Timeline for Why does my variac have only 60 mA of magnetization current?
Current License: CC BY-SA 4.0
14 events
| when toggle format | what | by | license | comment | |
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| Aug 12 at 8:37 | comment | added | Jasen Слава Україні | It's only mostly parallell each looped field line must cross the gap somewhere, and for each loop there's an awful lot of somwhere | |
| Aug 12 at 6:52 | comment | added | greybeard |
(@JasenСлаваУкраїні that gap would be perpendicular to the magnetic flow - irrelevant?!)
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| Aug 12 at 5:15 | comment | added | Jasen Слава Україні | strip wound toroidal transformer cores are near ideal. The only gap is between the layers of would transformer steel and that gap has a large surface area, and so is magnetically very small. | |
| Aug 12 at 1:21 | history | became hot network question | |||
| Aug 11 at 16:44 | history | edited | winny | CC BY-SA 4.0 |
Engineering notation
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| Aug 11 at 15:57 | comment | added | D.A.S. | Mag. current is only dependent on primary voltage with no load. Can you confirm how you measured the magnitude of primary current [Irms] with no load? | |
| Aug 11 at 15:49 | answer | added | Neil_UK | timeline score: 3 | |
| Aug 11 at 14:54 | comment | added | juhist | More calculations: at 400 turns and 0.06 A RMS (0.085 A peak) current, the magnetic field reaches around 1 Tesla for a 7 cm toroid made of µr = 10000 material. I understand this is near the limits of most transformer cores, so indeed, it could be that the magnetizing current is naturally that small. | |
| Aug 11 at 14:47 | comment | added | juhist | Another measurement: winding resistance 2 ohms. A 5.1 cm x 5.1 cm square "toroid" core would require 82 meters of wire for 400 turns. This would put the wire at 19AWG, which should handle 10 amperes, but in a toroid the wires are close to each other, but on the other hand, the insulation of transformer wire should handle higher temperature than the insulation of the power cord. | |
| Aug 11 at 14:42 | comment | added | juhist | Unfortunately, this Chinese variac probably does not have a datasheet, and it's in a case I haven't opened, but from weight (10 kg) and external dimensions, it probably has 7 cm radius, 26 cm2 area toroid transformer, which would give 400 turns for a µr=10000 core. Maybe it could be that the magnetizing current is that small. | |
| Aug 11 at 12:17 | review | Close votes | |||
| Aug 16 at 3:01 | |||||
| Aug 11 at 11:28 | comment | added | Antonio51 | Lm should be 12 H without a capacitor. With a capacitor of 10 uF in parallel, Lm should be ~ 1 H. | |
| Aug 11 at 11:21 | comment | added | Fabio Barone | Please edit question to include link to the variac datasheet. | |
| Aug 11 at 10:30 | history | asked | juhist | CC BY-SA 4.0 |