Best setup for charging 2 deep cycle 12v batteries on a boat?

[DeanHensler]

Hello everyone! Thanks in advance for any help.

I've got a pontoon boat that has 2 deep cycle 12v batteries. I have some 12v devices on the boat such as the stereo and running lights. I also have a 24v trolling motor on the front. The batteries are wired in serial for the 24v trolling motor and then I have some 12v devices wired to just one battery. I'm looking to install a solar system so I don't have to keep lugging the 12v deep cycle batteries on and off the boat to charge them at home. The harbor freight 45 watt solar panel package caught my eye because I'm looking to spend around $150 on this. I've heard both good and bad reviews on that and I imagine people on this forum can think up a better system for the same price.

So let's hear it please! I use the boat about once or twice a week and I generally need to recharge the batteries about every 10th time out, if that gives you an idea of how much drain the batteries get. I would plan to leave the solar panels on the boat in full sun all of the time.

[SunEagle]

I would not waste my money on the HF 45watt system. It is crap and will provide little to no amount of charging.

To size a solar pv system for your boat we would really need to know the Ah rating of those batteries and your location.

Also I am not sure if you wanted to charge the batteries while your boat is docked or while it is out moving around the water.

If it is the first then you could build a system that would probably allow you enough space for the panels

If you want to charge while using the boat, I will say you are in for a big surprise because you will not have the room for the panels or be able to have them face the sun continuously which is the only way to get anything out of them.

[Sunking]

Forget Harbor Fright panels as the box they come in is more useful and worth more than the panels.

Secondly and this is a Big Big deal and huge No-No is do not tap a 24 volt battery for 12 volts. You are just asking and begging to destroy both batteries. Use a Switching 24-12 volt converter.

Based on what you have said, you have no need for solar. Charge the batteries at home like you are already doing. That $150 you want to spend on solar would be a lot better spent on a good 24 - 12 volt Switching type converter. I can only assume your two 12 volt batteries are Marine Hybrid of roughly 80 to 100 AH each. To even make a dent in charging would require 200 to 400 watts of panels. An area larger than your boat. You would get more power out of the panels if you mounted them vertically to use a sails. It would cost over $700 and still be a sorry ass battery charger.

Smart money is for $150 you can buy a really good 30 amp 24 to 12 volt converter Or you can do something stupid and use Solar.

[DeanHensler]

I would not waste my money on the HF 45watt system. It is crap and will provide little to no amount of charging.

To size a solar pv system for your boat we would really need to know the Ah rating of those batteries and your location.

Also I am not sure if you wanted to charge the batteries while your boat is docked or while it is out moving around the water.

If it is the first then you could build a system that would probably allow you enough space for the panels

If you want to charge while using the boat, I will say you are in for a big surprise because you will not have the room for the panels or be able to have them face the sun continuously which is the only way to get anything out of them.

I want to charge while the boat is sitting at the dock, in the sun (it stays on the water all year). I don't need to charge while the boat is in motion. Also note that the lake I live on has a 10 hp restriction, so there is no wake at all. I as thinking of making something that would slide out from the top deck while the boat is docked. I live in Missouri.

The two batteries are 109Ah and 92Ah. I've had these batteries for 3 years with no problem having them wired in serial for 24v to the trolling motor and additional 12v devices wired to the 109Ah battery. It is a major pain to haul the batteries off the boat to my house to charge them, then back to the boat to install them again every 3 weeks or so. That's why I'm looking at solar.

[SunEagle]

Ok with a 24volt ~ 100Ah battery bank you will need about 10 amps of charging. That is relatively easy with a 200 watt panel and 15amp CC. The panels should be angle toward the sun when you want to charge the batteries but could be lowered flat and stored during high wind conditions.

Now the problem that both SunKing and I see is connecting 12volt loads to one of those 2 batteries in the 24volt system. That will cause uneven discharging and possibly charging issues if the 12volt loads are connected. It would be better to use a 24v DC to 12v DC converter.

Also to help keep even charging/discharging both of those 12volt batteries should be the same. That means model and especially Ah rating. The biggest problem with solar batteries is that they get uneven charges due to different resistance paths.

