What would happen if I used my old 8D's with my new 8D's?

softdown · July 2017

The old 8D's are FLA and weigh 125 pounds/each.....four of them. The new 8D's are AGM and weigh 170 pounds/each....four of them Manufacturer recommendations for charging the new AGM's are extremely similar to the Outback default settings...a standard FLA setting pretty much.

Four of the old 8D's are barely enough to power this place. Morning voltage is ~48 volts with the MATE showing an ~80% SOC. I don't know how they derive that curious number. They really aren't worth hardly anything more than scrap value I would guess. I may just run them until another cell goes bad. They do that about every six months or so. Five good cells and one bad cell so the battery gets scrapped. Not a true solar battery by any stretch.

By the way, I have found the old saw that "mixing new batteries with old batteries will make the new batteries mimic the old batteries"....to be utter garbage. While less than ideal, it is much cheaper than replacing the bank every time a battery goes bad....in the long term...by my estimation.

Each bank would have separate charging cables from the inverter/controller Outback MATE.

Estragon · July 2017

I have no direct experience to back up the received wisdom on mixing old and new. I suspect it depends a lot on the state of the old ones (eg. sulfation vs grid corrosion), so even if I did have direct experience, it would be n=1 and of limited value.

In the case of partial sulfation, the old batteries may appear to be charged, while the new ones still need more charge. Eventually, the new ones may sulfate to match the old ones.

In the case of grid corrosion, I would think that the battery might behave much like a new battery in terms of charge requirements, depending on exactly how and where the corrosion occurs, and eventually fail with a shorted or open cell. In that case, mixing old and new might not be so bad (assuming you could catch the shorted cell before Bad Stuff happens).

Old batteries are probably some mix of pending failures, which will be a function of lots of factors in their manufacture and over their lifetimes. Absent good, non-destructive ways to test them, it's probably more art than science.

To me, diminishing ability to handle loads (loss of capacity), would be a warning sign, and maybe time to start planning for replacement of the bank, rather than individual batteries.

Marc Kurth · July 2017

I am seriously hoping that people will post with solid technical reasons to support their opinion on this and not just Google based responses. I have strong opinions of this subject BUT I am always willing to listen and learn. THAT is what this place is all about!

What is your opinion at this point? (No, I'm not trying to set you up - just creating an anchor position to start the process)

Vic · July 2017

Personally, would just run the AGMs by themselves. Have NOT followed all of the comments on your situation ... assume that the AGMs are new-ish and in good condition.

Since you do not believe that old saw, then guess that you are hoping that others will just say, go for it.

In the case that the old batts might have a/some cells that are tending toward being shorted, you could possibly damage the AGMs that are in parallel.

Mixing batteries that are of different ages, design, and Capacity would be an interesting experiment ...

Good Luck! Single-String Vic

Estragon · July 2017

I don't know if my response qualifies as solid technical reasons. Some of it may come from google, but most from what I've learned here.

Marc Kurth · July 2017

Estragon said:

I don't know if my response qualifies as solid technical reasons. Some of it may come from google, but most from what I've learned here.

We posted at the same time and I was NOT responding to your post!

softdown · July 2017

Always been blessed/cursed with a powerful curiosity. A proper engineer/scientist would likely check each battery several times/day. One could possibly figure something out pretty quickly.

I have seven old 8D's with SG in the fair to good range. Was tempted to buy a new one and go another ~1/2 year before another battery dies. That is pretty much how these 8D truck batteries roll. Sometimes they die in 1 1/2 years. Half are still going from 2 1/2 years ago. They never die within the 1 year warranty period of course.

It is always the same thing with these truck 8D's made by Johnson Controls. A cell goes bad. Though I did find one with two bad cells a couple days ago.

If I ended each day with every battery at ~55.2 volts, it would seem that this experiment would be permissible.

The AGM's are in a room that is ~15 degrees cooler than the FLA's. That is why I moved them into a cooler room...to prolong their life. That took a very surprising amount of work with walls that are 1' thick. I overdo things at times...

softdown · July 2017

Best case scenario: The batteries work together and the new batteries only discharge to ~12.5 volts by morning. With seven old 8D's, I may be able to enjoy pretty incredible battery life.

