Replacement cement resistor needed

Thread Starter

AntDaddy

Joined Dec 13, 2021
4
I have a speed controller for a welder that was missing 2 resistors. I know that it had 2; (7 watt 4.7 ohm ) resistors. The closest I could find come out of a audio cross over. And I tried them breifly just to see if that was the problem. And it worked they just got hot. Well Im looking for a place to get the correct or a alternative resistor. Ive got a pic of the pcb with the correct ones.
Screenshot_20211211-222711_Chrome.jpg
 

dl324

Joined Mar 30, 2015
14,318
Welcome to AAC!

What is your tolerance and size requirement? Not many suppliers stock them. Jameco.com has 5 ohm 10W and 10 ohm 5W:
1639427596681.png
 

MrSalts

Joined Apr 2, 2020
1,557
Wait a minute. Is it possible that cement resistors are actually a thing?
From the description...
"The SQ series resistors are wound or deposited on a fine non - alkali ceramic core then embodied in a ceramic case and sealed with an inorganic silica filler. ", I'd say, yes.

We used to call them sandbar resistors.
 

Papabravo

Joined Feb 24, 2006
18,100
From the description...
"The SQ series resistors are wound or deposited on a fine non - alkali ceramic core then embodied in a ceramic case and sealed with an inorganic silica filler. ", I'd say, yes.

We used to call them sandbar resistors.
Can you confirm that both cermet and cement resistors are different? The former being "ceramic and sintered metal" and the latter being "sandbars" as you put it.
 

Thread Starter

AntDaddy

Joined Dec 13, 2021
4
It is not cement! It is cermet, which is a heat resistant material made of ceramic and sintered metal. I offer the correction to make your online searches more likely to succeed.
Thank you Im not too educated on this subject but I want too learn.
 

MrSalts

Joined Apr 2, 2020
1,557
Can you confirm that both cermet and cement resistors are different? The former being "ceramic and sintered metal" and the latter being "sandbars" as you put it.
I don't know. A lot of the old sandbar resistors were just extruded U-channels of hard ceramic and a coil of resistor wire (wound around a ceramic rod) is set inside. Then a potting compound (more ceramic?) packed inside to hold everything in place. . Users have to design carefully because of the inductance (and capacitance) of the "wire-wound resistor".

Cermets are a whole other thing and may be placed in a sandbar U-channel or other sandbar shape and potted but usually not in the very low values the wire wound resistors come in - but I haven't needed a high wattage resistor in years so the whole wire wound issues may be a thing of the past. I just don't know.
 
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