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johntaves · 11-23-2017, 02:06 PM

Can anyone explain why I have 9v and 11v wires?

I have a 04 gulf stream crescendo 8356 diesel pusher with freightliner chassis and cat.

I have removed the front TV, and the front and side cabinets and replaced with my own cabinets to eliminate the TV. That also eliminated the CRT backup camera, 2 fans, and 2 lights where 1 is controlled by a switch on the dash.

I am trying to make sense of the wires that I cut and am getting goofy voltages. My coach batteries are now 24v (part of installing solar) so I have a DC/DC converter that outputs 13.6. The starter batteries are reading 12.6.

I have found the fan wire, it reads engine voltage (12.6v, and 13.xv when engine is running). I found the reverse wire (for the old backup camera). I found some coach wires (13.6v). I found the ignition wire (to turn off the TV when on).

However, the wire that controls the passenger reading light, is reading 11.5v. I get that voltage at the switch on the dash too. The voltage does not change with the ignition or when the engine is running or with the starter battery disconnected.

There is another wire that reads 9.6v.

If I turn off the coach power, I get .25 volts slowly decreasing, which makes sense because the DC/DC converter has some capacitance. The 9v and 11v wires read similarly. So I know the 9v and 11v are eventually coming from coach power.

It used to have a Xantrex charger so the coach power would have been anywhere between 12 and 15v, so I get that if they wanted to put in some sort of appliance that couldn't handle 15v, they would protect it with some DC/DC thing that maybe output 11v.

I figured the 9v would be for the backup camera. It used to have a voyager. However, the backup CRT says input voltage 11v-30v, which tells me there is no reason to have protected it from the 15v that the charger could produce and of course it only needed to be connected the starter battery anyway.

I see no reason that the passenger light needed 11v and i don't see another 11v wire for the driver's side, which was the same light figure but was not switched at the dash.

I searched for a DC/DC converter, or any sort of power conditioning thing, but failed to find something. I didn't take apart the dash, so something could be lurking there. The compartment in front of the driver's tire has a pile of relays and fuses, but nothing that seems like it would be a converter. Everywhere I poke, I get 13.6v (coach) or 12.6v (starter). There is a big bundle of wires with "diode" on it.

The compartment in the rear between the starter and coach battery compartments has 2 lumps that I assume are the engine and transmission computers. Other than those 2 unknown lumps I only see relays and fuses in there.

Can anyone explain how i measure 9v and 11v? Oh, the trimetric meter says that I am drawing 1.5amps @24v. I have trouble believing that I am reading some voltage after some load, but maybe that's what is happening.

Thanks

jt

Winemaker2 · 11-23-2017, 02:57 PM

Dimmer on reading light?

MSHappyCampers · 11-23-2017, 02:57 PM

Hi !

Welcome to IRV2! We're sure glad you joined the gang!

The only thing that comes to mind is that the different voltages have different ground references. If that is the case, and you are measuring them from the same ground reference, then you could potentially get wrong readings.

Keep her between the ditches!

Good luck, happy trails, and God bless!

johntaves · 11-23-2017, 03:04 PM

Quote:

Originally Posted by Winemaker2

Dimmer on reading light?

Thanks for the idea.

The light is long gone. There would need to be a dimmer before the on/off switch. I will double check that neither the 9 or the 11 varies with the dash dimmer. I assume they don't because the dash dimmer is dead when the starter battery is disconnected and/or the ignition is off.

Winemaker2 · 11-23-2017, 03:06 PM

Driver map light ony old Winnie had a dimmer...just a thought

johntaves · 11-23-2017, 03:07 PM

Quote:

Originally Posted by MSHappyCampers

The only thing that comes to mind is that the different voltages have different ground references. If that is the case, and you are measuring them from the same ground reference, then you could potentially get wrong readings.

Even if these had a tortuous route back to ground, the voltage drop would only happen when there were some amps flowing. The volt meter of course draws next to nothing.

