Controller No 4 - Dual Fet Driver - Looking for Explosions in Wires

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2024-11-26, 21:38:13
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Author Topic: Controller No 4 - Dual Fet Driver - Looking for Explosions in Wires (Read 59550 times)

Peterae	Re: Controller No 4 - Dual Fet Driver - Looking for Explosions in Wires « Reply #150 on: 2010-05-16, 14:51:28 »
Group: Administrator Hero Member Posts: 3961	Yes WaveW my fet output is always only 32nS which is set using the dip switches, there some lags in the fet driver and fet and am probably really getting about 65nS. I am not fully sure whats going on here because if i really have 65nS pulses it's hard to imagine such high current draw. Just as another test i disconnected 1 channel and drove the coil with only 1 fet, i get similar results under about 3khz where the coil tail vibrates, i can only imagine for some reason at this low frequency something is stopping my fet from switching off. Just in case i have a damaged fet Channel i tried the other and still get the same effect Strange if i use over 5.5khz there is no longer this noise from the coil unless i start raising the coil volts dramatically until i reach a point where my pic starts crashing and i get re triggering.

Peterae	Re: Controller No 4 - Dual Fet Driver - Looking for Explosions in Wires « Reply #151 on: 2010-05-16, 15:17:01 »
Group: Administrator Hero Member Posts: 3961	Test Coil Specs Uses a UF4001 diode across it. Inductance = 41.25uH Resistance = 1.40 Ohms Q = 1.8508 Z= 2.946 Tested @ 10kHz If i connect a 120pF cap across either Drain/Sources the noise get's more prominent and occurs more easily. Here's another video i did varying under 5 Khz [youtube]http://www.youtube.com/watch?v=ZD8PR7CGJgQ[/youtube]

BEP	Re: Controller No 4 - Dual Fet Driver - Looking for Explosions in Wires « Reply #152 on: 2010-05-16, 15:43:43 »
Group: Guest	As you probably know, the wire movement within a strong magnetic field is not surprising. The audible sound from the coil, while in a strong magnetic field is for the same reasons, I'm sure. Placing a magnet nearby simply puts the coil in a more dense magnetic field. The frequency point of 5.5kHz doesn't surprise me either. On my 'magnet with coil tests' the interesting frequency was around 4.9kHz and didn't change much even when the coil inductance varied a great deal. When the 4.9 was hit multiple audio frequencies emanated from the coil. All lower than 4.9kHz. The resultant, lower frequencies did change with coil parameters. I'm thinking about resurrecting the test to see if the odd hidden sounds can be heard during playback. There were no KABOOMs, anomalous DC output, or extra pulses from those experiments that couldn't be easily explained.

poynt99	Re: Controller No 4 - Dual Fet Driver - Looking for Explosions in Wires « Reply #153 on: 2010-05-16, 15:44:37 »
Group: Administrator Hero Member Posts: 3217 It's not as complicated as it may seem...	A quick sim of your cct: Vsupply = 50V. PW = 65ns, T = 130ns. With and without flyback diode. Shown is VDrain. .99 ------------------------ Controller No 4 - Dual Fet Driver - Looking for Explosions in Wires nofbdiode.gif (21.15 kB, 869x934 - viewed 597 times.) Controller No 4 - Dual Fet Driver - Looking for Explosions in Wires withfbdiode.gif (23.12 kB, 868x940 - viewed 578 times.) --------------------------- "Some scientists claim that hydrogen, because it is so plentiful, is the basic building block of the universe. I dispute that. I say there is more stupidity than hydrogen, and that is the basic building block of the universe." Frank Zappa

Peterae	Re: Controller No 4 - Dual Fet Driver - Looking for Explosions in Wires « Reply #154 on: 2010-05-16, 15:50:10 »
Group: Administrator Hero Member Posts: 3961	Certainly shows how close i was sailing when running at 70'ish volts

