Combo VDC / Amp Meter

[oskar270]

I'm building a cnc and I want to install in the control panel a combo DC Volts / Ampmeter.


My knowledge in electrical is limited; I did use before a VDC meter and the connections to the power supply unit was very easy. But the Ampmeter seem difficult for me.


I will have a 36VDC / 9.7A power supply unit which will feed 4 stepper motor drivers and each driver is 3A


I don’t know which is better to see; that is the Amps on the drivers or just in the power supply unit?


I will purchase the combo meter from ebay


Thank you

 

[KeepItSimpleStupid]

My question is why?

I've worked on a RF transmitter and an Jeol Scanning Electron Microscope. Both had meters with a selector switch that would help you troubleshoot.

If you use this on a stepper, the current is going to pulse, unless you use a TRMS (AC+DC) meter, not TRMS (AC). These meters are tough to search for. 12 VDC measured with a TRMS (AC+DC) meter will read 12 rather than zero, which is the AC component.

I dont really want to get into a True RMS discussion, but I will if I have to.

I doubt, the meter would be useful.

However, I will suggest how you might do this:

Use an Alegro Hall Effect sensor for the current and for any voltages you need to read, you divide it down to something manageable.

Or, you could just install the current sensors and a selector switch and banana jacks to attach a meter too. So, if you want to check something use an auto-ranging DVM.

Here, would be an example sensor. Note, you will need a 5V power supply. The cool thing about this sensor is that the output is isolated.

So, I'm trying to dissuade you and I'm attempting to give you a couple of alternatives, but a LED light that the supply is on is probably fine.

The problem is the current when using stepper motor is going to be really difficult to measure, both accurately and hooking it up.

Not sure why you think you need it?

 

[oskar270]

Thank you for the help
A lot of people with cnc machines have a Volt / Ampmeter and don’t know why but since I will purchase one I was thinking it may a good idea to connect both (Volt meter and Ampmeter)



I understand what you say about the stepper motors and I agree but how about if I was to connect the meter to measure the Amps from the power supply only?

 

[KeepItSimpleStupid]

A voltmeter/Ammeter for the spindle motor is probably the only place it makes any sense at all because it gives you a way to calculate motor load.
The product of V and I, but them again, you have the waveform effects of the speed control unless you use an AC_DC TRMS meter.

I understand what you say about the stepper motors and I agree but how about if I was to connect the meter to measure the Amps from the power supply only?

Again, TRMS (AC+DC) is the way to go to do it right.

Take a look at this 1973 article, http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=7&ved=0CEsQFjAG&url=http://www.hparchive.com/Bench_Briefs/HP-Bench-Briefs-1973-11-12.pdf&ei=JJtwUrqqD8rJsQSJ04GYAw&usg=AFQjCNHhhAnlNYed0UD31HoibsOWA9PXSg&bvm=bv.55617003,d.cWc&cad=rja

In particular, AC measurement with DC offset. There are meters that will do the computation for you.

Here ya go: **broken link removed**

 

[oskar270]

Thank you for the links, will have to study to understand

 

[KeepItSimpleStupid]

I took a look at Fluke's website and found that the 287 and 289 handheld meters will do those AC+DC measurements. The meters are really pricey or way too expensive.

An alternative is to roll your own: RMS to DCconverter: https://www.analog.com/static/imported-files/tutorials/MT-081.pdf

The DC voltages are constant. As I said earlier, if you could just put a set of binding posts and a rotary selector switch , it leaves options such as using a scope. Ripple and value are the two things you usually check on a power supply.

You could build the CNC with servo or stepper motors, but most low cost systems are stepper. Not sure what kind of motor your planning to use for the spindle?

 

[oskar270]

As I said in my 1st post, my knowledge in electrical stuff is very limited and obviously I can not read electrical schematics. However I have done a lot of electrical / electronics work successfully by asking questions in various forums and been very careful. Building my own RMS to DC converter is not a thing I would like to do right now because I'm looking for a simple Ampmeter like many cnc builders are using.



Driving the cnc I'm using stepper motors which are common for hobby / commercial use. For the spindle I will be using a Delta VFD, M series, 0.75kW, 110VAC

 

[KeepItSimpleStupid]

Ever thought about using one of these: http://www.p3international.com/products/p4400.html for the spindle? Place it at the input of the speed controller at the 120 V side.

