There are a lot of different 12VDC vent fans on the market for RVs, campers, and vans. These fans can range from super simple 3 speed fans that just move air, to temperature controlled, variable speed units with automatic rain covers that open and close with the push of a button.
Whatever fan you choose, you'll want to make sure that you know at least three things:
- How much current the fan draws at different speeds and settings.
- How you're going to use the fan. Are you going to run it all night while you sleep? Use it just a few hours in the afternoon? Only turn it on when the dog smells? (LOL)
- How your intended use and current draw will impact your vehicle's battery life.
Measuring Current Draw of 12VDC Ventilation Fans
There are a few different ways to measure current draw, but the best way is to measure the draw at your vehicle's battery. That way, you can account for current loss between the fan's installation point and the battery. This article on FlashOffroad.com offers a good, quick explanation of measuring current draw. All you need is a multimeter (digital is easiest).
- Install the fan (or at least install the run of wiring you're going to use to power the fan)
- Turn the fan on to the lowest speed, then write down the current draw (in amps)
- Turn the fan on to the highest speed, then write down the current draw (in amps)
To be thorough, you can also record current draw at all fan speeds and settings. However, what you'll find is that the current draw if relatively linear...if a fan draws 0.5 amps at the lowest speed and 2 amps at the highest speed, you can split the difference to estimate current draw at the medium speed.
Once you have your current draw data, it's time to figure out how you're going to use the fan.
NOTE: If you're going to run other accessories off your vehicle's battery system for extended periods - like a portable 12VDC fridge, interior lighting, etc. - be sure to measure the draw of these accessories as well.
How Will You Use Your Ventilation Fan?
If you've purchased a basic fan that must be turned on and off - and if you plan on sleeping in your vehicle in the summer months - odds are good you're going to turn on your ventilation fan and leave it on all night (at least once). It's just too easy to fall asleep with that fan on, so you want to plan for as much as 12 hours of continuous use.
If you've purchased a fan with automatic temperature control, it's much less likely that you'll have to run your fan all night because the temperature control will take over at some point and shut the fan off. Still, nighttime temperatures don't always fall quickly, so an automatic fan could run for 6-8 hours continuously. Also, if the temperature is set very low, the fan could run all night.
Finally, if you're going to be in your vehicle waiting out a storm, it's great to be able to run that fan for a few hours without worrying about battery life. Basically, if you want to plan for the worst, you want to plan for 12 hours of continuous use.
Adding Up Your Power Needs
If we assume that your ventilation fan pulls 1.2amps at a medium speed setting, and if we assume 12 hours of use, here's the battery capacity math you want to use:
12 hours x 1.2 amps = 14.4 amp hours of battery capacity
However, in order to maximize battery life, you want to buy a battery that has more than double the capacity you need. That way, you won't discharge your battery more than 50%, thus maximizing the battery's life. In our sample calculation, our 14.4 amp hours of capacity should be provided by a battery with at least 30ah of capacity.
Finally, there are other devices to consider:
- 12VDC portable fridges use 1-2 amps of current at 12VDC
- LCD screens and laptop computers can use 2-3 amps of current at 12VDC
- LED lights, cell phone and tablet chargers, and other small draw devices use 1 amp or less at 12VDC
Using The ArkPak To Power Fans, Fridges, and More
The ArkPak is a portable power source that can easily support a vent fan, a portable fridge, lighting, battery chargers, and more. It uses any standard 12V deep-cycle battery (group 31 or smaller), which means you can easily find a gel or AGM battery that will supply 100ah of capacity that fits inside the ArkPak. If you look at "wet" batteries, you can find 130ah of capacity.
Powering all your accessories off the ArkPak is easy:
- First, when you install your ventilation fan, add an inline cigarette lighter plug (male and female) to the 12V harness. That way, you can "unplug" your ventilation fan from your vehicle's electrical system and plug it into the ArkPak whenever you need power for an extended time period.
- Next, make sure to charge your ArkPak from your vehicle whenever your engine is running. The included DC-DC charger can restore a completely discharged 100 amp hour battery in about 18 hours, or a 100 amp hour that's 50% discharged in about 9 hours. If you drive all day and camp at night, your vehicle's electrical system should keep the ArkPak completely charged for nighttime use.
- Connect all your accessories to the ArkPak every night when you shut your vehicle off. It will provide power all night long and - depending on the current draw - well into the next day. In fact, if your current draw is low enough, the ArkPak can run a fridge and a efficient fan for days.
If you stay at a campground or motel, you can also plug the ArkPak into a standard 110VAC outlet to charge it overnight.