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Brett's post on DRO grounding made me wonder if I should ask a similar question...
I'm doing some mods to my lathe involving a larger controller box to accommodate a typical Chinese RPM display and an amp gauge for the motor draw.
I bought a little 12vdc power supply board to power the RPM display - it's overkill (2A 12vdc supply) but I figure I may someday want to run some other 12v load and there'll be space in the box and capacity on the power supply.
The power supply board has 2 line inputs for AC and 2 outputs for DC.
Any reason I should ground the DC - to the lathe chassis the same way the AC ground is wired - sort of like you would do with 12vdc in a vehicle?
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No, the iron frame is a protective ground that eventually goes to the AC breaker box. ? its purpose is to short a stray wire to the ground. ?it is only for safety.
You do however need a DC ground point. ?And not more than one of them. ? Tie the DC grounds together as one and only one point. ?Likely this is done already. ?So you need to find it. ? Do not daisy chain the grounds. ?They all run to be point that is isolated from the chassis.
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On Dec 29, 2023, at 6:17?PM, chrisser via groups.io <chris.kucia@...> wrote:
Brett's post on DRO grounding made me wonder if I should ask a similar question...
I'm doing some mods to my lathe involving a larger controller box to accommodate a typical Chinese RPM display and an amp gauge for the motor draw.
I bought a little 12vdc power supply board to power the RPM display - it's overkill (2A 12vdc supply) but I figure I may someday want to run some other 12v load and there'll be space in the box and capacity on the power supply.
The power supply board has 2 line inputs for AC and 2 outputs for DC.
Any reason I should ground the DC - to the lathe chassis the same way the AC ground is wired - sort of like you would do with 12vdc in a vehicle?
|
The purpose of "grounding" is to provide a return path for a voltage to a safe place to keep a human from suffering harm - pretty simple.
The AC main ground should always be connected to the frame of the machine. The motor may be double insulated and if might be nearly impossible for AC line voltage to appear on a metal surface, but just in case, ground the machine to the AC ground pin.
The 12v supply - it should not be connected to the AC ground. You should isolate your boards so that they don't contact the machine ground. If you have small signals that need to be protected, use shielded cable and connect the shield to 12 return (minus) on both ends of the cable.
Brett's post on DRO grounding made me wonder if I should ask a similar question...
I'm doing some mods to my lathe involving a larger controller box to accommodate a typical Chinese RPM display and an amp gauge for the motor draw.
I bought a little 12vdc power supply board to power the RPM display - it's overkill (2A 12vdc supply) but I figure I may someday want to run some other 12v load and there'll be space in the box and capacity on the power supply.
The power supply board has 2 line inputs for AC and 2 outputs for DC.
Any reason I should ground the DC - to the lathe chassis the same way the AC ground is wired - sort of like you would do with 12vdc in a vehicle?
--
Buffalo John
|
Chris's advice is useful if you have high speed signals or analog signals that need to be protected from noise. If I am not careful, I will ignite a signal integrity war. Having been a EE designing high speed systems used on mobile platforms, it is easy to explain things that make it seem much more difficult to do well. In Chris's advice - you will want to make sure all users of the 12vDC signal get a direct pair of wires from the power supply and yes, you want to have no daisy chains of the supply wires. Also, you will note that I do not refer to the DC minus as "ground" - it is the return and we want to make sure we isolate it from the AC ground.
Always keep the AC side isolated from the DC side.
No, the iron frame is a protective ground that eventually goes to the AC breaker box. ? its purpose is to short a stray wire to the ground. ?it is only for safety.
You do however need a DC ground point.? And not more than one of them. ? Tie the DC grounds together as one and only one point.? Likely this is done already.? So you need to find it. ? Do not daisy chain the grounds.? They all run to be point that is isolated from the chassis.
Brett's post on DRO grounding made me wonder if I should ask a similar question...
I'm doing some mods to my lathe involving a larger controller box to accommodate a typical Chinese RPM display and an amp gauge for the motor draw.
