89’ TBI alternator 14.5 V or higher

[scoots90245]

I apologize in advance. If this has been covered, I could not find it. I thought I would upgrade my 89 Jimmy with the AGM battery I have found if this battery sits more than a week without running the truck there’s not enough power to start it when I googled AGM battery I have seen that it requires a 14.5 or higher voltage, and I’m wondering if there is an aftermarket or stock alternator that will bolt right in ? Thank you for any help. It’s posted somewhere that I cannot find.

 

[Wes Harden]

That's a good battery. When checking the charging voltage have you checked it at say 1500-2000 rpm? Try that before jumping on a new alt.
Short low speed trips can insufficiently charge your battery, esp if you have a couple electric fans ac and what not running. I haven't seen the 14.5v spec for AGM and have been working with them for years, never had an issue with a charging system at 1 volt over battery voltage. Fully charged battery is 12.6-7 volts 13.6v+ would be excellent result
Also test for a draw. Put a test light between the battery negative and the battery negative cable, if lights something is drawing with the truck off.
common possibilities
The Alt remove batt wire and see if light goes out.
Courtesy circuit, all doom lamps and cigar lighter.
Any add on accessory taking power from a battery powered cavity in fuse block
Horn/relay
There could others less likely no need to cover until we get there.

All of the above said if you still want a new alt talk with @500$k5 he'll get you set up with a good alt.

 

[Blue85]

Which pins does the small connector have? There are 2 main versions: https://ck5.com/forums/threads/alternator-voltage-fluctuation.340096/#post-4079031. Anyway, all you have to do to get more voltage out is to reduce the voltage going to the sense terminal ("S"). A diode should drop about 0.7V and bring up the alternator output accordingly. I don't know how far you can go with this before it causes any issues, because I've never tried.

Actually, how is it wired now? It's possible you have the sense line wrapped right back to the alternator output and you'll gain some voltage just by doing remote sensing.

The battery does say right on it that cyclical charge is 14.4V-14.8V and 13.5-13.8V is float charge.

What is the voltage out of the alternator and at the battery as it runs now?

Keep in mind, this approach is going to make all of the lights a lot brighter and they're all going to burn out a lot faster.

 

[Blue85]

It doesn't help that you're running adapters on the battery posts. You should use actual battery cables. The brass adapters are for charging in the store, not cranking a starter.

 

[scoots90245]

I’m gonna get on all this this weekend thank you for all the input. I will start with moving the cables. that will be the easiest and I’ll check the charging system as well as I can. I also appreciate the obvious on the battery that I did not see.

 

[Chickntrk]

What are you charging at now? I have an AGM in one of my Dodges but it charges at 14.7…..in fact both my Dodges do. I’ve never checked my Chevy.

 

[scoots90245]

I stopped by my garage. Did a quick check 14.26 V at 600 RPM even at 2000 3000 RPM. I took Blue 85 advice moved the battery cables that brought it up to 14.48
Thanks for that simple fix Blue85. Then I took Wes Harden’s advice and found a draw from the Horn/DM fuse I will head back over there this weekend to see if I can figure it out the horn works fine not sure what DM is. Thank you for everybody’s input.

 

[scoots90245]

Might’ve made a stupid mistake. The door was open when I was checking the fuses.

 

[Wes Harden]

yes this will give you a false light. I normally check with door closed 1st, then pull the courtesy fuse for continued testing.

 

[EddieExpedition]

It doesn't help that you're running adapters on the battery posts. You should use actual battery cables. The brass adapters are for charging in the store, not cranking a starter.

Out of curiosity, what is so bad about the brass lugs? I’m running them on my trucks with no issues that I can tell. Is there a better alternative for non factory cables on side post batteries?

 

[Wes Harden]

Is the extra connection that causes a small voltage drop, on the best cleanest, and at worst a large voltage drop.
I use a 3/8 bolt nut and washers to connect cables directly to the side post contact

 

[Blue85]

If you bolt a ring terminal, there is limited/unknown contact area, compared to a real battery terminal. Crimping the cable into the terminal is superior because they become practically one piece and there is almost no voltage drop, and likewise no localized heating that fatigues the connection over time. Bolting to a terminal/adapter is just adding another connection. Obviously, the top post terminal offers a lot more surface area than the side post, but a real side post terminal has a lot more surface area than those ring terminals.

 

[1-ton]

If your truck sits for a while, and the battery dies that means you have a power draw of some sort.

 

[scoots90245]

If your truck sits for a while, and the battery dies that means you have a power draw of some sort.

No draw, I thought there was because I was checking fuses with door open so it showed the Horn/DM but i closed the door haha no draw.
I replaced the top terminal clamps with brass conectors and am getting a full 14.5 - 14.6 volt charge the small side ring terminal was at 14.3 max. I am hoping this will give the AGM what it needs.

 

[scoots90245]

If you bolt a ring terminal, there is limited/unknown contact area, compared to a real battery terminal. Crimping the cable into the terminal is superior because they become practically one piece and there is almost no voltage drop, and likewise no localized heating that fatigues the connection over time. Bolting to a terminal/adapter is just adding another connection. Obviously, the top post terminal offers a lot more surface area than the side post, but a real side post terminal has a lot more surface area than those ring terminals.

Thanks I was stoked to find the Voltage charge to battery go from less than 14.28 up to 14.6 just by connecting to top post clamp/connectors.