Amp meter burn out

[gazza]

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.

 

I know!!!!!

 

I didnt challenge it as it makes no difference to most who buy one what its called.

 

It does make a very big difference on here though.....................................

[Boofleman]

Hello Arthur. Thanks for your message.

All I can recall is that the batteries were particularly low at that time. The domestics had been running the fridge, water pumps, etc., and the engine battery also runs the bow thruster which, had had a few bursts that morning.

The various replies I have received have lead me to think that the problem was caused by excessive charge being required.

My concern now is how to best avoid future problems.

Your (and all) advice very much appreciated.

Graham

[BruceinSanity]

Hello Arthur. Thanks for your message.

All I can recall is that the batteries were particularly low at that time. The domestics had been running the fridge, water pumps, etc., and the engine battery also runs the bow thruster which, had had a few bursts that morning.

The various replies I have received have lead me to think that the problem was caused by excessive charge being required.

My concern now is how to best avoid future problems.

Your (and all) advice very much appreciated.

Graham

I think you've had that answer already. You need a digital ammeter which has a shunt positioned as close as possible to the batteries, connected to them by heavy cables. Then the lightweight signal cable can reach to wherever you want the meter. I have a NASA Clipper BM2 meter which can handle 200A with the meter on the side of the wardrobe in the bedroom.

[adrianh]

It sounds to me like your shunt resistor has broken/burnt out resulting in the ammeter taking the full current instead of the low current (say 100 milliamps) that it is designed for.

It is always best to fit fuses in both ammeter connections, adjacent to the shunt, so that they will blow if the current rises to high (10amps possibly).

It sounds like you need to fit a new shunt and ammeter, and replace the wiring as the insulation will be damaged.

 

A shunt is a very low value resistor that causes a voltage drop across it according to the current flowing to or from the battery.

The voltage drop is used to produce a small current flow to an external high resistance meter. If the shunt goes open circuit then all the battery/charging current will try to go through the external circuit, as you have seen this can far exceed the capability of the wiring or meter.

[Tony Brooks]

It sounds to me like your shunt resistor has broken/burnt out resulting in the ammeter taking the full current instead of the low current (say 100 milliamps) that it is designed for.

It is always best to fit fuses in both ammeter connections, adjacent to the shunt, so that they will blow if the current rises to high (10amps possibly).

It sounds like you need to fit a new shunt and ammeter, and replace the wiring as the insulation will be damaged.

 

A shunt is a very low value resistor that causes a voltage drop across it according to the current flowing to or from the battery.

The voltage drop is used to produce a small current flow to an external high resistance meter. If the shunt goes open circuit then all the battery/charging current will try to go through the external circuit, as you have seen this can far exceed the capability of the wiring or meter.

 

Please ignore this, it sounds like no such thing. Most cheap boy racer type ammeters do not use shunts.

 

The original description was good and the cable colour and size clearly indicates that it is probably a cheap moving iron meter that does not use a shunt. The added information that the batteries were well discharged and the alternator is rated at 15 amps (I think I read that in the thread) again indicates a no ault problem, just a bad selection of equipment and cable one.

 

I do however agree that fuses either on both thin instrument cables close to the shunt (when you buy and fit your new meter) is a good idea.

[Wiltshire Moonraker]

I don't think anyone has answered this question from the OP, post #11. It's a mystery to me!

 

 

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?

 

[WotEver]

It sounds to me like your shunt resistor has broken/burnt out...

No it doesn't. Not at all. OP doesn't even have a remote shunt.

I don't think anyone has answered this question from the OP, post #11. It's a mystery to me!

 

Could be anything.

[by'eck]

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

 

 

 

Just come back to this thread following the above extra advice from the OP. The item described sounds a lot like an external shunt to me especially given the wiring from it to display instrument.

 

If the display developed a short this in turn would effectively short out the remote shunt with a significant amount of current flowing through the monitoring wires, explaining them overheating when carrying a substantial alternator charge current. When the OP deliberately joined these wires together in order to bypass instrument, they continued to overheat as one would expect. What is not explained is why he was forced to do this in order to maintain a 12 volt distributed supply. Almost sounds as though the shunt itself has gone open circuit however unlikely.

 

Worth checking for high resistance on the main shunt cables maybe which should be a lot thicker than those going to instrument, if the OP could confirm they exist.

Edited July 30, 2016 by by'eck

[WotEver]

One thing that makes me doubt this Warwick Organs thingy being a remote shunt is that OP describes the wires between it and the display as "heavy duty", suggesting that the meter is in the charging circuit and has an internal shunt. The other thing is that he refers to getting a replacement meter which definitely has an internal shunt.

 

But who knows? Maybe you're right.

[by'eck]

Yes tried to get more info on the shunt if it is such. Warwick Organs Ltd. was a valid although now defunct company - trail ended there.

 

I admit the thick wires to instrument display did initially throw me off track, but they were not thick enough to avoid overheating. I don't believe the OP has advised how thick though, so maybe a red herring.

[WotEver]

Quite possibly. I had no luck with the organ company either.

[Tony Brooks]

This is why the OP would do best, in my view, to get rid of the lot and fit a decent shunted ammeter. That way no guessing and as long as he connects it all properly it WILL work and it WILL give a fairly accurate reading.

[WotEver]

This is why the OP would do best, in my view, to get rid of the lot and fit a decent shunted ammeter. That way no guessing and as long as he connects it all properly it WILL work and it WILL give a fairly accurate reading.

Agreed