Model Boat Mayhem - Forum

Technical, Techniques, Hints, and Tips => The "Black Arts!" ( Electrics & Electronics ) => Topic started by: mersey dave on February 07, 2014, 11:59:26 AM

Title: what size resistors
Post by: mersey dave on February 07, 2014, 11:59:26 AM
Hi all, can someone tell me if I was to run LED's off 9 volts what size resistor would I need to use.

Best regards Dave.
Title: Re: what size resistors
Post by: malcolmfrary on February 07, 2014, 12:29:23 PM
It depends on the number and type of LED, and how you intend to wire them and how bright you want them.
A handy calculator here - http://ledcalc.com/ (http://ledcalc.com/)
Title: Re: what size resistors
Post by: More Coffee on February 07, 2014, 02:52:51 PM
Hi all, can someone tell me if I was to run LED's off 9 volts what size resistor would I need to use.

Best regards Dave.
I put together a dome light in my truck(40ultra bright super flux leds). I just made my circuit and used two 1watt 100ohm resistors..Its not the proper way to do it , but it can be done.
so it is possible to use 1 resistor light up the whole works.. I would stress that you bread board that circuit first ,more so if your leds are not all the same. its is possible to blow leds doing what I did.

Chances are , 3.2v and 20ma are general led power requirements ,On 9 volt
http://led.linear1.org/led.wiz (http://led.linear1.org/led.wiz)

Solution 0: 2 x 4 array, 1 extra LED
    +----|>|----|>|---/\/\/----+  R = 150 ohms
    +----|>|----|>|---/\/\/----+  R = 150 ohms
    +----|>|----|>|---/\/\/----+  R = 150 ohms
    +----|>|----|>|---/\/\/----+  R = 150 ohms
    +----|>|----------/\/\/----+  R = 330 ohms

The wizard says: In solution 0:
  each 150 ohm resistor dissipates 60 mW
  the wizard says the color code for 150 is brown green brown
  the wizard thinks シW resistors are fine for your application
  the 330 ohm resistor dissipates 132 mW
  the wizard says the color code for 330 is orange orange brown
  the wizard thinks シW resistors are fine for your application
  together, all resistors dissipate 372 mW
  together, the diodes dissipate 576 mW             
  total power dissipated by the array is 948 mW     
  the array draws current of 100 mA from the source.
 

Solution 1: 1 x 9 array uses 9 LEDs exactly
    +----|>|---/\/\/----+  R = 330 ohms
    +----|>|---/\/\/----+  R = 330 ohms
    +----|>|---/\/\/----+  R = 330 ohms
    +----|>|---/\/\/----+  R = 330 ohms
    +----|>|---/\/\/----+  R = 330 ohms
    +----|>|---/\/\/----+  R = 330 ohms
    +----|>|---/\/\/----+  R = 330 ohms
    +----|>|---/\/\/----+  R = 330 ohms
    +----|>|---/\/\/----+  R = 330 ohms


The wizard says: In solution 1:
  each 330 ohm resistor dissipates 132 mW
  the wizard says the color code for 330 is orange orange brown
  the wizard thinks シW resistors are fine for your application
  together, all resistors dissipate 1188 mW
  together, the diodes dissipate 576 mW             
  total power dissipated by the array is 1764 mW     
  the array draws current of 180 mA from the source.
Title: Re: what size resistors
Post by: mersey dave on February 07, 2014, 03:57:55 PM
WOW......didn't know you had to work all that out . Now my head is well done in. :-)) :-))

Thanks guys Dave.
Title: Re: what size resistors
Post by: More Coffee on February 07, 2014, 04:31:13 PM
Anytime..Good luck :-))
Title: Re: what size resistors
Post by: Stavros on February 07, 2014, 05:30:11 PM
Dave contact Component shop they will sell you the PROPER resistors for your needs just tell them what the Led's are and voltage you want to use and they will do the rest for you ................far easier than getting confused .com
 
 
Dave
Title: Re: what size resistors
Post by: More Coffee on February 07, 2014, 05:49:34 PM
Im a little perplexed.. Starvos..
Colors/ number's /letters/math ..we learned this in elementary school. nothing has changed but the application in a different environment.

