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Power supply help

Discussion in 'Power Electronics' started by kgthomas, Nov 19, 2013.

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  1. kgthomas

    kgthomas

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    May 16, 2013
    Hi I have built an LED lighting unit for my fish tank. I was planning on having an arduino control the dimming of the light. I am using one 45V power supply to provide the power for 7 strings of 12 LEDs, each string has the individual current controlled by LDD-H drivers. I have managed to get the LEDs all lighting without too much problem.

    I was running the arduino from an old 5V power supply I had for testing purposes, but I ultimately planned to have it feed from the 45V power supply using a HRD stepdown converter. I am using 3 HRD converters, one 12V for fans, one 11V for arduino and one 3-5V for power to a fish feeder. I had hooked the 12V one up and it was running no problems at all, I then hooked up the 11V one which has a variable resister to adjust the output voltage and set it to 11V. The 3-5V one I didn't need yet so I hadn't hooked it up.

    I checked the 11V output three times and checked the polarity with the centre pin being positive. I then plugged it into the arduino and this is when the problems started. I had the two items mounted close together on the project casing but shortly after plugging it in I heard a sizzle, bang and smoke coming from the arduino.

    I have since seen that the arduino has fried its voltage regulator and the MEGA16U2 chip at least if not more. I am certain that I had 11V running into it but I stupidly didn't check this again afterwards as I wasn't thinking. The fried arduino seems to be from too much voltage going into it.

    So I am wondering is it possible that the capacitor on the power line on the arduino went faulty and caused the failure? Or is it that there was too much voltage going into it in the first place?

    If it is too much voltage it is possible that the HRD converter fried itself and put too much voltage into the arduino? When I bought the HRD converters they were listed as being able to take up to 50V input. I have since checked the datasheet and it is a bit confusing as it says maximum input voltage 0-50V then below it on the same datasheet it says characteristics at 25 degrees C input voltage range 8-40V, so I don't know if they are capable of taking 45V or not?

    I am now worried as I had to hook up the light without the arduino controller to simply be a timer controlled light but the fans are powered by a HRD converter so I am wondering if it was the HRD that failed could the same thing happen to my fans?

    I have attached a picture of the bottom of the HRD that was hooked to the arduino and there appears to be some scorching around the pins but I don't know if this could have been caused by the soldering in the factory or by something blowing?

    I have now temporarily sealed up the lighting unit as I needed the light for my tank so I can't get easy access to the 45V power supply but I am wondering if I was to hook up the HRD to a 24V power supply will it output the same as what it would if it was hooked up to a 45V supply?

    Is there a better way that I can reduce the 45V supply to provide me with 12V, 11V and 3-5V, that would still take up the same sort of space as a HRD converter?

    I know it is probably something stupid I have or haven't done that has caused this but I really just can't see what, as I checked the voltage and polarity 3 times.

    Thanks in advance for any help that anyone can offer, even if it is just to point out where I have made a stupid mistake.

    Cheers Keith
     

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  2. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    What's the model number of the converter that you used to power the Arduino?

    Why did you use a 12V converter for the fans and a separate 11V converter for the Arduino? The Arduino should be able to run from 12V no problem...?

    The pins in the middle of your picture look OK. There's a bit of flux residue but no sign of damage.

    Can you post a photo of the top of that board as well?

    I think it's possible that the converter was damaged by 45V DC input, and it could have fed too much voltage into the Arduino, yes.

    What voltage do you measure at the output of the converter now?

    Did you have any other connections from the Arduino to any other part of the circuit?

    How are you planning to connect the Arduino to the LED controllers?

    I would recommend powering all the converters from a voltage lower than 45V. You can drop the 45V down to a lower voltage using a good quality converter that's rated for at least 60V input, or you can have a separate power supply.

    I would use a voltage rail of 12V which can power the fans and the Arduino, and also feed that 12V rail into the converter that powers the fish feeder.
     
  3. kgthomas

    kgthomas

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    May 16, 2013
    Hi thanks for taking the time to get back to me.

    The model of the converter is HRD05003
    0251

    I have attached the picture of the top of the board.

    I was using the separate 12V for the fans and 11V for the arduino to give a bit of room for over-voltage for the arduino as they are recommended between 9-12V but can handle up to 20V :mad: Ironic to think that even leaving some room for over-voltage I still managed to fry it. Ah well we live and learn apparently.

    I had the arduino connected with its screen and shield attached, so I assume these are also dead.

