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Registered Member #4362
Joined: Sat Jan 21 2012, 03:44AM
Location: Texas
Posts: 98
Please help. Im having troubles with this 1 tesla board.
I wound the correct 2.5 x 10 inch secondary with 36 awg wire. Im using the correct fets. And topload. Secondary is grounded by 8 foot ground rod.
The only deviation from your schematic is the use of 74ls74n and 74ls14n My gate transformer has 15 rounds on a toroid purchased from you I beleive. Bus voltage is 336 volts. My gate transformer is phased properly. My interupter is Steve wards universal with fiber optic output. The following pictures were taken at around 200 bps and around 20 us on time.
This first picture is from probe connected to outputs of ucc37321 and 322 (per step 3B in troubleshoot guide.)
The second picture is from Input to GDT after c8. 1u On both GDT outputs the pattern is the same.
My question is could that initial (false ring) Be killing IGBT's ? I have replaced c8 just to be sure but the pattern doesnt change. I tried the full range of Steves interupter but the double pusle remains.
EDIT : I just realized one pulse is when the GDT is pulled high and the other is when its pulled low. Right?
Registered Member #4362
Joined: Sat Jan 21 2012, 03:44AM
Location: Texas
Posts: 98
Sorry for double post. I couldnt edit in another picture. This is a close up of GDT. IGBT's were not installed at the time of the picture but when I put a new pair in the pattern remained.
Registered Member #4362
Joined: Sat Jan 21 2012, 03:44AM
Location: Texas
Posts: 98
The second scope pattern is without igbits but it looked the same with new ones installed. The scope probe was connected between Gate to source. Looked the same at both igbits.
I couldnt find 6.8 ohm resistors so I substituted 10 ohm ones. They are not wire wound type.
Registered Member #2919
Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652
E.TexasTesla wrote ...
The second scope pattern is without igbits but it looked the same with new ones installed. The scope probe was connected between Gate to source. Looked the same at both igbits.
I couldnt find 6.8 ohm resistors so I substituted 10 ohm ones. They are not wire wound type.
What's the V/div on the second pic? If that's Vge and it's 5V/div, there's something wrong there...it should swing up to 15V. Is your 15V rail actually 15V? Are pins 7 and 8 of the UCC chips at 15V? (did you accidentally install a 7805 in place of the 7815?) Also, while it is not the cause of your symptoms, I would strongly recommend switching to 6.8 ohm gate resistors.
Registered Member #4362
Joined: Sat Jan 21 2012, 03:44AM
Location: Texas
Posts: 98
V/div was at 1 volt in the second picture. Rail to rail on uccs is 12v.
I appreciate your guys help, I realize you are busy with college and such.
One thing that would help me would be a simple fixed signal generator (interupt) schematic And samples of scope patterns from gate transformer while using fixed interupt. Mabe a dummy load for testing.
I still cant beleive Im the only one having this circuit kick my butt.
Registered Member #2919
Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652
Can you remove the GDT and scope the output of the UCC's? If the rail is 12V and the output is not 0-12V, you have dead driver chips. Also, you really should be running a 15V regulator on the gate drive, not 12V - the transistors desaturate at 12V gate at 300A and tend to explode.
Registered Member #4362
Joined: Sat Jan 21 2012, 03:44AM
Location: Texas
Posts: 98
OK. I switched Vreg. to 7815. GDT removed for these scope pictures.
EDIT: Both scope probes were set on 10x for these pictures. My mistake. Patterns are still the same but the voltages were incorrect. Each ucc output was 0 to 15v
Dual trace scope set on 1v divisions. Chan. one "ucc1" is on top. Pattern taken from each UCC output to ground. Ucc2 has a very narrow pulse . I beleive enable pin signal is clipping it to soon.
Second picture is from Ucc output to ucc output.
Third picture is from pin 2 of Ucc1 to ground . When I adjust BPS and on time the time base changes but the voltages stay the same.
Registered Member #2919
Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652
E.TexasTesla wrote ...
OK. I switched Vreg. to 7815. GDT removed for these scope pictures.
Dual trace scope set on 1v divisions. Chan. one "ucc1" is on top. Pattern taken from each UCC output to ground. Aprox. 7 volts on each output with 15.2 v rail. Ucc2 has a very narrow pulse . I beleive enable pin signal is clipping it to soon.
Second picture is from Ucc output to ucc output. Its on 1v division and is at 15 volts peak to peak.
Third picture is from pin 2 of Ucc1 to ground . Looks very low. Aprox. 3 v swing. Pin 3 from ucc 1 to ground has a steady square wav. I assume normal due to no current flow. When I adjust BPS and on time the time base changes but the voltages stay the same.
Assuming your scope is in calibration and you didn't get your V/div wrong, you need new UCC's...the output should be 0-15V when unloaded.
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oneTesla - a small single-board DRSSTC
