the Otherpower.com Discussion Board || Maintaining two batteries with one charger?

Front Page - [Homebrewed Electricity-- (wind) (solar) (hydro) (steam) (controls) (storage) (mechanical)] - Classifieds - Site News
Everything - Newbies - [Remote Living-- (housing) (heat) (light) (water)] - Rants & Opinion - Diaries - Our Products

Maintaining two batteries with one charger?
By zmoz, Section Homebrewed Electricity Posted on Sat Dec 27th, 2003 at 07:26:33 PM MST
Would it be ok to leave two batteries on the same trickle charger?

Right now I have two car batteries sitting in my garage - one is brand new from my totaled Jeep, the other is from my boat. Both will be sitting in my garage until summer. I don't really want to buy one of those fancy battery maintainers for them. I have a 1 amp trickle charger...would it be ok to wire the batteries in parallel and hook the charger to them both? And then just leave it plugged in until summer? The batteries are different sizes...if that makes any difference.

Maintaining two batteries with one charger? | 10 comments (10 topical, 0 editorial)

Re: Maintaining two batteries with one charger? (none / 0) (#1)
by bill541 on Sat Dec 27th, 2003 at 08:42:53 PM MST
(User Info)

Usually when connecting two batteries in paralell, they must be of the same type and age. You can get away with it as long as you know your charger will never fail and that both batteries have the same voltage when bridging them together. I would not recommend doing this in your situation.

Since they are of different types (one starting battery the other a deep cycle?)you would probably be better off with an isolator between them and then connect that to the trickle charger.

Since you are only using a 1A charger, a couple of schottkey diodes could serve as the battery isolator. Connect both diode anodes together and then connect them to the battery charger positive lead. Connect the cathode (has the stripe) ends of the diodes to the battery + leads. One diode to one battery. Then you can connect both battery neg leads to the charger neg lead.

The diodes should be rated at =>25 PIV, and say 3 Amps to be safe. The diodes prevent any charge current going from one battery to the other and will allow for imbalances during charging.

There will be a small voltage drop across the diodes, but at least they wont go dead during storage.

Take care, Bill

Re: Maintaining two batteries with one charger? (none / 0) (#2)
by zmoz on Sat Dec 27th, 2003 at 09:29:44 PM MST
(User Info)

They are both starting batteries. The boat battery isn't a marine battery either, and is at least a few years old. Would it be better maybe to leave the charger on one battery, and change it to the other battery every week or so?

Re: Maintaining two batteries with one charger? (none / 0) (#3)
by witapple on Sat Dec 27th, 2003 at 10:02:16 PM MST
(User Info)

I have float charged several different types of batteries (same voltage) in parallel after making sure they were all fully charged and all of acceptable integrity. To the best of my knowledge there were no problems. They were all in great condition in the spring so i assumed it worked fine.
Dan W

Re: Maintaining two batteries with one charger? (none / 0) (#4)
by desertratjack on Sat Dec 27th, 2003 at 10:03:14 PM MST
(User Info)

No harm in trying to do what you want. If you find they are "imbalanced", then charge them alternately or do the shotky diode thing. It is good that you intend to charge them at all. If they are older batteries there is a possibility they won't make it 6 months even with the best care.

Re: Maintaining two batteries with one charger? (none / 0) (#5)
by zmoz on Sat Dec 27th, 2003 at 10:23:58 PM MST
(User Info)

So a continuous .5 amp charge for several months won't be a problem for these batteries?

Re: Maintaining two batteries with one charger? (none / 0) (#7)
by bill541 on Sat Dec 27th, 2003 at 11:13:11 PM MST
(User Info)

zmoz,

It is a good thing that you are keeping the batteries on a maintenance charge while storing them. Most people do not, and they should. You can keep the batteries on a continuous float charge around 13.8 VDC for a 12-volt flooded battery.You can remain at this charge rate for a long time with no dammage.

All you will be trying to do is make up for the self-discharge of the battery. If your charger levels off at around 13.8 VDC, then very little current will be flowing into the batteries and you will be below the gassing voltage.

It would be a good idea to check the electrolyte level now and again to make sure the plates stay wet. Your idea of swapping the charger manually between the two would work equally well as the battery isolator, just requires a bit of labor now and then.

Take care, Bill

[ Parent ]

Re: Maintaining two batteries with one charger? (none / 0) (#6)
by kell on Sat Dec 27th, 2003 at 11:07:28 PM MST
(User Info)

Long term you want to float; that's even less than a trickle charge. I'd check with an ammeter.

Re: Maintaining two batteries with one charger? (none / 0) (#8)
by zmoz on Sat Dec 27th, 2003 at 11:16:49 PM MST
(User Info)

Alright...thanks guys. I'll charge them both up seperately first, and then hook them up together. I will check the voltage/amperage after a couple days...

Re: Maintaining two batteries with one charger? (none / 0) (#9)
by Seth on Mon Dec 29th, 2003 at 11:29:34 AM MST
(User Info)

buy 2 2n4001 diodes from radio shack....... use them as a batery isolator....
I cant make u a pic.. but im sure tom or mech could. Since u havce only 1A of charge.. those diodes will handle the current fine.
Trying to move my solar pannels is fun.
[ Parent ]

Re: Maintaining two batteries with one charger? (none / 0) (#10)
by Harry Luubovv on Tue Dec 30th, 2003 at 07:03:18 PM MST
(User Info)

Hi Zmoz,
I do not recommend trickle charging two very different capacity ratings of battery with one set of charge leads even when one is not a deep cycle bat. As the high capacity bat will certainly discharge into the smaller cap bat, aside from what's going into the small cap bat from the charger itself. This will make the large bat unfull at times while the small bat receives more than its share of trickle charge. Aside from that, nothing's wrong with hooking them all together from one charger. But be sure that the polarities are hooked up the same between 2 bats ! ! Otherwise you will get some pretty hugh sparks ! ! Explosion is a possibility since the wet fluid inside the bat can be flammable especially during charge, even at slow charge and hotter weather or hotter room temperature.

But you don't really have to keep the charger on everyday during winter. Since this wears out the transformer inside the charger and other components. And if you are on alternative energy scheme, you are wasting off more electricity than you need to. I would recommmend trickle charging perhaps 3 days in a week. But have them on charge every day of the week if the weather gets to be very very cold, or if the bats are old old bats.

At last if anyone wants small capacity diodes at about one amp, I have tons of them new. I will send them to you free in an airmail envelope, they are small enough anyway. I am not going to bother charging for them since they are about a dollar or two each. In other words, I am not going to charge anything that you are going to use to charge something else with, this will become double charge :-) Just say so on this board, give your email or street address, or your proxy email address or your proxy street address.

Hey Yo, be nice,
be the best dice.
Be my friends,
again,
be your neighbour's friends.
Again,
be friends to yourself.
Luubovv.

[ Parent ]

Maintaining two batteries with one charger? | 10 comments (10 topical, 0 editorial)

Menu

� create account
� How to use the board
� FAQs
� search the board
� Google search the board
� Old Otherpower Board

Login

Make a new account

Username:

Password:

Total Views

��69 Scoop users have viewed this posting.

Related Links

� Also by zmoz

You must be a registered user to post here. It's easy and free, and the link is on the upper right side of your page.
All trademarks and copyrights on this page are owned by their respective companies. Postings are owned by the poster, but may be deleted or moved at the ADMIN's sole discretion. The Rest � 2003 Forcefield.
You can Email the board ADMIN here. PLEASE include the username you signed up with!