thorin

hey all,
i've just installed an electric fan and elec fuel pump and now the ammeter is pegging the gauge on the dash. i've probably added an add'l 20-23 amps to the alternator work load. should i switch to a voltmeter? i'm thinking my amp load is cool but has gone beyond what the gauge will read (40). i would like to keep the original appearance gauges if possible. thanks.
:seeya

Kid_Again

...sounds like you've pegged the alternator...what's it's rating?....you now have a decent load

thorin

i can only speculate it's rated at 65 amps. is there a way to tell as i cannot see any markings (it's chromed) and was on the car when i bought it (5 yrs ago).

toddalin

You didn't say whether it pegs low or high.

Don't know what year you have, but base alt in 63-64 and ??? was only 37 amps. Even upgraded w/ac and TI only went up to 60 something amps with some intermediate values in the low 40s.

thorin

sorry.....ammeter is pegging high, on the "plus" side. there is no ac and alternator has external voltage regulator.

Tom Piper

I'm assuming the ammeter in your vehicle is the same as the one in my '64.

This is my first thought:

The ammeter in my vehicle is what is called a "shunt" ammeter. With a shunt ammeter, only a percentage of the actual current is supposed to go through the ammeter because the ammeter circuit is in parallel with a larger wire that is intended to carry the majority of the current. The shunt ammeter is then calibrated to read the total current going through both circuits.
If the circuit that is intended to carry the heaviest load becomes open, then the shunt ammeter circuit now carries all the current, not just a portion of it.
This would cause the ammeter to read an extraordinary, and incorrect, high current.

Tom Piper

Tom Piper

If your pegging on the plus side, it sounds like something is wired incorrectly. If you were drawing too much current, it would be going negative.

Tom Piper

wombvette

I have all of the same items on my 66 plus AC , with the original guage and it reads normally. You need to go back and check how you have the stuff wired.

yooperod

:iagree:

I had a engine wiring go up in smoke once (due to a wrong ignition coil capacitor shorting to the shielding)
before I found the cause and I was going on a trip in 3 days
I change the harness and put fuses in the 3 main power wires
While on a trip one of the fuses blew (just to small)
This created an open ,which caused more currant to pass thru the alt gauge.
pinning it and burning it out.

rod

Veet 66

I did the same thing you did. I installed an electric fan and a couple of other electric devices. My amp. gauge at idle was in the neg. when the electric fan came on. My alternator was changed to an internal reg. at 65 amp. I removed my amp. gauge and sent it to Corvette Clocks where he changed the wire size in the gauge to compensate for the additional amp. This worked ok but I am not much for amp. gauges so I sent a used amp. gauge to him and he converted it to a volt gauge. It looks just like the amp. gauge in color only difference is the scale.
:auto:

toddalin

Gee, I put a 100 amp, one wire, internally regulated alt on my '64 and left all the old stock wiring in place. (Just using the hot battery wire to the alt.) Gauge reads just as it always has with no problems. Only difference is now you have to blip the throttle to about 1,200 rpm to start the charging cycle. It gets blipped anyway, so no BFD.

JohnZ

You have a wiring issue either in the alternator or the voltage regulator, or both. The midyear ammeter isn't really an ammeter at all, and doesn't carry ANY of the electrical load in the car (different from C1's, which were wired in series and carried all the loads); it's a sensitive shunt voltmeter. One wire goes to the battery terminal on the starter solenoid, and the other wire goes to the "hot" bus on the horn relay; those two wires sense the voltage present at those connections, and the gauge displays the voltage difference between the two points as "amps" as an indication of current flow to or from the battery. :thumbs:

MikeM

Check/clean the connection at the horn relay. If it is loose or dirty it will cause your problem.

thorin

man, you guys overwhelm me with your advice! there are many "opportunities" to look into here, first i think, will be the way i've wired the to added pieces. by process of elimination, i can work back toward the alternator if necessary.
you guys are great, thank so much for taking the time to help!
:seeya
ps. i'll let the list know how this comes out.

