[Gagandeep90]

Hello everyone,

I recently purchased a used 100w 1390 chinese laser cutter. But i knew i had to change the power supply and the tube at the time of the purchase. I ordered a HY-DY13 power supply and a 100w tube that i fitted in but the tube is arcing internally. I also tried to install a Ammeter to the machine to check whats happening with the power as it cuts 3mm acrylic at 6mm/s @ 50%. Any faster than that it wont cut it.

When the Ammeter is connected and i press pulse the needle jumps to max no matter what the power setting is set to. Any help would be greatly appreciated.

[robertk925]

I used these instructions to hook up my ammeter.
LensDigital - How to add ammeter to 50W Chinese laser cutter from eBay

[Gagandeep90]

Thank you for the reply. Thats the same instructions that i followed. But everytime i press pulse the needle jumps to full and the power in the tube is minimum. changing the power on the controller doesnt make a difference to the meter.

[robertk925]

Just to confirm, the ammeter is connected in series with the thin GND return wire from the tube to the PSU?

What is the range of your ammeter?

[Gagandeep90]

Yes. Connected in series with the GND wire from the tube to PSU. Yesterday i tried to connect a analog multi meter to the wire along with the meter on the machine. Now when i set the analog meter to to read at 25 DCmA both the meters work absolutely fine. but as soon as i remove the connection of the analog multimeter the meter on the machine jumps to max again.

I have a spare old tube which i tried to connect as well and test but still does the same. Im guessing its the power supply.

The range on the meter is 0 - 50

[kibrex]

Hello,

I have a 60w laser and it just died less than a year.
I want to ask how you keep the water clean.
Do you cool the tube with distilled water or add some chemistry to it to break it?

Thank you for your help

[robertk925]

Kibrex:

I have used RV (recreational vehicle/mobile home) anti-freeze fluid (which is pink in color) from Camco mixed with distilled water for the last 2 years in a very sunny office and have had no problems with algae or cloudy water.
RV Antifreeze Concentrate - Camco

[robertk925]

Gagandeep90:

Strange, I don't understand how the multimeter could affect the ammeter readings, unless it is adding some sort of resistance to the line? Can you read the amperage correctly with just the multimeter?

[kibrex]

Hello,


do you have a concentrate in the laser or do you have it diluted?


thank you for answer

[robertk925]

I mixed it according to the instructions on the bottle, which I think was either 1:1 or 1:2 concentrate to water.

[Gagandeep90]

Gagandeep90:

Strange, I don't understand how the multimeter could affect the ammeter readings, unless it is adding some sort of resistance to the line? Can you read the amperage correctly with just the multimeter?

Sorry for the late reply. I've made a video of what exactly is happening. The meter only shows this reading when the knob the multimeter is set to DCmA 25. If I set it DCmA 2.5 then it jumps to full again.

Link to video : https://youtu.be/gguo7F3TkVQ

[robertk925]

Helpful video, thanks. I am not an electrical expert, so I don't know how to troubleshoot this. Perhaps some sort of grounding issue? Or a defective ammeter.

[Gagandeep90]

I also think it could be some sort of grounding issue. I am going to take off all the wires and connect them back one by one to check it. will let you know how it goes. i doubt its the ammeter cause if it were it wouldnt work properly when i connect it with the multimeter. lets see. Thanks for all of your help. really appreciate it.

[CitizenOfDreams]

It is possible that your ammeter needs an external shunt resistor. Or maybe it has a bad built-in shunt. Could you post some pictures of your ammeter?

[Gagandeep90]

It is possible that your ammeter needs an external shunt resistor. Or maybe it has a bad built-in shunt. Could you post some pictures of your ammeter?

That is a possibility. This machine came with 2 ammeter because it had 2 tubes inside. But both the tunes were spoilt. So I removed 1 and replaced the 2nd one with a new tube, power supply and changed the card to RDC644XG. The control card was so old that even the Chinese suppliers dint know which one it was.

So far I've tried the following.

1. Replaced new power supply with old one
2. Replaced new tube with old one.
3. Replaced new control card with old one
4. Replaced ammeter with the spare one.
5. Bypassed the EMI filter.
6. Connected a potentiometer.

None of these things were able to fix the issue. The biggest problem is that my tube is not performing the way it should. I can barely cut 3mm acrylic at 4mm/s @ 60% power with the new tube. I've checked my mirror alignments and they are spot on.

The other possibility is that I messed up something in the laser settings on the card. I'm attaching a imagine of the settings if someone can cross reference that with their 100w machine it would be great.

Today I will still try to buy a new ammeter and connect it hopefully that will work.

[CitizenOfDreams]

The ammeter is easy enough to test: connect it to a fresh 9V battery through a 1K resistor. The needle should show around 10mA. If it goes off the scale, you know the shunt resistor is bad.

Also, you mentioned that you tried connecting a multimeter alongside the ammeter. Did you connect it in series or in parallel with the ammeter?

[Gagandeep90]

The ammeter is easy enough to test: connect it to a fresh 9V battery through a 1K resistor. The needle should show around 10mA. If it goes off the scale, you know the shunt resistor is bad.

Also, you mentioned that you tried connecting a multimeter alongside the ammeter. Did you connect it in series or in parallel with the ammeter?

The multimeter was connected in series exactly like the ammeter. I will test the ammeter with the 9v battery tomorrow and post results. Thank you for the help.

[Gagandeep90]

Ok, so I tested the ammeter with the 9v battery and a 1k resistor. They both jump to max. What are the odds of both the meters being spoilt. Placed an order for a new meter. Let's hope things go better this time and it's not something in the machine that's blowing the meters.

Thank you all for the help. I'll post results once I get the new meter.

[CitizenOfDreams]

I guess an arcing laser tube could have blown the shunt resistor inside the ammeter. Since the gauge itself seems to be working, you could in theory rig up an external shunt for it.

[spepin]

It sounds like your ammeter is either lacking an internal shunt, or the shunt is defective. A shunt is like a precision very low value resistor, which current passes through. As current passes through the shunt, it causes a voltage drop across the shunt which is proportional to the amount of current passing through. The panel meter is nothing more than a millivolt meter measuring this minute voltage drop. If you don't have the shunt in place, the meter will peg. When you add another ammeter (in this case, your multimeter) in parallel to the panel meter, the current is flowing through the shunt that is internal to the multimeter, and both meters will read the proper current. I would suggest you check with wherever you purchased the panel meter to see if it requires an external shunt, and if not, then ask them to send you a replacement meter.

Hope this helps.

On edit: I didn't notice the second page of replies, which hit on the shunt being the culprit as well.