They are about $20.00.

If you really wanted to, you could put one on the input to the stepper motor power supply. A power supply does have an efficiency, so you can take that into account,

Power supply efficiencies can range from about 80 to 98%.

What is the reason for the voltmeter/ammeter for the X-Y table?

Pin/Eff = Pout

So if the efficiency = 80% then Pin/0.8 = Pout; Pin is measured on the 120 V side.

At the same time, it pretty cheap.

 

[oskar270]

Nice this Kill a Watt gadget but no good for my needs, thank you. My cnc is for hobby use and will not be used often to justify power savings



Looking at ebay to get a Voltmeter, I noticed that most are combo meter (V & A) and since the price is the same for all, about $14 shipping included, I said why not? However reading the Amps I don’t know what it will tell me but eventually I will find out LOL.



When you have the time, is it possible to answer my questions in my post #1 in plain language? Like the red wire goes there, the Yellow wire etc. Looks like there is a variety of combo meters, some with 3 wires, some with 5 wires, some with 2 power sources and I don’t know the difference

 

[KeepItSimpleStupid]

Nice this Kill a Watt gadget but no good for my needs, thank you. My cnc is for hobby use and will not be used often to justify power savings

You TOTALLY missed my point. You just set it on on the power mode and I think your done. I don;t care one bit about saving energy.

However reading the Amps I don’t know what it will tell me but eventually I will find out LOL.

This is true. Where I worked, we used simple AC meters basically to keep an eye on the process. The voltages were repeatable, but power and current were not correct. We did experiment with an AC power meter to measure phase angle fired AC power for 30 VAC and 40 A. This was until I persuaded the company to totally change the technology to a DC power supply. We really would have liked a power meter on the power supply. You can get these today. It also saved quite a bit of rack space, We had a panel with a temperature meter, autotransformer, voltmeter and current mete and another with two temperature controllers that the new system replaced,

Show me a couple of ebay samples and I'll see if I can explain things better,

The problem with most meters is that the power supply feeding the meters has to be isolated. They can't share a common point.

Here is an example ebay combination meter with 3 wiring diagrams. **broken link removed**

This meter looks like it includes the required shunt resistor. A shunt resistor usually is a 4 terminal resistor. The larger terminals carry the current and the smaller ones are used for the measurement.

The basic "problem" with this meter is that the resistance has to be inserted in the negative power lead. Your CNC may not like that. Off the top of my head, I can't know. Ground is normally used as a reference.

This **broken link removed** unit says it will drop 75mV at 50 A

This, **broken link removed** has the shunt ( a low value resistor) clearly visible. Note the larger and smaller screws. The large screws would go in series with the motor and the smaller ones would connect to the meter.

The other caveat is that if the voltage is > 30 V, you have to use a DC-DC step down converter to get it between 4.5 and 30 V.

Been there, done that, The power supplies we used, used the positive output for the reference of the voltage programming and the current output.

With a little signal conditioning, another power supply, a hall effect sensor, you could make the meter work in the positive supply lead.

I know this is grey area for most people.

 

[oskar270]

Sorry about the Kill a Watt gadget, I misunderstood. However another point is that I want to have a nice looking control panel and it means my meters have to be build in (surface mounted).



Now I understand better what you are talking, thank you for your understanding.



I don’t have to show you the ebay samples because the links you provided are what I'm looking at. But these meters are for 30VDC and my power supply is 36VDC, 9.7A. I have seen on ebay meters with 50 and 100 VDC range and I will get the link and send it to you later.



Another point is that these meters say that if the Amps are less the 10, no shunt is required so since my power supply unit is 9.6A, is it a good idea to have a shunt?



I don’t understand what effect will have the resistance in the negative power lead. Why my cnc would not like that?



Sorry, signal conditioning, Hall Effect sensor etc. are not for me. I have a hard time understanding how to connect a simple Ampmeter, just imagine me go any further, lol



Much appreciated for finding the above links and again thank you for your understanding

 

[KeepItSimpleStupid]

Sorry about the Kill a Watt gadget, I misunderstood. However another point is that I want to have a nice looking control panel and it means my meters have to be build in (surface mounted).

