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geetee 06-11-2008 03:29 AM

parallel / series wiring question
 
Hi could anyone tell me 1st if i link two batteries together in a parallel formation to increase the amp/hours, would they need to be the same AH or could i use batteries of different amp/hours. And 2nd if i was to link in series formation to increase volts could i use different batteries of different volts and amp/hours. Would the lower power lose power first?

BillyD 06-11-2008 06:03 AM

If you hook in parallel you increase the amps series doubled the volts. Never tried different voltage. If the batteries are with in 2-3 volts OK more I don't know. What are you working on and are you talking lead acid or dry cell.

geetee 06-11-2008 07:12 AM

thanks for the reply.
they are lead acid, i have a leisure battery with 85AH and a deisel with 55 AH, giving me 140 Amp / Hours, I wanted to link them in parallel to help last longer for leisure use. i have a laptop the requires 24 volt so i also wanted to hook up a seperate 12 volt battery in series when ever i want to run the lap top and that is 17AH

joed 06-11-2008 08:26 AM

Lower rated battery would run out first in both cases.
Only problem with what you are planning is if the batteries are normal car batteries and not deep cycle they won't like being run down to nothing. The battery will be damaged. Car batteries are designed for high current short burts (CCA cold cranking amps) for starting not for complete discharge.

BigJimmy 06-11-2008 09:18 AM

Quote:

Originally Posted by geetee (Post 129492)
Hi could anyone tell me 1st if i link two batteries together in a parallel formation to increase the amp/hours, would they need to be the same AH or could i use batteries of different amp/hours. And 2nd if i was to link in series formation to increase volts could i use different batteries of different volts and amp/hours. Would the lower power lose power first?

I do a lot of work involving battery systems for railroad grade crossing warning systems which always involve interconnections of single cell batteries to create the desired voltage. Here are a few good "rules of thumb:"

1. When you connect batteries in series, the individual cell voltages will add (i.e. 4-1.5V D-cell batteries in your flashlight create an overall voltage of 6 volts). Cell voltages can be different.
2. When batteries are connected in parallel, the voltage does not change but the overall capacity increases (again, sum of individual capacities). Herein, voltage ratings of the interconnected cells must be the same.
3. Interconnected batteries should all be of the same type.
4. The issue with capacities is this: If the batteries will be connected to a charger, mixing capacities is not a good idea. Cell terminal voltages change as the batteries charge/discharge (remember that all batteries have some finite internal impedance). What happens is that the charger will tend to overcharge the lower capacity battery and undercharge the higher capacity battery. Bottom line: match your Ah capacities.

And, as Joe mentioned, your batteries should be chosen based on the application. They are not universal in their design or intended usage.

Jimmy

geetee 06-11-2008 02:42 PM

thanks for the replys very helpful, and will be getting another leisure battery to link up.

last question please.

If i put two solar panels together in parallel one is 10w and the other could be 5w would this be ok to give me 15w of power, they would be running as one into a 5amp charge controller.


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