using a voltmeter to find electric loss

[londonron]

is there anywhere i can find out how to use a voltmeter? I have one and can use it to check fuses and current so i am not a novice but need to know more.

my batteries seem to be going flat without any use of them. i didnt leave the lights on etc. so i want to go to the fuse board and disconnect each circuit in turn and see if there is a fault. so if i am holding a red and black wire connected to lets say a bilge pump what should i do ?

[Tony Brooks]

is there anywhere i can find out how to use a voltmeter? I have one and can use it to check fuses and current so i am not a novice but need to know more.

my batteries seem to be going flat without any use of them. i didnt leave the lights on etc. so i want to go to the fuse board and disconnect each circuit in turn and see if there is a fault. so if i am holding a red and black wire connected to lets say a bilge pump what should i do ?

 

If its a multimeter and the high amps range has not been burnt out I would suggest that you set the meter to that and clip it to the terminals for the fuse. If any current is flowing through that fuse the meter should show it BUT please do not try it on high current circuits like inverters. Many multimeters can only handle 10 amps.

 

If it is only a voltmeter leave it sent to 20v DC (or 200V DC for 24 volts systems) and connect that to the fuse terminals. If it shows a volatge you have a drain of some degree. The problem is that I suspect several circuits may well show a volt or so because of leakage due to damp. I would be tempted to say ignore anything under about 6 volts and remember things like car radios may well be wired with a permanent supply for the memory.

 

The answer to your direct question is to reconnect the red wire and then connect the black one back up via the meter however you have set the meter. For reading see above.

 

I do not advocate using a voltmeter for this purpose though.

Edited October 24, 2010 by Tony Brooks

[bottle]

is there anywhere i can find out how to use a voltmeter? I have one and can use it to check fuses and current so i am not a novice but need to know more.

 

Sorry Ron but this does imply that you are a novice. and so am I but I think you mean to say that you can use a 'multi-meter' to check fuses and current.

 

If your batteries went flat without anything connected (are you sure) then the fault lies in the batteries they will have to be checked first.

 

Two sites that will help you check the batteries and give some more information..

 

http://www.batteryfaq.org/

 

and

 

http://www.smartgauge.co.uk/technical1.html

[P R]

is there anywhere i can find out how to use a voltmeter? I have one and can use it to check fuses and current so i am not a novice but need to know more.

my batteries seem to be going flat without any use of them. i didnt leave the lights on etc. so i want to go to the fuse board and disconnect each circuit in turn and see if there is a fault. so if i am holding a red and black wire connected to lets say a bilge pump what should i do ?

if you disconect main supply cable from your battery you can conect your multi meter or volt meter between terminal and cable and should read zero, if you get a reading there is a voltage drain which you can then check by pulling fuses untill you find the problem one, then just have to check each device on that fuse

[Amicus]

Here's an idea for the knowledgeable herein. Couple of year ago I had the same problem as the OP, chasing a stray discharge, (oooer missus) this on a gurt jin-palace with complicated (for me) electrics. I had a whizz stroke of rare genius, if I could knock up a shunt with the same dimensions as a fuse, I could subsitute each fuse in turn and measure the current on the volts range. Just a Ya/Nay really, but with a bit a areth of doing sums one could get a ball-park of amps? Never got rountoit of course.

Maybe solder a pair of leads to a duff fuse and bring them out to a shunt?.

Wadda the panel think?

[londonron]

thats a bit mean. i have used one in my job for years. but applying it to a boats use and not the things and ranges i used before is a bit differant so thought best to ask.

 

If its a multimeter and the high amps range has not been burnt out I would suggest that you set the meter to that and clip it to the terminals for the fuse. If any current is flowing through that fuse the meter should show it BUT please do not try it on high current circuits like inverters. Many multimeters can only handle 10 amps.

 

If it is only a voltmeter leave it sent to 20v DC (or 200V DC for 24 volts systems) and connect that to the fuse terminals. If it shows a volatge you have a drain of some degree. The problem is that I suspect several circuits may well show a volt or so because of leakage due to damp. I would be tempted to say ignore anything under about 6 volts and remember things like car radios may well be wired with a permanent supply for the memory.

 

The answer to your direct question is to reconnect the red wire and then connect the black one back up via the meter however you have set the meter. For reading see above.

 

I do not advocate using a voltmeter for this purpose though.

 

 

 

 

 

great answer tony. thanks everyone else as well

[FORTUNATA]

" Many multimeters can only handle 10 amps."

 

When I started, I didn't know you had to do current tests in series. I was testing a fuel pump obtained from a scrapyard and wanted to see how much current was passing though. I put the red probe on the positive wire and the black probe on the negative pump wire. As there is no fuse on cheaper metres, the first I knew about it was a smell of burning plastic. Then I found the probes were literally melting in my hands. The metre was totally wiped out.

In a good metre the fuse would have popped first.

Still, I find them very useful. I recently encountered some guys who reckoned they had a clapped starter motor as the engine wouldn't turn. We could hear a click and that was it. I got my meter and tested for volts on the battery terminals. Only 6.5 volts. I then tested while the guys had the battery connected to a jump start and it was also only a fluctuating 5 - 6 volts. I recommended they try a proper charged battery and the problem was solved.

 

 

If its a multimeter and the high amps range has not been burnt out I would suggest that you set the meter to that and clip it to the terminals for the fuse. If any current is flowing through that fuse the meter should show it BUT please do not try it on high current circuits like inverters. Many multimeters can only handle 10 amps.

