| Author | Message | ||
     Bomber |
being mathmatically challenged, and having been called a scoff-law on a number of occasions, I find myself in need -- I've got two 13-watt lights, and can't remember my ancient Signal Corps training -- what capacity switch do I need for these puppies? thanks, gents! | ||
| Scott_in_nh |
Amps = watts/volts A=26w/14.5v A=1.79 | ||
| Redponcho |
Amps = watts divided by voltage. Then you need to apply a derating factor. This is to handle the current when the switch closes. 26/12=2.17 derating factor of 5 2.17 X 5 = 10.85 amp switch This is based on a 12 volt system for a lamp. | ||
| Bomber |
Thanks a million, Scott! | ||
| Reepicheep |
We all agree, but if you want more of the derivation... (I sure miss this stuff... the days when I was young and problems were easy  ). V=volts I=amps (current) R=ohms (resistance) P=watts (power) V = I * R I = V / R R = I / V P = (I*I) * R P = (V*V) / R P = V * I V = P / I I = P / V So... two 13 watt lights are 26 watts. Assume 14 volts for the "bus" voltage. 26 Watts = 14 / I (amps) Rearrange the equation, and you have 26 / 14 = X amps 26 / 14 = 1.86 amps Double checking (I never trust my path) 26 watts should equal 1.86 amps times 14 volts. Which it does. And if you want to be really anal about it, you can also derive that the resistance of the lights (hooked in parallel). 26 watts = (1.86 * 1.86) * R. So R would be about 7.5 ohms (meaning each light alone should be 15 ohms). And double checking *that*... (14 volts * 14 volts) / 15 ohms = 13 watts. I love it when a plan comes together I never trust my math until I have run it in a full circle and came back to where I started. For inrush current, for an inductive or capacitive load that would be a critical concern. I'm not sure about a fog light load however, wouldn't that be resistive?... I expect the initial current is higher, and as the filiment heats up the impedance goes up and the current goes down. But is it a factor of five? Plus, the switch ratings are probably steady state, I would expect they can handle much higher peaks. (Message edited by reepicheep on May 24, 2007) | ||
| Scott_in_nh |
good info Red, and I am no expert, but since our systems operate at I believe 14.5v, wouldn't it be 1.79x5=8.95 or a 10 amp switch? Also, considering the milliseconds that this higher load exists at, is even that important? | ||
| Redponcho |
I did use 12 volts for the formula. The derating factor comes from my aviation background. Everything is overkill for airplanes. No one likes smoke in an airplane! .A 2 amp switch will work but I would wonder about the life of the part. A 5 amp switch would probably suffice. | ||
| Bomber |
wow -- I LOVE it when folks smarter than me work on a problem! I've got a 20 amp toggle switch -- my time use rotary wing aircraft as taxis to and form work has me also not liking smoke! you guys are ACES in my book -- thanks a million HID lights, here we come! | ||
| Reepicheep |
Ahhhh! You didn't say HID before. Definitely use the bigger switch. That's an uber capacitive load. I know you are switching it, but do you want a 60-90 second delay circuit for your "on" relay? That will make it such that the motor is almost always running before the HID's come on, meaning you won't have 2 HID cycles for each bike startup, just one. My understanding is that the life of a HID is measured by number of starts, not by "on time". So the relay would let you still switch it, but the switch would have no effect until 60 to 90 seconds after the bike ignition switch has first been turned on. PM me a shipping address if you want one. I won't sell you one, but would be happy to have a man with a metal lathe in my debt . | ||
| Bomber |
Reep -- they aux lights, and won't be on alla time! you're understanding wrt switched cycles matches mine -- these are lil guys (more for showing up the wildlife that lurks on the side of the back roads in the toulies than for 100mph+ runs through the desert), and the manufacture sez a simple swithc is OK (of course, this COULD be a ploy to seel more lights ;-} ) and I'm already your bud, and buds don't count debts -- ya need sumpin spun up by a metal muncher, lemme know! | ||
| Spiderman |
Bombs, You need one of these! It has everything. I have one for work and home...  | ||
| Bomber |
OOOOooooooo -- a book! with cool stuff init! I DO need one -- where might one find such a treasure? | ||
| Spiderman |
