amdx <amdx@knology.net> wrote:> On 7/1/2020 12:13 PM, dagmargoodboat@yahoo.com wrote: >> On Tuesday, June 30, 2020 at 9:14:53 AM UTC-4, amdx wrote: >>> On 6/29/2020 8:33 AM, amdx wrote: >>>> On 6/28/2020 8:55 PM, Phil Allison wrote: >>>>> Robert Roland wrote: >>>>> >>>>> ==================== >>>>> >>>>>> >>>>>> An unloaded transformer is almost entirely inductive, so the PF will >>>>>> be very low. As the load increases, the PF will also increase. This is >>>>>> normal. All transformer are like that. >>>>>> >>>>> ** If the same tranny is undergoing core saturation, the current wave >>>>> is highly distorted and maxima tend to co-incide with zero crossings - >>>>> exacerbating the poor PF. >>>>> >>>>> >>>>> >>>>>> One thing to look out for with MOTs, is that they are run very "hard", >>>>>> i.e. they magnetize the core well into saturation. That way, the >>>>>> manufacturers can save on iron, which saves on weight, which saves on >>>>>> cost. Since the MOT is normally run at fairly low duty cycle, and with >>>>>> fan cooling, they can get away with that. You may find that the >>>>>> transformer with zero load will draw 100 W or more of real power. If >>>>>> you leave it running for some amount of time, it will get very hot. >>>>>> The remedy for this is to add some additional turns to the primary >>>>>> winding. This will, of course, require you to add some additional >>>>>> secondary turns to reach the output voltage you want. >>>>>> >>>>>> Intuitively, you might think that adding more primary turns would >>>>>> increase the magnetization, therefore worsen the saturation situation. >>>>>> The reason it does not, is that the added windings increase the >>>>>> inductance of the primary winding, which results in a reduction in >>>>>> magnetizing current. The current reduces relatively more than the >>>>>> increase in turns. >>>>>> >>>>> ** Magnetisation goes up and down with the number of primary turns and >>>>> applied voltage while inductance follows the square of the number of >>>>> turns. >>>>> >>>>> >>>>> >>>>> .....?? Phil >>>>> >>>> >>>> ??I have graphed the Voltage and Current of the original primary winding >>>> and after adding 37 Turns, 48 Turns and 60 Turns. >>>> Any comments? >>>>> https://www.dropbox.com/s/0n1y4yh5o0j2sg6/mot%20primary%20voltage%20vs%20current%202%20graphs.jpg?dl=0 >>>>> >>>> >>>> ?????????????????????????????????????????????????????????????????????????????????????????????????????? Mikek >>>> >>>> >>> >>> >>> I haven't got any response to the graphs, so without that, I'm going >>> to go with adding 60 primary turns, adjust the secondary to get the proper >>> secondary voltage and see if it delivers the required voltage at 8 amps. >> >> Great graphs. >> >> The first graph showed the virgin transformer was saturating (losing >> inductance) at 90 volts, where the current eyeballs-out to be about >> 20% higher than the straight-line slope beforehand. >> >> To my eyeball, aided with a ruler, the 62-extra-turns version hits >> that same 20% inductance loss / 20% "extra" current at about 115VAC. >> That looks reasonable to me. > > > Thanks for the input, Maybe I should have added a few more turns my > voltage runs about 122Vac. It's to late now, I have dipped and baked the > coils in an electric motor varnish, assembled it and then after assembly > dipped and baked the whole thing. Tomorrow, I will weld the core > sections together. > For those that don't know, MOTs are are one stacked E section and one > stacked I section that are welded along each outside edge. I just cut > the welds with a hack saw so I could install my coils. > > Mikek >I'd be interested to see photos of the finished transformer. The last one I messed with took way longer to cut the secondary winding out of than I expected. Was using a hacksaw and chisel and hammer. It wasn't as easy as it looks like in motor rewinding videos on youtube.
