Typical charging system voltage?

[driverdave]

To any and all of you that have ever driven your SVX while monitoring voltage:

What kind of readings do you get? Does it fluctuate more than you think it should? Does it drop below 12V when idling?

Basically, I've been battling alternator problems lately. I have 2 SVXes; a white one, and a black one. The white one died with no symptoms one day. I had it checked...it was dead. I had it rebuilt (mistake), and it seemed fine for about a month. Then I got the "multiple dash light" symptom. Took it back to rebuilder, and of course they said it was fine. Next, I ordered a Bosch (pretty cheap, so probly not the 110 amp model). Installed Bosch and still had dash lights. Next, I finally found a cheap volt guage for the lighter (jcwhitney) and the Bosch isn't charging. Next, I took the stock alt. out of the black SVX and put it in the white one. No more dash lights. But now I wonder about the voltage readings.

When I first start the car when it's cold, I get 14-14.8 volts. As I drive and it warms up, it starts going down to the 13's. After 20 min of driving (especially if it's hot out) it will hover in the high 12's at driving rpms and drop below 12 to the low 11's when I stop with the A/C on.

I did check the bosch in the black car and it wasn't charging, so it's going back. I then put the rebuilt alt. in the black car and it seems to be charging ok, although, I can't drive it long enough to warm up and see if it also drops the voltage.

Sorry for such a lengthy story, but has anyone else seen similar voltage readings with their SVX?

Any input would be appreciated.

[oab_au]

Originally posted by driverdave
To any and all of you that have ever driven your SVX while monitoring voltage:

What kind of readings do you get? Does it fluctuate more than you think it should? Does it drop below 12V when idling?

Basically, I've been battling alternator problems lately. I have 2 SVXes; a white one, and a black one. The white one died with no symptoms one day. I had it checked...it was dead. I had it rebuilt (mistake), and it seemed fine for about a month. Then I got the "multiple dash light" symptom. Took it back to rebuilder, and of course they said it was fine. Next, I ordered a Bosch (pretty cheap, so probly not the 110 amp model). Installed Bosch and still had dash lights. Next, I finally found a cheap volt guage for the lighter (jcwhitney) and the Bosch isn't charging. Next, I took the stock alt. out of the black SVX and put it in the white one. No more dash lights. But now I wonder about the voltage readings.

When I first start the car when it's cold, I get 14-14.8 volts. As I drive and it warms up, it starts going down to the 13's. After 20 min of driving (especially if it's hot out) it will hover in the high 12's at driving rpms and drop below 12 to the low 11's when I stop with the A/C on.

I did check the bosch in the black car and it wasn't charging, so it's going back. I then put the rebuilt alt. in the black car and it seems to be charging ok, although, I can't drive it long enough to warm up and see if it also drops the voltage.

Sorry for such a lengthy story, but has anyone else seen similar voltage readings with their SVX?

Any input would be appreciated.

Dave the charge voltage, should reflect the battery voltage. When you start the car the voltage would be down as the starter pulls a lot of current from the battery so the charge voltage will be down to about 12.4 or so. As you drive the alternator will charge the battery so the voltage will rise to a top of 14.7 or so.

Unless you have as hugemungus amp the voltage should stay up around 14.7 when running above 2500 rpm. When idling it will come down to say 12.5 Volts.

As you say your voltage goes down as the charge time goes up, this could be caused by a bad connection in the charging circuit. This connection is heating up to reduce the charge rate from the alternator.

Try running it till the voltage goes down, then lift the hood and feel for a hot connection between the alternator and the battery.
If you have a volt meter you can check for a voltage drop between the same things.

Harvey.

[Trevor]

Greetings Dave,

It would appear that you are sensing voltage at the lighter socket. There will be other loads on this branch of the circuit which will be causing a voltage drop at this point and this could be the answer to the low voltage recorded when the air conditioning is on.

You may therefore in effect NOT have a problem. As Harvey has advised check voltages directly at the alternator and battery. In order to ensure reliable readings from your accessory meter run a light cable pair direct to the battery. Thin flex will be OK as the meter should draw very little current. Compare readings with and direct without the flex if you have doubts regarding voltage drop.

This text from a previous message I posted in connection with the alternator mod. may help you confirm readings taken directly if you wish to get down to detail. Quote : -
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I have made measurements as follows, using two high class digital instruments in parallel as a check on accuracy of calibration.

1. Voltage dropped alternator + to battery + with dead flat battery and all lights and accessories drawing current, engine at 4500 rpm. --- 0.5 volts.

2. As above but with a fully charged battery (measured at 12.6 volts no load), --- 0.4 volts.

3. As 2, but with only engine electrics drawing current. -- 0.2 volts

4. As 1 above, but alternator frame to battery negative --- 0.13 volts

5. As 2 above, but alternator frame to battery negative --- 0.11 volts

6. As 3 above, but alternator frame to battery negative --- 0.08 volts

From the above the total voltage drop in the alternator to battery circuits can be summarized as ---

a, Conditions as 1 above, --- 0.63 volts

b. Conditions as 2 above, --- 0.51 volts

c. Conditions as 3 above, --- o.28 volts

Estimated charging current based on the above can be calculated as follows,

a. 0.63v / 0,008 = 78 Amps

b. 0.51v / 0,008 = 63 Amps

c. 0.28v / 0.008 = 35 Amps

I regard the above measurements as indicating that the charging system on my car i.e. OEM is working perfectly and this is born out by three trouble free years in my hands plus no indication of any repairs while in the hands of Japanese owners.

There is an advantage in having a small resistance between the alternator and the battery as this can form part of the over current protection for the alternator. What is more any such small voltage drop will not effect the alternator output voltage as the electronic regulator senses battery voltage directly via a separate pilot wire. It could be that Subaru designers had this in mind as I can not accept that they were trying to save on a few strands of copper or were ignorant in respect of basic Ohm's law.

Note that my measurements as above confirm those put forward by Lee.
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The best of luck with your trouble shooting with hope that a real problem does not exist, Trevor

[AFBeefcake]

I have an autometer voltage meter running off the lighter socket.

At start up around 13-14V

Sitting at a stop light run 13V with head lights on 12.5V

above 1500 RPMs 14V

all readings are with my stereo on , 4G wire upgrade, and a 115 amp alt.

[driverdave]

Thanks for the responses, guys. I will check all the connections and clean them up, but it sounds like it is fairly typical for SVX's to vary a bit.

That's what I was wanting to confirm, because my other vehicles (using the same guage in the lighter socket) held a steady 13.4-13.8V, regardless of load or engine speed.

I'm guessing this is one of the reasons that the alternator mod was designed in the first place.

AFBeefcake, where did you get your alternator, and how much was it?