Author Topic: on time  (Read 741 times)

Offline thedoc298

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on time
« on: January 02, 2024, 10:49:10 PM »
I have seen alot of drsstcs interrupters  that have a built in 100us max on time, but I see some act like they are pushing their coils at 100us and yet others, like the one I was just reading said he was running at 1000us and going for 2000us on time. My question is some say 50 to 100us and others are running all over the place. I know what on time is, but why is it wildly different. I know other types of coils could be different but these seem to be drsstc.  Im almost ready to first light my drsstc and one of the  interrupter I have is max 100us on time. (which can be changed) Thank for some insight
« Last Edit: January 03, 2024, 04:41:18 AM by thedoc298 »

Offline flyingperson23

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Re: on time
« Reply #1 on: January 03, 2024, 03:36:45 AM »
Traditionally, you want to set the on time so that the coil turns off right around the OCD trip point. For a coil with higher primary impedance, this will mean higher on time, as current rises slower. Usually, lower current/voltage coils will use higher on time to get the same spark length as a higher current coil. Anything over 400-500us is typically done with pulse skipping. This can get you crazy long arcs (see:
but also makes music sound a lot fuller, especially bass (see:
vs my coil https://youtube.com/shorts/Ns2FfKgEC-c at 1ms with half the onetesla's bus voltage). To do this, you need a pulse skipping driver (or really high impedance primary), good igbt/primary cooling, and beefy igbts for your coil size. Id say set your ocd to at most twice the max continuous current, as opposed to around 4x which is common for lower on time coils. You probably wouldn't want to run high on times with a single to-247 bridge either, due to its low thermal mass. Single board coils like the onetesla often are restricted to <100us as they don't have an OCD, so any longer will allow the current to ramp up high enough to kill the igbts.

Offline thedoc298

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Re: on time
« Reply #2 on: January 03, 2024, 04:45:35 AM »
Traditionally, you want to set the on time so that the coil turns off right around the OCD trip point. For a coil with higher primary impedance, this will mean higher on time, as current rises slower. Usually, lower current/voltage coils will use higher on time to get the same spark length as a higher current coil. Anything over 400-500us is typically done with pulse skipping. This can get you crazy long arcs (see:
but also makes music sound a lot fuller, especially bass (see:
vs my coil https://youtube.com/shorts/Ns2FfKgEC-c at 1ms with half the onetesla's bus voltage). To do this, you need a pulse skipping driver (or really high impedance primary), good igbt/primary cooling, and beefy igbts for your coil size. Id say set your ocd to at most twice the max continuous current, as opposed to around 4x which is common for lower on time coils. You probably wouldn't want to run high on times with a single to-247 bridge either, due to its low thermal mass. Single board coils like the onetesla often are restricted to <100us as they don't have an OCD, so any longer will allow the current to ramp up high enough to kill the igbts.

Wow, thanks for the education, always learning on this site. What value is considered a high impedance  primary. Thanks again
« Last Edit: January 03, 2024, 04:59:02 AM by thedoc298 »

Offline thedoc298

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Re: on time
« Reply #3 on: January 03, 2024, 04:53:41 AM »
Traditionally, you want to set the on time so that the coil turns off right around the OCD trip point. For a coil with higher primary impedance, this will mean higher on time, as current rises slower. Usually, lower current/voltage coils will use higher on time to get the same spark length as a higher current coil. Anything over 400-500us is typically done with pulse skipping. This can get you crazy long arcs (see:
but also makes music sound a lot fuller, especially bass (see:
vs my coil https://youtube.com/shorts/Ns2FfKgEC-c at 1ms with half the onetesla's bus voltage). To do this, you need a pulse skipping driver (or really high impedance primary), good igbt/primary cooling, and beefy igbts for your coil size. Id say set your ocd to at most twice the max continuous current, as opposed to around 4x which is common for lower on time coils. You probably wouldn't want to run high on times with a single to-247 bridge either, due to its low thermal mass. Single board coils like the onetesla often are restricted to <100us as they don't have an OCD, so any longer will allow the current to ramp up high enough to kill the igbts.

The coils are awsom by the way, love lightning. Thanks again for the tech nuggetts

Offline flyingperson23

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Re: on time
« Reply #4 on: January 03, 2024, 05:01:28 AM »
It depends on the size of the coil. With a given secondary Fres, larger MMC and fewer primary turns means lower primary impedance, and vice versa. For example, kaizer's drsstc 3 has a 800nf mmc and 8 primary turns, making it on the higher side for that size. A similar size coil has 400nf mmc and 12 primary turns, making it quite high impedance. Low impedance would be something like 1.5uf mmc. On my medium tesla coil, I started with 300nf mmc, which was too low impedance to get good results, so i reduced it to 100nf and got better results. I'm by no means an expert, but I'd say look at the number of primary turns. <4-5 = low impedance, >7-8 = high impedance. Something like that.
« Last Edit: January 03, 2024, 05:03:23 AM by flyingperson23 »

Offline thedoc298

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Re: on time
« Reply #5 on: January 03, 2024, 07:06:37 AM »
It depends on the size of the coil. With a given secondary Fres, larger MMC and fewer primary turns means lower primary impedance, and vice versa. For example, kaizer's drsstc 3 has a 800nf mmc and 8 primary turns, making it on the higher side for that size. A similar size coil has 400nf mmc and 12 primary turns, making it quite high impedance. Low impedance would be something like 1.5uf mmc. On my medium tesla coil, I started with 300nf mmc, which was too low impedance to get good results, so i reduced it to 100nf and got better results. I'm by no means an expert, but I'd say look at the number of primary turns. <4-5 = low impedance, >7-8 = high impedance. Something like that.

Ok, that is ball park, thanks.

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Re: on time
« Reply #5 on: January 03, 2024, 07:06:37 AM »

 


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