Im not talking anybody down. But the reality is , this whole electrical environment was put together by man , for man ...theres no reason any man could not pick it up ..
some get it quickly, others need a little more time..but no one cannot be taught.. We all have the ability to learn ,
Its a global phenomena , the technology is evolving , and peoples problem solving skills are diminishing.
I don't mind helping someone, but if you can teach that person , that knowledge will carry over. This is something that has been a corner stone of or society since humans have been living in groups .
A tribe wouldnt  flourish ,if the hunters did not share their experiences ,and teach the others.



 

 

(http://www.diyaudioandvideo.com/Electronics/Color/E24ResistorColorCodes.gif)
Title: Re: what size resistors
Post by: mersey dave on February 07, 2014, 06:19:57 PM
Dave contact Component shop they will sell you the PROPER resistors for your needs just tell them what the Led's are and voltage you want to use and they will do the rest for you ................far easier than getting confused .com
 
 
Dave

Thanks Dave, like you said far easier. :-)) :-))

Regards Dave.
Title: Re: what size resistors
Post by: More Coffee on February 07, 2014, 06:43:45 PM
LoL..

I know..Im guilty of it as well..
Title: Re: what size resistors
Post by: Stavros on February 07, 2014, 07:47:18 PM
You see More Coffee you might be more Aufee with the electrical side of things BUT some mayhemers arn't so WHY confuse them,they still have to get them from somewhere...........it is EASIER to SIMPLE to  direct them to a supplier who will NOT baffle them with science......................  I am RAF trained in electronics and even I just phone them up as it is FAR FAR easier for them to do it...............WHY ......................SIMPLES really ...............they do it on a DAILY basis
 
 
Dave
Title: Re: what size resistors
Post by: More Coffee on February 07, 2014, 08:41:52 PM
I agree.
Its why I hire contractors to do work. Not that I don't know how to do it, I make it my business to understand what needs to be done to avoid being ripped off.

The reason I hire them ,I really don't want to spend money on material and tools for a one time thing..the other reason ,5 guy's with the right tools ,doing what they do is often  faster and less stressful ..

But nobody gets the contract or money until Im clear in my own head and on paper exactly what has to be done . point for point step by step.
Its my money,his say so ..now everything has to jive. I learned at a young age ,trusting somebody to use my money to do something and not understand it fully is a bad idea.. And over the years ..I don't care if that money is a 3 cent LED
Title: Re: what size resistors
Post by: Geoff C on April 07, 2014, 04:58:27 PM
Hi Guys,    A slightly different question here,  I have a 6volt 4amp SLA battery and want to make a smoke unit using a resistor that will get hot enough to burn smoke fluid and also will not burn itself out.   Any ideas?    regards Geoff.
Title: Re: what size resistors
Post by: Stavros on April 07, 2014, 06:13:31 PM
Hi Geoff Why not save yourself the bother and use a proven one
 
http://www.cornwallmodelboats.co.uk/acatalog/graupner_2324.html (http://www.cornwallmodelboats.co.uk/acatalog/graupner_2324.html)
 
 
Dave
Title: Re: what size resistors
Post by: Netleyned on April 07, 2014, 06:28:34 PM
OK if you just want steam wafting from the funnel.
Controlling the amount with the speed needs a fan
driven system
Can be done home brew which modelling is supposed to
be all about.

Ned
Title: Re: what size resistors
Post by: malcolmfrary on April 07, 2014, 08:49:10 PM
Hi Guys,    A slightly different question here,  I have a 6volt 4amp SLA battery and want to make a smoke unit using a resistor that will get hot enough to burn smoke fluid and also will not burn itself out.   Any ideas?    regards Geoff.
Been there, got the tee shirt, eyebrows grew back OK.  Look in Maplin for their high wattage white porcelain power resistors.  The tricky bit is figuring out (informed guessing) just what the optimum value is, because said resistor will be working in a totally unexpected environment.  All the specs will tell you how to keep it in a safe, fairly cool range.  You want it hot enough to vapourize oil, and when it does that, it will effectively be oil cooled, throwing all the previous maths guesswork out.  5 Watt, 4.7 ohms, at a guess, fingers crossed behind my back.  Magic word is "Wirewound", colour coded film types will simply lot live long at the required temperature.
Get a few nearby values to play with, find some good wick (shortly before I gave it up, I was considering heat resistant woven insulation from the 'leccy department at B&Q).  A heatproof housing is a GOOD IDEA.  I made one out of fireclay, sort of like making pastry sheets, assemble, make holes in the sides near the top for the wires to come out, and bake in a hot oven.  Leave the resistor wires as long as possible, they dissipate heat hopefully into the box with the oil in.
The system produced plenty of smoke using just convection, a fan would certainly have helped, but run time was cut too far.
There is a strong case for the commercial units - they have been tried and tested, and they do work.  The case for home made is if the commercial ones are either the wrong voltage or just wont fit.
Title: Re: what size resistors
Post by: More Coffee on April 08, 2014, 01:52:12 AM
OK if you just want steam wafting from the funnel.
Controlling the amount with the speed needs a fan
driven system
Can be done home brew which modelling is supposed to
be all about.

