6 replies to this topic

[MINI 1]

hi , my mini has a ammeter clock fitted with 2 x heavy duty wires coming from it ,can somebody tell me where these go to make it work,and why do people fitt these instead of volt gauges ??????

ash

[minimender]

It fits in line on the feed from the battery.

It shows amount of discharge as well as charge. (don't fit it wrong way round or it will read backwards.)

Edited by minimender, 27 December 2007 - 08:13 PM.

[MINI 1]

ok , thanks for your help but been to the mini and seen that the two leads follow under the hood is their anyway of conecting it to the main wire coming from the battery without wireing into the boot ? any chance of having your num and ill ring you and try and get your help over phone.................hard to explain over emails

ash

Edited by MINI 1, 27 December 2007 - 08:41 PM.

[Bungle]

its no more use than a volt meter

just harder to wire in

[dklawson]

We really need to have a FAQs article on this topic as it comes up so often.

Ammeters on cars with alternators are (generally) dangerous. You do NOT wire it to the battery. When wired correctly (more or less), the two leads you found go in series between the heavy spade terminals on the starter solenoid and the fuse box. (On the early cars at least... the two ammeter wires would replace the heavy brown wire that goes from the solenoid to the fuse box). You don't go to the battery with the wires. You don't want battery current to the starter flowing through the gauge, only the output from the generator/dynamo.

The reason the gauges are fundamentally dangerous is as mentioned, because all of the current flowing to and from the battery (excluding cranking current) flows through the gauge. That was sort of OK when our cars had 22 Amp generator/dynamos. However, most cars beginning with the Mk3 had an alternator rated for at least 35 Amps. That means that you really should run heavy enough wires to and from your Ammeter to handle the maximum output of your alternator. So... if you have a 55 Amp alternator, you need a gauge calibrated for +/- 60 Amps and heavy enough wiring to match. Most Smiths/Lucas Ammeters are of the +/- 30 Amp range and not suitable for use with an alternator.

In addition to getting the wiring size and gauge range correct... you still have the issue of running heavy wires through the firewall to the gauge. Dangerous at best.

Here's the exception. SOME non-Smiths/Lucas Ammeters are of the so called "shunt type". Here a heavy duty resistor called a shunt is wired in series with the brown wire I mentioned above. A special ammeter (called a shunt type ammeter) is connected to each end of the shunt. It's basically a volt meter. It measures the voltage drop across the shunt as the current is flowing. It uses much smaller wires and the gauge itself is not carrying the current. You won't find Smiths/Lucas shunt type ammeters.

Closing Sidebar: This is a brief history lesson. In the early 20th century, Smiths and Lucas has a gentlemens' agreement on which firm would produce what products for the automotive market. This is how most of the wiring devices were the domain of Lucas while strangely... things like gauges and electric motors were the realm of Smiths. While Smiths had the rights to make the gauges... the exception were ammeters. For some reason, Smiths agreed to let Lucas make the ammeters. You won't find a Smiths ammeter until late in the 1970s or perhaps the early 1980s. Apparently the 60+ year old gentlemens' agreement fell apart at that time.

[robson]

very good post!

[MINI 1]

ye thanks alot that is a help.

ash