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Dummy load for high current - 2A test load and 3A

SHIN

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Hi.

I have some questions for dummy load:

Can I use dummy load at about 1A of current?
Is there dummy load for high current?

When I set the current of driver (V5, microboost) and the current was near 800mA, the serial diodes(1N4001?) of dummy load became very hot and my multimeter showed the fluctuation of the reading.

I don't know the maximum forward current of the diode(1N4001?) but I wonder if this could distort the reading.

Because the power output of my recent A140s (850mA) showed very high over the other member's. I double-checked all the procedure but couldn't find the reason. I don't think all the two of A140s are freak at the same time.

There must be some reason.....I have little knowledge of electronics.....:(
....but I like to DIY laser.....

Thank you.

SHIN
 
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jupiter8

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Re: Dummy load for high current.

Same question I was going to ask.
 

ZRTMWA

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Re: Dummy load for high current.

Did you put the test load on the red setting and not the blu-ray, as Drlava suggested? Or is ity a custom dummy load?
 

SHIN

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Re: Dummy load for high current.

Hi. ZRTMWA.

I have 3 of dummy loads.
One is made by myself. Two are purchased.
I tested all the three for setting. All 1N4001s were too hot to touch.

I will set the current of next one as drlava suggested. But I heard there is a problem of voltage-drop...
 

SHIN

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Re: Dummy load for high current?

I made my 2A test load today after this thread:

http://laserpointerforums.com/f38/test-load-44348.html

I appreciate HIMNL9 and many members for sharing the information....

It was made with:
7 of 1N5404 (3A, 0.7V voltage drop)
4 of 2W 1ohm resister(=1 of 4W 1ohm resister)
1 of 2W 2.7Kohm resister

It seemed to work fine and the readings were same as that of preset linear driver.
But I have little knowledge about electronics and I wonder if my calculation is right. Please help me.

Is this right? :

[total voltage drop]=[0.7V x number of serial diodes] + [resister voltage drop]
V = I x R
Power = I x V = I x [I x R]
If a driver for 445nm LD(voltage drop 4.1V) will be set to 1A, 4 or 5 of serial diodes(2.8 to 3.5V drop) is needed, because total voltage drop is not 2.8 to 3.5V, but 3.8 to 4.5V.

Though I post the picture of my test load, please don't laugh at a terrible amateur..:yh:

SHIN
 

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drlava

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Re: Dummy load for high current - 2A test load

Hi Shin, your calculations are correct. When you use a 1 ohm resistor, at 1A that in itself gives a 1V drop! because of this, I've started using a 200 milliohm resistor in higher current test loads, instead of 1 ohm. Then, mA = mV * 5
 

SHIN

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Re: Dummy load for high current - 2A test load

Thank you!! drlava.:bowdown:

Now I know the reason of my "freak" 445nm!!
And I can make 3A test load without 16 or 25 of 2W 1ohm resisters..

SHIN

PS) drlava. Would you mind making "v6" that can kill 445nm LD?
 
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chipdouglas

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Re: Dummy load for high current - 2A test load

It's funny how every body doing the exact same thing comes up with so many different results... I used the standard dummy load. 1n4001 diodes and 1ohm resistor and had no over heating problems or meter fluctuations up to 1000ma. i finally decided though to not stress my 445 out and set it at 810.

michael
 

jmgallego

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Re: Dummy load for high current - 2A test load

Hi Shin, your calculations are correct. When you use a 1 ohm resistor, at 1A that in itself gives a 1V drop! because of this, I've started using a 200 milliohm resistor in higher current test loads, instead of 1 ohm. Then, mA = mV * 5
@drlava This great!

I have been thinking about buidling an universal load test like HIMNL9's, but to include the ability to test for 445nm diodes. HIMNL9's test load circuit is describe in http://laserpointerforums.com/f38/test-load-44348.html#post589096.

Changing the 10 diodes to 1N5404 (3A .7V drop) to include the 445nm diode test and using a 200 milliohm resistor instead of the 1 ohm, would the mA = mV * 5 work? If it does, one even could leave the 1 ohm resistor with a jumper bypassing it and have the mA = mV

@ bobhaha: I just select how much diodes i have in serie in the circuit with the jumper, from 2 to 10 ..... here is the schematic



The other resistor is just for be sure that the capacitor at the end of the driver is discharged, when you take it away and attach the real LD ..... it don't influence too much the reading, approximatively 3 mA at max ...... and the clips are for connect the DMM more easy, or the scope.

I also thought to add a pair of GE diodes for the 0,4V step with another jumper, but then done nothing, cause it's almost impossible to find GE diodes that hold an ampere ..... at human prices, at least :p
To something like this:



Will this work? :D
 

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chipdouglas

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Re: Dummy load for high current - 2A test load

my math and electronics are weak.... why use 10 diodes? that will give a voltage drop of 7.

michael.
 

jmgallego

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Re: Dummy load for high current - 2A test load

For future higher current diodes? :thinking:
 
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SHIN

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Re: Dummy load for high current - 2A test load

It is likely that LD will need higher current in the future.

I think high current will make a significant amount of voltage drop at the resister of a test load, and there will be more voltage drop in 1Nxxxx diode.(0.8V, 0.9V...)
And even more, if the temperature of diodes and resister rise, voltage will drop more...

I wish some expert member will make "standard" high current test load and I wish he will show a simple method of using that test load.....

SHIN

PS) Hi. jmgallego.

That's a good idea. I made one as you suggested.
Resistor selector- upper(200milliohm, upto 3A, 5 x V = I), lower(1ohm, upto 2A, V = I)
 

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SHIN

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Hi. jmgallego.

2A/3A test load works fine. Thanks.
Scanty is the voltage drop of 200milliohm resistor of 3A setting.

SHIN
 

jmgallego

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Hi. jmgallego.

2A/3A test load works fine. Thanks.
Scanty is the voltage drop of 200milliohm resistor of 3A setting.

SHIN
Glad that worked for you too. I double checked the readings with those ranges and works great :D
 

bhank

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Alright well I've got a question. Will 1n5399 diodes work for a dummy load for a 445? I couldn't get enough 5404s near by so I looked around. I came across the 5399s and they are rated at 1.5A with a voltage drop of 1.1V at 1.5A. Sound ok?

Also I'll be using a 2W 1 ohm resistor. So my question is really, considering I'll be setting my current to about 1.1A, how many diodes should I be using? Correct me if I'm wrong, I may be thinking too far into this and just confusing myself, but shouldn't I use 4 diodes to give me a voltage drop of 4.4V at 1.5A therefore slightly less at 1.1A.

Again feel free to say whatever lol, like I said I may just be thinking too far into it. I've made test loads in the past I'm just not sure how accurate they were lol.
 
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SHIN

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Hi. bhank.:yh:

Maximum forward current of 1N53xx is 1.5A.
Voltage drop of 1N53xx is 0.9V at 1A.

To set 1.1A with 445nm LD(4.1-4.2V),
[V-drop at diodes 0.9 x 4] + [V-drop at resistor 1.1 x 1] = 4.7V

I think roughly 3 or 4 of 1N53xx is needed.:thinking:

Drlava's microflex v5 can supply maximum 1.2A to 445nm LD, NOT 1.5A.
Drlava's microboost can supply maximum 1.1A to 445nm LD.

SHIN
 

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