkering with it. Over the winter, I brought the wiring harness up to the original status.

    Now, after I took it out of the shed and started it for the first time, I noticed the following:

    - In key position II, with light: battery is not charged. Voltage after rectifier 4V (instead of 6 - 7 V).

    - The headlights are very weak. The filament just glows, like an almost empty flashlight.

    - If I pull the blue bridge on the yellow cable off the alternator (see picture), then no more current flows over the yellow / red cable to the switch and there to the driving light (gray cable). Then I have about 7V after the rectifier and the battery is charged.

    I then charged the battery and it's back to a full 6 volts. I had the assumption that the charging process draws too much current and brings the alternator to its knees (i.e. the voltage collapses). Result: same picture, max. 6V battery voltage after rectifier, instead of 7V. Light weak.

    Resistance "blue bridge" measured on ground (front and rear light in parallel connection). Result approx. 2 ohms. That didn't seem like much to me. But if you calculate the resistance of the 15W front light and 5 W rear light, then I come to 1.8 ohms. I.e. that could be realistic.

    Unfortunately, I cannot measure the alternating voltage from the alternator (yellow or Y) precisely because my alternating current meter has a range of up to 1000V and the pointer only twitches slightly. My test lamp burns differently, which roughly corresponds to the voltage. So bright when the lights are off. Dark when the light is on.

    Could it be that the alternator (yellow cable) is too weak or defective?

    Greetings Harald

    Circuit diagram bridge.JPG

  • What lights up or does everything work when the engine of your RV is off and you have the ignition key in position 2?

    Greetings from the south of Germany,

    Sven &

  • Hello Sven,

    Without the engine running and the key on level 2: idle lamp, turn signal, brake light work.

    Could it be that the coil of the Lima has too high an internal resistance or contact problems (transition resistance). Then with a higher current (light on) there would be a larger voltage drop at the contact resistance and there would be too little left for the light.

    Greetings Harald

  • Hello,

    so the theory with the large internal resistance or contact resistance could not be confirmed. I measured it. Ohmmeter shows zero ohms on line width, as when holding the cables together.

    My next guess is this Rectifier. It doesn't look entirely original in my opinion. He has passage. If I apply the 6V DC voltage of the battery to the ~ voltage side, then only 5.5 V arrive on the + side. (I had imagined that I had already tried it the last few days and it would have been 2V less. But now I'm not so sure anymore).

    What do your rectifiers look like? I once attached a photo of mine.

    Greetings Harald

    IMG_7629.JPG

  • Hello Harald, it is not a real rectifier, here only the negative half-wave is cut off via a diode.

    If you measure approx. 5.5V in the DC voltage range with your multimeter, that fits, because you have a voltage drop of approx. 0.5 to 0.7 volts across the diode.

    Can you measure a higher voltage on the battery with the engine running in comparison?

    Or how old is your battery, or what voltage does it have when you charge it externally via a charger?

    Greetings from the south of Germany,

    Sven &

  • Hello,

    I measured around a bit today.

    - Rectifier: has an internal resistance of 25 Ohm (forward direction). - Is that normal?

    - Alternator (yellow cable) output (measured with 500 V measuring range, 1 division 10V, lowest range):

    - all plugs removed - approx. 20 V ~

    - only rectifier connected - approx. 10 V ~

    - only light (blue bridge or red / yellow) connected - approx. 4 V ~

    - Light and rectifier connected - also 4 V ~

    Have you ever had problems with the alternator coil? In a Ducati forum I found something about the fact that the insulation can become porous ...

    Does anyone have the exact details of the alternator coil? I can't find anything about this in the service manual.

    Do you need a special puller to dismantle the rotor, or are there alternatives?

    Greetings Harald

  • Hello Sven,

    the battery is new and has almost exactly 6 V when it is charged with the charger.

    When the engine is running, I only have 6V on the battery / diode. Unless I unplug the light cable, then I have a little over 7V.

    Greetings Harald