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RE: Dupla cables


One thing is that power is drawn, not pushed.  If you think about it, if you
put a 40 watt light bulb in a socket it draws 40 watts even though the
circuit will push 10 times that.  So the transformer has only to exceed the
amount of amps being called.   My setup probably draws something like 4 amps
and my transformer will put out like 10. This is good because the
transformer never runs near capacity and consequently runs cool.

As to the safety issue a car battery puts out 220 amps at 12 volts. A
transformer to run your system using non Dupla cables will put out 10 amps
at 12 volts. I have never heard of anyone being electrocuted by a car
battery.  I asked the electrician on staff at the radio station I work at
and he said it was absolutely not a dangerous current.  The Dupla system
that uses a higher voltage is actually more current, and hence in theory
more dangerous.

For safety it is more important that the primary (house side) and secondary
(tank side) windings are separated.  You could tape both live leads to your
forehead with no I'll effect.  If you zip tied them to your tongue though it
would most certainly be unpleasant.  Most all new transformers will have
separate primary/secondary windings, my ACME transformer is made for outside
use and does.

I think that 150 watts in a 100-gallon are to many, especially if you are
using powerful lights under a hood.  The combined effect will over heat the
aquarium.  I really believe you only need to cycle the water through the
substrate 1 or 2 times a day.

I'm not sure if the analogy is totally accurate but... If electricity were
water, amps would be pressure (PSI), and volts would be volume (GPH).
Combine these to get Watts.  A light bulb or a stove or anything is kind of
like forcing that water through a series of water wheels, only so much can
get through at a given time.  In our case, with the heating cables, the AWG
30 wire is like a little tiny pipe.  Instead of having the electricity
exhort pressure on the walls of the pipe, as say a pump would, it creates
heat.   One weird thing is that as the length of the pipe or wire increase
the wattage lost to pressure/heat actually decreases.  If you think of
trying to blow up a tiny balloon vs. a big one.  Each breath added to the
long balloon is a smaller percentage of the total volume and so exhorts less
pressure on the surface of the balloon.

The Dupla cable is just a bigger pipe so it needs a greater volume of
electricity to expand/heat it.  Hence more power = more dangerous.

I used to do irrigation for a big, big farm.  I used to set up green house
irrigation too.  This is an easy way for me to think about this.

$150 is too much for suction cups and wire, even if you do have the money.


Adam R. Novitt

-----Original Message-----
From:	Mortimer Snerd [mailto:n9720235 at cc_wwu.edu]
Sent:	Wednesday, December 30, 1998 4:54 PM
To:	Adam R. Novitt
Subject:	Re: Dupla cables

I think I am going to go ahead a buy the Dupla cables.  I have the money to
spend, and, while it seems kind of stupid to not go the DIY route, I don't
to run the risk of problems, especially when you figure that I'm dealing
water and electricity.  This is even more important when you figure that I
have to tear the entire tank down if something goes wrong.  Kind of makes
sound like a deal...:-).  I do, however, need help understanding the way all
this works.  I posted a question to the APD today, and I am interested
especially in your response, because I think you have this stuff pretty well
figured out.  If you need me to, I can copy the questions to you.

I am also curious as to what theory regarding heating cables you subscribe
I seems to me to be more of the Dennerle school of thought, as you run lower
wattages than the Dupla systems.  Why do you think this?  I haven't made up
mind yet as to what wattage to use, and am thinking that a compromise may be
best way to go.  Any thoughts?

I think the problem with the Excel attachment is Netscape.  I have had
with a few other attachments recently.  It may also be designed for a newer
version of Excel than I have (5.0).  If you could email me the formulas, I
really appreciate it, so I can work things out by hand.

As for the help, I really appreciate the time you've taken with this.  While
may not use the advice you have given me, this conversation has taught me a
amount, and has given me options to choose from.  The hobby needs more
that are willing to answer what seems to some to be "stupid newbie
I know I asked lots when I was first starting out (still do, actually) and I
couldn't have gotten anywhere near as far if it hadn't been for lots of
help.  I
doubt that anyone in the hobby has.  It is nice to meet someone willing to
those favors.


Justin Collins

"Adam R. Novitt" wrote:

> ______________________________________________________I  I
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>   _______________________________________________ _____)   I
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> So the interior dimensions of the tank are 59 in by 17 in?
> If you then subtract 1 in. off each end, you won't have the wire right up
> against the glass, you'll get 58 in. by 16 in.  then subtract 2 from the
> long runs up and the length of the tank to allow for the return to the
> wall. So the long runs are 56 in. so that's 16x2=48 and 56x6=336 for a
> of 368in. or 30.7 feet.
> You could get 44.7 watts with 30 GA wire drawing 3.224 amps from a 12 volt
> transformer.
> If you did eight passes up and down the aquarium for 42 feet.
> You could get 51.8 watts using 28 GA wire drawing 4.32 amps from a 12 volt
> transformer.
> The attachment is a Microsoft Excel attachment,  sorry if I caused you any
> grief.  It was made by an ADPer a while back to do exactly this.  I'm only
> computing for 12 volt as this seems to be the easiest to find in high amps
> like this, and the results using wire you can actually get are pretty
> If you calculate a different wire length, or can get 9 volt transformer
> (46.4 watts with 26 GA wire @ 5.15 amps @ 42 feet) let me know and I'll
> calculate it.  When setting up don't worry about being a foot or two off
> it changes the resultant wattage very little.
> You may want to add in a foot right up front to make up for little wiggles
> in the wire and general slop. Perhaps 2 because 1 foot is only 2% of total
> length.  I personally would use only 6 passes because this way I think
> is less chance of heating the substrate uniformly, especially as water
> column temp start to climb in the spring and summer.  I also prefer a
> close to .5 watts to ensure enough flow.
> Let me know your thoughts on any of this.  I got help from a guy called
> Ashcroft, I'm really just passing on a favor that's owed anyway.
> Regards,
> Adam R. Novitt
> -----Original Message-----
> From:   Mortimer Snerd [mailto:n9720235 at cc_wwu.edu]
> Sent:   Wednesday, December 30, 1998 1:58 AM
> To:     Adam R. Novitt
> Subject:        Re: Dupla cabels
> I'm not sure why, but I'm having a hard time opening the attachment.  Is
> there
> anywhere I can download it?  Basically, I need cables for a tank that is
> 5'x18",
> with an appropriately sized transformer, which I can get locally.  I've
> already
> got a temp controller.  As far as wattage, Dupla, the high wattage kings,
> say in
> the Optimum Aquarium that .3-.5 watts is appropriate.  I'm currently tying
> to
> figure out what wattage their systems are and duplicate that.
> As for Mortimer Snerd, I'm not sure who he is.  I think it was a character
> from
> a children's TV show back in the 50's.  I just picked it up from a friend
> mine a bunch of years ago, and it kind of stuck to my computer.
> Justin
> ps: Thanks for all the help with this.  I appreciate it.
> "Adam R. Novitt" wrote: