Solar power ventilation

[jmeny]

Hi all,

I have a boat with extreme mold/mildew issues due to poor ventilation. I've looked into various brands of solar ventilators (nicro, marinco, etc) but based on their across-the-board terrible reviews have decided not to go that route.

I saw what looked to be a good idea that someone had done on another forum using computer fans as ventilation, as they move more air and draw very little amperage. I'd like to go this route but would like the fans to run continuously off their own dedicated battery, while maintaining said battery via a solar panel. I'm not real savvy with electrical at all, so bear with me if I'm way off track here.

The main question: What size solar panel would I need to properly maintain my battery while these fans run 24/7?

What I think I know (please let me know if anything I say is wrong)...

I will run two fans (let's assume 0.25 amp draw for each, so a total of 0.5 amp draw)
0.5 amps * 12 volts = 6 watts (average load current)
6 watts running continuously for 24 hours - 6 * 24 = 144 watt daily load

My existing 12V battery states a reserve power of 25 amps for 90 minutes.
I guess this means my battery has 37.5 amp hours?
So 12V * 37.5 Ah = 450 watt hours

Now for the panel - from what I've read, you should assume you get about 5 hours of the rated wattage daily
So I'd need the panel to generate 144 watts minimum over 5 hours
144/5 = 28.8 watt panel
I assume I would want to maybe double that to account for cloudy/rainy days when the draw would exceed the recharge?
So would a 50 watt panel do the trick for my purposes? 50 watts * 5 hours = 250 watts generated daily

And I guess I would just wire the panel and the two fans direct to the battery? Not sure if there are any other components I'm missing here...

Does this make sense or are there better alternatives? Recommendations on panels? A solar panel that I could run these fans directly from would be ideal, even if they could only run for a few hours after dark on stored energy...

Any other ideas/comments/suggestions are much appreciated, feel free to tear this apart!

Thanks,
Joe

 

[Silvertip]

Let's look at the power consumption issue first and how it relates to your battery numbers. Reserve capacity is actually the amount of time the battery can deliver (in your case 25 amps) over a given period of time (in your case 90 minutes) before it actually falls out of that capability. It doesn't mean the battery is dead. It merely means it cannot deliver 25 amps any longer. So lets run some numbers. Lets use 1 amp fan draw per hour for simplicity. Since the battery doesn't need to deliver 25 amps, but rather only 1 amp continuous, that means the load on the battery is 25 times less so theoretically the battery could drive those fans for 2250 minutes (25 x 90 = 2250). 2250 minutes is about 37 - 38 hours. Now for the solar panel issue. First, understand that these things are targets for thieves so keep in mind that fact and how secure the boat is. Solar panels are available in a number of sizes and capacities as you already know. Price and size varies according to "output capacity". A 50 watt panel delivers approximately 3.5 amps/hr depending the voltage used to calculate that current. So while charging, the panel would be delivering roughly 3 times more power to the battery than is being consumed by the fans. So what you have proposed will work. The only missing item would be the charge controller but your panel may come with one. Charge controllers prevent over charging the battery by shutting off the panel when the battery is fully charged.. Let us know how this works for you.

 

[jmeny]

Thanks for the reply, this is great info. Couple of follow up questions, if you don't mind.

Not sure if I'm allowed to post links to products here, but I'm looking at a 50W panel with charge controller that seems to fit the bill. I'm a little hesitant though - I don't know why everyone wouldn't go this route considering it seems so much more economical and reliable...

This panel claims to have a current MPP (maximum power point, from what I understand) of 2.91A. So this means that, under ideal conditions and panel positioning, this is the maximum amperage it would deliver per hour? And I assume that positioned flat on the roof of a boat is not perfect positioning, so it will probably produce less amps for me than is spec'd. So let's say I really get 2A/hr out of the panel, that would only produce 10A for me over the course of the day (5 hour assumption). Now if my fans are drawing 12A daily (0.5A/hr), wouldn't this lead to a slow drain of the battery? Or am I really overthinking this and the panel will produce more than 10A?

