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Discussion Starter · #1 ·
Who here is good at battery capacity math?

I’m going on camping trips in the southwest next week and for warm weather sleeping I’ve got a fan to run in the tent. I’ll plug a 12v socket converter onto the battery terminals and use a small power inverter to run the fan at night. On low speed it has to be less than 10 watts draw, if that.

How long can I run the fan before the battery is too low to start the engine in the morning?
 

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a 12v fan will be more efficient

you can buy an inline battery monitor/shutoff that you plug your 12v device into and it runs until battery is low, then shuts off to retain starting capability.

but whether you do it my way or your way (calculating and hoping) you should pack along a small jump box jic....
 

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The Nuclear Option
2015 Chevrolet Cruze LT 1.4L Turbo
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In order to calculate that, you'll need to know the minimum amperage required to start the car.

A 10 watt device would use ~0.83 Amps on a 12V system.

But I agree with @boraz , a jump pack would eliminate the need to worry. At least for most people.
 

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I know you are trying to run off the car but a typical RV dry camping setup would be twin 6V batteries in series as that will give more amp capacity. Twin 12s in parallel is a common setup as well.

These setups will last well past all night long pulling more power than just a fan. Your single battery should be fine.

But as suggested already, bring a fully charged jump pack.
 

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According to Google a 20 inch window box fan will draw 50 to 100 watts.


Solution B: For less than $30 you can get a small fan that runs on D cell batteries
 

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Discussion Starter · #7 ·
I will check out the 12v fan. How long is the cord?

The clamp-on thing for the battery has maybe a 2 foot cord so I'll have to use the little plug-in inverter and then an extension cord to get the 120v output to the tent where the fan can be plugged in.
 

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I will check out the 12v fan. How long is the cord?

The clamp-on thing for the battery has maybe a 2 foot cord so I'll have to use the little plug-in inverter and then an extension cord to get the 120v output to the tent where the fan can be plugged in.
doesnt matter how long the cord is

they sell 12v extension cords
 

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12V cords are limited to approximately 10 feet.

In concerns for 110V length limits and cable sizes needed depend on what load you are trying to power.

The 14 and 12 gauge extension cords are among the most popular used types of cords. While there are different gauges, including the 16 and 10 gages, 12 and 14 are the most common. However, they carry different power amounts depending on the length of the cord in question. For instance, for a length of 25 - 50 feet, a 14 gauge cord will be great for 14-15 Amps, whereas the 12 gauge will work for 16-20 Amps.
For 100 feet, the 14 gauge cord works for 11-13 Amps, while the 12 gauge cord is best suited for 14-15 amps. If your cord is 150 feet long, the 14 gauge is best suited for 1-7 Amps, whereas the 12 gauge will support 8-10 Amps. This shows that the extension cord's length also plays a part in the power it helps safely.
 

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12V cords are limited to approximately 10 feet.

In concerns for 110V length limits and cable sizes needed depend on what load you are trying to power.

The 14 and 12 gauge extension cords are among the most popular used types of cords. While there are different gauges, including the 16 and 10 gages, 12 and 14 are the most common. However, they carry different power amounts depending on the length of the cord in question. For instance, for a length of 25 - 50 feet, a 14 gauge cord will be great for 14-15 Amps, whereas the 12 gauge will work for 16-20 Amps.
For 100 feet, the 14 gauge cord works for 11-13 Amps, while the 12 gauge cord is best suited for 14-15 amps. If your cord is 150 feet long, the 14 gauge is best suited for 1-7 Amps, whereas the 12 gauge will support 8-10 Amps. This shows that the extension cord's length also plays a part in the power it helps safely.
12v cords ARE NOT limited to 10'

rofl

its a 12v fan that draws half an amp
 

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Okay so the Amazon cords are 12 feet instead of what I said, approximately 10 feet.

Just because you can buy a longer cord does not actually mean you should use a longer cord. For any electrical system you want no more than 3% power loss or 0.36V on a 12V system. It is recommended to keep a 2% loss for 12V automotive systems. Based on wire size and amp load the max distance can be calculated then there is the whole ampacity rating of wire to deal with.

12V accessories tend to be small gauge wire so the ampacity is relatively small on them. Longer small gauge wire will heat up with amp load, any wire will heat with amp load.

The fan I linked to earlier has a 1 amp rating which means you can have about 35 feet of 18 gauge wire, only 15 feet total if its a 22 gauge wire. If the amp rating is lower then you can safely extend the wire but if its higher then it drops in length. 5A is 3 feet for 22 gauge, or 7.5 feet for 18 gauge.


You have to know your amperage load in order to determine how long the cord can be. And you cannot just take a larger cord and plug it on to the built in pig tail of the fan. You are limited to the smallest wire in the extension circuit.
 

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Okay so the Amazon cords are 12 feet instead of what I said, approximately 10 feet.

Just because you can buy a longer cord does not actually mean you should use a longer cord. For any electrical system you want no more than 3% power loss or 0.36V on a 12V system. It is recommended to keep a 2% loss for 12V automotive systems. Based on wire size and amp load the max distance can be calculated then there is the whole ampacity rating of wire to deal with.

12V accessories tend to be small gauge wire so the ampacity is relatively small on them. Longer small gauge wire will heat up with amp load, any wire will heat with amp load.

The fan I linked to earlier has a 1 amp rating which means you can have about 35 feet of 18 gauge wire, only 15 feet total if its a 22 gauge wire. If the amp rating is lower then you can safely extend the wire but if its higher then it drops in length. 5A is 3 feet for 22 gauge, or 7.5 feet for 18 gauge.


You have to know your amperage load in order to determine how long the cord can be. And you cannot just take a larger cord and plug it on to the built in pig tail of the fan. You are limited to the smallest wire in the extension circuit.
i literally linked a variety, you can choose 12-18awg, 3-25'
 

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Who here is good at battery capacity math?

I’m going on camping trips in the southwest next week and for warm weather sleeping I’ve got a fan to run in the tent. I’ll plug a 12v socket converter onto the battery terminals and use a small power inverter to run the fan at night. On low speed it has to be less than 10 watts draw, if that.

How long can I run the fan before the battery is too low to start the engine in the morning?
I wouldn't chance it with an inverter and all that. Personally I use a fan that charges with a usb cable and has battery in it. I take several charged batteries and/or plug into my lithium jump box. Leave our car out of the equation.
 

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According to Google a 20 inch window box fan will draw 50 to 100 watts.


Solution B: For less than $30 you can get a small fan that runs on D cell batteries
They sell these at Walmart in camping or fan section for around $20
 

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Search Amazon for Camping fan. They hang from top of tent, have huge battery packs, so they run 8-12 hrs and recharge via USB while you drive.
 
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