    I am planning to connect the arduino to the LEDs using a prototyping shield to output the PWM signal to meanwell LDD-H drivers which will regulate the current.

    I haven't checked what I get out of the HRD converter at the moment as I can't get access to the 45V anymore. I can hook it up to a 24V supply I have for another project but I'm not too sure if the different input voltages will have an effect on the output of the HRDs?

    I do work in a university with an electronics department so I have emailed the guy who works there to see if I can hook it up to his power supply to measure the output voltage, just waiting for him to get back to me now.

    I must have a look for a good converter to drop down the 45V to 12V and see how I go with that, would you know of any particular models to look at?

    Cheers Keith
     

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  4. kgthomas

    kgthomas

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    May 16, 2013
    Mean to say in my previous post originally these HRD converters came with a fixed resister, I can't remember the exact size but I still have them at home. The fixed resister is possible to replace with a variable resister and the board is designed to accommodate this. I used a bourns 3296W 10K variable resister to adjust the output voltage, and I am wondering if it is possible that this somehow fried itself and ended up throwing all the voltage through the arduino?

    Cheers Keith
     
  5. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    You deserve a prize for answering all my questions!

    If the HRD has been damaged by the overvoltage then powering it from 24V will give you an unregulated, high output voltage, but if it wasn't permanently damaged, then it won't, so that's not conclusive.

    I don't have any suggestions for a replacement but make sure it's rated for at least 60V DC input, or use a separate off-line power supply.

    I have to say I'm not totally convinced that we know all that's going on here. It's definitely possible that it's a simple case of excessive voltage causing the HRD to lose regulation and feed too much voltage into the Arduino and damaging it, but I suspect there's more to it.

    Unfortunately, since I'm not there looking at your setup, I don't know what the missing piece of the puzzle might be. But you can help by posting photos and connection diagrams, and making notes on things you try and the outcomes.

    Edit: Thanks for the reference to the HRD. Links to the other components in your setup could also be useful.
     
  6. kgthomas

    kgthomas

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    May 16, 2013
    It's always best to answer all the questions of those trying to help you!!

    Really appreciate you help with this.

    I will try to make a list of everything and post them up here to see what can be discovered from it.

    I doubt if it could be a spike from the power supply as I also had my LED boards hooked up to the power supply, these are using LDD-H drivers and their maximum voltage is 52V so it would be unlikely I would think that a spike could disregulate the HRD at over 50V but not the LDD which has a max of 52V.

    I will put together a list of components and wiring diagrams and upload them to here.

    Cheers Keith
     
  7. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    You'd be surprised how many people ask vague questions, supply the absolute minimum of information, and simply ignore many of the questions we ask here.
    The HRD data sheet lists 50V as the absolute maximum input voltage, and 40V as the maximum recommended operating voltage. It is never wise to operate anything outside its recommended operating conditions. Usually, component data sheets say something like "proper operation outside the recommended operating conditions is not implied" and "exposure to conditions outside the recommended conditions may affect device reliability", but the HRD data sheet does not say this. I would assume it, though.

    In other words, "DON'T use the HRD regulator with an input voltage greater than 40V" is my interpretation.
     
  8. kgthomas

    kgthomas

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    May 16, 2013
    Yeah I see what you mean that I really shouldn't be using the HRD with anything more than 40V to be on the safe side. If I was to use a resister to drop the voltage before it entered the HRD would that help? Or would it just generate too much heat? I'm thinking I only really need to drop the input voltage by 6V to be below the 40V.

    Also I was thinking is it possible to wire some sort of fuse into the output of the HRD so that it blows if the voltage output goes above 15V? I don't think this will be possible as if I'm correct fuses blow due to current excess not voltage excess?

    Cheers Keith
     
  9. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    No, don't use a resistor. The voltage dropped across a resistor depends on the current through it. At light loads it will drop less voltage, so the voltage going into the HRD regulator could exceed 40V.

    Sometimes, zener diodes are suggested as a way to drop voltage in this situation, but it's not really practical unless the current is quite a lot lower than in your case.

    You're right that fuses blow on overcurrent, not overvoltage. You could use a circuit called a crowbar though; see https://en.wikipedia.org/wiki/Crowbar_(circuit)

    The problem with the crowbar is that your power supply must be able to supply enough current to blow the fuse when its output is short-circuited by the crowbar circuit.
     
