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Built my First 445nm Laser But.....

itsmei

itsmei

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I have finished my laser and I am using 7 x 4ohm resistors in Parallel to bring 0.57 of an Ohm. This should work out to about 1.4Amps right? I am measuring from the Multi Meter and the mA being Inputed are only 800mA even though I have a resistance of 0.57. I have a pot to adjust the current, so I can change it when I want. Is this effecting the ohms? I am running about 7.4V from 2 18650 batteries in Series. I forgot to mention thatbits a DIT LM317 driver.
 
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Ghostchrome

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The pot will affect the total resistance. It's just an adjustable resistor, and there will still be a minimum value there even when it's cranked all the way down. I'm assuming that it's hooked up in series with your other resistors? How did you figure 1.4 Amps?
 
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itsmei

itsmei

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Ghostchrome said:
The pot will affect the total resistance. It's just an adjustable resistor, and there will still be a minimum value there even when it's cranked all the way down. I'm assuming that it's hooked up in series with your other resistors? How did you figure 1.4 Amps?
Click to expand...

Woops sorry my Maths went a bit wrong it should actually be 2.19A which I am inputing. As I am using the LM317 the reference voltage is 1.25V. The calculation is 1.25 / 0.57 = 2.19A. The weird thing is I am currently getting 800mA which is less than harf. I did origionally only have 4 x 4ohm resistors to give me 1 ohm but then I thought I would add more resistors in parallel to boost the current up. In the end it only went up about 20mA per resistor. I think I should remove the 3 resistors I added and remove the Pot and see what the Input in mA is. What do you think I should do?

Edit: do you think it is lack of volts?
 
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midias

midias

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itsmei said:
Woops sorry my Maths went a bit wrong it should actually be 2.19A which I am inputing. As I am using the LM317 the reference voltage is 1.25V. The calculation is 1.25 / 0.57 = 2.19A. The weird thing is I am currently getting 800mA which is less than harf. I did origionally only have 4 x 4ohm resistors to give me 1 ohm but then I thought I would add more resistors in parallel to boost the current up. In the end it only went up about 20mA per resistor. I think I should remove the 3 resistors I added and remove the Pot and see what the Input in mA is. What do you think I should do?

Edit: do you think it is lack of volts?
Click to expand...

The LM317 cannot supply 2 amps I bet it is broken or in protection mode while active. Also the resistor may have changed sue to excessive wattage.
 
itsmei

itsmei

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midias said:
The LM317 cannot supply 2 amps I bet it is broken or in protection mode while active. Also the resistor may have changed sue to excessive wattage.
Click to expand...

I first had it set to 4x 4ohm resistors to give me 1ohm. This is about 1.25A but when i looked at the input current it was only 700mA.
 
midias

midias

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itsmei said:
I first had it set to 4x 4ohm resistors to give me 1ohm. This is about 1.25A but when i looked at the input current it was only 700mA.
Click to expand...

Did you use a heatsink? What was your input voltage?
 
itsmei

itsmei

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I have a very big heatsink because it is a Lab Style Host. I have 2x 18650 batteries in Series to give 7.4V. I am using a potentiometer and a a few resistors to equal out at 1ohm. I have two suggestions why it is not working:
1. The pot still have resistance when it is all the way down.
2. I think this is most likely is that there is not enough Volts.
 
itsmei

itsmei

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EDIT: I have done a few tests and the problem is 7.4V is no way near enough. It is not stable, I am attaching a 12V power supply so I can have it either battery powered (portable) or plug a power supply via a port for continual use. I do have a nice heatsink on the lm317 so it won't get hot. At least I can push it to about 1.5A.
 
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AUTO XX

AUTO XX

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Seems like an awful lot of waste voltage to dump.
2 lipos were always good enough for my lm317 builds (I only use lm350 now)
With 12V you have to dump all of that extra voltage as heat.
 
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