Printable Version of Topic

Click here to view this topic in its original format

914World.com _ 914World Garage _ Charging Issue, revisited....

Posted by: Aaron Cox Apr 16 2005, 12:03 PM

guys,

im having a heck of a time trying to figure out whats the problem. Gen light came on thursday night on my drive home. i measured voltage goin to the battery as follows:
car off ~13 volts
car idling 14 volts
1500 rpm 15.8 volts BAD

i borrowed a new voltage regulator from bill 'grimstead' and it did not rectify the problem.
all fuses are fine. all connections are solid. the belt is on nice and snug

with the car off, the G light is lit
car idling, it is lit, but very dim....
higher the rpm the less bright the bulb becomes....

now that i have eliminated the voltage reg as a failure mode...
do i have a crapped out alternator?

where is the best place to buy a new alternator?

help me before the WCC... i dont want to blow up my optima....

Posted by: echocanyons Apr 16 2005, 12:06 PM

my alternator was new as was my regulator and I still had a very dim light that was only noticable at night.
I drove it for over a year without any problems

I attributed it to bad connections but I could never figure out where.

Posted by: skline Apr 16 2005, 12:07 PM

I may have a spare alternator here. Have not tested it but it came off of a running car. You can try it if you like. If it turns out to be the problem, it's yours.

Posted by: Aaron Cox Apr 16 2005, 12:09 PM

jeff's 2.0 has one on it also....

i figure if im going to be in there....ill go with a new or rebuilt one.....
this sucks....

but the battery should never see more than 14v according to haynes manual.... how is it that both regulators are letting it see 16volts?????

Posted by: ws91420 Apr 16 2005, 12:10 PM

Almost sounds like the brushes are going on the alternator. If you have been draining the battery 15.8 v @ 1500 could be in the acceptable range if I remember correctly. When the brushes went in mine it did the same thing. They can be replaced as long as all other componets are ok.

Posted by: ws91420 Apr 16 2005, 12:15 PM

14v is the mean or average voltage that you should see at 2000 rpm with a load (resistance added to the circuit) so you could see a range.

Posted by: Aaron Cox Apr 16 2005, 12:17 PM

QUOTE (ws91420 @ Apr 16 2005, 11:15 AM)
14v is the mean or average voltage that you should see at 2000 rpm with a load (resistance added to the circuit) so you could see a range.

ok. so if i go back out to the car, start it up, measure voltage at the battery at many levels of rpm, what voltage should i say "yep...my alternator is effed!"

i was getting ~16v at like 2k rpm....

Posted by: ws91420 Apr 16 2005, 12:23 PM

But that is without a load on it. Alt are meant to be load tested for accurate readings. If you are 2200 rpm you adjust a load resistor to have a current flow of 33 amps. That load resistance causes a voltage drop which gives you the voltage. Basic electronics.

Posted by: Aaron Cox Apr 16 2005, 12:26 PM

ok. here is the best question yet.....

WHY did my alternator light come on in the first place??? and the subsequently go out the next morning...and now it is always dimly lit when the car is running?

Posted by: ws91420 Apr 16 2005, 12:34 PM

You have two brushes on that ride on the shaft that picks up the AC current that is generated. Yes I said AC. The diodes rectify the current into DC. The brushes are held in place on the shaft by springs. Last night as the alt heated up the brushes couldn't conduct the current as well. This am all is cooled down but the brushes are still worn that is why the light is dim. On mine if I remember right the new brushes were like an inch or inch and a half. My old ones about a quarter inch.

Posted by: Bleyseng Apr 16 2005, 12:35 PM

maybe its a loose fuse....

Posted by: Aaron Cox Apr 16 2005, 12:37 PM

welby,

you are the man. thanks for helping me with this....
so a minimium of new brushes are in order.....or just plop in another alternator.....

so..in the meantime, will i be hurting anything if i drive it....? maybe run out the battery if it isnt getting full charge?

Posted by: Aaron Cox Apr 16 2005, 12:38 PM

geoff,

i sprung all the contacts and all fuses are good

Posted by: bondo Apr 16 2005, 12:38 PM

QUOTE (ws91420 @ Apr 16 2005, 11:34 AM)
You have two brushes on that ride on the shaft that picks up the AC current that is generated. Yes I said AC. The diodes rectify the current into DC. The brushes are held in place on the shaft by springs. Last night as the alt heated up the brushes couldn't conduct the current as well. This am all is cooled down but the brushes are still worn that is why the light is dim. On mine if I remember right the new brushes were like an inch or inch and a half. My old ones about a quarter inch.

The AC is generated at the outside windings. The brushes are for the field, which is DC energized and controlled by the regulator. The more that goes to the field, the more that comes out on the AC side. I don't see how bad brushes could make it overcharge. It could be a bad battery, or it could be a bad diode that's confusing your meter. Got an oscilloscope?

Posted by: Aaron Cox Apr 16 2005, 12:40 PM

i dont have a sillyscope here....

now we have 2 converging opinions.....

seems like a new alternator is in the cards

Posted by: Bleyseng Apr 16 2005, 12:41 PM

sounds like the alt is putting out good voltage so it should be a regulator or wiring problem (sumthin loose).

