Aquarium Light Mk2 and other fishy bits.

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Rich
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Re: Aquarium Light Mk2 and other fishy bits.

Postby Rich » Sun Oct 14, 2012 8:41 pm

Yes, with that many LEDs the current adds up, sounds like the power supply is being overwhelmed.

bigal344
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Re: Aquarium Light Mk2 and other fishy bits.

Postby bigal344 » Sun Oct 14, 2012 10:43 pm

The power supply is a 2 amp one, which by my rough calculations should be almost enough current.
What i didn't mention in my post was that I get nice bright LED's with this very power supply connected directly to them, but when I run the power through the circuit, everything works as it should, just a
lot dimmer.....bit like myself really.....
:cry:


I do love Somershack Ben, should trademark that quick. ;)
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Re: Aquarium Light Mk2 and other fishy bits.

Postby Rich » Mon Oct 15, 2012 8:31 am

Check the base voltage on the transistor, the BC547 needs 0.7v to be turned on fully if I remember the data sheet correctly.
So that's between ground and base 0.7v or more.

Also measure the voltage across the emitter and collector, that voltage should be small. Whatever voltage is across the transistor isn't across the LEDs, so big is bad.

You might just have another pesky bad connection on the base components.

bigal344
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Re: Aquarium Light Mk2 and other fishy bits.

Postby bigal344 » Mon Oct 15, 2012 10:25 pm

Aha, time to get the multimeter out then, and have a look see at the data sheets.
That'll be the base saturation current then I guess? :)
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Re: Aquarium Light Mk2 and other fishy bits.

Postby Rich » Mon Oct 15, 2012 11:23 pm

Check voltage not current.

Not necessarily as high as saturation voltage, but at least switch on voltage (Vbe) on data sheet.

don't know what the current would be, probably micro amps

bigal344
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Re: Aquarium Light Mk2 and other fishy bits.

Postby bigal344 » Tue Oct 16, 2012 4:43 pm

Ah, yes that was what I meant!
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Re: Aquarium Light Mk2 and other fishy bits.

Postby bigal344 » Fri Oct 19, 2012 7:12 pm

Righty, the TIP31A has 0.55v at the base and a very weak output, unless I have found I shine a light on the LDR at which point the value rises to 0.87v and the LED's give a good bright light across the board!

I can't seem to find a value for Vbe as a minimum on any datasheets, only Veb0, which is listed as maximum voltage of 5v.

However I'm quite happy with the illumination with a bright light shone on the LDR, so could I increase the voltage percentage getting to the base by changing the resistor prior to it thus allowing more voltage through?

I may just have a play with this tomoro anyway and see what happens!! :D
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Re: Aquarium Light Mk2 and other fishy bits.

Postby Rich » Sat Oct 20, 2012 9:41 am

You coul try changing the 10k for a 1k erm... Shouldn't make much difference though because the LDR has a huge resistance range, like from 1k to 2M so the transistor should be on if the variable res... Change the variable resistor to a 1M ohm, try that. I had to play about with the resistors to get the BC transistor working satisfactory so don't be shy... Fire extinguisher on standby ha ha

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Re: Aquarium Light Mk2 and other fishy bits.

Postby Rich » Sat Oct 20, 2012 9:48 am

Or 100k might be better. You want the thing to turn off :-)

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Re: Aquarium Light Mk2 and other fishy bits.

Postby bigal344 » Fri Dec 21, 2012 12:30 am

Ok so I've finally got back on this and after some head scratching and swearing (luckily the kids were in bed!), I have found that the LDR resistance is to high when its light and is limiting the volts to the base and thus the flow through the transistor.
The resistance is measuring about 5.5k in daylight and around 20k+ in darkness which is fine, to prove this I've put a resistor, 2k I think, in the place of the LDR and voila the light is perfect!!

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So when its not quite so late, I need to work some more on this, but for the moment, the lights are finally on the tank and the fish are happy!
Especially Bones, our Plec, who was quite small when we got him, and as he spends most of his time hiding and we don't see him much, it was a bit of a shock to see that he's bloody huge!!

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