I bought a little 12vdc power supply board to power the RPM display - it's overkill (2A 12vdc supply) but I figure I may someday want to run some other 12v load and there'll be space in the box and capacity on the power supply.
The power supply board has 2 line inputs for AC and 2 outputs for DC.
Any reason I should ground the DC - to the lathe chassis the same way the AC ground is wired - sort of like you would do with 12vdc in a vehicle?
--
Buffalo John
|
I once had to tell the builders of Palo Verde?#2 that they had to bring everything?to a single point. "Star" grounding! "But that's miles!"? ?Bill
Chris's advice is useful if you have high speed signals or analog signals that need to be protected from noise. If I am not careful, I will ignite a signal integrity war. Having been a EE designing high speed systems used on mobile platforms, it is easy to explain things that make it seem much more difficult to do well. In Chris's advice - you will want to make sure all users of the 12vDC signal get a direct pair of wires from the power supply and yes, you want to have no daisy chains of the supply wires. Also, you will note that I do not refer to the DC minus as "ground" - it is the return and we want to make sure we isolate it from the AC ground.
Always keep the AC side isolated from the DC side.
No, the iron frame is a protective ground that eventually goes to the AC breaker box. ? its purpose is to short a stray wire to the ground. ?it is only for safety.
You do however need a DC ground point.? And not more than one of them. ? Tie the DC grounds together as one and only one point.? Likely this is done already.? So you need to find it. ? Do not daisy chain the grounds.? They all run to be point that is isolated from the chassis.
Brett's post on DRO grounding made me wonder if I should ask a similar question...
I'm doing some mods to my lathe involving a larger controller box to accommodate a typical Chinese RPM display and an amp gauge for the motor draw.
I bought a little 12vdc power supply board to power the RPM display - it's overkill (2A 12vdc supply) but I figure I may someday want to run some other 12v load and there'll be space in the box and capacity on the power supply.
The power supply board has 2 line inputs for AC and 2 outputs for DC.
Any reason I should ground the DC - to the lathe chassis the same way the AC ground is wired - sort of like you would do with 12vdc in a vehicle?
--
Buffalo John
|
Lots of folks don't get that a good ground is alot like a good
motorcycle helmet . Ya really need one . I could just see a bean
counter lookin to cut cost & sayin ya don' need that many
grounds from everything? .
animal
On 12/29/23 6:52 PM, Bill Williams
wrote:
toggle quoted message
Show quoted text
I once had to tell the builders of Palo Verde?#2
that they had to bring everything?to a single point. "Star"
grounding! "But that's miles!"? ?Bill
Chris's advice is useful if you have high speed signals
or analog signals that need to be protected from noise. If
I am not careful, I will ignite a signal integrity war.
Having been a EE designing high speed systems used on
mobile platforms, it is easy to explain things that make
it seem much more difficult to do well. In Chris's advice
- you will want to make sure all users of the 12vDC signal
get a direct pair of wires from the power supply and yes,
you want to have no daisy chains of the supply wires.
Also, you will note that I do not refer to the DC minus as
"ground" - it is the return and we want to make sure we
isolate it from the AC ground.
Always keep the AC side isolated from the DC side.
No, the iron frame is a protective ground that
eventually goes to the AC breaker box. ? its purpose is
to short a stray wire to the ground. ?it is only for
safety.
You do however need a DC ground point.? And not
more than one of them. ? Tie the DC grounds together
as one and only one point.? Likely this is done
already.? So you need to find it. ? Do not daisy chain
the grounds.? They all run to be point that is
isolated from the chassis.
Brett's post on DRO grounding made me wonder
if I should ask a similar question...
I'm doing some mods to my lathe involving a
larger controller box to accommodate a typical
Chinese RPM display and an amp gauge for the
motor draw.
I bought a little 12vdc power supply board to
power the RPM display - it's overkill (2A 12vdc
supply) but I figure I may someday want to run
some other 12v load and there'll be space in the
box and capacity on the power supply.
The power supply board has 2 line inputs for AC
and 2 outputs for DC.
