You already have the charged capacitors and a switch.
All you need to add is a Thyristor and a very simple trigger circuit, *all* of which is shown in the picture I uploaded.
SCR will auto turn OFF when current drops to zero.
Current will drop to zero in milliseconds when capacitors get discharged through the magnetizing coil.
What JonSnell said.
Why?
You can probably get Industrial SCRs capable of switching 1600V and beyond.
The full functional circuit is shown.
Outside pictures are mains connection, which you already have solved, and a couple safety relays, particular to this machine which is also meant for school Lab use so more precautions than a purely Industrial setting
Those are needed for SCR triggering, what you are asking.
6.8V is not *continuously* applied, of course, but through a switch or relay *only* when you trigger the SCR
100uF cap charged to 6.8V is fully discharged in 5.7 milliseconds (time constant 100uF and 57 ohm) and recharged in 1 second, WELL after the main caps are discharged.
Of course, you *must* disconnect main capacitor bank from its charging circuit before magnetizing.
You already have the charged capacitors and a switch.
All you need to add is a Thyristor and a very simple trigger circuit, *all* of which is shown in the picture I uploaded.
SCR will auto turn OFF when current drops to zero.
Current will drop to zero in milliseconds when capacitors get discharged through the magnetizing coil.
What JonSnell said.
Why?
You can probably get Industrial SCRs capable of switching 1600V and beyond.
The full functional circuit is shown.
Outside pictures are mains connection, which you already have solved, and a couple safety relays, particular to this machine which is also meant for school Lab use so more precautions than a purely Industrial setting
Those are needed for SCR triggering, what you are asking.
6.8V is not *continuously* applied, of course, but through a switch or relay *only* when you trigger the SCR
100uF cap charged to 6.8V is fully discharged in 5.7 milliseconds (time constant 100uF and 57 ohm) and recharged in 1 second, WELL after the main caps are discharged.
Of course, you *must* disconnect main capacitor bank from its charging circuit before magnetizing.
The thing that 6.8v is not applied constantly clears my doubt.
I have seen behaviour in some diy magnetizers that when the capacitors are discharged into coil it sometimes starts recharging the capacitor with small voltage. It may be due to residual magnetic effect. Do you think it will affect the scr turn off after dischrge?
All thank you for clarifying my doubts. It would have taken a lot of effort to type that much.
You´re welcome.
Small detail: no need to quote the above post in full ... it´s already there to see.
Let´s not fill the screen with duplicated text.
PS: have you already built the magnetizing coil?
Post a picture or two.
As of switching high power ... I got tired of burning SCRs and went back to an old reliable Siemens contactor, designed to switch on-off Subway/Metro electric motors.
600/800V RMS 600A RMS contacts, 380V coil ... works like a charm for some 35/40 years now.
Small detail: no need to quote the above post in full ... it´s already there to see.
Let´s not fill the screen with duplicated text.
PS: have you already built the magnetizing coil?
Post a picture or two.
As of switching high power ... I got tired of burning SCRs and went back to an old reliable Siemens contactor, designed to switch on-off Subway/Metro electric motors.
600/800V RMS 600A RMS contacts, 380V coil ... works like a charm for some 35/40 years now.
My magnetisation is better than any local speaker magnets. And at par will bigger brands like sony and pioneer. I have not done lab testing with the magnets but with same grade my magnetisation was better and like sony speakers with samr magnets i had same force after charging same magnets
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Just a side question: How do you make sure that you recharge a speaker magnet at it's correct polarity? I guess nobody wants to have the cone movement reversed after the procedure? And how do you make sure you're magnetizing to the correct field strength within the VC gap? Otherwise the speaker's original BL parameter gets compromised.
Best regards!
Best regards!
Hope you got a BIG SCR.
Many use so called "Hockey Puck" ones, because of the case type designed to be sandwiched between heatsinks.
Attaching:
* "hockey puck" SCR
* capcitor bank
* magnetizing fixture.
EDIT:
Some magnetizers used in Factories (such as RCF and probably the 60´s JBL one), and my "large one" allow for magnetization of speaker already inside the shipping box.
And speaker inside box may be magnet up pr magnetb down.
But the practical way is to have a (large) DDT switch between coil and capacitor bank , magnetize both ways, and label it "North up" and "South up".
Then you choose whatever´s needed at the moment.
In my small magnetizer at home, up to 105 mm magnets, I simply plug fixture into supply using an Industrial, 2 round pin connector.
If needed I unplug and invert it, easy peasy.
Many use so called "Hockey Puck" ones, because of the case type designed to be sandwiched between heatsinks.
Attaching:
* "hockey puck" SCR
* capcitor bank
* magnetizing fixture.
EDIT:
True: on winding direction, applied polarity and speaker orientation he he.
Some magnetizers used in Factories (such as RCF and probably the 60´s JBL one), and my "large one" allow for magnetization of speaker already inside the shipping box.
And speaker inside box may be magnet up pr magnetb down.
But the practical way is to have a (large) DDT switch between coil and capacitor bank , magnetize both ways, and label it "North up" and "South up".
Then you choose whatever´s needed at the moment.
In my small magnetizer at home, up to 105 mm magnets, I simply plug fixture into supply using an Industrial, 2 round pin connector.
If needed I unplug and invert it, easy peasy.
Attachments
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I tested the SCR. I guess there is internal resistor from gate to cathode.
What i did was i connected negative of 1.5V battery to cathode and positive to gate and voila it turned on. As it was just testing it turned off as there was no current passing through it.
Resistance while on was around 0.592 Ohms.
Is the measurement correct? Also do you think i got correct SCR or went overboard with ratings?
What i did was i connected negative of 1.5V battery to cathode and positive to gate and voila it turned on. As it was just testing it turned off as there was no current passing through it.
Resistance while on was around 0.592 Ohms.
Is the measurement correct? Also do you think i got correct SCR or went overboard with ratings?