Voltage Regulator Operation - 2016 Toyota Camry - Toyota Nation Forum : Toyota Car and Truck Forums
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post #1 of 8 Old 06-29-2017, 10:21 PM Thread Starter
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Voltage Regulator Operation - 2016 Toyota Camry

After a cold start at 65 degrees F, the battery voltage on my 2016 Camry measures 14.18 volts. The voltage then drifts down below 14.0 volts after no more than five minutes.

If the engine is restarted while still warm, the battery voltage only measures about 13.8 volts. Are these voltages within specification? I don't believe a battery accepts much charge current if the alternator voltage is very much below 14.0 volts.

The alternator does not charge the battery adequately if the car is used once a week and taken on 5 mile trips.

I've read that many cars today reduce alternator load to increase fuel economy. Is that the case with the late model Camry, or could my voltage regulator be out of specification?

Thanks for any help.
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post #2 of 8 Old 06-30-2017, 09:30 AM
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Believe charging v is normal, problem lies with short/infrequent trips.
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post #3 of 8 Old 06-30-2017, 01:20 PM Thread Starter
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Thanks for the reply. I had the same feeling that the voltages may be normal, although I expected a higher alternator voltage after the warm start. It's also possible that lead acid battery float voltage is lower at higher temperatures.

It just seems that alternator voltages used to be higher and above 14.0 volts for a longer time.

Does anyone know if the Camry has any ECU control of the alternator? Honda has a dual mode charging system that is quite sophisticated.

http://opensiuc.lib.siu.edu/cgi/view...text=auto_pres
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post #4 of 8 Old 06-30-2017, 01:54 PM
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Believe there is a feedback loop from alternator to ECM and back.
ECM may also look at under hood temp as part of the battery v regulation but don't think it has a dual mode such as Honda or you would have noticed.

Still have your original bat?
If it measures 12.6v+ and stays above 12v with lights on for min or so then its getting enough charge.
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post #5 of 8 Old 06-30-2017, 02:53 PM Thread Starter
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The battery is original and appears to be in excellent shape. I've had it connected to a Black & Decker 2A Battery Charger/Maintainer. The battery actually got depleted recently when the car was not driven for two weeks. The specific gravity indicated empty but after being on the Maintainer for a very long time moved up to 1.285 which indicates full charge. The voltage reads above 12.6 volts with the Maintainer disconnected and the surface charge removed. The headlight test also looks good showing above 12 volts even with the high beams turned on.

The real surprise was that after getting a jump start and driving around for 30-45 minutes the specific gravity still measured very close to empty. It feels like the charging system is designed to maintain the battery but not provide a quick recharge. On the other hand, the charge current could have been quite a bit if the battery float voltage is well under 13.8 volts for a discharged battery.

It's also possible that the depleted battery was badly sulfated. The Battery Maintainer appears to have restored the battery to almost new condition but it took several weeks.
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post #6 of 8 Old 07-02-2017, 04:54 PM Thread Starter
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To wrap things up, I thought I'd post this table found in the article referenced below. Absorption and Float Voltages are listed for different types of lead acid batteries.

Absorption Voltage -- Float Voltage

Flooded -- 14.2V to 14.5V -- 13.2V to 13.5V
Sealed --- 14.2V to 14.5V -- 13.2V to 13.5V
VRLA ----- 14.2V to 14.5V -- 13.2V to 13.5V
AGM ----- 14.4V to 15.0V -- 13.2V to 13.8V
GEL ------ 14.0V to 14.2V -- 13.2V to 13.4V

http://www.batterytender.com/Intro-t...Acid-Batteries

My feeling is that the 2016 Camry is a bit light in terms of charging to increase fuel economy and prevent overcharging. They would assume that the car is driven at least several times per week and for a reasonable distance. Infrequent use of the car would be a problem in part because the parasitic current drain is continuous.

Note that the Honda information posted earlier shows a charging range of 14.4-14.9 volts.

My guess is that the Camry uses a conventional temperature compensated voltage regulator located inside the alternator. If that is the case, the alternator voltage would be related to the temperature inside the alternator. That would mean that the only high current charging would occur after a cold start. Charge current would be fairly low at most other times.

I think my infrequent short trips resulted in a long slow discharge of the battery. The car had a noticeably weak start two weeks before requiring a jump start. I must have dismissed the weak start since the car had not been driven for a while. The car was then driven 4-5 miles and restarted for the return trip. At that point the car was not driven for two weeks and it failed to start.
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post #7 of 8 Old 07-02-2017, 05:28 PM
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Thanks for the battery write up.

Short /infrequent trips are also hard on the engine/oil.
Don't go for that 10,000 mile oil change propaganda.
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post #8 of 8 Old 07-03-2017, 04:15 PM Thread Starter
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The Toyota Maintenance Manual for my car changes the synthetic oil change interval from 10K miles to 5K miles if trips are under 5 miles and temperatures are below 32 degrees F. My short trips are typically 4-5 miles but generally at 65 degrees F and higher. I also would not drive 10K miles between oil changes.

I ran across an interesting thread on the Honda Dual Mode Charging System. One individual had his battery checked during routine maintenance at the dealer. The battery passed their test but was only 57% charged. I think that tells us that these smart charging systems may not keep a battery fully charged. Another thread said that charging systems today target a percentage possibly in the range of 80%.

One interesting thing about the Honda system is that the charging voltage is often higher if the lights are turned on.

The alternator in my car shows the names of the four connector pins (IG, S, L, M). That may give me some information about the charging system. I think the first three stand for Ignition, Sense, and Lamp. I've read that the Camry may only use 3 of the 4 pins but don't know if that would apply to the 2016 models.
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