A different fix for AGM charging

I’m posting this to both share my recent discovery (*of what I think I know) and to welcome any criticisms that might save my Tundra’s ECM from ignorance related damage IOW’s?

*Disclaimer: Don’t try this at home until some professionals here weigh in on what I’ve done.

This past weekend I turned myself inside out trying to put together a cure for the lack of circuit protection using my modified GM diode that stole the place of my alt-s 5amp fuse (to achieve a proper AGM charging rate) and try to get that protection back in place.

The HBK items are all out of stock and I think I now know why because when I attempted to put together a spliced inline dual fuse holder rig that would accommodate both the diode and the 5amp fuse (as shown elsewhere) I discovered 2 things the hard way.

1: There’s a difference between mini blade and micro blade fuses and

2: There seems to be a shortage of micro blade fuse taps.

and it was only due to happenstance that I took a gamble and tried this and as best as I can tell? It works.


It didn’t work with the diode in the top slot but only because the charging rate dropped back down to the original 13.5-13.7’ish numbers but when I plugged the diode in the bottom slot and the 5amp fuse in the top slot I got back up to the diode’s usual 14.2-14.4amp charge rate.

What I’m not savvy enough to confirm though is if I did indeed manage to reinstate the 5amp protection of the circuit but I’m thinking that this workaround did and for now I’m calling it a win unless someone points out otherwise and?

I’m all ears and wide open to educated opinions, advice and suggestions.

Thanks for reviewing.

 

That fuse isn’t doing anything. An add a fuse tap like that creates a new circuit, so now you have a 5A power source going to nothing. But the diode is still inline.

 

Honestly? I was afraid that would be the case after thinking it through a little deeper.

It seems the paradigm here is if you put the fuse coming off the alt and upstream of the diode where it would do its job? You still have the lower 13.5-7’ish charging rate but with the diode crossing over both legs I’ve achieved nothing because while the fuse might blow the diode won’t and will allow elevated amps through the circuit.

I’ve read where users of the HBK units weren’t getting the same charging rates as just the diode with no fuse and were getting charging rates that weren’t much higher than OEM.

I’m beginning to think the only dice to roll is to just run the diode and the heck with the fuse.

 

All that the 5A fuse is doing is protecting the voltage sensor circuit coming off the alternator, nothing else. My shade tree mechanic gut feel says that there's relatively low risk in leaving the fuse out of the design. Others with a better understanding of that circuit (@Jeff_5_7 or @RainMan_PNW) might be able to chime in and confirm one way or the other.

 

Don’t run it without a fuse unless that diode is also a fuse. Was going to explain how to use the add a circuit tap but too hard. Link to one for purchase that shows how to add a diode and keep fuse with the tap.

https://www.ebay.com/itm/266233428659

 

I Followed the link but found myself looking at what appeared to be a decapped/gutted version of what I have but with no fuse or diode and the pigtail clipped off with some black gummy stuff sealing it off.

can you clarify what’s going on there please? (And please pardon my ignorance)

 

They’re basically using a different form factor of diode inside of an add a fuse. Power goes up the left post of the tap, into the 5A fuse, into the diode, then back into the rest of the ALT-S circuit. I might hack up one later and see if I can get something to work. Thanks @Vizsla

 

I had a tap so mocked it up. Diode goes in the red wire however, could be in-line fuse holder for your current diode. Red wire goes to lower right terminal of empty bottom fuse position.

 

Gotcha and Thanks!

Now let me see what I can whip up here and I’ll submit a photo for approval to make sure I get it right! Thanks again!

 

I submit the following for approval @Vizsla

 

You could also pick one of these up:
https://www.hkbelect.com/product/438-mk2-micro-blade-5a-electronic-fuse-version-2020/
Not cheap, but very clean.

And, for what it’s worth, this is how the fuse taps work from a schematic standpoint.


It’s important to install them in the “right direction” or they won’t work at all for the new circuit.

 

DERP
I just realized that’s what you were referencing in the first post and that they weren’t in stock.

 

Two pack of low-pofile mini fuses can be gotten here:

BioFuse QTK Parent

https://www.amazon.com/BIOFUSE-BioFuse-QTK-PARENT/dp/B0B89LST4P

 

certainly not compact, but that is functionally correct.

 

The question is, what diode to use for this. I’ve got to assume a certain size/spec of diode is needed for the correct function and voltage boost?

 

Yeah I haven’t been able to crack that yet lol. I don’t remember enough about diodes from electronics class 20+ years ago

 

Have one of the EBay boosters around somewhere, will try to find it and see what diode was used.

 

if i had to take a guess...it is a zener diode in a reverse bias that alters the signal that is monitored to simply allow alternator's voltage regulator to run at a bit of a higher voltage.

 

Indeed. Checks out with the info here
https://youtu.be/RXJKdh1KZ0w

 

Your dork is showing

 

Are we now just coming to this realization?

 

Spent WAY too much time on this rabbit hole today, but looks like a basic 6A rectifier diode will do the trick.
Might be time for me to do some solder work

 

My one buddy made multiple of his own diodes using add a fuses, I’ll look for one in my pile tomorrow, hahah he eventually ended up using a pot switch, and showed me, cranking charging up to 17v or higher….. and then adjusts down as he sees necessary, I was kinda scared to be honest, you’d probably like this guy.

 

i must ask, why do you think it is a regular diode?

 

Constant charging of AGM batteries by use of the diode isn’t the answer. Just buy an AGM battery charger and charge the battery every 3-4 months. Especially if you have an Odyssey Battery. They will last a lot longer this way.

 

Welp sacrificed my GM diode in the name of science!

Diode P/N - AGP10G

 

this certainly doesn't hurt either.

 

looks and behaves like a regular 1 amp rectifying diode...about a .35-.38 voltage drop @12.44 vdc (my float voltage on my battery)

1 amp diode left, AGP10G from the GM diode on the right...

 

It should work, but you're going to need to flip the polarity of the fuse tap 180deg as the power source comes in on the terminal near the firewall of cab rather than the grille of the truck.

-JS