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Ammeters...


edwardatherton
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I have a 45-amp alternator and twin batteries running through a split-charge relay.

The ammeter only reads to 30 amps, so what can I do with the extra 15 amps...?

Could I put a second ammeter for the second battery (although it would still be possible to read too high on one or both gauges), or can someone tell me something about wiring in a shunt (how?)?

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Get rid of the ammeter. Ammeters were only ever designed to be run with a Dynamo. With an alternator you should be using a voltmeter.

What are you trying to gain with the split charge? If its only to run two batteries to give you a greater capacity thn all i do is simply wire them up in parrallel and forget about the split charge.

Cheers

Jon

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Get rid of the ammeter. Ammeters were only ever designed to be run with a Dynamo. With an alternator you should be using a voltmeter.

What are you trying to gain with the split charge? If its only to run two batteries to give you a greater capacity thn all i do is simply wire them up in parrallel and forget about the split charge.

Cheers

Jon

The ammeter is already there in the dash, so I might as well use it.

The split charge is running two batteries because we go camping quite a lot - it powers the fridge etc, and for winter driving I power the heated seats from the second battery in case I forget to unplug them overnight!

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I have a 45-amp alternator and twin batteries running through a split-charge relay.

The ammeter only reads to 30 amps, so what can I do with the extra 15 amps...?

It's only reading 30 amps because the circuit is only drawing 30 amps. Is the ammeter connected in the alternator output or to the battery positive?

The 2nd option is the usual as the ammeter shows charge/discharge, so you could be getting 30 amps into the battery but the alternator could be working at full output by putting 15 amps into headlights and so on.

A 45 Amp alternator only delivers 45 amps if it's asked to, the rating is really the maximum output.

Ammeters aren't restricted to use with dynamos, my RRC had one fitted as standard. I'd certainly agree that a voltmeter is better, easier and safer.

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It's only reading 30 amps because the circuit is only drawing 30 amps. Is the ammeter connected in the alternator output or to the battery positive?

The 2nd option is the usual as the ammeter shows charge/discharge, so you could be getting 30 amps into the battery but the alternator could be working at full output by putting 15 amps into headlights and so on.

A 45 Amp alternator only delivers 45 amps if it's asked to, the rating is really the maximum output.

Ammeters aren't restricted to use with dynamos, my RRC had one fitted as standard. I'd certainly agree that a voltmeter is better, easier and safer.

Mmm, this is more complicated than I thought...

The gauge is only reading 30 amps because that is all it can read - the scale only goes to + or - 30 amps.

When the battery is flat (running the fridge overnight for example), the alternator tries to charge at max charge (in this case about 45 amps).

When this happens, the ammeter needle sticks at the top of the scale until either the revs drop (and sometimes it needs a tap as well), or the battery charges up.

Obviously, having a pinned gauge cannot be good for the gauge internals, so how do I stop it doing this?

Is there a 45-amp (or higher?) gauge that I could substitute for the one in the dash (Series One 88")?

Would a second ammeter plumbed into the second battery work, or would both read the same?

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Ah - I misunderstood your post. I thought you were saying the ammeter only indicated a current 30 amps, I just assumed the full scale deflection was greater.

Yes you can get higher rated ammeters, I've seen 50-0-50.

You can shunt the ammeter, connecting a parallel resistance the same value as the resistance of the ammeter will half the readings, ie 20 amps reading means 40 amps current.

Without looking at the circuit it's difficult to be too specific but your ammeter may be reading the current going into both batteries, which will be high having just started the vehicle.

If you took the current feed to the 2nd battery from the alternator side of the ammeter rather than the battery side the ammeter will only register the current in the vehicle battery.

You could then put a 2nd ammeter in series with the +ve pole of the 2nd battery.

There are shunt ammeters which are really voltmeters which measure the voltage accross a remote shunt resistor. You mount this resistor close to the battery and the wires to the actual gauge can be quite thin.

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Shunt ammeters are much much better than the usual (cheaper) type, as Roger says, they require only low current (thin) wiring to the gauge which is much safer, and much better, as the main supply cable is kept as short as possible.

They are however, quite expensive. They're used a lot in the marine industry where the gauge/monitoring system is a large physical distance from the battery/alternator.

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