I understand that.

Now I understand better what you are talking, thank you for your understanding.

I don’t have to show you the ebay samples because the links you provided are what I'm looking at. But these meters are for 30VDC and my power supply is 36VDC, 9.7A. I have seen on ebay meters with 50 and 100 VDC range and I will get the link and send it to you later.

It just means more $ to use a 30 V meter for either a separate AC powered power supply or a DC-DC converter.

Another point is that these meters say that if the Amps are less the 10, no shunt is required so since my power supply unit is 9.6A, is it a good idea to have a shunt?

The Chinglish that I am reading suggests that the shunt is included with the purchase. In one of the links I posted, the drawings of what wire goes where, include a shunt, yet it wasn't in the picture. Read carefully. There is also a language barrier.

I don’t understand what effect will have the resistance in the negative power lead. Why my cnc would not like that?

Try a simple explanation. Suppose the motor controller had 2 digital inputs of DIRECTION and NOT ENABLE. If these digital inputs were OPTO-ISOLATED we would be good.

I'm suspecting that your controller expects motor ground and logic ground to be the same. If it does, then you can't put anything in the negative lead to the controller. If you do, the logic switching lever will vary 0-75 mV depending on how much current the motor is drawing.

Sorry, signal conditioning, Hall Effect sensor etc. are not for me. I have a hard time understanding how to connect a simple Ampmeter, just imagine me go any further, lol

Yep. Problem. Voltmeter generally go across the load or across the power supply + and - somewhere. Wires drop voltages because of the current flowing, so the voltage at the load is preferred.

Ammeters. You have to cut the circuit to insert them. They add a small amount of resistance. Hall Effect is a sensor where current in a semiconductor induces a voltage proportional to current. The way the sensor is designed, it can be put into the positive or negative lead.

Take your car for example. The starter is connected to the frame of the car, If you wanted to measure the current in the starter, you could not use one of the ebay meters. You could not break the ground connection. Also the starting relay is likely connected to ground too. This same kind of connection is probably necessary for your CNC. Would you like the relay pull in voltage to vary with the amount of starting current?

Much appreciated for finding the above links and again thank you for your understanding

Getting on the same page is going to be tough,

 

[oskar270]

Thank you for taken the time to help me and I understand that getting on the same page is tough for you

Now I get it that some meters have a separate power supply for the meter alone and I do have a 12VDC wallwart which will power my VDC cooling fan so I could also provide the power for the meter. Here is a link for one with higher voltage rate:

**broken link removed**

You are right, there is a language barrier with the Chinese and have to be careful

I now understand what effect the resistance will have on the negative lead and I agree with you that is not a proper way to connect the meter like that. But I know that my stepper drivers are opto-isolated but my BOB (brake out board) is not. In any case I thought the Ampmeter will measure the Amps from the power supply only. Does it make sense to have an Amp reading on the power supply only?

You are right again; motor ground and logic ground are the same

If I was going to go with the Hall Effect etc. are the parts required easily available? Is the wiring complicated? In any case, if I was to read the Amps only from the power supply then we may not have to go this route.

Don’t worry about been on the same page LOL. About 3 years ago, a guy from a forum guided me to build a Toroidal transformer (36VDC, 16A) and I succeeded. It was difficult at the beginning to understand the parts but the rest was easy, although kind of scary

 

[KeepItSimpleStupid]

I think you have the general jist of what's going on.

I think you know that accuracy is out the window without special meters. Now, I think you understand that putting a resistor in the ground/reference lead isn't a good idea when other stuff is involved. I think we both don't know why you need the meters?

Your link shows 220 VAC in and your in Canada, so I thought 120 VAC it is. Then you have 1 volt resolution with +- 1 digits, so you get a value that can be off by 2 volts. How's that for starters?

If I was going to go with the Hall Effect etc. are the parts required easily available? Is the wiring complicated? In any case, if I was to read the Amps only from the power supply then we may not have to go this route.

No, I think you still need to put the shunt in the non-grounded supply lead.

I haven't looked at the details, but most Hall Effect sensors will run off of 5V. Early on, I showed you a datasheet and I even picked on that was basically 1/2 way together (A small breakout PC board) with a 10 Amp range.

