Charge two batteries one controller

Hi all. Going outback soon. Have a near new 120 ah deep cycle battery which I intend to charge using panel and redarc srpo120 controller. My second battery (which came with camper) is a "100ah" wet cell . It'charges ok but I'm not happy with its performance on a discharge test using the Engel as a load. So I'm looking at getting another deep cycle agm to replace it. Can get a good deal on a 100ah agm of a different brand to my first battery . The battery guy says both batteries should be identical if I want to charge both from the redarc. The redarc manual says they just need to be the same type. I guess I could ask redarc but need an answer by tomorrow if possible as will be opportunity to pick up new battery on Saturday. What do you think? Anyone charging different brand/size batteries with the redarc.? Thanks doc
Back Expand Un-Read 0 Moderator

Reply By: Allan B (Member, SunCoast) - Thursday, Aug 11, 2016 at 21:47

Thursday, Aug 11, 2016 at 21:47
.
Hi Doc,

A number of people who do not fully understand electricity will insist that both batteries be identical specifications and of the same age. Sure, if you do that then you are acting safely. However, there is no real need to do that.

Connecting batteries in parallel for charging requires only that they be of the same type, i.e. both AGM's etc. Differences in the two batteries such as capacity or brand may result in differing current acceptance during charging but they will eventually both reach full charge at the same time.

Of course, there is no problem at all during the battery discharge. Each battery will contribute proportionally (but not identically) to the load and will maintain the same DOD (depth of discharge percentage)

The only issue with paralleled batteries is that when one battery becomes faulty, due to say internal discharge, it will sap energy from the good battery during standing.

So go for it. just be sure that they are the same chemical types.

Cheers
Allan

Member
My Profile  My Blog  My Position  Send Message

AnswerID: 603317

Follow Up By: oz doc - Thursday, Aug 11, 2016 at 22:31

Thursday, Aug 11, 2016 at 22:31
Thanks Allan , I wasn't actually thinking of joining the batteries in parallel as such. The redarc has two outlets for batteries to be attached and you can set the amount of charge to go into each one eg 70 % to the first one and 30 to the second. It is a pwm charger. I do have another charger(mppt) but that is another story. Doc
0
FollowupID: 872951

Follow Up By: Allan B (Member, SunCoast) - Friday, Aug 12, 2016 at 07:30

Friday, Aug 12, 2016 at 07:30
.
Sorry Doc, Having read your thread title I launched into a reply missing some of your detail and assuming it was a single controller with paralleled batteries.

However, the essentials of my response still apply. Just be sure that both batteries are of the same type as you acknowledged.

Have a good trip. I'm stuck at home this year with a host of family commitments. :(

Cheers
Allan

Member
My Profile  My Blog  My Position  Send Message

0
FollowupID: 872952

Follow Up By: oz doc - Friday, Aug 12, 2016 at 08:06

Friday, Aug 12, 2016 at 08:06
Thanks Allan. Normally I would test systems before leaving however it seems there is a conspiracy at play. Every blessed time I want to get the panel out all the black clouds in the Southern Hemisphere park themselves over my house! I've only had the panel 12 months. Last year when I used it for the first time the controller failed after 3 days and that was that . No more solar for the trip.doc
0
FollowupID: 872953

Reply By: Sigmund - Saturday, Aug 13, 2016 at 05:22

Saturday, Aug 13, 2016 at 05:22
The upstream battery will get worked harder than the downstream so put the younger one there when you install them.
AnswerID: 603356

Follow Up By: oz doc - Saturday, Aug 13, 2016 at 10:16

Saturday, Aug 13, 2016 at 10:16
Sorry sigmund ?upstream/downstream. Doc
0
FollowupID: 872984

Follow Up By: Sigmund - Saturday, Aug 13, 2016 at 12:42

Saturday, Aug 13, 2016 at 12:42
Upstream = the first connection to the charge circuit.
0
FollowupID: 872986

Reply By: Batt's - Tuesday, Aug 16, 2016 at 13:42

Tuesday, Aug 16, 2016 at 13:42
I have a 40amp Redarc bc/dc charger looking after 2 agm batteries hooked in parallel with each other a 105ah Amptec form Autobarn and a 105ah Giant from Aussie batteries no problem yet.
AnswerID: 603441

Follow Up By: oz doc - Tuesday, Aug 16, 2016 at 17:14

Tuesday, Aug 16, 2016 at 17:14
Thanks Batts. I don't have a bcdc just the redarc solar controller. I ended up shelling out for another 120ah Ah .doc
0
FollowupID: 873070

Reply By: chaz r - Wednesday, Aug 17, 2016 at 18:51

Wednesday, Aug 17, 2016 at 18:51
Whoever told you the batteries must be the 100 percent identical was misleading. I believe you have a solar panel controller and it theoretically can charge any lead acid batteries, that includes gel, AGM, deep cycle.

There is, I guess, only 1 thing to be noted in prior to your set-up, you need to check the operating voltage on both batteries. It's always better to catch up with same voltage level. Like I've got two AGM forming a dual batteries system, different models but they are 13.2V-13.7V ordinarily.

Even you've got 1 AGM, 1 another type, that really doesn't matter. Just make sure your redarc controller has been correctly connected.
AnswerID: 603470

Follow Up By: oz doc - Wednesday, Aug 17, 2016 at 19:35

Wednesday, Aug 17, 2016 at 19:35
HI Chaz, That's what I was thinking. After posting here and getting Alan's response about connecting the batteries together, I think this is what the battery guy was thinking I was going to do and why he suggested they be the same. The batteries are in fact totally separate apart from their connection to the redarc. Both being agm and having the same charge voltage requirement there should be no issue. I was originally going to get a 100ah however I ended up getting another 120 ah(different brand) at a good price so pretty happy with that. Will see how the system performs next week. Hoping for some sun- the all important ingredient.doc
0
FollowupID: 873098

Sponsored Links

Popular Products (13)