Used AGM 2 volt cells – Progress Report…

H2SO4_guy

There were batteries that were going to the scrap man that were C & D stationary batteries model AT-27 which are 2 volt AGM cells rated at 1495 AH @ the 8 hour rate and weigh 237 pounds each. These things are large! I didn’t buy any as there were only 6 that read 2.16 volts or better and I am holding out for a set of 48 volt batteries. I could have bought all 6 of them for $711 and when I sell them back I could get $440, which is only being on the hook for $271. About a month ago I did get 12 of the 2 volt AGM C & D cells @ 600 AH @ 8 hr rate and was trying to match those up, which I should add that even though I am using them out of their design spec for off-grid use, they are working perfectly. It is always a crap-shoot to get matching cells, but I am having an interesting time finding cells that work pretty well, and I can always sell them back if I want to for a difference of $.19 per pound, so the risk isn’t too great. They are supposed to get a semi load of stationary batteries in any day now. I did finally cobble a set of flooded 8-D cells together made up of 3 different brands of batteries and they are working very well together, but I haven’t ran them down more than about 80% SOC yet, although they are within .03 volts of each other, so it isn’t too bad.

The system is broken up into 4 different independent systems so if one fails the loads are just moved onto another system. Heck most of the lighting is run off of 12 year old (purchased for scrap) Lucent AGM 2 volt cells which are 115 AH @ 8 hour rate in a single 48 volt string. I hope to move in within a month or so, then it will be more apparent what can be done with the available power.

westbranch

Re: Used AGM 2 volt cells – Progress Report…

I have AT-15's. I have been reading C&D's tech papers about charging etc., and think I have a good set of numbers for Bulk, Absorb and Float.

What are your charge parameters? which charger are you using?

H2SO4_guy

Re: Used AGM 2 volt cells – Progress Report…

I called C & D about the 600 AH batteries model RHD-600 as the info on the net was for float 2.25 - 2.27 VPC and I couldn't get a voltage for bulk or absorb. I think they want them 'Floated' back to full charge after the Telco has an 'Power Event' and then they go back to being floated until the next event. After pressing him, he finally said that initial charge voltage is 2.35 VPC. I have a Morningstar TS-60 PWM CC set to 14.2 volts for bulk, but if I get enough for a 48 volt string, they will go on the Midnite Classic 150. (Both from NAWS, they are always good and fast shipping too. :-)

Westbranch:

What parameters do you use to charge your AT-15's?
How did you come up with the 950 AH rate? The specs don't list the 20 hr rate, but do for 8 and 24 hr rate. I think the 8 hour rate is more realistic as to what we may get in 'Real Life'
Do you have more info than can be found in the C & D file 12_387_msendur.pdf? If you don't have that one, I would be happy to send it to you, but you can also find it on their site.

Thanks,

Skip

westbranch

Re: Used AGM 2 volt cells – Progress Report…

email me, I will send you the C&D table they sent. 1 - 24 hr rates

go here for a bunch of good C&D docs. http://www.cdtechno.com/resource/support_doc.html

I used this one for my best stab at B/Abs/Float values. 2.4, 2.3, 2.25 Vpc....http://www.cdtechno.com/pdf/ref/41_2128_0212.pdf


still digesting all the info from that page of docs.

westbranch

Re: Used AGM 2 volt cells – Progress Report…

just looked up the AT-27 and it comes out to 1738 Ah @ 20 hr rate

H2SO4_guy

Re: Used AGM 2 volt cells – Progress Report…

Wow, good information! It will be good reading, thanks. I didn't get the AT-27 cells, kind of wish I had of, but I already had 12 of the C & D Liberty series RHD-600, which are 600 AH @ 8 hr rate. I looked them up and couldn't find a 20 hr rate, but did find many other rates like 8, 12, and 24 hr rates.

Why not get some more use out of the cells before they go to the scrapper? Don't know what you pay for them, but I pay $.50 per pound and can sell them back for $.31, so there is only $.19 per pound at risk. Not bad considering the new cost of batteries. I already know they will probably have a much shorter life than the 20 years of 'Float' service they were designed for, but mine are doing very well and charge up very efficiently compared to flooded.

