[chbot] Transformer for Spark Eroder
Trevor Wignall
zl3adz at gmail.com
Mon Nov 30 10:18:14 GMT 2020
As microwaves normally run around 800-1100W, and you need 75V or less at
10A which is 750W, you should get away with a single microwave transformer.
However you will probably need enamelled copper wire rather than
conventional insulated wire otherwise the insulation will take up too much
room and not leave enough for the copper. You may also need to wind two
secondary windings and connect them in parallel to achieve the required
current rating without having the wire too thick (which adds to eddy
current losses). I expect your secondary will take more than one layer of
wire, so you might need some insulating tape to separate the layers. Both
the tape and insulation need to have a decent temperature rating - not
normal PVC tape! (You might be able to salvage the tape from the
transformer and re-use it.
Beware - I have never rewound a transformer so the above advice is what I
have gathered second or third hand, etc.
Good luck.
Trevor
On Mon, Nov 30, 2020 at 8:15 PM Mark Atherton <markaren1 at xtra.co.nz> wrote:
> Hi Graeme,
>
> You need to remove all signs of the old secondary, and you may have to
> drift out a magnetic-short in the transformer, but in principle, you should
> be OK.
>
>
> Have a look at youtube for videos about making welders from microwave oven
> transformers, the only difference is you need many turns of thinner
> insulated wire.
>
> Regards,
>
> Mark
>
> On 30 November 2020 at 16:40 Graeme Absalom <clock_man_OK at hotmail.com>
> wrote:
>
> Hi
>
> Thank you for your concern for my safety, it is appreciated.
>
> I have another option that William has mentioned, if I understand
> correctly. It is to take out the high voltage wires from the microwave
> transformer and replace these. I have seen You tubes with this being done.
> I estimate from one clip that 60 turns would produce about 35 volts. Then
> using two in series would give me 70 volts (hopefully 10 Amp) which would
> suit me nicely. I was planning to use 10 Amp domestic plastic covered wire;
> would this be OK?
>
> Thank you to all those who posted advice.
>
> Graeme Absalom
>
> ------------------------------
> *From:* Chchrobotics <chchrobotics-bounces at lists.ourshack.com> on behalf
> of chchrobotics-request at lists.ourshack.com <
> chchrobotics-request at lists.ourshack.com>
> *Sent:* Monday, 30 November 2020 1:00 AM
> *To:* chchrobotics at lists.ourshack.com <chchrobotics at lists.ourshack.com>
> *Subject:* Chchrobotics Digest, Vol 158, Issue 13
>
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> Today's Topics:
>
> 1. Re: Chchrobotics Digest, Vol 158, Issue 11 (william fleete)
> 2. Re: Chchrobotics Digest, Vol 158, Issue 11 (Volker Kuhlmann)
> 3. Re: Chchrobotics Digest, Vol 158, Issue 11 (Mark Atherton)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Sun, 29 Nov 2020 12:40:31 +1300
> From: william fleete <fleetwil at gmail.com>
> To: Christchurch Robotics <chchrobotics at lists.ourshack.com>
> Subject: Re: [chbot] Chchrobotics Digest, Vol 158, Issue 11
> Message-ID:
> <
> CAFNRJjwCjim3SxYu0K2vH6UP3Y9_L4D92kKv7a3Lch_XYK_31g at mail.gmail.com>
> Content-Type: text/plain; charset="utf-8"
>
> 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
> >
> > Send Chchrobotics mailing list submissions to
> > chchrobotics at lists.ourshack.com
> >
> > To subscribe or unsubscribe via the World Wide Web, visit
> > https://lists.ourshack.com/mailman/listinfo/chchrobotics
> > or, via email, send a message with subject or body 'help' to
> > chchrobotics-request at lists.ourshack.com
> >
> > You can reach the person managing the list at
> > chchrobotics-owner at lists.ourshack.com
> >
> > When replying, please edit your Subject line so it is more specific
> > than "Re: Contents of Chchrobotics digest..."
> >
> >
> > 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
> >
> > _______________________________________________
> > Chchrobotics mailing list
> > Chchrobotics at lists.ourshack.com
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> > Please edit your Subject line to reflect new subjects.
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> > ------------------------------
> >
> > End of Chchrobotics Digest, Vol 158, Issue 11
> > *********************************************
> > _______________________________________________
> > Chchrobotics mailing list Chchrobotics at lists.ourshack.com
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> Message: 2
> Date: Sun, 29 Nov 2020 13:23:21 +1300
> From: Volker Kuhlmann <list57 at top.geek.nz>
> To: Christchurch Robotics <chchrobotics at lists.ourshack.com>
> Subject: Re: [chbot] Chchrobotics Digest, Vol 158, Issue 11
> Message-ID: <20201129002321.GA22482 at top.geek.nz>
> Content-Type: text/plain; charset=utf-8
>
> > I'm off to the recycling centre tomorrow for Microwaves 😊
>
> Do not, under any circumstances, plug in the microwaves to see if they
> still go, then attempt to take transformers out, unless maybe your life
> insurance is current or you've thought about how to deal with big
> capacitors holding kilovolts.
>
> In this case one wouldn't care about damaging anything else, I might be
> happy with safety glasses and a crowbar with a 30kV isolated handle.
> I'm sure Mark will also advise a change of undies...
>
> There are video instructions on youtube showing how to safely discharge
> those things, it's a multi-step process.
>
> Volker
>
> --
> Volker Kuhlmann
> http://volker.top.geek.nz/ Please do not CC list postings to me.
>
>
>
> ------------------------------
>
> Message: 3
> Date: Sun, 29 Nov 2020 13:38:42 +1300
> From: Mark Atherton <markaren1 at xtra.co.nz>
> To: chchrobotics at lists.ourshack.com
> Subject: Re: [chbot] Chchrobotics Digest, Vol 158, Issue 11
> Message-ID: <803475ae-048e-29cc-33c5-6152229d0d50 at xtra.co.nz>
> Content-Type: text/plain; charset=utf-8; format=flowed
>
> Thank you Volker.
>
> Standard kit for handling high energy kit:
>
> - Rubber gloves
> - Fire extinguisher
> - Change of underwear
>
> -Mark
>
>
> On 29/11/2020 1:23 PM, Volker Kuhlmann wrote:
> >> I'm off to the recycling centre tomorrow for Microwaves 😊
> >
> > Do not, under any circumstances, plug in the microwaves to see if they
> > still go, then attempt to take transformers out, unless maybe your life
> > insurance is current or you've thought about how to deal with big
> > capacitors holding kilovolts.
> >
> > In this case one wouldn't care about damaging anything else, I might be
> > happy with safety glasses and a crowbar with a 30kV isolated handle.
> > I'm sure Mark will also advise a change of undies...
> >
> > There are video instructions on youtube showing how to safely discharge
> > those things, it's a multi-step process.
> >
> > Volker
> >
>
>
>
>
> ------------------------------
>
> Subject: Digest Footer
>
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> ------------------------------
>
> End of Chchrobotics Digest, Vol 158, Issue 13
> *********************************************
>
>
>
>
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