Mysterious battery drain... where to begin?

[rwidman]

Originally Posted by Cadence

An ammeter my be useful for finding a faulty component, but that would not seem to be the OP's problem.

An ammeter will indicate if and how much current is flowing in the circuit. Knowing how much current is flowing allows you to disconnect things and look to see if this eliminates or reduces the amount of current flowing.

[Cadence]

Originally Posted by rwidman

An ammeter will indicate if and how much current is flowing in the circuit. Knowing how much current is flowing allows you to disconnect things and look to see if this eliminates or reduces the amount of current flowing.

A volt meter between the bat, and a disconnected bat. lead will do the same. An ampere can be put in line may give you the amount of drain Weather that helps isolate the source of a leak maybe if there are more than one leak by showing a drop in draw. Someone mentioned clamp on ammeters, I don't trust them at low current amounts.

[ur2slo]

Originally Posted by Cadence

A volt meter between the bat, and a disconnected bat. lead will do the same. An ampere can be put in line may give you the amount of drain Weather that helps isolate the source of a leak maybe if there are more than one leak by showing a drop in draw. Someone mentioned clamp on ammeters, I don't trust them at low current amounts.

E=I/R ..nothing has changed.. A VOLT METER will not work for draw.

A meter between the pos post and pos lead will show current (EMF) flow if said millimeter can rectify large current, usually thru shunt, & or a Hall effect clamp on will do it, but only accurate at higher than said currents, and typically hi current AC circuits .

Hook a fluke or any good digital multimeter, or ole Simpson!, in line (10 amp max) and start disconnecting stuff till it goes away...ta da! solved.

[Cadence]

Originally Posted by ur2slo

E=I/R ..nothing has changed.. A VOLT METER will not work for draw.

A meter between the pos post and pos lead will show current (EMF) flow if said millimeter can rectify large current, usually thru shunt, & or a Hall effect clamp on will do it, but only accurate at higher than said currents, and typically hi current AC circuits .

Hook a fluke or any good digital multimeter, or ole Simpson!, in line (10 amp max) and start disconnecting stuff till it goes away...ta da! solved.

An ammeter is just a voltmeter reading across a high resistance. No need for a Fluke an old Simpson 260 or a cheap no name $10 meter will work. At least quote Ohm's law right and EMF.

[ur2slo]

Originally Posted by Cadence

An ammeter is just a voltmeter reading across a high resistance. No need for a Fluke an old Simpson 260 or a cheap no name $10 meter will work. At least quote Ohm's law right and EMF.

lol made ya look.........

fry what ya want, but remember, they only put soooo much smoke in them when they build them. If you let the smoke out, ur screwed.

peace I'm out.

[ramblinrod]

Originally Posted by ur2slo

E=I/R ..nothing has changed.. A VOLT METER will not work for draw.

A meter between the pos post and pos lead will show current (EMF) flow if said millimeter can rectify large current, usually thru shunt, & or a Hall effect clamp on will do it, but only accurate at higher than said currents, and typically hi current AC circuits .

Hook a fluke or any good digital multimeter, or ole Simpson!, in line (10 amp max) and start disconnecting stuff till it goes away...ta da! solved.

You have missed the point, discussing how a voltmeter between the battery post and disconnected terminal will indicate if a load is present, without risking blowing the DVM fuse (if applicable).

Using the Vdc function, if a load is present, the DVM will read "high" (equal or near battery voltage), if a load is not present, the DVM will read "low" (equal or near 0 Vdc).

All one then has to do, is start isolating possible load circuits from the battery, until the DVM reads "low". That circuit, or a branch from it, is the suspect circuit.

[ramblinrod]

Originally Posted by Cadence

An ammeter is just a voltmeter reading across a high resistance. No need for a Fluke an old Simpson 260 or a cheap no name $10 meter will work. At least quote Ohm's law right and EMF.

Whoops, I think you mean an ammeter is a voltmeter reading across a LOW resistance shunt. (If it was high resistance it would seriously impede current flow when connected in series and there would be no need for a fuse.)

It is the voltmeter that is the high impedance device, so as not to drop significant voltage when across a voltage source.

And on the other you are correct, since I was a little boy E=I*R. (I doubt things have changed that much.) ;-)

[Cadence]

Originally Posted by ramblinrod

Whoops, I think you mean an ammeter is a voltmeter reading across a LOW resistance shunt. (If it was high resistance it would seriously impede current flow when connected in series and there would be no need for a fuse.)

It is the voltmeter that is the high impedance device, so as not to drop significant voltage when across a voltage source.

And on the other you are correct, since I was a little boy E=I*R. (I doubt things have changed that much.) ;-)

As I recall. an ammeter is paralleled to the line with a high resistant shunt and is only a calibrated volt meter reading across the shunt to register in amps? I doubt that has change but could have in my mind it's been a long time.

[Jim Cate]

Originally Posted by Cadence

As I recall. an ammeter is paralleled to the line with a high resistant shunt and is only a calibrated volt meter reading across the shunt to register in amps? I doubt that has change but could have in my mind it's been a long time.

No,shunts have very LOW resistance, not high. To measure the current, a sensitive voltmeter is placed to measure the voltage drop across that resistance. In marine applications, the voltage drop is on the order of 50 millivolts at the full rated capacity of the shunt.

