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tk709 · Posted: Fri Nov 28, 2008 6:16 pm Post subject: Oven question

I redid the oven on our vac table just like the TJ oven, only with cotter pins instead of ceramic insulators, and kept kicking the breaker. The oven was tested, and we are pulling 40 amps. What could I possibly have done to be pulling that many amps.

crashmann · Guru Joined: 27 Sep 2005 Posts: 501

Yikes! Pulling 40 amps?!? Now that's a problem!

You'll need to double check your connections from the power supply to the terminals on the oven coils. You should be alternating with hot on A (white), then neutral on B (black), hot on C, then neutral on D, etc... Or it could be neutral on A, hot on B...

Make sure none of the cotter pins are touching on the back of the oven. That will short circuit one segment into another. Very bad!

Also, use your multimeter, and (with the oven unplugged from the power outlet) measure the resistance from terminal A to the last terminal. If you are truly pulling 40 amps, then you should get a resistance reading of 3Ω

To measure the resistance of each segment, you will need to disconnect the terminals. Then measure from point A to B, B to C, etc... They should all be very close in resistance.

Post a picture of your wiring to the group if you can. You'll need to put it on Flickr, ImageShack, or another free picture site, then put the "image" code in your posting [img] url.jpg [/img] - the URL points to your picture.

How did you determine that you were pulling 40 amps?

Charlie

tk709 · Posted: Sun Nov 30, 2008 10:06 am Post subject:

Here is a pic of the oven wiring. We had an electrician look at it, but he was clueless as to the workings. He was the one who measured tested the oven, and said it was pulling 40amps.

I hope this helps.

jegner · Posted: Sun Nov 30, 2008 10:20 am Post subject:

This is the base for my machine, and it pulls much less, more like 26.5amps. Question, is your vacuum source on the same circuit as your oven? A shop vac will pull 15 amps all by it's self. Be sure to run your vacuum source off a different breaker. Also, show us a pic of the coiled wire side. Maybe your coils are too short?

Jim

ANH trooper · Master Joined: 20 Oct 2005 Posts: 305 Location: UK

Did the whole thing trip out?

I have cotter pins holding my coils and the tabs on the back have touched, making a segment trip out and the other segments go red hot!

Listen to Charlies' advice and get a multimeter. They are very simple to use and that's the only way you'll know the ampage for sure.

Is your power supply 110v or 240v?

tk709 · Posted: Sun Nov 30, 2008 6:15 pm Post subject:

Here is a pic of the coil on the oven. I used ceramic insulators at the contact points because I wasn't able to get the wires tight on the cotter pins.

I am using 110v and it did blow out the entire circuit. It blew our 30 amp fuses.

Fredo · Posted: Mon Dec 01, 2008 10:52 am Post subject:

After looking at the coil spacing on Jims oven and then the pic of your oven it seems to me you may have used less than the required length of coiled wire. Using less than required length of coiled nichrome for each segment will cause the amps to go way up. This may or may not be whats causing your overload. Congrats. on gettin the pic. loaded up. Wish the hell I could do the same. I'm as handy as a four armed monkey but I'm still a monkey see ,monkey do kind of guy. I guess I need a monkey trainer with computer skills to show me. Laughing

............Fredo

CJanssen · Posted: Mon Dec 01, 2008 12:06 pm Post subject:

ya, that wire is too short...i bet those coils get nice and red. I did the same thing on my oven, i cut the wire where the last segment started, tightened up my coils, and then added more wire to the last segment.

It probably wasnt the easiest way to fix it, but i am cheap and didnt want to waste any wire.

http://www.imperial-armor.com/ovencalculations.html

_________________
"What, you think your some kind of Jedi?"

tk709 · Posted: Mon Dec 01, 2008 3:53 pm Post subject:

Thanks for helping me figure this out. I knew it had to be something simple.

jegner · Posted: Mon Dec 01, 2008 9:17 pm Post subject:

Yep, coils are too short. Should look more like this:

cod · Posted: Tue Dec 02, 2008 5:05 pm Post subject:

get a multi meter and read the resistance of your coils . You can calculate the amp draw :

amps=volts/resistance

a 15 amp breaker can run:
R=120/15= 8 ohms maximum

a 16 ohm coil will run at 7.5 amps

so somewhere between 8 and 16 ohms reading on your coil is the max you can run on a 15 amp breaker (minus vacuums and other power draws)
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<.o'>

tk709 · Posted: Tue Dec 02, 2008 6:43 pm Post subject:

Redid the coils tonite. I am going to test it tomorrow.

Asok · Newbie Joined: 09 Nov 2006 Posts: 17

Charlie, if you need help, I am still without job and can come up and help.

tk709 · Posted: Thu Dec 04, 2008 4:48 am Post subject:

The oven works just fine now. Thanks for the help everyone.

jegner · Posted: Thu Dec 04, 2008 7:18 am Post subject:

Yea! Post some pics of it running if you have a chance!

I'd also love to see your armor project!

Jim