Re: Aquatic Plants Digest V2 #468

>From: Lyndle Schenck <LSCHENCK at dcscorp_com>
>Date: Wed, 22 Jan 1997 09:50:27 -0500
>Subject: Aquatic Plants Digest V2 #466 -Reply
>RE transformer question

You put your undergravel heater transformer in the water?!

I don't understand this. Why not leave it out of the tank?

>From: Controller <mike at odg_com>
>Date: Wed, 22 Jan 1997 10:21:01 -0500
>Subject: CO2 sources

>So my question is: is there an equally cheap alternative to yeast for 
>producing CO2? [What I really want is a 5lb CO2 bottle for < $ 50.00  :-)]

The initial cost of the CO2 cylinder may be high, but you only need to
refill an 20 lb. tank once a year or so, and it only costs about $12
to refill.

>From: David Soh <dsoh at iastate_edu>
>Date: Wed, 22 Jan 1997 10:11:42 -0600
>Subject: DIY electronics
>Can any electrical engineers out there reccommend a good beginners' guide to
>electronics? I have the blue prints for a DIY pH controller but I know very
>little about electronics and I would like to attempt at building it. Is
>Radio Shack a good source for these books ? TIA.

For a pH controller you want a gound grounding (ouch!) in analog
circuit design and some experience with op amps.

Here are some good books for that:

 Electric Circuit Analysis - Zeines (1972)
 Transistor Circuit Approximations - Malvino (1973)
 Operational Amplifier - Characteristics and Applications - Irvine (1981)

These are rather old, but I taught myself a lot from these.

Be prepared to study for a year or two, like anything else, this takes
some time.

As for Radio Shack, I don't think they have anything but experimenter

Try building these projects:

    1) a +/- 12 volt DC power supply ( 2 amps )
    2) an analog frequency generator ( .1 Hz to 500 kHz)
    3) a sensitive meter (capable of measuring picoamps, GigOhms, or
               millivolts with considerable precision).
    4) an analog thermometer that has two sensors (indoor/outdoor,
       or in tank/air temp)

After these projects you should be able to build just about any
reasonable control circuit.

It is really nice to have an oscilloscope, maybe you can find some
surplus models.

>From: Dirk 
>Date: Wed, 22 Jan 1997 12:49:26 -0600
>Subject: Re:  Transformer question (experts??)
>>After talking to a few transformer suppliers I have concluded that finding a
>>transformer that does not have the primary and secondary windings on the same
>>core is just not practical.
>I gather the way the transformer is wound is a safety issue, right?  And if
>I understand correctly, the safer the transformer, the more expensive it
>is, right?  I have corresponded with someone on this list who set up a
>DIYUGH a couple of years ago with what I think he called a "switching"
>tranformer.  Is this unsafe.  I guess what I'm saying is that I am woefully
>ignorant when it comes to transformers and I'm wondering what's at stake.

I have never use undergravel heaters, but I don't understand this

There are transformers called ultra-isolation transformers that are
rather expensive. They have extremely low capacitive coupling from
input to output. This reduces any coupling of voltage spikes (motor
noises, lightening, etc.).

I'm not sure what you are trying to protect in the UGH. The heaters
are resistive loads driven by a power supply. If the cables are
Teflon or some such, they are insulated. If you want to protect from
accidentally exposing a heater, a fast acting fuse circuit ought to do
the trick. (Assuming you ground the tank and have enough ions in the
water to make it moderately conductive.) Everyone should have a ground
fault interrupter on the tank outlets - that should be a given.

Perhaps you want maximum heat conductivity and don't want an insulator
on the wires?

The safest thing then is to use the lowest voltage and the highest
current. voltage * current = power, but low voltage (say 10 -> 20
volts is pretty save). We are taking DC volts here.

If you need 50 watts, that's 5 amps at 10 volts. That sort of power
supply is rather simple to build. I really don't see the safety
issue - I must be missing something major...

Jim Hurley        mailto:hurleyj at arachnaut_org
<URL: http://www.webcom.com/hurleyj/home.html>