Ned
its relatively simple actually.

All you need is a forward reverse brushed motor ESC to drive the fan.
The difference however, to keep the fan moving the same direction , proportional to throttle direction is two things.
A servo Y cable to operate your fan ESC of the throttle channel
A full wave bridge rectifier , often one can be found in an old hair dryer. The two output wires from the ESC ,go hooked to where the AC current would be hooked up on the rectifier, then the two DC output pins on the rectifier ,sort your polarity to operate the fan , and regardless which way your throttle is ,your fan will always be operating to blow the vapor out . in one direction only.



Title: Re: what size resistors
Post by: inertia on April 08, 2014, 08:49:36 AM
this whole electrical environment was put together by man , for man ...there's no reason any man could not pick it up ..
some get it quickly, others need a little more time..but no one cannot be taught.. We all have the ability to learn

The eternal optimist. I've met more than a few people who, when confronted with a length of wire, simply shrug and tell me "I don't understand electronics" - almost as if it was an immutable fact of life, like a disability at birth. My reply is that it isn't cool to be dumb - it's just lazy.

Ref the fan blower, the easiest solution is to stick your hand in your pocket http://www.action-electronics.co.uk/pdfs/P68S.pdf (http://www.action-electronics.co.uk/pdfs/P68S.pdf)  This gizmo supplies a slight breeze even at neutral, increasing as you open the throttle either way.

Suit yourself.

DM
Title: Re: what size resistors
Post by: Geoff C on April 08, 2014, 10:18:17 AM
Thanks Guys for the info.     I've read about the Action gizmo, great idea, I've also read some Posts on here about resistors too.     The values differ so much, ie. 1watt 5ohms to .5watt 12ohms, I've ordered some from Maplins.    I think most work better on 12volts but I'm 6volts 4amp SLA.   Regards all,  Geoff.
Title: Re: what size resistors
Post by: More Coffee on April 08, 2014, 04:54:18 PM
It doesn't matter really. But it really matters at the same time.
testing on the bench ,see what get hot ,or not .

I set my self up as a general rule of thumb ,on 12v system .
3 leds in a string with 1/4 watt 470ohm resistor.
1 led  1/4 , 1000ohm resistor.

if it really matters on the brightness , I'll use a 1000ohm potentiometer in conjunction with the resistors. this way I cant blow the led because theres always a resistance by way of the resistor.

leds generally work on 3.2v ,30milliamp..that's an extremely general assessment of a led .



Solution 0: 1 x 1 array uses 1 LEDs exactly
+6V
+ -|>|- -/\/\/\- + R = 100 ohms
 
The wizard says: In solution 0:鋲ach 100 ohm resistor dissipates 90 mW
付he wizard thinks 1/4W resistors are fine for your application Help
付ogether, all resistors dissipate 90 mW
付ogether, the diodes dissipate 96 mW
付otal power dissipated by the array is 186 mW
付he array draws current of 30 mA from the source.


Solution 0: 1 x 1 array uses 1 LEDs exactly

+12V
+ -|>|- -/\/\/\- + R = 330 ohms
 
The wizard says: In solution 0:鋲ach 330 ohm resistor dissipates 297 mW
付he wizard thinks 1/2W resistors are needed for your application Help
付ogether, all resistors dissipate 297 mW
付ogether, the diodes dissipate 96 mW
付otal power dissipated by the array is 393 mW
付he array draws current of 30 mA from the source.


The above,6 and 12 volt system for one led.
3.2v and 30ma current

the wattage goes up, on a higher voltage system ,hence a higher wattage resistor.

