Blown Bridge Rectifiers yes plural

[JohnnyRC]

Hello, I have a doubler circuit that keeps shorting my KBPC50-600v 50amp bridge rectifiers, two to date. I am using the doubler on an H configuration IGBT bridge. My caps are RIFA 400v 6000 uf big ones. They are within range. I have no way to check ESR unless someone knows how to check using one of these: http://www.ebay.com/itm/LC100A-High-...-/250853871796
There are snubbers in place to prevent kickback and my question is: wouldnt kickback kill the rectifier? Or high ESR on caps or single cap cause this?. I am running a double resonant tesla coil with this set up. I have seen my driving rig fail and the bridge runs continuous wave a time or two which could cause weakening of the rectifier.

[budm]

Re: Blown Bridge Rectifiers yes plural

Any SCH on how the whole thing is setup?

[JohnnyRC]

Re: Blown Bridge Rectifiers yes plural

here is the doubler circuit. i am using a variac for input for isolation i will post the bridge sch later tonight for reference. thank you


http://www.coolcircuit.com/circuit/voltage/vd.GIF

[JohnnyRC]

Re: Blown Bridge Rectifiers yes plural

guys, here is bridge sch. there is one cornell dubiler snubber capacitor .15 mfd 2000vdc in parallel with the diode array between collector and emitter on each IGBT that the sch doesnt show. thank you and i am a mere knowledge seeker and am having fun with high voltage!!

[JohnnyRC]

Re: Blown Bridge Rectifiers yes plural

ok i just realized that the diodes are bi-directional......had no idea diodes could do that but here are some specifics and is there a way to check bi-directional diodes? prferably without de-soldering.

P6KE220CA 600W BIDIRECTIONAL TRANSIENT VOLTAGE SUPPRESSION DIODE
Max Continuous Voltage 185V
Minimum Breakdown Voltage 209V
Maximum Breakdown Voltage 231V

[kaboom]

Re: Blown Bridge Rectifiers yes plural

Hello, I have a doubler circuit that keeps shorting my KBPC50-600v 50amp bridge rectifiers, two to date. I am using the doubler on an H configuration IGBT bridge. My caps are RIFA 400v 6000 uf big ones. They are within range. I have no way to check ESR unless someone knows how to check using one of these:http://www.ebay.com/itm/LC100A-High-...-/250853871796
There are snubbers in place to prevent kickback and my question is: wouldnt kickback kill the rectifier?

No. They direct current back into the caps, raising the bus voltage. Energy is commutated from the coil back to the bus. The impulse across the caps will be low, provided the ESR is low. You should have heavy litz wire or buss bar from the caps to IGBTs. Also, put a low ESR/ESL film cap, such as this:

http://www.ebay.ca/itm/TPC-CAPACITOR...item19da2ee715

across the rails feeding the IGBTs, as physically close as you can. This will keep the high frequency ripple away from your electros, keeping them cooler.

Or high ESR on caps or single cap cause this?. I am running a double resonant tesla coil with this set up. I have seen my driving rig fail and the bridge runs continuous wave a time or two which could cause weakening of the rectifier.

You're caps are rather large to be right after such small rectifiers. Also, I see no soft start, so you're pulling huge currents from the AC line upon power-up. We can't neglect the charging currents every half cycle, either.

I'd go for individual stud-mount diodes, or "modular" ones, in similar cases as your IGBTs.

What voltage are you feeding that rectifier with? 120V for ~340V across both caps, or 240V with ~680 across both?

ok i just realized that the diodes are bi-directional......had no idea diodes could do that but here are some specifics and is there a way to check bi-directional diodes? prferably without de-soldering.

P6KE220CA 600W BIDIRECTIONAL TRANSIENT VOLTAGE SUPPRESSION DIODE
Max Continuous Voltage 185V
Minimum Breakdown Voltage 209V
Maximum Breakdown Voltage 231V

Semis usually short, so use the continuity check on your meter. If one or more is shorted, the IGBTs, when switching on, will short the DC bus.

Hope it helps,
-Paul

[cheapie]

Re: Blown Bridge Rectifiers yes plural

Reminds me of when I tried to "upgrade" a cell phone charger with a huge primary cap. I plugged it in, and there was immediately a loud BANG as the primary bridge exploded. Tripped the circuit breaker too.

