12v Switch

[dave21]

Why do you want the meters?....... the battery warning light, which comes on when the battery voltage when being charged by the alternator drops significantly below 14.4V.

Because I want to know the state of my battery, the charge and the effect various plug-ins are having - like a cooler as I'm making a 1000k run. I already have pretty pointless lights that came with the car. i.e. When I had a beautiful Scorpio Exec it had a terrific diagram gauge where if a door or boot/bonnet was not closed properly it advise which one it was. Not wildly useful but what was was the bulb-out advice which showed which cluster it was. Now I have a more 'modern' Ford, one light advise something is not closed - guess what it is, and more useless one light to advise a bulb is out - go find it. It's doubly useless because it's always on despite all my 'nickable if out' bulbs are completely functioning.

Yes there's also a bulb to advise if the charging is low. Great, but what if the regulator's not regulating and the system is overcharging? Had that once, blew bulbs and did the batter no favours.

The gauge I have is duel readout showing volts and amps, and uses a 50amp 0.75mV shunt. I don't want/need it on all the time so I'm going to make it switchable. However, since posing the what switch question, it occurs to me a heavy duty switch is not needed as the meter itself is drawing negligible current, and, if wired to the lighter socket the socket circuit is already fused @15amps.

Thanks for the various replies.

 

[ian.settle1]

NickD stop being an argumentative git, all Tazz is pointing out is the principal use of what and how a shunt works not the actual design parameters. Way your going you'll be in the naughty boys room again.

 

[NickD]

All I'm concerned about is the OP and anyone else reading the thread being misled and confused and thinking they've got their understanding of basic electrical theory wrong or wasting their time building circuits with the wrong values. Is this so unreasonable? On an electrical discussion forum I would have thought that was important. I find it odd anyone thinks it's not.

 

[HandySparks]

No you right, the shunt is usually a 0.5 ohm resistor, and needs to be in series with the main positive cable to the battery, the amp meter then measure the voltage across the shunt, usually +1v to -1v which is proportional to the current being drawn, and shown in Amps

... all Tazz is pointing out is the principal use of what and how a shunt works not the actual design parameters.

'0.5 ohm' sounds like an 'actual design parameter'. In this case, it's clearly an inappropriate value for the shunt, given the level of current to be expected.

 

[dave21]

deleted, double post

 

[UKMeterman]

To the orginal poster,
Drop a line to LEM LEM ? current transducer, voltage transducer, sensor, power measurement and ask them to suggest a current sensor for the level of current you are expecting. This sensor will be fitted round the insulated wire you wish to measure current and also to a meter of your choice. This type of sensor will be far safer and easier to use than a shunt.
If you want any more help ask.