Battery Monitor - Page 2 - Fiberglass RV

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Old 08-01-2006, 12:17 PM   #15
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Name: Steve
Trailer: 2003 Casita 16' SD
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When camping for an extended time without an electrical hookup, I track amp-hours out.

Then at some point, I connect the Honda generator and run it long enough to get back to 70-80% full amp-hour capacity. About that time, most chargers are starting to ramp down the current anyhow. I get the most charge for the minimum generator time.

I like amp-hours because it's a (relatively) simple value for the meter to track and judging the charge state by voltage is tricky because of the wait time to get a stable voltage after any charge or drain load.

Now, if I were to completely surrender to the dark force, I'd spring for the optional battery temperature sensor since battery charge is temperature sensitive. Haven't been able to justify it. Yet.

Quando omni flunkus, moritati
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Old 08-01-2006, 02:14 PM   #16
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Trailer: 2006 Scamp 13' towed with a 2005 Dodge Dakota 4.7l Magnum W/full tow package (over kill)
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The state of charge of the battery depends on how many ampere-hours you've used versus how many ampere-hours you've put back in. Ampere-hours is just current (amperes) integrated over time.

If you start with a fully charged battery (say, 100 Ah) and withdraw 10 Ah then the charger replaces 5 Ah, you've run a deficit of 5 Ah. The battery now has 95 Ah of charge remaining.

If you have no charger hooked up to the battery, it makes no difference. There is no current going into the battery.

I understand all the electric stuff. (Byron's an electronic engineer) But I don't see where there's a need to monitor how many Amp hours are put back in, certainly not a $100 need. The only thing I can think of is if you are in the habit of partially charging your battery, but then you'd have to put a lot of time in understanding how your battery works to have any idea how much juice is left. I can see where it might be usefull for a short period of time to know how much you're using. But after a while that doesn't have a lot use either. You develope habits that allow you to do what's needed. Besides the amount of charge in a battery is at best an estimate. Temperature and battery age also play a part therefore any attempt to be exact isn't going to work.

Byron & Anne enjoying the everyday Saturday thing.
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Old 08-01-2006, 06:55 PM   #17
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Can 2 DOC Wattson meters be wired in. One for discharge and one for charge?
Nah, it would get too complicated adding the value from one meter and subtracting the value from the other meter.

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Old 08-02-2006, 04:06 PM   #18
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Here's my question to RC Electronics and their reply:

You are correct that it only measures in one direction from LOAD to SOURCE.
The integral of charge in and charge out of a Lead-acid battery is seldom zero. Hence any such system requires various assumptions and corrections to provide a reasonably accurate result. The low cost and simplicity of this meter rule against that. You're better off with two meters back to back.
Best regards,

At 08:39 AM 8/1/2006, you wrote:

Your specifications and your manual (particularly the connection diagrams) indicate that the meter will measure current (and charge) in only one direction.

If the meter is wired between the battery and the load and if a battery charger is on the load side of the meter, will the meter measure the charge as well as the discharge? An RV or a boat would have such a circuit (so does a car or truck) and the charging would be done automatically by the charger.

If the specifications are correct and the meter only measures 0-100 amperes rather than plus or minus 50 amperes, the meter would be of little use in such a circuit.


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