Is my ‘14 going to fully charge an AGM battery?

[jmden]

Depends on how you wanna do that install. I mean you can do a clean install inside the fuse box, or just add the diode in the wire (splice). Just be careful which way the diode points at, other than that the diode blocks the voltage. A shottky diode has lower voltage drop (0.2 - 0.4V) than a normal one (0.5 - 0.7V).

You can buy diodes in a mini fuse package. Probably the way to go.
Like Motorcraft 4f2z-14a604-aa

There are many threads about this. Google something like “GM alternator diode mod”.

Have read about that. Find the alternator fuse and replace with a diode/fuse. Pretty simple. It still retains the fuse function, correct? But will drop the voltage the alternator is sensing so it outputs a bit more. 14.6V would work, right? So I only need about .4V drop.

 

[DieselMonk]

I haven’t used that diode fuse. Don’t know what voltage drop it has. But it makes a clean install, even so it costs a lot more. Others used it. I suppose you could solder a diode on top of a blown fuse. It wouldn’t be a diode fuse, just a diode. Why I like it is because you could simply turn the diode around if you’d have it installed backwards. So less need of attention which way the diode is pointing at.

 

[jmden]

Depends on how you wanna do that install. I mean you can do a clean install inside the fuse box, or just add the diode in the wire (splice). Just be careful which way the diode points at, other than that the diode blocks the voltage. A shottky diode has lower voltage drop (0.2 - 0.4V) than a normal one (0.5 - 0.7V).

You can buy diodes in a mini fuse package. Probably the way to go.
Like Motorcraft 4f2z-14a604-aa

There are many threads about this. Google something like “GM alternator diode mod”.

OK. If I used the mini fuse Motorcraft diode part you referenced above, what happens to the fuse function? I did a search for the ‘GM alternator diode mod’ and got nothing.

 

[jmden]

Depends on how you wanna do that install. I mean you can do a clean install inside the fuse box, or just add the diode in the wire (splice). Just be careful which way the diode points at, other than that the diode blocks the voltage. A shottky diode has lower voltage drop (0.2 - 0.4V) than a normal one (0.5 - 0.7V).

You can buy diodes in a mini fuse package. Probably the way to go.
Like Motorcraft 4f2z-14a604-aa

There are many threads about this. Google something like “GM alternator diode mod”.

Now that I look, I do not see an alternator fuse listed in the owners manual. Am I missing it?

 

[DieselMonk]

The diode goes into wherever the sense wire is on your alternator.

 

[jmden]

The diode goes into wherever the sense wire is on your alternator.

I was looking in the fuse box to do the mini-fuse/diode.

Are you recommending the splice into the sense wire option over the replace the alternator fuse with a diode option? At this point the former may be my only option, unless I spend nearly $1k on a new alternator with a 14.8V voltage regulator, new ‘big 3’ cables I’d have to make and a lot of work.

Which is the best option?

I double checked the voltage at the battery terminals with everything electrical turned off that I could turn off. 14.35V, so one .4V diode would get me to 14.75, awfully close to the 14.8V I see recommended routinely.

 

[DieselMonk]

All it is, is a 0.4V voltage dropping diode in a mini fuse style. There are diodes that have a lower voltage drop (schottky 0.2V) and regular rectifier diodes that have like a 0.5 to 0.7V drop. Putting the diode into the sense wire will lower the expected sensing voltage on the alternator, and it thinks that is wrong and will work the output harder, so the regulator is happy again on it targeted 13.8V but the actual voltage is higher (so 13.8V plus the voltage drop from the diode 0.4V or so) on the battery. If you can follow my gibberish.
Anyone electronically inclined can do the mod for you too. It's not that hard, unless your alternator is ECU controlled. And I don't know what alternator you got.

