Another dead battery thread

[Scott Douglas]

Found the battery completely dead on Dec 30 when I went to prep the car for the New Year's Day run.
Disconnected the ground cable, hooked up battery charger, let it sit for a day at @6-7 amps.
Checked it in the afternoon of that day and found two cells low on electrolyte, I know, not good.
Next day decided to try to start car anyways as battery showed 12.6v.
Car started fine, went for a drive.
Shut it off when I got home and the red light came on with the key off. Figured that was why the battery went dead.
Put new battery in, hooked it up and red light is on.
Everything I've read says the diodes are bad in the alt when red light is on, key off.
So I pull alternator out. Have it tested, it is good (whew!).
If I re-install the known good alternator and hook up the new battery and red light is on, should I try to start the car and see if that clears the red light on when I shut it off, or do I stand a chance of hurting the alternator?
Just to make things interesting the car has an UNGO box, but, it has never caused a problem.
Help?

[wwest]

Originally Posted by Scott Douglas

Found the battery completely dead on Dec 30 when I went to prep the car for the New Year's Day run.
Disconnected the ground cable, hooked up battery charger, let it sit for a day at @6-7 amps.
Checked it in the afternoon of that day and found two cells low on electrolyte, I know, not good.
Next day decided to try to start car anyways as battery showed 12.6v.
Car started fine, went for a drive.
Shut it off when I got home and the red light came on with the key off. Figured that was why the battery went dead.
Put new battery in, hooked it up and red light is on.
Everything I've read says the diodes are bad in the alt when red light is on, key off.
So I pull alternator out. Have it tested, it is good (whew!).
If I re-install the known good alternator and hook up the new battery and red light is on, should I try to start the car and see if that clears the red light on when I shut it off, or do I stand a chance of hurting the alternator?
Just to make things interesting the car has an UNGO box, but, it has never caused a problem.
Help?

For some reason your regulator is suppying current flow to the alternator rotor slip rings key on or off. Plus side of the charging light/resistor is always connected to the battery but complete circuit is normally provided by the regulator only with ignition switch on.

[Scott Douglas]

Just to update this thread...
I took out the regulator and drilled out the rivets to see what was inside.
Looks like things may have gotten a little toasty in there...




I hope Pelican has 'will call' pick-up like they did when they were in El Segundo. It looks like I'll be needing one of these.

[emac]

Scott
As I recall from my "old" days, when they would overcharge the points were welded together.
Try to pull them apart and see if they move.

[HawgRyder]

Come on guys...this is 2013!!
Get a regulator with NO moving parts! (Solid State).
Look around at after-market suppliers for a replacement.
Also....there are 2 types of regulators...ones that shunt power to ground when not needed...and the other is a series type that cuts down the current when the battery is getting full.
The shunt type drags power ALL the time!
So...if the alt takes 20HP to drive it under full load...it will drag 20HP all the time.
The series type takes less HP to drive it when the battery is full.
Bob

[rick-l]

I'm not sure you have a known good alternator. The only way I can think of that the light would be on with the key off is if a diode is shorted and the alternator tries to power up all the electric systems through the light.

Can you take it apart and test the diodes especially the ones between the stator and the B terminal?

[emac]

Hey bob I said old days. Late 60's. lol
Ernie

[wwest]

Originally Posted by HawgRyder

Come on guys...this is 2013!!
Get a regulator with NO moving parts! (Solid State).
Look around at after-market suppliers for a replacement.


Also....there are 2 types of regulators...ones that shunt power to ground when not needed...and the other is a series type that cuts down the current when the battery is getting full.

"..2 types.."

I don't think so, going back to as far as 63ish the mechanical regulators have a voltage (and temperature) SPDT (Single Pole Double throw) "relay". NC (Normally Closed) pole position contact ("A") to pump up alternator output via connecting battery power to the rotor high side slip ring, and a NO position that connected a resistor in parallel with the rotor windings/power.

"A" position would connect with the ignition switch on and less than ~14.7 volts at the battery posts. Every time (100's cycles/sec) the battry terminal voltage rises above ~14.7 volts the relay pole wil move from "A" to "B".

PWM of the rotor power as a function of battery charge state. Full charge, the duration of closure "A" would be virtually negligable.

The shunt type drags power ALL the time!

No. There is a relatively low resistance wire wound resistor that is paralleled with the rotor windings in the above "B" position in order to quickly decay the rotor winding "charge". Maybe that's of which/what you speak..??


So...if the alt takes 20HP to drive it under full load...it will drag 20HP all the time.

You would need a 900A alterator for a 20HP "load"

The series type takes less HP to drive it when the battery is full.
Bob

".. it will drag 20HP all the time..."

Really wish to say BS to this but I'll be polite and just explain. The rotor current is PWM, Pulse Width Modulated, with either the old mechanical regulator or a new electronic one. At ALL times the rotor POWER period duration, dutycycle, is a inverse function of battery SOC. Fully charged battery and with minimum ancillary electrical load (CDI?) the rotor's stator POWERED portion of the cycle is minimum. Basically only frictional HP to drive the alternator if the battery is fully charged, 14.7 volts in the deal of winter, 13.5 volts for summer ambient temperatures.

90A alternator's maximum electrically induced load is about 1323 watts, or about 2HP. Pump all of that into the battery and it would shortly EXPLODE.

