Resistance wire and AC/DC electrics?

P

pjl83

New Member
I've been working on a project that I posted on here the other day. I was looking at using resistance wire to make a heated stirring attachment.

I am now ready to build a tester to try out my theory.

Using W=V2/R I worked out that using 230v I would need 5.7 ohm/metre to achieve my 100 watt target based on the total length of the wire needed.

However, I found examples of this equation being used accurately with DC electrics. Would the resistance wire behave the same with AC ?

If not, then how do I work out this equation using AC?

Any thoughts would help on this......................

Thankyou in advance!
 
Common power line frequencies of AC work just the same as DC current in resistance heating elements.
 
That's great. There's some nichrome wire on ebay that's around 7 ohms/metre.

I'll buy that and give it a go.

Thanks
 
230v AC is actually a waveform that rises to about 345v. The 230v AC is actually called 230v RMS which means "equal to DC." The AC voltage rises to a peak of 345v during part of the waveform and drops to 0v during part of the wave. The current taken during the peak is more than if the appliance was connected to 230v DC and when the voltage drops to below 230v, the current is less than if it were connected to 230v DC. But when you take into account the higher current and lower current over a complete cycle, the answer is exactly the same as if the item was connected to DC.
 
do you there might be an issue with inductance? The wire will be wound around an insulator with a 3mm diametre and the coils spaced at approx. 4mm apart and a total of 275mm long.
 
Your calculations are all wrong.
For 100 watts you need 530R = 75 metres
3mm dia = 9mm circumference = 830 turns
 
Inductance won't be a problem. However, how did you arrive at a 100 watt heater?

Ron
 
100 watts came from a unit that we use now for heating the liquid that this will be used for...

colin - you're correct! I've messed up somewhere

I've just gone through it again.....

I calculated W=V2/R

so.... I know my watts = 100 and my voltage is 230 ....... R= 52900/100
so.... R=529

The stirrer is 275mm long, 3mm diametre and the coils will be spaced at 4mm apart...

number of turns is.......275/4=68.75

so........... pi x diametre x number of turns
3.14 x 3 x 68.75 = 648mm

Total length of wire = 0.64 metres

ohms per metre is...... 529/0.64 = 826

Using the same calculations I found that 24v means I need 9 ohms/metre........ which sounds much more realistic...

Any thoughts? I've been staring at these sums for so long that I'm not not sure anymore

Thanks in advance....
 
can't give you any specs, but stainless steel aircraft safety tie wire has a fairly high ohms / mil-foot, but probably changes as it gets hotter, but at 100 watts, may be pretty stable. I've used it for a load resistor a couple of times using .032" wire.
 
Last edited:
You're not just planning on submerging the heating coil directly in a solution are you?
 
Sceadwian said:
You're not just planning on submerging the heating coil directly in a solution are you?
Click to expand...

Yep! you've sussed me. It's actually a bomb that I'm making lol

only joking........ It will be wound around an insulator and then insulated on the outside.
 
Juuuuuust checking =) What are you planning on using for insulation out of curiosity? It has to be liquid tight electrically non conductive and transfer heat well. Most of the heating coils I've seen have nichrome down the middle sealed with some kind of thermal epoxy around a metal coil that is what comes in direct contact with the solution.
 
If you use 24v, you won't need any insulation but the cheapest and best thing to use is a number of 12v car globes.
Or you can use a 240v 1,000w radiator bar on 24v.
 
Last edited:
I'm wanting to experiment with ceramic, though I'm still thinking of trying the tubular deign with a heater element in the top. Might be simpler and easier????

I've ordered some resistance wire and also a 12v immersion heater that plugs into a cars cigarette lighter. I will have a play with both and see how it goes........
 
Ceramic what? A hobbyist can't play with real ceramics generally, unless you have a high temperature kiln. Do you mean ceramic filled epoxies?
 
You must log in or register to reply here.

Similar threads

V
  • Question Question
Selection Guidelines - Convert DC Wall Wart to AC Wall Wart
2
Replies
28
Views
2K
Nigel Goodwin
C
Components for AC-DC rectifier
Replies
13
Views
3K
danadak
M
  • Question Question
PSU "Schematic" help me understand AC/DC Bridge Rectifiers, Proper Grounding, and Series AC Connections
Replies
8
Views
3K
Tony Stewart
  • Question Question
AC Blower Motor Speed Control
Replies
4
Views
774
ahsrabrifat
A
  • Question Question
RS485 bus: common ground wire needed or not?
Replies
5
Views
826
ahsrabrifat
A
Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…