  10. kgthomas

    kgthomas

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    May 16, 2013
    Hi Kris,

    Thanks for getting back to me about this. I will have a read through that link and see if I can understand the idea behind the crowbar circuit.

    Cheers Keith
     
  11. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
  12. kgthomas

    kgthomas

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    May 16, 2013
    Thanks Kris,

    That makes a bit more sense so what I am looking to do is to short out the power supplied if it goes overvoltage leading to a fuse blowing to cut the power supply. That sounds like what I am looking for, while an arduino is not the most expensive thing in the world I've already blown one and would prefer not to blow another so this will hopefully stop this happening.

    I am also just thinking I was using the extra 11v HRD to prevent any possible overvoltage to the arduino, but could I not add a voltage regulator after the 12v HRD? Onto the 12v HRD I will be running 3 12v PC case fans and it powers a small LED driver to run 3 LEDs run at 150mA so as the HRD can output up to 3A that should be fine and the 12V fixed HRD converter is running stable with no problems.

    I know I still am working on the idea that it was the HRD that blew itself and part of the reason for this is that at the time of the arduino blowing I had two of the HRDs hooked up and I'm thinking that if one of them blew because of too much voltage then surely the other should have blown also?

    I have just had a wee read about voltage regulators here http://www.rason.org/Projects/regulator/regulator.htm so I could use the HRD output to go through a voltage regulator and therefore regulate the voltage for the circuit, am I thinking correctly that then if the voltage out increased then I will still only get 12v feed to my arduino? I know voltage regulators can heat up a bit but I have a 4ft heat sink to cool my LEDs so this should be fine for keeping the voltage regulator cool also?

    Thanks again for all your help with this, I'm sure I must be doing your head in.

    Cheers Keith
     
  13. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    I don't understand why you don't want to power the Arduino from 12V.

    Yes, you could add a regulator to drop 12V to a lower voltage, but regulators need a certain minimum input-to-output voltage difference, called the "dropout voltage". Dropout voltage is usually a few volts for a switching regulator, but linear regulators are available with dropout voltages less than 1V. In your case you could use a 7809 linear regulator, which has a dropout voltage of around 2V, to drop 12V down to 9V. But if you're adding a crowbar, you might as well just feed 12V directly into the Arduino.

    For a linear regulator like the 7809, power dissipation is equal to the voltage across the regulator (i.e. input voltage minus output voltage), in volts, multiplied by current (input and output current, which are almost exactly the same), in amps. So if a 7809 is dropping 3V and supplying 1A, it will dissipate 3W which will require a small finned heatsink.

    The suspect HRD regulator could have failed because of excessive power dissipation, causing part of it to overheat. Power dissipation in the regulator increases with increasing load current. Was the Arduino drawing a lot of current out of the HRD?

    Re adding a linear regulator, I've answered that above. You can't regulate a 12V rail to 12V using a linear regulator because of the dropout voltage, but otherwise you've got the idea. But a 78xx linear regulator is only rated for 35V input voltage, so if the HRD fails, it could take out the 78xx as well. This is the reason for the crowbar, and with a crowbar there is no reason to add a 78xx regulator, as far as I can see.

    No worries :)
     
  14. kgthomas

    kgthomas

    20
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    May 16, 2013
    Hi Kris,

    Yeah I was thinking that the voltage regulator as an alternative for a crowbar circuit but I'm thinking that it might be easier just to go with the crowbar circuit as I would need to raise the voltage out of the HRD to around 14-15v to drop it back to 12v.

    I was planning on now powering the arduino at 12v as I would have protection system in-line to protect it from overvoltage.

    The arduino should not have been drawing a lot of current as it was only powering up at the time and only had the screen and screen adapter connected.

    I assume that I could then also drop the 12V from the HRD down to 3V for to power a fish feeder? Using zener diodes in series?

    Thanks again, if I ever am in New Zealand I owe you a pint or two for all your help with this.

    Cheers Keith
     
  15. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    Yes you can drop 12V down to 3V for the fish feeder. If it doesn't draw much current, you can use a linear regulator such as an LM317. Calculate the power dissipation to see whether a heatsink is needed or not and how big it needs to be. If it draws significant current - say 100 mA or more - you might be better to use a switching supply such as an adjustable buck regulator from eBay.
     
  16. kgthomas

    kgthomas

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    May 16, 2013
    Thats great,

    Thanks again for all your help

    Cheers Keith
     
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