Amp meter burn out

[Boofleman]

Hello all. Hoping you are enjoying this good summer weather.

Can someone help me with a 12 volt wiring problem, please?

 

Recently my boat amp meter decided to melt. In fact the heavy brown and yellow cable to the meter was also very hot. Stopping the engine also stopped the burning and, after a short while, I was able to remove the gauge. Only problem then was, nothing in the 12 volt system would work. I made a temporary join of the two heavy brown/yellow cables and all was restored but also, when engine running, so was the burning.

Fortunately I was not far from my mooring and was able to get a tow home.

I now have the cable joined to give me use of the general electrics but cannot start the engine for fear of melting the cables. The fact that the cables get hot without the gauge indicates to me that replacing the gauge will not solve the problem.

 

Some months ago I moved the amp meters (I have two) and thought I had labeled everything correctly. Although I have not made many hours cruising this burning problem has not been apparent until my last small trip.

 

As you may guess, 12 volt wiring is not a strong point for me so any replies need to be in simple terms. Can anyone help please ?

 

Many thanks

[Bod]

Where is the boat?

This is something that is best viewed, rather than guessed at.

 

Bod

[WotEver]

When you joined the two cables you did so with a nut, bolt and washers all done up really tight, didn't you?

 

Meanwhile I agree that it's probably best looked at by someone who DOES understand electrics.

 

Tony

[Tiggs]

I agree with Bod. You have a short circuit somewhere - and it needs finding.

 

(preferably by someone who knows what he is looking for and without connecting the batteries again, but you could try looking at the connections to your engine starter motor)

Edited July 26, 2016 by Tiggs

[by'eck]

When you moved the ammeters, did you extend with too thinner cable, since it sounds like this may be the issue?

 

As heavy cables are mentioned I would guess the ammeter shunt is part of the display instrument. If so all the measured current is passing through these cables including all 12 volt services. The reason the cable gets hot with engine running would likely be due to the alternators output current passing through the meter to charge batteries. If so then removing meter and shorting cables will not solve the issue as you have found.

 

I suggest you look into the possibility of inadequate cable thickness as a starting point.

[bizzard]

Or if the facia where the gauges are mounted is metal, the gauge metal clamp bracket behind might have been touching the ammeter live terminal or connector.

Edited July 26, 2016 by bizzard

[nicknorman]

As the others say, pretty hard to work out what's wrong from afar.

 

But since we've got nothing else to do...

 

You say the wires when joined together only get hot with the engine on. But is that with just the ignition switched on, or only with the ignition switched on and the engine actually running?

 

You would think that a dead short would be more catastrophic so I'm wondering if it's just a big load like the engine glow plugs/heaters on permanently.

[OldGoat]

Not very helpful perhaps but -

it is Not a good IDEA to have either ammeters with large currents flowing through them

OR

long lengths of wire connecting such devices

A better (best) method is to have a shunt near the batteries / power device with shin signal leads going back to a suitable instrument.

These are available inexpensively from ebay - so if the current instrument(s) are goosed......

[WotEver]

... if the current instrument(s) are goosed......

I saw what you did there.

[David Mack]

These are available inexpensively from ebay - so if the current instrument(s) are goosed......

 

... it might be wise to stop swanning around and duck in case burning wires start flying about. Or you could just chicken out and get someone else to fix it.

[Boofleman]

Many thanks to all for your advice and suggestions. I'll try to put together a reply that addresses most of the questions:

 

When I joined the two wires to the (removed) gauge I did do so with a bolt and nut and made a good tight joint.

The wires to/from the gauge are heavy cables - coloured brown/yellow. No thin wires are used. When I moved the amp meters it was only a few inches and I did not need to extend the existing cables.

I have seen, on the internet, mention of a shunt. On my system there is a 'lump' of some alloy metal that is cast with what seem to be cooling fins. It measures about 5 x 4 inches and about an inch thick. The only marking on it is "Warwick Organs" and "12 Volt". The brown/yellow cables to the amp meters come from this 'lump'. Would this be a shunt?

 

The gauges are mounted on a wood dash.

 

The wires get hot ONLY with the engine running and have only recently started to get hot. This has not happened immediately after moving the gauges but some months later.

 

I'm thinking that a short would occur all of the time, or at least all the time the ignition is on. However, this burning is taking place only when the engine is running (charging) and, as I have indicated above, not all the time the engine has been running.

 

I was rather hoping there would be a simple remedy so looks like I need to bring in a specialist. However, any further thoughts would be appreciated.

 

Again, thanks to all

 

 

[Jess--]

probably a silly question... when the ammeter failed what current was it showing just before failure?

 

it could be as simple as a big alternator into flat(ish) batteries is producing a higher current than the wiring can withstand

[mickp]

I would remove these cables and fit new ampmeter with remote shunt near the battery so no big curents go to your dash board then back again

[WotEver]

I would remove these cables and fit new ampmeter with remote shunt near the battery so no big curents go to your dash board then back again

Agreed. However we firstly need to know what the problem is (assuming there is one).

