Anybody install a diode to boost alternator voltage for your AGM batteries?

[4flyer]

Many of us are running AGM batteries, myself included. AGM batteries want a higher voltage than our alternators normally provide (14.6V+). One way to get around this is to add a diode to the alternator sense circuit to trick the alternator into upping the voltage (the diode makes the alternator think that it need to boost the voltage by ~0.7V). Has anybody done this in our 3rd gens? Thinking about doing this in my rig but wanted to see if there was experience in this topic!

Thanks!

 

[pluton]

I added this one---
MK4 Adjustable Alternator Voltage Booster | HKB Electronics
to the electrical system a few months ago. I set it to the +0.6 V position for the summertime. Odyssey PC-1500(34R) battery.
My experience so far: Short trips around town still don't recharge the AGM past about 70% capacity(estimated). Haven't done many long trips yet, only about 120 miles straight. I can't always check the battery resting voltage the next day after long commutes, so my results are incomplete at this time. Nothing has blown up, so I guess that's a good thing. There may still be a need for a weekly/biweekly full recharge for the AGM. BTW, my Renogy "solar suitcase" system (with the entry-level charge controller) will only charge the AGM to about 90% capacity (estimated).

 

[19963.4lsr5]

I added this one---
MK4 Adjustable Alternator Voltage Booster | HKB Electronics
to the electrical system a few months ago. I set it to the +0.6 V position for the summertime. Odyssey PC-1500(34R) battery.
My experience so far: Short trips around town still don't recharge the AGM past about 70% capacity(estimated). Haven't done many long trips yet, only about 120 miles straight. I can't always check the battery resting voltage the next day after long commutes, so my results are incomplete at this time. Nothing has blown up, so I guess that's a good thing. There may still be a need for a weekly/biweekly full recharge for the AGM. BTW, my Renogy "solar suitcase" system (with the entry-level charge controller) will only charge the AGM to about 90% capacity (estimated).

What voltage do you run now?


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[jgue467]

Its not really a great idea to charge to 100% anyway, battery life is extended the Most at 85% max hence why our alternators work they way they do.

 

[jross20]

Its not really a great idea to charge to 100% anyway, battery life is extended the Most at 85% max hence why our alternators work they way they do.

I did not know that applied to lead acid cells. I thought it was only ninh/nicd and lithium cells.

Good information

 

[brillo_76]

I could see extended long periods of of with the voltage being too high doing damage. 14.2 isn't that much above 13.8.

I am just curious as to why want to run AGM batteries? For off reading, camping?



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[shadow247]

I could see extended long periods of of with the voltage being too high doing damage. 14.2 isn't that much above 13.8.

I am just curious as to why want to run AGM batteries? For off reading, camping?



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AGM's are definitely known to be a stronger option for offroading. The cheaper non-agm batteries can break internally if you are stupid and crazy. So far I have been lucky with my Interstate battery, but plan to upgrade to an AGM at some point. You can also get more Reserve with some of the AGM batteries.

 

[pluton]

What voltage do you run now?


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Cold start (summer, L.A., 64ºF) it gives about 14.7V for under a minute, then as the engine compartment warms up, the voltage begins it long, steady march down to 14V or maybe 13.9V once fully hot. I suspect the boost will probably need to be dialed back when the weather cools off in November (cold starts at 45-50ºF). A 2 hour highway drive seems to yield a next-day (≈resting) voltage of 12.75V....not bad. Under the original factory charge settings it would never charge higher than a resting voltage of ≈12.55V or so.

 

[19963.4lsr5]

Cold start (summer, L.A., 64ºF) it gives about 14.7V for under a minute, then as the engine compartment warms up, the voltage begins it long, steady march down to 14V or maybe 13.9V once fully hot. I suspect the boost will probably need to be dialed back when the weather cools off in November (cold starts at 45-50ºF). A 2 hour highway drive seems to yield a next-day (≈resting) voltage of 12.75V....not bad. Under the original factory charge settings it would never charge higher than a resting voltage of ≈12.55V or so.

My 70a Alt 14.0-14.2 at first start then 13.8-13.9 after everything is up to temp here in south central PA. I think I put a new VR in it

Thanks for the info.


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[19963.4lsr5]

You can also get more Reserve with some of the AGM batteries.

Interesting, I need to look again. I don’t think I ever seen a AGM battery of the same group size as a flooded lead acid battery having equal or more RC.

