My take on the Aquarium Light!

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bigal344
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Re: My take on the Aquarium Light!

Postby bigal344 » Thu Aug 02, 2012 11:23 am

Once all assembled and sealed with aquarium sealant you get something like this.
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All the lights here are showing as white but there are 8 blue LED's. There are some extra holes which have been sealed up, these were put in prior to assembly as I had no idea how many blue LED's would be needed to give a nice moonlight effect.
It all swings down into place as the original did sitting nice and snug on the lip.
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The new lighting makes use of the original switch and looks no different from the old one really, result!!
You can just about see the LDR's on either side.
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Next up will be my sons new tank which comes without a lid, so a scratch build is called for I think!! ;)
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Today I have been mostly Nyaning.

bigal344
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Re: My take on the Aquarium Light!

Postby bigal344 » Mon Sep 03, 2012 6:49 pm

The bloody light keeps packing up and after taking it apart several times the original plastic lid has buckled so I made a nice new metal one which had the holes cut and was painted black to match the tank.
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While I was at it the main unit got a coat of good 'ol Plasticote, just to make it look a bit more sparkly!
Lights masked here.
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Back together and testing.
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Unfortunately, again for the tenth bloody time the daylight lights refused to work after a while, whilst the blue moonlight ones do. I strongly suspect that the transistor for the white ones is incorrectly spec'd.
With 21 warm white LED's, the total current draw is 420mA by my reckoning (20mA per LED), I'm trying to remember which transistor I used but I'm pretty sure that I used the same one for both daylight and moonlight sides of the circuit!
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Today I have been mostly Nyaning.

Rich
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Re: My take on the Aquarium Light!

Postby Rich » Tue Sep 04, 2012 8:57 am

What did you do to repair it the previous 9 times? If its the transistor, some smoke will have come out of it and it would never work again, or at least it would be working very hot.
I always make sure I over spec semiconductors and resistors.

bigal344
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Re: My take on the Aquarium Light!

Postby bigal344 » Tue Sep 04, 2012 9:23 am

Well, when i say 10 times....
I've taken it apart and found nothing wrong, but I've got it working again, albeit for a short while.
The transistor on the daylight circuit does get very hot, ie burn fingers hot!
Am i looking at things right by working out the current draw from all of the LED's how would i go about picking a suitable transistor for a project like this?
I have a couple of pages of scribble at home that I've been using to try and ascertain what is important in choosing! :o
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Today I have been mostly Nyaning.

Rich
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Re: My take on the Aquarium Light!

Postby Rich » Tue Sep 04, 2012 9:29 am

Look at collector current, usually iC on a data sheet. The rest of the parameters are usually ok for low voltage switching

You could put a multimeter in series with the diodes set to amps to check

Rich
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Re: My take on the Aquarium Light!

Postby Rich » Tue Sep 04, 2012 9:36 am

Look at T0-220 packaged transistors, you know the type with the hole in so it can be bolted to a heat sink.

bigal344
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Re: My take on the Aquarium Light!

Postby bigal344 » Tue Sep 04, 2012 8:58 pm

So, upon closer inspection and another strip down, it appears that both the daytime and nighttime circuits are running 2N904's which upon checking the datasheet shows an Ic of 200mA which is fine for the blue LED's which need 160mA whereas the white LED's need a total of 420mA, slightly over!!
I imagine that this is what is causing the temps on the transistor and probably won't do much for the life of the components!
How about a BC337 with an Ic of 800mA or a 2N222 with an Ic of 600mA, would these be a better bet, giving me a bit of headroom with the figures as well.
Also do I need to worry about voltage into the base to switch the transistor effectively, and what figure would this be on the datasheet. I have read some bits of info about the current needing to be enough to 'saturate' or switch the transistor fully on.
Always possible that this has absolutely nothing to do with what I'm trying to do here!! :lol: :oops:
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Today I have been mostly Nyaning.

Rich
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Re: My take on the Aquarium Light!

Postby Rich » Tue Sep 04, 2012 9:50 pm

The voltages on the data sheet are usually maximums between pins, so if your using a 12v power supply you know a transistor with a collector emitter maximum voltage of 25v it can't be exceeded no matter how you configure it. Most general purpose transistors (if not all) will be fine on 12v. Just look at the collector current and monitor temperature when running, even though the current is less than the maximum allowable a transistor will get very warm after a couple of mins.

Ahh, the good old BC series, Yes try them. The 2N series is American rubbish ha ha

Rich
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Re: My take on the Aquarium Light!

Postby Rich » Tue Sep 04, 2012 9:52 pm

Don't worry about the base voltage the variable resistors take care of that.

bigal344
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Re: My take on the Aquarium Light!

Postby bigal344 » Wed Sep 05, 2012 7:50 pm

Thats the conclusion I'd come to about the variable resistors, and also the voltage requirements are a lot more clear now thanks, I'm actually learning something now!!! :shock:
BC337 it is then, I'll try and get that swapped in this weekend hopefully. ;)
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Today I have been mostly Nyaning.


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