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dann2
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Hello,
I did not think of using the -12V from the computer power supply. When the + and - 12V are used to power the op-amp then all the problems the 741 was
having disappeared.
Also changed the values of the voltage divider at the input to the op-amp. I cannot obtain a 50 Ohm pot with a shaft for a knob anywhere. I can easily
get 1k sliders and pots.
Job completed. I used a second cps box to house the bits and pieces + a meter.
The whole shaboo is a very salubrious, austintatious, plush piece of engineering! (as you can imagine).
Dann2
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12AX7
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Yes, a 741 will be happy with +/-12V.
Tim
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dann2
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Hello,
Final circuit attached. It varies current out from 0 to 15 Amps when the 5 Volts output from the CPS is used.
It cannot do that if you supply the 12 Volts from the CPS as the 12 Volts output on my supply will only supply 8 amps.
I put back the 741 as it works OK.
Just wondering could this circuit be used to 'smooth' raw DC coming from a rectifier?
Cheers,
Dann2
[Edited on 13-10-2009 by dann2]
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12AX7
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It can be used for smoothing only as long as the voltage is high enough. You can't make voltage with it, it stores no energy. It can allow you to
use less storage, so ripple can be a larger part of the supply voltage without modulating load current. Simple way to test: put an AC meter across
the current shunt resistor (be sure it's an AC meter, not reading the DC component as well!), and connect more capacitors until AC goes to zero.
Notice if the circuit is oscillating, it will have quite a bit more AC on it, though it could also be past the meter's bandwidth. A 741 is pretty
slow, but just in case, a series resistor between -in and Rshunt should be added, 10k is enough, and a compensation capacitor (100pF is enough) from
741 output (in front of the gate resistor) to -in, to basically make an integrator for high frequencies.
Tim
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dann2
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Hello,
Great big lump of a power supply at link (in UK).
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=200...
Constant current mode, 7.5 Volts and lots of Amps for the Chlorate and Perchlorate making guru.
Dann2
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Swede
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I'm very late with this reply, and it no longer matters, but whoever stole that Lambda supply for 42 pounds sterling is going to be one happy camper.
Lambda made a series of those switching supplies in various voltages, and they all have CC/CV operation. I have one, 10V 100A, that is my favorite
supply.
There are a lot of them out there, available at really good prices with a bit of searching. Not trying to slam PC power supplies, but when you add it
all up, something like this Lambda is tough to beat for electrochemistry experiments.
Edit: This came off sounding bad. I am a huge DIY fan, and the advanced projects here are excellent, but I point this out more for a beginner who
doesn't have the skills, will, or time to put something together. A powerful commercial supply doesn't have to cost hundreds and hundreds of dollars.
[Edited on 15-12-2009 by Swede]
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12AX7
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Indeed, switching power supplies are not easily designed by novices.
Tim
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dann2
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Hello,
There is still an opportunity to shove one under your coat and skedaddle!!!!!!!
That guy has been selling them for quite some time. He must have a number of them.
Dann2
[Edited on 16-12-2009 by dann2]
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Swede
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Quote: Originally posted by dann2  | Hello,
There is still an opportunity to shove one under your coat and skedaddle!!!!!!!
That guy has been selling them for quite some time. He must have a number of them.
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If I lived in the UK, I'd be all over that supply. Two in series would give you anything (voltage-wise) you'd probably ever need. One alone, at
7.5V, should work fine for a well-engineered perchlorate cell. For chlorate, it's more than adequate.
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