[Scott Douglas]

Update:
We tried to test the diodes and couldn't find any leaking.
I took the alternator to a shop (old school type) and they tested it. It showed good on their O-scope and when they hooked up a regulator to it and put power on it it kicked the belt off like it was trying to put out a whole bunch of torque.
I'm 99.99% sure the alternator is good to go.
I just ordered a replacement regulator from our host. It should be here Thursday. Was going to do 'will call' but I just don't have the patience for the 405 fwy any more. I guess that's what happens when you commute on the same route for 29 yrs.
I'll get it back together and report back with the results.

[rick-l]

Originally Posted by Scott Douglas

Update:
We tried to test the diodes and couldn't find any leaking.
I took the alternator to a shop (old school type) and they tested it. It showed good on their O-scope and when they hooked up a regulator to it and put power on it it kicked the belt off like it was trying to put out a whole bunch of torque.
I'm 99.99% sure the alternator is good to go.
I just ordered a replacement regulator from our host. It should be here Thursday. Was going to do 'will call' but I just don't have the patience for the 405 fwy any more. I guess that's what happens when you commute on the same route for 29 yrs.
I'll get it back together and report back with the results.

hmmmm You do work on the alternator to get energy out of it. If it requires unusual torque that is also a sign of a shorted diode. Did the old school guy know what he was doing?

[Scott Douglas]

I'm pretty sure he would have told me if the alternator was bad.
He said he had other Porsche clients that he had rebuilt their alternators for so they could keep the original with the car. I'm sure he would've offered to do the same for me if it were bad.

[wwest]

Originally Posted by rick-l

hmmmm You do work on the alternator to get energy out of it. If it requires unusual torque that is also a sign of a shorted diode. Did the old school guy know what he was doing?

No, a single shorted diode simply results in more HEAT inside that phase of the alternator"core"/windings. The resulting excessive current flow results in saturation of the magnetic elements/structures. A single phase short in a 90A alternator would result in a constant 2/3HP load, substantially lower than the 2HP max.

Open that one winding, diagonal cutters, and drive away with a 60A alternator.

You could "short" all 6 diodes and it would still only require 2HP to turn the alternator.

Signed: An old school guy.

[rick-l]

I don't know about this. A shorted diode will result in very high current through the windings 1/3 of the time which is the same as a very big load.

[wwest]

Originally Posted by rick-l

I don't know about this. A shorted diode will result in very high current through the windings 1/3 of the time which is the same as a very big load.

Very high current, yes, enough, and at such a low voltage, to almost totally negate the effects of the "moving" magnetic field from the rotor.

The winding resistance is quite low so a saturation level of current flow would result in that stator widing virtually instantaneously, totally negating the voltage generating effects of the rotor moving magnetic field.

Been there, done that

[rick-l]

So if you wanted to slow a DC motor down quickly would you short the output or leave it open? It is the same thing isn't it?

[DRACO A5OG]

Originally Posted by Scott Douglas

Update:
We tried to test the diodes and couldn't find any leaking.
I took the alternator to a shop (old school type) and they tested it. It showed good on their O-scope and when they hooked up a regulator to it and put power on it it kicked the belt off like it was trying to put out a whole bunch of torque.
I'm 99.99% sure the alternator is good to go.
I just ordered a replacement regulator from our host. It should be here Thursday. Was going to do 'will call' but I just don't have the patience for the 405 fwy any more. I guess that's what happens when you commute on the same route for 29 yrs.
I'll get it back together and report back with the results.

Hey Scott, If you like I can will call for you and you can pick it up after traffic dies. Im 5 minutes from Pelicans

I myself need to have my alternator rebuilt so that is going to Lakewood along with my starter

[Scott Douglas]

Thanks for the offer, I do appreciate it, but I'm just not interested in driving that freeway at all. It'll make it here via USPS just fine and will be at my door tomorrow morning. By then my back will have recovered enough from bending over to put it back in, I hope.

[wwest]

Originally Posted by rick-l

So if you wanted to slow a DC motor down quickly would you short the output or leave it open? It is the same thing isn't it?

Normal operation of an automotive alternator is that each phase (of three) produces a sinusoidal waveform as it rotates. when the sineware reaches a peak voltage controlled by the regulator a diode "phase" becomes forward biased and current flows into the battery.

Note that the stator current flows ONLY during the diode forward biasing period.

If that DC pulse PEAK current flow level were to become EXCESSIVE the resulting magnetic field would/will begin canceling the rotor's magnetic field. In that way a 90A alternator will self-limit itself to/near its maximum current delivery rating.

So, with a diode phase shorted the phase current flow would rise to the self-limit value, but at a VERY low voltage. Normal operation = high current flow (90A) but at ~14 volts, 2HP. Shorted winding = high current flow (90A) but now at only 1-2 volts, 0.2HP.

What a "given" DC motor, PM motor, might do would depend on it's self saturating level. My sense is that you might slow the DC motor down more quickly using the appropriate parallel load resistance instead of a direct short.

Anyone...?

When you remove the driving voltage from a relay solenoid/coil the resulting inductive kick voltage will quickly rise to infinity provided a voltage discharge path is not found. Remove the driving voltage and replace it with a short and the relay will "hold" the energized position long enough for the copper wire coil resistance, LOW resistance, to dissipate the current flow.

Use a resistor in parallel in place of short and the relay contacts will open much more quickly.

[wwest]

Originally Posted by rick-l

So if you wanted to slow a DC motor down quickly would you short the output or leave it open? It is the same thing isn't it?

Neither, select the appropriate load resistance to switch into parallel rather than a short or open.

[rick-l]

If you short D1 you are doing a lot more than opening up one of the windings. Current is now free to move in both directions.

A bunch of charge is going to move around and to do that takes work.