Typhoon solar setup for trolling motor

[Ben Miller]

I've been using a 55 lb trolling motor to get to/from my mooring and out of the marina for a few years now. I'm happy with it as a source of propulsion, but not so pleased with having to haul a 50 lb battery back home to charge it every time it gets used (I killed my first battery by leaving it in a semi-discharged state for too long). So after a few years of hemming and hawing, I'm adding some solar charging to the boat so that I can leave the dang thing on the boat all summer.

I've never been able to find good guidance for sizing a solar panel for this particular setup. I don't have any other load on the battery, so no slow drains. Just the occasional heavy draw--50 amps at full throttle--for a short period of time. So I probably went a little oversized on the system. Overkill is unattractive to me, but on the other hand 1) I won't have to worry about not getting a full charge in a reasonable amount of time 2) I'll be self-sufficient, even if I went on a several-day trip and had to charge a phone, run the motor longer than usual, etc. 3) I could someday move the system to a bigger boat 4) This size of panel doesn't really cost much more than something smaller.

All that being said, here's what I'm planning on installing:

The battery--a group 27 deep cycle lead-acid battery--will live in a plastic battery box under the cockpit. I'll run some 8 AWG wire under the cockpit sole to a round access hatch that's already installed in the aft end of the cockpit above the tiller. I'll install a socket in the hatch cover (I like this better than drilling holes in the actual boat) and then a plug on the end of the trolling motor wires.

I got a Victron SmartSolar 75/10 MPPT charge controller which I'll probably mount out of the way in one of the quarter berths. I've got a 50W rigid panel on the way with a 20' cable. Once it gets here I'll find a good place to set it and rig up some kind of mount that will keep it in place but also be easy to remove and stow when I'm sailing. Maybe the motor mount would be a good place! I'll probably just run the cable through the companionway rather than a more permanent install.

Once all that is done I'll add a 12V socket somewhere so I can recharge the handheld VHF.

That's the plan. I'll post an update when I'm done. I'm curious if the board has any thoughts or feedback.

[rjnale]

Thanks Ben!
I'm very interested in your final design. I have never been able to figure out the solar panel charging numbers.
I've had advice that varied widely and never felt I could trust.
Plus the solar panel tech is so much better than just few years ago.
I also am using a 50lb thrust trolling motor with deep cycle battery setup.
I sail a Typhoon daysailer on an large inland lake. Works great. Only time an issue is in heavy wind if the bow falls off. Just not enough power to bring it back. I do a fast 360 spin and back on course.
I'm going to look up your equipment online.
Please post final design and pics.
Thank you

[Ben Miller]

Not done yet, but things are starting to come together. I'm not a pro and the more I read, the more confusing things get, but I'm forging ahead.

I got the 50W panel from Renogy. Seems like a decent piece of kit.

I also ordered some accessory cables from them also: 20' 12 AWG cables with MC4 connectors to hook the panel to the charge controller, and 8' 12 AWG cables to connect the charge controller to the battery. Their shipping department must be a little hectic right now, since they sent me two sets of the first item and a set of what appear to be 8 AWG cables (the spec on the jacket is "1x10mm2") rather than the second item. It's all usable to me, though, so I haven't made any fuss. I had some stranded 12 AWG lying around that I'm using for the controller-battery connection and I'll use the 8 AWG they sent me as extension cables for the trolling motor.

I have this all wired up in my backyard and it seems to be running just fine. In full sun without any attempts to aim the panel I'm getting 30-some watts out of it, which is right in line with my expectations. Victron offers two versions of their controller, one with built-in Bluetooth and one without. I spent the extra for the BT connection and I'm glad I did. Their apps seem to work well and provide good insight into the performance of the system.

[Ben Miller]

I wouldn't say I have the setup finalized, but it's all assembled and working. I "installed" the charge controller in the starboard quarter berth with some self-adhesive velcro (the heavy-duty kind). The battery box lives under the cockpit sole. Some 8 AWG leads run aft under the sole and terminate in an Attwood trolling motor socket. The motor itself has the corresponding plug, which makes it easy to attach/detach.

[John Stone]

As long as you’re happy and it works to your satisfaction then you hit a home run.

I am not an expert but here is what I have learned based on my own research and personal experience on my boat. Generally speaking, divide the panel’s max output voltage, for most 12v panels generally about 17v (should be written on back of the panel) to get amps per hour in full sun. For your boat 50 divided by 17 equals about 2.9 amps per hour. Inexpensive panels typically will provide less percentage wide. So, in 8 hours of full sunlight and no shadows, clouds, or poor angles you could in theory collect 24 amps per day. 15-18 will probably be more accurate. Remember, for lead acid an AGM no more than 50 percent max discharge so with a 100 ah battery you can discharge 50 amps. More than that you are shortening the life of the battery.

What you want is to be able to completely recharge your batter to at least 12.7 volts...a little higher is better. So you want the panel to have enough watts that it gets fully charged before you draw it back down again or at least so you’re not constantly drawing on your battery and it seldom (often?) does not get fully recharged.

Boats that have large battery banks, like 400 ah banks (or even bigger), need a lot of panel watts to get those batteries recharged. Or run the engine. Or use a wind generator. Or all the above. We need to get our battery fully charged if we want it to last.

I have run a 30 watt semi flex panel, a GV5 MPPT (5 amp controller) and a 100ah AGM for 5 years on the Far Reach as my only source of electrical power or charge capability. It’s worked pretty good. That includes almost 10,000nm of offshore sailing and about 16 months of live aboard.