Lastly. You could charge those batteries using a portable generator and charger which would probably be much cheaper then using solar. Also being able to take the charging system home might be safer then leaving the solar panels & charger available to be stolen.

Just something to consider and it should be easier then lugging the batteries back and for.

[Mike90250]

The other option, would be 2 large GT panels, and 2 Morningstar Sunsaver MPPT controllers, one on each battery, charges batteries evenly, even if you discharge them oddly

*GT Grid Tie 30-50V panels, and use the MPPT controller to drop that down to 12V. Just leave each panel & controller isolated and not ground bonded. Should be safe enough on a boat.

FUSES - are you useing fuses on the wires ??

[Ramomd]

Hello Mike, I have a ClubCar Golf Cart with a solar panel on the roof that sends 26.3 volts on a sunny day to the 4 Trojan 12v (each) battery bank. The original Controller / Inverter from Germany broke down and I bought a WELLSEE WS-MPPT30 Solar Controller 48v / 20A but it does not work. The original inverter/controller worked perfectly but there is no tag on it nor on the solar panel. Please advise which Controller / Inverter would you recommend. Thanks for your help!

[littleharbor]

Wellsee controllers are crap, are not real MPPT and not worth the 15 dollars or whatever you paid for it. Why are you using a 48 volt controller with a 18 volt nominal solar panel?
Is your golf cart 48 volt? If so that would explain why 26.3 volts isn't charging.

[Mike90250]

The best, little and honest MPPT controllers are from Morningstar (that I know of) 15 amps of output, and 75V max input

http://www.morningstarcorp.com/products/sunsaver-mppt/

There are others, and there are cheaper. These work all the time,

[Ramomd]

Thank you Mike,

I contacted MorningStar but they are recommending ProStar MPPT25 because I have 4 batteries 12v each in parallel to charge from the solar panel.

http://www.morningstarcorp.com/products/prostar-mppt/

Please advise and thanks for your help!

[SunEagle]

Thank you Mike,

I contacted MorningStar but they are recommending ProStar MPPT25 because I have 4 batteries 12v each in parallel to charge from the solar panel.

http://www.morningstarcorp.com/products/prostar-mppt/

Please advise and thanks for your help!

Hmmm. Looks like MorningStar is stepping up with newer equipment. I am impressed it now can charge multiple battery chemistries including Lithium.

[Sunking]

Hmmm. Looks like MorningStar is stepping up with newer equipment. I am impressed it now can charge multiple battery chemistries including Lithium.

Don't get to impressed. Any charge controller can do Lithium. If you look at the Operator Manual there is no setting for Lithium or NiCd. Like I said Lithium is easy peasy and any charger made for FLA can charge 4S LFP providing you can set the voltage to 14.2 to 14.4 volts and that falls under AGM/FLA setting in the dip switches. NiCd nah, as that takes some complicated Delta V detection which cannot be done. I can only assume by NiCd they intend you to charge at C/20 or less in Constant Current Mode and never shut off. Way to slow for any practical installation.

[Mike90250]

The size of controller depends on the size of the solar panel. Wattage / voltage = amps
Charging voltage is about 14V, so a 280W panel can be managed by a good sturdy controller. To charge batteries faster, you add more panels, and then you need a larger controller to handle the higher power.
And remember, a PV panel generally produces 80% of it's rated wattage. and solar power slowly ramps up from 8am to noon. At that time, the batteries already have some power in them, and the panel is not likely to be producing full power anyway,
The Morningstar line has good thermal foldback and current limiting, they can be used with a battery or power supply, and I would feel comfortable with up to a 300 watt panel on the 20A model.

[Bala]

The two batteries are 109Ah and 92Ah. I've had these batteries for 3 years with no problem having them wired in serial for 24v to the trolling motor and additional 12v devices wired to the 109Ah battery. It is a major pain to haul the batteries off the boat to my house to charge them, then back to the boat to install them again every 3 weeks or so. That's why I'm looking at solar.

If you have been charging the batteries individually on their own 12V charger then that would explain how you have gotten away with tapping 12V off a 24V system.

If you set up a 24V solar system and tap 12V off one of the batteries you will find that problems will occur quickly.

It is common on 24V trucks for people to tap 12V off one battery to run a two way radio, even this low current draw causes problems quickly.