drops under 12 v. with New Alternator

[rick-l]

Originally Posted by Early_S_Man

dralph12,

You have made reference to 'at/@ Ideal' more than a dozen times in this thread, and I would venture to say there isn't anyone out here reading your thread that knows what you are talking about!!!

Just what is this condition you call '@ Ideal???'

Did you notice posts #1, #8 and #18 from dralph12 look very similar?

Thanks for the info Loren.

[84porsche9113.2]

Originally Posted by dralph12

One more thing You may want to check the battery voltage with the car off
it should read 12.5 of not the battery may be running low.
remember if you recharge ithe battery remove the Neg. cable to isolate the battery during charging.
My Original problem was that after recharging the battery I would go out at night with ever thing on "Lights and fans" the next day I would check the battery and if would be below the full charge "say 12.35 volts" another day or so of driving and the battery would read 12.2.
So the alternator wasn't recharging the battery. Make sure to check all grounds on the car before diving into the alternator as a problem.

Okay, what do you mean by recharging the battery? You mean using a charger? I just installed a new optima to replace my old one (thanks for the tip about the cutting board mounting plate from the other thread). So I know the battery is fully charged. I do always run a 2 amp trickle charger though. I also have a negative battery disconnect switch. Are you saying when I am trickle charging the vehicle I should remove the negative? My battery seems to be taking the trickle charge and I haven't been disconnecting it. I know because the charger will say "charging" and then after a while it says "charged".

Assuming the battery charge without the car on is 12.5V, wouldn't you say if I am getting 14V at idle, that the alternator IS working to some degree? My question is that if my 14V drops to 12V when the a/c at a high fan speed, lights and radio are on, is that normal or does it indicate that maybe the alternator needs to charge at a higher rate?

Again, I don't think my battery is running low only because it is a brand new battery and I always leave it on a trickle charger when not in use.

[84porsche9113.2]

Originally Posted by Early_S_Man

dralph12,

You have made reference to 'at/@ Ideal' more than a dozen times in this thread, and I would venture to say there isn't anyone out here reading your thread that knows what you are talking about!!!

Just what is this condition you call '@ Ideal???'

I too don't really understand this special terminology. I had just assumed he was saying the voltage "at idle" based on the context of the term in the one reply he made to my post.

[dshepp806]

"""""Not easy (requires a hot plate or a torch) and not a good idea
as the diodes can be damaged with too much heat. The diodes
are usually damaged by using those "monster" batteries
and/or revving the engine when the battery is very low to
charge it quickly, i.e. exceeds the 90 amp rating.

Understood: requires simply the proper wattage, insofar as heat. As I stated, I did it...completely aware of avoiding heat damage to the components (This isn't my first soldering rodeo, cowboy...as I 've worked with multilayer boards)......overcurrent kills,..heat kills...yes!
"Do you know what the reverse standoff voltage is for those (8) diodes?"

There're more than 8 diodes (14).
The PIV of the diodes are usually 400 volts.

(that would be EACH...then would one allow serial parallel connections) I've not actually checked the specs on these diodes but sounds typical looking at component size..

"For the run the car without a battery crowd what is the open circuit peak AC voltage?"

The peak output of the alternator can reach 30 volts (bad regulator) which
usually destroys the DME or a CDI in the older cars. Is there any on board voltage regulators on the DME?

Best,

[dshepp806]

Sorry:

A rephrase:::::


Does there exist any onboard regulators on the DME PCB?

Thanks,

[Lorenfb]

"requires simply the proper wattage, insofar as heat."

Like "monster" unrealistic wattage and inappropriate for the application.

"(that would be EACH...then would one allow serial parallel connections)"

???????????

"Is there any on board voltage regulators on the DME?"

Of course! But they have a max rating too as do zener/transient protection circuits
being used in the DME ECM.

[dralph12]

ideal = idle Sorry English is'nt my first language most the time!!!

Speaking to the problem with the Car dropping to 12 volts under load "A/C On". I would say check all grounds. If all grounds are good remove the alternator and find somewhere you can have it tested.
My problem at the top of this thread was similar ,and turned out to be the alternator. I also found a bad ground on the transmission to body grounds strap. In the end it was the new alternator that fix the issue of having 14 volts at idle and 12 volts when I had the "A/C On" on.
I was told never to charge a 911 battery unless it is removed from the Car electrical system.
I remove the Neg. cable on the battery to archive this while charging the car battery.
Now that the car is working there is no need to charge the battery the car is able to now.

