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H3 HID's

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H3 HID's

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    H3 HID's

    For those that have these, did you have to change out the factory 10a fuse for them???? I installed mine and maybe 5 secs after having them on they poped the 10a fuse. I changed it out to a 20a fuse and left them on for about 15 mintues and they were fine. So the question is, is a 20a overkill??? I know the formula I = Tp/E, were as total voltage / watts gives me my amperage, but it has been a long time since learning DC power, so I cant remember if they same law applies. If it does, and the HID's are only rated at 35w, the formula would be, I = (35 x 2)/12 = 70/12 = 5.833. If that is correct then why am I blowing the 10a and the 20 is holding, unless there is a different formula when dealing with DC, or worse, I have a loose connection or something???

    Rule number one, never replace a fuse with a bigger one, the fuse is there to protect the wiring, the head light circuit is 10A per side, [head light bulb uses no more then 10A] if you install a bigger load., [HID lights] you need a circuit rated at 20-25 amps, that means retrofitting in a harness wired to a relay(s) and using the stock head light circuit to control the relay.

    The HID kit came with "transformers" and a wiring harness, the transformers should be wired to the batt. with the stock head light wiring used to "trigger" the transformers, like the control lead on an amp, that means much less then 10A of current would be used, so question is, why did the 10A fuse blow?
    Either the HIDs, [transformer] is defective or something is miswired.

    There are two 10A fuses for low beam, [fuse 3 and 4] and two 10A for high beam, [fuse 9 and 10] which one or ones blow? 94


      I am asking a simple question regarding a formula. It was the fog fuse, which there is only one, where as each individual low and high beam has it own fuse. The fogs share a 10 amp fuse. Do you know what size wire is rated for 20 amps if you are telling me that is what it needs??? That is #12 awg, huge in regards to what the headlights are wired with. So if you dont have any input in regards to the math then your comment is usless. The HID's I ordered came with a relay after the connection from the orginal connector for the headlights and before the ballast. The "ballast's" are not connected to the battery. That was an optional way of wiring them.


        Oh and it held fine with only one fog connected. Once I wired in the 2nd one and turned it back on, it stayed on for about 5-6 seconds and popped the fused right when the lights were starting to get to the yellow color.

        On another note, the HID's in both the low beam and fogs are a night and day difference over halogens...... It looks uber nice too.... All I am waiting for now is the PIAA 1541's to come and also the HID's and new fogs for my girls scion tc.


          Originally posted by japanjay View Post
          I am asking a simple question regarding a formula. It was the fog fuse, which there is only one, where as each individual low and high beam has it own fuse. The fogs share a 10 amp fuse. Do you know what size wire is rated for 20 amps if you are telling me that is what it needs??? That is #12 awg, huge in regards to what the headlights are wired with. So if you dont have any input in regards to the math then your comment is usless. The HID's I ordered came with a relay after the connection from the orginal connector for the headlights and before the ballast. The "ballast's" are not connected to the battery. That was an optional way of wiring them.
          his comments are useless?

          fcm = 12v

          and like he said... you need a circuit designed for 20-25amps, the amperage draw when ballasts start up is significantly higher than continuous use... even more than halogen bulbs...

          do you want proof?


          im not sure why you need a formula to complicate things...


            OMG whatever. I will find the info myself. I do electrical work on a daily basis. You all are not getting what I am saying. Check wire and amperage size according to the national electric code. 20A needs #12awg and 20-30A needs #10awg. We all know our cars do not have that wiring ran in our cars. The headlight and fog wiring is at most 14 maybe 16awg.

            Also, you are refering to amperage increasing during initial start, same thing happens when sizing say a large electrical motor in a warehouse. But you size the wire for the normal operating Amps and size the breaker to the FLC, full lock current, which is, if the motor jams the AMPs will skyjocket causing the breaker to trip and it also compensates for the large increase of initial starting amps to get the motor up to speed (now there are tons of different motors and all require different formulas for the sizing of the breaker depending on if they are single phase or the different types of 3 phase motors). You could have a motors breaker, or fuse mind you, rated at 200 amps and the wire only rated for 75 amps.

            How about someone that knows what I am asking answer my question..... If each individual headlight has its own 10A fuse, that means each light has its own specific fuse, where as the fogs share a 10A fuse, so now having 2 HID's on a single 10A the wiring will be fine once they are up and running, but for the initial 5-6 seconds the Amps will exceed the 10A rating, which is fine for the wiring as long as it doesnt stay over 10Amps for a long time, but not fine for the fuse which will trip when the 10A barrier is reached.


              Oh and when you refer to the box in the HID kit, it is not a transformer, it is a ballast. If it was a transformer it would have windings and a core of some material.

              I wire up HID's all day in the commercial world, whether it be high pressure or the rare low pressure sodiums, metal halides, mercury vapors, or regular old flourescents and they all have "balassts" not transformers. All of those, even ones that are a 1000w's literally, I have never had to size the breaker to compensate for the increase in initial draw amperage. They were all sized according to that formula. I = Tp x E. So if these are some different kind of HID that I have never delt with or the fact this is DC and not AC I am not sure and that is what I am looking for.

              Oh and transformers work proportionally. If I have a transformer taking 240v and putting out 120v and there is a 10a load on the 120v side then there will only be 5a on the 240v side.


                you must know more so... good luck

                maybe i'll just throw in one last bit of advice... KISS... keep it simple stupid.

                all your problems or worries would be eliminated... thread wouldn't have even been necessary if you just used a relay harness.

                if you think the fog light circuit can handle 20amps... well then you just answered your own question didn't you..

                by all means its your car... do what you want...


                  I am keeping it simple.

