Ammeter ?

SmokinBBC

SmokinBBC

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Joined
Mar 25, 2008
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Location
Oak Ridge, NC
Turned on the headlights and the ammeter went into negative territory....not much, just a couple degrees and stayed there. After startup cranking it goes positive a a few degrees and goes strait up after a couple of minutes.

Hooked up the multimeter.

headlights off, needle is strait up.
idling 13.75
1800 RPM's 13.9
2300 RPM's 13.9

headlights on, needle is a few degrees left of strait up.
idling 13.6
1800 RPM's 13.65 about the same at higher RPM's

If I load it up with turns signals, high beam, etc, needle moves more to the left....alternator stays at the 13.6 range or higher....never lower than 13.6..pretty steady.

So, alternator seems to be functioning properly. Battery is fully charged. So, is this normal? Alternator is rebuilt original 63amps. Belt is fine...can't really explain it.

BTW, the ammeter is a replacement and always acted this way....just got around to checking the alternator since it is getting darker earlier and the lights will be on more.

The only non original electrical item is the DUI HEI.

Do I need a higher amp alternator?
 
Assuming you have a mechanical/clutch/stock fan, the puppy you need load the electricals down with is the HIGH speed blower on your HVAC....and headlights, the rest don't count.....

:twitch:
 
Turned on the headlights and the ammeter went into negative territory....not much, just a couple degrees and stayed there. After startup cranking it goes positive a a few degrees and goes strait up after a couple of minutes.
Click to expand...

That's correct for a fully charged battery and working alt and ammeter.


headlights off, needle is strait up.
idling 13.75
1800 RPM's 13.9
2300 RPM's 13.9
Click to expand...

Good, but you may be able to see a very slight movement to center when shut off.


headlights on, needle is a few degrees left of strait up.
idling 13.6
1800 RPM's 13.65 about the same at higher RPM's

If I load it up with turns signals, high beam, etc, needle moves more to the left....alternator stays at the 13.6 range or higher....never lower than 13.6..pretty steady.
Click to expand...

Bad, looks like alt is not pumping out enough amps.

So, alternator seems to be functioning properly. Battery is fully charged. So, is this normal? Alternator is rebuilt original 63amps. Belt is fine...can't really explain it.
Click to expand...

Alt is big enough if working properly.
Since it reads positive when first starting up for a few minutes, I would assume the gauge is correct, so when it shows a discharge, you are using more juice from the battery than from the alternator.
An easy test would be to drive it for an hour+ with everything on and the battery should slowly discharge like your gauge shows.
If you have an ammeter that can handle 50+ amps then test it at the alt bat terminal or test it on a VAT40 or similar with full load on system.
 
Gene, when I load it up with heater fan and brights, the ammeter moves even further left(disharge). However, the multimeter stays pretty constant.

Nooni, what controls the amp output? Can this thing be rebuilt to supply the right amount of power or more power?

I could just buy a replacement, but then I would have another original vette part sitting in a box on the shelf somewhere.

There's guy at work who has a couple sitting on the shelf. He's going to check what they are. I may pop one of them on to see what the output is....proplem is, I think the SB pully is different than the BB...the BB is double width and sticks out further to align with the crank pulley.
 
SmokinBBC said:
Gene, when I load it up with heater fan and brights, the ammeter moves even further left(disharge). However, the multimeter stays pretty constant.

Nooni, what controls the amp output? Can this thing be rebuilt to supply the right amount of power or more power?

I could just buy a replacement, but then I would have another original vette part sitting in a box on the shelf somewhere.

There's guy at work who has a couple sitting on the shelf. He's going to check what they are. I may pop one of them on to see what the output is....proplem is, I think the SB pully is different than the BB...the BB is double width and sticks out further to align with the crank pulley.
Click to expand...

You can try one of the sbc alternators, one of the belts should line up, if not an impact zips them off easily.
I thought you earlier said this was a replacement, but if you want to keep the original case, just rebuild it, parts are pretty cheap.
The easiest way to test is just to take the complete car to a place like Advance Auto and they can do a full load test on the car for free.
 
The ammeter is a replacement.

The alternator is original and I definitely want to keep the case. I rebuilt it some years ago with a simple repair kit. The kits which include the bearing, etc are going for 25 to 30 bucks. I found the stator for 30 bucks. Still haven't found a rotor.

I am not an electrical guy, so I'm not sure what I would need to replace. Maybe buy a delco/remy 10si for 80 bucks and put those internals in my case?





I usually never let an AZ guy go near my vette....but I might have to make an exception this time.
 
Smoke, I been in 'lectricals' for a long time, make that 55+ years, did some design work on '80's Gel cell lead battery backup work for a small electronics company....we always dealt in voltages not currents with regard to battery charging and discharge levels....

IMO, ampmeters are a bad news way to monitor automotive or any battery/generator/alternator system performance....

the one true measure is a voltmeter....

SO, when you put DVM probes across battery terminals, does it EVER dip below 10.5 volts for cranking the engine? if so, battery is discharded/weak/bad JUST after engine fires, the alt has to go to 14.8 or damn close but not over, for a few seconds, dropping to not lower than 13.4 for the duration of running....the decline is depending on total run down time of the battery and other loads on the electrical system AND the ultimate capacity of the alternator....

