Is alternator output load dependant ??? - Toyota GR86, 86, FR-S and Subaru BRZ Forum & Owners Community

Mcgiiver · 01-03-2023, 04:47 PM

As I was driving around town, I noticed the voltmeter reading on the dash, is swinging between, 12.4 volts and 14.3 volts. Seems strange as I am used to voltage staying constant all the time around 14.3 in other cars. I get home and let the car idle, check battery voltage with a hand held voltmeter and the readings agree with the in dash meter. So I start turning appliances on and off, lights, brake lights, heater headlights all with the engine idling. The results are when there is no load or minimal load is being applied, the voltage drops to battery voltage of 12.6. When I turn on some load, the voltage increases to 14.3 and stays there until the load is removed, then the voltage again drops down to battery voltage. It appears to me that the alternator output is somehow correlated to the load on the system. It’s as if the alternator knows that the battery is fully charged and does not need to output a higher charging voltage. This may be designed in, to remove some mechanical load for purposes of decreasing fuel consumption. I have no problem whatsoever with the battery going dead. Does this sound normal? Has anyone else noticed this behavior?

dragoontwo · 01-03-2023, 05:20 PM

Yes. The ECU will regulate the alternator output. You can even see it go up and down while cruising.

Mcgiiver · 01-03-2023, 05:25 PM

Quote:

Originally Posted by dragoontwo

Yes. The ECU will regulate the alternator output. You can even see it go up and down while cruising.

Yes, I saw it varying while cruising, that is what scared me.

churchx · 01-03-2023, 08:31 PM

Shouldn't be issue of any sort, with exception of maybe using some 12V>A/C transformator (to eg. power laptop), some models of which due such variances may stop charging. Never had problems with car itself or mobile gadgets charged with 12V cigplug > usb adapters.

Grady · 01-03-2023, 08:39 PM

It is smart charging for AGM batteries. It looks at battery amps/temperature to determine if a fast charge is needed. A large system load will not discharge the battery.

Tcoat · 01-04-2023, 08:17 AM

Assuming they still use the updated system from '17.
It would be concerning if it DIDN'T fluctuate.

WNDSRFR · 01-04-2023, 11:58 AM

Aren't all alternators load dependent? Always have been. In the old days they used a voltage regulator. Now a days I think the ECU controls everything.

Tcoat · 01-04-2023, 01:20 PM

Quote:

Originally Posted by WNDSRFR

Aren't all alternators load dependent? Always have been. In the old days they used a voltage regulator. Now a days I think the ECU controls everything.

The beauty of the ECU is that the alternator can be sort of fine tuned as to exactly when it does and does not charge. The regulator could say "to much" or "to little" and switch the charging on or off but that was about it.

DarkPira7e · 01-04-2023, 02:20 PM

Quote:

Originally Posted by Tcoat

Assuming they still use the updated system from '17.
It would be concerning if it DIDN'T fluctuate.

I had no idea they changed this. Very cool, learned something today

Thank you for posting this

Tcoat · 01-04-2023, 02:40 PM

Quote:

Originally Posted by DarkPira7e

I had no idea they changed this. Very cool, learned something today

Thank you for posting this

All the facelift changes are here:

dragoontwo · 01-04-2023, 03:38 PM

Quote:

Originally Posted by Tcoat

Assuming they still use the updated system from '17.
It would be concerning if it DIDN'T fluctuate.

It's the same. Page 138 of a PDF I can't seem to upload. It's not above the PDF limit.

Tcoat · 01-04-2023, 05:20 PM

Quote:

Originally Posted by dragoontwo

It's the same. Page 138 of a PDF I can't seem to upload. It's not above the PDF limit.

Figured that the upgrade will still apply.
Upload the PDF as an image using the "insert image" icon above the text box.

dragoontwo · 01-04-2023, 05:37 PM

Quote:

Originally Posted by Tcoat

Figured that the upgrade will still apply.
Upload the PDF as an image using the "insert image" icon above the text box.

Tried that. Keep getting notification about missing security token.

Tcoat · 01-04-2023, 06:41 PM

Quote:

Originally Posted by dragoontwo

Tried that. Keep getting notification about missing security token.

Odd. I get the same with it. First for me.

01-03-2023, 04:47 PM	#1
Mcgiiver Member Join Date: Apr 2021 Drives: 2022 BRZ Premium, 2009 Toyota Tacom Location: Princeton , NJ Posts: 39 Thanks: 2 Thanked 5 Times in 4 Posts Mentioned: 0 Post(s) Tagged: 0 Thread(s)	Is alternator output load dependant ??? As I was driving around town, I noticed the voltmeter reading on the dash, is swinging between, 12.4 volts and 14.3 volts. Seems strange as I am used to voltage staying constant all the time around 14.3 in other cars. I get home and let the car idle, check battery voltage with a hand held voltmeter and the readings agree with the in dash meter. So I start turning appliances on and off, lights, brake lights, heater headlights all with the engine idling. The results are when there is no load or minimal load is being applied, the voltage drops to battery voltage of 12.6. When I turn on some load, the voltage increases to 14.3 and stays there until the load is removed, then the voltage again drops down to battery voltage. It appears to me that the alternator output is somehow correlated to the load on the system. It’s as if the alternator knows that the battery is fully charged and does not need to output a higher charging voltage. This may be designed in, to remove some mechanical load for purposes of decreasing fuel consumption. I have no problem whatsoever with the battery going dead. Does this sound normal? Has anyone else noticed this behavior?

01-04-2023, 08:17 AM	#6
Tcoat Senior Member Join Date: Jul 2014 Drives: 2020 Hakone Location: London, Ont Posts: 69,845 Thanks: 61,656 Thanked 108,284 Times in 46,456 Posts Mentioned: 2495 Post(s) Tagged: 50 Thread(s)	Assuming they still use the updated system from '17. It would be concerning if it DIDN'T fluctuate. Attached Images __________________ Racecar spelled backwards is Racecar, because Racecar.

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01-03-2023, 05:20 PM	#2
dragoontwo Senior Member Join Date: May 2020 Drives: 22 BRZ limited Location: Clarksville TN Posts: 1,183 Thanks: 217 Thanked 990 Times in 521 Posts Mentioned: 7 Post(s) Tagged: 0 Thread(s)	Yes. The ECU will regulate the alternator output. You can even see it go up and down while cruising.

01-03-2023, 08:31 PM	#4
churchx Senior Member Join Date: Mar 2015 Drives: 2014 GT86 Location: Latvia, Riga Posts: 4,333 Thanks: 696 Thanked 2,085 Times in 1,436 Posts Mentioned: 53 Post(s) Tagged: 1 Thread(s)	Shouldn't be issue of any sort, with exception of maybe using some 12V>A/C transformator (to eg. power laptop), some models of which due such variances may stop charging. Never had problems with car itself or mobile gadgets charged with 12V cigplug > usb adapters.

01-04-2023, 11:58 AM	#7
WNDSRFR Senior Member Join Date: Jan 2014 Drives: FR-S,GTI Location: Cocoa, Florida Posts: 1,155 Thanks: 228 Thanked 823 Times in 419 Posts Mentioned: 13 Post(s) Tagged: 0 Thread(s)	Aren't all alternators load dependent? Always have been. In the old days they used a voltage regulator. Now a days I think the ECU controls everything.

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