Ammeter Readings

[68Roadster]

I did some extensive searching thru previous posts but have not seen anything related to my current problem.
I replaced the battery today because of a bad cell. The car cranked right up after installation but I noticed that the ammeter follows the throttle movement.
Just idling, the ammeter reads about 20. If I tap the throttle, the needle jumps up to about 40.
I read about 13.5V across the battery while running, I read about 17.5V at the BAT terminal on the alternator while idling.
Do I have an alternator or voltage regulator problem? I have never seen the ammeter readings go up with the throttle.

Thanks in advance for the help.

Cee

 

[Vettehead Mikey]

It could be that your new battery is really low on charge and your alternator is going full blast trying to charge it.

Try putting your charger on over night and see what happens tomorrow.

 

[68Roadster]

Mikey,
The battery was at 93% charged when I took it outta the store. I had them check prior to leaving.
I've never seen the alternator put out that much voltage, makes me think the alternator or voltage regulator is bad, not used to seeing the ammeter needle move that much.
Thanks for the advice. I'll fire it up again after I get the mufflers back on and see what she does.

Cee

 

[brusso]

I did some extensive searching thru previous posts but have not seen anything related to my current problem.
I replaced the battery today because of a bad cell. The car cranked right up after installation but I noticed that the ammeter follows the throttle movement.
Just idling, the ammeter reads about 20. If I tap the throttle, the needle jumps up to about 40.
I read about 13.5V across the battery while running, I read about 17.5V at the BAT terminal on the alternator while idling.
Do I have an alternator or voltage regulator problem? I have never seen the ammeter readings go up with the throttle.

Thanks in advance for the help.

Cee

In theory, you have the same readings at the battery as you do at the alternator. Do to the cars being 20-30 years old, it's not uncommon to have a difference of 1/2 volt or so. Even that would be do to a voltage drop across the battery cables. Try taking some jumper cables and test this theory. First connect the neg battery terminal to the alt bracket. Then see if your voltage readings change at the pos alt terminal. If no or minimal change, remove jumper cable. Then connect pos battery terminal to pos battery connection on alternator. Be very carefull doing this. You don't want the jumper cable to wiggle free and touch ground. Unless you want to do some welding. For testing the positive side, I've used a heavy gauge wire, with eye connections, and temporarily connected pos batt terminal to pos batt connetion on alt. Use a wire of the same gauge as the wire on the pos batt terminal of alt.

If you had that 17 plus volts at the battery itself, I'd say don't waste you time and just replace alt. But where you have a huge difference in voltage's, I think that it is a battery cable or grounding cable issue.

 

[68Roadster]

brusso,
I'll check that stuff out....thanks for the help.
commando57,
I don't want to drive it until I can figure the problem out. I have never seen the ammeter needle swing all the way to +40 when I press the accelerator. If I let the car run, it won't even work its way back to 0. Something is causing the ammeter to stay at +20 and then move to +40 when I press the gas. It can't be normal.

Let y'all know what I find (if I find something).

Thanks again.

 

[JohnZ]

Sounds like the voltage regulator. You should show about 12.5V across the battery terminals with a fully-charged battery (engine off), and 13.5-14.5 across them with the engine running at 1500-2000 rpm. If you show more than 15V with the engine running, it's the regulator.

 

[goingballistic]

There is no way that the ammeter should be supplying 40+ amps to the battery unless the regulator is gone. Think of amps as the "power" that pushes the voltage to the battery. You're pumping that many amps because the regulator thinks the battery is dead, essentially one of the diodes in the regulator is shorted or open and the DC power is un-regulated, (i'd bet shorted if I had to)...shorted because the voltage that SHOULD be going to the battery is going to the frame and the alternator is being asked for more current (amps/power)...cause frames can take a lot of "voltage" to ground it's either that or you have a serious short on the high side of your voltage somewhere on your frame......................DO the lights brighten and dim as the RPM goes up and down????????? I suspect not if it's a short.the regulator thinks the voltage isn't getting there and hence more "umph" (otherwise known as amps) to keep the battery charged which is already charged. I'd find this problem soon, batteries have a tendency to "boil" if too much amperage is thrown at it for a long period of time

