Wanted Enclosed Car Trailer

Looks like a good thread to pose a technical question. I, too, have measured temperatures up to 140* inside my trailer in the summer time. I installed a Maxxair powered vent, that will automatically close in the event of rain. Currently I run it off the winch battery. However, I would like to run it from a solar panel. The vent can draw up to 4.5 amps. I have a left-over battery from another project that is 18amp hours. What size solar panel would I need to run the vent during the day and into the evening (after the sun goes down)?

If the battery goes to zero volts during the night, will I end up killing the battery prematurely? What other potholes do I need to watch out for?

Thanks, in advance!

 

Why not simply leave it connected to the existing battery and add a solar panel with a charging controller to avoid overcharging it?

 

ok, but what size solar panel?

 

I wouldn’t expect too large. You don't need to offset the actual current draw of the vent because the battery is supplying it. You just need to replenish the battery... a trickle, 2 amps or so, should do it. The trickle will be a constant when the sun shines enough to produce and the vent draw will be incremental. Now, you may or may not want to size the panel to provide additional power for other things, that depends on your plans. Personally, I would compare basic solar battery chargers against a actual panel with a charge controller and determine which made more sense.

 

I just googled solar charger and there is a 12 volt, 20 watt unit with charge controller for like $50.00. That translates to about 1.7 amps, which should keep your battery charged and the controller prevents overcharging. I am just using this as a example. There are numerous options.

 

So, 1.7 amps would be enough to keep the battery charged with a 4.5 am draw?

 

The 4.5 amp draw is going to be in short increments, when the vent opens and closes, the 1.7 amp charge will be constant, as long as there is adequate light to generate power, so you should be fine. Just as a simple illustration, lets say you get 12 hours of daylight to generate 1.7 amps. How many times do you think the vent will cycle? I think it will cycle once the temp reaches the trigger point, again when it drops below the set point, I doubt that cycle would repeat very many times in a 24 hour period. Without knowing the exact cycle time and frequency of the draw, and the amperage rating of your battery, it’s impossible to be specific. A typical 600 cca boat and rv type battery has around 35 amp hours so it will take many cycles to deplete it without a charger. A healthy battery will regenerate easily. I bet that 4.5 amp draw is the max draw, like at start up anyways, not a constant. That’s how most electric devices function. They require the max at start up and taper off. That small solar charger is a pretty small unit. I just picked it as a sample. You can get larger ones that produce more power, but if the vent is the only thing you are going to task it with, it would be overkill and the power generated would just be wasted by the charge controller because your battery will not require enough to maintain the charge. Now, if there is a fan that runs while the vent is open, that’s a different discussion and a larger panel may be merited.

 

My sense is that the 4.5 amps draw is to turn the fan motor.

 

After replacing the latches with SS, I also added a bike alarm. I used this because it has it's own battery and therefore I didn't need to add a 12v battery for a car alarm that would be constantly drained. Need to research just how much a car alarm draws, maybe it's so little I shouldn't worry.

I 3D printed the gray bracket holding the alarm to the frame. Ty-wraps didn't work well, when I tried to tighten them the holes in the frame just cut thru them. It's IP65 rated for outside.

With this alarm you do have to open the case to change the sensitivity. $13.74
https://www.amazon.com/dp/B0B6J8QTN6?psc=1&ref=ppx_yo2ov_dt_b_product_details

Watch the 1min:23sec video to see how sensitive it is to movement, it could be better. I also discovered that it also detects sound as you will see.

 

If you want it louder they have a train horn that is scary loud. Looks like noise sets it off more than movement.

 

Found it! Caller Motohorn. Stock horns 30-50 db. Motohorn 130-150 db! It’s an air horn comes with compressor.

 

They would probably get me for murder after that horn scared them to death !!!