Battery AHr Rating: How to Convert 1 AHr rating to 20 AHr rating

mnittler · February 2017

I have access to a used utility (C&D 4LCY7 SAN) battery bank that is currently being replaced after 8 years of service powering switchgear protective relays just because they are 8 years old. The SpGr looks pretty good, the individual cell voltages look good. The configuration consisted of 15 each 8VDC 212 AHr @1Hr rating, weight=310 lbs each. The batteries were originally wired in series for 120vdc. I intend to pick and choose the 12 best batteries from the group of 15 each and make 2 banks of 48V for my solar system. I currently use 3 banks of 8 each 3 year old Trojan T-105 6VDC batteries for 48V which will be replaced by the used battery banks. How would the 212 AHr rating @ 1 Hr compare to the Trojan 225 AHr @ 20 Hr rating? Just looking at the 310 lbs for the C&D batteries vs 62 lbs for the T-105 Trojan tells me they should have more capacity. What is the calculation to convert 1 Ahr rating to 20Ahr rating. The C&D batteries are lead acid type. The used C&D batteries have probably only been cycled to low 12 times in the 8 years during a power outage and have also not been in a controlled environment. Another question is how many years should T-105's last not in a controlled environment in South Texas?

Marc Kurth · March 2017

There is no universal conversion factor because different battery designs have different characteristics. With many common designs, the 1 hour rating of a NEW battery will generally be 50% to 70% of the 20 hr. rating,

If the 1 hr rating is the main published number, they were likely designed for UPS type duty with few, hard/fast discharges in lieu of a larger number of shallow discharge cycles expected with off grid systems.

At 8 years, I would be very skeptical about how much real life is left.

Put a fixed load on them and watch the time. You will have your answer.

BB. · March 2017

Assuming they are good quality AGM batteries--Here is Concorde Lifeline battery curve the 20 hour rate is 100%. They graph out from 1h to 120h rates in comparison:

https://www.solar-electric.com/lib/wind-sun/Concorde_Lifeline_tech_manual.pdf (see page 32).

Their 1h rate seems to be ~63% of the 20h rate.

212 AH (at 1h) * 1/0.63 ~ 337 AH (guess at 20h rate)

If you go by weight (20 hours is relatively "mild" discharge:

212 AH C&D * 6 volt Trojan * 1/8 volt C&D = 159 lb @ 6 volt battery
225 AH (6v Trojan) * 159 lb C&D * 1/62 lb Trojan = 577 AH capacity based on weight compared to Trojan (normalized to 6 volt)

Still a pretty wide range between the two methods.

As Marc says--Doing a load test and see what happens is probably best. For example, Concord rates their batteries at end of life when they have less than 80% of rated capacity.

Put a 20 Hour load on the battery and see how long it lasts (and recharge immediately to prevent damage from sulfation).

400 AH (guess) / 20 hour rate = 20 amp load for 20 hours to "dead"

-Bill

westbranch · March 2017

Have you got some pics of the cells? It is hard to search the C&D site without more info, also the group name or number would help.
tks

mike95490 · March 2017

There is a reason the 8 year old batteries are being switched out. At 9 years they start failing. Have fun with them for a year

littleharbor2 · March 2017

C&D does have a large number of batteries and battery types. I would think any battery with a 1 hour rating on it would be for high rate discharge /UPS type duty and not necessarily suited to 20Ah rating, daily cycle use.

westbranch · March 2017

Little Harbour2.... just checked out a few different batt. models and they ,C&D, list from 1 minute to 20 hrs on some and 1 min to 8 hrs on others so ???, we just have to wait for more data on them...

Estragon · March 2017

OP saying they were only discharged during a power outage suggests UPS type of battery. Knowing the longer discharge rates would still be useful in a UPS application if you needed a longer guaranteed uptime for gear. Remote telecom gear comes to mind.

westbranch · March 2017

Ah Hemm.....well it is best when the new data is posted at the bottom of the discussion.... so we all know that there is new information!

here is the data sheet for those batts.http://www.cdtechno.com/pdf/lit/12_324_0115.pdf

mnittler · March 2017

Ok, so based on the information westbranch found (Which I appreciate greatly) the batteries are:

C&D 4LCY7 SAN=Standard Case
4CLY-420
4CLY=Lead Calicium
210 Ahr @ 1 hr
315 AHr @ 3 hr
366 Ahr @ 5 hr
420 Ah @ 8Hr
4 cells/unit, 7 plates/cell
10.08" Long X 14.13" Wide X 22.75" H
Weight 310 lbs
The literature says for Telecommunications applications.

I have no way to put a load test on the batteries until they are in my possession since they are currently in use until the replacement batteries arrive.

2 each of the C&D batteries have one cell that the plates are whiteish in color so I imagine those cells might be going bad but that still leaves 13 that appear to be good to choose from.
Does anybody have any idea what the optimistic expected life of these type of communication batteries could be?
The C&D batteries have been connected to a commercial C&D battery charger that was furnished with the system their entire life.

What is the expected life of Trojan T-105 batteries (my first set that are currently 3 years old). If I purchase another set I will probably get Trojan L15's for the next set.
The Trojan T-105's are connected to a Xantrex (Schneider) XW6048 and furnish power during power outages and switch to battery power for a residence from 11:00pm to 6:00am every night with a 1 amp (240watt) assist from the grid and have been holding up the entire night (Normally runs 78-82% state of charge in the mornings).

Anyway would you chance trying the C&D batteries or stay with the 3 year old T-105's for now?

westbranch · March 2017

wet cells

httpwwwcdtechnocomproductvlaasset4lcyjpg

Battery AHr Rating: How to Convert 1 AHr rating to 20 AHr rating

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