5i25 daughter boards 5v com connected to chassis ground ???

More
31 Jan 2017 04:16 - 31 Jan 2017 04:18 #87039 by bevins
I was working on system tonight checking how I wanted to setup my power supplies with the mesa cards whether I use separate power supplies for VIN and field checking the ground and com for noise when the servo's move. I found that the common of the 5v logic power for the boards were tied to ground. That took my floating 5vdc power supply and the com was at chassis ground.

After scratching my head and checking, it seems it is coming from the computer. I checked the shield of the DB25 and it was at ground also. I checked the 7i77 and the 5v com is connected to chassis also.

Is this correct?

I thought what is the point of having a floating power supply if your going to tie it to ground. All along I was checking with the continuity on my fluke. I checked resistance and it seems there is a 10 ohm resistor that I assume is the protection.

Just wondering what the story is with this or am I overthinking this?
Last edit: 31 Jan 2017 04:18 by bevins.

Please Log in or Create an account to join the conversation.

More
31 Jan 2017 07:46 #87041 by tommylight
That is correct, evenif you get a laptop it will have the - or negative tied to ground.
I do understand your concern, as you usualy end up having common ground on almost everything on the machine, but that is the reason why properly done grounding is paramaunt on machines and especialy on plasma cutters.
I have mentioned the importance and the proper way of grounding on several occasions on this forum.
Back to your setup just as added info, i used separate 5V, separate 24V VIN and existing 24V Vfield on the 7i77 and the rest of the boards.

Please Log in or Create an account to join the conversation.

More
31 Jan 2017 10:28 #87050 by rodw
After carefully installing separate 5V and 24V power supplies which appeared to be best practice, I added manual MPG handwheels to my 7i76e, I had to tie the grounds of the 24V and 5V sections together before the encoders would do their magic! At that point, I began to wonder why I wasted money on the separate 5V power supply. Up until that point because it was an ethernet connection, the grounds were isolated. I think everybody is out to get you in this area!

Please Log in or Create an account to join the conversation.

More
31 Jan 2017 13:26 - 31 Jan 2017 13:30 #87059 by bevins
So whats the point of all this isolation stuff. It is all tied back to chassis ground anyway, so say someone swaps line and neutral on a 120vac extension then you have ac potential on your chassis ground, which is basically all your dc power supply grounds including field power.

Its not suppose to be though. I have a powersupply and has no ptential to ground until I connect into the system.
Last edit: 31 Jan 2017 13:30 by bevins.

Please Log in or Create an account to join the conversation.

More
31 Jan 2017 15:27 - 31 Jan 2017 15:29 #87070 by PCW
No, ground is still ground even if you swap line and neutral (just dont swap line and ground)

rodw: for the MPG you dont need to connect field power common and 5V logic common, but the MPG 5V must share the field power common.
if you want the field power isolated from logic power and use a 5V MPG you could power the MPG from a 5V regulator running on field power. (Thisis also true of the 7I76/7I77)
Because the 7I76E is connected by Ethernet, it is completely isolated from the control PC so isolation of 5 and 24V supplies is up to you.


If isolation of 7I77 logic power from the PC is important you can add a 7I77ISOL
Last edit: 31 Jan 2017 15:29 by PCW.

Please Log in or Create an account to join the conversation.

More
31 Jan 2017 18:56 #87086 by rodw

if you want the field power isolated from logic power and use a 5V MPG you could power the MPG from a 5V regulator running on field power. (Thisis also true of the 7I76/7I77)
Because the 7I76E is connected by Ethernet, it is completely isolated from the control PC so isolation of 5 and 24V supplies is up to you.


Thanks Peter,

So given I'm using 24V for field power, are you saying to use a 24 volt to 5 volt power supply to power MPG's to maintain isolation?

I did think that Ethernet had a significant advantage in a noisy plasma environment hence my choice of card so thanks for the confirmation.

Please Log in or Create an account to join the conversation.

More
31 Jan 2017 19:18 #87093 by PCW
If its important to keep it the logic 5V and field power isolated you can do that
but normally there's no great advantage
The following user(s) said Thank You: rodw

Please Log in or Create an account to join the conversation.

More
31 Jan 2017 19:55 #87097 by bevins
Thanks for the info Peter. I think I will leave it like it is unless there is a problem. I was just wandering and couldnt understand it.

Please Log in or Create an account to join the conversation.

Moderators: PCWjmelson
Time to create page: 0.163 seconds
Powered by Kunena Forum