07-10-2022, 09:11 PM
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#1
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Anybody install a diode to boost alternator voltage for your AGM batteries?
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!
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07-11-2022, 03:03 AM
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#2
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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).
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07-11-2022, 08:38 AM
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#3
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Quote:
Originally Posted by 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).
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What voltage do you run now?
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07-11-2022, 09:22 AM
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#4
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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.
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07-11-2022, 09:47 AM
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#5
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Quote:
Originally Posted by 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.
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I did not know that applied to lead acid cells. I thought it was only ninh/nicd and lithium cells.
Good information
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07-11-2022, 12:34 PM
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#7
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Quote:
Originally Posted by 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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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.
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07-12-2022, 01:16 AM
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#8
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Quote:
Originally Posted by 19963.4lsr5
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.
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07-12-2022, 04:03 AM
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#9
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Quote:
Originally Posted by pluton
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.
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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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07-13-2022, 04:14 AM
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#10
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Quote:
Originally Posted by shadow247
You can also get more Reserve with some of the AGM batteries.
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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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07-14-2022, 02:48 PM
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#11
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Quote:
Originally Posted by 19963.4lsr5
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.
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07-14-2022, 03:00 PM
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#12
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Quote:
Originally Posted by Endlessblockades
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.
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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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07-14-2022, 03:47 PM
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#13
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Quote:
Originally Posted by 19963.4lsr5
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
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Last edited by Endlessblockades; 07-14-2022 at 03:57 PM.
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07-14-2022, 05:51 PM
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#15
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Quote:
Originally Posted by Endlessblockades
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
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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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