DC voltage too high on shore power or genny

[Lintfisher]

We have a ‘95 2830IB Designer series.

I installed a SeeLevel II for tank monitoring. This RV has the monitoring panel on the range hood along with the water pump switch and genny switch. So the power for tank monitoring is all powered through the pump power on the DC side of the power panel.

Everything worked fine when we were on the house battery but I noticed that the monitor display went a little haywire when the shore power was connected or the genny was running and gave anything but accurate readings. It would go back to normal when back on house battery.

Checking the voltage at the display wires: on battery it was 12.7V, on shore power it was 19V, and on Onan genny it was 23V! I checked this at the Power panel too and got the same readings on the DC Main leads and all the fused circuits except for 3 that are unused and labeled “Accessory circuits”.. those 3 circuits read the proper converter voltage of around 13.6V.

Now it gets weirder….when I checked the voltages above, it was day time and I didn’t have lights or anything else on in the RV. The next evening I checked them again, but since it was dark, I had a few lights on. Now the voltages for shore power and genny running were typical converter voltage of 13.6V Go Figure!

I checked this again while I had the volt meter leads connected on both Shore and Genny and could switch a light on/off(any light, I tried several) with light off, voltage was high. With light on, voltage was 13.6V.

Any Ideas what could be causing this? I’m afraid I’ll cook the SeeLevel II monitor display if continue as is and they’re $90 to replace.

[JimD]

Your converter is what supplies the 12 volt charging voltage when either plugged into shore power or operating off the generator. Measure the voltage right at the converter and if it is way out of spec, replace the converter.

I wouldn't leave it powered up until you find the source of the problem as extra high charging voltage could damage the battery.

I have included the charge voltages from my converter.

I have the SeeLevelII system and if I ever use it to check voltage (I have a separate constant battery voltage display that I use) it always reads in range.

[Lintfisher]

Jim,

Thanks for your response! I was measuring voltage from the converter(old MagneTek).

In the attached photo, you can see the 3 wires coming from the converter below the DC fuse panel. Both the red wire and blue wire power different sections of the panel that I’ve boxed in Yellowowered by the Blue wire, and Green: powered by the Red wire.

I’m trying to figure out how having an interior light on affects the voltages.

Under Shore power or Genny, when I test the Red wire or any of those Green fuse sockets, I always get around 13.6V whether a light is on or not. When I test the Blue wire or any fuse sockets in the green box, if all interior lights are off, they will read at 18V or more, yet when even 1 light is on, they will read 13.6V.

The other photo explains about the 2 different load types(“A” being the Yellow box and “B” being the Green box) but I don’t really understand the difference unless they just mean the “B” power is cleaner, without interference for radios and such.

It seems like the battery is safe because that big red wire in the Green box is the one going to the battery so regardless of the condition, it’s not getting more than 13.6V.

I don’t know why the blue wire is sending that higher voltage to the coaches other devices(lights,motors,pumps) but they seem to handle it OK. The bummer is, that’s what is powering the SeeLevel II display in the range hood because its the water pump power. To run a wire from the “B” box would mean tearing apart the range hood and some cabinetry to get the wire up there which I’m hoping to avoid obviously.

But I’m really scratching my head on the voltage changing when a light is on or off!

[JimD]

Definitely a strange way of doing things by having 2 separate power feeds. From what I see online, there were upgrades to the old MagneTek converters because they were only single stage converters and weren't all that great.

Anyway, I will guess at what is happening using my electronic tech knowledge and power supplies.

The one solid voltage measurement is probably the one connected to the battery. The battery will load down the charge voltage and filter it basically so it is a smooth waveform hence the nice constant voltage reading.

The other line feeding 12 volt items looks like it is unfiltered and possibly the converter is throwing out a sawtooth or other waveform that is not a nice smooth filtered one. An unfiltered voltage will basically jump up much higher than its target value and then back down. This would easily be seen with a scope which most people don't have access to.

Ok, this "sawtooth" waveform will jump to some upper value which in your case is around 18 volts. Most meters will read these spikes and give you a reading closer to what the spikes are reaching. So why does it drop when something is turned on? Because you now have "loaded" down the circuit causing the spikes to greatly subside.

Many cheap battery chargers just throw out pulses to charge batteries. This is for any type charger not RV related. When you connect the battery the pulses will smooth out and the voltage reading will drop to around normal.

One of the things I noticed was a warning on one of the labels to not connect a capacitive load to the output. This tells me the output is pulsed because if you connect a capacitor to a pulsed voltage it will smooth it out but it smooths it out at the peak value of the pulses (until loaded a bunch). So if the pulses go up to 20 volts and you connect a capacitor to it, you will get a nice smooth 20 volts. Not good in an RV.

Sorry about all the electronic theory. I cannot help myself. It just comes leaking out of my brain since I dealt in it for over 45 years.

So, what should you do? If it were me I would chuck all the old tech there and install a modern converter with a fuse panel that connects everything to one voltage feed. There is no reason to have 2 separate 12 volt sections.

Your SeeLevel system, if connected to this pulsating voltage, will not appreciate that environment as you can see by it going nuts. A quick bypass to your problem is to leave a load on the pulsating line to smooth it out. Kind of a waste of power though. It may not take much of a load to smooth it out.

[Lintfisher]

Love the electronic theory Jim, that all makes sense.

Seems like I might be able to replace the converter only and feed that smoother voltage supply to the existing DC panel to both locations, so to where the blue wire and the red wires are terminated. See any problems with that?

Thanks for sharing all your knowledge!

Larry

[JimD]

I see no problem in just upgrading the converter since you know to tie the separate fuse busses together. Ah crap, I now have the tune "The Wheels on the Bus Go Round and Round" going through my head. Had my grandkid over yesterday and that tune came up.

[Lintfisher]

Jim,

One more question for you on this….I replaced the converter/charger module with an Iota DLS 45A and now I have the same voltage on both 12V fuse busses so I think I’m good with that now, but the Iota has a Chassis Bonding Lug that I’m guessing I need to tie in somewhere.

There’s a big bundle of ground wires all coming together from everywhere in the coach to the back of the fuse bus. Can I assume one of those ties into the chassis making that a good place to bond the Iota or should I tie it into the metal box that holds the fuse bus and line voltage breakers?

Thanks,
Larry

[JimD]

I would say that as long as all ground wire connections are tight, they all will lead to the same place which will be the metal chassis. If you can find the wire that actually connects to the chassis you could tie into the location where it connects inside.

I am assuming that the converter has a negative output lead that feeds everything that is 12 volts and that the bonding lug is just there as basically a safety ground because there is 120 volts inside. If that is the case I would assume you could connect the bond to any other 120 volt bonded box. That would probably be the breaker panel. In any event be it a safety ground or negative 12 volt line, they all end up connecting to the metal frame eventually.

Maybe an electrician on this forum could chime in with the "legal" mumbo jumbo.