Adding ammeter?

[kjdunne]

1989 Evinrude 40 hp E40ELCEC. Would like to add an ammeter to moniter charging system. Am I correct to place it in series in the red wire output of the rectifier? It would require about 30 ft. total wire to reach my console and back, including slack for steering, etc. I'm thinking of using 12 ga. wire for this. Would that be sufficient? Any thoughts or experiences from others who have done this greatly appreciated.

 

[Barnacle_Bill]

Re: Adding ammeter?

Why not add a volt gauge instead. Much simpler and will tell you if you motor is charging.

 

[Vic.S]

Re: Adding ammeter?

The table HERE gives recommended wire gauge vs amps and total length of cable run.

It would appear that 12AWG is suitable for a maximum of 5amps to avoid excessive volts drop on a 30ft run.

In series with the red wire is the correct place to fit it to monitor the current output from the charging system.

Agree though that a voltmeter is a lot easier to fit.

 

[samo_ott]

Re: Adding ammeter?

Some ammeters have a shunt resister that goes in series with the red wire and carries most of the load and then from there a small wire comes off it to the meter up front. Thus you do not need long heavy wires for the setup.

 

[kjdunne]

Re: Adding ammeter?

What would the correct voltage be? Something above 13?

 

[F_R]

Re: Adding ammeter?

When running, anything over battery voltage as it is when not running indicates that it is charging. It can go as high at 16 volts or more on an unregulated system. Ignorance is bliss. Without the voltmeter, you never know. With a voltmeter it gives you something to sit there and worry about.

 

[kjdunne]

Re: Adding ammeter?

I know these things put out very little current a low RPM, but will the voltage still be above battery voltage at idle?

 

[jay_merrill]

Re: Adding ammeter?

Yes ... if it is working correctly.

 

[Barnacle_Bill]

Re: Adding ammeter?

You will see very little voltage increase at idle if any. But that would apply to an amp gauge too. When everything is working properly you will see more of an increase as RPMs approach 2K and higher.

 

[72SideWinderSS]

Re: Adding ammeter?

...... Ignorance is bliss. Without the voltmeter, you never know. With a voltmeter it gives you something to sit there and worry about.

I like it !!!

 

[F_R]

Re: Adding ammeter?

I know these things put out very little current a low RPM, but will the voltage still be above battery voltage at idle?

Depends on the load. If you have a bait aereator and a radio and who knows what else going you will be using more current than the alternator is supplying. In that case, you will not see a voltage increase even though the alternator is working. That is a good arguement for an ammeter, it shows the net charge/discharge at any given moment.

If your only goal is knowing whether or not the alternator is working, consider a tachometer. You will get two functions that way. If the alternator quits working, you won't get a tach signal so it won't work either.

 

[kjdunne]

Re: Adding ammeter?

Thanks everyone. In my blissful ignorance, I was stranded with a battery that read 12 volts on my voltmeter, and would run my bilge pump, but would not crank the engine fast enough to start. My problem was I was using the starter a lot while fishing, and not motoring far or fast between drifts. Fortunatly, a good samaritan came by and gave me a jump start with a portable emergency battery. I will have one of those on my boat before my next trip. After a 25 min. cruise back to the launch, my battery was able to start the engine. I just thought an ammeter would remind me how much charge I was putting back into the battery. I think I'll add one even if it's a little bit overkill.

 

[jay_merrill]

Re: Adding ammeter?

Good points by F_R about load and the tach. Let me rephrase - if you don't have a bunch of stuff running, you will usually see the needle move somwhat after you start the engine.

Which, now that I think about it, makes me wonder if the needle would move anyway. For example, if you had a bunch of accessories running, would starting the engine result is less draw from the battery after it got going. And, would that in turn cause the voltmeter needle to move somewhat? I really have no idea. I guess that such a change would be more noticeable in an ammeter but, its still an interesting thought.

 

[guy74]

Re: Adding ammeter?

If your only goal is knowing whether or not the alternator is working, consider a tachometer. You will get two functions that way. If the alternator quits working, you won't get a tach signal so it won't work either.

Well, if the rectifier goes bad, the tach will still work as long as the rectifier doesn't short to ground, but the charging system won't work. BTDT So a woking tach doesn't guarantee a charging battery. I would never put an ammeter on anything, a voltmeter is better, easier to install, and less dangerous (fires from large current conductors). An ammeter won't tell you if you've charged your battery long enough either, so it wouldn't have helped you in the instance you gave as example.

 

[F_R]

Re: Adding ammeter?

To charge a battery, current must flow backwards through it. To make the current flow backwards, the charging voltage must be higher than the battery's voltage at the moment. So yes, there should be some upward movement of the needle if the charging current is greater than the discharge current. But if the battery is in a serious discharge state, it takes a lot of running before the voltage goes up very high. What I'm saying is you aren't going to see 16 volts on a half dead battery, even if the alternator is doing all it can do.

Trouble is those dash mounted voltmeters aren't the most sensitive or accurate things ever made. But for the price they aren't bad.