24V solar powered system - Question 1

[NeillHog]

Hello!

We have built a communications repeater station and it has been working for over 18 months.
It is set at 1700 meters in the Alps and supplies Internet and telephone services for a village and a few ski lifts.

https://plus.google.com/u/0/photos/...6105691627253201778&oid=103827427036815679772

There are four 12V 125Ah batteries - two by two giving a 24V output. There is a load of 20W permanently connected.
We can measure the system voltage via a GSM modem and I automatically get the actual system voltage sent to me before sunrise and an hour after sundown.
It works great but I would like to improve the monitoring system and have a question.

All the values that relate voltage to capacity assume that the battery has no load connected. But we always have the 20W being drawn. Is there an equation that allows us to take this load in to account?

Thank you and greetings from the snow covered Alps.
Neill

 

[crshears]

Hey Keith, where should the comma be? Or is there an extra zero in there? I'm wondering what could possibly make a battery bank cost $K80...

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[ScottyUK]

We have a sick NiCad bank worth about GBP £40k, so not out of the question. Just 'big'.

 

[itsmoked]

crshears;

Yeah... Hmmm maybe we should add a single decimal place on the right. 8k

This bank is a hideous 4 banks of 4 batteries. Yuck.


Keith Cress
kcress -

http://www.flaminsystems.com

 

[Sparweb]

It's true, my set of AGM batteries are not being used in ideal conditions. However, when one discovers them discarded in an alleyway, and the person responsible for taking them out of the building's basement doesn't even expect much at the scrapyard... well, you take the man's problem away for him. New, this stack was worth more. Lots more. I could tell just by looking.

The mishandling (during removal from the building) caused only cosmetic damage. Checking serial numbers revealed they were already 15 years old, confirming that they were simply out of warranty, not actually depleted. After sitting at float for a few weeks, I then purposely discharged them, and measured about 75% capacity remaining. I've seen very little degradation in the 6 years since then. None of them leak or vent any gas: I have never seen corrosion on the bus bars. There are two "bad" cells that always rest ~0.04V lower (2.15V resting) than the others. They will cause the death of the others, someday, but not soon.


STF

 

[mikekilroy]

SparWeb, next time you find big good batteries in your alley - or any alley for that matter, please send them my way! I will happily pay shipping!

http://www.KilroyWasHere<dot>com

 

[mikekilroy]

Neilhog, some side reading on another forum about cells, voltages, and life, may be useful to add to your already pretty good knowledge?

http://www.forkliftaction.com/forum/thread.asp?trid=16175

It appears that if you don't charge these occasionally with enough current to cause significant bubbling they will sulphate and have much shorter life.... As I am learning from OUR $ 80000 8k forklift battery.

http://www.KilroyWasHere<dot>com

 

[NeillHog]

Just to say thanks to those who took the time to give me such interesting answers. I have now contacted the company that sold us the batteries and they have contacted the supplier. So now I am waiting for the "official answer" before continuing.
Have fun
Neill