Rewiinding a MOT
Started by ●June 27, 2020
Reply by ●July 2, 20202020-07-02
Reply by ●July 2, 20202020-07-02
Phil Allison <pallison49@gmail.com> wrote:> dagmarg...@yahoo.com wrote: > > ============================= > >> >> The first graph showed the virgin transformer was saturating (losing >> inductance) at 90 volts, where the current eyeballs-out to be about >> 20% higher than the straight-line slope beforehand. >> > > ** Saturation can be avoided by running the MOT from a triac dimmer. > > Thousands of Carver "Magnetic Field" amplifiers attest that fact.Can you explain what the whole carver magic power supply is? I have an Carver (I think it was from the second generation of his company before Sunfire. It does't mention magnetic steering or whatever that is supposed to be. The insides are nicely made, with attention to detail, but that's really about it.
Reply by ●July 2, 20202020-07-02
Chris Jones <lugnut808@spam.yahoo.com> wrote:> On 30/06/2020 00:46, Michael Terrell wrote: >> Ceramic transmitting tubes and semiconductors also use BeO. Those warning labels don't always follow equipment through production and testing. A test tech on the GRC106 ended up in the hospital when one of the Eimac finals was damaged during shipping from Mexico to Cincinnati. They were just tossing the paperwork since they couldn't read English. Luckily for that tech, the man at the next bench saw him with the damaged tube. He wrapped a plastic bag over the tech's hands and the tube. He had someone call for an a.mbulsnce as he hurried him running to a sink to wet down the dust. He saved his coworker's life. After that, the paperwork was wired to each subassembly that contained BeO. YOLO. >> > > I can believe that BeO must be pretty nasty because they used to give > warnings about it, even back in the time when warnings were reserved for > actually very dangerous things. Nowadays due to every harmless thing > being plastered with warnings, they have become rather devalued and it > is much harder to identify what really is dangerous.yup. Starbuck Coffee in CA post the prop 65 warnings about dangerous chemicals (yes, coffee) in their stores. They have lots of free time in CA it seems.
Reply by ●July 2, 20202020-07-02
Chris Jones <lugnut808@spam.yahoo.com> wrote:> On 30/06/2020 01:02, Robert Roland wrote: >> On Mon, 29 Jun 2020 14:28:36 +1000, Chris Jones >> <lugnut808@spam.yahoo.com> wrote: >> >>> Have you ever seen any mention of BeO on the magnetron manufacturer's >>> datasheet? >> >> I have to admit I was parroting what I have read on the Internet. The >> text stated that roughly half of the magnetrons in microwave ovens >> contain a toxic substance. I have never read the datasheet of any >> magnetron. >> > > The datasheets I have read don't say either way what it is made of. When > disassembling dead magnetrons I choose not to break up the ceramic > parts, just in case I am very wrong about it being harmless.They're almost always a pink ceramic, and extremely hard to break up, even with a big hammer. I can't find a SDS on a magnetron either, but came across this interesting one. Looks like what's in your kitchen, but needs liquid and fan cooling: https://www.hitachi-power-solutions.com/en/products/magnetron/lineup/h0915/index.html output power is 10kW. What a beast. Looks like you run the filament hot, then drop the voltage once it's running. Maybe the current to the anode is so high it just keeps hot on it's own. Reminds me of "press to start" flourescent light fixtures.> The filament quite likely is thoriated tungsten too, and if it has > burned up due to loss of vacuum, I would avoid inhaling that dust. I've > probably breathed enough of that already from grinding TIG welding > electrodes.put electrode in a drill and walk up to the grinding wheel is what I was shown for sharpening those.> And I agree strongly with your comments regarding the extreme danger of > powering a microwave oven transformer on the bench whilst it still has > its secondary winding present.The capacitor is usually what gets people. Guess those bleed resistors fail open.
