Laser dead short

Hi Ive DIY laser all was fine then when testing a drag chain it pull wires well thats what i thought it did but it did blow apart a DC-DC step down 24vt - 12 to run cnc shield , Nano and 10Wt laser
how do i find the dead short i’m up to my 4th DC-DC thought it was the shield so replaced Still blow the DC-DC im no sparky but should be able to follow instructions ive been with out the laser for 3 weeks now cheers Richard

1 Like

Hi Richard
Can be tricky but this mostly works.
You will need a current limited power supply. Set the current limit to about 1A or something close to the normal load. This should not damage anything except what is already faulty. Disregard DC-DC step down converter and connect to 12V supply point.
Check for hot spot(s) either with finger (avoid ouches) or fast acting temp probe. Like the bare thermocouples often supplied with digital multimeters. A slow probe may miss the trouble spot.
Cheers Bob

1 Like

Hey Richard,

It sounds like there’s a short across the laser if it’s drawing that much current across the diode. Which laser, in particular, are you trying to use? I can see it’s listed as 10W so it should only be drawing ~0.8-1A normally at 12V, that would be nowhere near enough to fry most of those breakout boards. As Bob said, using a current limited supply is the way to go, that way even if you have got a short it’s less likely to damage any of your components.

i have the laser powered [not the D11 wire just the 12vt power] and it fires fine but there is no control as its not connected to the cnc shield
Bob i m not shure what you are saying re thermocouples sorry

the laser is chinese made no name running fo about 8months

A thermocouple is what is inside most temperature probes. In its raw state it is that little welded “blob” on the end of the temperature probe of most digital multimeters. Made of 2 dissimilar metals twisted or welded. Most common would be the “K” type. Very conveniently produces 0ºC at 0V and almost exactly 40 microVolts per degree up or down. Then processed and displayed but you don’t have to worry about all of that as it is a little complicated. There are lots of others which all have their own uses.

If you don’t have access to a current limited power supply you can use a 10Ω to 12Ω resistor in series with 12V. This will need to be 15W or 20W and this WILL get hot so be careful. Another approach would be to use a 10W to 15W incandescent light bulb. In all cases this set up is only to trouble shoot and find the fault.
Cheers Bob

thank Bob am i trying the test with a 10-15W car light globe accross the - & + of the D11 wire and gnd of the laser controll or over the power side my laser has 2 inputs the 12V power and the Yellow and black of the controller via the CNC shield /Nano’s D11
cheers Richard

To find your short circuit the globe should be IN SERIES with the power supply. You are feeding into what looks like a short so the globe limits the current and holds up the power supply until you can find and remedy the problem.
Cheers Bob

cheers that’s what i thought you where saying - the D11 line or controller line [ connects to the system via shield ] if there is a short in the controller line will pop the globe - should i have the 12V power line to the laser as on as well it’s separate power ATM cheers

The globe won’t pop. That is why it is used. It will hold up the power supply until you can find and fix the problem. I am really getting confused as to what you have got connected to what.
You have something destroying 24V to 12V converters right? You apparently have a short circuit on the 12V, right? Have you checked this with a multimeter, probably not. Connect the lot or what part is causing the problem to 12V with the globe IN SERIES. If there is a short the globe will not blow, it will light and limit the current to what should be a safe value. The shorting current should cause something to get hot. This will give you a starting point to find the problem. May even get a wisp of smoke. Just keep your eyes open.
Cheers Bob

yes your right DC-DC’s are blowing that supply’s the CNC shield, Nano and in the past the dc power[12v] to the laser. the laser it’self has 4 wires a + & - 12V line and black and yellow line to cnc shield Gnd pin & D11 also attached to the same shield are the direction and speed control wires to the 3 stepper drivers. yes all lines of power have been checked for voltage the DC-DC is producing 12.1V also running the multi meter on DC10A setting running it in series with the DC DC with the lasers yellow and it shows no numbers at all , all the above was with the lasers independent 12V supply off --checking for continuity across those 2 lines Yellow and black to the CNC shields/laser D11 pins controll shows no breaks in line
will pinch a globe from the car in a hr

Thank Rob for your advice just as i go i removed the laser put 12v power to it [no controller wires connected] just the diode and at the 2cm focus its still burning wood ok so its issue has to be the the board of the laser controller on the laser itself.
ill order a new laser – but i dont think one can buy those boards. cheers and many thanks for your help Richard