Raj174 · July 2017

I'm no pro with lead acid experience, but wouldn't you think the FLA's will take longer to charge and then feed off the AGM's?

Rick

Solray · July 2017

I would ditch the FLA batteries and use AGM batteries exclusively. FLA are a pain to maintain.

softdown · July 2017

Changing the subject a bit here. My experience has been that one doesn't need super healthy batteries to provide good service. What one can not tolerate is a single bad cell in any battery.

I lost service at 1am with seven decent batteries, the eighth battery showing two bad cells. Currently taking a charge which is a bit surprising really. Usually a battery with a bad cell will not take a charge. Though the charging has only been happening for ~20 minutes.

Does one bad cell effectively short out the entire string? That is how it seems.

FLA are not a bad "pain to maintain". Why do so many internet personas seem to think that everybody has buckets of extra cash anyway? I see this several times/day. Government agents trying to stimulate economy?

mike95490 · July 2017

Solray said:

I would ditch the FLA batteries and use AGM batteries exclusively. FLA are a pain to maintain.

Which is just fine if you are wealthy and don't mind spending 4x $ for same power of battery bank.
AGM has shorter life than flooded, and costs nearly twice as much.

bill von novak · July 2017

Solray said:

I would ditch the FLA batteries and use AGM batteries exclusively. FLA are a pain to maintain.

Adding water is easier than changing batteries. I'd much rather add water 10x than replace batteries 2x.

softdown · July 2017

Especially if one invests in water miser caps at about $5/cap. They seem to reduce water loss by at least 500%.

Estragon · July 2017

I'm using about 1.5gals/yr on my 3yr old bank now. When they get older, I assume they'll use more and may want to get caps.

Vic · July 2017

Estragon said:

I'm using about 1.5gals/yr on my 3yr old bank now. When they get older, I assume they'll use more and may want to get caps.

Pretty low water usage. The main banks here use about 80% of that amount each month, although the banks are watered every two months, and average about 2.25 to 2.5 US Gallons every two months per bank.

Have tried Water Miser caps, and have noticed NO reduction in water consumption whatsoever (not to be too argumentative).

So Estragon, what brand and model number are your batteries ... assume that you are referring to the consumption on the 370 Ah bank.

The batteries here are in their 12th year, and they DO use more Distilled Water now, than when new.

Thanks and sorry for the Topic Drift, Vic

Estragon · July 2017

The 1.5gals is for both banks (4xL16 12v and 8xL16 48v). The batteries are USbattery basic flooded L16. Nothing special. Both banks tend to be lightly used though. I have controllers set to bulk every 4 days, but when actively used voltage will usually trigger a bulk cycle before that. We try to time loads to the sun, and rarely draw banks to < 70%SOC. I EQ roughly quarterly, which is generally when I add water.

Solray · July 2017

First point is he already owns the AGM batteries so there will be a 0 dollar cost to use them.
Second point. No one said water is expensive, I do however think removing caps and checking all the time is a pain, unless you are advocating not checking water levels anymore in which case it's a wash.
I would not recommend FLA batteries of you plan on never checking the electrolyte levels though.

Estragon · July 2017

> @Solray said:
> I would ditch the FLA batteries and use AGM batteries exclusively. FLA are a pain to maintain.

I thought he had 8Ds, which I think are flooded. You suggested "ditching" them. Where is anyone suggesting not checking water levels?

Solray · July 2017

What??? I think you missed something.

BB. · July 2017

I deleted a less than useful post or two earlier...

-Bill "moderator" B.

Solray · July 2017

How is Estragon's post more helpful when he just said: I thought he had 8Ds, which I think are flooded. You suggested "ditching" them. Where is anyone suggesting not checking water levels?

BB. · July 2017

OK, I have restored post #18. Part of the post was quoted (he was faster than I was at deleting).

