13 replies to this topic

[MRclubman1100cc]

Hey got my self an amp meter today and i wouldn't have a clue how to conect it, iv'e looked in the search fourm and there isn't anything usefull, so does any one no how to connect it, it would be a big help thanx

Todd

[Bounce]

You have two types of Ammeter. The good type, and the 'I wouldnt use it unless you really have to' type.

The good type have a remote sensor that sends a signal to the gauge (like the AA/RAC man has when hes checking that your battery is getting a charge when you break down). Keeping the high voltage wire to a minimum.

The other type requires to be wired into the charging/supply circuit in series. Which means you need to run good size wires from your alternator, in behind your dash, connected to one terminal of your Ammeter. On the other terminal you need to, again, run some good size wires back into the engine bay and onto the starter motor (where your battery cable is connected). This all sounds good, but you need to remember that these wires are going to be having some heavy current flowing through them when the car is running. Especially when is cold, dark and wet.

And these wires are going to need to be fuzed for safety. What happens if one of them goes? You then lose all power to your car except the battery. And a good battery will only last 50 miles in the dry daylight with no music.


So let us know which type you have mate.

[MRclubman1100cc]

lol well i have the 'I wouldnt use it unless you really have to type'.

[Bounce]

Dont get me wrong, you can do it if you want. Its your car. But personally, if i wanted one id get 'the good type'

[MRclubman1100cc]

what if i used the double insulated cowax wire that they use for the houses, 250 Volts are running through them 24/7 and i havn't hurd a house burn down, only when people put faulty electrical appiences in thats the only time iv'e hurd of a house catch on fire due to electrical fualt....... so would that be a good idea to use that stuff

[Bounce]

Co-axial wire is not used for mains supply. Co-axial is used to transmit radio transmitions that come no-where close to 240V, not to mention the current capacity of it! Its not the voltage you have to worry about, its the ampage!

For a power supply system of a car your looking and the equivilent of 4AWG (American Wire Gauge) wire.

[Silicon Skum]

Co-axial wire is not used for mains supply. Co-axial is used to transmit radio transmitions that come no-where close to 240V, not to mention the current capacity of it! Its not the voltage you have to worry about, its the ampage!

I don't think he ment co-ax, I think he was refering to twin core cable, and NO it's ***NOT*** rated for that ampage at 12V! Very dangerous to use house wiring for 12V high amperage applications!

I'll explain this a little better;
Wire for house wiring current ratings are rated at 240V, at 240V the current required (amperage) for a given load is LESS than the same load at 12V. Also at 240V the power is AC (50hz in the UK) so the power is switched between postive and negative voltages 50 times per second, this also means that this is a short period of time where the voltage is at 0 volts (also 50 times persecond), and this alternating current is also VERY important to switch gear which would otherwise weld shut with a DC current. This type of loading (AC) requires a different (thinner) cable thickness to that of a 12V DC (direct or "constant" current). Higer voltage is able to transfer more efficiently than low voltage through a conductor, and more current is used at low voltages to give the same equivilent power (wattage). As lower voltages are transfered with LESS efficiency, there is much greater heat produced from a given cable thickness at 12 Volts than the same power (wattage) at 240 Volts.

So at 12V the cable thickness required is MUCH greater than any cable used in the home. If your try this with house power cable, you *WILL* cause a fire in your car! NEVER use mains rated cable for ANY 12V load in a car.

SS

[MRclubman1100cc]

Hey Silicon Skum yes that is the stuff im talking about thax for that info, so what stuff would u prefer to use?

[norway_triumph]

nothing wrong in using the 'I wouldnt use it unless you really have to type'. This is the "calssic" type and the only thing i have in my old cars. You should use as thick as possible wire to put this metre into the circuit. Ideally astarter-lead thickness, but you could go a little bit thinner if its not possible to get so thick cables through the bulkhead. but as stated beware as all the current drawn from the car will go through these cables. If in doubt wire it up. put all electricity appliances on and feel if the cables are getting hot - hot cables = to small diameter.

[Bungle]

i have a ammeter in my mini

just wire it in correctly and use grommets and it will be ok

[Dan]

nothing wrong in using the 'I wouldnt use it unless you really have to type'. This is the "calssic" type and the only thing i have in my old cars.

Because older cars run a dynamo, not an alternator. That limits them to 30 amps which is pretty safe under any circumstances. Alternators in Minis can run upto 65 amps depending on the age and 75 if you have an uprated one. If your car has a 65 amp alternator you can't use a basic ammeter as the type with internal shunts are pretty much only available up to 60 amps both ways and 65 amps will break it. If you break the ammeter in this intallation then all the power in the car fails and as Bounce says above you are running on the battery which won't last long to get you home. You wouldn't need to run cable anywhere near as big as the starter cables, they run 300 amps and are made from 12mm cable. 8mm will be fine for an ammeter and is rated to 105 amps at 12v (with PVC insulation).

The other important reason to use car cable instead of house cable is that it's far more flexible to cope with vibrations. The cable in the walls of your house is T&E solid core copper which work hardens with vibrations and so will weaken over time. Car cable is multi stranded and so is very flexible.

These gauges are also pretty worthless now as an alternator always charges, they were useful with a dynamo because they don't charge at idle so you needed to keep an eye on how much charge your battery was getting but with an alternator there is always charge available, so long as you don't have far too many accessories fitted!

It is possible of course and if I could get one that could be installed without any compromises then I'd have one but as yet I haven't seen one I like.

Edited by Dan, 27 December 2006 - 11:15 AM.

[dklawson]

Please listen to Dan.

A volt-meter is a much better, safer, and more useful choice for alternator equipped cars.

[Jimmyarm]

It would be fairly simple to wire in a bypass switch in case the ammeter failed, you would have to use appropriately rated components of course

As stated above, they are a bit pointless in a alternator equipped car though. Much better off with a voltmeter.

[Silicon Skum]

Hey Silicon Skum yes that is the stuff im talking about thax for that info, so what stuff would u prefer to use?

As already stated by others, I would also use 8mm cable, ALWAYS use a thicker guage cable than the load requires, less risk of a fire or over heated cable.

As for guages, I just use a cheap generic voltage guage for a caravan / motorhome battery bank (about £6 at Maplins), which I mounted in my side panel of my boot-board I made with some left over chip-board. You don't realy need to view the guage constantly (only for diagnostic reasons), and a boot install location is much easier due to short cable runs from the battery.

SS