Run time of Powered Vent on a Group 27 Battery?

Hi,

Running one fan @ 4 amps will take the battery down to 50% state of charge in 14 hours. If I add another 2 amps for parasitic loads, that number drops to around 8 hours.

Recharging with the truck will take many hours.

I would run the cords myself. You may wish to power only the converter. Mostly they may work well down to 102 volts. An Iota will still work at 95 volts.

trkoffroad wrote:
The RV has two Surflo Comfort Air powered vents, and I was wondering how many hours I could run one of them in the evening from a Group 27 battery before its flat?
If I run the fan on less than full power is it drawing less 12VDC power, or is the controller drawing any the fan doesn't?
Surflo says the fan draws 4a max.

There is electricity in the area, but I'm thinking it will be too far to run an extension cord to a charger for a daytime recharge.

With the one battery you have 50 amps usable to 50% state of charge. The refrigerator even on propane will need about 0.3 amps each hour when turned on to run the control panel and ignition. That may add up to 20 amps for the weekend alone. Using the water-pump, a light or two, can easily add up amps used.

I would suggest bring along a multi-meter to check voltage at the battery-terminals. You never mentioned the age of your battery, but it had better be reading 12.6 volts shortly after starting to camp (any reading over 12.7 volts is surface charge and will drop quickly after some battery usage).

The battery will read 12.42 volts @ 80% charge; 12.32 @70%; 12.20 @ 60%; 12.06 @ 50%; 11.90 @ 40%; 11.75 @ 30%; 11.58 @ 20%.

Your fan might cause the battery to read 0.1 to 0.2 volts low while running. Take a reading with it on. Turn it off and take another reading then. I would check your battery reading around 8:00 pm the first night to see where you stand. If you are not at least 12.50 volts (90%), your battery does not hold full capacity and you will have to cut back on usage.

If you do run the fan, check the battery voltage in the morning to see what your remaining battery capacity is. Base any future usage on the battery charge at that time.

Run your fan on low when you need to have the breeze for comfort. My turbo maxx is rated at 1.4A on low speed IIRC so it's reasonable to assume your fan is probably going to draw 2A or less. Most likely you'll be ok for a couple of nights, but beyond that all bets are off.

I got a 75W panel and basic Morningstar controller recently; with wiring and all I have less than $150 into it. I hacked a 6' extension cord and used the plugs in my wiring. Now I can set my panel in a sunny spot 50' away if I want to, and use my usual 50' extension cord to reach back to the controller that I'm plugging into the trailer's pigtail (the one that would otherwise run to the tow vehicle).

Even in shade, a solar panel will provide =some= charge. Don't discount it.

Lyle

trkoffroad wrote:

joebedford wrote:
Fridge on propane still needs 12V to run control circuitry.

Figured it did since it's lights are on when we are traveling. Also figured it was insignificant compared to interior lights, water pump etc but I don't actually know the real draw.

As does the water heater when operated on LP......... But IIRC, the fuse on an Atwood water heater control board is only 2 amps, so not a lot of power demand there.

FWIW: I dry camped earlier this year (3 days) in the Ocala Nat'l Forest. I had two Group 27 12v batteries in parallel. Even with management of the lighting, exhaust fan, etc. the batteries were down to approximately 60% of their capacity when we left to go home; think 50% is considered discharged on a deep cycle battery, but others here may have more info.

joebedford wrote:
Fridge on propane still needs 12V to run control circuitry.

Figured it did since it's lights are on when we are traveling. Also figured it was insignificant compared to interior lights, water pump etc but I don't actually know the real draw.

trkoffroad wrote:
Fridge and Water Heater will be on Propane.

Fridge on propane still needs 12V to run control circuitry.

Sounds like we might be able to make it a couple of nights.

Running the powered vent on a lower speed might get it down to 2amps.
We will keep light and water (pump) usage to a minimum.
CO detector is AA battery only, Propane Detector is 12v to the coach battery.
Fridge and Water Heater will be on Propane.
Its summer so won't be using the furnace.

I'll check the battery voltage with a DMM after the first night, and charge with an AC charger if I can get extension cords to reach or the Truck if I have to.

Unless you specifically rewire your trailer to power just the fan with the battery you will have other things that are powered while the battery is on. IE: carbon monoxide, propane leak detectors, radio memory and others. It has been my experience that just these things will kill the battery while the trailer sits. Two nights on one battery may max out your battery without running the fan at all depending on if you run the furnace, how many lights you use and so on...Everything in the trailer runs on 12 volts except your refer, water heater and television...

B.O.

If your battery is fully charged you may be OK. A sears group 27 is rated at 105 amps - 20 hour rating. So about 5 amps/hr for 20 hours. The higher the current draw the faster the battery is depleted. If it is a variable speed fan then the max current draw should be at the highest speed. I would run only one fan at a time.

Remember there are other items drawing DC power from the battery. Refrigerator, CO detector, TV amplifier.

Our bedroom ceiling fan has a thermostat so I set it and it turns off at the temperature we want it to. We also set it to pull air out of the RV.

I installed a second battery in our rig - both are in a battery box designed for 2- 6 volt batteries. We only dry camp twice a year at the racetrack - but having the second battery gives me some piece of mind.