Model Boat Mayhem

Technical, Techniques, Hints, and Tips => The "Black Arts!" ( Electrics & Electronics ) => Topic started by: Gopher on November 01, 2016, 08:35:50 PM

Title: voltage reducer v resistors
Post by: Gopher on November 01, 2016, 08:35:50 PM
Evening all just a quick question, voltage reducer v resistors which is better for led's?
Title: Re: voltage reducer v resistors
Post by: steamboat66 on November 01, 2016, 09:00:52 PM
due to their small power requirement (unless 1 watt or so power led), resistors. it keeps life simple.
Title: Re: voltage reducer v resistors
Post by: Gopher on November 01, 2016, 09:36:24 PM
Thanks for the reply, I was thinking of using one of the mini voltage reducer from the component shop to power 3 led's, I set one up using a resistor but it didn't seem as bright as with the reducer.
Title: Re: voltage reducer v resistors
Post by: NFMike on November 01, 2016, 10:14:58 PM
It's not the voltage that needs controlling for LEDs, it's the current. This is usually done with a resistor which is selected for the voltage supplied.
Even with a voltage reducer you ought to control the current, but as you have reduced the voltage you'll need a different value (less Ohms) resistor to get the same current and therefore brightness.

The advantage of reducing the voltage is that the resistor(s) won't get so hot.
Title: Re: voltage reducer v resistors
Post by: Gopher on November 02, 2016, 12:11:43 AM
That probably didn't come across right, the battery I will be using is a 7.2v, when I wired a white led with a resistor to the battery it wasn't as bright as it was with 3.3v, according to how I had worked it out I needed 195 Ohm the nearest was 200 which is what I got
Title: Re: voltage reducer v resistors
Post by: tigertiger on November 02, 2016, 02:58:05 AM
Sorry if I am stating something you already know here.


LED voltage rating is a push voltage rating. That is the minimum voltage needed to make them work. White LEDs are 3v push rating. The bigger the voltage, the brighter the light.  By tinkering with the resistance (i.e. using more than one resistor to a wider choice of resistances) you can get the LED to emit more or less light. Your extra 5 ohms could be making all of the difference that you see.
Title: Re: voltage reducer v resistors
Post by: Gopher on November 02, 2016, 08:30:17 AM
No that fine, I'm pretty new to it all so my knowledge is very limited, my way of thinking was the led wants 3.3v set the reducer to 3.3 and the jobs a good un
Title: Re: voltage reducer v resistors
Post by: malcolmfrary on November 02, 2016, 08:55:14 AM
That would be fine if the LED was a resistor, but it is a diode.  At the push voltage, it doesn't offer any electrical resistance, this is provided by the ballast resistor or a constant current source of which one is needed for each series chain of LEDs (including chains of one).
Don't be misled by LED flashlights - they usually rely on the internal resistance of their battery.  To increase confusion, some LEDs have the required current limiting built into the package.
As a general rule, as with many things in life, the brighter it shines, the shorter its life.
Title: Re: voltage reducer v resistors
Post by: Gopher on November 02, 2016, 09:32:34 AM
They are supposed to be bright, I got them from the component shop described as ultra bright wide angle, I have them in 3 spotlights
Title: Re: voltage reducer v resistors
Post by: g6swj on November 02, 2016, 09:41:16 AM
Component shop have a guide as to how to use LED's  - A GUIDE TO THE USE OF LEDs IN MODELLING

http://www.componentshop.co.uk/led-exp/



Title: Re: voltage reducer v resistors
Post by: inertia on November 02, 2016, 09:54:07 AM
There is also a very good article on using LEDs in the Winter 2016 edition of Model Boats magazine, currently on sale.
DM
Title: Re: voltage reducer v resistors
Post by: Martin [Admin] on November 02, 2016, 12:06:12 PM
(http://www.modelboats.co.uk/sites/2/images/article_images_month/2016-10/mb%20winter%202016%201%20article.jpg)

http://www.modelboats.co.uk/news/article/model-boats-winter-special-2016/24191
Title: Re: voltage reducer v resistors
Post by: Stan on November 02, 2016, 02:04:53 PM
HI Guys Just finished some wiring this morning on my new fishing boat. Just a few pictures showing the resistors under the wheelhouse floor. All my circuits are in parallel I have always used the formula in the component shop book and never had any problems. This post is for info only and I have no wish to influence your choice of led size or how you connect them.