 

If it is only a voltmeter leave it sent to 20v DC (or 200V DC for 24 volts systems) and connect that to the fuse terminals. If it shows a volatge you have a drain of some degree. The problem is that I suspect several circuits may well show a volt or so because of leakage due to damp. I would be tempted to say ignore anything under about 6 volts and remember things like car radios may well be wired with a permanent supply for the memory.

 

The answer to your direct question is to reconnect the red wire and then connect the black one back up via the meter however you have set the meter. For reading see above.

 

I do not advocate using a voltmeter for this purpose though.

 

Sometimes current can stray over dirt and damp. Only small current. It also helps to clean the terminals and grease with vaseline. They call it tracking.

One useful test it to do a volts test from battery terminal to hull.

 

if you disconect main supply cable from your battery you can conect your multi meter or volt meter between terminal and cable and should read zero, if you get a reading there is a voltage drain which you can then check by pulling fuses untill you find the problem one, then just have to check each device on that fuse

[Colin North]

I would agree that a multi-meter would not necessarily be the tool of choice.

 

There is still a little merit in having a small 12v (for 12v circuits, 24v for 24v circuits) bulb connected to a pair of fly leads. Using a 12v bulb of about 1.2w (little dash-board panel indicator bulbs)and a pair of leads, maybe one with a crocodile clip and the other with a probe, this can be used to:

Connect the croc clip to the +12v bus bar, then remove each fuse in turn and put the probe on the downstream side of the fuse connector (the appliance side). If the buld remains extinguished completely then you have extremely low or no leakage. If the buld fully illuminates, you have either found a circuit that is powered on, or a very high leakage.

Check quickly for dead fuses by connecting to the +12 bus bar and walking the probe along the appliance side of the fuses until you get a light. That's your blown fuse.

 

A 12v 1.2w bulb will fully illuminate with 100mA (0.1A) of current flow.

 

OK, its not all fool proof, but it can be a useful, quick test, its a lot easier to interpret, it sort of works in the dark etc...

[Gibbo]

I totally agree with Colin.

 

For the uninitiated I think a test lamp is a far more useful tool than a multimeter. Easier to use, easier to understand, less prone to error, cheaper, less fragile. I still use one.

[WotEver]

There is still a little merit in having a small 12v (for 12v circuits, 24v for 24v circuits) bulb connected to a pair of fly leads.

I have a wonderful little tool that was my late father's. It's a small cable reel in the form of a metal cage on a hub with a handle at one end for winding it up. At the end is a bulb holder. Wound onto the reel is a length of twisted twin with a croc clip on the black wire and a pointed bit of steel on the red wire. The whole thing's only about 80mm long and around 40mm diameter. It doesn't look home made but any maker's name has long since worn off.

 

Tony

 

I also have a three volume "Book of car electrics" published in 1924 with the foreward written by Sir Herbert Austin. It's leather bound, has shiny paper, and contains blueprints (real blueprints in blue) of the schematics of every car manufactured at that time.

[Gibbo]

Here's one of the most useful, simple, devices I've ever had. I've got one made up in an old marker pen case with two panel lamps, one red, one green.

 

 

B+ and B- have crop clips to go on the battery posts or somewhere in a panel. Both lights light up. Stick the probe on 12 volts and the bottom one lights up. Stick it on ground and the top one lights up. Stick it on something that isn't connected and they both remain lit. It removes the ambiguity of a normal test lamp where if it doesn't light up it could be because it's 12 volt or floating.

[blackrose]

Here's an idea for the knowledgeable herein. Couple of year ago I had the same problem as the OP, chasing a stray discharge, (oooer missus) this on a gurt jin-palace with complicated (for me) electrics. I had a whizz stroke of rare genius, if I could knock up a shunt with the same dimensions as a fuse, I could subsitute each fuse in turn and measure the current on the volts range. Just a Ya/Nay really, but with a bit a areth of doing sums one could get a ball-park of amps? Never got rountoit of course.

Maybe solder a pair of leads to a duff fuse and bring them out to a shunt?.

Wadda the panel think?

 

Or you could just read the amps discharge on your shunt-type battery monitor and pull out each fuse in turn until you find the faulty circuit. Isn't that the same thing (but simpler)?

[RLWP]

Here's one of the most useful, simple, devices I've ever had. I've got one made up in an old marker pen case with two panel lamps, one red, one green.

 

 

B+ and B- have crop clips to go on the battery posts or somewhere in a panel. Both lights light up. Stick the probe on 12 volts and the bottom one lights up. Stick it on ground and the top one lights up. Stick it on something that isn't connected and they both remain lit. It removes the ambiguity of a normal test lamp where if it doesn't light up it could be because it's 12 volt or floating.

 

Now that's clever!

 

Richard

 

It would be brilliant with appropriately coloured bulbs, say red for positive and black for - oh...

Edited October 28, 2010 by RLWP

[blackrose]

Where does one find an old transparent marker pen case... Short section of 3/4" clear plastic pipe perhaps?

[Gibbo]

Where does one find an old transparent marker pen case... Short section of 3/4" clear plastic pipe perhaps?

 

Mine isn't transparent. It's a normal plastic one with the panel lamps stuck through the side of it.

[Guest User]

A bit like the auto-electrics probes then ? ....