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question regarding amperage

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Reloadron

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Using you 5050 RGB LED and looking at a data sheet the forward voltage drops are as follows Red is 2.2 Volts, Green is 3.2 Volts and Blue is also 3.2 Volts. With the 5050 LED it depends which manufacturer's data sheet you look at so the forward voltage drops Vf vary a little. Each color is 20 mA or 0.020 Amp. If you power all three LEDs on the chip with a forward current of 20 mA using correct series resistors you end up with White. Here is a color chart showing the color combinations. Personally I see no merit to using a RGB LED where a plane jane decent bright RED LED should be plenty visible in daylight under a soffit but your choice on that. You can go with a simple single LED as an indicator or have just about anything you want. The project can be very simple or more sophisticated depending on what you want. Going with a 5050 RGB LED running off 12 Volts you get for the Red 12 - 2.2 / .020 = 490 so a 510 Ohm series resistor for the red, Green and Blue 12 - 3.2 / .020 = 440 Ohms so a common 470 Ohm resistor. 1/4 watt resistors are fine.

Ron
 

KevinW

Member
Hi Ron;
I haven't picked the light up yet but it's plug and play, it's a single 12 vdc fixture made for deck lighting and I expect the resistors are built in.
 

Reloadron

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Strips of 5050 LEDs are pretty common with built in resistors for 12 VDC use. If you want to take that route I would get a CT like I linked to earlier and remove the LED taking note which lead is the Cathode. I would replace the LED with a opto-coupler and either directly drive your LED or let the opto coupler drive a transistor or logic level mosfet capable of driving your LED load. Something along those lines. Without knowing exactly what your 5050 LED looks like as in a data sheet it's hard to say exactly.

Ron

Ron
 

Diver300

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LEDs should be driven with a fixed current, not a fixed voltage. The OP is trying to detect a current. With a current transformer, the current is reduced by the turns ratio of the the transformer, so if that is done the're little need to worry about the voltage.
 

ronsimpson

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so if that is done the're little need to worry about the voltage.
Normally yes I agree with you but; He has a LED that is Red, Green and Blue. The three LEDs (in one package) have different voltages. He needs to find a way to force the current to divide three ways. The idea is to aim for 12 volts and use resistors to set the currents. Some how a white LED is not good enough, or red. Also LEDs need DC not AC, the reverse voltage may kill the LED.
 

Reloadron

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The below leads me to believe the resistors to limit current are included.

I haven't picked the light up yet but it's plug and play, it's a single 12 vdc fixture made for deck lighting and I expect the resistors are built in.
I have a string or strip of 5050 LEDs which look like the below image.
RGB Strip.png

Each small section consist of 3 each 5050 LEDs along with the needed resistors. The strip is designed for 12 VDC operation. This particular configuration is common anode wired. Based on what the thread starter mentioned the LED combination he has in mind is already pre wired for 12 VDC. When deck lighting is mentioned I can only assume multiple LEDs in a single package.

Ron
 

Reloadron

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So we are up to post #27 and I am thinking there are some things that we don't know. ReloadRon I am going to leave you in charge. I don't have the time for this.
Gee thanks Ron. :)

Ron
 

KevinW

Member
It was a nice simple device, a resistor in series with the load, and a triac connected across it, which triggered the relay.
Nigel;
I can't quite picture this.
If the gate triggers the triac how is it wired across the resistor or is it wired to one leg of the resistor?
 

KevinW

Member
Ok, thanks.
I have the wiring in place and the light is three colours but I can pick any one of the three.
 

Nigel Goodwin

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I recently had occasion to look at a 'Radon Fan Warning Light', it was from a local school who were complaining it didn't light up, so they didn't know if the fan was working or not. In the event there was nothing wrong with it, except they didn't understand it's function - it actually lights up if the fan stops drawing power - as it used a SPDT relay I rewired it to work as they wished.

It was a nice simple device, a resistor in series with the load, and a triac connected across it, which triggered the relay. It would work just as well in this application, but obviously with a lower value resistor.
OK, sorry about been a bit late, but we had a 3D printer arrive, and got distracted :D

Here's the schematic of the Radon Fan warning light - reduce R1 for higher currents.

The triac was a BTA06-600T, and the relay an RTE24730.

Current Sensor.GIF
 

KevinW

Member
Nigel;
Thanks for taking the time and making the effort to find and post this circuit.
I'll give it a go.
Here is another indicator that I believe uses the display leds in a manner that creates a bridge rectifier.
ammeter
 

KevinW

Member
This is what I went with, light indicates 3.4 amps when block heater is working and drops to 0 when disconnected but the light remains on.
indicator light.JPG indicator light2.JPG
 

Les Jones

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What value resistor did you use for R1 ? If your load takes 3.4 amps it will need to be much less than 15 ohms. If you used 15 ohms you would be applying 51 volts to the gate which would have destoyed the triac. R1 would be disipating 173 watts.

Les.
 

Nigel Goodwin

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What value resistor did you use for R1 ? If your load takes 3.4 amps it will need to be much less than 15 ohms. If you used 15 ohms you would be applying 51 volts to the gate which would have destoyed the triac. R1 would be disipating 173 watts.
Perhaps you should read the posts :D

The 15 ohm resistor was for detecting a fan.
 

Les Jones

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Hi Nigel,
I was assuming that Kevin was using the schematic from post #32 to drive a light but did not reduce the value of R1 to a suitable value as you suggested in post #32

Les.
 

ronsimpson

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Nigel;
Thanks for taking the time and making the effort to find and post this circuit.
I'll give it a go.
Here is another indicator that I believe uses the display leds in a manner that creates a bridge rectifier.
ammeter

Question on that ammeter: what powers the light? When the current goes to zero what powers the light? Do you need to send line voltage to power the light? Is there a battery? The information from China did not answer any of these questions.
 
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