The BSA A7-A10 Forum

Technical => Lucas, Electrical, Ignition => Topic started by: RoyC on 28.09. 2017 14:10

Title: Resistor type
Post by: RoyC on 28.09. 2017 14:10
I have some indicators with 10w (total per side = 20w) bulbs,
I think that I will want a 20w / 25w resistor.
Looking on ebay I have found one, but, it asks for ohms, I haven't got a clue what they are on about.
Can anyone help please.
http://www.ebay.co.uk/itm/25W-Golden-Aluminium-Load-Resistor-Wirewound-Various-Values-High-Quality-New/122180980450?_trkparms=aid%3D555019%26algo%3DPL.BANDIT%26ao%3D1%26asc%3D20151005190540%26meid%3Dbee8261b28384ed4a34f8764e467d48b%26pid%3D100505%26rk%3D1%26rkt%3D1%26&_trksid=p2045573.c100505.m3226
Title: Re: Resistor type
Post by: Bsareg on 28.09. 2017 17:24
You will have to know the voltage you need to drop (12 to 6v etc) and the current (amps or the wattage of the bulbs) you need to draw, in order work out the ohms.
Title: Re: Resistor type
Post by: RoyC on 28.09. 2017 20:50
Thank you Reg.
Title: Re: Resistor type
Post by: muskrat on 28.09. 2017 20:51
G'day Roy.
Heres a calculator.
http://rapidtables.com/calc/electric/watt-volt-amp-calculator.htm
Cheers
Title: Re: Resistor type
Post by: RoyC on 28.09. 2017 21:01
G'day Roy.
Heres a calculator.
http://rapidtables.com/calc/electric/watt-volt-amp-calculator.htm
Cheers
Thanks for that Muskrat, just the ticket.
Roy.
Title: Re: Resistor type
Post by: Bsareg on 28.09. 2017 22:29
Nice calculator., but remember that it's the current and voltage drop across the resistor that will determine the wattage of the resistor
Title: Re: Resistor type
Post by: mikeb on 29.09. 2017 07:25
Roy why do you want a resistor for anything?. they suck power. that's bad on a E3L.
people use them with LED indicators to increase load if they have the wrong kind of flashing unit - better to get the right flasher.
or to drop the voltage for a bulb (eg 6V bulb on 12V system)  but that doubles the power consumed by generating heat. get the right bulb.

its better to get the right part than load up old electrics - are you sure you need resistors? what's the task?
Title: Re: Resistor type
Post by: JulianS on 29.09. 2017 09:42
I though a resistor was only needed when LED bulbs fitted, and then they  are usually available from the supplier of the indicator kit, such as Paul Goff or Vehicle wiring products?

http://www.vehicle-wiring-products.eu/section.php/151/1/indicators
Title: Re: Resistor type
Post by: mikeb on 29.09. 2017 09:49
Quote
I though a resistor was only needed when LED bulbs fitted
even then only if its an old-school flash unit. just get a new sort. $1.50 off e-bay.

EDIT: i may be slightly lying. in theory I'm right but i recall having to put ?220 ohm 1/2 watt resistors across the 12v LEDs on the b33 to make them work. still that's much less current than the low resistance loads that mimic incandescent bulbs. flasher like this:
http://www.ebay.com/itm/12V-2-Pin-Beeper-Motorcycle-Flasher-Relay-Turn-Signal-LED-Indicator-Blinker-New-/162258494835?hash=item25c75c2573:g:CBgAAOSwo4pYEqMe&vxp=mtr (http://www.ebay.com/itm/12V-2-Pin-Beeper-Motorcycle-Flasher-Relay-Turn-Signal-LED-Indicator-Blinker-New-/162258494835?hash=item25c75c2573:g:CBgAAOSwo4pYEqMe&vxp=mtr)
Title: Re: Resistor type
Post by: RoyC on 29.09. 2017 14:18
Roy why do you want a resistor for anything?. they suck power. that's bad on a E3L.
people use them with LED indicators to increase load if they have the wrong kind of flashing unit - better to get the right flasher.
or to drop the voltage for a bulb (eg 6V bulb on 12V system)  but that doubles the power consumed by generating heat. get the right bulb.

its better to get the right part than load up old electrics - are you sure you need resistors? what's the task?
The indicators that I have, have 10w bulbs in them, I have tried LED flasher units (don't work) so I thought that 2 x 10w bulbs plus a 25w resistor then I could use an ordinary flasher used for 21w bulbs.
Option 2
I have ordered a 12v 21w flasher that may work with my 10w bulbs http://www.ebay.co.uk/itm/12V-21W-3W-2-pin-Motorcycle-Scooter-Flasher-Relay-Can-Unit-With-Audible-buzzer/191789180692?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649
Title: Re: Resistor type
Post by: RichardL on 29.09. 2017 14:36
Assuming the bulbs are 12V, at 12V they are going to pass the current required to draw 10W of power and that's it. The fact that the flasher is rated for 21W just means that only half of its available current will be delivered, and that is as it should be for headroom and longevity of the flasher. No resister should be needed for the incandescent bulbs.

Richard L
Title: Re: Resistor type
Post by: Clive54bsa on 29.09. 2017 17:25
I saw this the other day, I was thinking about it for my B50 MX Dualsport.
http://www.signaldynamics.com/self-canceling-turn-signal-module/ (http://www.signaldynamics.com/self-canceling-turn-signal-module/)
Title: Re: Resistor type
Post by: mikeb on 29.09. 2017 21:06
Quote
No resister should be needed for the incandescent bulbs.
i'm with Richard on this. should work fine without resistors. at worst may blink slowly.
when tested if its not suitable I'd change flasher unit rather than load up the electrical system more with resistors.
Title: Re: Resistor type
Post by: RoyC on 30.09. 2017 09:01
Thanks for that. I hadn't thought of it like that.
Title: Re: Resistor type
Post by: RoyC on 30.09. 2017 09:10
Assuming the bulbs are 12V, at 12V they are going to pass the current required to draw 10W of power and that's it. The fact that the flasher is rated for 21W just means that only half of its available current will be delivered, and that is as it should be for headroom and longevity of the flasher. No resister should be needed for the incandescent bulbs.

Richard L
There will be 20w power draw (10w x 2) so 21w flasher should work and no resistor required, I hope. Will see when flasher arrives.
Title: Re: Resistor type
Post by: RichardL on 30.09. 2017 14:18
Right, forgot about front and rear.

Richard L.
Title: Re: Resistor type
Post by: duTch on 30.09. 2017 21:55

 I''m not the most electronically tech savvy, but why do you need extra resistance (by my understanding, bulbs do that anyway) ? I think resistors are needed when using LED's on a conventional flasher unit... *dunno*   Maybe a relay is what you need  *dunno*
Title: Re: Resistor type
Post by: RoyC on 01.10. 2017 10:38

 I''m not the most electronically tech savvy, but why do you need extra resistance (by my understanding, bulbs do that anyway) ? I think resistors are needed when using LED's on a conventional flasher unit... *dunno*   Maybe a relay is what you need  *dunno*


I hope that I won't need a resistor now with a 21w flasher unit  *smiley4*
Title: Re: Resistor type
Post by: RoyC on 02.10. 2017 09:40




I hope that I won't need a resistor now with a 21w flasher unit  *smiley4*
Resistor arrived, works great without a resistor.  *wink2* *yeah*