But, this has little to do with the subject under consideration: measuring the current drain from unwanted loads on a boat's battery system when everything is supposedly "shut off". Folks are arguing whether this measurement of the actual parasitic load is important, or whether simply establishing that there is in fact some load when none is expected is an adequate diagnostic tool.

Differences of opinion are present.

Jim

[rwidman]

Originally Posted by Cadence

An ammeter is just a voltmeter reading across a high resistance. No need for a Fluke an old Simpson 260 or a cheap no name $10 meter will work. At least quote Ohm's law right and EMF.

An analog meter needle moves when current flows through the coil and creates a magnetic field in the presence of a fixed magnetic field. It's a small motor opposing a pair of springs.

It's actually measuring current but displaying it however it's meant to be displayed. If it's a voltmeter, it's measuring current but displaying it as volts. If it's a fuel level meter it's displaying percentage of a full tank. If it's a temperature meter it's displaying in degrees of temperature.

[rwidman]

Originally Posted by ramblinrod

You have missed the point, discussing how a voltmeter between the battery post and disconnected terminal will indicate if a load is present, without risking blowing the DVM fuse (if applicable).

Using the Vdc function, if a load is present, the DVM will read "high" (equal or near battery voltage), if a load is not present, the DVM will read "low" (equal or near 0 Vdc).

All one then has to do, is start isolating possible load circuits from the battery, until the DVM reads "low". That circuit, or a branch from it, is the suspect circuit.

Or you can use a test light and judge the current by the brightness of the light!

Of the three, an ammeter is the tool of choice for measuring current. That's why they make them.

And if you don't want a constant load on your batteries, you don't want the current to be "low", you want it to be zero.

[ramblinrod]

Originally Posted by rwidman

Or you can use a test light and judge the current by the brightness of the light!

Of the three, an ammeter is the tool of choice for measuring current. That's why they make them.

And if you don't want a constant load on your batteries, you don't want the current to be "low", you want it to be zero.

But the point is that one does not need to measure current to determine load presence or absence.

"High" and "Low" are common terms for logic states.

To test for a load connected to a 12 Volt battery, with the voltmeter connected in series between the post and disconnected terminal:

~12 Vdc = High = True = Load Present

~0 Vdc = Low = False = Load Lack of Presence

There is no need to measure current, to determine load presence or lack of presence.

If one wants to measure current and get an actual reading, then using an ammeter will do it, just take care not to blow the fuse (if it is an issue for that meter).

If one just wants to know load presence or lack of presence, the voltmeter is the better choice, as there is no risk of blowing the fuse.

Its akin to determining if one has a brain or not.

The answer is derived by determining if there is any grey matter between the ears.

Grey Matter Presence = True
No Grey Matter Presence = False

There is no need to whip out calipers or a micrometer to measure the size of the brain, if one only wants to know if it exists or not.

But go ahead, use that ammeter to determine if the load is 3.67 A or 4.27 A. Now tell me, what does that actually do for you? It does indicate the relative size of the load. So what? It doesn't indicate where in the system it is coming from. The solution is still to start isolating circuits until the load is removed. (Exactly the same thing one does using the voltmeter.)

This really isn't brain surgery. ;-)

[ramblinrod]

Originally Posted by rwidman

An analog meter needle moves when current flows through the coil and creates a magnetic field in the presence of a fixed magnetic field. It's a small motor opposing a pair of springs.

It's actually measuring current but displaying it however it's meant to be displayed. If it's a voltmeter, it's measuring current but displaying it as volts. If it's a fuel level meter it's displaying percentage of a full tank. If it's a temperature meter it's displaying in degrees of temperature.

Fair argument but...

The impedance of the meter movement coil is constant.

So what causes the current in the coil to increase or decrease?

Answer: The voltage (primary variable) across the meter movement.

[Jim Cate]

But go ahead, use that ammeter to determine if the load is 3.67 A or 4.27 A. Now tell me, what does that actually do for you? It does indicate the relative size of the load. So what? It doesn't indicate where in the system it is coming from. The solution is still to start isolating circuits until the load is removed. (Exactly the same thing one does using the voltmeter.)

Well, here's where our logic paths differ, Rod. I'm not worried about the difference between your stipulated 3.67 or 4.27 A loads. However, to me there is a big difference in the trouble shooting process between a 3.67 A and a 20 mA load. On lots of modern boats there are heaps of such parasitic loads, coming from various electric and electronic devices, as I'm sure that you know. Those tiny loads are not going to provide the battery flattening that the OP suffers. Your 3.67 A very well might, and that's why I reckon measuring the loads is worth while. Disconnecting a 20 mA load ain't gonna solve his problem(s).

Jim

[Littlechay]

Give it a rest guys.

Ramblinrod obviously knows what he is talking about and his is the best, safest and fastest way of finding the source of the load.

Jim there should only be a couple of loads that are not on breakers!

Jim is then right in that once you have established where your loads are the best way to quantify said load is with an ammeter.

Usually in a fault finding scenario of this type you are not worried about the exact numbers; simply whether it is there or not.

Your both right, but Ramblins method is foolproof. Jim's ammeter will get there too but may involve a blown meter.