Snaggletooth Posted May 15, 2012 Share #1 Posted May 15, 2012 Ok, going with my basic knowledge of electronic stuff of which I have er........ NONE, I would guess one of you wizards out there can fill me in. I have a gizmo that is powered by 3 AA batteries so I'm looking at 4.5 volts. See, I can figure some stuff out. I would assume, and I do love that word, that it would be possible using resistors or other unknown objects I have have no idea of that I could reduce the bikes 12 volts down to 4.5 to power this gizmo with a hardwire setup. So tell me wise ones...... what am I looking for to pull this off? Mike aka Sparky Link to comment Share on other sites More sharing options...
KIC Posted May 15, 2012 Share #2 Posted May 15, 2012 A miracle... Link to comment Share on other sites More sharing options...
etcswjoe Posted May 15, 2012 Share #3 Posted May 15, 2012 Its not too hard however I would recommend finding a cheap 12 volt phone adapter and use it. You could also use this http://www.ti.com/product/lm317 Link to comment Share on other sites More sharing options...
dingy Posted May 15, 2012 Share #4 Posted May 15, 2012 Ohm's law comes into play here. You would need to know the devices current draw to calculate the size of resistor needed. Gary Link to comment Share on other sites More sharing options...
calperin Posted May 15, 2012 Share #5 Posted May 15, 2012 Dingy is correct, you need to check how much current are you use on your gizmo with your 4.5 V AAA bateries. Do you have a multimeter? if the answer is yes, put it on AMP, and the higher scale you have on it. Put the multimeter between the positive end of the battery and the gizmo. And the other side of the gizmo connected to the negative. Check the amperage, and the way to get the right resistor will be : (12v-4.5V)/(amperage reading). Also the power that the resistor will dissipate is (7.5V)*amperage. So when you purchase the resistor, not only you need to choose it for his value, but also for the power that is able to dissipate. Good luck.... :detective: Link to comment Share on other sites More sharing options...
Flyinfool Posted May 15, 2012 Share #6 Posted May 15, 2012 It might be safer/easier to just use a LM7805 regulator or a LM317T adjustable regulator. Odds are you are pulling less than 1 amp. The problem with using just a resistor is that you may get weird results as the bike voltage changes, or the device current draw changes. Link to comment Share on other sites More sharing options...
bongobobny Posted May 15, 2012 Share #7 Posted May 15, 2012 Go to radio Shack or Wally world or Target and buy one of those universal adapters that plugs into a cigarette lighter and has a switch to select whatever voltage you need... Link to comment Share on other sites More sharing options...
djh3 Posted May 15, 2012 Share #8 Posted May 15, 2012 I probably have a half dozen old car phone chargers in a cabinet around here. I can look and see what I got and send you something. I'd hate to see you let out the magical blue smoke. DJ's theroy on electricity. you need power and a ground and you dont want to be in between. Link to comment Share on other sites More sharing options...
Owen Posted May 16, 2012 Share #9 Posted May 16, 2012 The adapters for charging a USB device puts out 5v. That should not be a problem for your 4.5v gps. Link to comment Share on other sites More sharing options...
saddlebum Posted May 16, 2012 Share #10 Posted May 16, 2012 Resistance is not all you need to worry about. Currant draw is also a facter which then brings the third factor which is heat. The amount of currant drawn through a given resistance creates heat. Increase either one and the heat generated also wil increase. There are all sorts of ready made voltage supplies and convertors out there you should be able to find the one you need woth out having to mess with the above. Link to comment Share on other sites More sharing options...
Cougar Posted May 16, 2012 Share #11 Posted May 16, 2012 I think a RELAY is in order !!! Link to comment Share on other sites More sharing options...
Bob Myers Posted May 16, 2012 Share #12 Posted May 16, 2012 It might be safer/easier to just use a LM7805 regulator or a LM317T adjustable regulator. Odds are you are pulling less than 1 amp. The problem with using just a resistor is that you may get weird results as the bike voltage changes, or the device current draw changes. Yes! The resistor will be a linear device, buying a cheap phone charger or usb device will be regulated somewhat. I installed a cigar lighter on my Vulcan, just to power such items, and to protect the less than bulky wire I ran for the lighter plug, I used a self-resetting 2amp circuit breaker Link to comment Share on other sites More sharing options...
Marcarl Posted May 16, 2012 Share #13 Posted May 16, 2012 I have a resistor on my scoot that works for almost anything. If there is too much voltage it gets switched to amperage on the fly, and if the amperage gets too hot, it dissipates through the helmet. I have not tested it for small items, seeing as I don't have a small item situation, but I am sure that if I had a small item that would be resisted as well. As far as letting out the smoke is concerned, if and when that should happen, I suggest leaving the scoot where it's at and run for safety. Link to comment Share on other sites More sharing options...
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