Triggering SCR's
Tipp, Sat Mar 11 2006, 07:50PMOk, well I've been doing research and looking into this kinda thing, but it's confusing the hell out of me. I found a few site that showed me this:
What's the 9v battery for? It looks like he's running it in series with his bank voltage so it will appear +9v more. Resistor is obvisly for limiting current to the gate. Is that the proper way to trigger an SCR? [To have a higher gate voltage then anode?]
Link to site:
It's been a long week...maybe I'm just not thinking strieght...
Thanks once again for all your help...you guys are lifesavers...
[Edit: Fixed oversized picture]
Re: Triggering SCR's
..., Sat Mar 11 2006, 07:53PM
it is kind of hard to tell when we do not know what model the SCR is, but a 9v battery resistor and switch is a fine way to triger one.
..., Sat Mar 11 2006, 07:53PM
it is kind of hard to tell when we do not know what model the SCR is, but a 9v battery resistor and switch is a fine way to triger one.
Re: Triggering SCR's
Tipp, Sat Mar 11 2006, 08:00PM
Oh, sorry, duh!
Let me grab you a datasheet here... [this isnt the one in the pic, just used it as an example]
There y'are
Voltage code = 12 [1.2kV]
Tipp, Sat Mar 11 2006, 08:00PM
Oh, sorry, duh!
Let me grab you a datasheet here... [this isnt the one in the pic, just used it as an example]There y'are
Voltage code = 12 [1.2kV]Re: Triggering SCR's
Steve Conner, Sat Mar 11 2006, 08:43PM
A voltage between gate and cathode, and the current that it causes to flow, is what triggers the SCR. So there's a mistake in that schematic which shows the trigger voltage connected between gate and ANODE (or the cap bank connected backwards)
Steve Conner, Sat Mar 11 2006, 08:43PM
A voltage between gate and cathode, and the current that it causes to flow, is what triggers the SCR. So there's a mistake in that schematic which shows the trigger voltage connected between gate and ANODE (or the cap bank connected backwards)
Re: Triggering SCR's
Tipp, Sun Mar 12 2006, 01:51AM
So basicly, instead of attaching the 9v negitive to the anode, it should be connected to the cathode? Seems easy enough...is there any other precaution I should be aware of doing it this way? I dont want my 9 volt battery to go 'pop'
Already blew up a AA battery...but that was another project 
Tipp, Sun Mar 12 2006, 01:51AM
So basicly, instead of attaching the 9v negitive to the anode, it should be connected to the cathode? Seems easy enough...is there any other precaution I should be aware of doing it this way? I dont want my 9 volt battery to go 'pop'
Already blew up a AA battery...but that was another project Re: Triggering SCR's
Simon, Sun Mar 12 2006, 05:33AM
As long as you wire it up properly and the SCR is correctly rated, the battery should be fine.
You might want to take a peek at the Wiki page.
Simon, Sun Mar 12 2006, 05:33AM
As long as you wire it up properly and the SCR is correctly rated, the battery should be fine.
You might want to take a peek at the Wiki page.
Re: Triggering SCR's
rupidust, Sun Mar 12 2006, 08:08AM
Here is a nice quick sample to test an SCR.
rupidust, Sun Mar 12 2006, 08:08AM
Here is a nice quick sample to test an SCR.
Re: Triggering SCR's
Tipp, Sun Mar 12 2006, 07:32PM
Aight, well I tried sample circuit #1, and the LED turns on, but the thyristor won't latch. Is this normal for a huge power SCR like this? I have a 5P4M SCR in a TO-220 package which latches normally when tested in this manner.
[Edit: Currently reading the wiki page, whoever drew those pictures has some mad paint skills ]
Tipp, Sun Mar 12 2006, 07:32PM
Aight, well I tried sample circuit #1, and the LED turns on, but the thyristor won't latch. Is this normal for a huge power SCR like this? I have a 5P4M SCR in a TO-220 package which latches normally when tested in this manner.
[Edit: Currently reading the wiki page, whoever drew those pictures has some mad paint skills
]Re: Triggering SCR's
rupidust, Sun Mar 12 2006, 10:47PM
Here is the resized schematic.
rupidust, Sun Mar 12 2006, 10:47PM
Here is the resized schematic.
Re: Triggering SCR's
..., Mon Mar 13 2006, 01:09AM
the larger teh SCR the more power needed for it to latch. I think that you need about .5a for it to stay latched, and about .3a on the gate to trigger it.
..., Mon Mar 13 2006, 01:09AM
the larger teh SCR the more power needed for it to latch. I think that you need about .5a for it to stay latched, and about .3a on the gate to trigger it.
Re: Triggering SCR's
Simon, Mon Mar 13 2006, 02:41AM
Maybe lightbulbs would be better for testing SCRs like this. That aside, your SCR seems to be okay and you seem to know how to make it go.
Regarding the wiki page. I'll just take that as a compliment.
If someone has a ready-made SCR testing schematic, having a copy on the wiki would be handy.
Simon, Mon Mar 13 2006, 02:41AM
Tipp wrote ...
Aight, well I tried sample circuit #1, and the LED turns on, but the thyristor won't latch. Is this normal for a huge power SCR like this? I have a 5P4M SCR in a TO-220 package which latches normally when tested in this manner.
