Can you make my 12v LED light up?

Discussion in 'LEDs and Optoelectronics' started by Dave 2000, Nov 11, 2017.

  1. Dave 2000

    Dave 2000

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    Hi all, this sounds easy enough right?

    I will keep it as short as possible, please ask questions that you feel need answering.

    My vehicle used to have a two speed electric cooling fan fitted, the speeds indicated by two 12v LED's in a custom built module in my vehicles dashboard. These were fed via the same relays that switched the fan speeds, the relays controlled by a combination of engine temperature fan switches and AC presure switches. This has worked fine for years but the fan now getting old and OE fan replacements no longer available, copies are poor quality, so the decision was made to move to a more modern fan.

    My choice was dictated by a website stumbled on during my search for the replacement fan a Mercedes unit, but it is controlled via PWM. There is a supplier of controllers designed specifically for the Mercedes fan and he confirms that it should work with my system however, his dashboard mounted LED changes colours dependant on the fan speed related to engine temperature, and uses an LED that has a much lower voltage rating than my 12v unit. My custom dashboard display cannot be modified to accept his multicoloured LED so, I am looking for a way to use the PWM signal that tells the fan to start spinning to trigger a 12v supply to my present LED.

    I have asked the controller supplier about this but have not had a reply yet so, in the meantime I am researching to see if it is something I can purchase 'off the shelf' or even build myself? I may be wasting my time (and yours) as the supplier of the controller may already have it sorted?

    Given my limited electronics knowledge I gather the PWM signal changes to control the fan speed so guess this adds some complexity?

    A mechanic by trade, I have worked with relays in the fuel system that receive a signal from the ecu to keep a 12v relay active and supply 12v to the fuel pump, that more or less covers my knowledge in this area, but hope you get my way of thinking here?

    Any thoughts on this guys and girls?

    Regards

    Dave
     
    Dave 2000, Nov 11, 2017
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  2. Dave 2000

    Dave 2000

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    Tried editing a spelling mistake inthe above post and keep getting a spam warning message, so sorry for any errors you have come across.

    Regards

    Dave
     
    Dave 2000, Nov 11, 2017
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  3. Dave 2000

    73's de Edd

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    Sir Dave 2000 . . . . all of your post is being received well here . . from your Sunny Espanya . ..

    I am going to make some inital assumptions that your old dash indicator was merely using a RED ? BLUE? GREEN? . .which is it ? indicator LED which operates down in the 2-3 voltage . .ish ranges. (mandated by its color.)
    So they probably just inserted a series resistor to drop and get their 12V down to the LEDs specified voltage.

    On that new unit, it must have three leads coming into a dual section and can produce one color from one LED section or another color from its companion other color section in the die.
    OR it can also make a transitional blending of the colors, all in acordance to how much each one gets driven.
    FIO . . . did he tell you the colors and the color transitions . The only set of two that seem logical for a shifting color transition are Orange and Green or Orange and Red.
    Seems like the solution might be as simple as having two diodes cathodes connected and going to your old "HOT" wire to the original LED ( ? RED ? ) then the other leads of those steering diodes go to each of the end connections of the bicolor LED of the new equipment.
    That way either color or a blend of the colors always sends an activate signal to your old original LED to light up.
    Fill us in on the color questions above .

    ASIDE:
    As a connoisseur of same and for curiosity . . . . what's the year and series . . . . . of Mercy Days !

    73's de Edd
     
    73's de Edd, Nov 12, 2017
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  4. Dave 2000

    Alec_t

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    Won't you want the PWM signal to drive one LED or the other depending on the fan speed?
     
    Alec_t, Nov 12, 2017
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  5. Dave 2000

    Alec_t

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    Here's a suggested basis for a circuit which will turn on one LED when the PWM speed signal is above a low threshold and will turn on a second LED as well once the signal is above a higher threshold. The trim-pots allow the thresholds to be adjusted.
    DualLED_driver.PNG
    The circuit could be modified to have the first LED turn off when the second LED turns on.
     
