12v lighting for back country camp - opinions please!

[Curtludwig]

So I've got this camp in the backwoods of Maine. Okay, its not really the back woods but its a rustic camp, woodstove, gas lights etc.

The problem is I like to read in bed and theres no way to put a gas light so it'd be useable there with it still being safe. I'm tired of flashlights, they're not a good solution at all, even with rechargable batteries.

I have a 5w solar panel hanging around, and a couple of 12v lead acid batteries from some other projects so I'm thinking to rig up some 12v lighting that I can power with the 5w panel (since I have it and its not doing anything).

CF would work but its only a 5w panel and I only need spot lighting to read with. Plus in the winter time it can get quite cold in the camp and the point of this light (somewhat) is to allow me to snuggle into my sleeping bag and read without having to stoke the stove.

So I think it'll have to be LED. The bulbs I've looked at seem overly expensive and maybe not even bright enough. The information on Otherpower seems to indicate I should make this light myself... So yesterday I took a gander at eBay to see what was available for LEDs. I'm flummoxed, there are so many choices. Of course so many are in Hong Kong....

I think I'm going to pick up a set of 50 LEDs and try wiring them up straight with a resistor first. I'll test it out at home and see how it does with varying voltage. If I can limit myself to 3-4w I shouldn't really ever seem my voltage ever going that low right? If not I could give a try at the more complicated regulating supply but I want to try not to, my electronics knowledge is limited.

So whaddya think?

Thanks

-Curt

[ghurd]

I would lean toward 9 good LEDs at 15ma.  3 series strings of 3 LEDs and one resistor.  One resistor per string that is.  Total of 45ma.

A 5W PV should handle it no problem... as long as the battery is not large. Maybe a 7AH SLA.

A PB137ACV for the charge controller.

G-

[Curtludwig]

I was given to understand that I wouldn't need a charge controller with only 5w.

Is a smaller battery better in this instance? I was going to use a motorcycle battery that is 10ah I think. I'd wanted to use that battery because I have it and its light and portable. My other choice is 110ah marine battery in which case I probably wouldn't have to recharge but once a month or so.

[TomW]

Curt;

The rationale for a smaller battery is that batteries have a self discharge rate that you need to keep ahead of and the bigger the AH rating the more this value is. In extreme cases you will never keep the battery properly charged between uses. In your case, 5 watts is not a lot and a smaller battery makes the most sense. I am not aware of any "chart" that shows this but it can be substantial on a large AH battery. I will not attempt any math on this because my math sucks, but your motorcycle battery will probably be a fair size match despite it not being a deep cycle. Automotive batteries tend to not last very long in an R.E. application where they get drained very far very often. My theory here is if you have it use it and after its dead you will have some experience you can apply to the next battery.

Cheers.

TomW

[ghurd]

What Tom said.

And yes, you will need a controller with a small battery.  

The controller I mentioned is ~$2, and simple to connect.

You should get decent life from the motorcycle battery.

A few LEDs for an hour or 2 a night will leave the battery decently charged.

(I have done worse!)

G-

[alancorey]

Well, the PB137ACV is a charge controller that's a 3-terminal chip, costs under $1.  I think the manufacturer recommends using a couple of electrolytic capacitors on the input and output for bypassing, you can probably get these in the same place for under $1 or pull them out of some junk electronics.  The PB137ACV is a nice little 3-terminal regulator that's got an output of 13.7 volts, designed for holding lead acid batteries at float voltage.  Any system like this should get protected from overcharging: what if you don't read for a night or two?  http://www.newark.com/jsp/search/productdetail.jsp?SKU=89K1490&CMP=AFC-GB100000001

You can use the motorcycle battery while it lasts, or get a 7 amp hour SLA for around $15 that's designed for deep-cycle use and has a service life of 6 years.  Something like http://www.batteryspec.com/cgi-bin/cart.cgi?action=link&product=63&sub2=632122

Like Ghurd says with the LEDs.  Here's a pic of 9 of them mounted in a circuit board: http://www.otherpower.com/images/scimages/6871/dscn9810q.jpg and here's a small shed lit with 4 of those circuit boards: http://www.otherpower.com/images/scimages/6871/dscn9875q.jpg  That's under 3 watts total for the 4 boards.  I pointed them in different directions to try to cover the whole room, but you could aim them all the same for reading.

  Alan

[Curtludwig]

I'll read every night while its hooked up. This will be at our camp and when we're not there everything will go into storage.

I don't see the battery getting a very deep discharge with my only pulling 4 watts or so out of it. 10ah is 120w give or take a bit so I should actually be able to read for an hour every night for a week and not really need a recharge...

I figure once my reading light is in place and working everybody in the camp will want one so at that point I'll upgrade my PV...

Thanks everybody, this is exactly the info I needed!

[willib]

Or you could go fluorescent..

i bought an 8Watt drop light fluorescent , 12 V  at Pathmark food store , of all places , for $9 and change ..

a similar bulb alone cost $6 and change at Home Depot

its not real bright , but good enough to read by ,i think.

[Tritium]

Curt,

Get yourself over to CandlePowerForums.com and look around.

Thurmond

[Curtludwig]

I've considered flourescent but if you read my original post its not gonna work when its real cold. Thats my biggest problem with my current flashlight, its got flourescent bulbs that provide enough light but when its cold they flicker badly and aren't bright enough.

Sure I could get up and stoke the fire to warm it up but if I did that I could sit in a chair and read by the gas light. The whole point is to be able to stay snuggled in bed and read...

[AbyssUnderground]

CCFL's dont flicker when they are cold.