Stan.
Title: Re: voltage reducer v resistors
Post by: Gopher on November 02, 2016, 05:04:05 PM
Thanks Martin, been and picked up a copy, I shall have a read when grand children have gone home and I can sit and chill with a glass  of malt
Title: Re: voltage reducer v resistors
Post by: Subculture on November 02, 2016, 07:24:10 PM
You can run LEDs direct from a voltage regulator, but they must be run in series if doing so. If you run them in parallel, variations in the LED will cause one to offer a lower resistance path than the other. This makes it run hotter due to increased current flow, and it will eventually burn out. This is why you need current limiting resistors when running LEDs in parallel. In series the problem doesn't occur, but off course you lose some diversity, in if one component fails you lose the whole string.
Title: Re: voltage reducer v resistors
Post by: malcolmfrary on November 03, 2016, 08:54:24 AM
You can run LEDs direct from a voltage regulator, but they must be run in series if doing so. If you run them in parallel, variations in the LED will cause one to offer a lower resistance path than the other. This makes it run hotter due to increased current flow, and it will eventually burn out. This is why you need current limiting resistors when running LEDs in parallel. In series the problem doesn't occur, but off course you lose some diversity, in if one component fails you lose the whole string.
Running them in series requires current limiting just as much as parallel.  The formula is just a bit different.  Having it work without is down to good luck in the choice of power supply, and is not good design practice.
Title: Re: voltage reducer v resistors
Post by: Gopher on November 03, 2016, 09:12:21 AM
i am still trying to obtain the same brightness as when I connect the led to 2 AA batteries, when I put it through a resistor and on to a 7.2v it's no where near as bright and the 3 led's are in spotlights I would like to keep the as bright as possible
Title: Re: voltage reducer v resistors
Post by: Stan on November 03, 2016, 09:18:03 AM
Are these led standard ones or high brightness one?
Title: Re: voltage reducer v resistors
Post by: malcolmfrary on November 03, 2016, 09:22:10 AM
i am still trying to obtain the same brightness as when I connect the led to 2 AA batteries, when I put it through a resistor and on to a 7.2v it's no where near as bright and the 3 led's are in spotlights I would like to keep the as bright as possible
Measure the current using the 2AA, then measure using the 7.2 volt source and resistor.
Title: Re: voltage reducer v resistors
Post by: Gopher on November 03, 2016, 10:51:14 AM
They are the 5mm ultra bright wide angle ones from component shop
Title: Re: voltage reducer v resistors
Post by: Gopher on November 03, 2016, 05:58:14 PM
this is a picture of the resistors I got from Maplins, I  told the guy what I was doing and that I needed a 200 Ohm resistor this is what he sold me, the battery pack is giving me 7.68v, when I put it through the resistor it gives 6.40v and the 2 AA batteries give 3.13v, I must be doing something wrong but not sure what
Title: Re: voltage reducer v resistors
Post by: g6swj on November 03, 2016, 06:30:48 PM
If you have a meter - measure the resistance of the resistor in the pic

Can quite see the colours but that looks like 200k ohm

This is a link for a nifty little tool showing resistor values/colour bands ( use the + band button to get 3rd band)

 http://resistor.cherryjourney.pt

Jonathan
Title: Re: voltage reducer v resistors
Post by: Gopher on November 03, 2016, 06:39:23 PM
put my meter on it, it comes in at 195ish but the voltage is reading 6.40v I was expecting 3.3v
Title: Re: voltage reducer v resistors
Post by: Netleyned on November 03, 2016, 06:43:56 PM
Looks like 200k to me also.
Make sure you are reading
the right ohms scale on the
Meter.