So, somehow, you have to get a 5 V output to a 75 mV output for one of the meters and you might have to experimentally figure out a parameter or two without letting out the Magic Smoke for that 10 A one I picked out.

It might be tough since a lot of components are now surface mount. There is a company that makes surface mount to DIP adapters (in Canada) and will even procure from DigiKey and mount the component for you. You may have to make a, 1 of, prototype like Joe (see later in this post) did. That was a daunting task for Joe.

We might have to guess and breadboard something to see if it will work. I'm not one to simulate and tweak. I'm just not there yet.

Right now, I'm running Linux off of a CD. Life's been crap lately and I haven't recovered from a Hard drive crash, so I'm basically not using one.
So, I don't have the tools to draw pretty pictures anymore. A flood took out the scanner portion of my all in one printer. There is a 1 cm line slightly right of the left margin and I have to use an OLD, finicky XP laptop to scan something. Too many issues to take care of, but the stuff is relaxing as long as I don't have to do any real work. It''s nice bed time relaxation. Have I ever run Linux before - nope. Unix from the 70's and 90's though.

I don't know if the wiring is complicated or not. Take a look at this thread https://www.electro-tech-online.com/threads/help-with-water-pump.124250/page-114#post-1150350 which has had activity for more than a year. This is what a novice (Joe) can do with a soldering iron. alect did the design for the most part, ronv verified a lot of the modeling and I kept everyone on their toes with ideas and some physical forensic evaluation. alec and I are like in the top 10 when you look at the Members tab.

I'd like to read about the ammeter/voltmeter thing for a CNC if you have any links. I'm just not sure why. I did have full machine shop privileges where I used to work, so machining is there too. I also said that a friend in Australia bought a Chinese CNC. He made some mechanical improvements and safety improvements that required reverse engineering the controller. I think one of the most useful mods he mad had to do with electrically setting the tool ORG position.

The CNC thing all has to do with a real parallel port.

I've ordered a bunch of stuff from aliexpress which is where a lot of the ebay stuff comes from. It's just a different way of selling. One payee (Aliexpress) that releases money to the vendors after the goods are received and accepted. Very long lead times and orders can get cancelled.

See: http://www.aliexpress.com/wholesale?SearchText=dc+ammeter+voltmeter&CatId=0&initiative_id=SB_20131031211825&page=2

Note that reading between the lines. A < 10 A version has a built-in shunt. The wiring diagrams are for the external shunt. These are the stupid issues you have to deal with. The case had a mark of 50 A/75 mV and it showed a voltage and current calibration. Do we now how much? No.
So, I'm assuming that the 50 A version would require 75 mV to get a current reading. But, is that a 75 mV voltage source or must it be a low value resistor. Dunno.

With the language barrier, you would like to ask things like, would it work if I fed the shunt input to the meter 0-75 mV from say an external current limited 10 mA or less power supply?

This company I've dealt with a lot. See this datasheet: **broken link removed** Look at the ammeter and voltmeter applications. Their ammeter uses a shunt and the shunt goes in the + lead where it belongs, but you need an isolated power supply for each meter. Simple, not that easy and not <$20. The bezel is separate, the variable scaling is separate and the [ower supply is separate and it starts at $65.00.

See here: **broken link removed**

Block diagrams are so useful.

So, I'm like saying, if you can feed the Chinese 50 A meter that requires a shunt and 75 mV for 50 A a 0-75 mV signal and it's happy, you have a chance of making it work. I would not go out an buy a dozen without getting one or two to work first.

PS "the OP" is "the Original Poster" - easier

 

[oskar270]

Got to rum out this morning and I will reply tonight to your post which has very interesting point.

Here are two links from a forum which I frequent quite often

https://www.cnczone.com/forums/diy_..._fixed_gantry_router_build-2.html#post1129827

On the above link only Post 267 I think is related to Ampmeter (it’s a lengthy thread)

https://www.cnczone.com/forums/diy_...installing_ammeters_control_box_-_help-2.html

On this thread the same guy describes the Ampmeter problem he had. Lerned a few thing too now.

