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Old 04-20-2016, 12:54 PM   #31
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Originally Posted by WolfWhistle View Post
The OP can install a meter anywhere but if it is battery that holds interest then it must be connected at the battery.

The meter has small leads because its resistance and load is tiny. But it causes voltage drop... very little but it does. Its impedance is small... or high.

A load, any load (resistive) causes a voltage drop (DC to keep it simple). It is ohms law. There is resistance in a wire, any wire. Add this resistance to that of powered devices and current increases. Batteries can't magically increase voltage to compensate; so voltage can only be less across a load. With a digital volt meter read your batteries (not being charged - resting) while doing that, turn on an appliance that offers a substantially load then look... tell me if the reading changes. Try it you'll be amazed.

No, I won't be amazed. I know what will happen. We are getting way off topic though and not helping the OP at all now.


07 Dodge 1500 crew cab with 20" wheels, 08 Forest River Rockwood Signature Ultra-lite 8280SS
"The reasonable man adapts himself to the world; the unreasonable one persists in trying to adapt the world to himself. Therefore, all progress depends on the unreasonable man."
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oldtool2 is offline   Reply With Quote
Old 04-20-2016, 04:33 PM   #32
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Originally Posted by WolfWhistle View Post
The OP can install a meter anywhere but if it is battery that holds interest then it must be connected at the battery.
I think I understand the reasoning behind the disagreement now. You are envisioning measuring the current or AH from the battery - Trimetric or similar. In that case, a shunt (resistor) is placed in SERIES as close to the battery as possible to capture every bit of current flowing from the battery. The shunt is probably on the order of 0.005 ohms (must be accurately manufactured to get good readings) to keep the voltage drop across the shunt to a minimum. Even at that value shunt, it's easy to get a drop of 0.1 volts or more between converter and battery.

The OP is installing a voltmeter inside or outside her camper - which is a pop-up camper with limited 12V loading. The voltmeter, which is placed in parallel, not series, with the rest of the camper, has an internal resistance of 100K or better (usually 10M or better). The voltmeter's resistance - in parallel - would reduce the overall camper resistance in the 6th decimal place at worst. It's not going to be measurable or noticed.

If there is no shunt - OP was talking voltmeter, not Trimetric - then there is only the voltage drop in the camper wiring to make the voltage inside the camper different from the battery. A pop-up camper has minimal loads and minimal wire lengths compared to a 35ft travel trailer. You have a heater fan (4-5 amps) if in use, 2 inside LED lights (0.8 amps) if in use, an automotive stereo (unknown) if in use. The possible CPAP and heater use will be the only loads of concern, and the #8 wiring from battery to converter is not going to have any significant drop with 10 amps going through its 6-8ft length.

Hence my statement that it doesn't matter where the voltmeter is mounted or tapped in. It should be where ever the OP finds a mounting spot that is easy to read when she wants to check the battery voltage.

When camping with a CPAP, the recommendations are to wire into a 12V circuit like a cigarette lighter. Run the CPAP with the humidifying off. That will give you about 4 nights (no heater) of CPAP use without recharging and not running the dual golf cart batteries below 50%.

Fred W
2014 Rockwood A122 A-frame
2008 Hyundai Entourage minivan
camping Colorado and adjacent states one weekend at a time
trip to the Utah 5 begins Saturday

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Old 04-22-2016, 09:28 AM   #33
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Location: Albuquerque
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Go small solar

With the price of batteries, it is worth protecting your investment. I tent camp in the winter hunting seasons. I had CF electric lights in the tent. I just ran them off the battery, and they would last 5 days, no problem. The problem was that I had to buy a new battery ever year or two. I finally got smart and added a small solar panel. A 10 watt panel will not overcharge a single battery, and doesn't need a charge controller. A 20 watt panel won't overcharge your dual battery setup. Mount it somewhere on the trailer, run the power to your battery, and you'll never have to worry about your batteries, except to check the water occasionally. In our houseboat, we have the old style volt meter, no light, just a dial gauge. If you read this blog, that gauge will all you need to know. I have the Trimetric, but that may be more than you need for your setup.

State of Charge: Your Camper/RV May Be Killing Your Battery Bank |

mnoland30 is offline   Reply With Quote

voltage, pop up

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