    Alec_t, Nov 12, 2017
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  6. Dave 2000

    Dave 2000

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    Thank you guys for pitching and helping me out.

    @73's de Edd IIRC your right there are resistors in the supply to the dashboard LED's, it is awhile since the dashboard was out but pretty certain your right. With the present fan there are two temperature switches, one for slow and one for fast. The slow illuminates a green LED and the second speed an orange LED. The second speed is also brought into play by the AC pressure switch, as the two speeds cannot be activated at the same time without damaging the fan I used a changeover relay.

    If I understand the controller supplier correctly, there is an LED that is fitted to the dashboard, it blinks during fan start up and fan shut down but, stays on if the fan is at full speed.

    There is also an LED mounted on the controller itself, this changes from green thru orange to red in relation to fan speed and engine temperature, none of these will drive the 12v LED's.

    @Alec_t Yes the perfect scenario is green goes off and amber comes on but, as the new PWM will offer multiple speeds for example 25%/50%/75%/90% related to temperature I thought I nay have to compromise.

    So, my plan (if possible) is to have the green LED come on at any time the fan is activated, and the amber LED light up when the AC pressure switch is calling for fan activation regardless of engine temperature, the result may be both coming on at the same time, and as I read your last sentence it seems I may get my cake and eat it. Another thought is to replace the 12v LED's with lower current versions and have them controlled by the above circuit however, this would mean pulling the dashboard module apart, something I am loathe to do.

    I understand some of your diagram though unsure I could construct it and have it work reliably but, if the supplier of the controller cannot modify his production unit, perhaps he could refer to this diagram?

    Many thanks for taking the time to draw this up.

    Regards

    Dave
     
    Dave 2000, Nov 12, 2017
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  7. Dave 2000

    Alec_t

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    My suggested circuit can be easily modified (perhaps simplified) to do that. Does the AC pressure switch provide a path to the +ve supply line (i.e. high-side switching) or to ground? BTW, I have assumed your LEDs are high-side switched (as shown) rather than low-side switched. Is that the case?
    Sure.
     
    Alec_t, Nov 12, 2017
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  8. Dave 2000

    Dave 2000

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    The AC switch can supply pos or neg, presently switching negative. As it is awhile back since I designed and installed the electrical side of this I will need to dig out my wiring diagram, IIRC it is almost certainly 12v pos switched to the LED's as the pick up is from relays that supply the fan.

    Regards

    Dave
     
    Dave 2000, Nov 12, 2017
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  9. Dave 2000

    Alec_t

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    If the AC pressure switch can switch the +ve, then here's an option which would (a) turn on the green LED for any PWM duty cycle >20% if the PWM signal is a 5V one, or >10% if the signal is a 12V one and (b) turn on the amber LED when the AC switch closes.
    With D4 in place, the green LED goes off when the amber LED turns on. Remove D4 if you don't want that.
    DualLED_driver2.PNG
     
    Alec_t, Nov 13, 2017
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  10. Dave 2000

    Dave 2000

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    That looks great, thank you very much.

    I will contact the PWM designer and see what he thinks.

    Thanks again.

    Regards

    Dave
     
    Dave 2000, Nov 13, 2017
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  11. Dave 2000

    Dave 2000

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    The supplier of the controller (another Dave), thinks your last diagram will do the job. I have asked him to clarify one or two points but, this is all looking good.

    When the fan arrives I hope to test it for fit and functionality, if all good I should be able to move on and build the module to your diagram.

    Get back to you, and thanks again.

    Regards

    Dave
     
    Dave 2000, Nov 13, 2017
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  12. Dave 2000

    Dave 2000

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    @Alec_t

    Hi the fan gas arrived, fits perfect, about to order the PWM controller. I am going to have a go at turning your diagram into reallity. Given my lack of electronic skills, large hands and poor eyesight, I plan to order 2 x all the components from an online shop to allow for cock ups. As Spanish hobby shops are very thin on the ground, the nearest is the best part of a days drive there and back.

