[chbot] Chchrobotics Digest, Vol 158, Issue 11

Sat Nov 28 23:40:31 GMT 2020

I think the heater supply of a magnatron is only a few volts (2-3volts) at
a handful of amps, I might be wrong though. you could certainly re-wind a
MOT though if you are willing to punch out the HT winding.

On Sun, Nov 29, 2020 at 9:43 AM Graeme Absalom <clock_man_ok at hotmail.com>
wrote:

> Hi Mark
>
> Thank you so much for your advice. The current is controlled by a bank of
> 25 Ohm 50 Watt resistors that can be switched to allow more current. The
> switching is managed by four power FETs (IRFB4127).
> I would not risk any switchmode power supply.
> I spoke to Warren and he suggested transformers from old microwaves. They
> are 30 Volt and a high current. I could live with two of these in series
> and it still meets the alternative options in the book that I made the
> spark eroder from.
>
> I do have a question. Obviously, the output wires on the transformers must
> be connected so the phases don't work against each other. Can this be
> tested by reading the voltage and changing the orientation if the voltage
> is wrong? Would an error like this damage the transformers? If so, what
> checks could I do?
>
> I'm off to the recycling centre tomorrow for Microwaves 😊
>
> Thanks
> Graeme
> ------------------------------
> *From:* Chchrobotics <chchrobotics-bounces at lists.ourshack.com> on behalf
> of chchrobotics-request at lists.ourshack.com <
> chchrobotics-request at lists.ourshack.com>
> *Sent:* Sunday, 29 November 2020 1:00 AM
> *To:* chchrobotics at lists.ourshack.com <chchrobotics at lists.ourshack.com>
> *Subject:* Chchrobotics Digest, Vol 158, Issue 11
>
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> Today's Topics:
>
>    1. spark eroder power supply (Mark Atherton)
>    2. Re: Chchrobotics Digest, Vol 158, Issue 9 (Andy Gardner)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Sat, 28 Nov 2020 16:32:16 +1300
> From: Mark Atherton <markaren1 at xtra.co.nz>
> To: Christchurch Robotics <chchrobotics at lists.linuxnut.co.nz>
> Subject: [chbot] spark eroder power supply
> Message-ID: <0677a25b-eba2-6011-09ae-6e854d9587e8 at xtra.co.nz>
> Content-Type: text/plain; charset=utf-8; format=flowed
>
> Hi Graeme,
>
> How are you controlling the current ?
>
> I have some vague recollection that you were using an SCR or a TRIAC, in
> which case you need zero-crossing, so an SMPSU will not work.
>
> -Mark
>
>
> On 28/11/2020 3:13 PM, Robert W. Walker,  wrote:
> > Hi... There are a range of heavy duty transformers but, particularly,
> > heavy duty switch mode and regulated supplies that are commonly used and
> > are available for E-bikes, E-scooters, Mobility chairs etc. They range
> > from 12volts up to 70 volts or slightly more. Check out Google or
> > Alibaba, Aliexpress or Ebay....
> > Nga mihi...
> > Bob, ZL2ROB (QTHR)
> >
> > Mark Atherton wrote on 28/11/2020 12:46 pm:
> >> Hi Graeme,
> >>
> >> A 75V/10A transformer is a pretty specialist voltage, and while you
> >> might get lucky finding one, the idea of 3 x 24V/10A with secondaries
> >> in series sounds a more likely/lower cost option.
> >>
> >> You might be able to do something clever with beefy ex-UPS
> >> transformers, but they are not going to have their windings marked so
> >> there is a possibility of injury if you wire them up wrongly.
> >>
> >> Obvious places to scour include Echotech, Trademe, and Molten Media.
> >>
> >> Regards,
> >>
> >> Mark
> >>
> >> PS Warren may also have some ideas, or something squirrelled away :)
> >>
> >>
> >>
> >>
> >> On 28/11/2020 11:51 AM, Graeme Absalom wrote:
> >>> Hi All
> >>> I need some help. Recently I've been pondering on why my spark eroder
> >>> only delivers 3 Amps on the onboard ammeter. It hadn't worried me
> >>> before because it does work. It is rated for 10 Amp. I decided that
> >>> the transformer is far too small to deliver 10 Amps. I tried putting
> >>> in a 120 volt 12 Amp and proved that the installed transformer is not
> >>> capable but blew a power resister. Reading the book / specs again
> >>> what I need is a wire wound, iron core, 230 volts to 75 volts AC and
> >>> 10 Amp. The book uses 3 x 24volts AC 10Amp transformers in series.
> >>>
> >>> Does anyone know where I could get a approx 75 volt, 10 transformer?
> >>>
> >>> Thanks
> >>>
> >>> Graeme Absalom
>
>
>
> ------------------------------
>
> Message: 2
> Date: Sat, 28 Nov 2020 23:06:13 +1300
> From: Andy Gardner <ceo at andygardner.com>
> To: chchrobotics at lists.ourshack.com
> Subject: Re: [chbot] Chchrobotics Digest, Vol 158, Issue 9
> Message-ID: <e5a3975a-6cc9-e3ca-cc35-6078423a74a3 at andygardner.com>
> Content-Type: text/plain; charset=utf-8; format=flowed
>
>
> Many of the bigger UPS's run off 72 volts on the DC side, so there's a
> good chance a transformer can be found with the amperage required.
>
> On 28/11/20 12:46 pm, Mark Atherton wrote:
> > Hi Graeme,
> >
> > A 75V/10A transformer is a pretty specialist voltage, and while you
> might get lucky finding one, the idea of 3 x 24V/10A with secondaries in
> series sounds a more likely/lower cost option.
> >
> > You might be able to do something clever with beefy ex-UPS transformers,
> but they are not going to have their windings marked so there is a
> possibility of injury if you wire them up wrongly.
> >
> > Obvious places to scour include Echotech, Trademe, and Molten Media.
> >
> > Regards,
> >
> > Mark
> >
>
>
>
> ------------------------------
>
> Subject: Digest Footer
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> End of Chchrobotics Digest, Vol 158, Issue 11
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