Ned
Title: Re: voltage reducer v resistors
Post by: Gopher on November 03, 2016, 06:44:42 PM
Jonathan, I like that web site, it is a 200 Ohm,
Title: Re: voltage reducer v resistors
Post by: g6swj on November 03, 2016, 07:08:28 PM
If it looks like this then it's 200,000 ohm's (200K) - the second image is 200 ohm
Title: Re: voltage reducer v resistors
Post by: NFMike on November 03, 2016, 07:28:33 PM
this is a picture of the resistors I got from Maplins, I  told the guy what I was doing and that I needed a 200 Ohm resistor this is what he sold me, the battery pack is giving me 7.68v, when I put it through the resistor it gives 6.40v and the 2 AA batteries give 3.13v, I must be doing something wrong but not sure what

Are you just connecting the resistor to one terminal of the battery pack and then your meter from the other battery terminal to the loose end of the resistor?
Title: Re: voltage reducer v resistors
Post by: Subculture on November 03, 2016, 07:38:39 PM
Running them in series requires current limiting just as much as parallel. 

So if you have four white LED's wired in series fed from a regulated 12 volt supply, what value resistor do you use?
Title: Re: voltage reducer v resistors
Post by: Gopher on November 03, 2016, 08:38:36 PM
sorry for the delay in getting back, G6swj it's the top one, red, black, black, orange , brown. is it right or wrong?  Plague, pretty much, I have tagged into my feed for the voltage reducer that powers my nav lights and exterior lamps and finally Subculture, I am probably wrong but if you have 4 white led's in series you would need 13.2v, some one on here will know for sure
Title: Re: voltage reducer v resistors
Post by: g6swj on November 03, 2016, 08:51:11 PM
Gopher - The resistor you have is 199,800 ohms more than the one you thought you where buying - it is 200,000 not 200 OHM!!!

So I think another trip to Maplin may be on the cards...

Suggest you print off one of the many resistor colour code calculators from the net eg http://www.hobby-hour.com/electronics/resistorcalculator.php
and take it to Maplin so you can confirm what you are getting before leaving the store. Must be frustrating - stick with it - we are all learning from your journey :)

Regards
Jonathan



Title: Re: voltage reducer v resistors
Post by: Gopher on November 03, 2016, 09:01:26 PM
this might sound a bit daft but if it was that much higher than I needed why didn't it wipe my voltage out, it only dropped it just over a volt
Title: Re: voltage reducer v resistors
Post by: Stavros on November 03, 2016, 09:17:17 PM
Oh WHY oh WHY have you not contacted Component shop and simply tell them what Led's you bought off them and the voltage you are using and they will sell you the PROPER resistors.......................Maplin's I simply wouldnt give them time of day with resistors as they dont know what they are doing let alone selling........Young spotty nosed kids just out of their nappies.


Was in the local Maplins on monday and a customer wanted a charger for a 12v 10amp lead acid batt  and the young kid tried his best to sell him a car batt charger that was rated at 12amps I simply laughed and told him DONT and had to show him the correct charger that they sold ......THATS how GOOD they are NOT






Dave
Title: Re: voltage reducer v resistors
Post by: g6swj on November 03, 2016, 09:34:39 PM
Dave,

Good suggestion re CShop - but you don't learn squat - half the fun is working through "it doesn't work" to "yeah I did that" - and that's where the learning comes from, not just for the individual but the many "silent" forum users.  There are lots of people on here as you know who could answer this without batting an eyelid.

So Gopher which ever route you take do let us know how you get on.....

Regards
Jonathan

Title: Re: voltage reducer v resistors
Post by: Stan on November 03, 2016, 09:43:38 PM
HI Gopher did you order the resistors that put on the sketch I sent you last week? The value on the sketch were 195 ohms nearest value to this would have been 200 ohms, I have included some pictures of my latest wiring in my new fishing boat. If you use the formula in the C/Shop book you will have no problems.

stan
Title: Re: voltage reducer v resistors
Post by: Gopher on November 03, 2016, 09:47:07 PM
I like to try and work things out if poss that's why I ask daft questions, but I think I will contact  the c-shop need a few more bits and let them supply the right gear, I will prevail one way or another
Title: Re: voltage reducer v resistors
Post by: Gopher on November 03, 2016, 09:49:54 PM
Stan, I told the guy what I wanted, he sold me the wrong ones
Title: Re: voltage reducer v resistors
Post by: g6swj on November 03, 2016, 09:52:20 PM
I like to try and work things out if poss that's why I ask daft questions,

The only daft question is the one you didn't ask!
Title: Re: voltage reducer v resistors
Post by: Stan on November 03, 2016, 09:57:35 PM
Sorry to hear that you were sold the wrong ones lets hope when the new ones arrive this will sort out the problems you have had. I have  posted some pictures for you to have look at hang there all will come good.

