HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Jan 14, 2013, 10:47 AM
Registered User
Sarboy's Avatar
Joined Mar 2010
234 Posts
Discussion
Wire cutter power supply

I'm know there are lots of threads on these bit I'm still none the wiser.

I have a variable voltage and amperage power supply for my charger. I thought it would work for a wire cutter power supply. I have used it as power source but if the wire is more than 30cm long the temp is low and causes cutting to take forever or not cut at all.

The voltage shows 15v but with the ampage turned up it shows nothing. Why is this? Is it because there is no load?

What do I need to do to achieve a longer wire at a good temp? This is really bugging me.
Sarboy is offline Find More Posts by Sarboy
Reply With Quote
Sign up now
to remove ads between posts
Old Jan 14, 2013, 10:53 AM
Registered User
Ward Hagaman's Avatar
San Diego
Joined Mar 2003
2,315 Posts
A wire with a bigger diameter will require fewer amps to get to the same temperature, so you could try a bigger wire.
Ward Hagaman is offline Find More Posts by Ward Hagaman
Reply With Quote
Old Jan 14, 2013, 11:01 AM
Registered User
Sarboy's Avatar
Joined Mar 2010
234 Posts
Tried the biggest I have, .20 nichrome and still not good enough. Am I right in thinking the power supply should work? It's rated to 40 amps but it shows nothing when connected.
Sarboy is offline Find More Posts by Sarboy
Reply With Quote
Old Jan 14, 2013, 11:46 AM
Since 1952
Harry D's Avatar
Canada, AB, Edmonton
Joined Oct 2004
1,323 Posts
Quote:
Originally Posted by Ward Hagaman View Post
A wire with a bigger diameter will require fewer amps to get to the same temperature.
Not so. Exactly the opposite.
Harry D is offline Find More Posts by Harry D
Reply With Quote
Old Jan 14, 2013, 11:51 AM
The Prez....... again
kenh3497's Avatar
United States, IA, Rockwell
Joined Jul 2011
4,162 Posts
DO NOT QUOTE ME.... I believe the longer wire needs a little more voltage. I see a lot of guys are running a 24 volt transformer.

Ken
kenh3497 is online now Find More Posts by kenh3497
Reply With Quote
Old Jan 14, 2013, 12:01 PM
Registered User
Staffs, UK
Joined Nov 2003
10,666 Posts
If the PSU will cover up to about 20V and at least 5A and is has both variable voltage AND current it should be fine for any practical size of wire cutter I can think of, unless you're using some really odd wire. I often use a 20V 3A PSU but I only use about a 80cm max wire length.

But if it's really showing 15V and no current then either you don't have a good connection or you have the current limiter turned right down.

Steve
slipstick is offline Find More Posts by slipstick
Reply With Quote
Old Jan 14, 2013, 12:26 PM
Registered User
Sarboy's Avatar
Joined Mar 2010
234 Posts
Hmmm, maybe it's the connection. I have is 4 crocodile clips, two to the power supply and one at either end of the wire. I'm using speaker cable which is just striped and screwed to the clips. Should I solder it?
Sarboy is offline Find More Posts by Sarboy
Reply With Quote
Old Jan 15, 2013, 12:47 AM
Rob H
rph1225's Avatar
United States, MD, Rosedale
Joined Jul 2011
118 Posts
Quote:
Originally Posted by kenh3497 View Post
DO NOT QUOTE ME.... I believe the longer wire needs a little more voltage. I see a lot of guys are running a 24 volt transformer.

Ken
Maybe this will help, but I currently run a 12V transformer for a door bell through a dimmer and with 24ga Nichrome wire and have had great results. It usually runs at about 6V for blue insulation foam and slightly less for lightweight white foam. Also, my bow is 28" long.

I first tried Mig welding wire and it was too thick and required to much voltage to heat. Maybe try running a smaller gauge wire.
rph1225 is offline Find More Posts by rph1225
Reply With Quote
Old Jan 18, 2013, 08:32 AM
Registered User
Sarboy's Avatar
Joined Mar 2010
234 Posts
Thaks for all the help. I have been doing a little back to school electronics and think I have found my problem. This has been proven by experiment too.

If I pretend my wire is a resistor and by moving the crocodile clips along the wire I am making a variable resistor. If my voltage is 15v and I have my amps turned up to max, as I move the crocodile clips apart I will see the voltage remain the same but the amps start to reduce. This continues till the resistance is so high that the amps drop to zero.

That's the theory. So I put it into practice and it worked as described with the amps dropping to zero at about 60-65cm. This gives me a bow length of 50cm usable for 15v. So to increase the usable bow length you need to up the volts. Simple when you know.