[Edit: Currently reading the wiki page, whoever drew those pictures has some mad paint skills ]
Aight, well I tried sample circuit #1, and the LED turns on, but the thyristor won't latch. Is this normal for a huge power SCR like this? I have a 5P4M SCR in a TO-220 package which latches normally when tested in this manner.
[Edit: Currently reading the wiki page, whoever drew those pictures has some mad paint skills
]Maybe lightbulbs would be better for testing SCRs like this. That aside, your SCR seems to be okay and you seem to know how to make it go.
Regarding the wiki page. I'll just take that as a compliment.
If someone has a ready-made SCR testing schematic, having a copy on the wiki would be handy.
Re: Triggering SCR's
rupidust, Mon Mar 13 2006, 02:41AM
You are using 5P4M? That part is under powered. 8Arms and 80A surge.
Here is a schematic that illustrates marginal holding current I(hold) for SCR. When testing mininum condition for Latching, all components Vsupply, Vload, and SCR voltage Von-state need be considered.
Example:
For this SCR I(holding) = 80mA @24v. So why does this not work? 5vsupply - 3vled / 22 ohm(rlimit) = 90mA. The Led turns on but did not latch.
It worked after I factored in the on state voltage of the SCR, forcing me to lower the Rlimit.
rupidust, Mon Mar 13 2006, 02:41AM
You are using 5P4M? That part is under powered. 8Arms and 80A surge.
Here is a schematic that illustrates marginal holding current I(hold) for SCR. When testing mininum condition for Latching, all components Vsupply, Vload, and SCR voltage Von-state need be considered.
Example:
For this SCR I(holding) = 80mA @24v. So why does this not work? 5vsupply - 3vled / 22 ohm(rlimit) = 90mA. The Led turns on but did not latch.
It worked after I factored in the on state voltage of the SCR, forcing me to lower the Rlimit.
Re: Triggering SCR's
Tipp, Mon Mar 13 2006, 10:32PM
Yeah, the 5P4M was for LED experiments
Alright, well, I finally got the sucka working. There were 2 very amatur reasons why it wasnt working, which I shall rate on a scale of stupidness from 1 -10, 10 being the most stupid:
Reason 1: The power supply. I was working with 9 volts at 2.6 amps from a wall wart. All was fine and good, tested it on multimeter to make sure it was outputting correctly etc etc. I decided to hook up a 555 timer w/ LED right quick to see if anything else was wrong with it. Well, got it all hooked up and BAM! Nothing happened I've done this a million times, why isnt it working? I go over all connections and everything looks good. I replace the cap just to be sure. Still nothing. Hook it up to 9 volt battery. Works perfectly. Ok, so it's something with the power supply...
After playing around with it some more, I decide to hook the supply to an inductor [i]. I hear a humming. Uh-oh. Can someone say non-filtered? A medium size [470 uF] cap across the V+ and ground, and suddenly the 555 works. Explanation for the SCR not working with the supply before: because it was so un-smoothed, the 60 Hz got through and was turning the SCR OFF each cycle. Duh!
Stupidness = 7/10. Should have known this beforehand.
Reason 2: Like mentioned above, I was only running 30 mA [for an LED] through it, when the latching current is 400 mA!! A quick change to a crapload of parallel LED's solved this no problem.
Stupidness = 9/10. This was stated right in the datasheet, I might as well be blind
Well, now that I KNOW my beautiful SCR is working, it's time to work on other components for the coilgun. Thanks all for your help! I owe you all milk and cookies
Tipp, Mon Mar 13 2006, 10:32PM
Yeah, the 5P4M was for LED experiments
Alright, well, I finally got the sucka working. There were 2 very amatur reasons why it wasnt working, which I shall rate on a scale of stupidness from 1 -10, 10 being the most stupid:
Reason 1: The power supply. I was working with 9 volts at 2.6 amps from a wall wart. All was fine and good, tested it on multimeter to make sure it was outputting correctly etc etc. I decided to hook up a 555 timer w/ LED right quick to see if anything else was wrong with it. Well, got it all hooked up and BAM! Nothing happened
I've done this a million times, why isnt it working? I go over all connections and everything looks good. I replace the cap just to be sure. Still nothing. Hook it up to 9 volt battery. Works perfectly. Ok, so it's something with the power supply...After playing around with it some more, I decide to hook the supply to an inductor [i]. I hear a humming. Uh-oh. Can someone say non-filtered? A medium size [470 uF] cap across the V+ and ground, and suddenly the 555 works. Explanation for the SCR not working with the supply before: because it was so un-smoothed, the 60 Hz got through and was turning the SCR OFF each cycle. Duh!
Stupidness = 7/10. Should have known this beforehand.
Reason 2: Like mentioned above, I was only running 30 mA [for an LED] through it, when the latching current is 400 mA!! A quick change to a crapload of parallel LED's solved this no problem.
Stupidness = 9/10. This was stated right in the datasheet, I might as well be blind
Well, now that I KNOW my beautiful SCR is working, it's time to work on other components for the coilgun. Thanks all for your help! I owe you all milk and cookies
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