Any reason I should ground the DC - to the lathe
chassis the same way the AC ground is wired -
sort of like you would do with 12vdc in a
vehicle?
--
Buffalo John
|
I like to make a distinction between the use of ¡®ground¡¯ and DC return patch. ? It is simple. ?¡°grounds¡± do not carry current. ?For example, the rounded shield in a cable is always at zero volts and never carries current. ?There very well may be a so-called ¡°negative¡± wire in the cable that acts as a return path and does in fact carry current. ?You might be inclined to ask ¡°what is the difference¡±? ? Making the distinction between ¡°carries current¡± and ¡°never carries current¡± helps you keep it conceptually straight.
AC house wire has this same concept. ?In the common three-prong power plug (in the US) two conductors carry power, or current. and we know that one of them is connected to a grounded bus bar inside the breaker box. ?So isn¡¯t this ¡°neutral wire¡± a ¡°ground¡±? ? No, because it carries current. ? The third wire that is green or bare is a true ground and normally caries no current. ? ?DC grounds are not much different from AC grounds if you think in terms of ¡°current, no current¡±.
Note that in both AC and DC we usually tie one of the power wires to the ground at one and only one point.
An informative experiment is to put an AC volt meter across the neutral and ground of a wall socket. ?If the circuit is suplyiing power there will be a voltage on the meter. ?Yes, even if the neutral and ground are connected at the breaker box. ? All conductors have resistance and it is simply Ohm¡¯s law. ? Return paths are rarely at zero volts.
None of this matters in a simple Lathe. ?But some day you might want to do a CNC conversion and add some motors to the hand cranks. ?I did this to my HF mini-mill. ? You pretty much have to get this right if you are mixing high power motoers and computer electronics in the same box.
?
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On Dec 29, 2023, at 6:52?PM, Bill Williams <BWMSBLDR1@...> wrote:
I once had to tell the builders of Palo Verde?#2 that they had to bring everything?to a single point. "Star" grounding! "But that's miles!"? ?Bill Chris's advice is useful if you have high speed signals or analog signals that need to be protected from noise. If I am not careful, I will ignite a signal integrity war. Having been a EE designing high speed systems used on mobile platforms, it is easy to explain things that make it seem much more difficult to do well. In Chris's advice - you will want to make sure all users of the 12vDC signal get a direct pair of wires from the power supply and yes, you want to have no daisy chains of the supply wires. Also, you will note that I do not refer to the DC minus as "ground" - it is the return and we want to make sure we isolate it from the AC ground.
Always keep the AC side isolated from the DC side.
No, the iron frame is a protective ground that eventually goes to the AC breaker box. ? its purpose is to short a stray wire to the ground. ?it is only for safety.
You do however need a DC ground point.? And not more than one of them. ? Tie the DC grounds together as one and only one point.? Likely this is done already.? So you need to find it. ? Do not daisy chain the grounds.? They all run to be point that is isolated from the chassis.
Brett's post on DRO grounding made me wonder if I should ask a similar question...
I'm doing some mods to my lathe involving a larger controller box to accommodate a typical Chinese RPM display and an amp gauge for the motor draw.
I bought a little 12vdc power supply board to power the RPM display - it's overkill (2A 12vdc supply) but I figure I may someday want to run some other 12v load and there'll be space in the box and capacity on the power supply.
The power supply board has 2 line inputs for AC and 2 outputs for DC.
Any reason I should ground the DC - to the lathe chassis the same way the AC ground is wired - sort of like you would do with 12vdc in a vehicle?
--?
Buffalo John
|
chris wrote:
> I like to make a distinction between the use of ¡®ground¡¯ and DC
> return patch. It is simple. ¡°grounds¡± do not carry current. ...
Agreed -- that's an excellent way to think about it, and a good way to
describe it to others.
> None of this matters in a simple Lathe. But some day you might
> want to do a CNC conversion and add some motors to the hand cranks.
> I did this to my HF mini-mill. ...
