Since you are trying to understand your coaches voltages, I'll give you some details which I hope aren't too gory, but may help explain why you are seeing different voltages that might initially not make sense.
There's a number of different 'types' of 12v they could be, you'd have to just experiment to determine which one. They could be connected to:
- the chassis batteries, hot all the time
- the chassis batteries, only hot when the key is on or accessory position
- the house batteries, hot all the time
- the house batteries, hot only when the salesman switch is in the ON position
- the house batteries, managed/controlled by the Spyder system (I'm assuming your coach has a version of this).
If you are looking purely at the 'voltage' at a socket, then you should understand a couple characteristics that are at play.
- When the engine is running, the alternator will produce a charge voltage to the chassis batteries that is in the neighborhood of 13.5 to 14.2 ish volts. This may vary slightly for each alternator, just know what yours produces under normal circumstances. That isn't necessarily the voltage that the battery would show on it's own at that point in time if the engine were off, it's just the voltage that is driving current to the battery bank recharging it. So your chassis battery may be half charged, or full charged, but still showing that same voltage while the engine alternator is running.
- When the engine/alternator is running, coaches have a device (called different things and may work slightly differently, but effectively perform same function) called a charge solenoid, which when turned on my the alternator running, will connect the chassis and house battery banks together. It's purpose, is so the engine alternator while you are driving, will now also recharge the house batteries. So here again, the voltage you would expect to see if the socket was connected to house battery is the same charge voltage as the chassis batteries. (Technically it might be slightly different, if instead of a charge solenoid they're using a diode bank, but once again, you can learn how your's works). It is that same charge controller device that the red button on your dash turns on, that you press when you are trying to get enough battery capacity to start your engine if your chassis batteries are low.
- If the engine is not running, but you are connected to shorepower (or you are running the generator making 120vac), then your converter is working, and it will be charging the 'house' batteries. Newer converter have a technology called 'multi-stage', where it changes the charge characteristics used based upon the discharge state of the house batteries. Deeply discharged, will be in a bulk charge mode. Close to full capacity, will be in a float mode. They do this as to not overcharge your batteries and cause them to boil the water out. If you look up the technical specs of your individual converter, you can find the different voltages that you would expect to see. So on your little voltmeter, you should expect to see different voltages, depending upon which charge stage your converter was in.
- You will find a couple different possibilities for your chassis batteries, when the engine is not working and you are plugged into shore. You could have nothing keeping your chassis batteries charged, you might have a little trickle charger like a battery minder (which is plugged into 120vac, and trickle charges the chassis), or the prior owner might have installed a device like an amp-l-start, which steals some of the current that the house battery is getting from the converter, and uses it to charge up the chassis battery. There are some other possibilities as well. So what you should expect to see if looking at the chassis voltage might be something like 12.6 volts if nothing is charging, to something in the 13.5 volt range. You'll just have to investigate what your coach has.
- If neither the engine alternator is charging, or shorepower is charging, then you are running off your house batteries. Unfortunately the voltage you will see on the batteries varies, both by it's SOC (State of charge), but also whether the battery is 'at rest', having current being drawn from it, or having residual 'surface charge'. Google those terms to get an understanding of how they effect your voltage reading, and get the chart which shows for any given SOC, what voltages you would expect whether at rest or in use.
Personally, this is way too complicated to answer the simple question that I want to know which is 'how full are my batteries'. I didn't want to have to think about whether my batteries were at rest, or being charged....I just want to know are they at 100% capacity or 50 % capacity. or what in between. Some charging systems like my Magnum, have add on functions (BMK) which monitor the 'current' (amps) going into and out of the battery bank. It is no longer reliant on 'voltage' as it's only indicator. So my system now works like a fuel gauge, it gives me a SOC% to tell me that my battery bank is now full, or it's at 74% capacity or 57% capacity etc.
I do have one of the dash plug in voltage meters
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1 My dash outlet is on the house battery bank, and I use it only to know while I'm driving that my house batteries are seeing a charge voltage (ie, that the alternator is working, and that the charge solenoid has engaged). A regular LCD digital voltmeter (not analog dial) will be invaluable or seeing the subtle voltage differences.
So for your coach, I would determine whether my sockets were powered by the house, or the chassis batteries. Were they 'switched', or always on. If the engine is running, what is the charge voltage that you are seeing. If you are on shorepower, what is the charge voltage you are seeing depending upon the multi-stage charging you were in. If not charging, are the batteries at rest, or having current drawn out of them?
Hope this helps. Knowing how your specific coach is supposed to work, and voltages that you typically see, will help you identify when you see something wrong.
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