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Old 11-12-2015, 08:49 AM   #1
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voltage reading

I have new T-105, four of them, which replaced Interstate U2200. Interstates tested at 73% voltage when fully charged, so got the Trojans installed, testing at 100% after charging.

After night of dry camping, Intellitec BD1 voltmeter inside showed 12.1 volts, no better than the 6 year old Interstates were doing.

I put a voltmeter on the battery bank directly and got 12.34, a substantial difference. Is the reading directly off of the group of batteries more accurate indicator of their remaining charge? Why is the inside reading so much lower?


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Old 11-12-2015, 09:03 AM   #2
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Question . Were there any 12 volt loads on when your were checking voltage at the panel? Even an interior light or the fridge control board operating can lower the voltage reading at the panel.
Testing at the batteries is always the most accurate, and there is a chance of a discrepancy in the meters.

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Old 11-12-2015, 09:27 AM   #3
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I did not put into store mode first, so there would have been 12v loads, at least the fridge.
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Old 11-12-2015, 09:38 AM   #4
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That is the conundrum with voltage meters. Check while charging and it shows 13.2 and up. Check while the furnace is running and it may drop below 12 volts.
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Old 11-13-2015, 07:19 PM   #5
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I installed two 12v meters at the Battery location, this gives most accurate reading of voltage from the Batteries and charge amount. Any other location might give you a different reading do to bad connections and load on the wiring.
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Old 11-14-2015, 09:10 AM   #6
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The accuracy of the meter and connection point both make a difference.

Good meter directly at battery best.

Many options for this.

Confirm where your meter is reading and if accurate.

We are building a panel someday to mount inside with panel meters to directly read voltages.

Meters about 2 bucks on ebay so picked up 20 of them.

The readings vary so will pick ones that are correct.

A battery charger also in works with similar meters that also show amps and these are adjustable for calibration.

You could do same or bring in fused leads as monitor points so you can measure footage from inside.
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Old 11-14-2015, 05:37 PM   #7
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Companies such as Bogart Engineering sell battery monitors, should you wish to keep track of more than just voltages.

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Old 11-14-2015, 06:03 PM   #8
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FWIW - If I was seeing that much difference I would be looking for where the voltage drop comes from. It could be that the meter on the panel is tied to the 12 V line from the battery into the house after the distribution panel. If the system is operating correctly I would get nervous about more than 0.1 VDC difference. That is high but one is going through several connections by then.
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Old 11-14-2015, 06:42 PM   #9
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It could simply be the difference in meter accuracies.
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Old 11-15-2015, 06:48 AM   #10
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Possibly but not probably. A quarter volt drop is in the range of a dirty contact with current flowing. The easy part it that one can check at a lamp or DC socket and see what the voltage is in the house.
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Old 11-15-2015, 07:20 AM   #11
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In a past life I was involved in switch room engineering with dc power.

Voltage drops are somewhat critical and as a result wire sizes were nuts huge.

Most automotive circuits contain smaller wire due to short runs but in a mh the wire rated for 15 amps may be a number 14 but at 12 volts dc and a reasonable run of wire it would need to be maybe a number 10 or larger yo have less than the error reported by op.

Add selenoids and connectors and it gets worse.

Measure at battery with good meter to be sure then determine reasons for other readings to confirm accuracy of that system and voltage drops.

Our target voltage drop was 0.25 volts with a 48 volt system and distribution leads to some seemingly small equipment would be number 2.

A 0.1 different reading may be gravy.

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