 

[oskar270]

For sure I don’t know what the Amps reading on the meter will mean but I guess if it goes up or down from the normal value then there is something wrong. Perhaps if you have the time you can explain to me what the reading of the Amps means. I thought I mentioned before that when I searched ebay for a Voltmeter I found much more combo meters (Volts / Amps) than just Voltmeters and I thought why not get a combo? They are almost the same price.

Accuracy is not that important, we are talking here hobby stuff but of course accuracy has a wide range so lets say if the reading is out by 10-15% it should be ok. I would say that these meters should be able to do better than that

Sorry for the link with the220VAC meter, I notice it later but I was looking on the wiring diagram only to see if I understand it

So is it a good idea to measure the Amps only on the power supply unit?

That was a very lengthy thread re Joe, good job

Sorry for the problems you had with the computer and flood, hope all is ok now. We have a powerful wind storm today here and the lights are flickering so I hope I don’t loose the power or burn something. Never went to Linux myself but I did give it a try years ago and decided to stick with Windows

Regarding your fiend in Australia setting the tool to the ORG position, on my previous cnc I used 3 limit switches and along with the Mach3 software (controlling the cnc) I was able to home the machine on every start

Never order anything from Aliexpress, would you recommend them to buy the meter? I was thinking of this meter

**broken link removed**

Nicolas

 

[KeepItSimpleStupid]

For sure I don’t know what the Amps reading on the meter will mean but I guess if it goes up or down from the normal value then there is something wrong. Perhaps if you have the time you can explain to me what the reading of the Amps means. I thought I mentioned before that when I searched ebay for a Voltmeter I found much more combo meters (Volts / Amps) than just Voltmeters and I thought why not get a combo? They are almost the same price.

When you scope the current to a power supply for the steppers, you will basically get an AC current at a high frequency relative to the power line. It draws pulses, so it really isn't DC. DC with ripple, maybe.

For AC currents and/or voltage, you have to go back to Calculus. There is an Integral formula for average of a periodic function and it may look like this TRMS = sqrt(AVERAGE(X^2))). You square it, make it positive, then average it, and then square root it. It makes the value positive.

Now I need pretty pic and have to really do some work to get the concept across. Let's suppose I had a resistor with a constant V and a constant I. What I want is a number that when an arbitrary AC waveform is applied, I get the same value when a steady DC value of current is applied. It's doable, but it's expensive.

"Most" people are dealing with the powerline (50 or 60 Hz) and DC voltages < 24 VDC for the most part. The AC part of the multimeter has been fudged. I kinda full wave rectifies the input and charges a capacitor then it divides by some some number that makes a sine wave of say 120 VAC read 120 AC. So, it works for most people.

The numbers read by these simple meters can be WAY off.

Another way of looking at AC and DC for a fixed R is that the power dissipated for V * I is always the same if it is AC or DC.
This will fail if the waveform is not a sinusoid for AC. So a 12 V sinusoid and 12 V DC applied to 1 ohm resistor, the resistor will dissipate P = V*I watts or 12.

For a non-sinusoid, or an inductive load or RF frequencies even this breaks down.

For sinusoidal current and sinusoidal voltages P = V(t)*I(t) * pf. Here, we introduce the concept of Power factor or the pase difference of the voltage and current components. I always have to look up the concepts. Inductance moves it one way and capacitance moves it another. pf = cos(theta).

Accuracy is not that important, we are talking here hobby stuff but of course accuracy has a wide range so lets say if the reading is out by 10-15% it should be ok. I would say that these meters should be able to do better than that

It will be all over the map and dependent on speed, and again, that's what I'm asking you why measure it?

Sorry for the link with the220VAC meter, I notice it later but I was looking on the wiring diagram only to see if I understand it

You have to look carefully.

So is it a good idea to measure the Amps only on the power supply unit?

I've been asking that question all along. Why not propose it to the CNC group. If the discussion gets out of hand I might join.

That was a very lengthy thread re Joe, good job

I think there is like 1200 posts in that thread. It would take a significant time to read it. My link brought you in at the tail end.

Sorry for the problems you had with the computer and flood, hope all is ok now. We have a powerful wind storm today here and the lights are flickering so I hope I don’t loose the power or burn something. Never went to Linux myself but I did give it a try years ago and decided to stick with Windows

Problems at home have been cascading and are still spiraling downward.