The reality is ,
on 6v you need lower wattage resistors.
on 12v you need higher .
 however

Solution 0: 3 x 1 array uses 3 LEDs exactly

+12V
+ -|>|- -|>|- -|>|- -/\/\/\- + R = 82 ohms
 
The wizard says: In solution 0:鋲ach 82 ohm resistor dissipates 73.8 mW
付he wizard thinks 1/4W resistors are fine for your application Help
付ogether, all resistors dissipate 73.8 mW
付ogether, the diodes dissipate 288 mW
付otal power dissipated by the array is 361.8 mW
付he array draws current of 30 mA from the source.

by putting 3 leds in series vs a single led on 12v , a guy can still use 1/4 watt resistors.

as an experiment ,switch the 82ohm for a 470ohm resistor , the difference visually is little.







Title: Re: what size resistors
Post by: RMH on April 08, 2014, 05:29:49 PM
Well that's made things nice and clear
Title: Re: what size resistors
Post by: Netleyned on April 08, 2014, 05:49:43 PM
Floodlit Smoke %% %%

Ned
Title: Re: what size resistors
Post by: Geoff C on April 08, 2014, 06:18:08 PM
I found these on "Black Arts"
Title: Re: what size resistors
Post by: Steve Dean on April 08, 2014, 08:04:51 PM
The subject of the resistor value to use with LEDs seems to be a recurring topic despite the fact that I've written two articles in Marine Modelling International on this topic and another contributor has an article in the current issue. OK, so some folks don't buy magazines so let's make this real easy for those people who are terrified by some very simple math.


No need to get all bogged down in Ohms Law and lots of techie stuff that people like myself and Dave at Action deal with every day.


Here's the simple way. The important aspect is the forward voltage of the LED. This varies with the colour. For most red LEDs this typically 2 Volts and most other colours it's between 2.4 and 3.3 Volts.


Now here's a really simple formula:


(Supply Voltage - Forward Voltage) x 50


Therefore if we are using a 12 Volt battery and a Red LED with a voltage drop of 2 Volts, then the formula looks like this:


(12 - 2) x 50


As the first part of the formula is in brackets, then you do that bit first, i.e. 12 - 2  = 10. Then multiply the answer by 50. i.e. 10 x 50 = 500


Therefore you need a 500 Ohm resistor. As this is not a preferred value, then you use a preferred value that is the next value up. This is 510 Ohms.
You will quickly learn that LEDs are very bright, so therefore use a higher value resistor, something like 680 or 1K (1000) Ohms.


To help you get the hang of the formula we'll change the battery to 6 Volts. Then we get the following:


(6 - 2) x 50


Which is 6 minus 2, i.e. 4. Then multiply by 50 and the answer is 200. To stop the LED being too bright use something like 270 Ohms or even higher.


Next time you're at a show pick up a Component Shop catalogue and you will find this formula and some examples in the back of the catalogue.
The catalogue is FREE and their LED prices are very competitive.


Hope this helps you all.


Steve.
Title: Re: what size resistors
Post by: Stan on April 08, 2014, 09:11:16 PM
I use this simple method every time never had any problems. I am at present fitting LED to a model tug  fitted the resistors in place ready for wiring.

Stan. :(( :(( :(( :(( :-)) :-)) :-)) :-)) :-))
Title: Re: what size resistors
Post by: RMH on April 08, 2014, 09:28:50 PM
Thanks for the simplified calculations Steve that helps a lot as I'm about to try and work out what I need to light up the Severn

Rich
Title: Re: what size resistors
Post by: More Coffee on April 09, 2014, 03:27:44 AM
The subject of the resistor value to use with LEDs seems to be a recurring topic despite the fact that I've written two articles in Marine Modelling International on this topic and another contributor has an article in the current issue. OK, so some folks don't buy magazines so let's make this real easy for those people who are terrified by some very simple math.


No need to get all bogged down in Ohms Law and lots of techie stuff that people like myself and Dave at Action deal with every day.


Here's the simple way. The important aspect is the forward voltage of the LED. This varies with the colour. For most red LEDs this typically 2 Volts and most other colours it's between 2.4 and 3.3 Volts.


Now here's a really simple formula:


(Supply Voltage - Forward Voltage) x 50


Therefore if we are using a 12 Volt battery and a Red LED with a voltage drop of 2 Volts, then the formula looks like this:


(12 - 2) x 50


As the first part of the formula is in brackets, then you do that bit first, i.e. 12 - 2  = 10. Then multiply the answer by 50. i.e. 10 x 50 = 500


Therefore you need a 500 Ohm resistor. As this is not a preferred value, then you use a preferred value that is the next value up. This is 510 Ohms.
You will quickly learn that LEDs are very bright, so therefore use a higher value resistor, something like 680 or 1K (1000) Ohms.