To that end I'm looking at high volt power sources (24v). I recon this should do for a variable source:

http://www.roadking.co.uk/laptop-acc...l#.UPku8nwgGSN

Thanks again for the help.
Sarboy is offline Find More Posts by Sarboy
Reply With Quote
Old Jan 18, 2013, 03:37 PM
Rob H
rph1225's Avatar
United States, MD, Rosedale
Joined Jul 2011
118 Posts
Quote:
Originally Posted by Sarboy View Post
Thaks for all the help. I have been doing a little back to school electronics and think I have found my problem. This has been proven by experiment too.

If I pretend my wire is a resistor and by moving the crocodile clips along the wire I am making a variable resistor. If my voltage is 15v and I have my amps turned up to max, as I move the crocodile clips apart I will see the voltage remain the same but the amps start to reduce. This continues till the resistance is so high that the amps drop to zero.

That's the theory. So I put it into practice and it worked as described with the amps dropping to zero at about 60-65cm. This gives me a bow length of 50cm usable for 15v. So to increase the usable bow length you need to up the volts. Simple when you know.

To that end I'm looking at high volt power sources (24v). I recon this should do for a variable source:

http://www.roadking.co.uk/laptop-acc...l#.UPku8nwgGSN

Thanks again for the help.
In your scenario, I think that you may have the amps changing in the wrong direction. If you separate the alligator clips then you are increasing the overall resistance of the wire, which would require more amps to generate the same amount of heat. Therefore, I would try and find a 12V transformer with a higher amperage capacity.
rph1225 is offline Find More Posts by rph1225
Reply With Quote
Old Jan 18, 2013, 03:56 PM
Registered User
Staffs, UK
Joined Nov 2003
10,666 Posts
Nope, Sarboy has it right. Longer wire = higher resistance. Higher resistance and a fixed voltage = lower current. Basic Ohms Law I = V / R.

To get a fixed level of current through a longer wire requires MORE voltage.

Sarboy, it would be interesting to know what the currents actually are. E.g. what current do you see at 20cm ? At 40 cm ? Obviously the current can't possibly be zero at 60-65cm, so I guess whatever you're using to measure it can't register relatively low currents.

Steve
slipstick is offline Find More Posts by slipstick
Reply With Quote
Old Jan 19, 2013, 03:42 AM
Registered User
Sarboy's Avatar
Joined Mar 2010
234 Posts
I'm off to work now for a 24 hour shift but I'll do a bit of research tomorrow and post findings if I get the time. My measuring equipment is just my power source. It's ok but only goes to 0.1 amp and I would guess has an accuracy of +-0.1. Not too bad but not great either. I should really invest in a descent amp/watt meter.
Sarboy is offline Find More Posts by Sarboy
Reply With Quote
Old Jan 19, 2013, 04:23 AM
Registered User
Staffs, UK
Joined Nov 2003
10,666 Posts
I don't know what's happening with your setup but you can always try this calculator to see what power supply you SHOULD need.
http://www.jacobs-online.biz/nichrome/NichromeCalc.html

Steve
slipstick is offline Find More Posts by slipstick
Reply With Quote
Old Jan 23, 2013, 01:11 AM
Do it Right, the first time!
CoolerByTheLake's Avatar
United States, MN, Hermantown
Joined Dec 2008
5,845 Posts
I built a PS last year and used this transformer. 24V 4A Just use a regular 120V .dimmer switch to regulate the power. My biggest bow is about 50".

http://www.jameco.com/webapp/wcs/sto...0001_221365_-1
CoolerByTheLake is offline Find More Posts by CoolerByTheLake
Reply With Quote
Old Jan 23, 2013, 03:21 AM
a.k.a. Bob Parks
Glendale, AZ
Joined Jun 2008
2,360 Posts
Dumb question, is your power supply AC or DC output?
bbbp is offline Find More Posts by bbbp
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Question Hot Wire Foam cutter power supply richie967 Foamies (Scratchbuilt) 105 Dec 01, 2013 07:24 PM
New Product Hot Wire Foam Cutter Power Supply!!! mattius7 Foamies (Scratchbuilt) 2 Mar 01, 2013 08:40 PM
Wanted looking for a power supply for hot wire foam wing cutter joe_crash Aircraft - General - Miscellaneous (FS/W) 5 Dec 20, 2012 03:29 AM
Sold Hot-wire cutter variable power supply jim breese Aircraft - Sailplanes (FS/W) 1 Apr 13, 2012 01:48 AM
Power Supply Transformer, for hot wire cutter, or flight pack charging Salin Electric Plane Talk 1 Aug 25, 2002 04:38 PM