Posts that attribute actions/meanings/thoughts to others whom we do not even know (other than on the forum) is not useful.

Solray said:

First point is he already owns the AGM batteries so there will be a 0 dollar cost to use them.
Second point. No one said water is expensive, I do however think removing caps and checking all the time is a pain, unless you are advocating not checking water levels anymore in which case it's a wash.
I would not recommend FLA batteries of you plan on never checking the electrolyte levels though.

The 8D batteries are available in multiple forms. The original poster had old FLA and the new ones are AGM.

https://www.fisheriessupply.com/dyno-battery-heavy-duty-8d-marine-batteries-12-volts
Trojan 8D-GEL 12 Volt 225 Amp-hour Deep Cycle Gel Battery
Lifeline GPL-8DA AGM Sealed Battery 12V 255Ah

And different people have different experiences (for example, I have seen both praise and did not do much of anything with Water Miser caps on the forum).

-Bill

softdown · July 2017

Curious readings after hooking up the second bank new/older 8D AGMs that were fully charged though never used: I waited until bulk readings were ~54 volts on the old first bank of 8D FLAs. Just couldn't wait any longer.

The reading comparison between the two banks is highly similar except for one thing:
New 8D AGMs: 3 batteries at ~~14.5 volts. 1 battery receiving the black negative from the charger is at 15.1 volts.
Old 8D FLAs: 3 batteries at ~14.5. 1 battery receiving the red positive from the charger is at 15.1 volts.

Today, at least, I will try to check all batteries every hour.

softdown · July 2017

These battery banks are not run truly parallel. Separate cables from Outback 3648. Must say that they could allow more room for two sets of cables.

Readings have mostly normalized now.....grouped closed together.

Should temp sensor go to the cooler bank or the warmer bank? Moved the new bank into a cooler room for battery longevity,...quite a chore as it turns out.

Vic · July 2017

IMO, the RTS should be on one of the AGM batteries, as they are more sensitive to overcharge voltages.

Just where to place an RTS/BTS is just one of the numerous questions/issues that can result when running multiple strings of batteries, particularly ones that have differing designs, charge voltage requirements, and Absorb termination needs ...

As an aside, had thought a few years ago, that you really deserved to have a NEW, un-abused battery bank, so you could learn how (well) new batteries behave, compared to batts that have an unknown past. You now appear to have then -- the AGMs -- but, still you are running some potentially incompatible strings of old (and demonstrably failing) paralleled with the new ones. If for no other reason, tending this setup will take a LOT of time, good that you have the time ... (this is meant in only the most positive way, not as back-biting).

Just sayin'. Vic

softdown · July 2017

BB. said:

OK, I have restored post #18. Part of the post was quoted (he was faster than I was at deleting).

Posts that attribute actions/meanings/thoughts to others whom we do not even know (other than on the forum) is not useful.

Solray said:

First point is he already owns the AGM batteries so there will be a 0 dollar cost to use them.
Second point. No one said water is expensive, I do however think removing caps and checking all the time is a pain, unless you are advocating not checking water levels anymore in which case it's a wash.
I would not recommend FLA batteries of you plan on never checking the electrolyte levels though.

The 8D batteries are available in multiple forms. The original poster had old FLA and the new ones are AGM.

https://www.fisheriessupply.com/dyno-battery-heavy-duty-8d-marine-batteries-12-volts
Trojan 8D-GEL 12 Volt 225 Amp-hour Deep Cycle Gel Battery
Lifeline GPL-8DA AGM Sealed Battery 12V 255Ah

And different people have different experiences (for example, I have seen both praise and did not do much of anything with Water Miser caps on the forum).

-Bill

Interesting links. Gels are pretty popular in the sailing and liveaboard community. I had to quit saying bad stuff about them because so many people are getting favorable results.

Two of those batteries have battery posts for starting engines. I have not found a very good way to use those posts in a solar set up. Just more points to tighten and more points for corrosion creep. More places to lose power as I think all connections tend to do.

