Is it safe to use a conductive frame as a ground?

Hi all. I am tinkering with a project that involves using through bore slip rings.

A standard installation will require 1x 16-channel 2A slip ring and 4x 4-channel 2A slip rings with 12VDC.
The 16-channel slip ring (8x live+ground pairs, and 8x signal pairs) will feed into the 4x 4-channel (1x live+ground pair, and 1x signal pair) slip rings. The slip rings will be installed in an aluminium frame.

I was wondering, will it be safe and functional to ground the frame (aluminium) in order to reduce the number of channels required? Effectively, eliminating the need for a ground wire in the slip ring.

Regards,
T

I doubt it.

You are requiring the bearing itself to function as a slip ring. I suspect it is not a reliable slip ring and in fact, the ground is actually the most important connection of all to be reliable. :astonished:

@Paul__B: Hi Paul, here is a link describing what a slip ring is: Slip Ring. The slip ring itself is not a bearing. It is possible that you have a slip ring confused with something else.

Also, a slip ring is not intended to carry any form of load, it merely enables you to maintain electrical (power and/or signal) connectivity in a rotational environment.

Define ground.

Earth ground or Common?

Do you consider this circuit has a ground? |500x204

It does not.

TinManSA: @Paul__B: Hi Paul, here is a link describing what a slip ring is: Slip Ring. The slip ring itself is not a bearing. It is possible that you have a slip ring confused with something else.

My point was that you are confused. I was pointing out that a bearing is not a slip ring!

You need a proper slip ring for the ground connection. If you think that the frame can be used for the ground because both the outer (fixed) and inner (rotating) frames are structurally connected to the bearing(s) and so must be electrically connected, you are asking for trouble. How else to you propose to "save" a ground connection?

Paul__B: You are requiring the bearing itself to function as a slip ring.

I believe this line had me thinking you were confused. I don't think I am confused.

Using the frame as a common ground, I would achieve grounding therefore no need to provide grounding using a channel on the slip ring.

Using the frame as circuit common could produce a situation where there is a voltage difference between ground and circuit common. A situation where a person touching the frame can get shocked.

I completely agree with your remark Idahowalker!!
Added to that, if you have spillage on the frame and leakage to the live, that will cause a dead short.

But do you think, in practice, it could work ?

TinManSA: I completely agree with your remark Idahowalker!! Added to that, if you have spillage on the frame and leakage to the live, that will cause a dead short.

But do you think, in practice, it could work ?

You'll do as you will.

Idahowalker:
Define ground.

Earth ground or Common?

Do you consider this circuit has a ground?

It does not.

Don’t bury the OP with semantics. We have all used “ground” with “common” interchangeably. The only time it is significant is when you are dealing with mains power which has a neutral and earth ground.

Ironically, the circuit only shows an earth ground.

TinManSA:
I believe this line had me thinking you were confused. I don’t think I am confused.

Using the frame as a common ground, I would achieve grounding therefore no need to provide grounding using a channel on the slip ring.

If you do that how do you suppose the connection from the fixed part of the frame gets to the rotating part of the frame to give you a ground on the rotating part? If there’s no connection through a slip ring how else will it get there?

@SteveMann: Thank you for your valued comment, I did not consider myself educated enough to solicit a response, although I always took GND to be the abbreviation for GROUND, and not EARTH or COMMON.

@PerryBebbington: I did mention that the slip ring is a "through bore" (through hole) slip ring, which I presume could have caused of some confusion. Anyway, I use steel ball bearings at the ends of a 10mm threaded (steel) rod which serves as the axle. Both the static frame and the rotating frame is made of aluminium (also referred to as aluminum).

TinManSA: @PerryBebbington: I did mention that the slip ring is a "through bore" (through hole) slip ring, which I presume could have caused of some confusion. Anyway, I use steel ball bearings at the ends of a 10mm threaded (steel) rod which serves as the axle. Both the static frame and the rotating frame is made of aluminium (also referred to as aluminum).

And how is the rotating frame connected to the static frame? Through the bearing. How would electrical current get from the rotating frame to the static frame? Through the bearing.You are trying to use your bearing as an extra slip ring channel. Neither Paul or Perry is confused about how slip rings and bearings work, you are confused about how electrical circuits work.