Peterae	Re: Controller No 4 - Dual Fet Driver - Looking for Explosions in Wires « Reply #155 on: 2010-05-16, 16:08:25 »
Group: Administrator Hero Member Posts: 3961	Something's really screwed with my current setup, i thought i would run the system up and capture the pulse using 50 volts supply and a drive frequency below 450khz and above to show the difference, but as i swept using only 1 channel it blew the fet. It shouldn't have done this as i have done it many times before without any problems, it's either the longer wires on the coil or maybe the fet drivers are not working correctly. Enough for today, next week i will plug some new driver chips in and see if that cures these strange goings on. I wouldn't have expected this or the way the system behaved under 5khz so something is not right.

poynt99	Re: Controller No 4 - Dual Fet Driver - Looking for Explosions in Wires « Reply #156 on: 2010-05-16, 16:23:50 »
Group: Administrator Hero Member Posts: 3217 It's not as complicated as it may seem...	A couple ideas that may help save the lives of a few MOSFETs. .99 ------------------------ Controller No 4 - Dual Fet Driver - Looking for Explosions in Wires fet-protect01.gif (12.25 kB, 725x761 - viewed 572 times.) --------------------------- "Some scientists claim that hydrogen, because it is so plentiful, is the basic building block of the universe. I dispute that. I say there is more stupidity than hydrogen, and that is the basic building block of the universe." Frank Zappa

Peterae	Re: Controller No 4 - Dual Fet Driver - Looking for Explosions in Wires « Reply #157 on: 2010-05-16, 16:26:20 »
Group: Administrator Hero Member Posts: 3961	That is a great idea to limit the on time fantastic thanks.

poynt99	Re: Controller No 4 - Dual Fet Driver - Looking for Explosions in Wires « Reply #158 on: 2010-05-16, 16:36:23 »
Group: Administrator Hero Member Posts: 3217 It's not as complicated as it may seem...	And one final touch....450V worth of TVS protection on the Drain. If they still pop with these 3 safeguards in place, then it's time to look deeper. .99 ------------------------ Controller No 4 - Dual Fet Driver - Looking for Explosions in Wires fet-protect02.gif (13.15 kB, 730x737 - viewed 579 times.) --------------------------- "Some scientists claim that hydrogen, because it is so plentiful, is the basic building block of the universe. I dispute that. I say there is more stupidity than hydrogen, and that is the basic building block of the universe." Frank Zappa

Peterae	Re: Controller No 4 - Dual Fet Driver - Looking for Explosions in Wires « Reply #159 on: 2010-05-26, 19:57:50 »
Group: Administrator Hero Member Posts: 3961	OK guys I have almost finished the new controller board, but am using bigger fet's TO-249 Now WW aired concern i was not using insulation washers on my previous builds, so if the heatsink is isolated how important is it for me to use a Thermal washer, because this is holding me up, they are not that easy to get here in the UK unless i place a separate order costing pounds.

Room3327	Re: Controller No 4 - Dual Fet Driver - Looking for Explosions in Wires « Reply #160 on: 2010-05-26, 20:04:45 »
Group: Experimentalist Hero Member Posts: 568	Peterae, If the heat sink is isolated, it is not important at all. It's all right too if your parreleling mosfets, it just connects all drains together which you do anyway. --------------------------- "Whatever our resources of primary energy may be in the future, we must, to be rational, obtain it without consumption of any material" Nicola Tesla "When bad men combine, the good must associate; else they will fall one by one, an unpitied sacrifice in a contemptible struggle." Edmund Burke

BEP	Re: Controller No 4 - Dual Fet Driver - Looking for Explosions in Wires « Reply #161 on: 2010-05-26, 22:10:33 »
Group: Guest	The TVS's are a better move than electric isolation between the FET and heat-sink. Don't let the washers hold you up. If you still have problems see below: Sorry to disagree Room3327. In high energy pulse circuits it is best to electrically isolate the heat sink from the device. This is standard practice even with high-end switch mode power supplies and every HV generator I've used. (the HV wasn't at the fet. It wasn't a matter of arcing at the FET part of the circuit). On sub-ns pulses the wavefront induces a very short spike in nearby metals. Aluminum is really bad. One solution for me was to mount a small flat square of Al sheet on the PCB then mount the FET flat on the sheet. As long as the source (source of the spike - coil, wire, etc.) was on the same plane as the heat sink there was little problem. Of course, your heat sink can be one-half of an unintentional capacitor

