Alternator Voltage Question

derekl123

derekl123

New member
Alternator recently died and got a rebuilt one. I believe that the previous alternator was outputting 14.2 volts on idle consistently, but with this rebuilt one that I've had, it varies from 13.5 - 14V on idle. Is this normal?

I currently have a dual battery system with Odyssey 34R-PC1500T batteries. Odyssey's manual states for automotive applications with alternators, output voltage should be at least 14.2V. Will the current alternator output be enough to charge up my batteries (just slower) while driving?
 
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did you also put the batteries on a charger first? dont use the alternator to charge low batteries.

also did you do the big 3?

most alternators will put out 14v on cold idle and fluctuate 13.4-13.8 hot.
 
riceandpho said:
did you also put the batteries on a charger first? dont use the alternator to charge low batteries.

also did you do the big 3?

most alternators will put out 14v on cold idle and fluctuate 13.4-13.8 hot.
Click to expand...

Haven't seen the need to put on a charger since they read 12.6V initially. Haven't done big 3 yet, may do that and just get a high output alternator down the road. I've seen some voltage boosters online that claim to increase alternator voltage output to charge agm batteries properly. Any recommended ones out there? Is it even required if 13.4-13.8V is enough to float charge the batteries?
 
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derekl123 said:
Haven't seen the need to put on a charger since they read 12.6V initially. Haven't done big 3 yet, may do that and just get a high output alternator down the road. I've seen some voltage boosters online that claim to increase alternator voltage output to charge agm batteries properly. Any recommended ones out there? Is it even required if 13.4-13.8V is enough to float charge the batteries?
Click to expand...

put the batteries on a charger, i use a ctek multi xs 25000

i do use a high output alternator and its better,
now a days i dont really drive enough, so i put the charger on it twice a month to keep it topped off. i run dual group 31
my commute is about 8 miles one way, and my truck sits at my job about 12 to 13 hours. so i just top it off.

i havent use a voltage booster, but some members on here have. i get about 14 to 14.2 idle and hot. my hot can dip at the 13.9.
 
Voltage

That voltage is probably a little low for most AGM batteries. Like others have suggested, either top them off with good charger or find a way to upgrade your current charging system to get the voltage a bit higher.

I'm running an oreilly house brand AGM battery and the GM diode as an experiment, so far its working well. At first I was seeing as high as 15 volts, but the past few times I've driven the 4runner (not a daily driver) it's right around 14.5 with stock alt.

YMMV

Mike
 
derekl123 said:
Alternator recently died and got a rebuilt one. I believe that the previous alternator was outputting 14.2 volts on idle consistently, but with this rebuilt one that I've had, it varies from 13.5 - 14V on idle. Is this normal?

I currently have a dual battery system with Odyssey 34R-PC1500T batteries. Odyssey's manual states for automotive applications with alternators, output voltage should be at least 14.2V. Will the current alternator output be enough to charge up my batteries (just slower) while driving?
Click to expand...


That sounds about right as far as voltages go.

Because you're running an AGM, I'd consider adding the GM diode where the alt-s fuse is to up charging voltage a bit as a fully charged AGM is 12.8-12.9 and a fully charged LA is 12.65. 13.2 volts might not provide the delta needed to keep an AGM fully charged.
 

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shmabs said:
That voltage is probably a little low for most AGM batteries. Like others have suggested, either top them off with good charger or find a way to upgrade your current charging system to get the voltage a bit higher.

I'm running an oreilly house brand AGM battery and the GM diode as an experiment, so far its working well. At first I was seeing as high as 15 volts, but the past few times I've driven the 4runner (not a daily driver) it's right around 14.5 with stock alt.

YMMV

Mike
Click to expand...

Same set-up, working great so far.
 
chaz said:
i use this for my agm battery. Dirty Parts
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I also use this Dirty Parts diode. it does boost the charging voltage a bit, but I still put my AGM battery on the Odyssey 20 amp charger every once in a while to top it off.

Be aware that this diode may trigger a Charging CEL on your dashboard—it did for me, 2009 V8. This is in the Dirty Parts literature.
 
shmabs said:
That voltage is probably a little low for most AGM batteries. Like others have suggested, either top them off with good charger or find a way to upgrade your current charging system to get the voltage a bit higher.

I'm running an oreilly house brand AGM battery and the GM diode as an experiment, so far its working well. At first I was seeing as high as 15 volts, but the past few times I've driven the 4runner (not a daily driver) it's right around 14.5 with stock alt.

YMMV

Mike
Click to expand...

This!

I went to the junkyard and scavenged a bunch of GM diodes. Have one in my MY07 & MY19. Gave me a good ~.75v boost. On startup - especially after a cold start - I have seen up to 14.8v. After warm up I'm doing a pretty good 14.4v. Been running this setup for quite a while now (over a year) with no issues. Also helped a buddy do this mod on his MY16 4Runner that is heavily equipped for overlanding and he's commented that his accessories run better as well.

Simple. Effective. Still easily serviceable at any parts store or junkyard.
 
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