Stan.
Title: Re: voltage reducer v resistors
Post by: malcolmfrary on November 04, 2016, 10:21:44 AM
If you took your voltage readings without the LED in circuit, the very small voltage reduction is about what would be expected with a high resistor value dropping the current that the meter could read from.  If the LED was in circuit, the very high value of resistor might well limit the current below the level where the LED could properly switch on and show its expected properties.  The reading might well be just the effect of trying to read the voltage through a high value resistor.
With the correct value, you will get the right results.  Like I said earlier, you need to read the current drawn when the LED is fed by the voltage source and calculate the resistor value for the 7.2 volt source accordingly.  But 200Ω sounds about right, provided the store assistant can tell the difference between brown and orange, or K and Ω.
Title: Re: voltage reducer v resistors
Post by: Gopher on November 04, 2016, 01:42:56 PM
Going to order some more bits from c-shop I will talk to them and sort out what I need
Title: Re: voltage reducer v resistors
Post by: RAAArtyGunner on November 04, 2016, 11:23:40 PM

Gopher, off subject Trivia.
I take it that Mansfield is in the UK.
Because there are two Mansfield's in OZ.
One in the state of  Victoria, a country town, The other in state of Queensland, a Brisbane suburb.
This would then make you an ornery Oztralian.
Back to boats.
Title: Re: voltage reducer v resistors
Post by: inertia on November 04, 2016, 11:28:06 PM
There is only one true Mansfield.
Believe me.......
DM
Title: Re: voltage reducer v resistors
Post by: RAAArtyGunner on November 05, 2016, 12:35:18 AM

Correct,  O0 O0 the one in Brisbane.  %) %)
Title: Re: voltage reducer v resistors
Post by: tigertiger on November 05, 2016, 07:52:58 AM
No, the one in Monte Carlo  ;) :o
Title: Re: voltage reducer v resistors
Post by: Kipper on November 05, 2016, 11:56:27 AM
There is only one true Mansfield.
Believe me.......
DM

