Solar to Battery Question

[mtp553]

Hi there...really new at this, but I've been trying my best to learn about DC electrical systems. I am sort of taking over my Dad's boat. He's been using it as a day sailor, but I'm putting it back in cruising shape. Slowly.

The boat has two batteries - both of the same type - connected to the 3 way switch. Each battery (1 and 2) connected to the 1 and 2 lugs on the switch.

That switch, as i understand it, is really designed to separate out the starter bank from the house bank. But in our case, we've been using the two batteries for all purposes - starting and house. We generally keep the switch in the "Both" position which has the effect of paralleling the batteries. I realize this could cause trouble for cruising if we run the batteries down to the point they won't start the engine, but that's another issue.

I just bought a single 100W solar panel, which came with a controller. The boat is on the hard (south-central Canada) - so the engine won't be running. I want to use this solar panel to keep the batteries topped up during the winter. So i connected the controller to the lug that holds the cable from the engine. My thinking is that when the switch is on "Both", the alternator will charge both batteries, so the solar panel is basically standing in the position of the alternator during the winter - and it should keep the batteries charged up.

1. Anything wrong with this set up while the boat is on the hard?
2. Should I be buying an MPPT, or is this little controller that came with the panel sufficient?
3. When she goes back in the water - i take it that i can't use this system, because the alternator will be charging via this lug when the engine is running - this would cause problems in terms of presenting big amps to the solar controller (and wiring) - and there may be problems forcing the solar charge backwards through the alternator too i guess...not sure about that. So - how to I connect the solar to the existing system? Do i get a two output MPPT, and connect each battery to the controller/mppt - or should I parallel both batteries at the bank, and just run them to the #1 switch, leaving the #2 switch unconnected?
4. I am using #10 AWG for this single 100 W panel. Anybody think this is a problem?

Sorry if these are really dumb questions. Any help you folks could give me would be most appreciated. Just learning the ropes here.

[thomm225]

Any controller will work fine for two batteries that aren't running anything.

I used a 20 watt panel and a PWM controller while my boat was in the yard during the Winter of 2018 to keep my two batteries charged to a float of about 13.2 Volts.

I stored my 65 watt and 50 watt panels in the cabin during this period plus my other controllers.

How you hook it up is up to you.

My batteries are in parallel so I hooked my controller to one of the batteries which means it's hooked to both batteries.

I have an outboard with no alternator and no start battery so the two batteries are my "house" bank.

[Nord Sal]

You might consider an automatic charge relay so you can charge both banks regardless of the position of the battery switch. You could then avoid using the "both" position and (mostly) eliminate the risk of not having enough energy to start the engine should you forget about it and deplete your batteries.

You should be able to have the alternator and solar both wired to to charge the system, i.e., the alternator won't fry your charge controller when your engine is running.

MPPT is nice but not necessary. I'd use what I have.

10 AWG should be fine. You'll only see about 8.3 amps (100 watts ÷ 12 volts) of current maximum. Don't forget to fuse your system.

[DefinitelyMe]

Originally Posted by mtp553

Hi there...really new at this, but I've been trying my best to learn about DC electrical systems. I am sort of taking over my Dad's boat. He's been using it as a day sailor, but I'm putting it back in cruising shape. Slowly.

The boat has two batteries - both of the same type - connected to the 3 way switch. Each battery (1 and 2) connected to the 1 and 2 lugs on the switch.

That switch, as i understand it, is really designed to separate out the starter bank from the house bank. But in our case, we've been using the two batteries for all purposes - starting and house. We generally keep the switch in the "Both" position which has the effect of paralleling the batteries. I realize this could cause trouble for cruising if we run the batteries down to the point they won't start the engine, but that's another issue. [emoji2]

I just bought a single 100W solar panel, which came with a controller. The boat is on the hard (south-central Canada) - so the engine won't be running. I want to use this solar panel to keep the batteries topped up during the winter. So i connected the controller to the lug that holds the cable from the engine. My thinking is that when the switch is on "Both", the alternator will charge both batteries, so the solar panel is basically standing in the position of the alternator during the winter - and it should keep the batteries charged up.

