Ammeter & Alternator

[Dale Bowman]

The ammeter in my car has been "bust" since I bought it and I'm "currently" (sorry about that) looking at solving an electrical problem I have.

Reading some articles I've seen noted that the altenator output must not exceed tha ammeter rating (might explain why mines the way it is) & if you do have a higher output alternator then use a voltmeter instead.

Is anyone running a +/-60 ammeter with a high output alternator?

[289 Baz]

Hi Dale you could talk to Speedy Cables, they repair all types of gauges so they have a good idea of how they work, plus they could repair yours rather than buying new from the States, they could also re-calibrate it to read higher if required. I also think that the Amp meter should be wired in so as to sample the current not take the full load, but I am sure that some one will correct me if I am wrong. So you need to check how yours is wired in.

Barry

[Dale Bowman]

Hi Dale you could talk to Speedy Cables, they repair all types of gauges so they have a good idea of how they work, plus they could repair yours rather than buying new from the States, they could also re-calibrate it to read higher if required. I also think that the Amp meter should be wired in so as to sample the current not take the full load, but I am sure that some one will correct me if I am wrong. So you need to check how yours is wired in.

Barry

Hey Baz,

Already have a new AM, bought it sometime ago just not got round to fitting it, also have a voltmeter they included in the box which I didnt order?? ... bonus.

Looking at the wiring diagram the AM ios wired in series between the Maxi-fuse and the fuse box supply. (Maxi fuse coming direct from the battery via Isolating switch).

Dale

[Paul Blore]

Hi Dale you could talk to Speedy Cables, they repair all types of gauges so they have a good idea of how they work, plus they could repair yours rather than buying new from the States, they could also re-calibrate it to read higher if required. I also think that the Amp meter should be wired in so as to sample the current not take the full load, but I am sure that some one will correct me if I am wrong. So you need to check how yours is wired in.

Barry

I think the full load that you want to measure has to go through the measuring device, i.e. the gauge. With a volt meter you can "sample" the PD across a component, but the whole current passes through an ammeter.

Paul

[Dale Bowman]

I think the full load that you want to measure has to go through the measuring device, i.e. the gauge. With a volt meter you can "sample" the PD across a component, but the whole current passes through an ammeter.

Paul

Yeah that's the way it looks to me. (in series between the batt/alt connection and the fuse panel). The only fuzzy bit for me is the fact I have a 105amp Alt but an AM that is 60a max .... which is most probably why is went t*ts up to start with.

[Roger King]

I'm just reaching this stage with my car, too. The alternator output current should be wired to go through the ammeter. It would really make much more sense to have a voltmeter, but sense has nothing to do with originality (believe me, it really doesn't). The correct ammeter is a +/- 30A Lucas/Smiths.
CAI is one idea, they could probably modify an ammeter to work with the higher current. My solution was going to be to simply bypass the ammeter, and leave it looking pretty - I have a charging light to indicate charge and the ammeters in my other old cars never used to move much anyway.
I'd be interested to know what route you take Dale, and how it works out. I wouldn't have thought your problems in France were linked to the ammeter, though - but I'm no electrician!
Roger

[Karl]

Hello Dale,why didn?t you ask me on Saturday? I have a 100 Amp alternator and a +- 50 A ammeter. I wired it in the circuit so that all the alternator output current is going through the ammeter. So I can see if every consumer is taking the current that he needs, for example 10 A for ignition, 25 A for the fans, 15 A for the lights and so on . The alternator is only delivering what you ask, I have, when all the electrical consumers are on, a maximum current of 45 A.The correct way for wiring an ammeter is between the alternator and the battery plus. The consumers are on the alternator side of the ammeter. So you can see the loading current for the battery, no matter if consumers are on or off (needle is in the positive area) or, when the alternator is not turning, the current which is drawn from the battery ( needle goes to negative). The starting current must never go through the ammmeter!
Any questions, please ask1
Regards Karl

[Dale Bowman]

These are from the wiring system that my car uses.

As you can see in the first diagram the main "MAXI" fuse is connected on the ALT / Batt side of the system (In my case to the Isolation switch instead of the solenoid)
The second diagram show the optional addition on the ammeter which, as I said earlier, is in series in the "916" cable from the maxi fuse to the fuse panel.

Also note the second CAUTION about the ammeter rating exceeding the Alternator output.

http://i1125.photobucket.com/albums/l59 ... 2409dc.jpg

http://i1125.photobucket.com/albums/l59 ... f5599d.jpg

I'm going to do some digging behind the dash to make sure the cable from the ammeter to the fuse panel isnt shorting. Like Roger, I am thinking of putting the new ammeter in "unwired" purely for asthetics & add a voltmeter to one side out of the way.
I may just try without the ammeter for now see if the maxi blows again, if not, wire up the new one BUT if I do I'll be getting a sub 60a alternator

[Roger King]

We really don't need these high-output alternators in our cars - we don't have all the electrical stuff more modern cars have. The problem is finding a low-output alt! Best bet are the original-style copies for concours cars. I think the one I have is 60A - it's as low as I could get.
All sounds eminently sensible, Dale.

[Karl]

Hello Dale,
if your car is wired as your drawings show it everything is correct. Instead of a maxi fuse the us car builders also used a "fusible link", a piece of wire, which will get interrupted when it carries to much current without causing a fire. this, or a fuse, should always be in the ammeter circuit.
Don`t be afraid of an ammeter, even with a high output alternator. Again, it is only for checking the loading and unloading current of the battery. It has worked for years in a million of cars. A volmeter will only tell you that it is 14 Volt when the alternator is running and tell you the battery voltage when the alternator stops. With the ammeter you can actually follow what happens. After starting the engine the battery voltage is a little lower, so more current flows to the battery for a while and, as cthe charging increases, reduces to a very small current. I like to see the current, so I always know that things are correct. The current output from the alternator has nothing to do with the ammeter range, because the consumers are connected before the ammeter, only battery charging oes through ammeter. Happy wiring!
Karl