Charging parallel batteries
10-24-2002, 10:25 PM
#1
3rd Gear
Thread Starter
Join Date: Oct 2002
Location: nc
Posts: 3
Likes: 0
Received 0 Likes
on
0 Posts
Charging parallel batteries
I can't get a straight answer on this (despite searches in rennlist, pelican, and roadfly).
I have a '69 911E (with Webers). My battery charger can trickle at 2 Amps, but somewhere it says not to use it for batteries in parallel. Can I use it for my batteries? Which battery do I attach it to (and how do I attach it)? My batteries are grounded (once) negatively.
I have a '69 911E (with Webers). My battery charger can trickle at 2 Amps, but somewhere it says not to use it for batteries in parallel. Can I use it for my batteries? Which battery do I attach it to (and how do I attach it)? My batteries are grounded (once) negatively.
10-25-2002, 12:22 AM
#2
Addict
Rennlist Member
Rennlist Member
If they're in parallel, just connect to one of the 2 batteries and the second will charge automatically. It will draw double the current (but same voltage) as a single battery. Charger says not to charge multiple batteries in parallel because the resistance gets alot lower and it could short out the charger, however, most chargers have shorting protection built in. If it has an ammeter, just make sure you don't exceed 2A as stated...
10-26-2002, 05:59 PM
#3
Advanced
Join Date: Jun 2001
Location: Danville, CA
Posts: 70
Likes: 0
Received 0 Likes
on
0 Posts
Grant G---or will it just take twice as long to charge the batteries?? The 2 deep cycle batteries in my motorhome are in parallel and the charger shows the same current draw as one battery--but it seems to take a lot longer to charge the pair of batteries using an automatic charger. <img src="confused.gif" border="0">
10-26-2002, 06:38 PM
#4
Addict
Rennlist Member
Rennlist Member
Well, it will draw double the current, unless the charger has some current limiting function. Placing the batts in par. means that the resistance is cut in half, which means double the current for a set voltage (Ohm's law). However, it the charger is limited at 2A, for example, then it will take twice as long (like in your motorhome).
10-27-2002, 03:01 AM
#5
Advanced
Join Date: Jun 2001
Location: Danville, CA
Posts: 70
Likes: 0
Received 0 Likes
on
0 Posts
Grant--assuming the current is doubled (Resistance halved--Ohms law as you mentioned) for two batts in parallel--would they BOTH now receive the doubled current or would the doubled current then be split between the two batts?
10-27-2002, 03:50 AM
#6
Racer
Join Date: Mar 2002
Location: San Jose
Posts: 293
Likes: 0
Received 0 Likes
on
0 Posts
George,
The current would be split between the 2 batteries (Kirchoff's law for current conservation). The battery with the lower internal resistance would receive the higher current; the sum of the current for each battery has to add up to the original current supplied by the charger.
*****
The current would be split between the 2 batteries (Kirchoff's law for current conservation). The battery with the lower internal resistance would receive the higher current; the sum of the current for each battery has to add up to the original current supplied by the charger.
*****
10-28-2002, 08:34 PM
#7
I get confused about the difference between batteries hooked in parallel and batteries hooked in a series. One of the two hookups yields 24 volts instead of 12. I suspect that it what your charger instructions were worried about. The dual battery set-up of the early 911 is designed to be a 12 volt system. I've never had a problem with charging both batteries by hooking a 2 amp charger to either side. I usually do the passenger side because it's easier to reach.