Have you written that conversion up, or do you have a pointer to
someone else's similar conversion? I have a home-made CNC mill
(running LinuxCNC), which is capable of cutting wood, and some
non-melting :-) plastics. It's very satisfying to use, but I'd love
for it to be more capable. Always seemed like converting a "real"
mill would solve a lot of problems.
paul
=----------------------
paul fox, pgf@... (arlington, ma, where it's 42.1 degrees)
|
Thanks for the advice everyone.? Makes sense to me now. Have another question, this time about AC. I found a wiring diagram that matches what I see in my old Speedway/Homier.? I noticed the AC fuse is on the white/neutral wire.  So I guess I get that from an overload perspective, it doesn't matter which leg the fuse is on.? But if the overload is caused by a partial short, it seems to me that the chassis is still attached to AC ground, which eventually is bonded to neutral.? And, assuming the emergency switch isn't disconnected, the black hot is still hot even when the fuse is blown.? This seems sorta dangerous to me, especially if the outlet is something like the 20amp circuits in my garage.? Isn't there some small danger that the right fault that was larger than necessary to blow the 10amp fuse and smaller than necessary to blow the 20amp breaker would potentially energize the chassis?? This is the type of thing that would be addressed by a GFCI breaker I suppose. I'm replacing the fuse with a compatible circuit breaker and lengthening some of the other wires.? Should I move it to the other side of the AC circuit while I'm at it?
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RE:? fuse on the neutral side.? There might be a couple of reasons why it's on that leg.? The first is that the fuse is user-replaceable so it's less dangerous in terms of inadvertently coming in contact with AC when replacing a blown fuse.? The second is that the controller may be designed so that the emergency switch opens up when the controller loses power (as in, when the fuse opens up).
A third is that the schematic you've got is incorrect.? It wouldn't be the first time.
These are just guesses on my part.?
Mark
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The fuse must be on the hot leg. You can fuse both L and N, but if the fuse blows in that diagram and the emergency switch is engaged (either from failure on the switch or re-engagement) then line voltage flows to the circuit. While the N return is opened by the fuse, shorting from L to the chassis will let current flow.
Always have fuses or breakers on the L side.
RE:? fuse on the neutral side.? There might be a couple of reasons why it's on that leg.? The first is that the fuse is user-replaceable so it's less dangerous in terms of inadvertently coming in contact with AC when replacing a blown fuse.? The second is that the controller may be designed so that the emergency switch opens up when the controller loses power (as in, when the fuse opens up).
A third is that the schematic you've got is incorrect.? It wouldn't be the first time.
These are just guesses on my part.?
Mark
--
Buffalo John
|
The schematic that came with my Micromark/MicoLux #84631 7x16 (purchased in 2014) shows the fuse on the Line:  I can't think of any reason it would be otherwise: protecting the neutral and not the hot is bad practice. The fuse is downstream of the power switch and the hot contact for the fuse is at the bottom of the fuse holder so the only way you could touch the hot side would be to stick something into the holder; the holder is designed to protect you from touching the fuse until it is completely out of contact with the circuit: 
|
The purpose of a fuse is to protect the wires and prevent a fire. ?In that case it does not matter where the fuse is. ? As for AC electrical safety that is the job of the breaker box. ? New construction requires GFI and ARC prevention breakers in the panel box. ?Yes, these cost $100+ each but that is the current standard and they work well. ? If you have a new up to code system you can be in the bath tub and drop the hair drier in and be fine, even with no GFCI outlets.
In your garage, if it is an older building, you would not have the new-stile breakers, but you would be required to have GFCI outlets installed. ?Again don¡¯t worry, you can put paper clips into a GFCI and not burn your fingers. ?If the lathe is in the garage and the garage has GFCI, you are 100% safe even if standing in a pool of water. ? If the garage is from the 1960¡¯s and lacks GFCI, then spend $20 and buy a new outlet. ? Or spend $100 and replace the breaker.
Again fuses are there to protect the wire and prevent it from melting, ?That is it. ?You should have a fuse on the DC side of any DC power supply. ?The fuse is sized to be less than the ampacity of the wire.
