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Battery Bank Configuration

Battery Bank Configuration

Battery Bank Configuration

Somewhat new to the battery arena.  I'm looking into a system that utilizes (2) identical battery banks paralleled charged from a single charger.  Do I need any isolation between the banks preventing one from draining the other?  The charger does not support multiple outputs, but is rated for the combined capacity of the battery banks.
I'm also looking into a battery bank system that is charged via a combination of wind and solar inputs.  Are there any widgets that I might need between the solar panel, wind generator, and battery bank.  I'm certain that I would not want to directly connect all of the +VDC together and all of the -VDC together.

RE: Battery Bank Configuration

We frequently run parallel banks of batteries in commercial installations (some customers require parallel banks to eliminate single point battery failure from allowing the system to go down). There are no isolators and most of the time there are multiple chargers, but all paralleled together at the DC Main panel.

As long as the parallel banks are on charger, there won't be a problem with circulating currents between the banks. We even have situations of old (but still serviceable strings) in parallel with newer strings..

There can and will be different current levels on charge (and discharge) into the respective banks, but even that is not an issue..

Only if you have them paralleled and off charger for an extended period time would I begin to have any concern about circulating currents.

Can't add any value on the solar and wind charger question, other than IF they have properly designed regulation, they should behave together.. What the above statement means is as one charger source picks up on its power output (varying sun, wind, etc), all chargers on line should begin to load share or back off on their charge level, and vice versa, with all in unison, maintaining the proper battery voltage. Some cheaper, simple charging systems are not designed to operate with external loads present, or play well with others, and can end up overcharging..

Commerical sites with appropriately designed hardware for an application somewhat analogous to yours, are essentially constant voltage chargers set to proper battery float voltage (which varies with temperature), operating and carrying the external load (as long as commercial AC is present) and, capable of dealing with a varying state of charge (after there has been a commercial AC outage)... probably close to what your intended environment. Keeping ambient battery environment temperature relatively constant can be important here.

Some systems have a time vs current monitored auto controlled equalize function built in that can be triggered after heavy dischage.

If you know what you are doing, and have the proper designed equipment, what you want to do can work. It would be best if you can find a hardware supplier that has a line of integrated products designed to do this if your knowledge is limited. Otherwise you need to assess your knowledge and capability to be the systems integrator.  

RE: Battery Bank Configuration

Hi, can I setup a mixed nicad and lead acid battery bank to improve the realibility of starting a standby gen set. The nicad is old and lead acid is brand new. I already have trickle and boost charger in place to charge both batteries.

Jeremy Shu
facility Mananger

RE: Battery Bank Configuration

No, the charging requirements are different so using a common charger wouldn't work. If you are planning to decouple the two batteries from each other by electromechanical means (e.g. a contactor) or by diodes then you could argue that adding a second battery to an installation with only one battery will improve reliability IF the contactor or diode arrangement doesn't actually degrade it. It needs some careful design to avoid improving one area of reliabilty at the expense of making the overall system less reliable.

A NiCad battery has better performance over a wider temperature range than the lead-acid battery, but the cost is substantially higher. If reliability was the ultimate aim then a flooded NiCad is arguably the better choice although whether the additional cost is justified depends on the application.

Are you considering a second starter motor on this set? Some designs have a position for a second starter even if it is not installed.

If we learn from our mistakes I'm getting a great education!

RE: Battery Bank Configuration

Hi Scotty,

Then how about I deploy two banks of new lead acid to replace the aged Nicad to increase the % of success in starting a standby 250kva gen set. replacing the age nicad cost twice as much as two lead acid. We are operating in Malaysia which do not require a cold start performance from battery. I also have 3 other 500kva, 150kva and 300kva running on lead acid.  I also read that Nicad has memory problem and the nicad currently in use is only being use for starting during weekly PM which may have derated the nicad? am i right??

RE: Battery Bank Configuration

I assume you are looking at a flooded cell lead acid battery? Yeah, that should work but verify that the charger can be configured for the lead-acid battery. Most float chargers should be ok, it tends to be rapid chargers which are incompatible. You could safely run two identical strings of lead-acid cells in parallel of a common charger.

By the way, normally it's better to start a new thread for a new question rather than tacking on the end of an old one. Too late now, but next time... smile

If we learn from our mistakes I'm getting a great education!

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