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Ammeter
- Thread starter Acollin
- Start date
Jay Laifman
Donation Time
Keep in mind that the later cars had a different range. I believe it coincided with the generator to alternator change over.
Jay Laifman
Donation Time
And that is exactly the danger/problem with these - pulling all the power through the firewall to the dash, and back. I do believe that the factory wiring is to run all the power coming off the alternator through the ammeter. I've seen people say there is a "shunt" way of doing it. I have no idea what that is.
The proper way to wire the ammeter is between the solenoid and everything else but the starter motor. That way all current TO and FROM the battery, except starter motor current, goes thru the ammeter. If you wire it such that the "...lead from the alternator will pass thru the gauge" then it will only show current FROM the alternator INTO the battery and system. It will always read plus or zero, never negative. So if the alternator dies, your gauge will show zero, even tho the battery is supplying all the power to the car, and the battery is discharging. You'll end up dead on the road and puzzled as to why the ammeter never showed that the battery was getting discharged.
Tom
Tom
Jay Laifman
Donation Time
I see the difference that Tom is making - and that is probably how my car is wired. Though Tom's description still has the same problem. All the power running the car off the alternator is going through the firewall and that one gauge. Yes, I run it that way. And I've done it that way for some 30 years. However, some here have still advised that it's not a good idea.
There should be no concern about the high current going thru the firewall. It's only about 30 Amps max and only that level for a few minutes after starting. After a few minutes the battery is nearly charged and there is little current flowing thru the ammeter and thru the firewall. And just about every other wire going thru the firewall has the potential to carry very high current if the insulation gets cut thru and the conductor contacts the chassis. So regardless you need to be sure the firewall grommet is in good shape.
There has been some concern expressed that if the ammeter fails,and becomes an open circuit, you would lose all electric power. True, but I have never heard of such a failure. And the only solution to that is to use a Voltmeter instead of an ammeter. That solution has some merit, but I have determined/ decided it's not worth the trouble to change.
By the way, when adding an ammeter to a SV it is not obvious how/where to actually run the wires. In my car I ran the heavy brown wire from the solenoid to the ammeter (thru the firewall). Then from the ammeter, I ran a heavy brown wire back thru the firewall and connected it to terminal 1 of the fuse holder, where the other brown wires are connected, and ALL the brown wires should be connected, including all the ones previously connected to the solenoid. But there are more brown wires to be connected at the fuse holder than there are posts on terminal 1, so I made a spare junction out of an old fuse holder.
Tom
There has been some concern expressed that if the ammeter fails,and becomes an open circuit, you would lose all electric power. True, but I have never heard of such a failure. And the only solution to that is to use a Voltmeter instead of an ammeter. That solution has some merit, but I have determined/ decided it's not worth the trouble to change.
By the way, when adding an ammeter to a SV it is not obvious how/where to actually run the wires. In my car I ran the heavy brown wire from the solenoid to the ammeter (thru the firewall). Then from the ammeter, I ran a heavy brown wire back thru the firewall and connected it to terminal 1 of the fuse holder, where the other brown wires are connected, and ALL the brown wires should be connected, including all the ones previously connected to the solenoid. But there are more brown wires to be connected at the fuse holder than there are posts on terminal 1, so I made a spare junction out of an old fuse holder.
Tom
Last edited:
One of the push-on connectors on my ammeter came loose a couple times, once while I was driving on the highway, and my car died. The connector was still attached to the gauge, but wasn't making solid enough contact. I don't remember exactly how it was wired, but it was not the simple way Tom recommends. Still, I switched to a voltmeter after finding that there was evidence of arcing on it at an Invasion a few years ago.
I don't think I'll be running 400 Watts of current into my dashboard. If that's how the original meter was configured, I'll be rewiring it to use a shunt on the engine bay side of the firewall and then send a very small fraction of the current to the meter. If the meter has an internal shunt, I will disconnect it. I see a 30A shunt on eBay for $25. Kind of spendy, but it looks like a quality part.
Same goes for the headlamps - I'll be using a relay on the engine bay side of the firewall to keep the current loads on the headlamp switch down to a dull roar.
Same goes for the headlamps - I'll be using a relay on the engine bay side of the firewall to keep the current loads on the headlamp switch down to a dull roar.
PC, so what do you feel you gain by using the shunt inside the engine bay? Safety? As I said there is only 30 Amps of current running thru the ammeter for a few minutes. That drops way down pretty quickly and goes to about zero after about 10 min on the road. And even if there were 30 amps running thru the firewall hole continuously what are you concerned about? The heavy gage wire handles that current with almost no loss of voltage. Maybe you're concerned that the insulation on the wire might get cut and touch the chassis. If that's your concern note that it's an even worse situation if one of the wires to the gauge from the shunt contacts the chassis, because you probably use smaller gauge wire for that. And I don't know how you plan to match the external shunt to the meter movement in the gauge.
Regarding use of a relay for the headlights, that probably makes sense as it reduces the contact erosion on the switch and reduces the voltage loss going to the headlights, resulting in slightly brighter light.
Tom
Regarding use of a relay for the headlights, that probably makes sense as it reduces the contact erosion on the switch and reduces the voltage loss going to the headlights, resulting in slightly brighter light.
Tom
RootesRooter
Donation Time
One potential problem to avoid with ammeters is making sure the clamp that holds the gauge to the back of the dash can't make contact with the terminals on the back of the gauge, which are in pretty close proximity. One good touch could cook the ammeter and kill the ignition.
65Beam said:
Yes, I agree. And that's why I said earlier:
And Rootes Rooter, I agree about the clamp, which is grounded, and connected to the case which is also grounded.
In other words, gotta be careful to avoid shorts. But no need to be concerned about 30 amps going thru a right sized wire.
Tom
Yes, I agree. And that's why I said earlier:
And Rootes Rooter, I agree about the clamp, which is grounded, and connected to the case which is also grounded.
In other words, gotta be careful to avoid shorts. But no need to be concerned about 30 amps going thru a right sized wire.
Tom