Skip

PorkChopsMmm

Re: Used AGM 2 volt cells – Progress Report…

Where are you finding these batteries? Can you share your source or how you locate such large batteries? I have never been able to find anything like this.

H2SO4_guy

Re: Used AGM 2 volt cells – Progress Report…

I am finding these in Kansas City, Missouri. Just about every major area has places that are a clearing-house for batteries going to the scrapper. This one company I am dealing with is supposed to get a truckload of stationary batteries in any day now and I will keep you posted. You can talk to the battery rebuilders in your area. Look for used forklift batteries, and where they send theirs to and you may find where the Telco's send their's when they are replacing many at a time. Also data centers often have LARGE batteries. One I know of has 4 volt C & D cells that weigh 435 pounds each and they are flooded. I have found that a weekly dozen cookies lets them lookout for me much better. I also offered a $20 cash bounty to anyone calling me when the mates to the 600 AH batteries that I have come in, and when they do, there are often skids of them! I recently saw 2 volt cells in 1495 AH (@ 8 hr rate) and 1955 AH (@ 8 hr rate). There was enough to make 1 string of 12 volts on the 1495 AH ones, but I want to match up the 600 AH ones that I have if possible. My goal is to get a 48 volt string and a 12 volt string and when the cells start failing on the 48 volt string, I'll have spares. The risk is $.19 per pound, so it isn't that big of a deal. The 1200 AH @ 12 volts (@ 8 hr rate) of batteries are worth about $8400 new and I paid $635 for them. I can sell them back for $386, so I am only at risk $248 (Plus cookies). So far they are working wonderfully running lights, saws, and all kinds of loads while the place is under construction.

PorkChopsMmm

Re: Used AGM 2 volt cells – Progress Report…

Those are good prices for a lot of battery. I have a 48V bank -- which means I would need a quite a few of those batteries. I also would need many additional panels to feed them. Keep me posted -- I don't have room in the budget until Spring but those prices rival buying an additional set of golf cart batteries which have a much shorter life and not nearly the storage capacity.

H2SO4_guy

Re: Used AGM 2 volt cells – Progress Report…

I purchased some used 8-D batteries that are flooded and about 225 AH (I think) @ the 20 hr rate for $60 each plus a core trade in for each. That is $240 per set of 48 volts and I can resell them back for $145 so the at risk money is only $95. The 48 volt string of 8-D batteries is much the same capacity as a set of golf cart batteries and weigh about 468 pounds for the 48 volt string. Mine ended up being 3 different brands of batteries and they work very well on a 48 volt Exeltech XP-1100. I know the stories about not mixing, but for this little money, I'll take my chances.

Skip

Cariboocoot

Re: Used AGM 2 volt cells – Progress Report…

H2SO4_guy wrote: »

I know the stories about not mixing, but for this little money, I'll take my chances.

Skip

For that kind of money you could definitely take the chance.

The reason behind not mixing different brands/models/ages applies mainly to adding brand new batteries to the mix; since they will immediately be affected by the old ones drawing on the new, so to speak, you're tossing money out right away.

The other big caution is if the capacities of the different batteries is too far apart you end up over-charging one type and/or under-charging the other.

Maybe it doesn't get explained well enough, but there's a lot that can be "got away with" which would not be in keeping with good practice when designing a new system that needs to be close to 100% reliable and as long-lasting as possible.

PorkChopsMmm

Re: Used AGM 2 volt cells – Progress Report…

H2SO4_guy wrote: »

I purchased some used 8-D batteries that are flooded and about 225 AH (I think) @ the 20 hr rate for $60 each plus a core trade in for each. That is $240 per set of 48 volts and I can resell them back for $145 so the at risk money is only $95. The 48 volt string of 8-D batteries is much the same capacity as a set of golf cart batteries and weigh about 468 pounds for the 48 volt string. Mine ended up being 3 different brands of batteries and they work very well on a 48 volt Exeltech XP-1100. I know the stories about not mixing, but for this little money, I'll take my chances.

Skip

Wow, that is much cheaper than 6V golf carts from Sam's. My last purchase of 8 of them was ~$780 or so . I don't even know what 8D's are going for at Sam's right now.