Reply by ●July 2, 20202020-07-02
Cydrome Leader wrote: ===================== >> > ** Saturation can be avoided by running the MOT from a triac dimmer. > > > > Thousands of Carver "Magnetic Field" amplifiers attest that fact. > > Can you explain what the whole carver magic power supply is? >** No magic, Bob just borrowed an idea from some DC PSU designs where rather than having multiple regulator devices and huge heat sinks after a transformer based supply - you put a hefty *phase controlled* triac in the AC feed to a transformer to * pre-regulate the average DC output. Then you can use small heat sinks and drop maybe 1.5 volts at most. Bob did not need pure DC for his amp design or full output for long periods - just enough DC for domestic audio use. So he just used the unregulated DC voltage to control the firing angle of the triac and left it at that. This meant he could make the power tranny *much* smaller than usual and far cheaper. The transformers were engineered to operate normally at 70% of the AC supply so the triac chopped the AC wave to get this peak value - increasing the firing angle when needed to make up losses under load. The amps used 8 x DC rails, typically +/- 25, 50, 80 & 120 volts with 8 output transistors all in series. This allowed the heat developed by a class B stage to be much reduced so needing way less heat sinking. The aluminium case became the only heat sink. The result as the "Carver Cube" - tiny and light weight though packing a 200 wpc punch for short periods until the tranny started to cook. My testing showed full sine wave power on both channel at 8 ohms was available to 2 or 3 minutes at most - and 90 seconds with 4 ohm loads. Then the resin inside the tranny started to emit smoke - I kid you not. ..... Phil
Reply by ●July 2, 20202020-07-02
On 2020-07-02, Cydrome Leader <presence@MUNGEpanix.com> wrote:> > I'd be interested to see photos of the finished transformer. The last one > I messed with took way longer to cut the secondary winding out of than I > expected. Was using a hacksaw and chisel and hammer. It wasn't as easy as > it looks like in motor rewinding videos on youtube.I drilled holes through the captive part of the winding. that loosened the packing and allowed me to chisel out the remains -- Jasen.
Reply by ●July 2, 20202020-07-02
On 2/7/20 3:57 pm, Cydrome Leader wrote:> I'd be interested to see photos of the finished transformer. The last one > I messed with took way longer to cut the secondary winding out of than I > expected. Was using a hacksaw and chisel and hammer. It wasn't as easy as > it looks like in motor rewinding videos on youtube.Don't remove the winding - grind the weld off the E-I core. Use some long thin screws to hold it together first. Then you can remove the bobbin hole, un/wind what you will, and re-assemble. Re-welding isn't necessary as long as you arrange for the gap to be tightly held shut.
Reply by ●July 2, 20202020-07-02
On 7/2/2020 12:57 AM, Cydrome Leader wrote:> amdx <amdx@knology.net> wrote: >> On 7/1/2020 12:13 PM, dagmargoodboat@yahoo.com wrote: >>> On Tuesday, June 30, 2020 at 9:14:53 AM UTC-4, amdx wrote: >>>> On 6/29/2020 8:33 AM, amdx wrote: >>>>> On 6/28/2020 8:55 PM, Phil Allison wrote: >>>>>> Robert Roland wrote: >>>>>> >>>>>> ==================== >>>>>> >>>>>>> >>>>>>> An unloaded transformer is almost entirely inductive, so the PF will >>>>>>> be very low. As the load increases, the PF will also increase. This is >>>>>>> normal. All transformer are like that. >>>>>>> >>>>>> ** If the same tranny is undergoing core saturation, the current wave >>>>>> is highly distorted and maxima tend to co-incide with zero crossings - >>>>>> exacerbating the poor PF. >>>>>> >>>>>> >>>>>> >>>>>>> One thing to look out for with MOTs, is that they are run very "hard", >>>>>>> i.e. they magnetize the core well into saturation. That way, the >>>>>>> manufacturers can save on iron, which saves on weight, which saves on >>>>>>> cost. Since the MOT is normally run at fairly low duty cycle, and with >>>>>>> fan cooling, they can get away with