# Printrun doesn't connect when 12 V is on

I'm able to connect to Arduino+RAMPS through USB. I can even check end stops with M119. However, if I plug it to the power supply, my MacBook goes crazy and restart itself! Things I have tried:

• Uninstalled OSX, installed Ubuntu, I get readiness error when PSU is connected.
• Bought a new pair of RAMPS + Arduino.
• Run RAMPS all naked without anything on it.
• Measured PSU output, 12.2 V is stable.

I'm at a point I started to think my MacBook's USB ports are messed up. It is a 2008 model, do you think that would be right to blame?

Update

Tried a new and a very short USB cable: It worked for the first time and I'm able to home all axes, but laptop's trackpad gets very hard to control for some reason. I can only use an external mouse.

• It seems like your update could be posted as an answer, i.e. the solution, to your issue. It sounds a bit like you are having (additional) grounding issues. Are your MacBook and the RAMPS using the same ground, i.e. are they using the same mains circuit? – Greenonline Jun 9 '17 at 17:16
• I don't have any grounding other than the PSU itself which is using a grounded plug. Is there anything else I should connect from RAMPS to PSU for e.g.? All my devices are connected to the same powerstrip which has a current protection. – morevitamins Jun 9 '17 at 17:46
• Sounds ok them, if you are using the same power strip, although, is the PSU on the printer correctly grounded (at the bottom of the unit)? See Upgrading the large delta printer - Power supply output grounding – Greenonline Jun 9 '17 at 18:01
• @Greenonline First time I see this, I don't have that small wire between earth and V-, definitely will try! – morevitamins Jun 10 '17 at 2:52
• @Greenonline you made my day!! It worked and now I'm able to use the longer cable & trackpad jiggering is gone! Please add that as an answer and I would be happy if you share how you discovered PSU wasn't grounded internally as expected. – morevitamins Jun 10 '17 at 3:20

It sounds a bit like you are having (additional) grounding issues1. Are your MacBook and the RAMPS using the same ground, i.e. are they using the same mains circuit?

If you are using the same power strip, then the next thing to check would be that the PSU on the printer correctly grounded (at the bottom of the unit).

From David Crocker's superlative blog, see Upgrading the large delta printer - Power supply output grounding:

### Power supply output grounding

While taking some measurements on my machine, I discovered that the negative side of the output of the 12V LED power supply I am using was not connected to ground inside the power supply as I expected. This presents a safety hazard. So I added an additional wire from ground to the spare negative output terminal of the power supply.

1 Why do I think this? Three reasons:

1. Because grounding issues is one of the most common, and over-looked, problems, in circuit design;
2. I have often had peripheral devices, that use a separate additional power supply, cause a PC laptop to go "haywire" (or worse, die) once connected via RS232/USB (especially charge sensitive devices on the laptop, such as the track pad), due to different, or floating, grounds, and;
3. I had recently read the blog and made special note to check all of my power supplies as they are all terrible, cheap, Chinese knockoffs, and grounding circuits in Thailand are usually non-existant, or, at best, poorly wired up.
• Thank you for the rare knowledge, it really fixed all of my issues! Today's computers may have better USB ports but all they are doing is hiding the problem! This should certainly go to reprap wiki. – morevitamins Jun 10 '17 at 5:39
• About grounding circuits in Thailand are usually non-existant, that seems true for a lot of countries. For example, Vietnam doesn't have 3-pin plugs even for heavy duty home electrical equipment like refrigerators and airconditioners, and the grounding hole in home and office sockets is usually just a dummy to accommodate grounding pins rather than provide grounding. – Samveen Oct 25 '18 at 4:49