Ideally you want the MPPT controller to be matched to the panel. My set up can only produce about 1.7 amps per hour. So the GV5 works. In fact, since you can only produce about 3 amps per hour on your set up the GV5 is better suited for you too. Don’t know if it matters if your controller rated at 10 amps and is higher than you need has any negative consequence. I just don’t have that kind of experience.

I typically use about 5ah per day, which is about 10-20 times less than most folks on a similar sized boat.... Anyway, I can typically recharge my batter to 100 percent in three hours in good sunlight. If I used more amps per day then I need more solar watt panels. And in fact, now that I am installing LED nav lights (I used kerosene nav lights before) my ah usage will double offshore to 10 ah per day. So I may add another 30-50 watt panel to make sure I can get that battery fully recharged every day...if there is sunlight.

So, my thoughts are if you are using 50 amps a day on a 100 ah battery you have two issues. The first is your bank is not big enough and second is you need more watts unless you are only using those 50 amps once ever three or four days and your battery is able to get fully recharged before you discharge it again.

Again, my experience with solar panels is limited to my system on my boat.... if your system is working fine for you and meets your expectations then that is all that counts.

[Ben Miller]

Thanks for summing up the ground rules, John! I am also not an expert, but from what I've read you're right on about lead-acid capacity and recharging and panel capacity.

Fortunately, I'm not using 50 Ah a day. My trolling motor can theoretically pull 50A at full throttle, but I only run it for maybe 10-15 minutes total per trip in and out of the marina. So we're talking more like 8-12 Ah. That's a back-of-the-envelope estimate, and part of the problem is that I don't know exactly how much I'm drawing, and therefore how much I need to replace. This is apparently a pretty unusual use case, where I'm drawing no power 99% of the time, and then there are these bursts at 50 A--pretty much the opposite of your situation, even if in the long run we might use a similar number of Ah.

My hope is that my system will generate enough to recharge the battery in a few days. That depends on the sun, obviously, but sunny days are pretty reliable here in the middle of summer.

Point taken about the sizing of the charge controller. This is the smallest model offered by Victron, and I chose it for a few reasons: I read good things about the brand; I wanted MPPT to maximize the charge I could get with a smaller panel; unlike the Genasun, it will work with both lead-acid and lithium batteries, if I ever want to upgrade my battery bank; and lastly, I like being able to easily get charge metrics out of it without having to buy a separate battery monitor. This whole exercise is kind of an experiment, and that information will tell me if my battery is getting back to full charge and how quickly.

I took the boat out last Saturday, so this week is my first real-world run of the system. If I can get out to the boat this weekend I'll report back on what I see.

[John Stone]

Thanks for summing up the ground rules, John! I am also not an expert, but from what I've read you're right on about lead-acid capacity and recharging and panel capacity.

Fortunately, I'm not using 50 Ah a day. My trolling motor can theoretically pull 50A at full throttle, but I only run it for maybe 10-15 minutes total per trip in and out of the marina. So we're talking more like 8-12 Ah. That's a back-of-the-envelope estimate, and part of the problem is that I don't know exactly how much I'm drawing, and therefore how much I need to replace. This is apparently a pretty unusual use case, where I'm drawing no power 99% of the time, and then there are these bursts at 50 A--pretty much the opposite of your situation, even if in the long run we might use a similar number of Ah.

My hope is that my system will generate enough to recharge the battery in a few days. That depends on the sun, obviously, but sunny days are pretty reliable here in the middle of summer.

Point taken about the sizing of the charge controller. This is the smallest model offered by Victron, and I chose it for a few reasons: I read good things about the brand; I wanted MPPT to maximize the charge I could get with a smaller panel; unlike the Genasun, it will work with both lead-acid and lithium batteries, if I ever want to upgrade my battery bank; and lastly, I like being able to easily get charge metrics out of it without having to buy a separate battery monitor. This whole exercise is kind of an experiment, and that information will tell me if my battery is getting back to full charge and how quickly.

I took the boat out last Saturday, so this week is my first real-world run of the system. If I can get out to the boat this weekend I'll report back on what I see.

Ben
My fault—I misunderstood. Sounds like your system is sized just right. Good call on the combo controller/monitor. They didn’t have that when I put my system together. I typically like separate systems so one component going down does not effect others but my situation is different than yours. Your choice makes a lot of sense. I think Victron is pretty good stuff. I have their V 700 monitor and I am happy with it. I’d be interested to hear more about what you learn as I’m still trying to get smarter about solar. I have some decisions to make up ahead....

[Ben Miller]

FINALLY made it out to the Typhoon for a sail, which means I also was able to grab the charging history off of it. (Side note: The Bluetooth app makes it very easy to export this data, which I love.) A little fiddling in Numbers and here's what we get.

Charging history

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For context, I went for a sail on 8/1. Used the trolling motor to get in and out of the harbor. I got back to the mooring around 2:00 pm and set out the solar panel. 8/1 was just a partial day of charging and the charger was in bulk charging mode the full time. On 8/2 it spent some time in bulk mode, then absorption, and then moved into float, which I think means that at that point the battery was fully charged. That's exactly what I hoped for--a full charge in a day or two.

The yield history tells me (I think) that once the battery is full the charger limits its yield to around 40 Wh a day. The max on the graph would be about 7.5 Ah (90 Wh/12V). There was a day earlier in the history (not on the graph) that yielded 11.6 Ah.

Yield in Watt-hours

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Lastly, this graph of solar radiation from my weather station gives some idea of how sunny each day was.

Sun history

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[Walter Hobbs]

Thanks for posting.
Great info for those of us who may be considering solar in the future. Batteries on my 27 only went dead once due to my carelessness, but solar may have kept them alive. Food for thought.