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load resistors

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Swapped incandescent to LED and now they either don't flash or flash that fast you can't see the flash.

Memory is telling me I need to add a load resistor to trick some black box into waking up, all good on that.

Off went the 12V 10W globes.

Locally all I can find is 12V 21W or 12V 5W load resistors. I'd prefer local and the 5W as they are a lot smaller.

Does anyone know if the 5W will do the business or how to work out what will?

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What type of light is this?  And what does it do?  What are the specs or do you have a link to the LED you have replaced it with?     I ask as I suspect if might be a capacitance issue or maybe just a bad contact?


If you are certain you need a load resistor, then based on a 10watt/12v globe, the resistance you are after is 14.5ohms.  But that doesn't make sense at all because,  why would you just throw away current as heat?  when you are trying to save it by using a LED bulb?  


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My comments are answering mcp as well as KM.

So In very basic terms, as there are many different versions and complexity of design, the little black box that makes the indicators flash is simply a switch and circuit that switches on/off due to the load. With no load, as in LED's, they go nuts.  The idea of this design is that the driver will know if a bulb in the circuit has failed. But we have Drivers today that find that a challenge of understanding anyway.
The LED does not produce much of a load, so the switch opens/closes really quickly. More modern complex units are fully solid state timed switches and will work ok with LED's.

The load KM is talking about tricks the more basic unit into thinking the Bulbs are all OK. The load is calculated based on presenting the correct load to the flasher unit to allow it to operate a a correct flash interval.

Usually the indicator and Brake bulbs are 21W. So the 21W load resistor should be the one you want KM.

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WR250F, a full noise dirt beast which the previous owner stuck some indicators on and made it road legal. It's handy for a 7am Sunday zip into the black block of West Rodney to burn a tank of dinosaurs on the gravel and many 'paper roads' out that way. It will be moving north shortly to live on the farm and spend its days ya hooing around the back blocks of mid northland, yes Steve it's coming at you :) :) 

But when plying in the dirt indicators get wiped out fast and can also remove body parts so when heading into the bush the indicators have to come off. But I found a set of micro LED ones that are no bigger than just the bulb of the old ones so in my new found hobby of pulling motors apart and rebuilding them* I've mounted the micro in a manner they can stay when going dirt. But in doing so found out about the lack of load hence the investigation and need of load resistors.

* - I've always maintained and done basics fine but only ever pulled anything significant apart a couple of times, all in the middle of the deep blue as they stopped working. I did get them all back together and working again but they were exercises very much in the 'hit n hope, busted now so can't make it worse' theory. Started in lockdown bored one day, I pulled a lawnmower that hadn't gone for many years apart and got it going again so I thought a the logical step from a Briggs n Stratton lawnmower engine was a highly tuned and engineered Yamaha motor.

A suss of the local bike shops said the system is 'pre-led' so there probably isn't a flasher unit capable that will also fit. These machines don't have any fat including room as I've found out. I wired in a simple plug so I can use a battery monitor, finding room just for that wee thing was tricky than you'd think.

I have found 12V 10W load resistors in Sydney. $10 a pair so chinese shitters I suspect but from a reputable place and for bike lights so worth a punt I reckon. This is a fun hobby thing so the learning alone is worth the crack.

The globes/bulbs in the old ones are 10W.

Educate me time -

I see lots of specs mentioning Ohms but there seems no pattern to them, in relation to load resistor sussing. As I don't know much about them I looked for patterns to see if something popped out but nothing did. With one lot Narva 12V 21W resistors it says this 'Note: Load resistors must be mounted to metal surfaces. Operating temperatures can reach 170C damaging plastics, carpets and painted surfaces. ' but that was the only one that made any comment like that. It did raise an eyebrow as I thought 'Shite! that's hot', which is why I though go smaller may equal less heat??? 

Then MOC says this.

11 hours ago, mcp said:

If you are certain you need a load resistor, then based on a 10watt/12v globe, the resistance you are after is 14.5ohms.  But that doesn't make sense at all because,  why would you just throw away current as heat?  when you are trying to save it by using a LED bulb? 

So, this Ohms and heat comment, can you explain that a little more?

Never to old to learn and this is proving a wee bastion of sanity for the few minutes I can grab here n there amongst what is a very crazy existence at the moment.

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Ohms is the name given to the resistance to electrical flow. 1 Ohm is considered a very low resistance  and thus allows a greater flow of electricity than say 1000 Ohm.
0 Ohms would be a perfect conductor.
The wattage or power rating of a Resistor is the amount of heat the resistor can dissipate safely without affecting the resistance or burning up and failing completely. So a 1Watt resistor can safely dissipate 1W of heat. Resistors are made from many different materials. Some can be carbon film and some high heat dissipating ones are wire wound.

The Bulb is actually very similar to how a Resistor works. It is a filament of wire that can be heated to a very high temperature and yet still remain intact and strong enough to be able to handle vibration. Tungsten is often used. Cold, it presents a very low resistance. As the electrical energy flows across the filament, that resistance causes the filament to heat up until it is hot enough to emit light. As the temperature increases, the resistance increases, till an equilibrium is reached between electrical flow and resistance and the Bulb emits the designed amount of light output. At that point, the bulb is consuming energy and producing light via the radiation of heat. That energy should be equal to the rating of the Bulb. Lets say 10W. Thus a 21W bulb is consuming more energy, getting much hotter and thus creating a brighter light. That is why White light has a range of Colour temperature, measured in Kelvin. Brighter the White light, the higher the Colour temperature. But it gets confusing here, because very White light is considered is becoming more Blue and considered "cold" and lower white tends to be reddish and is considered Warm.

The older basic Flasher units are simply a Bimetal with a switch contact on the end. The Bimetal has a coil of wire wrapped around it which measures as a high resistance. It could be say 1K Ohms. When the indicator switch is closed, an electrical current flows through the winding of wire. The normal Bulbs are cold and almost a short. So the greater amount of current flows through the 1K winding around the Bimetal. This heats the Bimetal which in turn, bends and closes the switch contact. The switch contact now allows the Electrical energy to flow unimpeded and the coil of wire now starts to cool. The increased electrical energy causes the Filiments to suddenly glow and the impedance instantly rises. The Bimetal is cooling and and trying to open the contacts, which it eventually does and the electrical energy now flows through the coil again, not enough is flowing through the bulbs, so they go cold again ti; the Bimetal heats and closes and on goes the cycle.

The modern flasher that IT has described is all done by electronic timing. The only issue and reason why I didn't suggest an LED flasher unit is that I doubt one would be available for your Bike. Of which I figured you were likely playing with. 

I hope all that made sense.


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Ah ha, that all makes sense. It's a lot easier to understand that hocus pocus when you actually hands on with it. So fitting the 21W option, the one that notes heat build up, wouldn't be a worry for me as I wouldn't be pushing 21W though them but the 5W could be as it must be pushing twice that to run the old 10W bulbs. That the right thinking?

The resistors I have coming say they are concrete, which seems a bit Ya What??? From Aussie so maybe a translation issue :)

I can't find the flasher unit on the bike and stuff is jambed in weird places. There is some pile of stuff jambed up where I can't get at it but I am going to pull off the carby to tickle the hot start cable so I may find something up above that. There is that little room the oil lives inside the frame....and quite a bit of it I found out when I drained it.

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Concrete - likely a ceramic housing that has a wire wound resistor inside it.
Are the resistors special made for purpose? as in, they have a plug fitted or something?  Because I probably could have given you something that would have done the job.
Understand that commonly, 21W bulbs are usually used for Brake and Indicator and 10W is used for Park/Number plate lights.

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