http://www.amazon.com/Pocket-Ref-Thomas-J-Glover/d p/1885071337/ref=sr_11_1/002-6606515-5292806?ie=UT F8&qid=1180030520&sr=11-1 I got mine at a local Mom&Pop hardware store, right next to the farmers almanac... This book has a ton of info in it including Ohm's law, semphore, morse code, roman numerals, tons of conversion, drill and tap charts, airports even military ranks and clothes size conversion charts! This book rocks... | ||
| Reepicheep |
Thanks Bomber! | ||
| Sleez |
try here for some basic dc circuit explanations; http://www.physics.uoguelph.ca/tutorials/ohm/Q.ohm .html | ||
| Bomber |
sometimes, after reading/avoiding some of the longer thread round here, I take a break -- then, something like the Matt threads, or this one, happens, and I feel more at home -- thanks a million, fellas! | ||
| Bluzm2 |
Bomber, I'll second the Spidy book. It is fantasic. Lots of obscure formulas and stuff. I think it's on it's 4 revision. I too picked mine up at my local ACE hardware store. Brad | ||
| Blake |
Watt y'all getting all amp'd up about? Sorry I have a low resistance to this stuff. Don't let it phase you. | ||
| Iamike |
Bomber- The biggest problem I have with my fog lights is the switch getting wet from rain. I haven't found a switch that I like that is waterproof. I finally started covering the switch with some cellophane to keep it dry. Looks tacky but it saves buy a new switch every so often. | ||
| Court |
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| Hughlysses |
The most important thing to know is the "smoke theory" of electricity. All electrical devices work on the basis of magical smoke which is carefully encapsulated inside. If you do something wrong like overload the device, hook up the wrong power, etc. you'll let the smoke out and the device will no longer function. This was graphically demonstrated to me in my ME 401 (automatic controls) class when we plugged in 3 400 hz servo motors to a 60 hz 115V outlet before the professor arrived for our lab. Sparks were seen and smoke rose from the motors, so we quickly unplugged them. Prof walks in ~2 minutes later, opens a cabinet, and pulls out this huge military surplus gizmo. He plugged it into the wall socket, and it emits this high-frequency whine. Then he plugs the servo motors into it and nothing happens. We all look at each other like "oh s**t". He notices the looks on our faces and says "You guys didn't plug these things directly into the wall socket, did you? Well, you let the smoke out of them." and he proceeded to explain the smoke theory of electrical devices to us. Come to think of it, that's about the ONLY thing I remember from ME 401, except that "poles in the right-hand half-plane" are a BAD thing. | ||
| Bomber |
Mike -- I found a good switch and separate waterproof cover at, wait for it, the local ACE hardware store! (I was very surprised!) local Boater's emporium had lots of high-dollar panels with switch labeled LORAN and ANCHOR and FORWARD DECK GUN and the like on em, but they're as big as the bike's enigne -- no switches . . . . . Hugh -- I, too, have repeatedly proven the majik smoke concept -- given the highly electronic nature of the bike I'm working on (the shop gremlins in the Luddit Lounge Section of the Entroy Lab are all agog at the 21st Century-esque nature of the bike, and keep looking for the choke, kickstarter, and zenier diode the size of an artichoke - -none to be found), I'm trying to be careful round the smoke pathways -- that, and this is the bike I told my Wingman and best riding buddy that I'd keep stock. ;-} | ||
| Firemanjim |
Stock is such a pliable word---- | ||
| Bomber |
ROFLMAO! good point -- prevarication rocks! | ||
| Sleez |
Court, ugly's is a great ref!! cheers!! | ||
| Sleez |
i also use this online conversion site a lot!!!; www.onlineconversion.com | ||
| CJXB |
being mathmatically challenged I am not the least bit mathematically challenged, being an accountant and all, and I have NO CLUE what ya'll are talking about, making my head hurt !! Wonder if I might need that cute little spidy book, hmmm !! Blake, trying to be a comedian in this thread, just left one where you were trying to sing (cop thread), sheesh you can't do either !!!  | ||
| Reepicheep |
(and for the record, there was a typo in my derivation above, but the numbers are right... Y'all are getting sloppy not catching me ). | ||
| Mr_grumpy |
Derrrr What?  As a former auto & heavy truck mechanic I always just wire through a relay, generally have loads of odd bits lying around, somehow the bottom of my toolbox just attracts stuff when I'm in the local breakers yard. | ||
| Vegasbueller |
Ugly's +2 votes. I keep one at home and work too! |
