Re: [amsat-bb] KR400 controller question
Thanks George, I tried it with and without the resistor and couldn't see any difference with the LEDs so wondered if it was just put in to increase the life of the bulb. I'll leave them in and see how we go.
The controllers now look like this adding a splash of colour to the shack. http://www.ukdx.org.uk/tv/rotator/400s.jpg
Paul Sussex Coast. JO00
On 06/01/2019 22:33, W3AB/GEO wrote:
Paul,
It appears that one unit uses 28V to light the bulb & the other uses 14V. If the mod is for the unit that is 14V, leave the resistor in the circuit.
Sent from my two way wrist watch 73 de W3AB/GEO On Jan 6, 2019, at 03:26, Paul <paul@ukdx.org.uk mailto:paul@ukdx.org.uk> wrote:
As both my KR400 controllers have blown bulbs I've modified them to use LEDs as per https://bit.ly/2TzeHud There is however a small difference that I'd like an opinion on as I'm not very electronically minded. Eddie modified his KR-400RC however on my KR-400 controllers there is an additional 100R between the transformer and bulb. What is its purpose and should I leave it in or remove it when adding the diode, limiting resistor and LEDs shown in the mod? CCT grabs showing the difference https://bit.ly/2FbKIo5 Paul Sussex Coast. JO00
On 1/7/19 3:28 AM, Paul wrote:
Thanks George, I tried it with and without the resistor and couldn't see any difference with the LEDs so wondered if it was just put in to increase the life of the bulb. I'll leave them in and see how we go.
The controllers now look like this adding a splash of colour to the shack. http://www.ukdx.org.uk/tv/rotator/400s.jpg
Paul,
Given this circuit:
Vsupply --- 1N4001>| --- ////\ --- LED>| --- "Gnd"
You can calculate the proper resistor value with the formula:
Vsupply - Vf - Vdiode ---------------------- Iled
Vf is the LED forward voltage, Vdiode is the forward voltage of the 1N4001. Putting some numbers in there for a typical application with the CREE C503B-RAN-CZ0C0AA2):
(28 - 0.7 - 2.1) / .020 = 1260 ohm
The absolute maximum rating of this LED is 50mA, so we can round down to a 1.2kohm resistor safely. No need for additional resistors beyond this one.
To add additional LEDs, you can either put them in series and add up all the forward voltages in that equation, or you can go parallel and add pairs of resistor+LED.
Since you've got a half-wave rectifier, you might want to add a capacitor after the 1N4001 to smooth out the ripple (and the obnoxious flickering). A good value would be about 10uF.
A more efficient way to drive LEDs is to use an IC, which can also provide PWM dimming via digital or analog (knob) input.
https://www.maximintegrated.com/en/products/power/led-drivers/MAX1570.html
73,
--- Zach N0ZGO
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Zach Metzinger