Why is this? ?Because it only takes a few milliamps to kill you. ?That 5 amp fuse will blow and 5,000 milliamps but you are dead at 100 milliamps. ? ?So if you are worried about electrocution, use GFCI, and if you are worried about a fire use a breaker of a fuse.
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On Dec 30, 2023, at 6:21?AM, chrisser via groups.io <chris.kucia@...> wrote:
Thanks for the advice everyone.? Makes sense to me now.
Have another question, this time about AC.
I found a wiring diagram that matches what I see in my old Speedway/Homier.? I noticed the AC fuse is on the white/neutral wire.
<Lathe wiring.jpg>
So I guess I get that from an overload perspective, it doesn't matter which leg the fuse is on.? But if the overload is caused by a partial short, it seems to me that the chassis is still attached to AC ground, which eventually is bonded to neutral.? And, assuming the emergency switch isn't disconnected, the black hot is still hot even when the fuse is blown.? This seems sorta dangerous to me, especially if the outlet is something like the 20amp circuits in my garage.? Isn't there some small danger that the right fault that was larger than necessary to blow the 10amp fuse and smaller than necessary to blow the 20amp breaker would potentially energize the chassis?? This is the type of thing that would be addressed by a GFCI breaker I suppose.
I'm replacing the fuse with a compatible circuit breaker and lengthening some of the other wires.? Should I move it to the other side of the AC circuit while I'm at it?
|
Remember when replacing fuse there three basic types standard,? slow blow and fast blow.?
Slow blow is use for motors and welders.
Fast is used on electronics.? Check with manufacturer to see witch use.?
Dave?
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On Dec 30, 2023, at 6:11?AM, Paul Fox <pgf@...> wrote:
chris wrote:
I like to make a distinction between the use of ¡®ground¡¯ and DC
return patch. It is simple. ¡°grounds¡± do not carry current. ... Agreed -- that's an excellent way to think about it, and a good way to
describe it to others.
None of this matters in a simple Lathe. But some day you might
want to do a CNC conversion and add some motors to the hand cranks.
I did this to my HF mini-mill. ... Have you written that conversion up, or do you have a pointer to
someone else's similar conversion? On the electrical and computer side, it is just LCNC with three stepper motors, So the LCNC documentation applies. But on the mechanical side, there is custom-made parts that fit the motors to the HF mini mill. These are VERY specific to the exact mill because screw holes have to line up. As it turns out converting a mill is not hard. You don¡¯t need to make strong cast iron parts as the motor mount only has to handle the moter¡¯s torque reaction. A 4 Newton meter motor can only push with 4 newton meters of force on the motor mount. 3D-printed plastic is strong and rigid enough to handle that. But, that style of conversion where you put motors on existing hand wheel makes the CNC machine only as good as the manualy machine because you are keeping the old lead screws and nuts and keeping all their slop and backlash. A better conversion would replace the lead screws with ball screws that have close to zero backlash. I did replace the Z axis system with a ball screw because the Harbor Freight Z system is very poor. Yes it is written up in the CAD files. Here is a render from CAD. If anyone wants I can post a link to CAD files that could be turned into 3D prints. The X and Y axis are obvious from the picture but the Z axis is a complete replacement. You can see that the ball screw is stationary. It does not rotate. The ball nut spins and there is a big thrust bearing under it that takes the full weight of the machine head. When I first started, I figured I would do the conversion using plastic parts, then use the mill to make better parts from metal. But the plastic seems to be mostly good enough (just one part has too much flex) I have a home-made CNC mill
(running LinuxCNC), which is capable of cutting wood, and some
non-melting :-) plastics. It's very satisfying to use, but I'd love
for it to be more capable. Always seemed like converting a "real"
mill would solve a lot of problems.
paul
=----------------------
paul fox, pgf@... (arlington, ma, where it's 42.1 degrees)
|
The fuse can only protect when there is only one path for a return current and fusing N does not protect L from returning on GROUND. Yes, it does matter where the fuse is.
