Page 2 of 3 FirstFirst 123 LastLast
  1. #11
    Quote Originally Posted by Iwant1 View Post
    How accurate are the secondaries in a transformer? I'm asking to see if there will be any premature failure if they are not equal, from one coil working harder than the other.
    That's precisely the reason I said '24V or 25V transformer (preferable)' in the previous post. Wondered if someone would pick up on that :)
    If they're not equal then more current will flow in the secondary windings, but I don't think it's likely to be a big enough difference to cause failure.


    Quote Originally Posted by Iwant1 View Post
    I will be using pm752 drivers which I've had lying around for 2 years. Their datasheet says typical voltage is 48v and max voltage is 75v. In another post I read Gary saying to Jonathan that 72v from a toroidal supply is bit on the high side for the pm-752 driver. When I do the calculation 50 X √2 I get 70.7v. Is this the output I will be getting or are there other factors which bring it down by a few volts

    I remember that one, to which I replied saying I'd checked the actual voltage at the MOSFETs and the spikes on switching were well below their rated 100V so I was happy to do it. That was with a 25+25V transformer from rapid, with the same PM752 drives from Zapp.
    70.7V is correct, but the diode will drop about 1.1V, so more like 69.6V. However the mains voltage does have a fairly wide tolerance. It looks like those transformers output 50V with 230V on the primary, however the mains voltage could be 240V (depends on numerous factors). That would make the output voltage 240/230*50*
    √2=72.7V... still less than mine which has been fine for a long time now. You could always add a couple of turns of thick wire out of phase to reduce the output voltage, but crude but it works...
    Old router build log here. New router build log here. Lathe build log here.
    Electric motorbike project here.

  2. #12
    Sent you a pm Jonathan regarding a build if you're up for it?

  3. #13
    Think I should say that if you choose the top pic Jonathan drew you will be getting double the voltage of the 2 secondery ouput ratings IE: 2x24=48V but only half the rated Amps of both seconderys but if you wire have 48V seconderys and wire parallel you get the same 48V but double the amps.

    No difference really has lower voltage seconderys have higher amps, roughly double, if the higher seconderys are double the voltage.!! . . . So 2 x 24Vac 12A seconderys can either give 48V @ 12A wired series or 24V @ 24A wired parallel. . . . So obviously 2 x 48Vac 6A seconderys wired parallel will give 48Vac @ 12A.

    The 48Vac when rectified to DC will give roughly 68V IE: 48Vac x 1.4 = 67.2Vdc

    Heres a pic of one (Big one) wired in parallel using 4 x 4700uf caps.!! ( Ignore the chocy block on the input that was a temp bodge.!) Click image for larger version. 

Name:	psu.jpg 
Views:	163 
Size:	128.1 KB 
ID:	6346
    Has you can see nothing too it. . Simplizzzzz.

  4. #14
    Quote Originally Posted by JAZZCNC View Post
    Think I should say that if you choose the top pic Jonathan drew

    [yada yada]

    48Vac @ 12A.
    Didn't see the point of that...In short, the power has to stays the same, hence why I specified what power transformer to get as then so long as you wire it for the right voltage, the current will be correct by default.

    Quote Originally Posted by jonbabbz View Post
    Sent you a pm Jonathan regarding a build if you're up for it?
    Yes I am. I'll sort it tomorrow - need to check what bits I have as I might already have everything you need.
    Old router build log here. New router build log here. Lathe build log here.
    Electric motorbike project here.

  5. #15
    Quote Originally Posted by Jonathan View Post
    That's precisely the reason I said '24V or 25V transformer (preferable)' in the previous post. Wondered if someone would pick up on that :)
    If they're not equal then more current will flow in the secondary windings, but I don't think it's likely to be a big enough difference to cause failure.
    I've always wired mine parallel and never had a failure or problem yet.!

  6. #16
    Quote Originally Posted by Jonathan View Post
    Didn't see the point of that...In short, the power has to stays the same, hence why I specified what power transformer to get as then so long as you wire it for the right voltage, the current will be correct by default.
    Yep but I find folks under stand better when it's spelled out and the difference known.? He could have been wondering why or how 24V could give him 65+V.?

    Just me being OTT maybe.?

  7. #17
    Quote Originally Posted by JAZZCNC View Post
    still have change to buy a small 5V 1A reg supply.!
    Don't need much change for that :)

    http://www.ebay.co.uk/itm/UK-DC-5V-1A-Switching-Power-Supply-adapter-100-240V-AC-Promotion-/200791372447?pt=UK_Sound_Vision_Other&hash=item2ec 019329f#ht_3691wt_1037

    Quote Originally Posted by JAZZCNC View Post
    Yep but I find folks under stand better when it's spelled out and the difference known.? He could have been wondering why or how 24V could give him 65+V.?
    I guess.
    Old router build log here. New router build log here. Lathe build log here.
    Electric motorbike project here.

  8. #18
    Jazz where did you get your transformer from? Is it this one?

    http://www.rapidonline.com/Electrical-Power/Toroidal-Transformer-1000va-0-50v-0-50v-88-3852
    Last edited by jonbabbz; 14-07-2012 at 12:46 AM. Reason: added link

  9. #19
    Was thinking something a bit easier and neater than that.!!
    http://www.ebay.co.uk/itm/DC-5V-5A-R...item2a1fbcca51

    Edit: I've had 2A version of these for 5 before this was just an example.
    Last edited by JAZZCNC; 14-07-2012 at 01:00 AM.

  10. #20
    Quote Originally Posted by jonbabbz View Post
    Jazz where did you get your transformer from? Is it this one?

    http://www.rapidonline.com/Electrica...-0-50v-88-3852
    Nope got it here I think.? http://www.airlinktransformers.com/c...ard_range.html

    You don't need or want 1000Va for 68V-ish @ 12A 625Va will do fine.
    With toroidal setup You only really need about 68% of total motor amps so 12A will be fine for 4x4.2A motors.!

Page 2 of 3 FirstFirst 123 LastLast

Similar Threads

  1. NEW MEMBER: newbie from bristol soon to be up and running
    By uppy121 in forum New Member Introductions
    Replies: 16
    Last Post: 01-04-2013, 12:38 AM
  2. PS806-5 Power Supply
    By Washout in forum General Electronics
    Replies: 7
    Last Post: 11-11-2012, 03:07 PM
  3. axis not moving when running code
    By geny in forum Computer Software
    Replies: 0
    Last Post: 21-10-2012, 08:02 PM
  4. 4th Axis running as CNC lathe using milling machine
    By Jonathan in forum Milling Machines, Builds & Conversions
    Replies: 6
    Last Post: 21-08-2011, 10:34 AM
  5. Running costs of CNC machines?
    By .kyle in forum General Discussion
    Replies: 1
    Last Post: 19-05-2011, 08:05 PM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •