Refurbishing Rheostats

This forum is for (a) to help other members source materials, and (b) for topics regarding equipment repairs.
Post Reply
bigmack
Posts: 816
Joined: 15 Dec 2015, 10:49
Job Title: Lab Technician
School: FCAC
State/Location: QLD

Refurbishing Rheostats

Post by bigmack »

We needed a prac that involved 12 Rheostats . As usual I was alerted to the fact that the last time anyone used them they were really touchy and could I check them out . Indeed they were . Connecting a light bulb in series with them and a power pack , the light would flicker and/or die as the slider was moved up and down the resistor .
I looked at the cost of new ones and realized I was looking at over $1000 to replace them with a similar quality unit .

So I fixed them .

These are the type ,they were very common in schools and although they are over 40 years old , they ended up as good as new .

Start by undoing the screw at the end of the slide bar and the nut at one end of the rod that goes through the Resistor. (They are Nylock nuts so they will be tight until almost completely undone .)
Rheostat.jpg
Disassemble the bits .The important thing to watch are the two little springs in the slider don't go ping .
Dismantled.jpg
Start by scrubbing the top of the Resistor with a scouring pad .It should quickly go from dull and grimmy to shiny .
Also give the slide bar a gentle wipe after cleaning with metho . The Slide bar is Chrome plated so you don't want to be too aggressive and damage the plating .
Clean the resistor.jpg
In all of mine , the Carbon Brush had worn a groove in it . .......see those little springs ......don't loose them .
worn Brush contact.jpg
I held the slider assembly parallel and run it up and down a coarse file a few times and it easily removed the worn groove .
Re-face the Brush.jpg
You do not have the required permissions to view the files attached to this post.
bigmack
Posts: 816
Joined: 15 Dec 2015, 10:49
Job Title: Lab Technician
School: FCAC
State/Location: QLD

Re: Refurbishing Rheostats

Post by bigmack »

File a chamfer on the edges of the brush and clean the inside of the Slider where the bar slides inside
Slider assembly.jpg
Reassemble the unit and aply a small drop of oil to the four sides if the slide bar so that the slider moves a bit more freely.
Drop of Oil.jpg
Check that the slide bar is not crooked like in this picture ( the Left pointing arrow is pointing to the brush assembly not being parallel to the Resistor ), if it is then loosen the nut and bold at each end of the slide bar and twist the bar until it is straight...then tighten the nut and bolt but don't over tighten as you might crack the plastic /Bakelite bushes
croocked slide bar.jpg
Check that the slider knob is tight on the slider mechanism . in several of mine , the screws had worked loose . They are hidden under "bungs" which can be easily removed with a pointy thing .
Hidden screwws.jpg
While your at it , check the nuts that tighten the resistance wire to the contact posts are tight too .


So there you have it . A fully working set of Rheostats for a few hours work . \:D/

EDIT: Wear gloves if you are going to be doing any hand modelling that day.........'cause that carbon dusts gets in :giggle:
You do not have the required permissions to view the files attached to this post.
Last edited by bigmack on 18 May 2017, 15:44, edited 2 times in total.
linotas
Posts: 659
Joined: 21 Mar 2011, 22:39
State/Location: TAS

Re: Refurbishing Rheostats

Post by linotas »

:clap3: :thumbup:
User avatar
Whspa
Posts: 345
Joined: 01 Jun 2006, 10:00
State/Location: NSW

Re: Refurbishing Rheostats

Post by Whspa »

:clap3: Wow! Thanks for that. Great instructions.
Merilyn1
Posts: 1476
Joined: 12 Mar 2013, 08:10
Job Title: Labbie
School: Wollondilly Anglican College
Suburb: Tahmoor
State/Location: NSW

Re: Refurbishing Rheostats

Post by Merilyn1 »

Thanks for sharing that Richard. Although they are very clear instructions, I don't think I could trust myself to get them working again - maybe there's a business opportunity waiting for you? I have to buy new ones here as we don't have any at all, and yes, they are very expensive.
User avatar
me
Posts: 71
Joined: 28 Aug 2006, 10:00
Job Title: Lab Assistant
School: Castle Hill High
Suburb: Castle Hill
State/Location: NSW

Re: Refurbishing Rheostats

Post by me »

Thanks for that bigmack, it was only last week I thought that I should try to get ours working a bit better but had no idea where to start.
User avatar
melsid
Posts: 355
Joined: 07 Apr 2013, 07:11
Job Title: Lab Rat
School: PHS
State/Location: NSW

Re: Refurbishing Rheostats

Post by melsid »

Thanks so much, Ours are getting on a bit, so a refurb is on the list...
M
Vicki L
Posts: 76
Joined: 20 Jun 2007, 13:18
School: Murrumburrah High School
Suburb: HARDEN
State/Location: NSW

Re: Refurbishing Rheostats

Post by Vicki L »

Great info. Thanks for sharing.
User avatar
Laverne
Posts: 29
Joined: 21 Jun 2008, 12:51
State/Location: NSW

Re: Refurbishing Rheostats

Post by Laverne »

Thank you very much. Just might have to investigate ours and see if they need a service.
bigmack
Posts: 816
Joined: 15 Dec 2015, 10:49
Job Title: Lab Technician
School: FCAC
State/Location: QLD

Re: Refurbishing Rheostats

Post by bigmack »

Pleased it was of some help . It really isn't difficult but by all means ask if you are worried about anything .
Once you have the first one done , the rest are easy .
CC
Posts: 226
Joined: 22 Mar 2007, 10:00
Job Title: Labbie
School: Goulburn High School
Suburb: Goulburn
State/Location: NSW

Re: Refurbishing Rheostats

Post by CC »

Thank you so much. We were in the same position, I've just done one as soon as I found the instructions and it works like a charm.
bigmack
Posts: 816
Joined: 15 Dec 2015, 10:49
Job Title: Lab Technician
School: FCAC
State/Location: QLD

Re: Refurbishing Rheostats

Post by bigmack »

Pleased it worked Cindy
User avatar
Labbie
Posts: 3234
Joined: 28 Nov 2006, 10:00
Job Title: Retired
Suburb: At Home
State/Location: NSW

Re: Refurbishing Rheostats

Post by Labbie »

Bump
Regards Labbie

Lab Manager/Lab Tech, mind reading etc etc
Now retired :wub:
Post Reply