Years ago I got drawn into a problem that involved a clad welding machine, a very large high current welding machine.

"Clad welding is the process of adding a material to the surface of a component, rather than joining it to another piece. This is helpful in changing the design of, adding a protective layer to, or repairing an existing component".

We were adding a layer of Inconel to a stainless steel tube (316 Stainless Steel). The part rotates as the weld head travels through it. The slip rings were large and multiple rings in parallel because:

Jiggy-Ninja: And how is the rotating frame connected to the static frame? Through the bearing. How would electrical current get from the rotating frame to the static frame? Through the bearing.You are trying to use your bearing as an extra slip ring channel. Neither Paul or Perry is confused about how slip rings and bearings work, you are confused about how electrical circuits work.

You can't have a path to ground through the bearings. Rest assured as pointed out, really bad things will happen. I also saw this once with a large Coachman RV. The engine had a ground strap to the chassis and the transmission had a ground strap to the chassis. Someone left off the engine ground strap so now the engine ground was through the transmission. Eventually the forward bearing and seal of the transmission literally was burned up. Every engine start the path for current flow was through the transmission. Now if you want to use a frame or chassis as ground then have at it but you likely will get some very unwanted surprises. Ron

Jiggy-Ninja: Neither Paul or Perry is confused about how slip rings and bearings work, you are confused about how electrical circuits work.

Yes, I decided to give up after #4. :roll_eyes:

There seems to be so contention here, perhaps there is a misunderstanding of the OP's situation.

Please bear with me with my attempt to simplify the situation.

@TinManSA In your original problem statement you mentioned you have 16 slip rings and I'll guess you would like to move the common connection to your circuit to the frame leaving a slip ring for some other circuit.

Lets assume you have only two sliprings, and you wish to light an LED on the rotating member. You have your power supply (9V battery)

Battery + is on slip ring #1 Battery - is on slip ring #2

The LED is connected to the rotating(?) side of the two sliprings. The LED is illuminated.

Now through so act of god slip ring #2 fails. You say ah ha I can run the Battery - through equipment frame.

You connect Battery + to slip ring #1 Battery - to the equipment frame /structure

On the rotating side you connect the LED+ to slip ring #1 LED- to the equipment frame.

We don't know your equipment structure. Can you tell us how the Battery - gets electrically connected to the LED- ?

Thanks John

JohnRob:
In your original problem statement you mentioned you have 16 slip rings and I’ll guess you would like to move the common connection to your circuit to the frame leaving a slip ring for some other circuit.

Thank you for trying to understand what I am trying to achieve here.

The standard config, using the 16-channel and 4-channel slip rings, all power and signal connections are done through the slip rings (see attachment).

My original question was to determine if I could use the aluminium frames, steel axle and steel bearing (all conductive material) as “common” (GND), thereby freeing up channels on the slip rings.

I trust the attached image will help clear up confusion.

Regards,
Tino

Tino,

Thanks for the image, perhaps it helps others but it does not address what I am trying to get you to understand. Unless I see direct answers to the questions and points raised my me, Paul__B, Jiggy-Ninja, Ron_Blain and clarified by others then I am not going to help any more.

It seems to me that you were hoping we'd all say 'yes, of course, that will be fine'. Only we are not saying it will be fine, now you are trying to tell us we are wrong. What is the point of this? You asked us what we think and we all think pretty much the same thing; you should not do what you are suggesting.

Re-read the points and questions we have all raised and answer them directly, rather than avoiding them.

Good luck with your project.

@Perry:

I am not pushing for "Yes, you can do it" answer. The point of asking a question, in my case at least, is to get an answer and an explanation of why it can not be done.

Instead of asking for clarity, I am confronted with semantics. JohnRob is the only one who has made an effort of trying to understand what I am looking to achieve.

If the answer is NO, at least offer an explanation so that I can learn. Isn't asking questions an integral part of learning ?

Tino

@TinManSA

To the best of my ability I have done as you asked, others have done the same in their own way. I do not think you have dealt with my point nor the same point asked in different ways by other people. If you don't understand what we are saying then ask specific questions about what we have said. Saying you are 'confronted with semantics' does not help us to help you; what specifically has someone said that you do not understand and need clarifying?

I don't think I am the right person to help you.

Good luck.