I think from what is said above that you have a bad diode in the stack and the alt is in fact bad....but the only true way to find it is to look at the alt output stud with a oscilloscope....but the DVM is saying the same thing....
many years/decades? ago I went through this same shit, and I found a bad diode with my 'scope'....the waveform was fischtoonk.....

:crutches:
 
Here is a test from cold start-up.

Connected cold 12.3
Cranking 10.2
High idle 1100rpm 14.6 (ameter right of 0 around +10)

High idle lights on 14.4 (ammeter not yet at 0)
High idle lights/fan 14.2 (ammeter approaching 0)
High idle lights/fan/brights 12.7 (ammeter moved left of around the -20 mark and engine bogged down)

Cruise 2200 rpm 14.0 (needl strait up)
Cruise lights 13.8 (needle a couple of degrees to the left)
Cruise lights/brights 13.7 (needle more to the left)

Idle 725 rpm 13.8
shut down(not running) 12.4


Looks like it sends plenty when the battery is charging right after cranking.:confused:

Haven't done a load test at AZ yet.
 
SmokinBBC said:
Here is a test from cold start-up.

Connected cold 12.3
Cranking 10.2
High idle 1100rpm 14.6 (ameter right of 0 around +10)

High idle lights on 14.4 (ammeter not yet at 0)
High idle lights/fan 14.2 (ammeter approaching 0)
High idle lights/fan/brights 12.7 (ammeter moved left of around the -20 mark and engine bogged down)

Cruise 2200 rpm 14.0 (needl strait up)
Cruise lights 13.8 (needle a couple of degrees to the left)
Cruise lights/brights 13.7 (needle more to the left)

Idle 725 rpm 13.8
shut down(not running) 12.4


Looks like it sends plenty when the battery is charging right after cranking.:confused:

Haven't done a load test at AZ yet.
Click to expand...

I have to say those figgers look totally kosher to me, I see no problems.....

but that's not to say you COULD still have a buzzy/bad electrical connection somewhere....that shit can drive one krazy.....

I seriously doubt you have a battery/alternator failure.....MAYBE a wiring issue, but I doubt it too....

get a voltmeter from a 80's Chebby pickup, it should fit in the vette just fine....EARLY shark, not later....

:D:friends:

edit, I would have liked to see about .3 volts (300 mv) higher on all your readings, but I write that off to maybe your voltmeter reading a tad lower than mine, rather doubt it's the car, the overall levels are very consistent with what I like to see.....
 
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SmokinBBC said:
What about the drop to 12.7 and engine bogging down? Maybe a wriing problem in the high beams?
Click to expand...

NO, when engine boggs down at lets say ~!650 rpm idle the alt will not put out full voltages.....they get very lazy, but simple changes of the pulley are fine for idle in traffic, but you hit 5 grand with crank speeds and that alt is spinning even faster than hell, it's coming apart internally.....so there are limitations....

the only way to cure your problem is with a higher rated alt, I would go CS144 these daze, my older similar output thing is a 17SI off a old '79 caddy Seville....but it's getting rare and out of stock these decades now....

the mechanicals should be the same, as the only diff is the larger diameter...
and the regulator plug....but that's easy.....

if your idle is less than say 700 rpm's the alt will tend to drop out ....but at say 800 rpm, it's still putting out say 13.5 or so....you are fine...

that is measured at the output heavy red wire stud....

EDIT, I looked at your profile and listed as a '70 and in fact I dunno/remember if you have a SI series alt, with the regulator plug looking like -- on the connections or one of them super small things with that relay crap regulator on the typical firewall? location and the reg plug looking like || on the arrangement....if you got the later one, you seriously need upgrade and not mess with it, just too damn old for modern cars.....
 
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SmokinBBC said:
It's a 10si 3 wire, internal regulator. 63amp
Click to expand...

Yeh, about what I got off all the 10SI alt's in the past...ok for a stock car, barely....

I"d rather have overkill, so to upgrade, it be ME....

if you do, go the CS144 route, and have done with it...junkyard cheep and typically a regulator will fix them, if necessary....

or go to Rockauto.com and get one new/rebuilt for grins....
 
The only way I test alt output is with amps. The voltage test is an okay quicky test.
For reference, a 63 amp 10si with a bad battery will put out around 50 amps max at rpm and at idle around 20 amps. The low or bad battery just simulates a carbon pile load like a VAT40 machine.

If wanting to keep the original case, the switching the guts with a new alt is a good way. I've done it before many times and is the chapest fastest way. Sometimes the windings go bad where they will not produce the rated amperage.

Here are a couple links.
Do a voltage drop test first.
http://www.autoshop101.com/forms/elec05.pdf

http://www.equiserv.com/ProductInfo/vats/vat-40/VAT40um.pdf
 
Rather than a bad regulator....how about a bad connection at the horn relay.

I was getting ready to pull the trigger on an 80amp upgrade kit when I decided I would try to hunt down another problem. The parking brake light dims but doesn't go all the way out when the parking brake lever is down. I pulled the the console and the switch is working properly....new problem...more hundting to do.:censored:


Anyway, I decided to check the connections at the horn relay. And wouldn't you know it, the connection for the small wire that goes to the alt plug was loose. Pulled it and cleaned the connections....now the Ammeter blips to the right and then goes strait up when loads are added!:banghead:

Thanks for all the help guys.
 
I wiggled and loosened the brake pressure safety swich and the light went off. put it back on and light still off. Brakes are firm, no leaks and MC is full.

Nothing like a 41 yo car to drive you nuts.
 
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