What resistor is this? - Page 1
Forum section: electronics / beginners

author: laserpon3
author_rank: Contributor
timestamp: December 07, 2012, 04:12:01 am
content: I am familiar with resistors but.On dave's video of the lab power supply design part 3 he uses some weird big white resistors. [0:38]https://www.youtube.com/watch?feature=player_detailpage&v=8-qar5vgnbc#t=38sI have also seen this resistors being used in another lab power supply making video:What type of resistor is this?I can't seem to find them or find a proper place to buy them (as I don't know what they are).Why are these used for dummy load instead of the more common resistor types? less heat? more durability? higher resistance?From what I believe, dummy loads are a lot of resistors connected to eachother. I'm not sure, but searching dummy load resistor doesn't give me anything looking close to this.

author: Psi
author_rank: Super Contributor
timestamp: December 07, 2012, 04:29:11 am
content: Quote from: laserpon3 on December 07, 2012, 04:12:01 amIt's a "ceramic wirewound resistor". They're the next step up from a normal resistor in terms of power handling.The small white ones start at around 5W and some of the larger ones are 40W+Quote from: laserpon3 on December 07, 2012, 04:12:01 amDigikey have them in the "Through Hole Resistors" section.Just parametric sort based on above 5W and you will find lots of them.eghttp://www.digikey.co.nz/product-detail/en/SQP20AJB-1R/SQP20AJB-1R-ND/1680006Quote from: laserpon3 on December 07, 2012, 04:12:01 amMore common? those kind of resistor are really common.There are other types as well. Like these more expensive mountable ones, some of which can handle 100W if mounted properly.

author: nadona
author_rank: Regular Contributor
timestamp: December 07, 2012, 04:31:03 am
content: I think they call it cement resistor. Maybe you get the clue by reading this paper.http://www.yageo.com/documents/recent/Leaded-R_PSP_2011.pdf

author: laserpon3
author_rank: Contributor
timestamp: December 07, 2012, 04:40:40 am
content: Thanks guys!This answered the question for me!

author: SeanB
author_rank: Super Contributor
timestamp: December 07, 2012, 04:47:58 am
content: Wire wound resistors in a ceramic boat. Common at high power, as the case is an insulator even when red hot. Most round wirewound ones with a dip coat are conductive through the coating when they get hot enough.

author: T4P
author_rank: Super Contributor
timestamp: December 07, 2012, 05:47:47 pm
content: And there are massive/powerful wirewound ones that are green in colour and you can see the wound wire on the substrate! But they are quite dangerous ... exposed wire, who wants some of that?Usually they look like thatBut ...sometimes they come like that

author: Short Circuit
author_rank: Frequent Contributor
timestamp: December 07, 2012, 06:01:12 pm
content: Quote from: T4P on December 07, 2012, 05:47:47 pmMost resistors have exposed wires... Big ones no different than your standard 1/4W PCB resistorsAnd you want to shield them from unintended touching anyway, these things can get hot, very hot.Operating temperature range up to 225 degrees (TE range), much hotter during short term overload condition.You don't want people to touch that by accident.

author: SeanB
author_rank: Super Contributor
timestamp: December 07, 2012, 07:57:38 pm
content: The conductivity is a problem if it is mounted in a metal clamp and it gets hot, which then causes a leakage to the clamp of the resistor voltage. It is possible to have enough current flow to make it go into thermal runaway.

author: IanB
author_rank: Super Contributor
timestamp: December 07, 2012, 11:37:25 pm
content: Quote from: laserpon3 on December 07, 2012, 04:12:01 amIf you are in the USA (you have no location in your profile) then go have a look in RadioShack or maybe Fry's. You will find resistors looking just like that in power ratings of 5 W, 10 W or 20 W.