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Old 23-09-2010, 10:10   #1
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12vdc Panels, 24vdc Battery Bank

HI, I HAVE JUST BOUGHT 2 80W 12V SOLAR PANELS, I HAVE 4 140A BATTERIES WIRED IN SERIES TO SUPPLY 24 V. CAN SOMEONE PLEASE EXPLAIN IN REAL IDIOT SPEAK HOW I WIRE THEM EXACTLY, DO I NEED A REGULATOR. IF SO WHICH ONE RECCOMENDED. I LIVE ON BOARD AND DONT THINK THERE IS AN OVERCHARGE POSSIBLE. BUT HEY, THATS WHY I AM ASKING.
CHEERS, JOHN
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Old 23-09-2010, 10:27   #2
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regulator

Get yourself a MPPT controller. Three that come to mind that would work for your size array are the Morningstar Sunsaver 15, the Solar boast 2000, and the BZ250 from BZ products. The last two ahve displays, the Morningstar does not (but is very small).

Make sure you get an MPPT controller, not PVM. You will get 20% more out of your panels this way. Wire the panels in Series to put 24v nominal into the contrller, and then output 24v to your batteries. Easy as pie!

Chris
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Old 23-09-2010, 10:41   #3
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Hi Thanks, I have just checked prices and am in shock, but if thats what it has got to be then so be it.
Do i mount the regulator in the engine room, near the batteries and at what point do i wire the panels in series, in the engine room or where they are mounted. Sorry i am a bit slow, and finally what size cable would you reccomend.
Thanks for your speedy help.
John.
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Old 23-09-2010, 10:54   #4
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Quote:
Originally Posted by nostramo.moody View Post
HI, I HAVE JUST BOUGHT 2 80W 12V SOLAR PANELS, I HAVE 4 140A BATTERIES WIRED IN SERIES TO SUPPLY 24 V. CAN SOMEONE PLEASE EXPLAIN IN REAL IDIOT SPEAK HOW I WIRE THEM EXACTLY, DO I NEED A REGULATOR. IF SO WHICH ONE RECCOMENDED. I LIVE ON BOARD AND DONT THINK THERE IS AN OVERCHARGE POSSIBLE. BUT HEY, THATS WHY I AM ASKING.
CHEERS, JOHN
Wire them in series - That way you'll get a nominal 24 volts out of them, and the maximum amperage output will still be only about 4.5 amps.



The above diagram is for 6V batteries, but it's the same principal with your 12V solar panels...

Invest in an MPPT solar charge controller to help better utilize the maximum power available from them. Check out BlueSky, MorningStar as a couple of manufacturers of MPPT controllers.

You'll only see close to 4.5 amps for only a few hours a day, and only if there's no shadows at all on your panels.

Your battery bank is four 6V batteries wired in series? Your whole bank is 140Ah? If so, then the peak amperage output of your solar panels will be 3.2% of the total size of your bank, capacity=C=140Ah. That's about three times what's needed to keep a fully charged bank maintained properly. In a perfect world.

However, you'll be drawing power off that bank - probably a lot more than 4.5 amps to run various devices, so don't expect the 160 watts of panels (again, 160W in a perfect world), to keep up with your daily needs. You didn't say anything other than you're a liveaboard, and you're right - you probably won't have to worry about overcharging. You might want look at beefing up the panel bank if you can afford it and have the space available... To give any more advice, you'd have to let us know what other charging systems you have (shorepower, engine/genset), whether you're at a dock or on the hook, your daily power consumption, confirm your battery bank configuration (12V or 6V batteries, series or series/parallel), etc...
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Old 23-09-2010, 11:01   #5
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Thanks,
we are mostly at anchor,we have a 40 amp battery charger (24V)240v supplied that we power by a portable genny. We can run engine with 90 amp alternator, that only seems to put 20a in. We have 4 12V 140 amp batteries, we are very economical on power, led lights etc but do like to run our fridge that uses 3 amp when running.
Thanks for the prompt supply
John.
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Old 23-09-2010, 11:07   #6
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Like Witzgall says.

For the wiring between your panels and the charge controller, use sufficiently heavy gauge wire to keep the voltage loss to less than 2-3% (with a 24V system you probably won't need anything heavier than 12 gauge, but here's a calculator: Voltage Drop Calculator, Amperage Tables, Wire and Cable Technical information

Your charge controller will come with instructions. These will probably call for an appropriately sized fuse on the positive side between the charge controller and the battery bus post. The negative will directly to the battery bus post. The charge controller's temperature sensor will go directly to the terminal(s) on one of the batteries. Follow the charge controller's instructions to make sure it's programmed for your battery type and voltage.
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Old 23-09-2010, 11:13   #7
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I hate to be a contrarian here, but if you are a full time liveaboard, then your daily amphour useage will be much more than two 80 watt panels can put out. Therefore there is no need for a controller. If you really want a controller then a cheap non MPPT controller will be more cost effective.

