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led motion light

conntaxman

Jun 17, 2011
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Im trying to make/get a simple/cheap motion detector light run off solar or 12vdc. I just picked up a light from wal mart here is the link.
http://www.walmart.com/ip/Mr.-Beams-Security-Spotlight/16664171?findingMethod=rr
it has 3 /// 1 1/2 volt d cell batters in it. looks like they are in series,= 4 1/2 vdc.with a bright led. I don't know what size led, but would like to find out.It must be atleast 1 watt.
Now ,I plan on useing a 317 pos. votl reg. .5volt out put to charge the batters . with the small solar panel I will be making.
Im thinking that the 5 volts should do it fine.
Need some coments, and or some better ideas.
John
 

Harald Kapp

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Nov 17, 2011
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Hello John,
just to mention it: standard batteries cannot be recharged, you'll need rechargeable batteries. But I'm shure you knew that.
As for charging: how to charge depends on the type of battery you are going to put into the light. NiCds charge differently than NiMhs charge differently than Lead cells..
An LM317 in most cases will not be a suitable charger. There are specialized ics on the market depending on your requirements (voltage, current, cell chemistry etc.).

May I suggest:
1) find out the wattage of the LED(s) by placing an Ammeter in series with the lamp and the batteries. From I*U you'll get the power of the LED(s).
2) find suitable rechargeable batteries. I'd use NiMh as you'll be able to get them in D-size perfectly fitting the lamp without modifications.
3) find a charger circuit that fits your needs. I did a Google search using the keywords: charge battery from solar cell
This turned up some interesting sites, e.g.:
http://www.techlib.com/electronics/battery_chargers.html
http://www.boatus.com/boattech/casey/30.htm
http://www.instructables.com/id/Solar-Battery-Charging/

I'm pretty sure you will find a suitable solution on one of these pages.

Regards,
Harald
 

conntaxman

Jun 17, 2011
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hi Harald. I went to the links, they were pretty good.and tks for your answer.Yes I will take the light apart and test the current the led uses, What I really wanted was the motion sensor. Its cheaper to buy this whole light then build a M.sensor.
I have been looking at different charger's drawings on the net,their are quite a few.some good some not so good.
tks and have a nice day.
John
 

conntaxman

Jun 17, 2011
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Question. I took apart a motion sensor that was 120vac. inside we have a small transformer 120 going in and coming out on the three legs is 12vac- neutral - 12vac. each 12volt ac leg goes to a IN4001 rec. diode, but why is it when I test the other side im getting 15vdc? Im putting the com . lead on the center tap of the transformer, is that why? I what to hook it up to a 12 volt battery so it will work of the battery.I think I should be able to just hook up the + from the battery to each diode .Seeing that I have 12 vac going into both diode's.
Thank for your answer
John
 

conntaxman

Jun 17, 2011
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While checking the cir. a little more I noticed that both diodes tie together, but still why was i getting 15vdc their when I had 12vac coming in at the other end.
john
 

jackorocko

Apr 4, 2010
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Question. I took apart a motion sensor that was 120vac. inside we have a small transformer 120 going in and coming out on the three legs is 12vac- neutral - 12vac. each 12volt ac leg goes to a IN4001 rec. diode, but why is it when I test the other side im getting 15vdc? Im putting the com . lead on the center tap of the transformer, is that why? I what to hook it up to a 12 volt battery so it will work of the battery.I think I should be able to just hook up the + from the battery to each diode .Seeing that I have 12 vac going into both diode's.
Thank for your answer
John

How many diodes are you using? Two would explain the 15Vdc, since only one dode is conducting on each pos/neg cycle of the AC. 12 * 1.414 = ~17V minus the diode voltage drop.
 

conntaxman

Jun 17, 2011
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Jack. I just hooked it up and it works ,and the relay is pulling in also.That would be the feed for the light that would be attached. Their are 2 diodes. Were do you get the 1.414 ? At least now i wont have to build one from scratch.Its cheaper to just buy one and change it inside it you can.Guess I just lucked out on 12 volts.Because that is what I wanted to use.Im making a solar out door light.
Thanks for the reply.
John
 

jackorocko

Apr 4, 2010
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Were do you get the 1.414

when you take an VAC and rectify it, you must always multiply by 1.414 to get the full VDC. the equation is 12v * sqrt(2) == 12v * 1.414

http://www.play-hookey.com/ac_theory/ps_rectifiers.html

You don't have both diodes forward biased at the same time do you? Can you draw us a schematic? or at the very least read the page I linked to so you can better understand what a half wave bridge should work like.
 
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