Solar Charge Controller for Special Project on the Ocean

dvillal · October 2016

I need a solar charger for a mobile platform. It will be on a small boat (less than 8 feet) in the ocean so it will rock a lot. It will have a 100W 12V solar panel and I plan to have an 80 amp load (not all the time, but it needs to be able to handle at least that much). Now I know most solar charge controllers have connections for 1) the solar panel, 2) the storage battery, and 3) the load. Is the only reason you would attach the load to the charge controller is so that you could cut-off the battery when the charge gets to low? If that's all, it would be cheaper for me to get a 10A controller and attach the load directly to the battery? Or will that cause other issues as well.

Also, what I've read is that MPPT's are worth it for higher voltage systems. Since I'm just having a single 100W panel at 12V, I'm thinking I would get a PWM module. Does this make sense with all the above?

Lastly, if I want the battery to be lifepo4, do I have to buy a special controller? The lifepo4 battery I would get has its own integrated PCM (protection circuit module) which provides complete internal cell balancing.

Sorry I'm a little lost and confused. If you can answer one or all of my questions I would be grateful for the input.

Dan

BB. · October 2016

Do you have a battery bus voltage, ah per day, panel mounted flat on top of bouy, etc.?

Low voltage cut off is usually to save the loads, not the battery (10.5 volts will kill a lead acid battery). And typical lvd will not pass 80 amp surge.

LiFePO4 batteries will be damaged with over or under charging. They do not use temperature adjustments. Some cheaper controllers can bypass temperature offset. More expensive controllers can be programmed.

Single power system or triple redundant?

Roughly, a 100 Watt panel with 4 hours of sun per day will give you around 200 Watt·Hours per day.

-Bill

dvillal · October 2016

No, this will be an unmanned boat that will be on the water the full day. I will have one 12V 40 amp-hour battery to run the motor (the load). I know the solar panel won't have enough juice to run the motors alone, but at least it can recharge the battery (with no load) in one or two days of good sunlight.

I have other equipment protecting the motors so just want to know the best way to wire this up. Whether to get an 80A charge controller for the motor or if I can get away with a 10A controller and just have solar panel recharge the battery and attach the motors directly to the battery. I don't know if it is a good idea to recharge a battery while putting a load on it.

Thanks for the info on the LiFePO4 batteries.

I imagine this is a single power system, although I am not sure what you mean by triple redundant.

Hope this helps.

Dave Angelini · October 2016

I used a C30 on my sailboat in 1992. They still make one that is almost the same here in the store.
https://www.solar-electric.com/tracc35solch.html

BB. · October 2016

For "mission critical" systems, the USCG uses 3 redundant power systems (and other stuff) (i.e., 3x 1 panel+1 controller+1 battery bank connected in parallel/behind switch gear).

Many Li Ion cells are "protected" which means that they disconnect if the are operated at too low of state of charge (low cell voltage). Once the protection "trips", I think the cell is "dead" forever.

These cells are not in my area of expertise--What is it that you expect/require from the battery bank + solar panel + charger? How much WH/AH per day (loads and charging). Where (roughly) will the boat be set loose (hours of sun per day)? What season (summer/winter above the arctic circle is way different than at the equator)? If you have gear above the solar panel, power output will drop (any shading "kills" the output of solar electric panels). Will the panel be horizontal, at an angle, vertical? If not horizontal or if there is shading, will the panel be (somewhat) pointing at the sun during the day?

Will you be remote monitoring? Will the "local brains" decide when to power the motor/sensors? If it drifts for 4 days, is that OK? etc...

You will not need an MPPT controller for a small/single panel system. MPPT controllers usually have more features (computer communications/programmable) and in sub freezing temperatures they can "get more power" from a solar panel--But if you are towards the poles in freezing weather, there is not much sun anyway.

To figure out how fast the solar panel will recharge, really need to know how big the battery bank is (type of cells) and how much you will discharge it in one day.

I think I am overthinking this... the boat is set loose one day, then hauled back in to recharge. It is possible that you may be better off just setting up a charging station on the trailer/dock and/or use a small Honda eu1000i or eu2000i genset if you need it recharged for use in the next day or two.

-Bill "just guessing" B.

Dave Angelini · October 2016

I did not see anything in the OP's post about critical so to me this is like a weather balloon, it is expendable and can be replaced.
I do think your idea of doing this at the dock is best. The battery calculation, then the battery size & type, then the charging.
A marine rated group 27 liquid lead acid or an AGM or GEL battery is easily available and easy to charge.

Marc Kurth · October 2016

I have a customer who deploys buoys in the arctic ocean. The hull is cleverly designed to ride-up on the ice instead of getting crushed by it. But they sent new buoys out every year "because of the cold" before they called me for help. They had convinced themselves that lead-acid batteries just couldn't stand up to the environmental conditions.

A simple re-design with a bit more PV on multiple angles, off the shelf Morningstar charge controllers, lots of silicone sealant and higher quality AGM batteries changed their world. We have hit the 4rd year of recovering the buoys during the thaw, instead of blowing them off. The dollars that they are saving would support me nicely for the rest of my life.

Marc

jonr · October 2016

...Li Ion cells are "protected" which means that they disconnect if the are operated at too low of state of charge (low cell voltage). Once the protection "trips", I think the cell is "dead" forever.

My experience is that they have a diode that allows charging even if they have been over discharged.

mike95490 · October 2016

Li cells cannot be reliably charged below 0°C, so the only choice is now AGM, which should function to about -35°F before they freeze. (75% charge remaining)

Image: https://us.v-cdn.net/6024911/uploads/editor/78/dx3vfkrufafr.jpg

Dave Angelini · October 2016

I never saw anything from the OP about cold temperatures in this thread.
I had Surrette wet batteries on my boat. They were designed to stay liquid tight and upside down for 2 hours with loads connected.
For months if you turned off the battery switch. Very forgiving of human distractions and on a boat at sea, there are many!

My latest insruance job was a guy on the other side of the Sierra who came home after being in the mideast for 3 months.
His house was burned down and being remote he did not really have it set-up for communications. His mistake!
When I looked at the house blueprint there was a battery room 4x6x8 feet.
The installer had been told that AGM batteries did not need ventilation. Possible ligtning or a bad controller but impossible to tell.
This is very common bad knowledge in the battery industry.

The installer then went out of business and a very sad ending. Be careful out there!

Marc Kurth · October 2016

Dave Angelini said:

I never saw anything from the OP about cold temperatures in this thread.
I had Surrette wet batteries on my boat. They were designed to stay liquid tight and upside down for 2 hours with loads connected.
For months if you turned off the battery switch. Very forgiving of human distractions and on a boat at sea, there are many!

My latest insruance job was a guy on the other side of the Sierra who came home after being in the mideast for 3 months.
His house was burned down and being remote he did not really have it set-up for communications. His mistake!
When I looked at the house blueprint there was a battery room 4x6x8 feet.
The installer had been told that AGM batteries did not need ventilation. Possible ligtning or a bad controller but impossible to tell.
This is very common bad knowledge in the battery industry.

The installer then went out of business and a very sad ending. Be careful out there!

You are correct, temperature was not mentioned as an issue I was simply sharing some experience about a rough duty application in a salt water environment using an off-the-shelf charge controller.

Didn't mean to derail the thread........

Solar Charge Controller for Special Project on the Ocean

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