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Old 16-06-2015, 06:58   #1
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Help connecting solar to batteries

Hi guys,

Sitting aboard my boat in denmark after having cruised down the swedish coastlin and i finally have time and energy to connct the solar power i brought along with me.

Now previous owner has had 2 batteries installed. Both lead acid, one starter 44ah and one leasure 75ah.

The way i see they are connected is:

Negative are linked together on both batteries but the positives arent connected directly together. They each go to their own on/off switch. The negative wire is then lead back where i can no longer see, i guess connected t the engine block.

Both batteries are hooked up to the engines alternator.

Question. Where do i fit the wires from my solar charger? I need to hook up straight on the batteries i guess? But which positive pole?
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Old 16-06-2015, 07:15   #2
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Re: Help connecting solar to batteries

Take a multimeter, set it to read DC voltage, & touch the probes to the wires from the panels. If it's readings are negative (assuming a digital meter) then switch the probes around. And it should give you positive voltage readings. Once you've done that, then you know that the wire that the black probe is on is the ground (negative), & that the red probe wire is the positive.

There is a catch or three on hooking up the panels though:
Do you have a fusing system (for safety)?
Do you want to, or need to, run a charge controller? Especially as, with that sized battery capacity, you can possibly (probably) over charge them with the panels without some type of controller or regulator.
Do you plan on running Diodes, or some type of system to prevent power loss through the panels when they're not charging?

Also, given your questions, it'd be wise to at a minimum, have someone around who understands electricity very well, while you're building your system. That, or hire out the job.
That, & definitely do some reading on 12v boat systems. Nigel Calder is a great author to start with, as well as some of the other recommendations on here.
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Old 16-06-2015, 07:46   #3
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Re: Help connecting solar to batteries

Depends on a few things:

1) Which bank are you trying to charge?
2) What's the wattage of the panel(s)? Are they for maintenance or bulk charging? Do they go via a charge controller?
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Old 16-06-2015, 08:00   #4
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Re: Help connecting solar to batteries

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Originally Posted by DefinitelyMe View Post
Depends on a few things:

1) Which bank are you trying to charge?
2) What's the wattage of the panel(s)? Are they for maintenance or bulk charging? Do they go via a charge controller?
1. I guess just the leisure bank. But if the batteries are connected in parralel, then i read its not good that one has moe juice than the other?

2. 50 watt panel simply for topping up the battery when charging usb items lik phone, small bluetooth speaker etc.

Yes they go through a charge controller. Steca pr 10/10
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Old 16-06-2015, 08:04   #5
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Re: Help connecting solar to batteries

I connected it directly to the leisure battery to try it out and it works. Pulling 2amps from the panel on a clouded day,

But i guess, now only the leisure battery is being charged?

As batteries are only connected directly through the negative pol?
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Old 16-06-2015, 08:08   #6
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Re: Help connecting solar to batteries

If both batteries are connected to the alternator, then they are essentially paralleled whenever both switches (start and leisure) are ON.

Since the leisure battery may be deeply discharged after a long while at anchorage, when you turn the switch to engage the start battery it will be paralleled with the leisure battery, and current will rush toward the leisure battery from the start battery. Not a great setup.

Ideally, you want to hook all charging systems (alternator, battery charger, solar, etc.) to the leisure battery bank. Then, since the start battery requires very little charging, keep it topped up via a device like the EchoCharge or any of several ACRs. I prefer voltage followers like the EchoCharge or DuoCharge. These are totally automatic, one-way devices which will maintain your start battery without the need to switch anything.

Sounds like it would be easy to install such a device (EchoCharge by preference). We'd need a detailed circuit diagram to be sure.

So, to hook in the solar panel(s) you only need to hook the panel(s) to a controller and hook the controller to the leisure battery. You need appropriate fusing in the circuit, one near the battery and one on the input to the controller from the solar panel(s).

Bill
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Old 16-06-2015, 08:21   #7
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Re: Help connecting solar to batteries

Hi Bill,

Exactly.

So when I have the solar charger connected directly to the leisure battery, it only charges the leisure battery. But what if i turn on both switches and then making e batteries in parallel? Will i then charge both batteries, even if the solar charger is only hooked up on the leisure bank?
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Old 16-06-2015, 08:23   #8
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Re: Help connecting solar to batteries

OK, in that case the controller will prevent over-charging at least, but yes, it is not good to connect them in parallel and charge them together. The smaller bank would be chronically over-charged and the larger one under-charged. Both are not good for the batteries.

You could connect the positive cable from the charge controller to the positive terminal on the house bank. Another option is to connect the positive cable from the charge controller to the battery switch on the load side. That way, the solar array will charge whichever bank the switch is currently set to draw from, which may be desirable under some circumstances.

