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Battery rating

Battery rating

Battery rating

(OP)
We have a battry bank in which the Maximum batterries are C10 300 AH, also in the same bunch there are three 420 AH C120 batteries. The contractor supports this installation by submitting Manufacturers letter that both the brands have same product definition & are equal. Is it true.
I think technically two different AH batteries can not be combined, it will affect the charging & discharging behaviour of the entire bank.
Your opinions are required

RE: Battery rating

Different AH ratings should not be mixed in series.

If they were in separate series strings and charged separately that would work with the strings paralleled.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Battery rating

You did not give any information on how the two different battery types  are configured in the system..

Are the different battery types contained within one series string?

Or, do you have two parallel strings of different battery types making up each string, but within a string all batteries are of the same type?   

RE: Battery rating

The contractor could be right. But, you have a right to ask me to supply capacity rating factor table and prove that the two batteries are identical on a given scale.
Generally speaking, C10 battery with 300AH rating will have less than 300AH capacity for discarges less than 10hr duration and vice versa. Hence, I would not be suprised if 300AH battery delivers 420AH at C120 rate.

RE: Battery rating

You can ask the contractor to prove it by doing a complete charge and discharge test connected as designed. monitoring each cell voltage.

RE: Battery rating

(OP)
There is a correction it is not 300 Ah, it is 342 Ah

There are two battery Banks each having 20 cells, Out of twenty in one bank two & other bank one cell is of 420 AH rest others are 342 AH.
To replace these batteries the new three cells which contractor has brought are also 420 AH. The explanation by manufacturer is that both the products are equal to each other. Also the 420 AH is Solar Bloc, for photovoltaic application.  for what purpose Solar bloc is used.
 

RE: Battery rating

It's not good to just replace cells in a battery string in the first place. If you found out some cells that are not properly charged compared to the other cells in the string, you do equalizing charge first, i.e. raise the charging voltage for some time and allow the cells to level out their charge. You then measure the specific gravities and compare the cell voltages. If for some reasons you found out that three of your cells really need replacement, make sure the replacements are of the same characteristics as the others in the string/ bank.
 
One more thing, you never mentioned what your battery banks are serving. Are they required to deliver large currents in so short a time or are they going to deliver a specified level of current for a long time. Please remember that batteries for photovoltaic systems are "deep cycle type" of batteries - batteries that serve constant loads for long hours (like night time for example).
A C10 battery allows you to discharge 342/10 = 34.2 amperes for 10 hours. C120 battery allows you to discharge 420/120 = 3.5 amperes for 120 hours and depending on the electrical characteristics values of the 420AH cells, maybe it could deliver 35A at a 10-hour discharge rate (very near the 34.2 amps of the C10 battery)!
You have to ask for the electrical characteristics values of the 420AH batteries from your contractor and verify if that type of battery can discharge 35 or so amps at 10-hour rate.

RE: Battery rating

It is never good practice to mix different battery types in a string.
Is there a reason why the contactor did not supply the 342Ah @ C10 batteries? Are they obsolete?
The question that is most important is this:
Are the C10 ratings for both batteries the same?
Are the C120 ratings for both batteries the same?
If they are (The battery manufacturer should have a table to prove this)then I would agree with the contractor that they are suitable for use in your application.

UPS engineer http://www.powerups.co.uk

RE: Battery rating

(OP)
Is there any battery Installation Standard, which mentions that no different batteries can be connected in one string.

RE: Battery rating

zaza123,
The requirement for electrical equipment when connected in series is for the capacities to be matched. That is basic electrical principle. Replacement of a faulty cell is difficult because of matching. The new cell will typically have a higher capacity than the aged cells (if the replacement cell is the same type). Think about how big a mismatch will be if you will replace a faulty cell with a different type?
I hope you are trying to make sure your new project work and not justifying a wrong install.
Hope this helps.  

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