AGM BATTERY CHARGING - ALTERNATOR VOLTAGE BOOSTER

This thread has helped me to better understand a situation I ran into about 5 yrs. ago with a 2006 Toyota Avalon. The alternator gave up the ghost and needed replacing/rebuilding. I pulled it off and had it rebuilt. Afterwards, the voltage read higher than one usually sees on a warmed up engine. I now suspect a different internal regulator with a higer set point or diode was used.
5 yrs. late - all is well - no issues.

 

This is interesting.... I had not looked into this at all in spite of running an Advance Auto AGM battery in my 2009 for the last 5 years or so. I had assumed they operated and charged pretty much like standard lead-acid batteries. It is still working well but probably could benefit from the diode mod, especially as winter sets in and the battery is getting older. The reason it came to my attention recently is that I replaced the standard battery in my 2016 Corvette with an AGM and the system is charging it at a higher voltage (14.7-15.0) for 20 or 30 minutes after startup after which the charge rate falls to our more typical lower 13.5-14.0V levels. I assume controlled by the ECM. And the manual for battery maintainer I use on it says to use the "winter" setting when maintaining AGM batteries. This boosts the voltage a bit. So, I am going to do the diode with the add a circuit holders to maintain the fuse protection for the alt-s circuit. I run a ScanGage 2 with one reading set to voltage so will be able to monitor the results in real time.

 

I’d verify your vehicle doesn’t have AGM support, I know a bit of GM vehicles do.

 

I am pretty sure it does. Pretty sure... not positive.

 

Just got this little mod done... retaining the 7.5A fuse... following the photos and how-to at the beginning of the thread and using a diode from DigiKey. See pic below. This bumped up my voltage about 1/2V. Of course voltage varies some with battery state of charge and a little bit with RPM coming off idle. I have a ScanGage2 and have voltage as one of my constantly monitored parameters and it is essentially 1/2V up from where it used to run in all operating conditions.

That adjustable gizmo from Oz looks nice but not for the the $150 asking price. This simple mod works perfectly and the 1/2 volt bump is probably just about right.


One minor detail... the fuse box cover would not go back on due to interference between the diode and the fuse removal tool snapped inside the cover. I relocated that by clipping in on in a different area of the fuse box itself. You can see the little white tool in the pic.

Not sure if this is entirely necessary as my AGM battery is about 5 years old and has done pretty well with the lower standard charge voltage. But still worth a try.

 

Ok, here's the writeup on the 130 amp alternator for 2TR and the higher voltage regulator
https://www.tacomaworld.com/threads/701909/

Not sure if the 1GR has a hairpin style regulator but if so this regulator swap could be an option

 

I went out to my truck not starting today. Battery so dead that no dash lights came on in the ignition on position. Jumped her and battery light was on, don’t recall seeing that on last time I drove it but may have missed it. Anyway, I pulled the diode and put the stock fuse back in and the light went away. Haven’t tested the diode for continuity yet. Definitely a little WTF moment.

 

Did you check the diode to see if it's working? If it failed full biased, it should have no affect. If it failed open circuit, the alternator would go to full field voltage.

Edit. Add picture to better explain

 

Ended up not being the diode, I think, because it ohm’d out good on my meter. I had a spare diode that produced the same readings. Still not sure why the battery light came on though, and went away after switching to the stock fuse. Alternator produces voltage within spec (14.2 on cold start). I replaced the dead battery with a cheap Costco lead acid one and went back to the stock fuse for the time being. Going to put bigger AGM batteries in the cab or bed soon, so I’ll revisit this diode again then. Probably in line with the fuse next time.

 

Did you check the polarity/direction of the fuse? If it's put in backwards the battery light will be on.

 

Thanks. Read the OP? I had already been using the diode for 2 yrs

 

Just picked up the “North Star” X2power and grabbed the diode. Did the inline add a fuses on the alt-s and open slot. Boom. Instant from 13.9 to 14.5. Good stuff!

 

Where did you order the diode from?

 

Straight from local Ford dealer. Ordered it local pick up and they got it in in 2 business days

 

Just recently replaced my alternator, it is now reading 14.7-14.9 at idle, driving around town around 14.5-14.7. This is using an AGM battery along with the FORD diode.

 

That’s great! Oem or upgraded?

 

Just an OEM unit.

 

Have a question. So I got an agm 24f for my 2010 a few months back. Added this diode. It’s working fantastic. No problems.

Only thing I wonder about is that something does smell hot but I’ve checked everything. Fuses/diodes are fine and not hot. Battery is fine. Nothing melting. I can’t find anything abnormally hot (more than normal engine temp). But something smells hot. Only happens when the truck is on and for maybe a few minutes after it’s off. Then no sign. No performance issues, no spikes. Runs 14.6V at start then runs down to 13.9-14.2 after idle. Very faint smell as well. Only notice it in the driver engine side.

Could it be an issue with the battery itself? Anybody notice this after they upgraded at all?

 

Just a heads up... I did the diode mod back in January and my alternator just failed. No way to show direct linkage cause and effect but my alternator failure does seem premature. So I am going back to no diode stock charging for my AGM battery. It worked fine like that for 5 years before the diode. YMMV, of course, and I know there are many of you who will chime in that you have been running the diode for thousands and thousands of miles and years and years. That's great. But I'm out for now.

 

Miles on the original part?