Electronics question

[jay66uk]

I am going to build something that uses a very small 12v fan as the only electrical component. The fan is rated at 1.5 amps and will run 24/7. I am going to hook it up to a car battery and hook that up to a solar panel.

I want, as far as possible, to be able to set it up and forget about it.

I know very little about how to do the sums to work out how big a battery I need and how strong a solar panel to get. Both cost loads more for small increases in capacity/output.

I am guessing that the worst case (in winter) I will get about 8 hours of charge out of the solar panel (as they still charge when cloudy/raining). That's a third of the time.

To keep the battery topped up do I need a solar panel rated at 4.5 amps? Or would I need a stronger one?

Alternatively, how long would a fairly standard car battery last on a constant 1.5 amp draw? (It could work out better to buy two batteries and swap one out to recharge it off the mains.)

Ta very much.

 

[Doctor Congo]

Jay, a quick scan of a car battery site say they rate between 38 and 63 amp hours, I would look at the higher end of that range as your fan will take 36Ah/day and I'm not sure how well lead adcid battries respond to repeated deep discharge cycles (thats not how they are used in cars).

You would probably be better off with an uprated solar panel too, I'm not sure exactly how they are rated but assuming it gave 4.5A for 8 hours perday that is 36Ah/day, the same as your fan is using and so wouldn't account for energy lost charging the battery.

I also don't know if the panel output would be regulated in any way or what it could rise to. It would need to output more than 12v in order to charge a 12v battery and may need current limiting (to avoid battery damage) just in case that big yellow thing in the sky ever decides to visit us. If necessary I could probably knock you a simple regulator together for no more than a couple of quid.

 

[jay66uk]

Thanks for the info, mate.

The solar panels I'm looking at come with all the regulator gubbins for charging 12v out of the box (and a thingy to stop the battery discharging to the panel in the dark), but thanks anyway.

Looks like a big battery, then, and perhaps double the solar to 9 amps....

 

[Doctor Congo]

That sounds a better bet to me (without seeing datasheets), alternatively ...

 

[jay66uk]

:-)