Spencerleehorton

48v switch, resistors and cap!
« on: May 23, 2020, 01:57:50 PM »
having trouble with blowing a few leds and to my mind ive got the values right but want to check with you guys.

Im feeding in 48v to DPDT lug, center two lugs are connected and i take a 3.9k off to the + of hte led and off the center lugs i put a 470R resistor which then has a 220uf/63v cap then feeds the two 6.8k resistors to pins 2 and 3.

Why do I keep blowing leds? I've got about 2.9v going to blue led, if i remove the 470R i still keep blowing the resistors?

any diagrams for this? ive taken my arranement form the api-312 48v but just used a 3.9k resistor.
website: www.mohawkstudios.co.uk
email: [email protected]

If it hisses its probably the wrong impedance!!!
Or a snake!!!


PRR

Re: 48v switch, resistors and cap!
« Reply #1 on: May 23, 2020, 03:04:29 PM »
> any diagrams for this?

We should be asking you for diagram. Your text makes sense to you but is not instantly clear to others.

However this all sounds very familiar??? Weren't you burning LEDs about 5 months ago?

Spencerleehorton

Re: 48v switch, resistors and cap!
« Reply #2 on: May 23, 2020, 04:24:37 PM »
Yeah it's taken me this long to get around to try and fix all of them!!!

My little sketch should hopefully help
website: www.mohawkstudios.co.uk
email: [email protected]

If it hisses its probably the wrong impedance!!!
Or a snake!!!

ruffrecords

Re: 48v switch, resistors and cap!
« Reply #3 on: May 23, 2020, 04:35:31 PM »
You circuit should give you 12mA through the LED. Do you really need that much? Try 10K resistor instead which should give you 5mA.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

Spencerleehorton

Re: 48v switch, resistors and cap!
« Reply #4 on: May 23, 2020, 05:11:00 PM »
Ok Ian thank you I'll try that and see what happens!
website: www.mohawkstudios.co.uk
email: [email protected]

If it hisses its probably the wrong impedance!!!
Or a snake!!!

john12ax7

Re: 48v switch, resistors and cap!
« Reply #5 on: May 23, 2020, 05:28:41 PM »
Check the specs,  leds don't often need much current,  1-2 mA can be good enough.

Also the way you have it you are discharging 48V through 470 in the off position.  That's a lot of peak power.  That resistor may not last long either.

Spencerleehorton

Re: 48v switch, resistors and cap!
« Reply #6 on: May 23, 2020, 05:37:01 PM »
Discharging 48v how?
Its disconnected in the off position?

what would be a better config for my neves then?
« Last Edit: May 23, 2020, 05:41:04 PM by Spencerleehorton »
website: www.mohawkstudios.co.uk
email: [email protected]

If it hisses its probably the wrong impedance!!!
Or a snake!!!

john12ax7

Re: 48v switch, resistors and cap!
« Reply #7 on: May 23, 2020, 06:15:41 PM »
In off the cap will still have 48V that will discharge. When you connect the 470 to ground that will be one discharge path.  Along  with the mic and led path.

Edit : on second thought you have the same issue at turn on with the resistor (I'm not a morning person). So you can disregard what I've said.  Just use the right power rating as originally specified.

« Last Edit: May 23, 2020, 06:35:21 PM by john12ax7 »

Spencerleehorton

Re: 48v switch, resistors and cap!
« Reply #8 on: May 23, 2020, 06:57:30 PM »
Part of why I spoke about this was to iron out any kinks, what would be a better config?
website: www.mohawkstudios.co.uk
email: [email protected]

If it hisses its probably the wrong impedance!!!
Or a snake!!!

Spencerleehorton

Re: 48v switch, resistors and cap!
« Reply #9 on: May 24, 2020, 03:56:35 AM »
Is this a better config?

Apart from using a 10k rather than 4.7k or I have some 9.1k as some 48v are a little lower
« Last Edit: May 24, 2020, 04:52:33 AM by Spencerleehorton »
website: www.mohawkstudios.co.uk
email: [email protected]

If it hisses its probably the wrong impedance!!!
Or a snake!!!


Spencerleehorton

Re: 48v switch, resistors and cap!
« Reply #10 on: May 24, 2020, 06:25:59 AM »
I suppose what I'm really asking is what does the 470R resistor do in this config?
Does it limit the current available for the mic to 102ma?
And is this what's having an impact on the current for the led and why they are going pop?
I'm going to order some leds!! And take away the 470R resistor and see if they don't blow!
website: www.mohawkstudios.co.uk
email: [email protected]

If it hisses its probably the wrong impedance!!!
Or a snake!!!

john12ax7

Re: 48v switch, resistors and cap!
« Reply #11 on: May 24, 2020, 07:01:02 AM »
You need that resistor to limit the in rush current,  otherwise your switch may go pop.  There was another thread recently about this. The value should be lower though so it doesn't drop too much voltage. You also don't want C to be too big.

You can do it as attached.  Some typical values you might see are:
R1 = 200
C1 = 100 uF
R3 = 10k to 20k, check your LED datasheet for its current specs.
R2 can be large, like 100k. It provides a DC path to ground,  not always needed,  but good to include imo.
« Last Edit: May 24, 2020, 07:06:26 AM by john12ax7 »

Spencerleehorton

Re: 48v switch, resistors and cap!
« Reply #12 on: May 24, 2020, 07:32:26 AM »
So just to check I got this right!!!
website: www.mohawkstudios.co.uk
email: [email protected]

If it hisses its probably the wrong impedance!!!
Or a snake!!!

JohnRoberts

Re: 48v switch, resistors and cap!
« Reply #13 on: May 24, 2020, 09:46:40 AM »
So just to check I got this right!!!
I didn't immediately recognize what that was in bottom right corner.... (my guess is LED).

The 100k across the cap seems redundant as the LED will discharge the cap down to 2V or less.

JR
Don't only half-ass tune your drums. Visit https://circularscience.com to hear what properly "cleared" drums sound like.

Spencerleehorton

Re: 48v switch, resistors and cap!
« Reply #14 on: May 24, 2020, 11:30:56 AM »
john12ax7 put

R2 can be large, like 100k. It provides a DC path to ground,  not always needed,  but good to include imo.

and ive followed his diagram?

thoughts?
website: www.mohawkstudios.co.uk
email: [email protected]

If it hisses its probably the wrong impedance!!!
Or a snake!!!

john12ax7

Re: 48v switch, resistors and cap!
« Reply #15 on: May 24, 2020, 05:17:17 PM »
Move the ground off of the switch.

The 100k is redundant,  but that is partially the point.  It ensures the cap will discharge,  even  if other things change,  like perhaps the led path to ground is no longer connected.

Spencerleehorton

Re: 48v switch, resistors and cap!
« Reply #16 on: May 24, 2020, 06:09:18 PM »
Ok great stuff, the 200R is to stop the current rush, the 100k provides a drop to gnd if the led blows and I just need to wire the gnd off the switch.
Will give this a go tomorrow, thanks all.
website: www.mohawkstudios.co.uk
email: [email protected]

If it hisses its probably the wrong impedance!!!
Or a snake!!!


 

Related Topics

  Subject / Started by Replies Last post
5 Replies
1159 Views
Last post November 22, 2010, 06:19:36 PM
by Walrus
12 Replies
5576 Views
Last post April 12, 2014, 11:59:14 AM
by Spencerleehorton
23 Replies
4736 Views
Last post August 18, 2012, 01:41:48 AM
by Dualflip
4 Replies
1204 Views
Last post August 16, 2013, 07:12:04 PM
by rocksure