                  Say you have 2 600w HID high pressure sodiums lights.

                  2 x 600 = 1200w

                  1200w / 120v = 10A breaker

                  35w x 2 = 70w

                  70w / 12 = 5.833A

                  5.833A at running amperage, not initial amperage. What I am asking is, is this the right formula for DC power. I know I can use a relay for a control, but why do that when the HID wires are 16awg that come in the kit. To me that shows that the amperage spikes for the first few seconds, because if it always pulls high amps then the 16awg wire would burn the insulation off and then short out.

                  Actually dont worry about, I will ask the old timers at work about this.

                  Just an question I have thought about, but who follows the convential flow theory, edison theory, or electromagnetic theory? Edison for me is hard to phathom in regards to cars.
                  Last edited by japanjay; 20 Sep 2009, 21:33:24.


                    When I get back from vacation I am going to stick a fluke inline with the circuit and see exactly what it pulls at initial draw.


                      OMG, whatever, go find it yourself then and don't get your panties in a knot because you got treated like the 12 volt DC No0b that you are.

                      You said nothing about it being fog light HIDs.
                      That is why I asked which fuse is blowing.

                      You said nothing about the fuse blowing only after 2nd bulb installed.
                      A pretty good indication you are overloading the circuit, circuit works fine with one bulb is overloaded with two bulbs, I don't need a formula to figure that out, and neither should you.

                      BTW I know they are ballasts, that's why "transformers" is in quotes, sorry, I thought I was speaking to a No0b.

                      Maybe you just don't want to hear what you need to do and as tilegend said, keep it simple.

                      Because the number one rule is never replace a fuse with a bigger one then the answer to your question, "So the question is, is a 20a overkill??? would be yes.
                      Your formula, either right or wrong means diddly-squat and the only math needed is the ability to add two and two together.
                      You can not install a bigger fuse + you need a "bigger" circuit = install a relay, or maybe the "That was an optional way of wiring them" is there for a reason.

                      Or not, you can just become one of the other 12V No0bs who come back here now asking how to change the dash harness because you were just driving along when smoke started pouring out of your dash and now nothing works, but thank God the car did not burn to the ground.

                      So yea, I guess I have nothing to add to your math, so I guess you will have to wait for someone that knows something. nuff said.94
                      Last edited by fcm; 20 Sep 2009, 21:57:09. Reason: typo


                        BWHAAA. Funny guy. Read the NEC and come back on here. I need an answer form someone that knows DC formulas and actual electrical theory, not someone that goes by hear say.......

                        Oh, but what a minute, I found what I was looking for, Hmmmmm lets see here,

                        5.83 + 5.83 = 11.66 > 10


                        So 16awg, or in canadains system, 1.29mm, can carry, wait for it,......... OMG 18 AMPS!!!!!!!!! But then you have to factor in the insulation rating and heat factor. So I think 11.66 will be fine, and that explains why the 10a fuse blew once it heated up...... I guess I answered my own question. Thanks for the help nuuuuuuuub......

                        Why would I need a relay when the HID wiring is the same size as the factory fog wiring size???? I could understand if it was say a 200w bulb and HID wiring in the kit was #8awg, but being only 35w, and combined they carry a 11.66a load then it doesnt make sense to go through all that work. Like you all said, KISS.........
                        Last edited by japanjay; 20 Sep 2009, 22:21:07.


                          I think the topics states which lights I was refering. I didnt think after stating "H3 HID's" I would have to state it was for the fogs, since the low/high's are H4H bi-xenon, unless you thought I was putting HID's in my turn signals did you??? Calling me a noob...... Lulz what a nublet......


                            Why would I need a relay
                            LMAO, famous last words, your right, stick a 20A in there, nothing can go wrong.

                            Shit, 35 years of working on 12V DC and I know nothing, I guess I will just have to start all over again, and jeez I will have to quit my job at Dave Ward Auto Electric/Air Wolfe Auto A/C and electrical, I will have to tell Dave that a guy on GTIC says I know nothing.
                            So sad, I was looking forward to building our next all electric car over the winter.94


                              Well for doing what you do, I would think you would be better at backing up info with actual hard facts, not just do it because you say it is right. We both are in the Electrical field, I deal with everything from Distribution HV to 12vDC security and fire alarms. Been almost 4 years since messing with the DC stuff, but being that we both work with the same stuff, "electrical theory", then we both know that we dont do things just because someone says, "hey, thats how I always done it and never had a problem...." I got online and looked up the NEC which I am sure you are aware what that is, and found what the Amperage rating is for the wire we are working with. If that book, now granted we both know that book and the NFPA70 govern the electrical world whether it be Commercial or residential, and that if it says 16AWG, or in your world 1.29mm, can hold 18A then I will be fine with a 20A fuse for the time being. I am actually going today to see if I can find a fuse that is smaller then 15A but bigger then 12A, but I dont think I am going to find anythign but a 10A and 15A. With the 15A fuse in there the wire will be just fine since it is under the maximum allowable 18A and more then what the load is pulling......

                              I know your type, delt with ya before in the past. One of those guys that goes off what they were taught and what they have "always done" not some that reads books and learns the real reason why things are done and if what they have been doing for the last 15 years is even right, or is it over kill and wasteful.......

                              I did the math, and that is, what in engineering, is right. Unless you can say, that my math is wrong, or that there is something I am forgetting when crunching basic electrical theory regarding DC circuitry problems, then please correct me, that is why I posted this. But if you are going to say, "that is how I have always done it," then just sit back and learn something new. Maybe even pick up a

                              And wiring in an electrical car is not that impressive, how about wiring in a substation designed to power a small town.