Electromagnets

Discussion in 'Supporting Physics' started by Mandy, Mar 23, 2018.

  1. We do have trollies, but they're full of all the other trays full of equipment that need to go out for the lesson!
    I can only fit the PSUs on the top shelf as the rest of it fills the other two shelves. We use the grey Satz units as we can fit 8 of them into a gratnell tray and can easily put a class set of 16-18 on one shelf.
     
  2. Nick Mitchener

    Nick Mitchener COMMITTEE

    Get dedicated power supply trolleys. We have 6 of those, another dedicated trolley for ramps and dynamics carts, another two for rayboxes/prism's etc. Biology have 3 dedicated trolleys for microscopes, another for desk lamps. Saves a great deal of work and time.
     
  3. Nice idea, but I just can't unfortunately.
    I don't have the space for them in the prep room, I don't have the space for them in the labs during a lesson, I don't have time to be moving 2 trolleys per lesson, and above all I don't have the money to buy them!
    With 12 teachers in 10 labs and only 3 technicians on site at any time changeovers are difficult enough already. It would be impossible to move two trolleys to the same room especially when they go from one lab to another the very next period.
     
  4. Nick Mitchener

    Nick Mitchener COMMITTEE

    11 labs, 14 teachers, 3 techs. We do have a preproom each, but the trolleys stay in labs moving about as required. On top of that I store physics equipment in cupboard in four laboratories as well as the preproom, just wouldn't have space otherwise. We are very well resourced, but budgets are continually revised downwards making it hard to replace anything.
     
  5. Sadly we're not very well resourced and the budgets are decreasing each year. From January technicians will also be expected to invigilate exams so despite struggling for time to get our jobs done already, things will be even worse going forward.
     
  6. Nick Mitchener

    Nick Mitchener COMMITTEE

    That's the point I'd leave.
     
  7. We use the other SATZ ones. The 3A ones. Long wires is key. I have 8 in each Lab so I don't have to move them (couldn't afford more 40 in total) but it wouldn't be a massive deal if I did need to move them for a special occasion.

    Or you could use batteries for electromagnets.
     
  8. It hasn't gone down well and there are many staff looking to leave, myself included.

    I didn't think of batteries, that might be an option as I've got lots of AA holders that I might be able to use.
     
  9. How do you lock these power supplies at 6v?
     
  10. Elizabeth Gould

    Elizabeth Gould COMMITTEE

    SLS Select Education do iron cores for this purpose for £1.89 each :)
     
  11. Nick Mitchener

    Nick Mitchener COMMITTEE

    The old irwins have a socket cap screw that you screw in so that the pointer can't get past the head of the socket cap.

    It isn't 100% enough force will achieve something. You do occasionally get called out because they aren't working but that is because the screw stops the selector between 6 and 8, so it is off if left hard up against the screw, they need to select either 2,4,or 6.
     
  12. PhysicsSimon

    PhysicsSimon COMMITTEE

    I'd most definitely trial it with batteries before giving out a class set - I used to have a data sheet from Duracell which basically said (from memory) - don't pull more than about 1amp for a few seconds or you'll kill it.....I can no longer find this advice online (think they've changed it) but I'd be hesitant to use them all the same.

    If you're pulling say 5A (makes the maths easier & you're tripping out 3A supplies) then a brand new, alkaline 2500* milliamp hours AA will last for half an hour maximum even if it can cope with the very high current drain.

    *This is the quoted capacity of a brand new, top of the line AA - other figures may be available (pound shops!!!), one German industrial brand quotes 2700 but they're pretty rare I think
     
  13. Same as Nick, I insist that they use 8 Amp power supplies only.
    If you are using stuff like for example Rapid Electronics plastic insulated wire here are a few facts... And a good reason as to why the SATZ units are useless for this task.

    Actual conductor diameter: 0.6mm
    Recommended maximum current: 3A
    Absolute maximum current short term: 12A
    Electronic conductivity: 98%
    Resistance per metre: 0.061
    Average length of wire used in making of an electro magnet: 2m
    Resistance of wire at two metres: 0.122
    Power pack maximum current rating is 8A
    Current at 2V is 16A!
     
    Last edited: Dec 5, 2018
  14. Thanks guys, that's very useful information that I wasn't aware of. Despite being the Physics technician, I'm self taught in the role and electricity stuff isn't my forte!
     
  15. Nick Mitchener

    Nick Mitchener COMMITTEE

    I keep one of those on my bench as a bench power supply. The DC output is a bit pants in waveform but they seem quite robust.
     
  16. Mandy:
    1. We have an excess of Irwin power supplies. If you wan to buy any, let me know and we can try to come to a suitable financial arrangement.
    2. There is no way on this Earth that invigilating is technical (or support staff) work. Refuse to do it.
     
  17. Carol Taylor

    Carol Taylor Footsore

    Flights of stairs to contend with. I have gradually bought in 10 of the tall grey ones, HOD has grabbed those. We still have about 16 orange unilab, 10 of which I tend to house in the room of whoever is teaching most physics that particular year and 4 in another lab. We also have some small grey SCI-mart ones which seem to be easy to damage. There were 10 but now about 5 dotted around.
     
  18. is this internal exams, when it should be a teachers responsibility, or public exams, when there is plenty of other work you should be doing, tell the teachers they can't have any pracs as you are standing in the hall all day. :rolleyes:
     
  19. Not had chance for a while to look at the forum, yet alone find a comment that no-one else has point out!

    If you opt for batteries, don't use rechargeable, internal resistance is quite low and sometimes catch fire when short-circuited (which an electromagnet essentially is).
    Having to skim due to time, have you tried using variable resistors to alter current preventing the SATZ supplies from overloading?