On 30/06/2020 15:14, amdx wrote:> 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. > Also, I'll put a switch on the primary, but I can't guarantee that > switch will always get turned off after the power switch on the leaf > blower is shut off. My wife will be the user, I can put a light in the > circuit, she would be certain to turn off an unneeded light.If you want to power a 12V battery leaf blower from the main forget it. Either you will end carrying a heavy MOT with a normal extension cord or you will need a very thick one to minimise voltage drop at 12V.
Rewiinding a MOT
Started by ●June 27, 2020
Reply by ●June 30, 20202020-06-30
Reply by ●June 30, 20202020-06-30
On 6/30/2020 8:38 AM, bilou wrote:> On 30/06/2020 15:14, amdx wrote: >> 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. >> Also, I'll put a switch on the primary, but I can't guarantee that >> switch will always get turned off after the power switch on the leaf >> blower is shut off. My wife will be the user, I can put a light in the >> circuit, she would be certain to turn off an unneeded light. > > If you want to power a 12V battery leaf blower from the main forget it. > Either you will end carrying a heavy MOT with a normal extension cord > or you will need a very thick one to minimize voltage drop at 12V.Ya, I expect some voltage drop on the drop cord, I will make that up by increasing turns on the secondary. It's a 20 Volt leaf blower. I'll find the voltage drop of the cord before I wind the secondary. Mikek -- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus
Reply by ●July 1, 20202020-07-01
Phil Allison <pallison49@gmail.com> wrote:> Cydrome Leader wrote: > > ====================== >> >> >> Microwaves are high production items. They've cut every possible corner >> possible. If your original microwave said a line voltage of +/- 10% of 120 >> volts was OK, you can rest assure it won't be happy 1% out of that range. >> Removing the shunts will surely botch up the least amount of copper and >> iron design they used. > < > > ** In defense of the much maligned MOT - when operating as intended in an oven they do a brilliant job. > > A small, low cost and efficient power supply that delivers a whopping DC voltage with a low PF to boot. > > Believe it or not, the load current is almost sine wave - allowing ovens of over 1kW to run on 120VAC.Agreed. The business part of a microwave oven is dead simple- 1 transfomer, 3 windings, 1 diode, 1 capacitor and the magnetron. More parts are required to run the piezo buzzer. MO transformers are some of the first I've seen with the plasma welded laminations. I still don't understand the shunted transformers in mercury arc lamp ballasts or ferroresonant power supplies, although they appear to be related.
Reply by ●July 1, 20202020-07-01
amdx <amdx@knology.net> wrote:> On 6/30/2020 8:38 AM, bilou wrote: >> On 30/06/2020 15:14, amdx wrote: >>> 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. >>> ????Also, I'll put a switch on the primary, but I can't guarantee that >>> switch will always get turned off after the power switch on the leaf >>> blower is shut off. My wife will be the user, I can put a light in the >>> circuit, she would be certain to turn off an unneeded light. >> >> If you want to power a 12V battery leaf blower from the main forget it. >> Either you will end carrying a heavy MOT with a normal extension cord >> or you will need a very thick one to minimize voltage drop at 12V. > > Ya, I expect some voltage drop on the drop cord, I will make that up > by increasing turns on the secondary. It's a 20 Volt leaf blower. I'll > find the voltage drop of the cord before I wind the secondary. > > MikekThat's quite some effort you're putting into this. Can you get a dead computer UPS from a dump or business? They have the type of tranformer you may be able to use as is for getting around 12 volt battery charging voltage. I once had the great idea of replacing internal batteries of a UPS with some large external ones. During the runtime test the UPS basically exploded. They lack proper cooling to operate past the expected runtime of the internal battery without overheating. It's another great example of designing out all extra unneeded costs of a product while just meeting specs.
Reply by ●July 1, 20202020-07-01
On 6/30/2020 11:45 PM, Cydrome Leader wrote:> amdx <amdx@knology.net> wrote: >> On 6/30/2020 8:38 AM, bilou wrote: >>> On 30/06/2020 15:14, amdx wrote: >>>> 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. >>>> ????Also, I'll put a switch on the primary, but I can't guarantee that >>>> switch will always get turned off after the power switch on the leaf >>>> blower is shut off. My wife will be the user, I can put a light in the >>>> circuit, she would be certain to turn off an unneeded light. >>> >>> If you want to power a 12V battery leaf blower from the main forget it. >>> Either you will end carrying a heavy MOT with a normal extension cord >>> or you will need a very thick one to minimize voltage drop at 12V. >> >> Ya, I expect some voltage drop on the drop cord, I will make that up >> by increasing turns on the secondary. It's a 20 Volt leaf blower. I'll >> find the voltage drop of the cord before I wind the secondary. >> >> Mikek > > That's quite some effort you're putting into this. Can you get a dead > computer UPS from a dump or business? They have the type of tranformer you > may be able to use as is for getting around 12 volt battery charging > voltage. > > I once had the great idea of replacing internal batteries of a UPS with > some large external ones. During the runtime test the UPS basically > exploded. They lack proper cooling to operate past the expected runtime of > the internal battery without overheating. It's another great example of > designing out all extra unneeded costs of a product while just meeting > specs. >The leaf blower is designed for 20 Volts. Yes, way more time involved than money saved, but I have time and I'm enjoying the journey. I made a couple of winding forms and wound the additional coil for the primary and a secondary with 40 turns, Preliminary test shows 21.7 Volts with approx 8 amp load. Tests showed a 1.1 V drop in the cord I plan to use. I wish I had added about 3 more turns, I suspect a fully charged battery would run closer to 22 Volts. I still could cobble them in, but doubt I will. I will varnish dip and bake the coils tomorrow. Mikek -- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus
Reply by ●July 1, 20202020-07-01
On 01/07/2020 06:45, Cydrome Leader wrote:> I once had the great idea of replacing internal batteries of a UPS with > some large external ones. During the runtime test the UPS basically > exploded. They lack proper cooling to operate past the expected runtime of > the internal battery without overheating. It's another great example of > designing out all extra unneeded costs of a product while just meeting > specs.Thanks that's a useful story. Sometimes in addition to limiting runtime the battery also adds thermal inertia to a device.
Reply by ●July 1, 20202020-07-01
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.> Also, I'll put a switch on the primary, but I can't guarantee that > switch will always get turned off after the power switch on the leaf > blower is shut off. My wife will be the user, I can put a light in the > circuit, she would be certain to turn off an unneeded light. > > > MikekCheers, James Arthur
Reply by ●July 1, 20202020-07-01
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 -- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus
Reply by ●July 1, 20202020-07-01
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. The OP has air cooling available too - so little to worry about. Just rewind the secondary with thick wire or bifilar. .... Phil
Reply by ●July 1, 20202020-07-01
On 7/1/2020 7:38 PM, Phil Allison 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. > > The OP has air cooling available too - so little to worry about. > > Just rewind the secondary with thick wire or bifilar. > > > .... Phil >I used #16 wire for the secondary, should be good. I'll test it tomorrow after welding it back together. Mikek -- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus
