Battery charging question

[Carter Mac 26]

I recently bought a 1993 MacGregor 26S. The previous owner had installed two new batteries (automotive type and size) but the wiring was a complete mess. I have re-wired the boat, including new bow red/green lights, stern light, cabin-head-and V berth lights, an electric faucet, a 1-2-both main switch, new breaker panel, new 30 amp fuse and holder, neg connector bus, etc. I'm not an expert but know the basics, especially after consulting a basic sailboat wiring diagram. Per the diagram, I connected both battery neg posts to each other using a 10 gauge wire. All component negs go to a common bus, and to the neg post on battery 2. The positive post of battery 1 is connected to the "1" terminal on the 1-2-both switch and the positive post on battery 2 is on the "2" terminal on the switch. I've tested all components and all is well. We're off for the July 4th weekend on Friday and I want to charge both batteries. Should I disconnect anything or should I just put the pos charger clamp on the pos post of battery 1 and the neg charger clamp on the neg post of battery 1, while leaving everything connected? And then do the same for battery 2? Or should I disconnect the jumper wire that is connected to both battery neg posts? Any advice is appreciated.

 

[Scott T-Bird]

Is the neg buss connected to a ships ground, such as an engine block? I'm not sure why you have the negative jumper across the neg posts. I would eliminate that and run separate cables from the posts to a negative buss (not on your panel). Are you charging with an automotive trickle charger? Just to be safe, I would disconnect the batteries and charge them independently.

 

[dlochner]

For the short term, Scott's answer is good. But for the long term you may want to rethink your electrical system and include a permanent multi-stage marine battery charger and wire both batteries into one bank. Doing so will be more efficient, have greater capacity, and make your batteries last longer.

Check out the Musings with Maine Sail on this site or his website Welcome To MarineHowTo.com Photo Gallery by Compass Marine How To at pbase.com

 

[Benny17441]

Yes you can charge both batteries at the same time. Remember than when combined two batteries really become a larger single battery and can be charged as one. I would connect the charger clamps to the corresponding posts on whichever battery is more accessible and just select the battery switch to Both. If you want to charge just one connect the clamps to the intended target battery and move the switch selector away from Both.

 

[Ron20324]

That 10-gauge ain't gonna be big enough. Use the same size as the pos cables.

 

[dlochner]

That 10-gauge ain't gonna be big enough. Use the same size as the pos cables.

Ron makes a good point. Any cable connecting the batteries to each other need to be large enough to carry the current between the two if there is a short. A 10 gauge wire with the full capacity of even a Group 24 battery will start a fire.

 

[Carter Mac 26]

Excellent advice! Thanks guys.

 

[Ken Cross]

Do you have electric start? If not the 10 gauge is plenty for your load. Protect against shorts with fuses at the battery terminals.

We began sailing with a Mac 26D. It's a simple boat without huge loads unless you add something unusual. It also sails fast for its size and motors fast with little horsepower. I hope you enjoy it a lot.

Ken

 

[MitchM]

1. wiring negative #1 to negative #1 is acceptable, however your wire size of #10 between negative posts needs to be upgraded to at least a #2 gauge not a #10. new neg DC color code is yellow , old was black. 2. connections between charger and + poles of battery also to be at least #2 and on some boats 1 0 or even 00, depending on length of wire between charger and + posts.color DC + wire is red. 3. ABYC requires your negative ground battery system to be grounded by connection of the battery negative to the engine block, and from there to the prop shaft and into the water. 4. connectors are to be ring style onto battery posts and DC charger, crimped then made waterproof. (no soldered connections. ) batteries to be secured against shifting. 5. all wiring to be supported at intervals not exceeding 18 inches.6. are your batteries both the same marine dual purpose? if one (usually the house) battery is deep cycle not dual purpose you need a very large fuse (200 to 400 Amps) in the + lead. 7. Don't use an auto or home charger with a single induction coil which allows continuity between AC source and neg terminal of battery. marine chargers have transformers that are dual wound and prevent this.

 

[dlochner]

1. wiring negative #1 to negative #1 is acceptable, however your wire size of #10 between negative posts needs to be upgraded to at least a #2 gauge not a #10. new neg DC color code is yellow , old was black. 2. connections between charger and + poles of battery also to be at least #2 and on some boats 1 0 or even 00, depending on length of wire between charger and + posts.color DC + wire is red. 3. ABYC requires your negative ground battery system to be grounded by connection of the battery negative to the engine block, and from there to the prop shaft and into the water. 4. connectors are to be ring style onto battery posts and DC charger, crimped then made waterproof. (no soldered connections. ) batteries to be secured against shifting. 5. all wiring to be supported at intervals not exceeding 18 inches.6. are your batteries both the same marine dual purpose? if one (usually the house) battery is deep cycle not dual purpose you need a very large fuse (200 to 400 Amps) in the + lead. 7. Don't use an auto or home charger with a single induction coil which allows continuity between AC source and neg terminal of battery. marine chargers have transformers that are dual wound and prevent this.

Good advice here. After reading it, I'm wondering if the OP mean 1/0 gauge wire and not 10 gauge. An easily misplaced or omitted backslash can really change the meaning.