[dshepp806]

Loren,

They were installed in the first place...Monstrous? (non-technical term: yes) There is an appropriate heat for the application.


"???????????" ::: The PIVs stated are for the individual diodes, right? If multiple diodes are connected in various fashions, PIVs for the "circuit will change". Im mean, one could increase the PIV through series strings.....is my recollection incorrect?

The question as to onboard regulators was simply to inquire if they were there...understanding that most digital circuitry WILL make use of Regulation devices, as well as transient protection. I think it a given that these components have ratings. (?) My question wasn't related to "ratings".....

But now, I'd like to ask about these ratings of the FACTORY installed components,...specially versus newer components (since '89 anywaze)...on the repair of these DME's, when addressing the components related to regulation AND transient protection, is it not prudent to ensure any/all improvements are made upon repair?(slightly increased heat/wattage specs, etc.???????????? Just curious.........?

Thanks!

Best,

[84porsche9113.2]

Originally Posted by dralph12

ideal = idle Sorry English is'nt my first language most the time!!!

Speaking to the problem with the Car dropping to 12 volts under load "A/C On". I would say check all grounds. If all grounds are good remove the alternator and find somewhere you can have it tested.
My problem at the top of this thread was similar ,and turned out to be the alternator. I also found a bad ground on the transmission to body grounds strap. In the end it was the new alternator that fix the issue of having 14 volts at idle and 12 volts when I had the "A/C On" on.
I was told never to charge a 911 battery unless it is removed from the Car electrical system.
I remove the Neg. cable on the battery to archive this while charging the car battery.
Now that the car is working there is no need to charge the battery the car is able to now.

Dan,

Thanks for the advice! Well, as I say the car runs great and the a/c even works great. However, now that I've installed the voltmeter gauge, I do notice the voltage drops subtstantailly with the a/c load on.

As far as checking all grounds, a few years ago, I installed a heavy gauge wire running direclty from my battery to the transmission ground strap point and I also installed a new transmission ground strap. So I'm sure the ground is pretty solid. The ground strap at the battery looks also intact. Although I think at one time my a/c blower did stop working so I think I may have tried to "supplelment" this ground with another wire attached to the chasis (in the front storage area where the blower is located). Maybe I wired this wrong? But in any case, it did fix the problem and got the blower working again, the a/c has been working fine ever since that.

I am not very familiar with automitve DC electrical systems. The one thing that concerned me was when I installed the voltmeter, I tapped off the hot wires to the a/c switch. Although i was reading 12V across ground and the power wires to this switch, I also noticed I was getting "continuity to ground" across those exact same hot wires. What does this mean? If one prong of my meter is on ground, and the other goes to the hot of the a/c and the meter rings and there is continunity to ground, doesn't this indicate a short? If so, why wouldn't the fuse blow and/or why is the a/c still working?? (I thought anytime 12V positive connects to ground or the body, it will short)?

I am not really understanding this situation as well as I'd like to. I've not had much motiviation to because the car and a/c runs fine. Now my only indication of a problem is that the voltage seems to drop too low when the a/c is turned on, and the fact that I recently found out I have continuity to ground across the a/c power wires at the a/c fan switch location.

[glenncof]

To know 'precisely' the battery voltage the voltmeter should be connected directly to the battery terminals. Any place else you can have voltage drop (called IR drop = current (I) x resistance (R)).

Cigarette light seems like a good spot for positive so long as you don't use it when checking voltgae. Ground I would get close to negative wire off battery.

[84porsche9113.2]

Originally Posted by glenncof

To know 'precisely' the battery voltage the voltmeter should be connected directly to the battery terminals. Any place else you can have voltage drop (called IR drop = current (I) x resistance (R)).

Cigarette light seems like a good spot for positive so long as you don't use it when checking voltgae. Ground I would get close to negative wire off battery.

Glenncof,

Thanks for the info. Just tapping into any source for the voltmeter gauges should get be "in the ballpark", no? I know, I probably should be running 2 wires directly from voltmeter gauge to battery (if I was going to run a ground, might as well run a postive as well -- not that much more work). But I guess I took the quick and dirty method and just wanted to be able to determine an excessive over or under voltage condition-- even if not precise. If the reading was "good enough" to prevent battery damage, then it would be good enough for my needs...