Also, this charge controller that it comes with is something I'm totally unfamiliar with. It appears to act like a bus terminal, but I just want to be sure. It has + and - terminals for the battery, the panel itself, and what appears to be an accessory of your choice. If I were to wire the fans to the accessory terminal screws on the charge controller, would they only use solar power while the panel was producing electricity and then switch to the reserve battery at night?

Last question, I swear! This panel only comes with a 3' wire, which will be way too short. I assume I can just add the length of wiring I need via butt connectors without any issues, right?

Thanks!
Joe

 

[Silvertip]

Where are you that you only have 5 hours of sun? Yes you can add wire - within reason. Voltage drop occurs as length increases. The fans are always powered from the battery. The panel and charge controller charge the battery. The panel passes it's output to the charge controller. The charge controller regulates the charging process to prevent over charging.

 

[jmeny]

Ok, thanks again, it seems like I'm being overly cautious sizing it at 50A and it should work ok. I think I'm ready to tackle this, I'll let you know how it goes. I'm in Maryland, but I was using a 5-hour figure based on information I've read about sizing panels for expected output. Below is some info I got from BoatUS.

"Expect average output to be the equivalent of about five hours of rated output per day. That makes the expected daily output of a five-watt panel about 1.65 amp-hours (5 x 0.33)."

Best,
Joe

 

[bruceb58]

Where are you that you only have 5 hours of sun?

What he likely meant was 5 "equivalent" hours of sun. You can have sunlight for 12 hours and only get 5 equivalent hours of sun.

 

[Silvertip]

OK -- got it. The size and type of boat you have will dictate how much air you need to move to handle the humidity. These fans don't draw much power but then they aren't very big fans either. Fan size may alter your numbers considerably which take us to one of your earlier comments. One of your earlier questions was regarding why solar power was generally discouraged in this forum. Fact is it is NOT discouraged for your requirement. Where solar is not practical is in high current applications. Many folks feel as long as you have a solar panel you could power a house. That obviously is true only if you have a solar panel that's the size of the house itself. You would also need a huge battery bank and a pretty stout charge controller. Another example is many boaters feel solar would be an ideal way to keep a trolling motor battery charged. Remember the 25 amps for 90 minute reserve numbers you quoted in your first post? Consider even the smallest trolling motor requires more than 25 amps when run wide open. It would take a couple days at full sun to replace the current used in just one hour with the panel you are looking at. Now consider fishing all day with that motor (factoring the on & off time) and you should see why solar is not the answer in that scenario. You could add one more device to the system you are looking at and that would be a timer or humidistat. A timer would let you set fan on and off conditions. The humidistat could allow setting the fans to turn on at a specific humidity level. Cycling the fans can greatly enhance run time. But I would certainly try the system without it. One other addition would be to add the fan battery to the boat electrical system so that battery gets charged under way. Let the engine alternator do the "heavy lifting" and let solar play catch up as needed when docked. There is ample information in this forum about how to add an auxiliary battery to the boat electrical system. As another option, sail boat owners often use wind generators to keep batteries charged. You could even use one of those in conjunction with the panel. Yup -- sophistication drives up the cost. No free lunch when you own a boat.

 

[jmeny]

More great info. I did consider running these with a timer, but figured I would try them without first. Hadn't thought about a humidistat, that's another interesting idea I'll have to look into. At a minimum, I do plan to hook each fan to a dedicated switch so they can be turned off manually if I want.

100% agree about your comments about running homes, trolling motors, etc. Unless you want to spend a whole lot of money, I think these panels are really most practical for powering small devices. The only hesitation I had about hooking into the house battery would be that, if these fans do end up drawing down the battery, I'd have to worry about not enough juice for the ignition system if I had been away a while.

Last thing that I thought was very interesting was the amount of air these computer fans move. They're rated in cubic feet per minute instead of cubic feet per hour. The ~$180 marinco units move 600-1000 cubic feet per hour, based on whether you get a 3 or 4" model. The $8 arctic computer fans I plan to install each draw 0.2 amps and move 77.3 CFM, over 4600 cubic feet per hour for a single fan. And even with the cost of the panel and charge controller, this should cost me around $100 while also providing the ability to run/charge other small accessories.

We'll see if this works, really appreciate all the feedback.