1. Anything wrong with this set up while the boat is on the hard?
2. Should I be buying an MPPT, or is this little controller that came with the panel sufficient?
3. When she goes back in the water - i take it that i can't use this system, because the alternator will be charging via this lug when the engine is running - this would cause problems in terms of presenting big amps to the solar controller (and wiring) - and there may be problems forcing the solar charge backwards through the alternator too i guess...not sure about that. So - how to I connect the solar to the existing system? Do i get a two output MPPT, and connect each battery to the controller/mppt - or should I parallel both batteries at the bank, and just run them to the #1 switch, leaving the #2 switch unconnected?
4. I am using #10 AWG for this single 100 W panel. Anybody think this is a problem?

Sorry if these are really dumb questions. Any help you folks could give me would be most appreciated. Just learning the ropes here.

Not dumb questions at all. As you have no doubt gathered there are many, many ways of doing this stuff and some are better, some are worse and some are just different. But to answer your questions in short:

1) Fine, however the charge controller might not like to be turned on and off, so if you're setting it up like that then leave it on always.

Consider connecting to the other side of the switch, or even directly to the batteries. If you always use the two batteries together then you basically have one bank, so no need to split the charge. You can split the output from the controller by making a 'Y' in the cable and connecting to the 1 and the 2. Better yet connect both batteries to one terminal (either 1 or 2) and leave the other spare, essentially making your switch an on-off switch.

Short answer: it will work as you suggest. Just always leave the switch in the 'all' position.

2) no, an inexpensive PWM controller will work just fine for your application.

3) if I understand your explanation correctly then no, you shouldn't have any issues with conflict between the alternator and the charge controller or with back-feeding. When the engine runs it will complement the solar.

4) it depends on the wiring run and what you consider to be acceptable losses, but in short yes, 10AWG should work fine.

[mtp553]

Thank you all very much for taking the time to answer my questions. I really appreciate it.

[Uncle Bob]

Hi, the instructions from the manufacturer of my controller (morningstar) say that the controller output should be direct connected to the battery and appropriately fused within 7 inches of the battery. That is how I did it and no problem for years.
Similar instructions accompanied the controllers fitted by friends to their boats.

[roverhi]

Have doing what you are planning for 10 years, though when I'm around switch back and forth between the two batteries. i'm often away from the boat for a month or way more at a time and switch to both when I leave. Should install a charge separator but haven't gotten around to it.

One BIG reason not to use the 'both' selection is a failure in one battery bank will drain the other bank into the bad one leaving you with no charged batteries.

I bought a charge separator at a consignment store. One of the reasons I haven't installed it as I hear these old separators waste significant charging energy in their internal switching so aren't good on a boat not connected to shore power. Any truth to that??

[DefinitelyMe]

Originally Posted by roverhi

Have doing what you are planning for 10 years, though when I'm around switch back and forth between the two batteries. i'm often away from the boat for a month or way more at a time and switch to both when I leave. Should install a charge separator but haven't gotten around to it.

One BIG reason not to use the 'both' selection is a failure in one battery bank will drain the other bank into the bad one leaving you with no charged batteries.

I bought a charge separator at a consignment store. One of the reasons I haven't installed it as I hear these old separators waste significant charging energy in their internal switching so aren't good on a boat not connected to shore power. Any truth to that??

Yes there is truth to that. Isolators use diodes to direct the power. There's a slight loss. But given that you have not been treating your batteries as a single bank you will most likely have an imbalance between them, which means the loss is probably acceptable (i.e. you're better off using the isolator rather than continuing as you are). You'll get more life out of your batteries.

[T1 Terry]

First question, is the regulator on the back of the portable panel? If it is, very carefully remove it from the back of the panel so you can mount it close to the house battery. Now fit a suitable plug to the cable from the solar panel to the wiring connections on the regulator so the panel can be unplugged if needed without disturbing the regulator. Now wire the battery terminals to the wiring connections marked for the battery on the regulator with a fuse (probably 20 amps max) even though the regulator will never transfer 20 amps to the battery, the wire size you use will handle 20 amps without burning and this is the part you need to protect with the fuse.
Get a voltage sensing relay and link the house battery to the start battery, this will link the two batteries together while the house battery has more than 12.8v at the terminals, but will disconnect when the house battery drops to 12.4v saving the house battery from draining the start battery, yet keeping the start battery topped up when required.
Leave the 3 way switch turned off, no need to power stuff that doesn't need to be powered.