If it's still the same as when I resided there in the early 80's ................... thank god there is only one.  :-)
Title: Re: voltage reducer v resistors
Post by: Colin Bishop on November 05, 2016, 12:02:57 PM
Jayne....?
Title: Re: voltage reducer v resistors
Post by: inertia on November 05, 2016, 12:30:36 PM
If it's still the same as when I resided there in the early 80's ................... thank god there is only one.  :-)
Nah. The rest of t'shops have since closed but t'sparrers still fly back'uds to keep t'muck out their eyes.... I doubt if there is any equivalent paradise in Oz; it's only been there a few billion years, after all.
For the benefit of our Oz cousins, Mansfield used to be a colliery town in North Nottinghamshire. The pits have long closed but it's still filthy-dirty and the rancour between the former members of the two rival pit unions still festers there. O, and they now have another Victorian employer who pays poverty wages and fines his slaves for going to the loo. His name is Mike Ashley and he owns JJB Sports and some football club up north somewhere..... ;D
For what it's worth I always use resistors with LEDs, mainly because I have boxes of the things!
 DM
Title: Re: voltage reducer v resistors
Post by: Gopher on November 05, 2016, 04:13:40 PM
Sports direct
Title: Re: voltage reducer v resistors
Post by: inertia on November 05, 2016, 05:39:46 PM
Yep - you're right. I don't use either, not being the huntin', shootin' and fishin' type (are there any of those old duffers left??).
He's still a thoroughly nasty piece of work, though.
The folk of Shirebrook deserve better.
DM
Title: Re: voltage reducer v resistors
Post by: Gopher on November 05, 2016, 09:35:17 PM
Got a lot of family in Shirebrook, it' like a mini eastern block state now, it's full of polish, Latvians and so on all working at sports direct
Title: Re: voltage reducer v resistors
Post by: RAAArtyGunner on November 06, 2016, 12:52:39 AM
Nah. The rest of t'shops have since closed but t'sparrers still fly back'uds to keep t'muck out their eyes.... I doubt if there is any equivalent paradise in Oz; it's only been there a few billion years, after all.
For the benefit of our Oz cousins, Mansfield used to be a colliery town in North Nottinghamshire. The pits have long closed but it's still filthy-dirty and the rancour between the former members of the two rival pit unions still festers there. O, and they now have another Victorian employer who pays poverty wages and fines his slaves for going to the loo. His name is Mike Ashley and he owns JJB Sports and some football club up north somewhere..... ;D
For what it's worth I always use resistors with LEDs, mainly because I have boxes of the things!
 DM
Maybe our fore fathers had  some weird sense of humour in naming places in New Australia or to remind them of what they had gone before?                                                                                                         
Title: Re: voltage reducer v resistors
Post by: inertia on November 06, 2016, 09:00:57 AM
Maybe our fore fathers had  some weird sense of humour in naming places in New Australia or to remind them of what they had gone before?                                                                                                       
You can be sure of it. Melbourne Mk1 is actually in South Derbyshire, although I don't think there's an Alice Springs anywhere in UK. On the other hand the NE of the USA looks like a map of old English place names.
DM
Title: Re: voltage reducer v resistors
Post by: tigertiger on November 06, 2016, 09:04:53 AM
There is a village named California, just north of Bath and East of Bristol, in the UK.
Title: Re: voltage reducer v resistors
Post by: NFMike on November 06, 2016, 09:22:21 AM
There is a village named California, just north of Bath and East of Bristol, in the UK.
I think you mean Pennsylvania, unless there is a Cali too.  :-)
Title: Re: voltage reducer v resistors
Post by: Colin Bishop on November 06, 2016, 10:19:31 AM
Names are repeated all over what used to be the British Empire. In the course of a visit to Nova Scotia (geddit?) this year, we left Halifax, stayed overnight at Liverpool on the River Mersey and had lunch in Yarmouth. There were many other examples of towns being named after the original UK ones.

Colin
Title: Re: voltage reducer v resistors
Post by: Gopher on November 08, 2016, 06:42:28 PM
just a quick update, today I received a little parcel from the component shop full resistors and led's, I ordered what I thought was right, but just to be sure I emailed and asked them to check I gave them the voltages I work with, they were extremely helpful and  told me I had got it right, I have tried a random sample and I am a very happy bunny, maplins are kicked well into touch, and if any of the component shop guys are on here many thanks and the same to everyone else who had an input, although we did wander a bit at the end, how we go from voltage reducers to Mike Ashley I'm not sure
Title: Re: voltage reducer v resistors
Post by: Stan on November 08, 2016, 06:54:35 PM
Pm sent.




Stan
Title: Re: voltage reducer v resistors
Post by: Stavros on November 08, 2016, 08:01:13 PM
Funnily enough I spoke to iain personally about this today and he knew all about it ..........Iain is a member on here and he will see what has been posted




Dave
Title: Re: voltage reducer v resistors
Post by: inertia on November 08, 2016, 11:25:11 PM
I think you mean Pennsylvania, unless there is a Cali too.  :-)
There's a California just to the south west of Derby city centre. Sunshine and surf don't get a look-in there. It makes Shirebrook look like The Seychelles.

Mike Ashley is marginally more interesting than LEDs....unless you're deeply interested in LEDs. Those MPs missed a trick today; one of them should have pocketed the "hidden" camera and said nowt. Perfect blackmail material...  http://news.sky.com/story/sports-direct-denies-knowledge-of-hidden-camera-in-tray-of-sandwiches-10649803 (http://news.sky.com/story/sports-direct-denies-knowledge-of-hidden-camera-in-tray-of-sandwiches-10649803)

Maplins resistors are unfeasibly expensive, even if you buy a lot. Don't.

DM