Voltmeter conversion

[fintubi]

ERA has instructions and schematics for replacing the in-dash ammeter with a voltmeter.

The key step is simple: eliminating the ammeter from the connection between the load side of the master circuit breaker and the line side of Fuses #1 and #2.

There's also a recommendation to add a heavy-gauge wire between B+ and the alternator BAT terminal, especially when a high-output alternator is used. I gather the reason for this is to provide a direct path to support charging a depleted battery at higher current than the master breaker rating.

My question: if this is done, does the master breaker retain any function? The new connection to the alternator presents unfused B+ at the line side of Fuses #1 and #2 via the original orange alternator wire, effectively jumpering the feed to the same fuses via the breaker.

Thanks,
Bill

[patrickt]

Originally Posted by fintubi

My question: if this is done, does the master breaker retain any function? The new connection to the alternator presents unfused B+ at the line side of Fuses #1 and #2 via the original orange alternator wire, effectively jumpering the feed to the same fuses via the breaker.

Thanks,
Bill

The additional wire that is recommended for alternators that may feed 80 or more amps runs from the B terminal off the alternator (the charging voltage) directly to the battery thus bypassing the 50 amp circuit breaker. A short to ground on this new wire is not going to be protected by the circuit breaker and will indeed provide one hell of a fireworks show. However, a short to ground on other areas of the wiring circuits, that don't back feed through this new wire, would still be protected. But, I can't think of any circuit that wouldn't back feed through this new wire so the circuit breaker effectively protects nothing.

[CJ428CJ]

I converted from an ammeter to a volt meter and also installed a high output 1 wire alternator on my ERA. I was also concerned with that wire being unfused so I simply added a fuse. You can get a 125A fuse from Littlefuse that works well (part no. MEG125BP). I simply "bolted" it directly to the solenoid terminal and then shrink wrapped it to protect it. I've attached a picture.

[patrickt]

Mucho goodo. Now you know that if the starter solenoid sticks in the closed position it will cause the starter to run continuously even while the engine itself is running. And even turning the ignition key “OFF” will not stop the engine or cranking because the stuck solenoid is feeding the ignition circuit via the white wire off the solenoid (which was originally used to bypass the ballast resistor). If you happen to be running an MSD ignition, which does not use a ballast resistor, the white wire connection to the starter solenoid is not necessary (and only presents a problem if the solenoid sticks). You can disconnect it. If your solenoid ever sticks you'll think back and say "dang that patrickt is a wonderful guy."

[CJ428CJ]

Never thought of that. I was aware of that wire bypassing the ballast resistor so full voltage is applied to the coil during cranking but I never thought about the potential consequences. I run an MSD so I’ll have to disconnect it.

Chris

[patrickt]

We've seen it happen and it's actually kind of funny. It sounds really bad and when the driver turns the key off and pulls the key out it still runs and sounds horrible. Then they hop out of the car and pull the coil wire out and invariably get an arm numbing shock in the process. That stops the engine but the starter is still cranking. Finally, they pull a battery cable off and then, when their senses come back to them, the say "well wtf just happened and why?"

[RockBit]

I opted for a voltmeter instead of an aamp gauge. When I wired my instruments, I read the instructions for doing this and called Doug. Doug said all I had to do was connect the two large wires that went to the ammeter together with a piece of metal. I did this and put heat shrink over the connection. I then installed the volt meter using a switched 12v wire and ground.

This has worked fine for five years. Is there any downside to this method?

[patrickt]

Originally Posted by RockBit

This has worked fine for five years. Is there any downside to this method?

None at all.

[Morris]

Originally Posted by patrickt

We've seen it happen and it's actually kind of funny. It sounds really bad and when the driver turns the key off and pulls the key out it still runs and sounds horrible. Then they hop out of the car and pull the coil wire out and invariably get an arm numbing shock in the process. That stops the engine but the starter is still cranking. Finally, they pull a battery cable off and then, when their senses come back to them, the say "well wtf just happened and why?"

One of the first items a tech inspector at any SCCA, IMSA, or NASA will check is when you turn off the main power Switch ..does the motor stop.....if not they will not pass you to run in the event....

[patrickt]

Originally Posted by Morris

One of the first items a tech inspector at any SCCA, IMSA, or NASA will check is when you turn off the main power Switch ..does the motor stop.....if not they will not pass you to run in the event....

Uhhh, how 'bout "it does, if you also pull this other wire out over here...."

[cycleguy55]

Originally Posted by RockBit

I opted for a voltmeter instead of an aamp gauge. When I wired my instruments, I read the instructions for doing this and called Doug. Doug said all I had to do was connect the two large wires that went to the ammeter together with a piece of metal. I did this and put heat shrink over the connection. I then installed the volt meter using a switched 12v wire and ground.

This has worked fine for five years. Is there any downside to this method?

The only downside I see is the risk that somehow the insulation on that live connection will contact something that wears through the heat shrink tubing and creates contact with a ground. The risk SHOULD be quite low, but may warrant additional measures such as ensuring it's properly secured in the wire harness, etc. which is just good practice anyway.

As long as it's properly protected and secured it should be fine.

[RockBit]

Originally Posted by patrickt

None at all.

Thanks Patrick!

[fintubi]

In the particular case of the slabside cars, there's a technique given in the wiring manual which is functionally the same as RockBit's solution but even easier to implement:

On the slabside harness, the + and - ammeter connections pass through a duplex Powerpole high-current connector under the dash on their way to the meter. Since Powerpole connectors are genderless, the two poles on the firewall side of the connector can be plugged into one another, creating a direct connection from the circuit breaker to the fuse block. The pin stacking the two poles into a duplex has to be removed, and some tape unwrapped to give enough slack, but otherwise easy peasy. And reversible!

Bill