 

[jmden]

All it is, is a 0.4V voltage dropping diode in a mini fuse style. There are diodes that have a lower voltage drop (schottky 0.2V) and regular rectifier diodes that have like a 0.5 to 0.7V drop. Putting the diode into the sense wire will lower the expected sensing voltage on the alternator, and it thinks that is wrong and will work the output harder, so the regulator is happy again on it targeted 13.8V but the actual voltage is higher (so 13.8V plus the voltage drop from the diode 0.4V or so) on the battery. If you can follow my gibberish.
Anyone electronically inclined can do the mod for you too. It's not that hard, unless your alternator is ECU controlled. And I don't know what alternator you got.

Yes. I understand all that.

I don’t see a fuse in the fuse block for the alternator or I would try that route.

Is there a down side to splicing in a diode in the sense wire? Does this cause any damage or lower life of any other component in the vehicle?

 

[DieselMonk]

Well... the only thing that hurts the vehicle would be installing the diode and then running regular flooded battery.

 

[twodollars]

I've been running agm batteries in my old 97 dakota and my 77 gmc motorhome. Never an issue with state of charge. And using stock alternator in both.

 

[jmden]

I've been running agm batteries in my old 97 dakota and my 77 gmc motorhome. Never an issue with state of charge. And using stock alternator in both.

Yeah, I get it but the reality is that AGMs require a bit more voltage than wet cell lead acid batteries to fully charge. It's a different charging profile than for wet cell lead acid batteries. My resting battery voltage is about 12.7V. I've been in contact with tech support at Odyssey and they confirm this is about 85-90% charge and never fully charging the battery is harmful to it. I may already have damage to mine which reduces the lifespan and capacity of the battery. This is why aftermarket alternator companies include a special voltage regulator that holds 14.8V if you have an AGM battery.

 

[jmden]

Well... the only thing that hurts the vehicle would be installing the diode and then running regular flooded battery.

You don't happen to have an amazon link to the proper diode do you? There's so many different ones. I probably will plan on installing one rectifier diode, just want to make sure I get the right one.

Will this work: https://a.co/d/bF9op6Z


It sounds like I should just order a pack of diodes and install one (.4V) in the alternator sense line. This has got to be the easiest and cheapest option. And, I just got this from Odyssey technical support:

"3. Alternator Diode Trick:
Adding a diode to the alternator’s sense wire can indeed trick the regulator into a higher voltage output (usually adding around 0.5-0.7V). If you search forums, they have many options on how to achieve this. GM does it with a diode shaped like a fuse."

 

[DieselMonk]

yes you are looking in the right direction. Can be something almost anything like a SB5100, 10sq100, 1N5401, MUR410 etc. maybe look at an old junk circuit board and rob one off. Look at the spec sheet of that diode and find the Forward Voltage. Higher this Forward voltage, the higher the regulator output.
The only problem this way is that you have to have the diode pointing the right way, because if the diode is backwards, it will block the sense voltage going to the alternator! If you get that diode that looks like a fuse and a fuse holder, you can easily point the diode the other way without playing with the harness.

 

[jmden]

yes you are looking in the right direction. Can be something almost anything like a SB5100, 10sq100, 1N5401, MUR410 etc. maybe look at an old junk circuit board and rob one off. Look at the spec sheet of that diode and find the Forward Voltage. Higher this Forward voltage, the higher the regulator output.
The only problem this way is that you have to have the diode pointing the right way, because if the diode is backwards, it will block the sense voltage going to the alternator! If you get that diode that looks like a fuse and a fuse holder, you can easily point the diode the other way without playing with the harness.

https://a.co/d/9hd6AI2

These should work, right? Folks are using these in YT vids for same purpose. Make sure the end that is grey is pointed to the alternator they say. Some YT vids are saying not to leave these in all the time if you have AGM batteries. It seems to me that as long as your voltage is at or close to 14.8V, leaving them in shouldn't be a problem, right?