that. You may find that the >>>>>>> transformer with zero load will draw 100 W or more of real power. If >>>>>>> you leave it running for some amount of time, it will get very hot. >>>>>>> The remedy for this is to add some additional turns to the primary >>>>>>> winding. This will, of course, require you to add some additional >>>>>>> secondary turns to reach the output voltage you want. >>>>>>> >>>>>>> Intuitively, you might think that adding more primary turns would >>>>>>> increase the magnetization, therefore worsen the saturation situation. >>>>>>> The reason it does not, is that the added windings increase the >>>>>>> inductance of the primary winding, which results in a reduction in >>>>>>> magnetizing current. The current reduces relatively more than the >>>>>>> increase in turns. >>>>>>> >>>>>> ** Magnetisation goes up and down with the number of primary turns and >>>>>> applied voltage while inductance follows the square of the number of >>>>>> turns. >>>>>> >>>>>> >>>>>> >>>>>> .....?? Phil >>>>>> >>>>> >>>>> ??I have graphed the Voltage and Current of the original primary winding >>>>> and after adding 37 Turns, 48 Turns and 60 Turns. >>>>> Any comments? >>>>>> https://www.dropbox.com/s/0n1y4yh5o0j2sg6/mot%20primary%20voltage%20vs%20current%202%20graphs.jpg?dl=0 >>>>>> >>>>> >>>>> ?????????????????????????????????????????????????????????????????????????????????????????????????????? Mikek >>>>> >>>>> >>>> >>>> >>>> I haven't got any response to the graphs, so without that, I'm going >>>> to go with adding 60 primary turns, adjust the secondary to get the proper >>>> secondary voltage and see if it delivers the required voltage at 8 amps. >>> >>> Great graphs. >>> >>> The first graph showed the virgin transformer was saturating (losing >>> inductance) at 90 volts, where the current eyeballs-out to be about >>> 20% higher than the straight-line slope beforehand. >>> >>> To my eyeball, aided with a ruler, the 62-extra-turns version hits >>> that same 20% inductance loss / 20% "extra" current at about 115VAC. >>> That looks reasonable to me. >> >> >> Thanks for the input, Maybe I should have added a few more turns my >> voltage runs about 122Vac. It's to late now, I have dipped and baked the >> coils in an electric motor varnish, assembled it and then after assembly >> dipped and baked the whole thing. Tomorrow, I will weld the core >> sections together. >> For those that don't know, MOTs are are one stacked E section and one >> stacked I section that are welded along each outside edge. I just cut >> the welds with a hack saw so I could install my coils. >> >> Mikek >> > > I'd be interested to see photos of the finished transformer. The last one > I messed with took way longer to cut the secondary winding out of than I > expected. Was using a hacksaw and chisel and hammer. It wasn't as easy as > it looks like in motor rewinding videos on youtube. >I was lucky, mine came out easy. I cut off on side and and used a square chunk of iron to drive each side alternately, it came out whole, no separation of the wires. Mikek -- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus
Reply by ●July 2, 20202020-07-02
On Wed, 1 Jul 2020 18:34:30 -0500, amdx <amdx@knology.net> wrote:>Tomorrow, I will weld the core >sections together.I believe I read somewhere that you should not do that. With an ordinary welder, you will be putting enough heat into the core to risk damage to the insulation between the layers of steel in the core. The factory welding technique is extremely fast, so that much less heat is required. Firmly clamping them together was the recommendation. -- RoRo
Reply by ●July 2, 20202020-07-02
On Thu, 2 Jul 2020 05:57:03 +0000 (UTC), Cydrome Leader <presence@MUNGEpanix.com> wrote:>The last one >I messed with took way longer to cut the secondary winding out of than I >expected. Was using a hacksaw and chisel and hammer. It wasn't as easy as >it looks like in motor rewinding videos on youtube.It seems they are not all the same. I have done two. One was easy, while the other one was terrible. -- RoRo