Geoff

Posted by: Aaron Cox Apr 16 2005, 12:43 PM

QUOTE (Bleyseng @ Apr 16 2005, 11:41 AM)
sounds like the alt is putting out good voltage so it should be a regulator or wiring problem (sumthin loose).

Geoff

ive swapped out 2 regulators... didnt change. i checked all the connections.....

my car is pissing me off.....

Posted by: ws91420 Apr 16 2005, 12:46 PM

The reading Aaron is getting is false because he does not have a load on it. An alternator must be load tested for accurate results. I was descriding how a alt works wasn't sure where the change from AC to DC occured in the alt just that it went through the diodes.

Posted by: brp914 Apr 16 2005, 12:48 PM

imho alternators dont go bad by generating excess voltage. I have had the alt light come on due to shorts on the same cicuit that it is on. In my case it turned out to be the engine compartment light. The wire to it had been spliced at some point in the past. Well it unspliced and was dangling down and shorting against the body. For some reason the alt light was especially bright when braking. I've heard where the reverse light wire doing the same thing. Better do a little troubleshooting with your vom and a schematic. IIRC this stuff goes to fuse 9. I wonder if pulling this fuse and looking to see if your alt light goes out would help locate the problem. good luck

Posted by: ws91420 Apr 16 2005, 12:49 PM

Mine with the bad brushes put out good too at higher rpm but got worse over time. I am speaking on this from personal experence. First thing I did was replace regulator I tested it at AZ and it was bad. Then this problem came later.

Posted by: Bleyseng Apr 16 2005, 12:49 PM

Does the lite get brighter as you add load to it? Turn on the headlites, fogs, heater fan, etc and see.

If that makes the light come on brighter then odds are a diode is going out as the Alt is just putting out part of its juice.

Geoff

Posted by: Aaron Cox Apr 16 2005, 12:50 PM

QUOTE (Bleyseng @ Apr 16 2005, 11:49 AM)
Does the lite get brighter as you add load to it? Turn on the headlites, fogs, heater fan, etc and see.

If that makes the light come on brighter then odds are a diode is going out as the Alt is just putting out part of its juice.

Geoff

going to go check that now....

Posted by: ws91420 Apr 16 2005, 12:54 PM

People read previous posts. His voltage reading is inacccurate because he is not load testing. At 2200 rpm you adjust a varible resitor till you get a current reading of 33 amps and check the voltage. The varible resistor creates a voltage drop so Aaron's 15.9 v unloaded could be 14v with the load.

Posted by: bondo Apr 16 2005, 12:55 PM

QUOTE (ws91420 @ Apr 16 2005, 11:46 AM)
The reading Aaron is getting is false because he does not have a load on it. An alternator must be load tested for accurate results. I was descriding how a alt works wasn't sure where the change from AC to DC occured in the alt just that it went through the diodes.

It takes alot of current to push an optima over 16v, unless its bad. It shouldn't be able to happen if everything is right. It could also be a short in the harness that's giving the full battery voltage 12v to the field. That COULD make the alt light come on, but I'm not sure. Most FLAPS will test your charging system for free while its in the car.

Posted by: ! Apr 16 2005, 01:23 PM

Because your car is too low and is riding on the bumper stops....

Posted by: Aaron Cox Apr 16 2005, 01:27 PM

geoff, the light didnt get any brighter from what i could tell...

Posted by: messix Apr 16 2005, 01:52 PM

K.I.S,S
keep it simple.... look for bad grounds... motor to chassis and motor to battery. also dont over look corrosion at the alt. mounts and connections.

it could be a bad battery. low internal resistance will cause high charge voltages. test it with a battery load tester. or charge with a battery charger to full charge 13.5 volts @ 2amps then put as much load on it from head lights, high beams, blowers and with a vom look at the voltage drop. try to calculate amp load, ie; headlights 55 watts = 55/12=4.5amps and then you can calculate voltage drop/ time and amp load will tell battery condition.

Posted by: messix Apr 16 2005, 01:57 PM

sorry amend to last post
while doing last test, engine off . not running

Posted by: pete-stevers Apr 16 2005, 01:58 PM

Aaron my funny-lookin brother, Greg had a similar problem checked every darn thing on the car including replacing the brushes.... he ended up sanding down the contacts to the body......and fixed....not sure if it relates to your electrical poltergiest....it drove him .....so good luck
steve

Posted by: lapuwali Apr 16 2005, 02:50 PM

QUOTE (ws91420 @ Apr 16 2005, 10:54 AM)
People read previous posts. His voltage reading is inacccurate because he is not load testing. At 2200 rpm you adjust a varible resitor till you get a current reading of 33 amps and check the voltage. The varible resistor creates a voltage drop so Aaron's 15.9 v unloaded could be 14v with the load.

If the VR is working, and the wiring is good, and the battery isn't internally shorted, the voltage across the battery terminals should never be over 15v at any time. I'm completely lost as to where you're coming up with this "load testing" business. The battery IS a load, and if the car is running there's a non-zero load on the battery, as the ignition and injection systems take up 5-6amps just doing their jobs, even at idle. So, there's always a load when the engine is running.

