Changing from an Amp gauge to a Volt gauge

[chrissrv195]

Hey guys, I have just purchased a brand new set of Teleflex Lido gauges for our '79 SRV195. They look awesome but I didn't realize the set came with a volt gauge & I have the old amp gauge in the boat. Teleflex Marine says the volt gauge can't be used in place of the amp gauge and to contact them for help with changing the wiring. I have tried hooking the volt gauge up but it always reads 18 volts & I'm afraid if I keep going I'll end up ruining the new volt gauge. Does anybody know how to change the wiring around so the new volt gauge can be used? The wires I have are (1) red/white wire that goes to my key switch, (1) large red/white wire that is not hot, (1) large red wire that is hot (12 volts) & (1) wire that supplies juice to my switch panel. Or if nothing else would it be easier to find an amp gauge in the same style? Thanks in advance.

 

[Theresamarie11]

Hey guys, I have just purchased a brand new set of Teleflex Lido gauges for our '79 SRV195. They look awesome but I didn't realize the set came with a volt gauge & I have the old amp gauge in the boat. Teleflex Marine says the volt gauge can't be used in place of the amp gauge and to contact them for help with changing the wiring. I have tried hooking the volt gauge up but it always reads 18 volts & I'm afraid if I keep going I'll end up ruining the new volt gauge. Does anybody know how to change the wiring around so the new volt gauge can be used? The wires I have are (1) red/white wire that goes to my key switch, (1) large red/white wire that is not hot, (1) large red wire that is hot (12 volts) & (1) wire that supplies juice to my switch panel. Or if nothing else would it be easier to find an amp gauge in the same style? Thanks in advance.

I've only had voltage gauages on my boats and having an amp gauge is entirely different. In general the voltage gauge has one main lead grounded and one lead goes to the point you want to measure voltage at. It's high impedance and doesn't have much current go through it.

Now the amp gauge is just the opposite (at least ones I know of). They are very low impedance and the current flows through the gauge electronics for the circuit your measuring current for. In fact, you can think of the voltage gauge as being in parallel with the circuit and the amperate gauge as being in series. So I can see that just putting a voltage gauage in where an amp gauge was, will not really work. It's basically going to look like an open circuit and measure the open circuit voltage. I'm surprised anything works as it would seem that the circuit, without the amp gauge in it, would be entirely open circuited.

If this is foreign then you should definitely get a boat mechanic involved.



Terri

 

[fc3]

There are two styles of ammeter (the correct term for "amp gauge"). One has an internal shunt and the other type uses an external shunt. Generally, ammeters are wired such that the battery is on one leg and the alternator and loads are on the other leg. That is it's wired in series with the positive lead to the battery, excluding the starter motor lead. In this way, the ammeter directly measures whether the battery is being charged or discharged. It is in many respects, superior to a voltmeter.

Since most meters only need a 1 ma for full deflection, running 100 A though it isn't going to work. Thus a shunt is installed. Most of the current flows though the shunt, and a small amount flows around the shunt to the ammeter. The ammeter is wired in parallel to the shunt.

Now if you have an internal shunt ammeter and remove the ammeter, then the circuit to the battery is broken. You have to connect the wires together when you take an internal shunt ammeter out of circuit. An external shunt ammeter can simply be removed. The up to 1ma current flow though the meter is negligible, so you can just insulate the leads and call it a day. Better would be to located and remove the shunt.

Connecting a voltmeter can't be more trivial. Generally ABYC defines three wire color codes that you are going to be interested in locating. The purple wire is the hot wire from the ignition. You want to wire the voltmeter's positive terminal to that wire so that when the ignition is on, so is the meter. You don't want to connect to a red wire since that's always on and you'll always have almost a 1ma current drain 24x7. Ground the ammeter to the black wire. (More modern ABYC specs call for yellow in the negative 12 VDC circuit, but your boat predates that change.) Finally, if there is a light in the gauge, the blue wire, if I remember correctly, is the color code for helm illumination.

Best regards,
Frank C

 

[chrissrv195]

So it's ok to connect both large red wires together along with my small red/white ignition wire, attach them to the battery connection on the key switch, & then run the ignition wire from the switch to the voltmeter & run ground to voltmeter ground post? That's how I've done it & everything seems to work fine, good charge reading on gauge & also charging battery. Just wanted to doube check so I don't screw up anything. Thanks for the help!

 

[Loyd Dinneen]

I have a 77 mercruiser 470 sda 240 and have just converted it from the rectifier to a alternator conversion kit and was going to install a volt meter and take out the amp gauge. Well looking at the wiring on the amp gauge there is a mass of wiring going to it mainly to the right hand post. There seems to be alot of large red wires and some wires run over to other gauges. Question I have can I just tie them together as they come off the gauge posts and tape them up, the only wire I need to keep is the hot going to the ignition switch and a ground wire for the voltage gauge has anyone ever done this?