Take what i say with a grain of salt however. Every boat in the world has a different setup. Some are great, some are terrible, but there is no correct answer. There are however some general rules which should always be followed, such as:

- Do not connect different sized banks in parallel and charge or discharge them together.
- Use large cables, particularly between the charge controller and the batteries, to minimise voltage drop.
- Make the wire runs as short as possible. Again, this is particularly important between the charge controller and the batteries
- Monitor voltage (at least) and make sure the voltages that the charge controller is supplying during each stage of charging are as per the manufacturers recommendations .
- Mount the panels in such a way that shading, or partial shading, is avoided as much as possible. A single line of shading across the panel will drastically reduce the output.

Finally, i think you'll find that for that kind of useage, if you set it up right, a 50W panel will be quite sufficient to provide all the power you need. I recently installed two 20W panels in a day-racer. Battery banks are 2 x 75Ah. The owner is very pleased. Never needs to run the engine for charging any more. Runs lights, stereo and charges phones and stuff and the system copes very well.
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Old 16-06-2015, 08:45   #9
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Re: Help connecting solar to batteries

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Originally Posted by Nicks View Post
Hi Bill,

Exactly.

So when I have the solar charger connected directly to the leisure battery, it only charges the leisure battery. But what if i turn on both switches and then making e batteries in parallel? Will i then charge both batteries, even if the solar charger is only hooked up on the leisure bank?
Yes, the batteries will both receive a charge because, essentially, you have connected them in parallel if both switches are ON.

How can you tell for sure? Do you have a digital multimeter? Just measure the voltages on each battery.

Bill
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Old 16-06-2015, 08:46   #10
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Re: Help connecting solar to batteries

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Originally Posted by DefinitelyMe View Post
Use large cables, particularly between the charge controller and the batteries, to minimise voltage drop.
- Make the wire runs as short as possible. Again, this is particularly important between the charge controller and the batteries
-
thanks again for your answer, very helpful!

One problem I have, is that my batteries are located in the bottom of the boat and where i wanted to place the charge controller doesn't allow short wires. I purchased 1,5 meter wire from battery - housebank, but thats a bit too short. I would probbly need atleast another 1 to 1,5 meters. Would that be anissue?

You also mention that i could run the positive from my solar charger to the positive battery-switch. That would be great, but it would not sort out the cable length issue, as i believe there are a couple of meters of cable from the batteries to the switch.

Would 3~m of cable be too long? 6mm thicknss)?
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Old 16-06-2015, 11:18   #11
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Re: Help connecting solar to batteries

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thanks again for your answer, very helpful!

One problem I have, is that my batteries are located in the bottom of the boat and where i wanted to place the charge controller doesn't allow short wires. I purchased 1,5 meter wire from battery - housebank, but thats a bit too short. I would probbly need atleast another 1 to 1,5 meters. Would that be anissue?

You also mention that i could run the positive from my solar charger to the positive battery-switch. That would be great, but it would not sort out the cable length issue, as i believe there are a couple of meters of cable from the batteries to the switch.

Would 3~m of cable be too long? 6mm thicknss)?

That's not too bad. Not great, but not too bad. Basically, the shorter the run and the thicker the wire, the less voltage drop you have, which means the batteries are being held closer to the optimum voltage, the charge controller is reading the battery voltage accurately, and ultimately you are getting more power into your batteries. It makes a big difference. If 6mm is the diameter of the bare wire (excluding the insulation), that is pretty good. For that run length on both sides (positive ad negative) you're looking at a voltage drop of about 0.03V which is not too bad. If your regulator allows you to set the voltages yourself, you can compensate for this somewhat by setting them 0.03V higher.

Regarding connecting them to the battery switch, yes it does compound the problem of run length but not too too badly provided that the connections are good and your battery cables are nice and thick. I'm assuming the switch is located right next to the batteries themselves? What's the run length there?........
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Old 16-06-2015, 18:26   #12
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Re: Help connecting solar to batteries

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Originally Posted by Nicks View Post
Hi Bill,

Exactly.

So when I have the solar charger connected directly to the leisure battery, it only charges the leisure battery. But what if i turn on both switches and then making e batteries in parallel? Will i then charge both batteries, even if the solar charger is only hooked up on the leisure bank?
Are you sure you don't already have a 12v DC battery isolator between the batteries and the alternator? The cable from my Alternator goes to an isolator which splits to the two battery banks.

My solar setup also has the Panels going to a controller through another isolator with two outputs to separate cables to the battery banks.

As you noted your Neg posts are simply going to ground. You want to keep your Pos posts separated Typical Battery Isolator Circuits - ARCO I'm sure someone can give you a more accurate answer, but that's my simple way of looking at it.
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