 

[68Roadster]

JohnZ and going ballistic,
Thanks for the input. I am starting to check all the power wires coming off the 2B battery + cable. I think I have a big short there somewhere as a fully charged battery installed Friday is dead today.
I have a new volt. reg to install once I get done shooting wires. I think I have melted a wire down at the starter, by product of trying to jump the car off after sitting idle for 6 months. I think the connections weren't too good at the time plus the battery had a bad cell.
I agree, it acts like the alt. is trying to pump out max juice to a system that is shorted to ground.
More to come, appreciate everyones help.

 

[68Roadster]

Well an hour or so uncovered one problem. The attached photo shows the fusible link in the red wire from the horn relay to the starter solenoid. This was undoubtedly the puff of smoke I saw when trying to jump off the battery.
I don't show any shorts to ground in the positive battery cable so I know thats good.
How does one go about replacing these fusible links? I searched here, looked thru my Chassis Manual, surfed the web, etc but have yet to find anyone who sells them or tips on replacing. The harness came from M&H Electrical, maybe they can sell me a link. Seems as though others have said you can get them at auto parts stores. I'll check tomorrow.
The link is not broken although the wire looks pretty crispy. Could this be causing the weird ammeter readings and the battery drain??
Cee

 

[dman]

something made alt go allmost full feild ... for it to put out that much voltage an amps ... most pos when you jumped car with old dead bat and bad cell ... and let it run to try charge bad bat... it put alt in full feild via voltage reg ..and this over loaded alt and reg and wire ,,, most pos takeing reg out or cooking it in full feild state ...my best guess??????

 

[brusso]

Looks like you've gotten some great input so far. The charging system is relatively simple. There are just many little things to check and, like anything else, people have different opinions of what to check in which order. The bumpers are only so far apart. The trouble has to be between them. One thing I would add is possibly bringing the alt to a parts store that can test it for you. Most do it for free and I wouldn't drive it, as you already said, until we get this fixed. Good luck.

 

[goingballistic]

Fusable links are designed to protect the wiring harness from "frying". If the link goes, its because you were drawing too many amps through the link.

Now back to my original statement. You said you have no shorts but yet you have an incompleted circuit ( fusable link blown)......you may not show a path to ground from the plus side because the link is blown.

the way this works: Power is generated from the alternator in an AC fashion ( AC being alternating current) the regulator converts it to DC ( Direct current) via a bridge rectifier ( consists of four diodes) if one of those diodes shorts or opens, the regulator no longer functions as a DC rectifier ( regulator). Now you are driving AC Current and voltage down the harness. No big deal right.....wrong. Everything in the car runs off DC NOT AC, now it's a matter of time ( usually rather quickly......see your smoke comment) before something "lets go" ( see fusable link).

I you have an OHM meter, disconnect the battery and check between the positive terminal of the wires and the negative terminal wire it should show open (zero ohms) or at least a very high resistance ( usually through the starter coil), now check and see if there is the same continuity ( ohms) between the plus side wire and a good solid ground on the chassis...is the reading the same?? If it is I would suspect the regulator is blown, if it's not I would think you have a chassis short. Before you do this make sure you replace the fusable link or at least jumper around it......DO NOT RUN THE CAR WITH A JUMPER AROUND THE LINK!!!!!!!! I guarentee you will find the problem really quickly if you do and the repair may be rather costly......ever seen a car on fire????

Regulators are easily checked, your local auto parts store may be able to check it for you, alternators are also checkable and this may well turn out to be the alternator NOT the regulator. It's hard to trouble shoot problems like this without seeing what you are seeing........if you have direct questions, you can PM me or drop me an email.
Cheers, Paul.

 

[dman]

alt should be good it is puting out 17 volts an 40 amps .. if diode was blown volts and amps would be to low .... or not at all .....ps the full wave 3 phase ac output is rectified via rectifer not reg.. sounds like bad reg at this point ....