Winemaker2 · 11-23-2017, 03:07 PM

Quote:

Originally Posted by Winemaker2

Driver map light ony old Winnie had a dimmer...just a thought

Or maybe just a poor connection somewhere on the feed??

YC1 · 11-23-2017, 04:30 PM

Sounds like a bad connection. Grab a 12 volt bulb from something, like the old light it was connected to and use that as a load for those wires. IF the voltage goes lower it is a bad connection and you need to trace those wires.

If you really want to trace the wires connect a signal tracer and chase them down. They are not expensive.

Sure curious why you would go to 24 volts and use a DC/DC converter. Seems like a waste of power.

johntaves · 11-23-2017, 10:04 PM

Quote:

Originally Posted by YC1

Sure curious why you would go to 24 volts and use a DC/DC converter. Seems like a waste of power.

I wanted to use the bogart engineering sc-2030 solar controller. As far as I can tell, it is the only one that measures the amps going in/out from the battery, instead of just measuring the amps/volts leaving the controller. By going to 24v battery bank, I halve the amps coming down from the roof for the same watts. That means I can run smaller wires. The sc-2030 will output max 30amps, so with 24v I have double the watts. A nice benefit is that the motors (slides and jacks) always get 13.6v.

There are drawbacks. I can't charge from the alternator, but so what? If solar can't keep up, start the generator when driving. The other drawback is that I can't add 50% more capacity by adding 2 more batteries.

There is a loss in the DC/DC, but I doubt that I will know what I am missing.
It means I have a something like a 215ah battery instead of a 220. I doubt I will find that my batteries are too small by 5%.

YC1 · 11-24-2017, 05:09 AM

deleted

wildmanbaker · 11-24-2017, 07:32 PM

You do know that there are solar charge controllers that can handle up to 48 volts, and outputs 12 volts. Just like you mentioned, the advantage it more ampere output from the same amount of panels. I do not see any advantage to using 24 volts and a DC to DC converter, but you already have the system, so good luck.

garbonz · 11-24-2017, 08:53 PM

Makes no sense, the solar controller handles the voltage reduction. Don't need the batteries to do that.

twinboat · 11-25-2017, 03:47 AM

Standard PWM solar controllers clip the voltages from the panels at the charging voltage settings ( 12 or 24 volts ). They work like quickly switching a light switch on and off so the room doesn't get to bright.

If the panel is producing 18 volts ( in the OPs case 36 volts ) , PWM lets 13.5 ( 27 ) to 14.6 ( 29 ) get to the battery, wasting the other 4 or 5 volts.

MPPT controllers convert the higher voltages to usable voltages, so all of the panels output is used. If the panel is producing 18 volts, it converts the 18 volts into 14.6 volts, while increasing the amps. No waste.

My MPPT controller theoretically can converts 108 volts@ 7 amps to 14 volts@ 60 amps. That's with 3 panels in series and 12 gauge wire from panels to controller.

wildmanbaker · 11-25-2017, 10:50 AM

Quote:

Originally Posted by twinboat

Standard PWM solar controllers clip the voltages from the panels at the charging voltage settings ( 12 or 24 volts ). They work like quickly switching a light switch on and off so the room doesn't get to bright.

If the panel is producing 18 volts ( in the OPs case 36 volts ) , PWM lets 13.5 ( 27 ) to 14.6 ( 29 ) get to the battery, wasting the other 4 or 5 volts.

MPPT controllers convert the higher voltages to usable voltages, so all of the panels output is used. If the panel is producing 18 volts, it converts the 18 volts into 14.6 volts, while increasing the amps. No waste.

My MPPT controller theoretically can converts 108 volts@ 7 amps to 14 volts@ 60 amps. That's with 3 panels in series and 12 gauge wire from panels to controller.

Exactly. By the way "Voltage X Current = Power", you can up the double the voltage and half the current, but it is still the same power, with some losses of course. The OP already had his system working and has accepted it, so..... Just sayin.