ive got 2 brand new 140AH batteries yet to install.
Id like to make them like a big battery so connect them up.
i know it seems dumb to most , maybe but i dont wanna fry any more batteries!

I also need to connect my panel to these batteries and my outboard charging wires.
whats the best/right way?

Ive also got a battery switch which im thinking to only have as an on/off, rather than select between the 2 batteries as they will become one battery. How does this all work!

This is a huge topic but a few quick points.

Battery capacity is important. It is like your bank balance. But you also need to know your daily usage and your recharge capability. Recharge is like your income.

It is no good putting big batteries on a boat with a high usage and low recharge capability. All of them need to be linked.

Start with usage. If you have a fridge then it will really cost you. On our cat we might do 100 Amphours per day. We need to ensure the batteries don't ever go below 50% discharge (or you shorten life dramatically). So I need at least 200 AH of battery capacity. I also need about 110 AH of recharge. There is always inefficiency. So two big 200 watt solar panels do this fine.

Your outboard will be pretty much useless in charging a big battery. They have regulators in them that back off at the first sign of increasing voltage, they are meant for tinnies. Don't rely on the outboard. As you have an outboard you are stuck with solar panels and maybe a small petrol generator. Solar panels are better.

Try to get usage down by going LED lights, no fridge, and being a bit of a nazi about usage - no electric toilet etc. Then work out the amount of panels required. Remember that in NSW in winter the sun is low and around for less time of the day. In the summer you will have heaps of power but you need to rate the panels for short weak sun days if your batteries are to survive ther winter. Even heading north is an issue as the sun is to the north and shaded by the sails.

Get a good regulator and put this in line to protect the batteries. I have a Morningstar 30 to handle the 400 watts panels.

cheers

Phil

Thanks Kanakama. My power draw is minimal. Only have 100Watt panel. Was gonna get 2 of these but didnt happen. could still happen on my way up the coast as theyre flex panels and easy to install.
i do have a fridge, but im only going to use it every 3/4 days for about 2/3 hours to freeze my milk bottles full of water that go in my 80 L Esky. The fridge draws 2.3A every hour when used as a freezer(-15degrees, thanks Donk!). I have LED nav lights and interior lights. I have a TP22 tiler pilot, however this will be used downwind. Sunday for EG, leaving Syd harbour its Westerly - ill sheet to tiller. Monday/Tuesday, Nor west - Sheet to Tiller. So really the only thing ill be using is my nav lights monday night and i use my stereo all the time. VHF wise im only using a handheld icom with good range and good battery life. Wont leave it on all the time. I will be charging alot of things(phones/tablets/lappy -even my garmin GPS watch occassionally) though but will try to do this in the day.
My outboard has done really well charging the 40AH battery ive got connected. But really the new panel is a champion with its controller.
Really i need to know: where the positive/negative goes from the panel on the 2 batteries once they are linked and where the postiive/negative goes from the OB on the 2 batteries once they are linked. Thanks :)

Propised diagram

Here Steve,

zbattery.com/Connecting-Batteries-in-Series-or-Parallel

Steve, connect the two batteries positive to positive, negative to negative, pos cable to #1 battery then to #2 battery, neg cable to #2 battery then #1 battery. This spreads the load evenly between both batteries so you wont have an early failure of one battery.
Solar connection direct from controller to batteries in a similar fashion, pos to pos of #1, neg to neg of #2, with a fuse within 150mm of the battery in the pos wire.
All loads from the 12 volt distribution panel.
I would wire the output from the outboard to the batteries in a similar way.
Hope this helps, Cheers Bob.

If you connect both batteries together in parallel and one starts to fail, the other will discharge into the failing battery.

I'd use the 4 way battery switch so you can select off, 1, 2 or 1&2.

Cheers
Bristle

Bristols right Steve. What you are planning will work but it defeats the idea of keeping a charged battery spare for engine start in case you need it. If your giant battery dies you've got nothing left. Maybe you need three batteries, two in parallel to give you the giant saloon power and a third reserved for engine start.

ive got a third battery thats good spare and dont need engine start batteries.

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Trek said..
Bristols right Steve. What you are planning will work but it defeats the idea of keeping a charged battery spare for engine start in case you need it. If your giant battery dies you've got nothing left. Maybe you need three batteries, two in parallel to give you the giant saloon power and a third reserved for engine start.

