Home |
Search |
Today's Posts |
#1
|
|||
|
|||
Microwave Oven Transformers Specifications.
Does anyone know what kind of AC voltage a Microwave oven transformer would
put out? Are they center taped or just a single coil? I need a replacement for my homebrew 3-500z single tube amp. I only used it for low power AM and I don't need "maximum voltage". Dan/W4NTI |
#2
|
|||
|
|||
Dan/W4NTI wrote:
Does anyone know what kind of AC voltage a Microwave oven transformer would put out? Are they center taped or just a single coil? I need a replacement for my homebrew 3-500z single tube amp. I only used it for low power AM and I don't need "maximum voltage". Dan/W4NTI They are a single winding on the secondary and not designed for continuous use. You would have to switch the primary to prevent overheating when you aren't transmitting. -- Former professional electron wrangler. Michael A. Terrell Central Florida |
#3
|
|||
|
|||
I have gleaned 1.5KW commercial microwaves for their transformers (they had
timers which maxed out at 1 hour!), removed the secondary and replaced it with heavy copper wire to make 13.8 V high amp supplies for mobile linears converted to shack use. The ones I have come across--where I bothered to measure the voltage of the secondary, were 3000+ V, as I remember 3300-3500 V. Two matched transformers should be able to serve as a center tapped transformer without much re-engineering. In amplifier use, a transformers 50% duty cycle specs should be sufficient--I wouldn't be surprised if they could serve well in amps (and it never hurts to make sure the xfmr benefits from a fans output.) The only red flag which pops up in my mind is if there would be sufficient isolation of the primary from the secondary at low freq. rf., if not, something there could probably even be worked out (and, my worry may be false to begin with.) In extreme cases, a heat sink could be fitted to the exposed section of the top and sides of the core (heat conductive epoxy would work.) And, hey, if I guy gets long winded and smokes a xfmr, a trip to the dump for a replacement is cheap! Take care, those transformers can pack a lethal wallop! Regards, John -- I would like to point out, I do appreciate the "Been there--done that!" posts. Indeed, now your observations, comments and discourse should be filled with wisdom--I am listening!!! "Dan/W4NTI" wrote in message news Does anyone know what kind of AC voltage a Microwave oven transformer would put out? Are they center taped or just a single coil? I need a replacement for my homebrew 3-500z single tube amp. I only used it for low power AM and I don't need "maximum voltage". Dan/W4NTI |
#4
|
|||
|
|||
John Smith wrote:
I have gleaned 1.5KW commercial microwaves for their transformers (they had timers which maxed out at 1 hour!), removed the secondary and replaced it with heavy copper wire to make 13.8 V high amp supplies for mobile linears converted to shack use. The ones I have come across--where I bothered to measure the voltage of the secondary, were 3000+ V, as I remember 3300-3500 V. Two matched transformers should be able to serve as a center tapped transformer without much re-engineering. In amplifier use, a transformers 50% duty cycle specs should be sufficient--I wouldn't be surprised if they could serve well in amps (and it never hurts to make sure the xfmr benefits from a fans output.) The only red flag which pops up in my mind is if there would be sufficient isolation of the primary from the secondary at low freq. rf., if not, something there could probably even be worked out (and, my worry may be false to begin with.) In extreme cases, a heat sink could be fitted to the exposed section of the top and sides of the core (heat conductive epoxy would work.) And, hey, if I guy gets long winded and smokes a xfmr, a trip to the dump for a replacement is cheap! Take care, those transformers can pack a lethal wallop! Regards, John The welded cores can cause problems. This has been discussed on the various sci.electronics.* groups a number of times -- Former professional electron wrangler. Michael A. Terrell Central Florida |
#5
|
|||
|
|||
I have missed that. What are the problems?
