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Old 23-07-2007, 15:41   #1
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Voltage reading battery/fuse board

Can someone tell me why does the voltage reading at the fuse board read so much less than using a multi meter at the battery? Is this because of voltage drop over the wire and joins to the fuse board?
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Old 23-07-2007, 17:39   #2
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First, check the accuracy of your panel voltmeter with your multimeter connected directly to its connections. If there is a difference, you got it, voltage drop. Take a length of wire and connect it to the battery bank +, connect and tape the other end to your multimeter red lead. Take your miltimeter and it's black lead along the circuit and check each connection and component. Then move the battery connection to the bank (-) connection, and do the same along the neg. circuit. The meter (digital, I assume) will read with a -, only the numbers are important. There must be a steady load on the system, turn all lights on and turn off stuff that might switch on and off.
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Old 23-07-2007, 18:26   #3
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Does the voltage AT the meter with the VOM read the same as the gauge does? If so the problem is in the wiring. If not it sounds like a bad/inaccurate gauge.

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Old 23-07-2007, 18:42   #4
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thanks, will check it out.
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Old 23-07-2007, 19:16   #5
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Seafox, how much less is "so much" less?

And is the fuse panel connected to the A/B switch with the same heavy battery cable that should be running to that switch?
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Old 23-07-2007, 22:16   #6
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Reads 12.5 at batt and 12 at fuse board.
Batt has heavy duty cable to A/B Switch. Fuse board has some fairly thin cable to it though.

Boat was wired 20 years ago before all the flash gadgets we have today were invented. (chartplotters, inverters etc)

Will check the voltage at both points like jef suggests.

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Old 24-07-2007, 02:00   #7
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Somewhere in between the two, you have unacceptable voltage loss. Unless that last "thin" run to the fuses from the switch is awfully long, I have to think that's not the only culprit.

After 20 years the battery switch could also be wearing internally.
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Old 24-07-2007, 02:14   #8
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I will chuck the multi meter on the analoge meter when I go to the boat in the weekend. Prob just a faulty analoge meter.
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Old 24-07-2007, 02:46   #9
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Another think to consider is the wire itself. Perhaps it is not tinned copper and it has corrosion inside the wire. I was getting odd readings on my old Quad cycle and it was poor connections/corrosion. Each wire was fused so it had a crimp on connector and the spade was secure with a screw and then the fuse holder and this at both ends of the fuse... it was on open type and of course both ends of the wire. So this one wire the electricity had to jump through 8 or 10 mechanical connections.

I have since rewired the boat, use tinned copper, properly crimps with heat shrink and use anti corrosion at the connections, plus I don't use open fuses any more. I hate the ATG glass type fuses and try to use ATC which are color coded and one can read their rating.

With all the gear on the boat I must have 20 or 20 fused wires, aside from the fuses on electronics. Wire size is important as are the connections.

AB tests will reveal all.

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Old 24-07-2007, 04:54   #10
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Quote:
AB tests will reveal all
what does the AB stand for?

I bet the wire is corroded. It is very old.
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Old 24-07-2007, 05:40   #11
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A/B testing is a method used to compare the performance of 2 different alternatives (A vs B, or this vs that); most usually applied to web site advertising (or hit rate) optimization.
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Old 24-07-2007, 13:36   #12
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I think you will find it is just the cheap analogue meter Darryl. They are useless IMO and should be thought of as nothing more than a ruff indicator. Certainly not accurate enough to give relevant measurements.
In saying that, even Digital can be out. Digital panel systems need "tunning" to get them set accurately.
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Old 24-07-2007, 13:46   #13
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Daryl, if you are reading "12v" from the little "battery test meter" in your power panel, and then comparing that to a real meter you are using on the batteries?

OH. Yeah, forget about it. I tried to adjust one of those panel meters so it would read accurately, and found that even though it reads from something like 9-16 volts? If I set it to read 11.5V (dead battery) correctly, it would be off by 1/2 volt at 14V (normal charging range) and there was no way to get it to read right through even a 3-volt portion of the range.

Those test meters in the panels should really have NO NUMBERS ON THEM, just a line you draw for "normal" and "recharge". If you want a meter in the panel, but an electronic one, even a cheap electronic one, and custom install it.
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Old 24-07-2007, 21:04   #14
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look at where you are getting negative from. You may not really be reading from the battery -. Also, do you have a battery isolator, used with one alternator and two batteries? there is a .7 volt drop across the diodes.
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Old 28-07-2007, 18:52   #15
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No battery isolator Captnknopf. All real simple here

I checked the batts with the multi meter as soon as I got to the boat today. They both read 12.31 Volts at the battery. I reckon the bad one sucked some volts from the better one so that they both read the same. I think 12.3 is around 70% charged.

On the fuse board I used the multi meter to check the gauge (12v BEP marine gauge). Using the meter on the gauge batt number 1 read 12.22 rested and 12.12 with the bilge pump going. The batt was just on the red in each cell with the hydrometer bulb.

On the fuse board using the meter to check the analogue gauge, Batt number 2 was 12.23 rested and 12.15 with the bilge pump going.


I started the motor on Battery number one by itself. It turned the motor over a bit slower that normal before the motor started. It is Winter here though.

The analogue gauge read 12V so I have turned it up to 12.2 (it was out .2 roughly from what the multi meter said and what it said).
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