    Is there anything in particular I should be careful about when ordering, quality of components, correct part numbers etc? Or.......is it possible to purchase 'off the shelf'?

    Many thanks for your time

    Regards

    Dave
     
    Dave 2000, Nov 22, 2017
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  13. Dave 2000

    73's de Edd

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    If you can't find those "generic" parts being shown in post # 9 at your electronics supplier, they shouldn't even be calling themselves a supplier !
     
    73's de Edd, Nov 22, 2017
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  14. Dave 2000

    Alec_t

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    The 'working voltage' of C1 needs to be >12V, so I'd suggest 25V or so. Observe correct polarity when you connect it.
    Almost any small signal (low power) NPN and PNP silicon transistors are appropriate. Common types are 2N3904 (NPN) and 2N3906 (PNP).
    Any general purpose silicon diode will do for D3 and D4.
    R6 and R7 are the resistors assumed to be present already in your '12V LEDs'.
    You will need a circuit board. Go for strip-board (e.g. Veroboard).
     
    Alec_t, Nov 22, 2017
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  15. Dave 2000

    Dave 2000

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    @73's de Edd

    Quote "If you can't find those "generic" parts being shown in post # 9 at your electronics supplier, they shouldn't even be calling themselves a supplier!" Unquote.

    I think you misread my post? I know very little about electronics, I also said I would be purchasing online as there is no supplier short of 3 or 4 hours away. So that leaves me looking through lists of thousands of components, most of which I do not understand. I do appreciate that what may appear to you as a simple diagram with simple components, unfortunately I am not so savvy in this area.

    @Alec_t

    Thanks for the reply, I will be looking for an online supplier tonight, in the UK there is a company called Maplin, IIRC they ship to Europe, I will get back to you.

    Many thanks

    Regards

    Dave
     
    Dave 2000, Nov 22, 2017
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  16. Dave 2000

    Dave 2000

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    After an hour on the net it seems this is mot as straightforward as it appears...to me.

    I found around ten different types of capacitor, and probably 50 types of resistor!

    I put down the tablet, I will have another look over the weekend.

    BTW, I have purchased the pulse width modulator, so will need to get moving. I have found an electronics supplier in Spain who will post the components to me.

    Regards

    Dave
     
    Dave 2000, Nov 24, 2017
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  17. Dave 2000

    Dave 2000

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    OK I gave a company called RS components in Spain, I just need to know the correct type of capacitors to use in your diagram @Alec_t there are at least a dozen different types, even a paper capacitor WTF?

    Resistors I have them covered as do I the diodes and transistors, sorry to be a pain mate, capacitor types have my head in a spin.

    http://es.rs-online.com/web/c/componentes-pasivos/condensadores/

    Regards

    Dave
     
    Dave 2000, Nov 25, 2017
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  18. Dave 2000

    Dave 2000

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    Quick update, PWM ordered and paid for, electronic components have been ordered and paid for, and as I was not sure of resistor or capacitor types, I ordered what I am familiar with on circuit boards.

    Annoyed that I needed about 9 pieces, and was happy to order 18 however the last count was...............about 100!

    Still they are cheap enough to throw in a box where they may sit for a few years.

    Let you know how I get on.

    Regards

    Dave
     
    Dave 2000, Nov 27, 2017
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  19. Dave 2000

    Dave 2000

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    Well I made the circuit up...........three times, NOW I know why they sell items in batches of 10's and 20's, it's for ham fisted people with dodgy lamps...like me!

    It looks right to me, so just waiting for the PWM to arrive, unsure if or how to test this circuit so will wait until the controller arrives.

    Get back to you.

    Regards

    Dave
     
    Dave 2000, Dec 3, 2017
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  20. Dave 2000

    Dave 2000

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    @Alec_t Hi mate, apologies for my fopa, there was me (electronics numbskull) letting you (electronics guru) know there was a Maplin store in the UK, then many days later I see your in Wales.........UK!

    Sorry again, no offense meant.

    Regards

    Dave
     
    Dave 2000, Dec 5, 2017
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