Tom Piper

thorin

I think I have it figured out from your symptoms.

Here is the short version:
Don't connect any new loads/accessories to the battery positive (+) cable at either end. This cable is connected at the batter plus side and goes to the starter. If you connect anything on this cable, the ammeter doesn't see it to measure the current drawn for it.
The place you want to connect additional loads/accessories is at the horn relay where all the positive wires are connected together. If you connect them at the horn relay, the ammeter will be aware they are there and how much current they are drawing.

Here is the long version:
From the factory, the only load the ammeter doesn't see is the starter current. If the starter current (about 300 amps) was going through the ammeter and wiring, it would last about one start and go up in smoke.
If you connect any loads at either end of the battery plus cable to the starter, the ammeter won't see these loads either. But, the ammeter will see the alternator output that is supplying these loads.
The ammeter calculates the sum of the current going to the battery. For a given load, if the load is drawing 10 amps from the battery to function (that's 10 amps of negative current to the battery) and the alternator is supplying 10 to the battery to supply that load (that's 10 amps of positive current to the battery), the ammeter will measure 10 amps minus 10 amps, which is zero.
By connecting loads at the positive battery cable, the negative current for that particular load is not known to the ammeter. So, for a 10 amp load, you will see 10 amps of positive battery charge when there is really zero.

When I look at my '64, I see a problem when trying to connect additional very heavy loads. The wiring in my car from the plus side of the starter to the horn relay is about a 10 gauge wire -- good for about 30 amps total. An extremely heavy load may be too much for this wire -- when you consider the loads already on it.
The easiest solution might be to do what a previous post said -- don't use an ammeter, go to a volt meter (like most modern vehicles use). This way, you can connect the load right at the battery cable and the volt meter will still be correct.

Tom Piper

thorin

damn tom, some very interesting stuff! plus, you write it in such a way even an "electrically-challenged" fool like me can follow along. thank you for offering such super advice, i'll be digging into the issue this tuesday i hope (about the 1st day this week i'll get some time) and will report to the list what happened.
ya know, colorado is a great place to visit, you ever been (hint, hint)? just kidding but i sure wish you lived around the corner! thanks a ton!
:seeya

magicv8

I'm going to install an electric fan this winter. I already installed a 135 amp alternator to run it and my auliliary headlamps. Check the Details page linked off my home page (listed below) to see where I put 2 60amp fuses - one to protect the harness and the other to run the added stuff directly off the alternator.

toddalin

Actually makes perfect sense because I wired up a JBL 240 watt amp directly at the battery with 8-gauge cable and it dosen't change the alt gauge reading when it comes on. You just know that pulls some amps. :yesnod:

magicv8

I hate burst your bubble Tom, but the ammeter isn't an ammeter it's a galvanometer measuring voltage drop between the starter and the horn relay.

It isn't adding any currents and it is a rough guess at amps - my A-C car came with a 61 amp alternator and a 40 amp "ammeter"/galvanometer.

C1 cars had ammeters. C2 cars do not.

PS One of my winter projects will be to gut the ammeter in favor of a voltmeter - as you suggested.


[Modified by magicv8, 10:07 PM 11/3/2003]

Tom Piper

thorin, disregard this post -- you don't need to know any of this.

As far as I am concerned, all "shunt" ammeters are really voltmeters -- just, some can be designed to carry more current than others. But, for the discussion here, I figured, since the meter says "amps" on the front, I would refer to it as an ammeter for simplicity. The meter (whatever you want to call it) simply measures the voltage drop across a known resistance (in this case, the resistance of the wiring and circuitry that goes from the starter to the horn relay).
In fact, this is why changing this wire to a heavier gauge to accomodate more current will make the "meter" read even more inaccurately.

Somehow, it seemed more confusing for the intended audience to suggest changing from a voltmeter to a voltmeter. And, I don't think this is the forum that I will start talking galvanometers.


Tom Piper


[Modified by Tom Piper, 7:21 AM 11/4/2003]