The purpose of a fuse is to protect the wires and prevent a fire.? In that case it does not matter where the fuse is. ?
--
Buffalo John
|
Correct, it DOES matter that the fuse goes on the HOT side.
You essentially have one in, and two outs.? Fusing one of the outs is not doing you any favours.
In this case you can blow the fuse, and power is still going through your device - that can cause much excitement if the device isn't grounded, or even if it is (hot chassis and all that jazz).
And for the love of god don't put fuses on both the live & neutral.? (And yes, I've seen fused earths, gotta cover all the bases to be extra extra safe, y'know.? Gah. See)
Tony
The fuse can only protect when there is only one path for a return current and fusing N does not protect L from returning on GROUND. Yes, it does matter where the fuse is.
The purpose of a fuse is to protect the wires and prevent a fire.? In that case it does not matter where the fuse is. ?
--
Buffalo John
|
My whole life I have operated on the principal of a fuse is the first thing inline on the positive side after the source, switch, to the consumers. In some cases, DC, there may be a large fuse inline from source, switch or battery, that then branches off to other consumers. And those lines that go into separate consumers all have their own lower rated fuses. But never have I heard of fuses being in the return side or the negative side. Even though power, DC , runs from neg to plus side. Anyway, we are talking about the basic 120 circuit. I just looked up the circuit in my micro mark 7x16 lathe and sure enough, the fuse is located just after the switch on the power side.
george
On Sunday, December 31, 2023 at 06:50:44 PM PST, Tony Smith <ajsmith1968@...> wrote:
Correct, it DOES matter that the fuse goes on the HOT side.
You essentially have one in, and two outs.? Fusing one of the outs is not doing you any favours.
In this case you can blow the fuse, and power is still going through your device - that can cause much excitement if the device isn't grounded, or even if it is (hot chassis and all that jazz).
And for the love of god don't put fuses on both the live & neutral.? (And yes, I've seen fused earths, gotta cover all the bases to be extra extra safe, y'know.? Gah. See)
Tony
The fuse can only protect when there is only one path for a return current and fusing N does not protect L from returning on GROUND. Yes, it does matter where the fuse is.
The purpose of a fuse is to protect the wires and prevent a fire.? In that case it does not matter where the fuse is. ?
--
Buffalo John
|
Breaking the high side line and not the neutral was painfully demonstrated to me years ago. My M-in-L needed me to drill a hole and handed me her ancient Sears 1/4" all metal drill. When I let go of the power switch I got 115 VAC to the hand. She that happened often. It had the old two wire cord without a polarity plug. 50-50 chance the neutral was being switched and a huge buildup of copper/grease inside the case caused a low resistance to the case. When plugged in and used it was possible to energize the case. Didn't take me long to put a new three wire card on that beast. I would have tossed it but she was frugal to a fault.
|
Appreciate everyone's thoughts.
On the diagram I posted, that emergency switch has traditional spade connectors. So one easy fix is to just swap the white and black connectors, putting the fuse on the hot leg. That puts the potentiometer switch on the neutral, which I guess isn't all that big a deal.
However, I plan on keeping the orientation of the two wires to the emergency switch and moving the fuse (breaker) to the hot side anyhow as it just makes more sense to me. Will revise the diagram for my needs going forward and stick a copy in the control box so I can't loose it.
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On Monday, January 1st, 2024 at 8:53 AM, Don Burns <donaldgburns@...> wrote:
Breaking the high side line and not the neutral was painfully demonstrated to me years ago. My M-in-L needed me to drill a hole and handed me her ancient Sears 1/4" all metal drill. When I let go of the power switch I got 115 VAC to the hand. She that happened often. It had the old two wire cord without a polarity plug. 50-50 chance the neutral was being switched and a huge buildup of copper/grease inside the case caused a low resistance to the case. When plugged in and used it was possible to energize the case. Didn't take me long to put a new three wire card on that beast. I would have tossed it but she was frugal to a fault.
|
chrisser
BuffaloJohn
davesmith1800