Even the power supplies I have made which power 1500+ liners have held up fine. I do notice they seem to run a bit warmer than their expensive counterparts. I am convinced without arguement that their efficiency is lower than a more conventional xfmr--one reason--microwaves are usually only in operation for short periods of time. However, all I can see which might be happening is my electric bill is a few cents higher... Regards, John -- I would like to point out, I do appreciate the "Been there--done that!" posts. Indeed, now your observations, comments and discourse should be filled with wisdom--I am listening!!! "Michael A. Terrell" wrote in message ... John Smith wrote: I have gleaned 1.5KW commercial microwaves for their transformers (they had timers which maxed out at 1 hour!), removed the secondary and replaced it with heavy copper wire to make 13.8 V high amp supplies for mobile linears converted to shack use. The ones I have come across--where I bothered to measure the voltage of the secondary, were 3000+ V, as I remember 3300-3500 V. Two matched transformers should be able to serve as a center tapped transformer without much re-engineering. In amplifier use, a transformers 50% duty cycle specs should be sufficient--I wouldn't be surprised if they could serve well in amps (and it never hurts to make sure the xfmr benefits from a fans output.) The only red flag which pops up in my mind is if there would be sufficient isolation of the primary from the secondary at low freq. rf., if not, something there could probably even be worked out (and, my worry may be false to begin with.) In extreme cases, a heat sink could be fitted to the exposed section of the top and sides of the core (heat conductive epoxy would work.) And, hey, if I guy gets long winded and smokes a xfmr, a trip to the dump for a replacement is cheap! Take care, those transformers can pack a lethal wallop! Regards, John The welded cores can cause problems. This has been discussed on the various sci.electronics.* groups a number of times -- Former professional electron wrangler. Michael A. Terrell Central Florida |
#6
|
|||
|
|||
On Mon, 4 Apr 2005 22:03:21 -0700, "John Smith"
wrote: I have missed that. What are the problems? Even the power supplies I have made which power 1500+ liners have held up fine. I do notice they seem to run a bit warmer than their expensive counterparts. I am convinced without arguement that their efficiency is lower than a more conventional xfmr--one reason--microwaves are usually only in operation for short periods of time. However, all I can see which might be happening is my electric bill is a few cents higher... Regards, John I couldn't get the laminations apart because of the welds. I would go down to the garage and chisel away at them every couple of day, but I finally gave up. My intended use was a hi current 13.8 V supply Te KX4OM |
#7
|
|||
|
|||
Michael A. Terrell wrote:
The welded cores can cause problems. This has been discussed on the various sci.electronics.* groups a number of times The key phrase to search for is "magnetic shunt". Typically the magnetic shunt consists of two extra blocks of laminations between the primary and secondary bobbins. This has been added to give the transformer a current-limiting characteristic, which is necessary to power a magnetron - but is exactly the opposite of what you need for normal vacuum tubes. In many oven transformers, the magnetic shunt blocks can be driven out with a large punch, to leave a more normal-looking transformer. The not-so-good news is that you're still left with a transformer that has a very high secondary voltage and rather high secondary resistance, which will give poor voltage regulation in typical amateur use. Also one end of the secondary winding is usually grounded to the core. Even if you can get to the grounded end to disconnect it, the insulation close to the core is not designed for typical full-wave bridge applications. Some people have had limited success with a pair of identical transformers connected as a "centre-tapped" winding... but remember that in two separate transformers the core magnetization by the DC components will not cancel. It all seems like a lot of effort for rather poor results. -- 73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
#8
|
|||
|
|||
Yes, I see.
I never attempted to get the laminations apart. Using a hacksaw blade, I cut the secondary turns and drove them out of the core with a punch. Next, I used teflon tape around the core for insulation, and wound the heavy thermaleze insulated wire though the windows in the core to complete my low voltage winding. Regards, John -- I would like to point out, I do appreciate the "Been there--done that!" posts. Indeed, now your observations, comments and discourse should be filled with wisdom--I am listening!!! "Ted Bruce" wrote in message ... On Mon, 4 Apr 2005 22:03:21 -0700, "John Smith" wrote: I have missed that. What are the problems? Even the power supplies I have made which power 1500+ liners have held up fine. I do notice they seem to run a bit warmer than their expensive counterparts. I am convinced without arguement that their efficiency is lower than a more conventional xfmr--one reason--microwaves are usually only in operation for short periods of time. However, all I can see which might be happening is my electric bill is a few cents higher... Regards, John I couldn't get the laminations apart because of the welds. I would go down to the garage and chisel away at them every couple of day, but I finally gave up. My intended use was a hi current 13.8 V supply Te KX4OM |
#9
|
|||
|
|||
Ian, welcome back!
I trust your move has been successful. ---- Reg. |
#10
|
|||
|
|||
Reg Edwards wrote:
Ian, welcome back! I trust your move has been successful. Well, not quite, not yet. Still in the process of selling up down south, and doing what work we can on the new place in Scotland. My silence of the past several weeks has concealed a mad scramble to finish all the outstanding jobs, before being sent to W6 for another three weeks solid work. Thank goodness for jet-lag, and an excuse to take it easy for a few days. -- 73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
Reply |
|
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
EM field og GSM and microwave oven in V/m ? | Antenna | |||
BiQuad Design Specifications for Microwave? | Antenna | |||
Source for Microwave Diodes? | Homebrew | |||
Crystal Oven Pinout | Homebrew | |||
Crystal Oven Pinout | Homebrew |