Steve,

There are different schools of thought here. The first school of thought is that by paralleling, the batteries together share the load, reducing the depth of discharge, increasing the life of the battery. The risk here is that if some goes wrong (or you forget to turn off the fridge), it can ruin both batteries. This risk can be reduced if the batteries have a fuse or if you have a low voltage cut out relay on your fridge. Some of the battery controllers have integrated load control output that you could use instead of a low voltage cut relay. This is set and forget.

The second school says that it is better to have the batteries independent and run the system from the A or B battery. You can do this via a 3/4 way switch and/or charge them via a battery combiner/relay. Managing the power will be an active manual process.

Note that you can only parallel the batteries if they are same age and type (as is on your case). Don't leave your "spare" battery discharged for any length of time if you want to use it as a spare.

If I was in your situation I would parallel them, with a fuse and feed the entire system from the load output of a solar controller to protect the batteries from discharging. Guaranteed I would forget to switch some thing off and flatten the batteries without a low voltage cut out.

If you want KISS then you could just switch the batteries with a 3 or 4 way switch.

... and take a multimeter and some spare wire with alligator clips that you can use to bypass everything in an emergency. Connect the solar cells directly to the batteries and monitor with the multimeter.

Hope this is not too confusing.

Andrew

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Andrew68 said..

Steve,

....
Andrew

Steve,

I think I recall you have some integrated controllers.

The drawing below shows the system I am running. I have a few more terminal blocks, but you could connect it like I have in the drawing. This will work providing the load is within the output of the solar controller. Make sure you read the controller instructions (there might be some settings) and be prepared to connect the battery output directly to the switch panel if the controller dies.

I have assumed that the outboard is not earthed anywhere else, if it is then you need to tie all the earths of the battery and load together, ideally on a bus with solid terminals. Leave the solar cells "floating"

Please make sure your system is fused and you have some spare fuses. 20A will probably be fine, but you might need 50A if the fridge has a high start up current.

There are quite a few ways to skin this cat and I am sure others will have different ideas.


Andrew

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Sectorsteve said..
ive got 2 brand new 140AH batteries yet to install.
Id like to make them like a big battery so connect them up.
i know it seems dumb to most , maybe but i dont wanna fry any more batteries!

I also need to connect my panel to these batteries and my outboard charging wires.
whats the best/right way?

Ive also got a battery switch which im thinking to only have as an on/off, rather than select between the 2 batteries as they will become one battery. How does this all work!

Steve that's a handsome battery bank, something to keep in mind is that when its exhausted its going to need 280 ah to recharge ie. 10 amps for 28 hours. No problem if you can get shore power to give a boost, but that's not always so easy. All modern fridges have low voltage cut out so they can't trash the battery. But be aware big batteries take big charging. As a guide I live on a 130ah battery with a 300 watt solar array. No engine input. When cruising more power is required for vhf, anchor light etc. given that you've got to nice batteries and limited charging, I'd suggest selecting them one at a time so that you have a reserve so to speak

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woko said..

Sectorsteve said..
ive got 2 brand new 140AH batteries yet to install.
Id like to make them like a big battery so connect them up.
i know it seems dumb to most , maybe but i dont wanna fry any more batteries!

I also need to connect my panel to these batteries and my outboard charging wires.
whats the best/right way?

Ive also got a battery switch which im thinking to only have as an on/off, rather than select between the 2 batteries as they will become one battery. How does this all work!

Steve that's a handsome battery bank, something to keep in mind is that when its exhausted its going to need 280 ah to recharge ie. 10 amps for 28 hours. No problem if you can get shore power to give a boost, but that's not always so easy. All modern fridges have low voltage cut out so they can't trash the battery. But be aware big batteries take big charging. As a guide I live on a 130ah battery with a 300 watt solar array. No engine input. When cruising more power is required for vhf, anchor light etc. given that you've got to nice batteries and limited charging, I'd suggest selecting them one at a time so that you have a reserve so to speak

wow good points! ive hooked up the battery switch. looks like i should go to my original plan of actually using the switch. i only have the 1 panel but it has alligator clips so it can go onto any battery via the controller.

What about if i used this system here?
If i can use this system is there a way to use the 1 panel, with its alligator clips to charge both batteries if i had the switch in the 1+2 position? Or would i have to just move the clips to the battery i want to charge