Wire the two panels in series: pos wire to plus of one, neg of that one to plus of other, neg of other to negative wire. Use 14 gauge wire. Wire the pos wire to a 15 amp breaker or fuse to your batteries.

If you are going to be away from your boat with all refrig, etc off for more than a few days, pull the fuse or trip the breaker to keep from overcharging your batteries. No need to do that if you have a controller which is an advantage.

David
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Old 23-09-2010, 11:17   #8
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Depends on your boat's layout, but consider putting the charge controller near your battery bus terminal posts, for a short wire run. You also want the controller close enough to your batteries to run your temperature sensing wire (if your controller has this feature). Finally, if your charge controller has a status display - a light or readout - you will probably want it visible. On my boat this meant putting the charge controller in the electrical panel. Besides, no reason to subject the controller to the heat of the engine room if it's not necessary.
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Old 23-09-2010, 11:24   #9
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David makes a good point.
1) It would be cheapest to skip the controller.
2) A cheap, non-MMPT controller will allow you to leave the boat for a period of time so the panels can top off your batteries and keep them topped off.
3) An MMPT controller will allow you to get the most amps out of your panels. I

It really depends on your own economic analysis.
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Old 23-09-2010, 11:34   #10
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Thanks Guys,
My economic situation is, no controller would be a good option.
I have a Adverc battery monitor with 4 positions, one free that i could monitor the panels with. Could i do this and retrofit a controller if i have problems.
Thanks.
PS. my battery bank will need replacing soon, so i am not too concerned about damage although i am about safety.
Cheers.
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Old 23-09-2010, 11:53   #11
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As I understand it, if you connect your panels to the battery bus terminal posts, then there's no need to connect your battery monitor to the panels themselves. Your battery monitor should continue to operate as before. While the panels are providing charge, the battery monitor will display the resulting voltage and current flow into the batteries. That's what my monitor does.
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Old 23-09-2010, 12:08   #12
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I'll have to side with the no controller. Spending BIG bucks to buy a MPP controller to get 20% more power out of a couple of 80 watt panels makes no sense. Instead spend the money to buy another panel. with that big a battery bank and that small a solar panel it will take days to weeks to overcharge with no load on the batteries, and months to a year to burn them dry. If you had a Kilo watt solar array that operated at 30 volts or higher get a controller, for 80 watts that would be overkill. Just hook up the panels in series to get the 24 volts you need and relax, you will barely get enough power to keep the batteries topped off on a good summer day.
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Old 23-09-2010, 12:48   #13
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If you ever leave your boat for more than a day, be sure and disconnect the solar panels. Once the batteries are charged to capacity, the solar panels will turn the water in the batteries into copious amounts of hydrogen and oxygen. Can we say 'bomb'. A great way to explode your batteries, btdt, and possibly set the boat. Knowing my ability to forget things, there is no way I'd go without a controller for safety reasons.
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Old 23-09-2010, 15:15   #14
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Spending BIG bucks to buy a MPP controller to get 20% more power out of a couple of 80 watt panels makes no sense. Instead spend the money to buy another panel.
I here what Capn Bill is saying, but if you do decide to install a controller, and you also want a little more charging capability, might I suggest that 160W is about the crossover point where an MMPT controller is a sound economic decision. Let's just say you want 20% more power, or 32W. How much will it cost?

Option A: A 85W panel at affordable-solar.com = $400 (ie, $160 per 32W)
Option B: A new Blue Sky 2512i MMPT controller at ecodirect.com = $168 (providing about 20% more efficiency).

It's basically a wash, even though this assumes buying an entire 80W panel in order to benefit from economy of scale (a hypothetical 32W panel would cost more per watt).

Meanwhile, the benefit of Option B is less weight and windage aloft. Plus, now you have a 3-stage controller that will safely charge and maintain your batteries while you're ashore.

The basic 2512i doesn't display voltage, but it will show you the controller's charge status, which is all you really needed.
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Old 23-09-2010, 16:06   #15
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MPPT controllers also have the added benefit of using a pulse charging method that will top off your batteries a bit higher than conventional charging. This means more amps are available from your battery bank, and if they are wet cells, you will get longer life as they do not need equalization as much.

Chris
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