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Offline Igore1

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Re: 2018 XRX LED indicators
« Reply #10 on: February 27, 2020, 08:44:53 AM »
 :152:

Oh yes.  I bought 2 resistors and 4 indis. 
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Offline Igore1

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Re: 2018 XRX LED indicators
« Reply #11 on: March 03, 2020, 08:14:23 AM »
Update!  Fixed - I bought 2 resistors at 21.5 Ohms each, wired in parallel wired the new LED rear indicators (still have original triumph LEDs at the front) and all working fine now.

The aftermarket cheap indicators are much brighter than the old OEM ones, so quite pleased with my purchase.  Think I'll change out the fronts also as they new ones are a little slimmer, brighter and have a rubber stalk to avoid the common stalk snap.

Based on the resistance the rears are now pulling 0,56A.  Assume that if I change out the fronts I will need two more 21.5 Ohm resistors to keep the load within 1-2A total.

For info, it was stated in an earlier post that I should check power rating of the resistors to ensure they don't overheat - this is not possible as power rating of a resistor is a factor of voltage and resistance.  P = (VxV) / R so it's not possible to get it wrong.  You just need to be sure that the current draw is correct.  For example my resistors were 12V, 21.5 Ohms, this means they draw 0,56A and are 6.7W rated (they give off that power as heat, so 6.7W og heat generated)
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Online CB250G5

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Re: 2018 XRX LED indicators
« Reply #12 on: March 03, 2020, 11:22:31 AM »
I'm not sure that's the simplest way to work out the resistor wattage requirements.  For me:

From School, Ohms Law  V=IR.  V is a nominal 12 v  and R is 21.5 ohms

So the current draw, I, is V/R    12/21.5 = 0.56A

Power = V*I   so 12 * 0.56 = 6.72W

I'd be looking for a minimum of 10W resistors, for a decent safety margin, and making sure that they get some cooling air.
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Offline T800XC

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Re: 2018 XRX LED indicators
« Reply #13 on: March 03, 2020, 11:24:34 AM »
*Originally Posted by Igore1 [+]
...For info, it was stated in an earlier post that I should check power rating of the resistors to ensure they don't overheat - this is not possible as power rating of a resistor is a factor of voltage and resistance.  P = (VxV) / R so it's not possible to get it wrong.
Hmmm...not strictly true. The power 'rating' is a function of its composition. The power 'dissipated' is a function of the applied voltage and resistance.

I'll leave this here...https://en.wikipedia.org/wiki/Resistor




*Originally Posted by CB250G5 [+]
I'm not sure that's the simplest way to work out the resistor wattage requirements.  For me:

From School, Ohms Law  V=IR.  V is a nominal 12 v  and R is 21.5 ohms

So the current draw, I, is V/R    12/21.5 = 0.56A

Power = V*I   so 12 * 0.56 = 6.72W

I'd be looking for a minimum of 10W resistors, for a decent safety margin, and making sure that they get some cooling air.
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Offline Djairouks

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Re: 2018 XRX LED indicators
« Reply #14 on: March 03, 2020, 11:45:08 AM »
Absolutely the voltage applied on the resistor times current traversing it is the power P=U*I.

Also sometimes it's easier to use ohm's law U=R*I and combine both so you get P=(R*I)*I, so you can also calculate power directly knowing current draw among your resistor value, as sometimes circuits can act as voltage dividers and confuse people, then you use P=R*I^2.

Offline Igore1

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Re: 2018 XRX LED indicators
« Reply #15 on: March 03, 2020, 12:17:30 PM »
As you say you want to know the resistors are a bit beefier than needed to be safe.  That's why they are actually rated for 14V which calculates out to just over 9W rated.

Just to keep it simple it's not something you actually have to think about if you buy from a reputable manufacturer as it's already worked out by an electrical engineer (I am one)

V=IR
P=IV
simples.
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Offline Djairouks

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Re: 2018 XRX LED indicators
« Reply #16 on: March 03, 2020, 12:35:18 PM »
*Originally Posted by Igore1 [+]
As you say you want to know the resistors are a bit beefier than needed to be safe.  That's why they are actually rated for 14V which calculates out to just over 9W rated.

Just to keep it simple it's not something you actually have to think about if you buy from a reputable manufacturer as it's already worked out by an electrical engineer (I am one)

V=IR
P=IV
simples.

Never hurts that people know a bit more what they are doing, I am also an engineer but I really dislike this mentality, of don't bother figuring out things, just buy from officials or ask dealership to do it.
All said reputable people aren't always as reputable as they seem, others also will try to sell you unnecessary stuff to make money, so in my book it is always good to be interested to learn about what you are doing, especially in the motomotive industry, people tend to try and fool those who have no clue.

Without going too far in electrical theory of course !
« Last Edit: March 03, 2020, 01:24:51 PM by Djairouks »

Offline T800XC

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Re: 2018 XRX LED indicators
« Reply #17 on: March 03, 2020, 01:09:47 PM »
*Originally Posted by Igore1 [+]
...That's why they are actually rated for 14V which calculates out to just over 9W rated...
This is the bit that's the wrong way around. By design the resistors have a rated power which is usually based on the product range, from which you can derive their maximum working voltage for each resistance in the range. i.e. V = (PxR)1/2

Motorcycle indicator resistors such as these 9W versions from Oxford Products... Oxford OF374 Resistors ...typically contain a Vitrohm Ceramic Wirewound Resistor such as these... Vitrohm KH214-8 Resistors.

As it stands, it seems like you have suitable resistors for the job so time to enjoy riding!  :306:
  
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Online philmcglass

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Re: 2018 XRX LED indicators
« Reply #18 on: March 03, 2020, 03:09:50 PM »
I believe that resistors are rated for power dissipation rather than voltage.
Power dissipated is I^2 * R.
T800XC advised that load needs to be between 1 and 2A. Lets pick 1.5A

If you want a specific current from 12V need to select the resistor value.
Say you need 1.5A then resistor needs to be 8Ohms.
Power = 1.5 * 1.5 * 8 = 18W.
But you can include the duty cycle say 50% so average power 9W
To give a bit of derating (say 30%) then a 12W resistor is suitable.

But the actual voltage is closer to 14V on a vehicle.
So the 8 Ohms will give a current of 1.75A.
Power will be closer to 24.5W peak or ~13W average.
So basing calculations on 12V supply may result in under-spec resistor power rating.

Or reselect the resistor to cope with 14V supply.
9Ohm may be suitable.

14/9 = 1.55A
Power = 21.7W peak ~11W average.
Could select 15W resistor.
Can't remember all the available values depends on range E12/ E24.
E12 nearest is 8.2Ohm E24 has 9.1Ohm.

https://www.electronics-notes.com/articles/electronic_components/resistors/standard-resistor-values-e-series-e3-e6-e12-e24-e48-e96.php
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