[Boofleman]

Hi Jess,

Although my nose was stuck to the dash trying to ascertain where the burning smell was coming from, I did not think to look at the amps being produced. However, you may have hit on a point because that morning the fridge was thawing and the lights dimmed when I flushed the loo.

I have 3 x 110 Ah leisure batteries but I think one may be on the way out.

 

If this should be the reason (as you suggest), how would I protect my wiring and meter at future times the batteries are low ?

 

Thanks

[WotEver]

Sounds like one of your batteries has died with an internal short. That would have caused the alternator to work flat out in an attempt to charge it, resulting in high currents and warming of the cables.

 

To prevent it in the future? Firstly keep an eye on the battery health and replace them before they die completely. Also, as has previously been suggested, fit a shunt-based ammeter which is a better solution anyway by virtue of the shorter cable runs.

 

Tony

[Tony Brooks]

I agree with Jess on the present information, no fault but faulty choice of equipment. Those brown and white cables are almost certainly the ones that came with the meter and although they look thicker than many of the other cables they are far from thick, especially if you have a 50 amp plus alternator.

 

Whatever else the ammeter and wiring may be doing it is almost certainly compromising the charging system. Much better to fit an ammeter with remote shunt to minimise the run length of the charging cables.

[Boofleman]

Hello guys, Thanks so very much. It seems I am getting somewhere and, at least if nothing else, by upgrading the circuit I'm making it safer.

 

However, and sorry to be a bit thick and a pain, but can anyone give me some clarification on the installation of the shunt? There is an very good article on Canal World that details the installation of a shunt but it refers to a digital ammeter. I have a replacement 2" Bosh round dial meter that just has an in and out terminal plus the lamp. I'm assuming the shunt is merely wired in series into the -ve feed from batteries to fuse box. Then taking feeder wires from each side of the shunt up to the ammeter. Should I do same for both ammeters (engine battery and domestic batteries)?

 

Am I on the right lines and anything else I should do ?

 

Thanks a million

Graham

[WotEver]

Sounds like your Bosch replacement is another analogue meter much the same as the one you've removed and is unsuitable for use with a shunt.

 

You want something like this (but not from the US, that's just the first one I found).

http://m.ebay.com/itm/161045814625

[gazza]

I ditched our old moving coil type analogue meter for one of these.

 

http://www.simtekuk.co.uk/product.php/durite_marine_ammeter_80-0-80_amp/?k=:::1742194

 

Put the inductive pick-up on the output from alternator to battery and jobs a good un.

 

Not a brilliant match for the rest of our Faria gauges but it works well with minimal wiring.

Edited July 27, 2016 by gazza

[Tony Brooks]

I ditched our old moving coil type analogue meter for one of these.

 

http://www.simtekuk.co.uk/product.php/durite_marine_ammeter_80-0-80_amp/?k=:::1742194

 

Put the inductive pick-up on the output from alternator to battery and jobs a good un.

 

Not a brilliant match for the rest of our Faria gauges but it works well with minimal wiring.

 

but not really accurate enough to measure tail current so its probably best to bight the bullet and fit a shunted digital ammeter. Even if the OP and Gazza does not understand the importance of tail current now it is very likely they will do in time and f that gauge is fitted they will need a more accurate one.

[nicknorman]

I ditched our old moving coil type analogue meter for one of these.http://www.simtekuk.co.uk/product.php/durite_marine_ammeter_80-0-80_amp/?k=:::1742194

Put the inductive pick-up on the output from alternator to battery and jobs a good un.

Not a brilliant match for the rest of our Faria gauges but it works well with minimal wiring.

Hmmm well something wrong there. You can't use an "inductive pick-up coil" to measure DC current. It's probably a Hall effect sensor but if the manufacturer doesn't know how to describe their own product I'd be worried!

[Arthur Brown]

Have you found what the change was that happened at the time when the ammeter changed from reading correctly and getting hot enough to burn. It's rare that an ammeter will start to overheat for no reason, usually if you over current an ammeter it melts and fuses and the current stops.

[gazza]

 

but not really accurate enough to measure tail current so its probably best to bight the bullet and fit a shunted digital ammeter. Even if the OP and Gazza does not understand the importance of tail current now it is very likely they will do in time and f that gauge is fitted they will need a more accurate one.

 

 

It gives an indication of what the alternator is bunging out, for the rest of you that want to sit glued to the ammeter crack on!!

 

i understand perefectly well tail currents, i'm not interested in the slightest though, as long as i know its charging via a not too accurate volt meter and ammeter i'm happy, we have yet to have all our electric leak out

Hmmm well something wrong there. You can't use an "inductive pick-up coil" to measure DC current. It's probably a Hall effect sensor but if the manufacturer doesn't know how to describe their own product I'd be worried!

 

I didnt state that as the that web page calls it an inductive pick up.

 

I have a feeling it would cause more confusion, especially as i know how emotional electrical threads can get

Edited July 28, 2016 by gazza

[WotEver]

I didnt state that as the that web page calls it an inductive pick up.

I believe that was Nick's point. The website states "uses inductive pickup coil".

 

It doesn't.

 

Tony

 

Edited to get the quote bang on.

Edited July 28, 2016 by WotEver