# installing sealed acid Batteries in parallel form



## 104664 (May 22, 2007)

Hi everybody
I want to install four batteries in parallel form for my MH. My Mh has a charger from Cramer CBC-Kn3-V1 ( I have the schematics diagrams) for 12v and 15A output. I have four batteries 12v 38Ah recollect from other applications. Is necessary the compensation of current between batteries?. The max. current in charge is 7A.
Had somebody made this connection?
Can I buy something for it?


----------



## Scotjimland (May 23, 2005)

Hi

Not sure exactly what you are asking but have a look here, I think it may answer your question ..

>>Interconnecting Batteries<<


----------



## mangothemadmonk (Aug 6, 2006)

Are you saying you have 4x38amp batteries? Which would give you about 110amps approx. Are these batteries all the same age? As they say always use the same amperage batteries which you have, but make sure all are the same age, so one duff one doesnt bring the good one/s down.. 

Have you thought of buying 1 battery of equal or more amps? That would save on weight and space and the time wiring them altogether?

Johnny F


----------



## JohnsCrossMotorHomes (Jul 21, 2007)

Hi, you can get 110amp leisure batteries, fit two and have double the capacity, they cost around £69 each and 85amp ones £39 at the moment on ebay

Is it worth the bother using old secondhand ones?

Regards


----------



## 104664 (May 22, 2007)

*batteries*

Hi all
ScotJimLand, I knew it.

The four batteries are free cost. I did'nt pay anything for the batteries.
All the batteries are the same age and the same work from.
The question is: when the battery bank is charging, the charger delivery max. 15A, if all batteries are in the same condition, each get the current 15A/4, but if one battery of the bank is open (doesn't work fine ) the current for other battery is 15A/3. Is it clear? 
Obyously, I need a thermal protection and current limit.

The Sealed lead acid batteries have the current of charge limit to 0.2xCapacity Ah in this case 7A for each other.

thank all


----------



## 105062 (Jun 10, 2007)

Even if they are free I would not bother with them because they could 
1, damage your charger, 4 is a large bank regardless of the fact they are only 38ah their combined internal resistance will be high dragging a lot of current from your charger,
2, discharge each other as they are not new, 
3, actually give a lot less than 4 x 38amps because they are not new.
4, combined there is a lot of acid and a lot of gas will be given off
5 they will weigh a lot and take up too much room, use a lot of petrol just to drive them around.

A new 110ah battery could cost a lot less money than sorting out the charger to cope with them all safely


----------



## sallytrafic (Jan 17, 2006)

Tribute_650 said:


> Even if they are free I would not bother with them because they could
> 1, damage your charger, 4 is a large bank regardless of the fact they are only 38ah their combined internal resistance will be high dragging a lot of current from your charger,
> 2, discharge each other as they are not new,
> 3, actually give a lot less than 4 x 38amps because they are not new.
> ...


Point 1 High internal resistance equals low current not high I doubt that the internal resistance will be much different from 110Ahr ones when charged unless they are old.

Maybe similar amount of acid

Might be a little more weight

Why do you think more gas?

Have you considered Tribute_650 that a 38Ahr batt may be a lot smaller physically than a 110Ahr one?

Until quillo gives us more info I don't think we can properly judge it.

In general quillo for other reasons (that can include the possibility of one cell dragging the others down) its better to have 1 battery than several in parallel.

5A per battery is only a little high, one tenth of the 3hr rate used to be considered normal, but is now routinely exceeded. At lot depends on the charger I will try and look up its spec and get back to you.


----------



## sallytrafic (Jan 17, 2006)

I'm sorry Quillo I can't find anything about the charger do you have a description does it say its a 2 3 or 4 stage charger?


----------



## 105062 (Jun 10, 2007)

Frank, No I had not considered they could be small, good point, I imagined 4 of the batteries I have in my MG which are normal car size and 40ah.

Sorry, Yes, I had meant to put Low resistance due to a high build up of stuff in the bottom as Quillo had stated they are re-used so thats old in my book..

Would not the internal resistance be different due to ohms law if I remember from college days. Put 4 batteries in parallel and the resulting resistance is 1/4 that of one battery hence pulls 4 times the charge current. OK if the battery is new but if they are tired can compound the stress on the charger.

I still would bin them and buy 1 new purpose made battery!


----------



## sallytrafic (Jan 17, 2006)

Tribute_650 said:


> Frank, No I had not considered they could be small, good point, I imagined 4 of the batteries I have in my MG which are normal car size and 40ah.
> 
> Sorry, Yes, I had meant to put Low resistance due to a high build up of stuff in the bottom as Quillo had stated they are re-used so thats old in my book..
> 
> ...


Middle aged for a battery that hasn't been misused is forty years - not likely to be found on a motorhome as nearly all are 'misused' but qiuillos batteries could be from a UPS in which case if they have never performed they will be as new. I have removed standby batteries from lighthouses that were still giving 95% of capacity we changed them because batteries in wooden cases that are sealed with tar are just a bit old fashioned these days, where would you get the spares!

Your interpretation of batteries in parallel and ohms law is fine but I think again I think you are assuming the properties of each of these smaller batteries is the same as your bigger battery. It is likely that they will be individually higher but when they are in parallel be about the same. A thought experiment should explain it. If you cut up your 110 amp battery into four parallel parts and joined it all together by external wiring would the internal resistance have changed?

Still it is likely that a single battery will be easier quillo.

Perhaps if you told us a bit more about the batteries it would help.


----------



## 104664 (May 22, 2007)

*I insist*

Hi everybody
The post is so very long...I could try to answer all...

Ok, sallytrafic you are right, the batteries were from a hospital UPS, I think they are good conditions .they were working on a UPS for Critical Care Unit.
The internal resistance is the same , teoricaly, for all the batteries, all are the same type, model and manufacturer. the problem is the teoricaly supposes that two, for example, batteries breakdown and they will open their internal resistance. The current from the charger, 15A maximum, will pass across the other two batteries.This batteries have the charging current limited to 7A. These batteries are sealed and the excessive current in charging make up the temperature and they could explode.

The charger is totally analogic, it is controlled with operationals IC and SCR´s. This charger applies 14v square form to the batteries , the square form is controlled by the voltage measure from the batteries and then will be continuously 14v when the batteries is totally charged.

I think and will try to connect all the batteries in parallel mode with termal protection for each other.
Thank all


----------

