Jump to content

IGNORED

Ammeter Question


superfunk

Recommended Posts

Hi,

I'm not familiar with this ammeter in the car, more use to voltmeters. I start the car and it runs well. When I rev the engine, the ammeter follows. It does not go past about 40amps, but its following the revs of the engine. Putting a voltmeter to the battery shows 14-15 volts, again raising with the revs, but not going much over 15. Is this normal, or is it a sign of an electrical problem... volt regulator, bad connections, etc

.. oh yeah, its a '71 and has the original style external regulator.

Thanks,

Adam

Link to comment
Share on other sites


:finger:

Sounds unwell!

The ammeter, if all is normal, should be only just on the + or CHARGE side of zero.

To have the needle follow the engine revs is an indication of no regulation in the charge circuitry.

It should NEVER approach 40 amps under normal conditions.

In terms of voltage, the battery should be at or near 12V with engine off, rising to ~13.8V with engine running.

14 -15V is too high, indicating once again lack of regulation.

So, yes, there seems to be a lack of alternator regulation going on:rolleyes:

I wouldn't suggest driving under those conditions, the battery will get very excited/overcharged and may EXPLODE.

Replacement of the regulator is my best guess.

Make sure your battery and alternator connections are in good order when you fit the new regulator.

Actually, now might be a good time to convert to an internally regulated alternator:classic:

Link to comment
Share on other sites

I have a spare external regulator sitting here that I don't need. Yours for $5.00 + postage if desired. It was brand new from NAPA last year, their $40.00 variety (not the $18.00 cheepo). I had a similar problem with a voltage regulator before it eventually it blew all of the bulbs that were on when the VR gave it's last gasp (literally exploded several of them), and fried the fusible link. Of course it was dark at the time and I had to drag my girl home at midnight. Anyway, consider the upgrade to the higher output 280 internally regulated alternator along with the plug unit that takes care of all the wiring issues. If you decide against the upgrade (which I DO recommend), drop me a PM. The regulator I have has about 5 hours on it and it's getting very dusty on my workbench. Good luck!

p.s. please take the advice to get it fixed before driving any more lest you will be tempting a malfunction that can easily result in a very expensive fire.

As for the plug adapter.... Arne, weren't you involved with making those available at one point? (I could be wrong there, but somehow I think of your yellow Z - which I really like - when I think of those adapter plugs.)

Link to comment
Share on other sites

Im going to stick with the alternator for now. It seems to be working fine, and I cant justify buying a new one at this very moment. Just a couple things I thought I should clear up. It is always on the positive side. Also, my battery froze (oops) and this is hapening after thawing it out and putting a good charge on it. Could the battery be messed and causing that? Either way, im going to get a regulator.. just curious.

Link to comment
Share on other sites

So, if you let the car run does the ammeter return closer to zero? Having the charge up around 40 right after you start the car is pretty much normal as long as it returns to close to zero after a few minutes. What are you running as far as radio and other electronic and electric equipment? All these things play into the equation. Yes, freezing the battery never does them any good. The age of the battery also plays into this equation.

Link to comment
Share on other sites

Its a fairly new battery. The ammeter sits mear zero at idle right after start up. It only goes up when I rev the engine. It will go up to near 40 if I rev it high, and fall back near zero at idle. This is while running minimal electrics. Turning on lights or radio has a minimal effect on the gauge.

Also 14-15 volts at the battery, is that too much?

-Adam

Link to comment
Share on other sites

I have a spare external regulator sitting here that I don't need. Yours for $5.00 + postage if desired. It was brand new from NAPA last year, their $40.00 variety (not the $18.00 cheepo). I had a similar problem with a voltage regulator before it eventually it blew all of the bulbs that were on when the VR gave it's last gasp (literally exploded several of them), and fried the fusible link. Of course it was dark at the time and I had to drag my girl home at midnight. Anyway, consider the upgrade to the higher output 280 internally regulated alternator along with the plug unit that takes care of all the wiring issues. If you decide against the upgrade (which I DO recommend), drop me a PM. The regulator I have has about 5 hours on it and it's getting very dusty on my workbench. Good luck!

p.s. please take the advice to get it fixed before driving any more lest you will be tempting a malfunction that can easily result in a very expensive fire.

