Recharging 4 12V batteries in parallel

[uchacker11]

I have 4 lead-acid batteries in parallel that I need to recharge. The batteries are Genesis NP7-12FR batteries rated at 12V, 7.0Ah. I need to create a circuit so that when I plug it into a 120VAC wall socket the batteries are charged. I was thinking of using a DC power supply but have no idea what size to use. Any help would be appreciated.

 

[Pumblechook]

I would suggest a good 13.8 V (well stabilised) supply possibly with current limit. They would probably charge at something like 2 Amps (guessing really) each initially so that is 8 A x 13.8 V = 110 Watts. Ham radio stores will have lots of 13.8 Volt PSUs used for running radio transceivers. Steering diodes in series with low value resistors (for current monitoring - 0.1 - 0.25 Ohm...measure the voltage across them) in series with each battery would be a better arrangement but may not be very convenient if the batteries are connected as a parallel pack in normal use.. The diodes will drop 0.7 V so you will need 14.4 Volts. The resistors will act as current limiters.

 

[dlgoff]

Welcome to PF uchacker11.

I'm guessing that you have a UPS. If so you might want to consider constant charging.
From the Genesis spec sheet (http://www.tnrbatteries.com/ennp72.html" ):

Standby use: Apply constant voltage charging at 2.275 volts per cell (or 2.25-2.3VPC)