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  1. #1
    Hi,

    I've been reading the following thread:

    http://www.mycncuk.com/threads/11628...per-CNC-Router


    and I've got a question regarding a DIY bulit power supply that is mentioned in post #9 and my question is regarding the current output....

    Jazz recommends against using the Zapp Automation one (in post #8) as it maxes out at 6A, but from what I can tell the specs for the DIY version that is recommended and built using a 500VA 45V are exactly the same and it's output is 6A too.

    The only 230V single primary that they (Rapid) sell is a 500VA one.

    So my question is...

    What kit/parts do people use if they want their DIY PSUs to provide more than 6A output? To enable future use of additional motors?

    Cheers
    Last edited by joe.ninety; 19-02-2020 at 01:20 PM.

  2. #2
    AndyUK's Avatar
    Lives in Southampton, United Kingdom. Last Activity: 15 Hours Ago Has been a member for 2-3 years. Has a total post count of 330. Received thanks 68 times, giving thanks to others 30 times. Referred 1 members to the community.
    https://www.rapidonline.com/single-primary

    Are you sure they only sell a 500VA one?

    Edit: oh I see. You're saying only one that has two 45V secondaries.

    In that case you just have to play around with the secondary voltage, e.g. using 2x25V in series, or go to a different supplier.

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  4. #3
    Hmmm, the more I think about it the solution seems to be to wire the two 45V outputs from the 500VA tranny in parallel thereby doubling the output amperage to 12A.

  5. #4
    AndyUK's Avatar
    Lives in Southampton, United Kingdom. Last Activity: 15 Hours Ago Has been a member for 2-3 years. Has a total post count of 330. Received thanks 68 times, giving thanks to others 30 times. Referred 1 members to the community.
    Yes sorry didn't do the maths on your numbers and didn't realise you were only talking about a single secondary. Wiring in parallel was assumed. 500VA will net around 12A at ~64V.

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  7. #5
    and I've got a question regarding a DIY bulit power supply that is mentioned in post #9 and my question is regarding the current output....
    What will the drives take as max voltage and will the drives take AC and well as DC
    ..Clive
    The more you know, The better you know, How little you know

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  9. #6
    Wiring secondaries in parallel is a perfectly acceptable solution - just remember you need to make sure the phase of each secondary is matched (you normally find one end of each secondary marked on any schematic with a 'dot' - wire dot-to-dots and non-dots-to-non-dots... if that makes sense). Don't worry, if you get it wrong your fuse will politely inform you.

    The only issue to consider is that the power loss in a system rises as a square of the current drawn - you'll have less losses for a given wiring CSA if you can distribute your load across individual secondaries, rather than wiring everything to parallel secondaries. But, provided you over-spec the wiring, and/or avoid daisy-chains on the power distribution then you shouldn't have problems.

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  11. #7
    I should explain...

    Probably like most people who are new to CNC'ing, once the bug bites I just want to get on with something ASAP. Unfortunately, I've come to discover that every decision seems to rely on another until you've gone full circle and are back at the start ;-) Well that's how it feels anyway.

    I was hoping that the PSU would be something that it was possible to get started on, and that it would be possible to 'spec' one up that could work across a variety of motor choices, and also still be usable in the future on possibly a larger machine. So essentially an over engineered/spec'ed one.

    My curiosity was piqued by Jazz saying that a 6A PSU didn't allow much leeway for expansion. So as I stated, I just wondered what people were using if they wanted 45V but at a higher VA output. Was the reason that 45V was recommended over 50V simply because the 50V version has a lower current output... 5A on the 50V compared with 5.56A on the 45V?

    The simple answer might be to just buy another brand as Andy suggested.

    Cheers

  12. I built my own PSU there was nothing to it just a transformer, bridge rectifier and 3 capacitors.

    It sounds far scarier than it actually is took about an hour including time to smoke cigs and drink tea.

    I have since quit smoking so I think 30 mins is realistic.
    http://www.mycncuk.com/threads/10880...60cm-work-area My first CNC build WIP 120cm*80cm

    If you didn't buy it from China the company you bought it from did ;)

  13. #9
    AndyUK's Avatar
    Lives in Southampton, United Kingdom. Last Activity: 15 Hours Ago Has been a member for 2-3 years. Has a total post count of 330. Received thanks 68 times, giving thanks to others 30 times. Referred 1 members to the community.
    Yeah, it's not difficult just be aware of the safety.

    Plus, if you get AC drivers it's just the torrodial. Nothing else.

    Doing it beforehand however is not your best plan, bit of a false economy because you'll end up with something that isn't quite right or you'll make compromises on the rest of the build to suit.

    First, figure out what you want to cut. Materials, sizes.
    Then work out your physical constraints on machine size.
    Then find a similar build log and start CADing. As you come up against different problems look to other build logs for solutions then add your own twist. It's just not worth spending time and money until you know what you want and have speced it out across the board.

  14. #10
    Quote Originally Posted by joe.ninety View Post
    I should explain...

    Probably like most people who are new to CNC'ing, once the bug bites I just want to get on with something ASAP. Unfortunately, I've come to discover that every decision seems to rely on another until you've gone full circle and are back at the start ;-) Well that's how it feels anyway.
    Every answer raises two new questions. You'll have to get used to it I'm afraid!

    There are plenty of sources of transformers. Have a look at RS Components for example. Even if you don't buy from them, you'll get an idea of the range available. Note that the DC voltage (that's appalling English, but everyone knows what it means) you will get from a finished supply is higher than the RMS voltage rating of the AC transformer, if a DC supply is what your drivers require. I've linked to the site linked below before but it's a good intro to DC PSU design. A supply for a CNC machine can be allowed to have quite a high ripple voltage and thus less capacitance than would be needed for, say, a hi-fi audio amplifier.

    http://www.skillbank.co.uk/psu/
    Engineering is the art of doing for ten shillings what any fool can do for a pound.
    Wellington.

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