Rigol oscilloscope prices have sky-rocketed!
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From: kreed on 5 Jan 2010 05:34 On Jan 5, 6:42 pm, "E" <inva...(a)invalid.invalid> wrote: > "VWWall" <vw...(a)large.invalid> kirjoitti > viestiss :wN6dnWD6k6DfPt_WnZ2dnUVZ_tedn...(a)earthlink.com... > > > > > Mr.T wrote: > >> <m...(a)sushi.com> wrote in message > >>news:8e1c962a-a471-448b-89b6-7239675017f0(a)k17g2000yqh.googlegroups.com.... > >>> Surplus isolation transformers are pretty cheap. > > >> Yeah when we had surplus stores here I got many big transformers that > >> way. > >> They all (electronics surplus stores) disappeared years ago > >> unfortunately. > > > You can make an isolation transformer that will handle a kilowatt from two > > junked microwave oven transformers. Just remove the HV windings and the > > magnetic shunt, leaving the primary windings. Connect them together with > > two coils wound on each core with a few turns of No 12 insulated building > > wire. Calculate the number of turns to not exceed 20A at the intended > > maximum load. > > Would it work if I just connect HV windings together? > So as to avoid any rewounding job. > -ek If you have to do it - try using a pair of 240 - 110v / 48v / 24v units back to back or other matching voltage low voltage surplus transformers. I did this 25 odd years back using 2 surplus (free) 240v to 24v @15a units back to back, and it worked fine for many years. It wont be as efficient as a single purpose designed transformer, and will be heavier and run hotter. Remembering that there will be 2 lots of losses, and that normal transformers aren't designed to be used "backwards", you will NOT get the full rated VA out of this arrangement, it will cost more in electricity use. I wouldn't even contemplate that idea of putting microwave HT windings back to back - it would be an absolutely totally and instantly LETHAL device if anything went wrong, not just an irritating "ZAP". Please, Please Please do NOT muck about with these things. these voltages (remember that unlike TV EHT supplies these oven transformers have plenty of current behind them) can even punch through damaged or underrated insulated tool handles and to your hand, delivering a lethal shock ! If there was a breakdown to the output winding, which could possibly happen with old parts - specially ones from faulty microwaves pulled from rubbish dumps, or that had mouse / insect infestations - I would hate to think what could possibly happen to anyone or anything connected on the 240v isolated "secondary" side. If you didnt join the 2 HT windings together in a proper way, and insulate properly the connection point could even arc, starting a fire. Either physically remove the HT winding first if you are going to muck around with it, or better still, just do yourself a favour and chuck the microwave oven transformer (and the modification idea) in the rubbish bin before someone gets killed.
From: kreed on 5 Jan 2010 05:35 On Jan 5, 5:15 pm, "m...(a)sushi.com" <m...(a)sushi.com> wrote: > On Jan 4, 11:09 pm, "Mr.T" <MrT(a)home> wrote: > > > <m...(a)sushi.com> wrote in message > > >news:23b6594d-3c71-45d0-885a-bb5cbf16ce1f(a)a32g2000yqm.googlegroups.com.... > > > >Topaz transformers show up from time to time at electronics flea > > >markets. In the days when small company owned a Vax, the Topaz was > > >your isolation transformer. > > > Yep, had a Topaz myself once, but I've never seen one going cheap in > > Australia! Not to say it can't happen, but you'd have to be very lucky, not > > something the OP can necessarily go and buy at a reasonable price just > > because he wants it. And not something you'd want to carry in your car > > either, to use with an inverter supply! > > > MrT. > > Freight for a Topaz down under would be significant. Topaz has made > some units that are small, well small for a Topaz. Maybe 12x8x8 > inches. Ouch ! That is one hell of a transformer :)
From: Phil Allison on 5 Jan 2010 05:50 "Mike Harrison" > Yes, ** Sorry pal - but you are DEAD WRONG !! > although MOTs, being cheaply made are likely to run close to saturation, ** CLOSE to SATURATION ? How about HARD INTO SATURATION !!! The off-load primary rms current is typically ** 75% ** of the full on-load current !!! How about 1250VA consumption - OFF LOAD !!!! > so you may find they > behave slightly less well than a properly rated isolation transformer. **ROTFLMAO The Poms are still the MASTERS of understatement !!! > By all means try it, ** VERY BAD ADVICE !! > as the raw materials are available often for free, and take great care of > the > HV, which WILL kill you easily! ** In the case of " E", Darwin might be well pleased. ..... Phil Make sure you connect the cores to a good mains earth.
