Giant pot! - Page 1
Forum section: electronics / general

author: lmester
author_rank: Regular Contributor
timestamp: February 26, 2018, 06:14:45 am
content: I rescued this giant from the trash!I work for a public school district. Some science labs were being shut down. This big boy is a three terminal device. I'd call it a potentiometer. The label on the slider says "rheostat". I think of a rheostat as being a two terminal device. A pot is a three terminal device. A pot can be used as a voltage divider. I believe that I read somewhere that the term "rheostat" was also used as a general term to describe a variable resistance (two or three terminal device) that's designed to handle high power. This giant can handle 430W! Anyone have any ideas on rheostat versus potentiometer? What exactly do these terms mean?I'm not sure what I'll actually use this for. Maybe an ocassional need for a high power dummy load. It does look great! I like equipment that lets you see how it works. The slider moves across the big coil of resistance wire. The amount of wire on each side determines the resistance to each end terminal. A very good teaching tool. I think It's unfortunate that it was being discarded. The next generation of E.E.'s and Electronics tech's will just think of a pot or rheostat as a "black box" device that changes it's resistance when the knob is turned. They'll have no idea how it's actually constructed.

author: capt bullshot
author_rank: Super Contributor
timestamp: February 26, 2018, 06:19:16 am
content: NIce. At work we've got some ten of these things in the lab. People use them for load resistors on switched 24V outputs and other stuffBTW is that 5335 counter showing the resistance

author: lmester
author_rank: Regular Contributor
timestamp: February 26, 2018, 06:24:32 am
content: Quote from: capt bullshot on February 26, 2018, 06:19:16 amThat's another project. The 5335 is monitoring a DS3231 clock module. It was just a convenient spot to take a picture of the giant pot.

author: BravoV
author_rank: Super Contributor
timestamp: February 26, 2018, 06:26:12 am
content: Quote from: lmester on February 26, 2018, 06:14:45 amWith this .. there is no hesitation at all naming it another giant potentiometer too.More details (here).

author: lmester
author_rank: Regular Contributor
timestamp: February 26, 2018, 07:05:52 am
content: Here is another pot that I have in my collection of ancient electronics. I know it's history since I was the one that pulled it from the equipment. It was used to adjust the modulation power output of a Simplex time clock carrier current transmitter. This system was used to automaticcally set the time on clocks in an entire school building. It sent a signal out over the building power lines that the slave clocks used to adjust their time. FYI, this system was in the same school that I got the giant Cenco pot from.

author: Ampera
author_rank: Super Contributor
timestamp: February 26, 2018, 07:09:04 am
content: We're one step closer to building a real Frankenstein's Monster, guys.

author: helius
author_rank: Super Contributor
timestamp: February 26, 2018, 07:10:02 am
content: A variable resistor that was designed to dissipate power is properly called a rheostat, whether it has 2 or 3 terminals. Potentiometers are voltage divider sources and dissipate little power when used in that manner.

author: lmester
author_rank: Regular Contributor
timestamp: February 26, 2018, 08:33:20 am
content: Quote from: helius on February 26, 2018, 07:10:02 amA three terminal variable resistor that's not designed to dissipate power is a potentiometer. A two terminal variable resistor that's not designed to dissipate power is just called a variable resistor. A two or three terminal variable resistor designed to dissipate power is a rheostat. Is this correct?

author: Brumby
author_rank: Unknown
timestamp: February 26, 2018, 09:34:02 am
content: That works for me.

author: calexanian
author_rank: Super Contributor
timestamp: February 27, 2018, 08:58:21 pm
content: Cenco made stuff for educational use. Most of it was much larger and robust than otherwise needed for survivability with students and ease of seeing during demonstration.

author: shakalnokturn
author_rank: Super Contributor
timestamp: February 28, 2018, 09:07:07 pm
content: I remember using similar things in high school here, the winding was a little more enclosed, that proved to be convenient in avoiding burns in some cases.A friend of mine picked a couple of them up in the 200W range and used to make them glow (&chime/tweet) testing his audio power amp projects.IIRC he used them with the slider around center and end connections linked together for "less abusive use".

author: alm
author_rank: Super Contributor
timestamp: February 28, 2018, 09:13:10 pm
content: Quote from: lmester on February 26, 2018, 06:14:45 amKeep in mind that that 430W rating is if you use the full length of the resistance element. If you set it to only 10% of its value, the power rating is only about 43W. No problem if you're feeding it from a constant current source (hence the current rating printed on it), but it can catch you off guard if you feed it from a voltage source and set it to a low resistance value.

author: lowimpedance
author_rank: Super Contributor
timestamp: February 28, 2018, 11:27:22 pm
content: I see the 5335 is also propping up a couple of clocks of less electronic in nature , (400 day clocks best guess) !.Quote from: lmester on February 26, 2018, 06:24:32 amAnd here is a pic. of another smallPOTrheostat and a standard pot for size comparison.

author: lmester
author_rank: Regular Contributor
timestamp: March 03, 2018, 02:45:27 am
content: Quote from: lowimpedance on February 28, 2018, 11:27:22 pmI do have a fairly large collection of mechanical 400 day torsion clocks. These clocks are actually electronic. One is an early quartz clock and the other uses a transistor switched ATO movement. I'll post pictures in another thread. These clocks may be interesting to electronics people. Not quite as interesting as the giant rheostat