VERY Basic 12V Clarification

[aontkos]

I have a pretty basic question regarding 12V electrical draw. I am considering making a sunroof insert that houses two 12V fans that draw 0.3A. This should make camping out of the 4-Runner a little more comfortable in warm weather.

I am currently running an Optima YellowTop that has an advertised C20 capacity of 48Ah. If my logic is sound, then if I run two of these fans for 8hrs, then they've drawn a total of 4.8A from my charging system.

I am assuming that this is pretty minimal draw for a healthy deep-cycle battery. Is this correct? I would imagine that a short drive should be able to recharge the draw from running these fans and starting the truck.

Any insight is appreciated!

 

[RonJR]

Your math is correct, although the correct terminology is that the total draw after 8 hours would be 4.8 amp-hours.

My concern would be whether a .3 amp fan would really move enough air to be all that helpful. That's a pretty small fan - the kind of thing you'd find in a desktop computer. I'd think you'd want something that pulled 1 amp or more.

 

[aontkos]

Your math is correct, although the correct terminology is that the total draw after 8 hours would be 4.8 amp-hours.

My concern would be whether a .3 amp fan would really move enough air to be all that helpful. That's a pretty small fan - the kind of thing you'd find in a desktop computer. I'd think you'd want something that pulled 1 amp or more.

Thanks for the response. I am also concerned about the power of the 12V fans because they are exactly what you said- computer fans. However, I have two small clip-on fans that draw 0.3A and are about 7" and they push plenty of air. I just don't want to run these fans off an inverter all night, so something that can hook up directly to a 12V source is ideal.

I guess that raises another simple question- could two 1A fans be run all night without running into charging issues?

 

[RonJR]

Keep in mind that .3 amps at 120 volts is 10 times the power of .3 amps at 12V. Power = amps x volts. So a .3 amp 120V fan would be equivalent to a 3 amp 12V van.

A 48 amp-hr battery deep cycle battery should easily run 2 1-amp fans for 8 hours. That would be 16 amp-hr, 1/3 of the battery's capacity. The deep cycle battery will be fine with that. It would probably take a couple of hours to recharge fully.

Wait a minute: For some reason I thought you were using a separate battery for this. If this is your starting battery, you'll want to be more careful. Plus, I would not assume that your starting battery is a deep cycle - most aren't. You should probably try this out overnight in your driveway a couple of times to make sure the truck will start in the morning.

 

[aontkos]

Wait a minute: For some reason I thought you were using a separate battery for this. If this is your starting battery, you'll want to be more careful. Plus, I would not assume that your starting battery is a deep cycle - most aren't. You should probably try this out overnight in your driveway a couple of times to make sure the truck will start in the morning.

Yeah, I'm starting to realize that running a dual battery or having a small auxiliary battery that recharges via a solar setup may be required for this. I was hoping to avoid the additional cost of an extra battery just for the sake of comfort, but I don't think that can be avoided- especially if I want to do it right.

 

[nevada]

Yeah, I'm starting to realize that running a dual battery or having a small auxiliary battery that recharges via a solar setup may be required for this. I was hoping to avoid the additional cost of an extra battery just for the sake of comfort, but I don't think that can be avoided- especially if I want to do it right.

you could get a much smaller battery just to run the fans.

however, I expect you will find having a 2nd battery is very convenient, and will end up finding a use for a bit more capacity. in which case, a larger battery would be more appropriate.

im not sure how cold/warm it will be during the night. it may be, that you don't need/want the fans to run the entire night. that would save a bit of power, and let you get away with just using the main vehicle battery.

 

[RonJR]

With a decent primary battery (80 amp hours or so), you shouldn't have trouble running the fans all night and still being able to start the truck in the morning. Since you'll only do this in warm weather, it's not like you'll need a bunch of battery power to turn the engine over to start it the next morning anyway.

A more versatile alternative might be to buy one of these lithium battery jumper packs. They store compactly, aren't horribly expensive, and give you plenty of short-term juice to get the vehicle started if for some reason your primary battery runs down. Then you could use your primary battery for the fans without worrying about the small chance of not getting started the next morning.

 

[aontkos]

This has remained on my mind for a few weeks now, so I'll just revive this thread. I know that there are a multitude of threads on various forums that discuss the ins and outs of dual battery systems, but I'm still trying to figure some things out.

For a relatively simple dual battery setup, would there be any foreseeable issues with having a cranking battery linked to one of these and a house battery that is connected to a fuse box that feeds fans, usb ports, an inverter, etc? It sounds simple to me, since I don't desire a fancy monitoring system or in-cabin switch, and it will isolate the cranking battery when the alternator is not charging.

Here's a video for the folks that don't feel like reading.

 

[fourwd1]

I have dual batteries in my 83. I just got a continuous duty 100A relay and used it to isolate the 2 batteries. Engine off, batteries isolated , engine on and they're in parallel and charging.
I wired all the accessories to the 2nd battery , primary is for starting.
But when starting the 2nd battery comes online as well, which is perfect in case something happens to the primary battery. Cost about $35 for the relay.

 

[HSP22]

I got my Relay for $40 locally

 

[nevada]

I got mine locally too. just a 12v high amp, constant duty solenoid. I have it wired in manually. I switch it when I want it on. as simple as it can get.