Battery Draining

Fed

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Tim I never said he should replace his rectifier and only suggested the rectifier would be the likely culprit.

I should add, here is the essence of the thread.
Any thoughts on what might cause this to occur or what I should check?

With the 0.5V, 0.1V & missing? 0.4V it seems to me that Mark has already started to isolate the problems but that's only a guess at this point.

Voltmeter, ammeter & even ohmmeter, same = same = same, they all measure current flow.

Vic the voltage readings mean that Mark (OP) has a leakage back to the battery negative.
 

bruceb58

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Voltmeter, ammeter & even ohmmeter, same = same = same, they all measure current flow..
A voltmeter does not measure current flow. Neither does an ohm meter.

Vic the voltage readings mean that Mark (OP) has a leakage back to the battery negative.
Maybe you should read his post #14. He had the cable going to the positive post of his battery disconnected.
 

Fed

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Let me rephrase Bruce.

Voltmeters, ammeters & ohmmeters all react to current flow.

The way this is going we'll be correcting spelling mistakes soon, is it nitpick day or something?
 

oldboat1

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Thanks for all the info and suggestions. I won't be back to the boat until the weekend but here is some additional information and the method I used to get the reading. This battery is a year old and the prior battery was losing a charge as well. The only accessories are the boat lights and bilge pump. Both were off and the key was out of the ignition at the time I ran the test.

Well, I'll continue to assume that your battery doesn't seem to hold its charge between boat trips. (You have a one or two year saga going on, which keeps it interesting!)

Motor or starting circuit issues aside -- if you have an automatic bilge pump in your boat, it may be the type that cycles on briefly to sense the presence of water. And of course the pump may operate if you are getting water in the bilge. If you have an old hull, you could have water logged floatation, and some ongoing draining into the bilge -- where the water gets grabbed by your pump -- which can run down your battery.

A couple of my pumps are wired through a momentary switch for manual operation, but hard wired through a float switch for automatic operation. (This is apparently how Trojan boats wired them up in the early '80s.) Anyway, it's possible your pump is not actually turned off and is operating while you are away from the boat. Disconnecting the battery would prevent that, of course.

Maybe something else to explore.
 

bruceb58

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Let me rephrase Bruce.

Voltmeters, ammeters & ohmmeters all react to current flow.

The way this is going we'll be correcting spelling mistakes soon, is it nitpick day or something?
No....apparently you do not know how a multimeter works.

To measure volts, it uses its internal voltage measuring circuit(ADC) to measure voltage. For current it uses its internal voltmeter to measure a voltage across a shunt. For ohms, it injects a small current and measure a voltage. A voltage is not a current flow no matter how many times you say it.

I can 100% guarantee you there is no current flow when the positive battery cable is disconnected from the battery so all his measurements mean nothing.
 

redneck joe

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Dam i need some popcorn while i learn. Ive gota similar issue on my 1984 75 rude which is why I subscribed to the thread.
 

bruceb58

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Google galvanometer.
And that has what to do with a multimeter measuring voltages?

BTW...nobody uses a galvanometer in the last 30 years.

Bottom line, he needs to use his multimeter to measure current and then start disconnecting things to isolate what is causing the current draw.
 
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Fed

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Or he needs to use his multimeter to measure volts and then start disconnecting things to isolate what is causing the current draw and why.
FWIW I think we could calculate the amperage from the voltage displayed given the internal resistance of the meter at a particular scale setting.

Does anyone know what a typical diode leakage would be, maybe there's nothing wrong with it?

My system has two leaks and I traced one back to the 2 way radio, apparently there's a diode directly across the input socket (before the on/off switch) for reverse polarity protection.
The other leak I traced back to the rectifier/regulator, more diodes hiding in there but not directly testable by memory.
What we need is an engineer!

You still here Mark, very interested in what you find.
 

interalian

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Leakage as I said before. Need to put the meter on AMPS across the circuit to test for current draw. You can use a voltmeter to measure voltage drop across an active circuit, not an open one if you want the reading to mean anything.
 

Fed

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When Mark put his voltmeter between the battery positive & the main motor lead he completed the circuit.
 

interalian

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^^yes, but with an extremely sensitive instrument and the reading is probably meaningless. If a 100 ohm resistor was parallel to the meter I'd bet it reads zero.
 

bruceb58

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When Mark put his voltmeter between the battery positive & the main motor lead he completed the circuit.
A meter has many mega ohms of input impedance so it isn't completing any kind of circuit.
 

bruceb58

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Does anyone know what a typical diode leakage would be, maybe there's nothing wrong with it?
Yes..if you put a large enough reverse voltage on a diode you will get a leakage current. It's typically a few micro amps! LOL

BTW...electrical engineer for 34 years.
 

F_R

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I have a 1980 Johnson 85hp. With the engine off and the key removed from the ignition I performed some tests using a hand held voltage meter. I have found that there is .5 volts draining from the positive battery terminal to the wire going to the starter solenoid. I also found that there is .1 volts draining through the wire going to the charging system. Any thoughts on what might cause this to occur or what I should check?

Thanks


OK, I understand your reasoning behind your test. You are reasoning that there is some sort of continuity between the battery cable and ground, such as through the starter. The fallicy is that modern digital multimeters will measure the tiniest bit of voltage or current. Even a bit of moisture or dirt will provide enough of a ground to get that voltage reading you are getting. And there is the alternator rectifier also. It blocks any reverse current through the alternator, but not absolutely 100%.

Bottom line is if there was any significant grounding of the positive cable or anything connected to it, you would be seeing more like 12V with the test you are doing. In other words, it is a false test, giving meaningless readings. It aint broke.
 

Fed

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Although the leakages may be tiny it doesn't change the fact that voltmeters use current (Amps) to generate a reaction then display that reaction as Volts.
If anything the test confirms the leakage is tiny and can be disregarded when the reading is only 0.5 Volts.

I did read on another post you were an engineer Bruce but I assumed you were a train driver. ;)

Moving right along I guess a 6 Volt reading would make the ground resistance (Fault) approx the same as the internal meter resistance say 10 Meg ohms.

What I find interesting is my readings were roughly the same as the OP's yet it seemed to make a huge difference to my battery discharge rate when I disconnected the battery leads while the boat was not in constant use, perhaps there was something else in play but I can't imagine what.
 

Tim Frank

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Although the leakages may be tiny it doesn't change the fact that voltmeters use current (Amps) to generate a reaction then display that reaction as Volts.
.

Still don't understand how voltmeter internal function relates to this or the OP's problem. Wrong tool ....wrong application.
I have a thermometer that operates electrically using a thermocouple....it too, uses a current to display a reading.
It would be just as useless in finding a current leak here as would a voltmeter.

Ainsi-soit-il....
 

Fed

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I got to this point because it's pouring rain outside.
 

bruceb58

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Fed ....you are entertaining...I at least have to say that. Each new post amazes me more than the previous one! :)
 
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