Joe

 

[Silvertip]

A four inch computer fan may work quite well. Here in Minnesota winter fishing through the ice is akin to having a cabin (although small) right on the lake. Any type of heater in a fish house creates a layer of stratified air at the ceiling so I used such a fan mounted on a six inch PCV pipe suspended vertically between the holes in the ice. The warm air being forced down over the holes kept them ice-free and you could fish in a tee shirt. Granted, the house was only 6 x 8 feet but you are simply moving air, not trying to keep a fish house at 65 degrees in sub 20 degree or colder weather. A small battery powered the fan. No need for a charger as the battery was charged at home.

 

[fishrdan]

Any resistance to air flow will reduce the air flow from those fans. If you have a tight fitting cover with limited air flow, get "high static pressure" fans, their fins are wider to help push air against resistance.

Computer fans can have sharp edges, so be sure to put a grill over the exposed side(s), so you don't cut a finger

FWIW, I have an old Delta 120MM server fan, (noisy, high RPM, draws 2-3 amps) that I prop under the boat cover when the boat is soaked, and I need to dry it out while covered. It's attached to a 2' section of pipe and runs off a 120VAC/12VDC power supply. Does a nice job of drying out the boat in a couple of days, just have to leave all the hatches open.

 

[Scott Danforth]

This is a perfect use of a solar panel in a boat.

However I would use a few fans to circulate air, two on the intake, and at least one on the exhaust. I like the idea of a PVC duct on the fan to allow you to direct the air where needed.

 

[jmeny]

Glad to hear it sounds like I'm on the right track here! My buddy and I were talking about trying out ice fishing, would love to give it a shot someday just to try out something new.

Fishrdan, hadn't even considered the fan blades being sharp, thanks for that advice! Looks like guards are an inexpensive addition for peace of mind, so I'll definitely order a couple. Unfortunately I already bought the fans I'm going to try, we'll see how they do. If they don't move enough air I'll look into the high static pressure fans as you suggested. You're right, those fans have 7 wider blades as opposed to the others which seem to have 9 blades. Maybe since my cover is canvas there will be enough air exchange.

Scott, currently my thinking is that I'll have one fan blowing from the bow of the boat (it's a covered bow where the anchor is stored and moisture can build) and one fan exhausting out a window. I would love to try the idea of rigging another with a PVC duct from the bilge area as well, but need to make sure my panel will keep up with the daily amp draw first. Great ideas.

Cheers,
Joe

 

[jmeny]

Hey all,

Got another quick (possibly dumb) question for you. Fans came in the mail today. I had planned to just cut their 3-pin connectors off and splice new wire in to connect to my battery. My concern is that the wire on these fans is really small stuff, maybe 26AWG - definitely smaller than anything I've ever worked with. I don't want to run that small of wire to the battery (~10' run), just feel like it would be easily broken on a boat.

I was hoping to connect to something heavier, say 18AWG, but didn't know the best way to do that. Figured crimping butt splices to something that small with diff diameter wires is probably a bad idea, and I have zero experience soldering. Also not sure if differing gauges would cause any issues with voltage drops, resistance, etc (not real electrical-savvy, in case you haven't noticed).

Anyways, I'm wondering if it would be best to buy short 3-pin quick disconnects/extensions that have the heavier gauge wire and splice into them for my runs. Or if there's an easier way, I'm definitely ready to be enlightened!

Appreciate the help,
Joe

 

[fishrdan]

I would solder the connection since the fan wire is so small, difficult to get a good crimp between that and 18AWG. While not the "right" way to do it by any means, you could fold over the 22AWG wire a couple of times, to fill up the butt connector, then crimp. Heat shrink tube the connection, to protect it against moisture/corrosion.

I would glue (silicone, marine sealant, etc) the wire connections to the fan frame, and wire-tie the 18AWG wire to the fan frame, so any pulling is being done against the 18AWG wire.

One of the 3 wires of the fan won't be used, yellow if the wires are color coded. If it's not color coded, + is the center wire.

 

[jmeny]

Sounds like a plan, thanks. Figured out the + by trial and error, good to know that's the norm when not color coded.

Joe