Assuming that my gauge may have slightly inaccurate readings (due to possible voltage drop) since tapped off the fan swtich ground and hot wires and not connected directly to the battery, what about the other issues? -- do you think that getting continuity to ground off the postiive (hot) fan switch wires is a problem, even though the a/c and car seems to be running fine with no other issues??

[dralph12]

On my last post when I said "14 volts at idle and 12 volts when I had the "A/C On" I meant 12.5 volts Sorry!
Have you checked the new meter? You can by checking the battery @ the battery, and checking the voltage @ the switch to see if there the same with the car on @ idle?

two things
1. your reading"continuity to ground" when the car is off?
without looking at a schematic I would say your reading thought the A/C motor windings.
2. 12 volts is a low reading with the A/C on and the RPM's above 2.5k ? or at idle?
ether way its low.
12 volt reading with A/C on at Idle would say to me that your battery needs to be charged.
12 during driving " above 2k RPM's" would say our alternator isn't putting out the correct power.
If you read 12 volts when the car is running " your driving it " and turn the A/C off what is the reading?
that is the reading across the battery with the A/C off car at Idle?
and at 2k RPM's

However if you can read 12.5 volts across the battery with the car off and you take the car out for a drive come back let the car cool off for a hour and still read 12.5 volts across the battery the Alternator is doing its job.
You shouldn't have to charge the Battery after you drive the car.
That was My problem " alternator not having the power" to run the car, A/C Fans. and charge the battery. I would come home and read across the battery and it would be below full charge 12.5 volts.

[84porsche9113.2]

Originally Posted by dralph12

On my last post when I said "14 volts at idle and 12 volts when I had the "A/C On" I meant 12.5 volts Sorry!
Have you checked the new meter? You can by checking the battery @ the battery, and checking the voltage @ the switch to see if there the same with the car on @ idle?

two things
1. your reading"continuity to ground" when the car is off?
without looking at a schematic I would say your reading thought the A/C motor windings.
2. 12 volts is a low reading with the A/C on and the RPM's above 2.5k ? or at idle?
ether way its low.
12 volt reading with A/C on at Idle would say to me that your battery needs to be charged.
12 during driving " above 2k RPM's" would say our alternator isn't putting out the correct power.
If you read 12 volts when the car is running " your driving it " and turn the A/C off what is the reading?
that is the reading across the battery with the A/C off car at Idle?
and at 2k RPM's

However if you can read 12.5 volts across the battery with the car off and you take the car out for a drive come back let the car cool off for a hour and still read 12.5 volts across the battery the Alternator is doing its job.
You shouldn't have to charge the Battery after you drive the car.
That was My problem " alternator not having the power" to run the car, A/C Fans. and charge the battery. I would come home and read across the battery and it would be below full charge 12.5 volts.

1. yes - continuity to ground when car is off.

2. 12V with car at idle. Increasing rpms does not seem to bring it up that much.

I do think my alternator is working, when I turn on the car w/ A/C off, it jumps from 12.5 to 14V. So it is doing something at idle.

But after installing the voltmeter gauge, I was just curious whether it is normal for the a/c on at fan position 2 or 3 to pull the voltage down as low as 12V at idle?

If alternator is working w/ a/c off (14V at idle), and I turn a/c on but it drops to 12V, is something wrong? At fan position 1 it only drops to 13 or 12.5V, but at higher fan position will drop to about 12V.

If it is normal than I don't need to worry. I was just wondering why the alternator didn't compensate for the large drop to 12V when a/c is turned on to fan position 2 or 3 at idle....

[dralph12]

YES In troubleshooting my 86 911 12 is low.
unless your meter is reading different that battery truly is.
if you do a search on battery voltage your see that
12.5=full
12.25 = half full
12.0 is time to recharge the battery.
The question is?
What is the battery reading when your volt meter is reading 12 volts.
I would hate to see you drive your car a hour or two away from home. Have you voltage drop from 12 to 11 volts and then have it not start.

[84porsche9113.2]

as glenncof explained, because the voltmeter gauge is not connected directly to the battery, I may be seeing voltage drop and an incorrect reading.

I can easily double check the gauges accuracy by reading directly from the battery with a handheld meter with the car idling and a/c on. will post my results after taking the reading...

thanks for your help and replies...

