Understanding length of time for absorption & finish charge

[wopachop]

Im referencing the Trojan guide for charging flooded batteries. They are a mix of old 8v Trojans and newer 8v Generic Brand. I have the charger set for 2.45v per cell. (i didnt temp compensate, weather app says its 65F right now)

Trojan says to do a maximum of 4 hours absorption. At that time im still not dropping to the 1-3% finish charge range.

I can tell the charger to drop to a constant current charge. Which i just did its at 2a for a 170ah battery. My question is how long do i leave it on the constant current finish?

Ive read the Trojan guide over and over and all im seeing is " The finish phase ends when the battery is fully charged." How long is that?

My charger does have a setting on what % to stop the charge at. I will have to check what its set to. I messed with it a couple months ago. Lets say i set it to 3%. That means when the charger hits the 3% finish charge the length of time would be zero. But that could be well passed the 4 hour absorption charge.

Does a smart charger for flooded batteries have a time setting that automatically switches to a finish current? I would like like to use my charger to mimic what the smart chargers do. I dont have to wait for the 4 hour maximum absorption time to drop the voltage.

I also dont have to follow Trojan 100%. When i ask advice before there were other brands people linked. I bookmarked their instructions but have not looked recently.

Oh...i do have a tool to measure specific gravity. I dont think i want to dip it in these old batteries. I try to keep the tool all nice. Its only been used on my brand new 6v. I suppose the answer to my question is going to be that i cant use time. You have to use SG. Geez great.

What about an educated guess on timing? New batteries versus older batteries. I swear some of these have to be 10-15 years old now.

[full_mosey]

BFL13 wrote:

...
LY has seen with AGMs (me too) that after they get down to "end current" at 0.5a/100AH and you leave them at 14.x volts they will keep warming up and that takes more amps, so amps start going back up. Time to lower the voltage!
...

You and LY need to use temperature compensating chargers that automatically roll back Voltage and then Amps cannot run up.

Of course you can hang around observing while your batteries charge, or use a shutoff timer if you don't want to hang around.

My Solar chargers and my inverter/charger both automatically calculate the Absorb time and charge Voltage.

But you guys run for the garlic and holy water when any dares to speak well about anything automatic. 🙂

HTH;
John

[wopachop]

Thanks for all the help. The last of 6 batteries was actually the lowest at 7.91v (35% charge). That sucker looks old!! With a 17a 10% charge it hit 2.45v per cell in 30 seconds!! I left it on late into the night with the garage open. For those who like all the fun numbers this is the amperage the battery took while maintaining 2.45 at maybe 55-65F. I should have adjusted for temp huh? Its easy to do on this charger. I need to memorize the adjustment factor. Thats part of the fun!!

1h45m 7.3a
3h 6.46
5h 5.5a
6h12m 5.09a
9h 4.24a

So if you go by the trojan guide of 1-3% finish charge on the 170ah battery the 3% would be 5.1a. That happened at 6 hours and it could have easily gone longer.

[Vintage465]

wopachop wrote:

Vintage465 wrote:
This is way over my head. My solar charges my four 6v using 14.8 volts and when I see the Panel voltage gauge jumps to 20v on the gauge and my battery voltage is over 13.5v..........it's done.

I learned something from this forum that might relate to your setup. The flooded 6v like a big strong charge current. Which you probably wont get from your solar.

I had batteries die premature. Only 2 years old. They were on solar 24/7 and rarely cycled. I figured they died from living on float charge during the day.

The smart guys on here told me they most likely died from being undercharged. My solar setup was not giving the strong charge current the flooded batteries wanted.

It might benefit you to turn on a bunch of lights at night. Cycle the battery down. Then if you run your generator once a month maybe the trailer charger is giving a somewhat stronger charge than the solar.

After I revamped my solar and put the controller in the pass thru, ran hefty conductors, it charges fast and hard unless it's rain clouds. Nearly always charging @ 14.v plus and right around 20 amps. I also shake them up once a month with a 15.3 volt equalization for 3hrs.

[Vintage465]

BFL13 wrote:
ISTR old batteries will have more heat loss when charging and when you get down to the end for tapering amps, the lowest the amps get to will be higher, where more of those amps are going to heat instead of charging.

So your "end current" or whatever you call it, will be higher than with new batteries.

LY has seen with AGMs (me too) that after they get down to "end current" at 0.5a/100AH and you leave them at 14.x volts they will keep warming up and that takes more amps, so amps start going back up. Time to lower the voltage!

I am guessing these 8v batts are for a golf car. You can use four T-1275 12v or six 8v to get your 48v.

What is the make/model of your charger if it is not one of those kind that comes with a golf car? It has settings of interest not found in many chargers.

My bad. getting read to respond to the wrong post!

[landyacht318]

My previous AGM, in its final 6 months of deep cycling life would never approach 0.5% of capacity@ 14.7v, but stall above that and then amps would start rising.

Its replacement just keeps tapering to 0.0x amps at any voltage if left at absorption. when i lower it to 13.6v at 0.5%, and leave it overnight, when I crank it to 14.7v the next day it tapers to 0.0x, the X being as i can't accurately measure amperage less than that.

I've two smaller chinese AGMS, 18 and 22Ah, The Ub12180 and UB12220. Both when newer refused to actually taper to 0.5%, but after a few deep cycles would. One of them will not go below 0.5%, but the newer one will. Both find bottom amps and bounce. amps start rising at some point. I try to not let this happen and at 0.5% call it macaroni and remove them or lower voltage to 13.6v.