To help you get the hang of the formula we'll change the battery to 6 Volts. Then we get the following:


(6 - 2) x 50


Which is 6 minus 2, i.e. 4. Then multiply by 50 and the answer is 200. To stop the LED being too bright use something like 270 Ohms or even higher.


Next time you're at a show pick up a Component Shop catalogue and you will find this formula and some examples in the back of the catalogue.
The catalogue is FREE and their LED prices are very competitive.


Hope this helps you all.


Steve.

On the same note, leds maintain their colour . meaning where an incandescent light will fade and turn yellow because its a heated filament, leds as you know are semi-conductors built around parameters, a guy wont be able to produce that warm mast light look unless he chose's warm white or amber leds.
Just thought Id throw that in ,just in case the ext question is yellowing and ultra bright white led, a guy may have to put varnish on it and build it up ,maybe even sand the outside of the led to give it some hue ,if its a clear led.

dosent make sense ...does it.. :-X
Title: Re: what size resistors
Post by: Geoff C on April 09, 2014, 09:58:02 AM
However, We seem to have drifted off resistors for smoke units and gone to resistors for leds, as so often happens.     Thanks for all the relevant smoke info, it's much appreciated.      If and when I put leds in my smoke unit I have all the info I need, many thanks indeed.        Regarding lights, has no-one heard of grain of wheat/rice bulbs yet?      I use 6volt bulbs powered by 4.8volts ( 4 AA batteries )  and the light is perfect and they'll never blow.      How many tug models have we seen with masthead and side lights as bright as searchlights ?     Too many I fear.     best regards, Geoff.
Title: Re: what size resistors
Post by: Geoff C on April 09, 2014, 12:15:47 PM
6volt bulbs on 4.8volt battery pack,   regards,  Geoff.
Title: Re: what size resistors
Post by: More Coffee on April 09, 2014, 02:51:07 PM
Yeah it happens {:-{

have to remember though, conversations do run along.

In regards to resistors for a smoke unit.

while resistor's are handy,

I mentioned before ,about using a full wave bridge rectifier to run a fan the  of an ESC.

I mentioned getting that part from an old hair dryer ,

when your done scrapping that hair dryer ,

you will be left with a bunch of bits , a switch,a thermal switch, motor and ducted fan, and the heating element wire for the hair dryer. nichrome wire..
A guy can experiment with what length of wire will produce the smoke he wants.

then its just a matter of measuring the resistance of that length of wire ,to make replacements.

simple..all a guy needs is an old hair dryer to begin bodging  a smoke unit 

http://en.wikipedia.org/wiki/Nichrome

grain of wheat bulbs are incandescent .there life span and current requirements

like any incandescent bulb ,everytime you turn it on you risk blowing it ,

Leds are solid-state and low current requirements ,can last 20years, and more than 500,000 power on cycles, can run upto 750,000hrs.

a guy could easily get this out of and incandescent bulb. Just don't cycle it of or on.

I have a Compact flouresent (different beast I know)bulb on my back porch ,13watt ,it been there 6years , I don't turn it of , I vee replaced every other bulb from that same package ,except for that one, no cycles no wear and tear .
Title: Re: what size resistors
Post by: RMH on April 09, 2014, 02:58:47 PM
The thread actually started off about LED's and somehow drifted onto smoke units !!
Title: Re: what size resistors
Post by: More Coffee on April 09, 2014, 03:00:53 PM
But ,you may want to put a power indicator led on your smoke unit :-))

Its all good .
Title: Re: what size resistors
Post by: Netleyned on April 09, 2014, 03:43:42 PM
Still looking for Red and Green oil for my old steam tug
running lights.
Used to get Aladdin Pink, Regent Green .
Police and lifeboats used ESSO Blue.   %% %%

Ned
Title: Re: what size resistors
Post by: Geoff C on April 09, 2014, 05:57:39 PM
Thanks everyone for all your comments, kind regards, Geoff.
Title: Re: what size resistors
Post by: More Coffee on April 09, 2014, 06:29:38 PM
Led calculator

http://led.linear1.org/1led.wiz

http://led.linear1.org/led.wiz