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Car Forum / MINI / April 2004Ammeter installation
Has anyone installed an ammeter in their Mini? How did you do it? I borrowed one from my brother and ran 10-gauge wire from the solenoid to the dash and back, where I put in a small plastic box to gather all the accessory wires together there. It worked fine, except that when I turned on the headlights (low/dip beam) my engine would sputter at idle - even with most other accessories off. Even with the basic alternator, I figured the problem was the long wire run into the dash and back, along with the wire gauge being too light. I removed the ammeter, having measured what I wanted to measure, but I'd like to put one in permanently at some point. Soooo...I looked into types of ammeters. Seems the 100-amp (plus) ammeters have a local shunt between the battery and accessories, then you run very light wires to the ammeter. However, it is IMPOSSIBLE to find an external-shunt ammeter below 100 amps! I've looked! So now I have a 30-amp ammeter, which I figure I'll hook up using 6-gauge wire. This will be heavy wire, but conservative, seeing as how it will give me only about 1/2 VDC voltage drop in the whole run to the dash and back. I also figure I'll be selective about what accessories I wire through it! The ignition doesn't need it, but the headlights, fan, wipers, and such all should. Any comments or ideas? Thanks in advance! > Has anyone installed an ammeter in their Mini? How did you do it? Generally speaking, you are better off not installing one, and fitting a volt meter instead. > I borrowed one from my brother and ran 10-gauge wire from the solenoid to > the dash and back, where I put in a small plastic box to gather all the > accessory wires together there. This is the problem, younow have a long run of high current capacity wire which runs through the bulkhead twice and has no fuse. Any chafing and you are likely to have a fire. > It worked fine, except that when I turned on the headlights (low/dip beam) > my engine would sputter at idle - even with most other accessories off. > Even with the basic alternator, I figured the problem was the long wire run > into the dash and back, along with the wire gauge being too light. No. If the long run introduces additional resistance then it will reduce the current drawn by the headlights and reduce the electrical load, and hence physical load on the alternator. > I removed the ammeter, having measured what I wanted to measure, but I'd > like to put one in permanently at some point. If you really really must have one then you want one with an external shunt resistor. > Soooo...I looked into types of ammeters. Seems the 100-amp (plus) ammeters > have a local shunt between the battery and accessories, then you run very > light wires to the ammeter. However, it is IMPOSSIBLE to find an > external-shunt ammeter below 100 amps! I've looked! Thats really the only way to go for an ammeter. Local shunt (in the guage itself) is just horrid. > So now I have a 30-amp ammeter, which I figure I'll hook up using 6-gauge > wire. This will be heavy wire, but conservative, seeing as how it will give > me only about 1/2 VDC voltage drop in the whole run to the dash and back. "Only"?? > I also figure I'll be selective about what accessories I wire through it! > The ignition doesn't need it, but the headlights, fan, wipers, and such > all should. But then you've completely lost the only real point of an ammeter-it no longer tells you whether you are charging or discharging. > Any comments or ideas? Thanks in advance! Get a voltmeter instead. Instead of telling you how much current is going into or out of you battery at any time, it tells you whether your battery is flat. If it reads very low, you turn a few things off and keep the engine running until it rises, so that you can start your car next time! Great notes, Graham - and you're right, if given the choice between ammeter and voltmeter, the voltmeter does tell a lot more in the grand scheme of things. I have a voltmeter to install also, but had been thinking an ammeter is sure nice for instant feedback regarding the net charge/discharge on the electricals. But a voltmeter would indeed give all the same information in the end, plus tell me if my regulator has died before the battery starts boiling! A couple notes - by "only about 1/2 VDC voltage drop" I meant one-half volt - which is in the charge/discharge range of a healthy battery. Graham said: > But then you've completely lost the only real point of an ammeter-it no > longer tells you whether you are charging or discharging. True enough if you bypass any major-drain electrical accessories. But since the ignition circuit doesn't take a lot of current, bypassing it for the ammeter would still give a "mostly" accurate picture of the charge/discharge on the battery. I still hate the idea of having my lights run through a long wire, after having converted them to a relay-based system! My conclusion is that it's probably best to forget the ammeter, unless someone somewhere can produce a 30- or 60-amp ammeter with an external shunt. Thanks again, Graham... > > Has anyone installed an ammeter in their Mini? How did you do it? > [quoted text clipped - 53 lines] > keep the engine running until it rises, so that you can start your car > next time! > Great notes, Graham - and you're right, if given the choice between ammeter > and voltmeter, the voltmeter does tell a lot more in the grand scheme of [quoted text clipped - 3 lines] > information in the end, plus tell me if my regulator has died before the > battery starts boiling! Yes, as you clearly understand, a voltmeter is a more useful thing. > A couple notes - by "only about 1/2 VDC voltage drop" I meant one-half > volt - which is in the charge/discharge range of a healthy battery. I'll repeat myself: >>"Only"?? 0.5V is enough to make a quite visible difference to the brightness of your headlights! I certainly wouldn't tolerate an unnecessary half volt drop. > Graham said: >>But then you've completely lost the only real point of an ammeter-it no >>longer tells you whether you are charging or discharging. > True enough if you bypass any major-drain electrical accessories. But since > the ignition circuit doesn't take a lot of current, bypassing it for the > ammeter would still give a "mostly" accurate picture of the charge/discharge > on the battery. I still hate the idea of having my lights run through a > long wire, after having converted them to a relay-based system! Precisely! > My conclusion is that it's probably best to forget the ammeter, unless > someone somewhere can produce a 30- or 60-amp ammeter with an external > shunt. I would agree completely. > > My conclusion is that it's probably best to forget the ammeter, unless > > someone somewhere can produce a 30- or 60-amp ammeter with an external > > shunt. > > I would agree completely. As has been pointed out, a voltmeter is probably more use to you than an ammeter. However, if you a want to make your own ext shunt ammeter it is not that hard, an ammeter is after all just a voltmeter with an extra, usually much larger, series resistor. I personally do run an ammeter on my mini, in the early days before I reloomed the whole shell, charging was always a niggling fear. An ammeter lets you know exactly what is going on. Mark, I'm curious how you did it - I do realize that about an external-shunt ammeter, but I'm not sure how to design it. I guess I'd have to have a shunt with a highly-accurate resistance, right? Then calculate the voltage drop and calibrate the appropriate voltmeter? > As has been pointed out, a voltmeter is probably more use to you than > an ammeter. However, if you a want to make your own ext shunt ammeter [quoted text clipped - 4 lines] > reloomed the whole shell, charging was always a niggling fear. An > ammeter lets you know exactly what is going on. > As has been pointed out, a voltmeter is probably more use to you than > an ammeter. However, if you a want to make your own ext shunt ammeter > it is not that hard, an ammeter is after all just a voltmeter with an > extra, usually much larger, series resistor. An ammeter is usually just a voltmeter *in parallel* with a *small* resistor - I'm sure that's what you meant to say! A voltmeter "across" ( shunting, in parallel with) a resistor measures the voltage developed due to the current flowing in that resistance QED it's now an ammeter. (On the other hand, a voltmeter in series with a resistance works differently - the resistor just scales the voltage that the voltmeter sees). Cheers RMC, England |
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