But saying that it’s been more than a few years since I even compared them against each other.


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[Endlessblockades]

Interesting, I need to look again. I don’t think I ever seen a AGM battery of the same group size as a flooded lead acid battery having equal or more RC.

But saying that it’s been more than a few years since I even compared them against each other.


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I did a little research recently and the claimed RC ratings are pretty much the same between an AGM (Optima/Odyssey) and flooded batteries (Interstate for example) in the Group 35 and 34r sizes - about 100 mins. Northstar AGM were maybe 15 mins more.

AGM style is much more tolerant of vibration and can be mounted in any orientation - so they say.

 

[19963.4lsr5]

I did a little research recently and the claimed RC ratings are pretty much the same between an AGM (Optima/Odyssey) and flooded batteries (Interstate for example) in the Group 35 and 34r sizes - about 100 mins. Northstar AGM were maybe 15 mins more.

AGM style is much more tolerant of vibration and can be mounted in any orientation - so they say.

I actually sat down and looked today.

Our rigs call for a 24F. Interstate MTP is 130RC. Their MTX AGM is only 120RC.

However, the Northstar AGM blows them away with 160RC. But the northstar battery is all but 400 dollars.

A group 27F battery is a wider group 24 and should fit with no mods needed and they are almost 100ah in a flooded battery.


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[Endlessblockades]

I actually sat down and looked today.

Our rigs call for a 24F. Interstate MTP is 130RC. Their MTX AGM is only 120RC.

However, the Northstar AGM blows them away with 160RC. But the northstar battery is all but 400 dollars.

A group 27F battery is a wider group 24 and should fit with no mods needed and they are almost 100ah in a flooded battery.


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Weird that the optima site recommends the wimpier 35 when i plug in my specs...

Hooo doggie, the N* NSB-AGM27 has a 195 minute reserve

 

[brillo_76]

All AGM is sealed gel paste batteries. Using fiberglass mats...

The pros is they are non Spillable sealed. They wear out just like the standard lead acid.


Gelled sealed batteries have been around a long time. I do think the paste is different in the AGM sealed.

I haven't researched them much tough.

You folks can look into Dakota lithium as well..

DL+ 12v 60Ah Dual Purpose 1000CCA Starter Battery Plus Deep Cycle Performance – Dakota Lithium Batteries

They probably work very well as they are deep cycle

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[19963.4lsr5]

Weird that the optima site recommends the wimpier 35 when i plug in my specs...

Hooo doggie, the N* NSB-AGM27 has a 195 minute reserve

Some sites are weird about screwing up battery sizes. At one time napa told me I had group 78 batteries in my cummins. Umm, no they are dual 27’s.


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[Endlessblockades]

The pros is they are non Spillable sealed. They wear out just like the standard lead acid.

You folks can look into Dakota lithium as well..

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AGM claims to last 2X longer

Those look sick but you can drop $1000 on a Dakota battery if you're not careful. I start to wince north of $200.

 

[brillo_76]

AGM claims to last 2X longer



Those look sick but you can drop $1000 on a Dakota battery if you're not careful. I start to wince north of $200.

Time will tell. I don't blame folks for not getting the Dakota lithium.

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[19963.4lsr5]

Weird that the optima site recommends the wimpier 35 when i plug in my specs...

Hooo doggie, the N* NSB-AGM27 has a 195 minute reserve

I just measured the MTP-24 in my Toy and the spare MTP-27 on my work bench. Their height and width are within 1/16” of each other.

So there you have it. Wider battery fits in stock location with factory hold down.


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[pluton]

AGM claims to last 2X longer

New Odyssey 34R into the 4Runner when I got it in 2013. Replaced it...still starting the car fine...in 2020. Turns out it had about 1/2 of it's original capacity due presumably to my relying on the car's charging system alone to keep it charged. The Die Hard Platinum (same size) that I bought a few months earlier in 2013 for fridge duty, which was always recharged fully on a 5 amp Battery Tender and then a smart charger after every camping trip, still works, with most of it's original capacity apparently still available.

 

[brillo_76]

One thing I learned from my father in law. If you not using a lead acid battery. You keep it on a battery tender. He had batteries last 10 to 13 years or so on all his equipment. All the lawn mowers etc lasted a alot longer on battery tenders. I was shocked at first. But it really makes sense as keeping them fully charged is alot easier on the plates.

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