Andy Lef Posted September 11, 2017 Share Posted September 11, 2017 A very quick one.Want to buy one of these (maplins £14.99, rather than DTs) and need to match bolt size and length to the central hole on the rear of the light to attach a P-clip to it.Any ideas of the bolt size and length required. .many thanksAndy Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted September 11, 2017 Member Share Posted September 11, 2017 M4?Jonathan Link to comment Share on other sites More sharing options...
Andy Lef Posted September 11, 2017 Author Share Posted September 11, 2017 M4 it is then, thank you Jonathan. 10 - 15 mm length should be adequate. Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted September 11, 2017 Member Share Posted September 11, 2017 Too soon!Just got a a reply from Demon Tweeks:"The thread is listed as M5 depth is not listed but we would expect around 15-20 mm. The two outer tabs are usually the only mounts required."Jonathan Link to comment Share on other sites More sharing options...
Andy Lef Posted September 11, 2017 Author Share Posted September 11, 2017 Thanks againI have an M5 handy so will try that when i get the chance. I in tend to just use the center hole for the PCLIP - if that doesn't work i will move on to the hinge. I think that the center hole will give me the best seating.unless the wisdom on here decrees otherwise? Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted September 11, 2017 Member Share Posted September 11, 2017 Somewhere in the archives there's a trick using an electrical cable thingy...Jonathan Link to comment Share on other sites More sharing options...
Wrightpayne Posted September 12, 2017 Share Posted September 12, 2017 I have the maplin version tye wrapped to the cage diagonal, using the lugs either side. I looked at using the threaded brass insert but thought it looked quite fragile and would get pulled out if the lamp were knocked. I also used the Caterham wiring loom extension and added an in line resistor to protect the LED's, as described in forum posts.Ian Link to comment Share on other sites More sharing options...
Paul Deslandes Posted September 12, 2017 Share Posted September 12, 2017 As Ian suggests, these lamps come without a current limiting resistor and will burn out rapidly if some form of current limiting isn't included when connected to the car's nominal 12V supply. As a minimum you should add a 15 Ohm 2 Watt resistor in series. This will get quite hot so make sure it's mounted in the clear. Maplin 15 Ohm 3 Watt (Maplin code 15R) will do the job.Paul Link to comment Share on other sites More sharing options...
Andy Lef Posted September 12, 2017 Author Share Posted September 12, 2017 Thank you all. As a follow up to Paul's assist. I have also got these fitted, had them for a while but wondered whether they should have resistors for the brake lights?They already have directional diodes in line for the indicators (to make them work properly - by the dashboard light info here ). Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted September 12, 2017 Member Share Posted September 12, 2017 I have also got these fitted, had them for a while but wondered whether they should have resistors for the brake lights?Looks like it from that web page.Jonathan Link to comment Share on other sites More sharing options...
Andy Lef Posted September 12, 2017 Author Share Posted September 12, 2017 Jonathan yup saw it but only states for the indicators rather than for the brake lights.WDYT?Better safe than sorry? Link to comment Share on other sites More sharing options...
Paul Deslandes Posted September 12, 2017 Share Posted September 12, 2017 If they're LEDs then they'll all need resistors in series. Other than the indicators, as to whether there are resistors already fitted, the webpage is silent. I would suggest a phone call to check and also establish the rated current for each lamp so the correct resistor value(s) can be calculated. Although tempting, I wouldn't common up the lamps into pairs to share a resistor as you could find one lamp with a slightly lower forward voltage hogging the current, leaving the other one dim or extinguished.BTW the price for the resistors seems extortionate Paul Link to comment Share on other sites More sharing options...
Andy Lef Posted September 12, 2017 Author Share Posted September 12, 2017 Paul thanksLED indicators have new electronic LED flasher relay in the fuse box so that covers off the resistor for them.Suspect that I wil have to fit one each to the Tail/Brake clusters for each side? In line resistor to reduce power to LED = resistor added to positive wire from power to light............ confirm for a electrical novice? and yes the resistors must be something prety special to cost that much! Link to comment Share on other sites More sharing options...
Paul Deslandes Posted September 12, 2017 Share Posted September 12, 2017 Yes, that's right, resistor in series (in line) with the positive connection to each light. To calculate the value of the resistor you need to know the rated current and the forward voltage (Vf) of the light element. Assuming the supply is 13.8 volts, (Vs), subtract lamp voltage (=Vs-Vf) and divide by the current in amps. This gives the value of the resistor ® in Ohms. Note: the lamp current may be specified in milliamps (mA) which is one thousandth of an amp. In which case R=(Vs-Vf)/mA X 1000.e.g. if Vf = 9.6V and current = 250mA, R=((13.8 - 9.6) / 250) X 1000 = 16.8 Ohms. Nearest 'preferred value = 15 Ohms.Resistor Wattage = amps squared X R.In above example = .25 (250mA/1000) X.25 X 15 Ohms = ~ 1Watt. Always go higher with Wattage so 2W in this case.The above example is for the Maplin 52mm LED cluster that can be used as a race rain light and is much higher powered, and hence current, than I would expect your new lights to be.If you need help with the calculations, just sing out.Paul Link to comment Share on other sites More sharing options...
Mrp Posted September 12, 2017 Share Posted September 12, 2017 This might helphttp://led.linear1.org/1led.wiz Link to comment Share on other sites More sharing options...
Paul Deslandes Posted September 12, 2017 Share Posted September 12, 2017 A very useful calculator. Link to comment Share on other sites More sharing options...
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