The alternator just pumps out current until the voltage regulator stops it. As bondo said, it varies the field current to do this, and the field current passes through the brushes. Less current means less output, and the VR operates in a feedback loop, measuring the current coming out to vary the field current and keep it in bounds.

My guess on Aaron's problem is BOTH voltage regulators are bad, even the new one. It's been known to happen.

Posted by: ws91420 Apr 16 2005, 03:33 PM

The battery is not a load it acts like a capacitor when the car is running. To effectively test any altenator you have to put a load on it. The factory manual states to test an alternator to hook up a VOM, an ammeter, and a variable resistor. Rev the engine to 1400 or 2200 or 6000 rpm. Change varible resistor till you get apporiate amp reading for rpms used. Then measure voltage. 14000 rpm = 10 amp 2200 rpm = 33 amp 6000 rpm = 50 amp This all assuming you still have stock 50 amp alt. Basic electronics you get a drop in voltage after the resistance. If the problem Aaron has described is what I think it is load testing wont do any good either because I tested mine and it did fine at the appropriate rpm but the light was still a problem till I replaced the brushes. This was on my other 914 I was driving till this one was ready and now that alt is on my 76.
BTW the brushes help power the field. the current goes from the outer windings to the diode trio and to the batt post.

http://www.allpar.com/eek/alternators.html

Load testing is a standard practice for testing alternators and batteries. Check any service manual of a car that has an alternator.

Posted by: lapuwali Apr 16 2005, 04:36 PM

Welby, I know how alternators work. I also understand basic electronics.

Your procedure is quite correct for testing an alternator that's not installed in the car, or is in the car but isn't hooked up to anything. However, when the car is running, no "variable resistor" is required. The battery has internal resistance. So do capacitors, for that matter. Any resistance is a load. From what I read, Aaron was not measuring the output of the alternator by disconnecting it from everything, he was measuring it with it in a running car, which meant the ignition and injection HAS to be getting power from the battery, so it presented a charging load to the alternator. Indeed, it presented the same charging load that is present most of the time when the car is running. If the voltage is higher than 15v under those conditions IT'S TOO HIGH.

Buy a $30 voltmeter and hook it up to your battery terminals and drive around in the car. You'll find the voltage typically stays around 13-14v, assuming your car is operating properly. It never gets above 15v unless something is wrong.

Posted by: ws91420 Apr 16 2005, 04:45 PM

I am An ASE certified parts specialist (which is more than knowind an alternator from a generator) before you comment on how to test on a car read a manual. The procedure is from the Porsche factory manual so if if they don't know what they are doing then who does. I have worked on cars since I could help my dad who was an ASE certified technician with over 30 yrs experience and numerous awards for training.

Posted by: plas76targa Apr 16 2005, 04:50 PM

Aaron -

I may be throwing a curve into your analysis.. but I had a similar problem with my car - high voltage. I replaced the VR, had the alternator out and tested, cleaned all grounds, still high voltage. WTF? Somewhere I had read a post about the relay board. So I borrowed one locally and that fixed the problem. Might be worth a try.

I will note, my gen light never came on. It does work, it would come on at key turn and go off like normal after the car started. With yours coming on as you've described the RB might not be your problem. Anyway just my $.02 - hope you have it solved by WCC

Posted by: ws91420 Apr 16 2005, 05:16 PM

QUOTE (lapuwali @ Apr 16 2005, 03:50 PM)

The alternator just pumps out current until the voltage regulator stops it. As bondo said, it varies the field current to do this, and the field current passes through the brushes. Less current means less output, and the VR operates in a feedback loop, measuring the current coming out to vary the field current and keep it in bounds.

That proves my point of the brushes. When it got hot the less current light comes on. Next AM brushes making questionable contact light flickers. The car does not produce a sufficent load on its own to load test an alt. Also you can not test an alt with a bad/shorted battery because that will give a false reading. If you go to your FLAPS and they test your alt on the car thay rev it to 2000 rpm and if you listen you hear the machine click and a countdown starts for 60 sec and at the end it clicks again. The click is a load being applied and taken off. If you put your hand over the machine you will feel the that is generated by the resistor that is used.

Posted by: Aaron Cox Apr 17 2005, 02:10 PM

and the final consensus is?

ill drive it around with a VOM meter hooked up to it...

Posted by: Brad Roberts Apr 17 2005, 02:18 PM

Flip a known good relay board into it.

B

Posted by: Toast Apr 17 2005, 02:27 PM

And while you're at it, lower the mount for the relay board for your AX career.....ya know...lower center of gravity

Posted by: Aaron Cox Apr 17 2005, 03:45 PM

QUOTE (Brad Roberts @ Apr 17 2005, 01:18 PM)
Flip a known good relay board into it.

B

ok. ill have to try that.

i used the VOM's continuity meter... the alt harness makes it to the regulator just fine....
maybe its elsewhere on the relay board..

thanks B

Toasty....
real funny.... dont convolute a tech thread