As for the plug adapter.... Arne, weren't you involved with making those available at one point? (I could be wrong there, but somehow I think of your yellow Z - which I really like - when I think of those adapter plugs.)

I would take him up on the regulator. It will probably solve your charging problem. Then look into upgrading the system at a later date.

Link to comment
Share on other sites

As for the plug adapter.... Arne, weren't you involved with making those available at one point? (I could be wrong there, but somehow I think of your yellow Z - which I really like - when I think of those adapter plugs.)
I came up with the concept for the adapter, and oversaw the initial orders. They were built for me by Dave Irwin (he of headlight relay fame), who still builds them today. I'm no longer directly involved, but you can contact Dave about them in several ways, one of which is a mail link on the alt. adapter info page.
Link to comment
Share on other sites

What happens with the 240Z ammeter when a alternator upgrade is done with a alternator that puts out about twice the amps that the ammeter is rated at? A 45 amp ammeter and a 85 amp alternator. I would think that a ammeter should be matched to the alternator output.

Link to comment
Share on other sites

isn't it a good idea to switch to a volt meter at that point? That way the wiring can be updated so that the full amperage doesn't run all the way into the passenger compartment and through the dash.

-Trevor

Link to comment
Share on other sites

Since the output of the alternator loops through the ammeter before going to the fuse box I would say that something needs to be changed. Any addon accessory past the ammeter/fuse box will push the ammeter to its limit or over. The 75 280Z used a shunt under the hood to drive the ammeter with its millivolt output going to the ammeter that is actually a millivolt meter with a amp scale on it. Then in about 76 the ammeter was changed to a volt meter.

Link to comment
Share on other sites

Essentially, the ammeter measures what is going into or out of the battery, NOT the load on the electrical system.

[if it did measure the total load, then, yes, it would have to be ranged to match the capacity of the alternator].

The ONLY time an ammeter DOES measure the total load, is when the engine is OFF and the ignition is ON.

In this case, it will read "-" always, since the storage battery is DISCHARGING.

So, in a normal system, the battery is a storage device which provides a ready current source to turn the starter.

Also, it provides enough reserve to power up any electrical circuit/accessory, including the alternator exciter windings, until the alternator starts to function at a certain RPM.

Then the alternator can take over the load, which may only be 20A or so, right up to its' rated capacity under extreme conditions.

What you then see on the ammeter, is not that total load, but the charge current that the alternator feeds into the battery, the trickle current.

This current is determined by the potential difference of the battery voltage to the alternator voltage, the potential difference, PD.

The storage battery is nominally 12V, the alternator normally supplies a voltage of 13.6 - 13.8V.

Hence the flow of current INTO the battery or ammeter reading slightly on the "+" side of "0'.

In a normal system , a simple test to demonstrate the workings, is to have the engine idling with a "+" indication on the ammeter.

Then, switch on the headlamps.

You will observe a quick but definite flick of the ammeter back to "0", maybe even go "-" but it will recover and settle back to the small "+" value.

This is the alternator not supplying the extra load, the battery supplying the shortfall current, the regulator sensing the increased load and then compensating for it by increasing the alternators current output.

Quid pro quo.

If the ammeter doesn't settle back to the "+" reading, there is a regulatory/charging issue.

If you don't already have one, the installation of a maxi-fuse/fuseable link on the output of the alternator, to match the cabling rating is alwas a good idea.

A 85A alternator will make short work of a cable system with a rating of 30A.

Any fuse is there to protect the wiring, period.

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...

Important Information

By using this site, you agree to our Privacy Policy and Guidelines. We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.