Peterae	Re: Controller No 4 - Dual Fet Driver - Looking for Explosions in Wires « Reply #162 on: 2010-05-26, 22:11:23 »
Group: Administrator Hero Member Posts: 3961	Thanks Room I realize the heatsink would be live also, but was not sure how the increased surface area of the drain would alter the sharp nS pulsing. EDIT WW i missed your post as it appeared just as i was posting, i do have some TO220 washers which although are not large enough to insulate the whole metal area, i am wondering they may insulate enough and move the rest of the metal far enough to isolate them totally, it's not as if i have large potentials between the heatsink and the drain anyway so there should be no chance of discharge or spark jumping across the gap, and i also will not be running these very hot hopefully so i don't really need 100% surface area in contact

Room3327	Re: Controller No 4 - Dual Fet Driver - Looking for Explosions in Wires « Reply #163 on: 2010-05-27, 01:26:29 »
Group: Experimentalist Hero Member Posts: 568	WW, Peterae, it's OK to disagree with me, I guess I stand corrected. I probably should not have said it is not important at all, I have just never found much difference myself in testing and I thought it would certainly be alright for Peterae to test without insulation washers. But I can see that what you say is good info. --------------------------- "Whatever our resources of primary energy may be in the future, we must, to be rational, obtain it without consumption of any material" Nicola Tesla "When bad men combine, the good must associate; else they will fall one by one, an unpitied sacrifice in a contemptible struggle." Edmund Burke

BEP	Re: Controller No 4 - Dual Fet Driver - Looking for Explosions in Wires « Reply #164 on: 2010-05-27, 02:33:52 »
Group: Guest	I must apologize. Making spikes of odd variety has been a passion for a long time. I should have explained that I believe Peterae's situation is a bit unique. Yes, in almost all cases there is little worry about the electrical connection. It is also very rare that anyone need worry about such short rise and fall times. This project is no different except when the 'noise' is happening. Regardless of the cause of the noise, noise can contain some incredibly short pulses. If the failure cause is avalanche in the failing device there isn't much to do except limit current. If the failure cause is the reverse potential created by the collapse of the magnetic field of the coil (due to FET avalanche activity) there is a strong possibility the rise and fall time of the BEMF pulses are short enough to create effects closer to radiation than Faraday induction. Believe it or not... I realized I was being a windbag and just deleted a huge amount from this post

Peterae	Re: Controller No 4 - Dual Fet Driver - Looking for Explosions in Wires « Reply #165 on: 2010-05-27, 07:47:40 »
Group: Administrator Hero Member Posts: 3961	Room & WW Thanks guys it's always good to hear views, i am really glad to have you both here reading what i am doing, as a collective we stand much more chance in achieving our goals. Peter

Grumpy	Re: Controller No 4 - Dual Fet Driver - Looking for Explosions in Wires « Reply #166 on: 2010-05-27, 14:01:24 »
Group: Tinkerer Hero Member Posts: 3948 tExB=qr	Just leave the heatsinks off and keep the current low.

Peterae	Re: Controller No 4 - Dual Fet Driver - Looking for Explosions in Wires « Reply #167 on: 2010-05-27, 15:25:50 »
Group: Administrator Hero Member Posts: 3961	I tried that G trouble is during re triggering you have no control how long it's on for and can get very hot very fast without a sink to disperse the heat.

Grumpy	Re: Controller No 4 - Dual Fet Driver - Looking for Explosions in Wires « Reply #168 on: 2010-05-27, 16:14:16 »
Group: Tinkerer Hero Member Posts: 3948 tExB=qr	I use a delay line to control the on-time and force it to turn off when the delay line reflects. The trigger just dumps the delay line (a capacitor made of coax) through the switch. I think 10 feet is about 3ns (as a course rule of thumb). You could use a cap if you don't need the square pulse shape.

Peterae	Re: Controller No 4 - Dual Fet Driver - Looking for Explosions in Wires « Reply #169 on: 2010-05-27, 16:48:54 »
Group: Administrator Hero Member Posts: 3961	Maybe i was wrong in saying i cant control the ON time as with the next controller i have implemented Poynt's mod as above, so hopefully this will control the ON time. We will see how it goes, but anyway it has a heatsink right now

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