[84porsche9113.2]

Originally Posted by dralph12

YES In troubleshooting my 86 911 12 is low.
unless your meter is reading different that battery truly is.
if you do a search on battery voltage your see that
12.5=full
12.25 = half full
12.0 is time to recharge the battery.
The question is?
What is the battery reading when your volt meter is reading 12 volts.
I would hate to see you drive your car a hour or two away from home. Have you voltage drop from 12 to 11 volts and then have it not start.

I forgot to ask.. What volt reading "should" I be getting at the battery with the a/c on, at idle?? 12.5V, or higher??

[dralph12]

On my car with a new alternator, Battery, and volt meter I read 13.5 to 14 volts at Idle just after starting the car with the A/C on.

After driving the car for five or more min., and it warming up, My idle drops to 500 RPM's and
at a stop light with engine at Idle and A/C on meter reads 12.5

Ok I just went out to my car and started it "its cold" so Idle is 1K
Car off battery 12.5 volts
Car battery @ Idle 13.7
Car battery at Idle with A/C on 12.9

[rnln]

Originally Posted by dshepp806

Agree with Wil...check the diodes, F/R biased...then pop 'em with a heat gun . measure again,...looking for thermal induced breakdown..

Best yet, get it to a shop and have em do as Wil noted for you. Hope you're clear on the no-no of battery disconnect WHILE ENGINE IS RUNNING,,...parked, .... slowly rolling,.............. at 150MPH ,...........or even 10 feet of vertical levitation.........ultimately, an expensive bad habit... I'm sure foamy911 would agree that you may even find a Honda shop that could check it for you....?

Once we know the ALT/REG is good then, all can go forward...

Best of luck

umm.. this is the second time I heard so I gotta ask. What does this have to do with Honda shop? IN fact, I have heard many times people are using the "disconnect batery (-) method. Don't know what/how i\happen to the alternator.

dralph12,
some simple conclusion?
1- go get a new batery to see if the problem is gone. If it is, batery is the problem maker. If not, the alt is.
2- If you don't want to do that to autozone/Sears, come by my place. I have a used batery and I think it's still good, 1200a dry cell. You can try it on, as long as you don't trash it after all.

In the pass, I had same problem with 3 diff. rebuilt alt. We had to replace the alt. 3 times to get a good rebuilt one. So don't be supprise if your second rebuilt alt, is bad.

[911pcars]

Originally Posted by dralph12

On my car with a new alternator, Battery, and volt meter I read 13.5 to 14 volts at Idle just after starting the car with the A/C on.

After driving the car for five or more min., and it warming up, My idle drops to 500 RPM's and
at a stop light with engine at Idle and A/C on meter reads 12.5

Ok I just went out to my car and started it "its cold" so Idle is 1K
Car off battery 12.5 volts
Car battery @ Idle 13.7
Car battery at Idle with A/C on 12.9

I was going dizzy reading this thread.

Here are my thoughts:
The open circuit voltage of a fully charged battery should be high 12s, possibly low 13s. If your fully charged battery is only 12.5V, it's not up to vehicle specs.

The charge voltage of the alternator should be around 14.5 volts. If the A/C is ON,
the charge voltage should still be around 14.5 volts. If not, raise idle and measure again. If not to spec, it's either the alternator, the regulator or a malfunction in the circuit (excessive resistance, bad connection, etc.).

A multitude of electrical accessories can ask for more than an alternator can create. In that case, you need a larger capacity alternator. However, I don't think that's your case. From your symptoms, the alternator isn't fully charging the battery nor supplying sufficient voltage for the electrical system.

MHO,
Sherwood

[84porsche9113.2]

Originally Posted by dralph12

I was told never to charge a 911 battery unless it is removed from the Car electrical system.

Dan,

FYI, I contacted shumacher via email (the manufacturer of my battery maintainer/trickle charger), and below is the response I got. They are telling me I don't need to disconnect if I am just maintaining the battery... I would hope they are correct since they are the manufacturers, so for now, I will continue to leave the battery connected when charging. Also, I haven't had time to run my car yet, but I will tomorrow and will post my measurments then. Thanks.


"There is no reason the battery cables need to be removed from the battery……..unless the battery is being removed from the car, or there is work being done on the car that requires battery disconnect.

NO, What you were told is incorrect"