[JohnnyRC]

Re: Blown Bridge Rectifiers yes plural

[QUOTE]No. They direct current back into the caps, raising the bus voltage. Energy is commutated from the coil back to the bus. The impulse across the caps will be low, provided the ESR is low. You should have heavy litz wire or buss bar from the caps to IGBTs. Also, put a low ESR/ESL film cap, such as this:

http://www.ebay.ca/itm/TPC-CAPACITOR...item19da2ee715

across the rails feeding the IGBTs, as physically close as you can. This will keep the high frequency ripple away from your electros, keeping them cooler./QUOTE]


"impulse across the caps will be low, provided the ESR is low". Can you please explain this? low ESR = low loss. high ESR = heat and lossy is that right?. sorry just trying to understand what is happening.as far as the bus it is right on top of the bricks. the reason for this is to minimize induction spikes due to current reversal...i am very grateful for the help. attached is a photo of the bus

thanks for the tip on the snubber cap


[QUOTE]You're caps are rather large to be right after such small rectifiers. Also, I see no soft start, so you're pulling huge currents from the AC line upon power-up. We can't neglect the charging currents every half cycle, either.

I'd go for individual stud-mount diodes, or "modular" ones, in similar cases as your IGBTs.

What voltage are you feeding that rectifier with? 120V for ~340V across both caps, or 240V with ~680 across both?
/QUOTE]

haha which explains why i have had to re-set the gfi every now and then depending on where the 60hz cycle is when i plug it in....

i have several variacs that i use. one is 0-140v the other is 0-280v

thanks for the tip on modular diodes i just didnt really want to spend too much on my "little hobby" hehe

[QUOTE]Semis usually short, so use the continuity check on your meter. If one or more is shorted, the IGBTs, when switching on, will short the DC bus.

Hope it helps,
-Paul/QUOTE]

I just found these and they are local too http://www.ebay.com/itm/370762975536...84.m1497.l2649

thanks for the tip on checking the "Semis" easy enough

[JohnnyRC]

Re: Blown Bridge Rectifiers yes plural

[QUOTE]Semis usually short, so use the continuity check on your meter. If one or more is shorted, the IGBTs, when switching on, will short the DC bus.

Checked the semis they are all ok. It figures cause I just bought 100 of them....Anyone need some bi directional diodes they are line voltage!
I plan on making a few more of these with similar config so no big

[kaboom]

Re: Blown Bridge Rectifiers yes plural

[QUOTE=JohnnyRC;325065]

I just found these and they are local too http://www.ebay.com/itm/370762975536...84.m1497.l2649

thanks for the tip on checking the "Semis" easy enough

Keep in mind, those TVSS diodes are really rated in Joules. "1.5kW" but only for a few microseconds. That works out to a few tens of Joules at most, and will be elaborated upon in the device's datasheet.

You should be good with 'hanging' a film cap right off your bus, either with copper strap 'angles,' or short runs of heavy Litz. It's about the impedance of the entire current loop, not just that of the filter caps. In your case however, it looks pretty darn good, plenty of copper...

[JohnnyRC]

Re: Blown Bridge Rectifiers yes plural

[QUOTE=kaboom;325227]

Keep in mind, those TVSS diodes are really rated in Joules. "1.5kW" but only for a few microseconds. That works out to a few tens of Joules at most, and will be elaborated upon in the device's datasheet.

You should be good with 'hanging' a film cap right off your bus, either with copper strap 'angles,' or short runs of heavy Litz. It's about the impedance of the entire current loop, not just that of the filter caps. In your case however, it looks pretty darn good, plenty of copper...

i will replace the TVSS's as i'm not really sure if they are blocking or not. ohm meter reads open but... with high voltage could be shorting the bus.. plus getting 100 of them. earlier you mentioned ripple currents across the bus caps do can you explain please as i'm a meager noob

[budm]

Re: Blown Bridge Rectifiers yes plural

It reads open because it is Bi-directional TVSS which the Diodes are connected back to back inside the body.

[JohnnyRC]

Re: Blown Bridge Rectifiers yes plural

It reads open because it is Bi-directional TVSS which the Diodes are connected back to back inside the body.

i checked for shorted TVSS is there another way to check these?

[JohnnyRC]

Re: Blown Bridge Rectifiers yes plural

jeez guys can anyone please explain ripple current? is it inductive spikes?

[kaboom]

Re: Blown Bridge Rectifiers yes plural

i checked for shorted TVSS is there another way to check these?

Get a 400-500V DC supply and a 56K, 10W resistor. Connect one end of the resistor to the output of the supply. Connect the other end to a lead on the diode. Connect the other lead of the diode to the supply common. Measure the voltage across the diode. Be sure to test the diode in both directions- simply reverse the diode while leaving everything else alone.

You'll be measuring the clamping voltage across the TVSS this way.

[JohnnyRC]

Re: Blown Bridge Rectifiers yes plural

Get a 400-500V DC supply and a 56K, 10W resistor. Connect one end of the resistor to the output of the supply. Connect the other end to a lead on the diode. Connect the other lead of the diode to the supply common. Measure the voltage across the diode. Be sure to test the diode in both directions- simply reverse the diode while leaving everything else alone.

You'll be measuring the clamping voltage across the TVSS this way.

Thanks I just changed the TVSS's and seems to be running fine. Thanks for the advice.