T1 Terry

[ussvdharma]

Absolutely the MPPT is the one to use...keeps on charging even on cloudy days....check out the technical aspects of the MPPT...your solar panel gives out only so many watts of power (voltage-current). The mppt controler up the voltage when it dropes below that of the battery so that charging continues....although the current droops because the voltage went up. Thus on cloudy days you still charge.....

[DefinitelyMe]

Originally Posted by ussvdharma

Absolutely the MPPT is the one to use...keeps on charging even on cloudy days....check out the technical aspects of the MPPT...your solar panel gives out only so many watts of power (voltage-current). The mppt controler up the voltage when it dropes below that of the battery so that charging continues....although the current droops because the voltage went up. Thus on cloudy days you still charge.....

The OP wants a system for keeping the batteries topped up while the boat is on the hard over the winter. Optimisation of the system is not the goal here.

[thomm225]

Dear Mr. OP, you can make this as simple or as complicated as you want. (see posts above)

A small panel and PWM controller will work fine to keep two batteries not being used charged while the boat is in storage.

PWM's keep charging on cloudy days also.

You don't need links, relays, isolation diodes etc. unless you want to play around with that stuff.

I have yet to mount my controllers or panels since I'm still trying different setups. This since 2012.

My panels are tied on at least the 65 watt panel on aft lazarette, and 50 watt panel on stern railing with leech line. The one that fell was a 20 watt panel which I have hooked directly to the batteries ........ (no controller) when I'm on the boat and need power. The 50 watt panel is hooked to a Chinese PWM Controller which charges to 14.4 Volts but that panel faces sideways so it works. The 65 watt panel is on a PWM set to Float at 13.7 Volts.

I had a Victron MPPT Controller but it failed and is now out of the system.

It's totally up to you: simple or complicated.

https://www.youtube.com/watch?v=-nXfjcCuiPk

[DefinitelyMe]

Come on guys and girls. The OP's question is whether his setup will work. The answer is yes. Presenting a load of ways to 'improve' his system by buying relays, or new charge controllers or any other expensive stuff is not constructive.

[OS2Dude]

Originally Posted by DefinitelyMe

Come on guys and girls. The OP's question is whether his setup will work. The answer is yes. Presenting a load of ways to 'improve' his system by buying relays, or new charge controllers or any other expensive stuff is not constructive.

I believe you will find the answer is NO. The solar controller has one set of battery wires, one positive and the other negative. The two batteries should be connected together in parallel and the positive wire connected to the positive of one battery and the negative wire to the negative of the other battery. (The same connections the load would be attached to.) Going through the 1-B-2 switch puts the charge between the batteries as two separate entities. This is not how the charger is meant to work. It -MAY- charge, but it is not going to do it well and may likely get confused if one battery reaches capacity before the other.

[thomm225]

Originally Posted by OS2Dude

I believe you will find the answer is NO. The solar controller has one set of battery wires, one positive and the other negative. The two batteries should be connected together in parallel and the positive wire connected to the positive of one battery and the negative wire to the negative of the other battery. (The same connections the load would be attached to.) Going through the 1-B-2 switch puts the charge between the batteries as two separate entities. This is not how the charger is meant to work. It -MAY- charge, but it is not going to do it well and may likely get confused if one battery reaches capacity before the other.

It's not the end of the world if one battery reaches charge before the other.

I had a diesel engine on my good old boat when I first bought it but after it failed and I bought an outboard, I put the starter battery in parallel with a deep cycle battery and they lasted about 5 years.

Yes the starter battery would charge up before the deep cycle and stop the charge as they were in parallel, but we are talking what maybe a year of difference.......

As I mentioned, you can make it way complicated or very simple.

Btw, I was charging these batteries with a pwm controller that was unadjustable and had no float adjustment either. It charged the batteries to 14.4 volts and stopped there at which time I'd unhook the controller for a few days. The controller cost $12.00