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meter help

L

laserhacker

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May 1, 2008
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ok i have built my driver. and i am using 4 aa batterys. when i hook up the meter to check for ma. i get a reading of 42.1 to start. as i lower the res on it i get 195.2 does that sound at all right. or did i build it all wrong
 





I take you mean DDL's driver, if so you can't use 4 AA batteries, you need 5 - 6 AA batteries. Otherwise your circuit will start to drop out from the start.
How are you testing the driver? Are you using the 1 ohm resistor method or are you simply using the current function on your multimeter? And also, how many ohms is the pot you're using?
 
i am using the function on my multimeter. an i have a 25 ohm 3 watt rheostat and 1 10 ohm 1/2w resistor
 
Ok, have you tried turning the rheostat to the lowest resistance? Your driver seems to be working fine but just in case, turn the rheostat to the lowest resistance and measure the mA with your multimeter. Even though the rheostat is letting all the current through, the 2 10 ohm resistors should limit the current to 250mA, so when you measure you should get a reading close or exact to that.
 
i have turned it down. but i see what you are talking about now. i am using only 4 aa i need 5 or 6. to get it up to 250.
and it is right then when i am at max resistance resistance i will get a 40 reading then. if so i get it then. i now need my LD to come. should be here monday
 
i added the 5th battery to it and i am now hitting that 250ma. i have a 20x dvd burner coming. what is the max ma i should push it to.
 
Oh, if you're going to be using a 20x diode then you should have used a 3 ohm resistor instead of the 2 10 ohm resistors.
Hold on a sec. before I go any further, what DVD did you order? I want to see if the one you ordered has a long open can diode in it and not some weird shaped diode.
 
its a sony nec. i think you are the one that told me about it. so i need 2 x 3ohm or am i good with the 2 10's
 
Oh ok, did I tell you about it??? I don't remember. Hold on, oh yeah it was me. ;D Sorry, it's just that I can't remember every person on the forum.

Anyway, the sweet spot for these diodes is 420mA, you achieve that current by using a single 3 ohm resistor. 250mA is not a lot for a long open can so you'd be under powering it.
 
ok i will get the new parts just need the 3 ohm then. i will keep this driver for playing around and testing then. and will make a new one. thank you for the help. great forum here.
 
so can i use the same LM317 driver and just change the resistors to 1 3 ohm. and should i change the batterys to 2 x 3.6v.
 
Yup! same driver, different resistors. And the batteries are up to you, as long as you have at least 6 or 7v
 
ok i will do that then. now my meter i have said it is good for 200ma . to i need to get a new meter to check that i am hitting 420ma. or am i good still. i have a craftman 82344. or did i read that wrong and it is ok
 
laserhacker said:
radioshack has a 3.3K ohm 1/2W 5% Carbon Film Resistor pk/5 is that the right one to use.
Click to expand...
No - that is 3,300 Ohms ! you want 3 Oms total :-) The EASIEST way to get that in radioshack is to go with 5 Ohms - two 20 Ohm resistors in parrellel, or you can go for 2.5Ohms, by doing three ! just match up the color codes, and twist the ends all together, like a big resistor sandwich - that will get you to 2.5 Ohms, and (someone correct me if I am wrong, please) at a normal 1/4 watt per resistor, you would them be at .75 Watts with the resistors like that. When you combine them in series, (again, someone correct my math, please !) you HALVE the resistance, but double the wattage. Unless you are using TINY resistors - that will make a huge honking resistor pack - but shopping at Rat-Shack, you don't have to many choices. If you have a Fry's electronics near you, they sell lower Ohm resistors, as do many, many places online.
 
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