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Registered Member #1403
Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968
Teodor Zafiroski wrote ...
UPDATE: I have searched for a power supply that can give that output current at such voltage without sagging, and was unable to find any within my budget, but I have picked up one 12V 45Ah Lead-Acid battery from a car, it's not new but it hasn't been used a lot, only a couple of months. Could I use it as the power source?
You would need two batteries in series, 12V is simply too low to drive the MOSFETs properly. You will not switch fast enough, thus spending almost the entire time in the linear region, dissipate so much heat that the MOSFET will eventually fail from heat or it will all fail from slow switching, both gates staying on, not getting switch completely off, etc.
Registered Member #48007
Joined: Wed Jun 18 2014, 01:00PM
Location: Prilep, Republic of Macedonia
Posts: 33
So why did I bother searching for a computer PSU in the first place? In the meantime I found another large lead acid, and It has almost the same characteristics, except that it is old. My secondary diameter is 50mm, about how large primary diameter should I use, I'm going to wind it with 1.7mm copper wire...
You would need two batteries in series, 12V is simply too low to drive the MOSFETs properly. You will not switch fast enough, thus spending almost the entire time in the linear region, dissipate so much heat that the MOSFET will eventually fail from heat or it will all fail from slow switching, both gates staying on, not getting switch completely off, etc.
Why would 12V not be enough to switch a simple NFet? As long as there is adequate current supply to the gate, 12V is plenty. This isn't a DRSSTC with IGBTs where you benefit from overdriving the gates. Most fet gates reach saturation at under 8V anyway, and beyond that is just charging the miller capacitance.
My 3kW CW SSTC runs +-12V Vgs with no problem, and no signs of running in the linear region. I've used the same gate drive on coils up to 1MHz at lower continuous power levels too, all with only 2.5A of peak gate current (5ohm Rg).
Registered Member #1403
Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968
Sigurthr wrote ...
Mads Barnkob wrote ...
You would need two batteries in series, 12V is simply too low to drive the MOSFETs properly. You will not switch fast enough, thus spending almost the entire time in the linear region, dissipate so much heat that the MOSFET will eventually fail from heat or it will all fail from slow switching, both gates staying on, not getting switch completely off, etc.
Why would 12V not be enough to switch a simple NFet? As long as there is adequate current supply to the gate, 12V is plenty. This isn't a DRSSTC with IGBTs where you benefit from overdriving the gates. Most fet gates reach saturation at under 8V anyway, and beyond that is just charging the miller capacitance.
The Royer oscillator does not have a great track record for supply voltages sagging under 12V.
My 3kW CW SSTC runs +-12V Vgs with no problem, and no signs of running in the linear region. I've used the same gate drive on coils up to 1MHz at lower continuous power levels too, all with only 2.5A of peak gate current (5ohm Rg).
Registered Member #48007
Joined: Wed Jun 18 2014, 01:00PM
Location: Prilep, Republic of Macedonia
Posts: 33
Mads, three guys at thе macedonian forum for electronics have made an induction heater using the schematic at RMCybernetics, it is a simplified mazzilli driver, it has everything except the zeners and the resistor parralel to the zeners, and they've succeeded in that.
What could happen if I was to connect this circuit to a 12V car battery? Тhe gate voltages are limited to 12V with the zeners anyway...
Also, when using such a high current power source like a car battery, I am very afraid of a short circuit making the wires to vaporize and exploding the MOSFET's to pieces, could I connect a regular 15A house breaker to protect against short circuit?
@Mads, ahh if sag is expected, yes, you're right. You'll get lockup in a traditional Royer. I wouldn't expect sag from a fully charged deep cycle SLA cell though.
I have a simple royer ZVS Flyback driver that I use on a high current supply or SLA, but it only draws 24A at full load on 13.8V.
Registered Member #48007
Joined: Wed Jun 18 2014, 01:00PM
Location: Prilep, Republic of Macedonia
Posts: 33
Sigurthr wrote ...
I wouldn't expect sag from a fully charged deep cycle SLA cell though.
It's not even an SLA, it's the type where you can fill/refill acid and it has some sort of plastic screws so the acid can be refilled. Can someone explain to me the problem with sag? I haven't met this term when talking about batteries...
Registered Member #42796
Joined: Mon Jan 13 2014, 06:34PM
Location:
Posts: 195
Teodor Zafiroski wrote ...
Can someone explain to me the problem with sag? I haven't met this term when talking about batteries...
if the voltage sags below 10V the mosfets will not fully turn on so it will dissipate alot of heat in the case of a ZVS this also cause both mosfets to be partially on further worsen the situation eventually (actually quite rapidly) one will pop
but for a big battery this isn't a problem
i ran mine from a 12V 4.5AH battery and i think is not even fully charged and i get no heat on mosfets i use IRFP260N for which the datasheet suggest Vgs +/- 20V
Voltage sag is when a power source cannot supply the current required by the load without the voltage falling to a lower than ideal level. For example, a 12V 1A power adapter for the wall outlet is designed to supply at most 1A at 12V, but at 1.2A it might only be capable of 10V, at 2A only 8V, etc. (and that's a rather nonlinear nonsense load curve of pseudo-random numbers to explain the concept, by the way).
Registered Member #48007
Joined: Wed Jun 18 2014, 01:00PM
Location: Prilep, Republic of Macedonia
Posts: 33
dexter wrote ...
i ran mine from a 12V 4.5AH battery and i think is not even fully charged and i get no heat on mosfets i use IRFP260N for which the datasheet suggest Vgs +/- 20V
Mine is 12V 45Ah, well above yours which was 4.5Ah, so I shouldn't expect sag... I use the IRFP260N's too, seems that it could work together nicely! The only thing left to do is the primary, which I will wind with a couple of cm larger diameter than the primary, I just need to calculate the inductance and test it, I have some exams this week, but I will try to test this as soon as possible.
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Royer SSTC
