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Newbie not getting full amps from driver with test load

MMcCubbing

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The title sums things up pretty well, but let me give you some background.

I am pretty much a complete newbie to everything electronic, mechanical, and optical. I have some background in computer programming but have largely stayed out of the hardware side of things. I have built a Lowrider v2, a CNC machine, based on the designs from V1 Engineering. The machine is working well and I have now shifted my focus to adding a laser to it. I am working based on the "The 2.8 watt, $100 Laser Upgrade for MPCNC" guide from Leo69, using an NDB7875 445nm Diode from DTR, and a 3A TTL driver from techhood. The diode is not yet connected as I have gotten stuck calibrating the driver with a test load.

I am using a RABMo 1.4a as the control board for the Lowrider, and the pins on it are outputting the correct signal (0-5V) as I adjust the laser power from 0-255.

I am on the second last page of the guide and have a test load set up based on that guide and am trying to adjust the trimpot to calibrate the driver but can't get it to put out more than 0.4A when it says to be calibrating it to 1.7A. Given that I'm a newbie, I'm assuming that I'm probably missing something obvious but I can't for the life of me figure out what it is.

I can't upload the pictures to the forum as they're too large but here is a link to an album with my driver and test load. (C&P as I don't have the post count to actually link, sorry)
photos.app.goo.gl/UewZdNEgRBLjBmrLA

PS: I did try searching the forums but couldn't find anything relevant.
 



MMcCubbing

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Oh, sorry, is the Google Photos link not working? I can reupload them to IMGUR In the morning and then post them
 

Cyparagon

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The URL works for me, although not elucidating.

This sounds like a classic case of low input voltage. Is your power supply 12V and capable of over 1A? Verify this voltage under load.

Also, drop a diode from your test load. 3 is plenty.
 

MMcCubbing

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I'm using a 12V 6A rated power supply at the moment. Verified the 12V supply at the driver and removed a diode from the test load. Getting virtually the same results other than a 0.01V difference on the test load.
 

94Z28

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I'm using a 12V 6A rated power supply at the moment. Verified the 12V supply at the driver and removed a diode from the test load. Getting virtually the same results other than a 0.01V difference on the test load
Are you sharing Grounds between the PWM signal source and the driver? If not, this will cause issues. I have seen some of these cheap drivers require more voltage than 5V to get max output.

I would do like myself and use a separate adjustable 5V power source to simulate the output and see if it will increase. Share grounds between the 12v power supply, and the 5v power supply and feed the driver with the test load hooked up. See what results you get.
 

MMcCubbing

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The PWM signal is coming from the Rambo board which is currently sharing the power supply with the driver. Nothing else is running off it as I have disconnected the stepper motors and other components.

I don't have a power supply that's 5V other than a USB charger, but I could cut one of my old cables and rig that up to provide the 5V signal instead of the Rambo board and just take Rambo out of the equation.
 

94Z28

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The PWM signal is coming from the Rambo board which is currently sharing the power supply with the driver. Nothing else is running off it as I have disconnected the stepper motors and other components.

I don't have a power supply that's 5V other than a USB charger, but I could cut one of my old cables and rig that up to provide the 5V signal instead of the Rambo board and just take Rambo out of the equation.
That's not gonna really give you any control over the output; it may be full power all the time. I guess you COULD try that, but the point would be to test the PWM and if it functions. Just make sure you check the output of the charger, sometimes they are 5.4v instead of 5.0v. The PWM on my last engraver driver actually took more than 5v to get maximum output due to the MOSFET that was used in the circuit. It has a 12v Control Board.

If you are getting 5v output from Rambo board's output pins then that isn't likely the problem, unless its too little voltage to max out the PWM. Many boards are only capable of a few mA output though, and you should check the 5V Output for sag.
 

Cyparagon

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For troubleshooting purposes, ditch your PWM controller. Use a voltage divider to supply 5V (or use an aux 5V supply) on the TTL pins instead. Also try shorting the TTL pins together - some drivers use an inverted signal here. A picture of said setup may also prove useful.
 

94Z28

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For troubleshooting purposes, ditch your PWM controller. Use a voltage divider to supply 5V (or use an aux 5V supply) on the TTL pins instead. Also try shorting the TTL pins together - some drivers use an inverted signal here. A picture of said setup may also prove useful.
He stated he doesn't have a 5V aux supply and wanted to use a phone charger with cut cables.. I told him it could work; but it won't be adjustable obviously.

If this is a laser engraver there is likely only three pins on the input... TTL/PWM, Ground and +12V
 

MMcCubbing

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Sorry for the delay in testing and getting back. It's just because of who I am as a person :ROFLMAO:

I was able to set up an old 5V 1A USB charger as a constant source for the TTL input on the driver board. With that and the 12V 6A supply running just the driver the maximum output I was able to get from the driver, measured across the resistor in the test load, is 0.89 V when I should, apparently, be getting 1.7 V.

This is much better than before when I was getting 0.4 V but is still almost half of what it should be.
 

Encap

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Contact them people who sold it or who made it. Maybe the 3A TTL is no good- who knows?
Let them know the problem and tell you how to make it work correctly or offer to replace it with one that works.
Would save time and money if they can help.
 
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94Z28

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Are you feeding the driver with a 12v 1 amp capable power source? Otherwise if there's no pot to adjust I'd ask for a refund. The driver isn't setup properly.
 

WizardG

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Can you post the exact driver you're trying to use? Some require jumpers be installed or removed to change the range of current they will output, with the pot for fine tuning. Some, as mentioned above, require more than 5V to get full TTL output. Others have buffering on the TTL input limiting frequency response.
 

Anthony P

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some of those cnc drivers have jumper pins to set output and then a pot for fine tuning.
 

Encap

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Can you post the exact driver you're trying to use? Some require jumpers be installed or removed to change the range of current they will output, with the pot for fine tuning. Some, as mentioned above, require more than 5V to get full TTL output. Others have buffering on the TTL input limiting frequency response.
He posted a link to a photo of it in post #1. OP's photo is here: https://photos.google.com/share/AF1...?key=ejFMRWV4WlVOQW1VSXZ1ZFFYdGhMM3FadUtDY1BR

Appears to be this one from Techhood: https://www.ebay.com/itm/Analogue-T...493673?hash=item3d97e6d9a9:g:SUEAAOSwbEFd10cK
Not much in the way of details in the listing however.
He is better off asking Techhood and having them give instructions for use with his diode and use in general and/or give a replacement than playing a guessing game if nobody knows the definite actual real world answer on LPF.
If it is defective and needs replacement or an entirly different driver he will know faster than any other way from what Techhood says, I would think.
 
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