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Old Apr 13, 2012, 08:50 AM
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What's up Steve, any more progress on this project?

Mike
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Old Apr 13, 2012, 09:40 PM
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Sorry, Mike, computer was dying, so had to order a new one, and then spend a day reconfiguring, installing, transferring data. Now I've got taxes to do, a major work progress report due the 20th, etc. Will be back here as soon as I can -- thanks greatly for the data! I will definitely use it and upgrade the calculator. Haven't flown since the Mambo maiden -- it's been 3 weeks of wind here!
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Old Jun 06, 2012, 04:40 AM
denvoyager
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Is this all DC or AC? I have a 240volt sytem and a transformer that takes it to 12v AC. Can I use this for the bow,or do I need something else, I have a dimmer switch.
Really,a wiring diagram would be good,any ideas where I can get hold of one? Terminology seems to be a problem, using household stuff especially is different across the pond!
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Old Jun 06, 2012, 08:12 AM
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Quote:
Originally Posted by denvoyager View Post
Is this all DC or AC? I have a 240volt sytem and a transformer that takes it to 12v AC. Can I use this for the bow,or do I need something else, I have a dimmer switch.
Really,a wiring diagram would be good,any ideas where I can get hold of one? Terminology seems to be a problem, using household stuff especially is different across the pond!
That should work ok, depends on the rating of the transformer. How many amps?
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Old Jun 06, 2012, 09:13 PM
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Southern Vermont
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Quote:
Originally Posted by denvoyager View Post
Is this all DC or AC? I have a 240volt sytem and a transformer that takes it to 12v AC. Can I use this for the bow,or do I need something else, I have a dimmer switch.
Really,a wiring diagram would be good,any ideas where I can get hold of one? Terminology seems to be a problem, using household stuff especially is different across the pond!
There are probably a hundred wiring diagrams for bow power supplies floating around. Just do a little searching. This thread is focused on using a spreadsheet calculator to determine what bow you can run with your supply., and what size wire that setup would take.

My CNC wire is AC and manual bow Is DC. The spreadsheet seems to be usable for both, though technically there is a small difference. Since most homemade power supplies are variable, rather than fixed voltage, the diference isn't very important.

If your output is 12 V AC, you could put a variable control on the mains side of it -- I use a router speed control. from Harbor Freight. Some people use light dimmers.

As mentioned above, you need to know what the rated amperage output of your transformer is, then put that and the voltage into the spreadsheet to determine bow size and wire size -- presently, stainless steel wire is the only type calculated for.
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Old Jun 07, 2012, 01:30 PM
If I build it, it will fly
United States, NY, East Rochester
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I picked up a couple spools of SS wire from Harbor freight last week for a bow. Finally got around to opening them & measured actual thickness.... 0.036"

Is there a way to make the wire diameter field an editable constant field?

~psguardian
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Old Jun 07, 2012, 07:28 PM
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@psguardian, I could write it with a variable instead of calculated wire size as another calculation section But I'd have to know which variable you want to now calculate, since you aren't calculating wire size any more. It could be power supply voltage, or amperage, or wire length. But one would have to be chosen as the calculated value.

But the easy way is actually just to enter values for V, A and Length in the original spreadsheet, and just change them until you get .035 as the wire size. For instance, you probably already know what wire length you want. So that leaves voltage and amperage of your supply. If you've got an idea of what kind of supply you would like to use (automotive battery charger, or a 12V or 24 V transformer) you know the nominal voltage and the max permissible amps, so plug those values in and see what wire thickness you get. If it is smaller than .035 (probably is) turn down your variable control from 100% and watch the wire size until it's right.

Hopefully, you will be above 25% when the wire size is right. If not, consider using a lower voltage supply, like a 6 V transformer, battery charger, etc. It's better not to be too close to the bottom end of your adjustment - although probably do-able.

The whole purpose of this sheet is to allow people to size things so they will work together from the start rather than making trial and error purchases.
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Old Jun 07, 2012, 07:46 PM
If I build it, it will fly
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I completely agree with eliminating t&e. This SS wire was the only stuff I had access to. I am using an old psu, rail values are as follows

3.3v @ 45a
5v @ 50a
12v @ 22a

I am trying to make two bows to run with this supply, out of the 0.036" SS wire.
A 12"-18" bow, & a 48"-54" bow.

I do have one dimmer dial switch but i'm not sure if it could be used on the low voltage lines?

~psguardian
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Old Jun 07, 2012, 08:22 PM
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Quote:
Originally Posted by psguardian View Post
I completely agree with eliminating t&e. This SS wire was the only stuff I had access to. I am using an old psu, rail values are as follows

3.3v @ 45a
5v @ 50a
12v @ 22a

I am trying to make two bows to run with this supply, out of the 0.036" SS wire.
A 12"-18" bow, & a 48"-54" bow.

I do have one dimmer dial switch but i'm not sure if it could be used on the low voltage lines?

~psguardian
Nope that's a regulated fixed power supply, so you can't use a dimmer switch at all. You could probably do some adjustment with an "air resistor" -- on the output-- that is coils of wire -- effectively making the wire length longer.

I'll try out a few things on the spreadsheet and get back to you. But .035 is thick wire, and 12-18" is a short bow. That means probably very low voltage to work.

Have you considered the brushed motor ESC route to get variable voltage?

It may be possible to do the smaller bow with dry cell batteries, even. I picked up two D cells at the dollar store for, tyou guessed it, a dollar, and have been thinking about it.

Let's work it out in the spreadsheet as an example. Back in a few.....
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Old Jun 07, 2012, 08:43 PM
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Edit: Example deleted due to error in original version of calculator, and to avoid confusion.

See Post 50 for an updated corrected version of the hot wire calculator.
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Old Jun 07, 2012, 08:46 PM
If I build it, it will fly
United States, NY, East Rochester
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Thanks! I know this is thick stuff, I was thinking it was thinner... The label of the (only) bin on the shelf said .025". Disappointed that its so much thicker, but its what I have to work with for the moment. I appreciate your input on this rope of a wire.

~psguardian
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Old Jun 07, 2012, 09:04 PM
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Edit: Worked out example deleted due to error in original version of calculator, and to avoid confusion.

See Post 50 for an updated corrected version of the hot wire calculator.
Last edited by vtdiy; Today at 08:41 PM.
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Old Jun 07, 2012, 09:15 PM
If I build it, it will fly
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So then if I'm reading this right the desired length is what my bow will be, & the aprox amp draw is how much current will be USED from the pwr supply rated amps. My wire won't draw max amp & melt?

~psguardian
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Old Jun 07, 2012, 09:34 PM
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The wire has resistance, hopefully calculated correctly here, and that should limit the current that it can draw from the PSU.

Your situation is a bit more worrisome (with a fixed supply) than with a variable supply because with a variable you could slowly ramp up and would notice any problem. With a fixed supply, it's a one shot deal, and you're the first to try it as far as I know

Let me double check one thing I've just noticed here -- the current shown is the same for the 16" x 1.5 V bow as it is for the large bow. I just want to make sure that is not a mistake. We haven't tried a fixed supply or anything with wire as thick as yours -- so working with a small range of what is possible.
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Old Jun 07, 2012, 09:49 PM
If I build it, it will fly
United States, NY, East Rochester
Joined Jan 2012
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I have accidentally created a dead short on this PSU already (laid - on + with the 12v rail), auto safety shut it down on contact. Unplug all, replug all, flip switch & it powered right up. I run my 6amp lipo charger with it, no worries at all here. I'll try to take a vid of a test cut so you will have some real world feedback (also have a laser temp gun).

~psguardian
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