 

[DieselMonk]

Then put a switch to it, so you can switch the diode in or out.
My 24 charges the AGM anywhere between 12.8 and 15.0VDC. But the ECU is doing that in mine.

So in one way the die because undercharging and the other way from overcharging? Pffft.

 

[jmden]

Then put a switch to it, so you can switch the diode in or out.
My 24 charges the AGM anywhere between 12.8 and 15.0VDC. But the ECU is doing that in mine.

So in one way the die because undercharging and the other way from overcharging? Pffft.

Why would I switch (link to suggestion?) the diode out?

 

[DieselMonk]

There is no link to my last suggestion. I just came up with it in order to give an option to have both modes (AGM and flooded). All you need to do is make a wire bypass in parallel with the diode and a switch. Switch off = diode on (AGM mode), switch on = bypass the diode as the wire jumper completes the circuit in parallel (normal flooded mode).
I suppose you could also do that with a automotive inline fuse holder and a fuse in parallel with the diode. Fuse out = AGM mode. Fuse in = flooded battery mode. Power always goes the path of least resistance. When the bypass wire circuit is complete the power will go around the diode, rendering it useless so to say.
Or:
You cut the sense wire and install the inline fuse holder (with pig tails) into the sense wire. Buy that automotive fuse looking diode. Put the diode in the fuse holder = AGM mode. Put a regular 10 amp fuse into the holder = regular flooded mode.

 

[jmden]

There is no link to my last suggestion. I just came up with it in order to give an option to have both modes (AGM and flooded). All you need to do is make a wire bypass in parallel with the diode and a switch. Switch off = diode on (AGM mode), switch on = bypass the diode as the wire jumper completes the circuit in parallel (normal flooded mode).
I suppose you could also do that with a automotive inline fuse holder and a fuse in parallel with the diode. Fuse out = AGM mode. Fuse in = flooded battery mode. Power always goes the path of least resistance. When the bypass wire circuit is complete the power will go around the diode, rendering it useless so to say.
Or:
You cut the sense wire and install the inline fuse holder (with pig tails) into the sense wire. Buy that automotive fuse looking diode. Put the diode in the fuse holder = AGM mode. Put a regular 10 amp fuse into the holder = regular flooded mode.

Why wouldn’t I just always keep the diode in so that it’s always in ‘AGM mode’.

 

[DieselMonk]

Sure. I’ve got like 3 AGM batteries in cars and tractors that were not designed for AGM batteries. I just swapped the old flooded battery for an AGM and didn’t bother with the diode in the sense wire since the battery is only there to start the car / tractor. It’s not like an Overland or off road vehicle. How long did they last? I had an Odyssey AGM in the GT500 for 13 years (need a new one now), still run a Motormaster AGM in a tractor for 6 years , and a Magnacharge AGM in another tractor. Works fine so far. So this overcharging and undercharging theory on the internetis probably more unique to high current draw and drawing a lot of power in total over time situation. Everyone their own.To me I think it is more important to buy a good AGM battery and that isn’t always the case. An AGM handles more abuse than a flooded battery, true, but it will die at some point too. It’s also up to the owner to maintain a battery these days.
What is there to maintain on a AGM battery? You will be surprised what cleaning up the battery posts and the battery clamps will do, specifically on the newer vehicles. This gets forgotten fast.
A good AGM lasts you 6 years on a start stop vehicle and about 10 in a non start stop car. Ooofff… makes me feel real old now to be able to talk out of my experience with that crap.

 

[jmden]

So while driving around with a voltage monitor/USB port adapter in the 12V power outlet, I’m seeing 13.9 -14.1 and it seems when we are driving in warmer weather (mid to upper 80s) that voltage is dropping to 13.6-13.7V. Does this make sense? Or, do I have an alternator going bad? It’s a OEM alternator that was replaced by dealership about 100k ago, at about 25k miles. I occasionally run a 50amp DC to DC charger off the battery and am already wondering if I’m asking too much of the stock 175amp alternator.