The screwy 31, a flooded marine battery, at the end of its life exhibited similar behavior, amps would taper to a certain point at absorption voltage, then start rising.

My charging sources are constant voltage, not constant current, other than when the the charger's output terminals are still below the absorption voltage I have chosen.

If I try to achieve constant current I fiddle my voltage potentiometers, keep raising them from a low point to keep the amps in the 5 per 100Ah of capacity range, but very rarely bother. The times I do this are on the smaller agms when I dont want them feasting on 25+ amps. the 18AH AGM says 5.4 amps max, the 22Ah AGM says 6.6 amps max. I double this rate almost each recharge but tripling/quadrupling that amount is not something i do other than to see what the quench amperage would be, as a data point, for future reference as they age.

Neither small Chinese AGM warms significantly when doubling the maximum recommended rate. I'd not double the recommended rate in 90f+ ambient temps and I might not choose to do so once they have aged and accumulated more cycles.

I don't have any more flooded batteries to cycle, but adjustable voltage charging sources and the hydrometer removed all the mystery and guesswork with the screwy 31.

[time2roll]

wopachop wrote:
Im referencing the Trojan guide for charging flooded batteries. They are a mix of old 8v Trojans and newer 8v Generic Brand. I have the charger set for 2.45v per cell. (i didnt temp compensate, weather app says its 65F right now)

Trojan says to do a maximum of 4 hours absorption. At that time im still not dropping to the 1-3% finish charge range.

Call it done at that point. I believe part of the issue is mixing the age of batteries.

[JimK-NY]

My Lifeline AGM batteries call for charging up to 0.5%. That is 1.5 amps for my 300 AH battery bank. Even at 14.3 volts, it takes a long time to reach that level. I would guess I need to maintain the 14.3 volts for about 4 hours to completely charge the batteries.

[BFL13]

ISTR old batteries will have more heat loss when charging and when you get down to the end for tapering amps, the lowest the amps get to will be higher, where more of those amps are going to heat instead of charging.

So your "end current" or whatever you call it, will be higher than with new batteries.

LY has seen with AGMs (me too) that after they get down to "end current" at 0.5a/100AH and you leave them at 14.x volts they will keep warming up and that takes more amps, so amps start going back up. Time to lower the voltage!

I am guessing these 8v batts are for a golf car. You can use four T-1275 12v or six 8v to get your 48v.

What is the make/model of your charger if it is not one of those kind that comes with a golf car? It has settings of interest not found in many chargers.

[wopachop]

Vintage465 wrote:
This is way over my head. My solar charges my four 6v using 14.8 volts and when I see the Panel voltage gauge jumps to 20v on the gauge and my battery voltage is over 13.5v..........it's done.

I learned something from this forum that might relate to your setup. The flooded 6v like a big strong charge current. Which you probably wont get from your solar.

I had batteries die premature. Only 2 years old. They were on solar 24/7 and rarely cycled. I figured they died from living on float charge during the day.

The smart guys on here told me they most likely died from being undercharged. My solar setup was not giving the strong charge current the flooded batteries wanted.

It might benefit you to turn on a bunch of lights at night. Cycle the battery down. Then if you run your generator once a month maybe the trailer charger is giving a somewhat stronger charge than the solar.

[wopachop]

landyacht318 wrote:
When Amps stop tapering at absorption voltage, and start rising, call em done, is another method.

Or are you afraid of wearing out the spring on your DC Clampmeter's clamp?

Im confused by amps tapering, and then rising. I dont think im following exactly what you mean.

The charger itself is listing the amount of amps. (although i have used a clamp meter to check what the charger says and then how many amps are actually going through the wire next to where it attaches to the battery.....i had to make bigger cables because of excessive drop)

I set the charger to 10% of C20. On my old batteries it hits 2.45v in like 10-30 seconds. The amps taper down and maintain the 2.45v. Problem was that at 4 hours of absorption the charge current was still higher than 3%. Looks like the answer to my question is to leave it hooked up. Even if it takes 14 hours. (the newer batteries hit 2.45v in about 2 mins....which makes sense because the c-rating of my old batteries must be toast)

Note these are batteries that i fully charged 6 months ago. They have been sitting unhooked in the garage.

[wopachop]

Interesting BFL13 that link is saying max absorption time is 12 hours. That would make more sense for what im seeing. At the 4 hour make the current is still well above the 1-3% finish charge.

Makes sense Landyacht has seen it take 14 hours.

The 8v's really help to rinse the conditioner out of my hair.
(thats a joke)

[BFL13]

Trojan's IVI approach needs a special charger, not easy. Yes their 4 hour time does not fit their other statement that times will vary.

IMO ignore all that and use this approach even with Trojans, only use Trojan's voltages with theirs. This is an IV method which is a lot easier to do with the available chargers. Note the times to end each phase.

And yes, believe the hydrometer.

https://www.eastpennmanufacturing.com/wp-content/uploads/Renewable-Energy-Charging-Parameters-1913.p...

[2oldman]

I'll bite.. why are you using 8v batteries, and OLD ones at that?

[MEXICOWANDERER]

No can do ACCURATELY.
Chemistry by derivites?
Slightly less inaccurate guesswork?

A census count after sundown by the number of rooms lit?

[Vintage465]

This is way over my head. My solar charges my four 6v using 14.8 volts and when I see the Panel voltage gauge jumps to 20v on the gauge and my battery voltage is over 13.5v..........it's done.