This from the https://www.fisheriessupply.com/dyno-battery-heavy-duty-8d-marine-batteries-12-volts link: "These 12 volt batteries are available in either deep cycle or starting versions. This is the starting model." I suspect a mistake because the CCA (1250) is low for the weight of the battery (141 lbs). Plus the way they are advertised.

Marine deep cycle batteries are not talked up here. Though I have a couple made in 2007 and still serviceable for light duty.

softdown · July 2017

Vic said:

IMO,   the RTS should be on one of the AGM batteries,   as they are more sensitive to overcharge voltages.
Just where to place an RTS/BTS is just one of the numerous questions/issues that can result when running multiple strings of batteries,   particularly ones that have differing designs,   charge voltage requirements, and Absorb termination needs ...
As an aside, had thought a few years ago, that you really deserved to have a NEW, un-abused battery bank,   so you could learn how (well) new batteries behave, compared to batts that have an unknown past.   You now appear to have then -- the AGMs -- but, still you are running some potentially incompatible strings of old (and demonstrably failing) paralleled with the new ones.    If for no other reason,   tending this setup will take a LOT of time,   good that you have the time ... (this is meant in only the most positive way, not as back-biting).
Just sayin'.   Vic

That was pretty polite. Are you Canadian?

I went from bad solar batteries to some of the very best batteries I think. I was unable to sell the unused AGM's because sitting for two years scared people. They said I must have bought them for scrap value. I plan to move unto a large sailboat in a couple years so I am saving some unused AGMs for that. Including 8 well used AGMs, in a few years, is not going to help the resale value of this place much.

Plus I have seven serviceable FLA 8D's. One goes bad about every 1/2 year. Not a big deal after I have recovered from the inevitable loss of sleep. I can see getting a lot more life out of my new AGM's with the old FLA's pulling a large share of the load.

Very interested in what my 6am voltage and SOC readings will be now. Four old FLA's performed almost as well as eight old FLA's for what that may be worth.

You are entirely right from a purist view point. Mixing the banks is not the "Right Stuff". Being a South Florida landlord, I have to be the master of making lemonades from lemons. i.e.- Getting a foot out of an 7" dollar. A/C issues, vandalism, theft, septic systems, hot water heaters, roaches, rats, drive by shooters, rabid "government officials", appliances etc. I may suffer from PTSD from being a South Florida landlord. It is very common to lose money with many of the issues being directly exacerbated by being in South Florida. A sunny state with shady people to be sure.

softdown · July 2017

Now the old 8D readings have become interesting:
The battery with the positive charging cable is reading 14.3. Mfd in late 2011 and placed in service in early 2015.
The battery with the negative charging cable is reading 13.02. Mfd in 2016, my newest battery.
The other two old batteries are reading 13.7.

I have always found very strong correlations between SG and voltage. Willing to bet the old battery now has higher SG readings. Also wondering if a weaker battery accepts a higher charging voltage more readily. Perhaps this high "float voltage" will disappear after the sun hands the duty baton over to the moon? I will probably report on findings.

Running the RJ5 temperature sensor through foot thick walls was absolutely 2 1/2 bi**hes. Impossible without a wire puller, tape, and vaseline. Even removing vaseline impregnated tape was tricky.

softdown · July 2017

Disclaimer: Windy and rainy plus charging an 8D with 12 volt charger. Tomorrow morning will almost assuredly disappoint. Already down to 91% SOC at 6pm. Though that read out seems like witch craft most of the time.

Marc Kurth · July 2017

@softdown:

I do a LOT of 24/48/72, 2v cell strings for 48v AGM battery banks. When I speak with the Chief Engineer at a particular battery manufacturer about variations in individual cell voltages, he invariably responds with: "Marc, what are the individual cell voltages in a 48v bank with 8D's?" He goes on to explina that the same thing happens internally with a 6v, 8v or 12v battery. Please note that this applies to batteries of the same type and vintage.

After a lot of years doing this, I have become a huge believer in long float time to let batteries reach the same level.

Marc

What would happen if I used my old 8D's with my new 8D's?

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