From: geoff on 5 Jan 2010 15:34 David L. Jones wrote: > geoff wrote: >> David L. Jones wrote: >> >>> "Hello, Please don't worry, the problem is, an another seller has >>> complaint by ebay that i'm selling the rigol oscilloscopes at a >>> dumping price" He then offered to complete the original low price >>> transaction >>> outside of ebay. >> >> Why should 'dumping prices' be a problem ? > > It shouldn't be a problem until a local official seller that can't > possibly sell them for the same price complains. > There are countless companies like (presumably) Rigol that have > diferent wholesale pricing in different countries, so an official > dealer in say Australia can't even buy it for less than what someone > in China sells it for at a profit. Or to hold on to their dealership > they aren't allowed to sell it under a certain price. > With the advent of ebay and online trading, the world is a global > marketplace, so these sorts of traditional regional pricing models > make it a big fat mess. > You can bet your bottom dollar the ebay sellers in China are (or > were) not dumping the scopes at a loss, they made a very tidy profit. > > I have since heard that another Rigol seller also had their auctions > banned for "dumping". So this appears to be the reason for removal of > the hundreds of Rigol's that were for sale on Ebay. > So it's likely that one (probably official Rigol) seller, that may > not even sell on Ebay, spoiled all the fun by complaining. Sounds more like parallel importing and selling at a lower price than the local dealer, rather than 'dumping'. That's not illegal in USAor NZ. Dunno about Oz. geoff
From: miso on 5 Jan 2010 21:46
On Jan 5, 12:34 pm, "geoff" <ge...(a)nospam-paf.co.nz> wrote: > David L. Jones wrote: > > geoff wrote: > >> David L. Jones wrote: > > >>> "Hello, Please don't worry, the problem is, an another seller has > >>> complaint by ebay that i'm selling the rigol oscilloscopes at a > >>> dumping price" He then offered to complete the original low price > >>> transaction > >>> outside of ebay. > > >> Why should 'dumping prices' be a problem ? > > > It shouldn't be a problem until a local official seller that can't > > possibly sell them for the same price complains. > > There are countless companies like (presumably) Rigol that have > > diferent wholesale pricing in different countries, so an official > > dealer in say Australia can't even buy it for less than what someone > > in China sells it for at a profit. Or to hold on to their dealership > > they aren't allowed to sell it under a certain price. > > With the advent of ebay and online trading, the world is a global > > marketplace, so these sorts of traditional regional pricing models > > make it a big fat mess. > > You can bet your bottom dollar the ebay sellers in China are (or > > were) not dumping the scopes at a loss, they made a very tidy profit. > > > I have since heard that another Rigol seller also had their auctions > > banned for "dumping". So this appears to be the reason for removal of > > the hundreds of Rigol's that were for sale on Ebay. > > So it's likely that one (probably official Rigol) seller, that may > > not even sell on Ebay, spoiled all the fun by complaining. > > Sounds more like parallel importing and selling at a lower price than the > local dealer, rather than 'dumping'. That's not illegal in USAor NZ. Dunno > about Oz. > > geoff Bingo. Only the manufacturer can dump. Like I said, the story doesn't pass the smell test. Further, nobody has pointed out on ebays website where they would take such action. The issue is by refusing to sell something, you also subject yourself to legal action. This is why most companies simply wait for the temporary injunction before taking action. |