 

[brusso]

the way this works: Power is generated from the alternator in an AC fashion ( AC being alternating current) the regulator converts it to DC ( Direct current) via a bridge rectifier ( consists of four diodes) if one of those diodes shorts or opens, the regulator no longer functions as a DC rectifier ( regulator). Cheers, Paul.

I wonder why they call it the "diode trio" ?

 

[geekinavette]

A typical "full wave" bridge rectifier circuit uses 4 diodes. Been a while since I looked at an alternator schematic, but as I recall an alternator only has 3...hence the "diode trio".

 

[brusso]

A typical "full wave" bridge rectifier circuit uses 4 diodes. Been a while since I looked at an alternator schematic, but as I recall an alternator only has 3...hence the "diode trio".

I guess that you missed my sarcasm.

 

[mrvette]

Under NO circumstances should the alternator be putting out over 14.8 volts, unless the sense wire is drastically out of wack OR the regulator,


the diode trio is the one that runs the regulator circuit, with the main rectifier pack consisting of 6 diodes, the alt is wound 3 phase delta connect, meaning there are 3 diodes grounded at one end, the 3 phsase of the field coil, meaning stator in this case, and then 3 diodes going positive out to the terminal....the armature is energised by the regulator output, and controlled supposedly, by system overall voltage, typically at the horn relay distribution block....now there is either a resistance wire OR a lightbulb saying alt/bat/gen on the dash...glows red if alt is not putting out....like when key on, and engine still.....
that goes to the other terminal.....

IF you have an ampmeter, the ampmeter is in series with the regulator input, black or black/wh wire, if someone changed the 2 pin plug, it's most likely a red wire with the lightbulb/resistance wire being white, but most sharks were wired with that wire brown in color.....meaning they are really easy to confuse if you have to rewire it....

from the back of the alt. when key is off, the MOST CLOCKWISE reg terminal will have battery voltage on it, the other should NOT....
with key ON, engine still, the other should have slight voltage, with the most clockwise being the same....
with engine running, there should be the nearly the same voltage on both terminals, light bulb not lit, of course....

I suspect you have bad reg wiring, OR you have a bad regulator....

GENE

 

[geekinavette]

I guess that you missed my sarcasm.

heheheh yeah after midnight the brain just refuses to cooperate and I miss a LOT of things. D'oh!

Bill

 

[Hib Halverson]

Typically, the ammeter will move to positive, as rpm picks up, if current is flowing into the battery. That the alternator output voltage is 17.5 indicates a problem. It should be down around 13.2-14.0. With an output votage of 17.5 and the battery at 12.6 or so, there will be current flow from the alternator to the battery In fact, with 17.5v out of the alternator, your new battery will get overcharged and fried in short order.

My guess is you've got a regulator problem but I'd test the system per the service manual, first.

 

[68Roadster]

I appreciate everyones help!
I have not had much time to mess with this, I'm beginning to wonder if I will ever get to drive this car again. Heres what I have so far:

1) The fusible link at the starter was the source of the puff of smoke when I opened the hood. The insulation is burnt off as the picture shows but the wire is intact. I have yet to replace that. I think this was the result of not having a good ground connection when I went to jump the car off.
2) I have checked almost all of the wiring in the starting/charging circuit for shorts to ground. No defects noted. All wires as mentioned at the alternator/VR that should have power do.
3) The new battery was drained 3 days after installation. I have not had battery drain issues on the car prior to doing the rear end work. Courtesy light switches and clock are new and the car is a radio delete so I think this is a non issue other than the fact that it has drained. I let the car idle about 20 minutes the day I put it in while the alt was pushing 17 volts/20 amps.
4) I'm trying to get the battery to take a charge now. It reads about 12.5 volts but the little green eye is not glowing (several Earnhardt like words come to mind)

Have I fried the battery??
I think the voltage reg is bad (as most have suggested) and I have a new one ready to go.
My intentions are to replace the fusible link, make absolutely positive I do not have any shorts to ground, replace the VR, install the battery and try again. It still baffles me that the amp guage follows the throttle, could the bad VR be the cause of this??

Thanks again. I'll let ya know what the outcome is.

Cee