Regarding your fiend in Australia setting the tool to the ORG position, on my previous cnc I used 3 limit switches and along with the Mach3 software (controlling the cnc) I was able to home the machine on every start

X, Y and Z org sensors are different. Usually the org sensor is more precise.

What I'm talking about is basically the tool Z origin relative to the workpiece. For instance, tis video:

A fixed precision insulated metal plate. The tool, makes contact from "ground" to the block, thus you can set the Z of the tool to the workpiece height. Say it's contact + 0.200", if the block is 0.200 thick and Z down is positive. You always have to do edge and center finding and the CNC can automate that process.

Never order anything from Aliexpress, would you recommend them to buy the meter? I was thinking of this meter

**broken link removed**

Nicolas

Probably not a bad choice. You will need a say 5V power supply. Maybe order one for me (Northeast US) to be able to play with. You might even need two power supplies per meter.

With both ebay and aliexpress and Chinese parts, expect the only documentation is the documentation on the ebay and aliexpress website.

The first step would be to measure the voltage to ground on both sides of the shunt with a voltage applied, but no load, I would expect that voltage to be zeroish

The next step would be to take a 0-75mV DC impedance source (power supply) and a variable series resistor and to vary the series resistor until it reach 36.5 mV. Take out the pot and measure the resistance.

That's the basic info that's needed before continuing. You might have to cut a trace or something.

So, off the top of my head, possibly two 5 V power supplies that are isolated for each meter. One has to power the meter because of the 30 V limitation.

I'm SUSPECTING that you can supply a signal from COM to IN+ of 0-75 mV and my initial question is the input Z of that point and whether Com is connected to the external power supply common.

We also don;t know the range of the current calibrate control.

We might find out that using a 12 V supply for the meter and a 12 to +-5 for the signal conditioning.

I just don' know what to expect.

Worst case, I would expect to use an external power supply for the meter for the 30 V limitation.
and possibly an isolated DC-DC converter e.g. https://www.digikey.com/product-detail/en/NKA0505SC/811-1419-5-ND/1926980 +5 and -5 DC-DC converter and a hall effect sensor + some sort of "glue electronics". The +- V dual supply may be the way to go.

The "glue electronics" might consist of a voltage divider (5V to 75 mV) and an Instrumentation AMP such as an AMP02: https://www.google.com/url?sa=t&rct...Nl9ydgOhe-PUzTg&bvm=bv.55819444,d.cWc&cad=rja

So, as you can see it's a PITA to make a high side current monitor.

What the Chinese are supplying is a dual voltmeter, one with a 50 V scale and one with a 75 mV scale, so there is lots of reuse. The cost is in the real estate (the PCB), the case and the power supply.

 

[oskar270]

Sounds complicated the function of the Ampmeter. From one of the links I sent before the guy had 3 Ampmeters, one for the spindle, one for the vacuum and I forget what the 3rd one was for. As far as I know the guy never had a problem with them and looks like the wiring for them was quite simple (shown in one of the links). My idea was to have something similar and if I measure the Amps just on the power supply should be easy

Sorry for the cascading problems, hope they will be gone soon

That was a nice video. I do have a similar gadget but is only for the Z axis and got it from the cnczone forum when a guy posted the script for the Mach3 software and how to make one. Very simple. Do you know how your friend made that plate for the X.Y,Z and the script?

When I understand what I need for the meter I will order it along with two 5V power supplies and I don’t mind mailing the second power supply to you. I also know that documentation with these guys does not exist or what they send is garbage. Basically you are on your own

You are right, making a high side current monitor its PITA. So if I was to measure the Amps just on the power supply do I still need to do get all the items you mentioned for the testing?

Nicolas

 

[KeepItSimpleStupid]

Nicolus:

This guy

is clueless and I told him so in a comment. He cuts a precision resistor to agree with his meters. Yeah, right!

If you want to measure the current and voltage of a single power supply, using the negative lead, I think will be fine UNLESS the negative of that power supply is grounded. So, I don't think anything else is needed but the meter.

Grounds have mysterious loops and when they do, yikes! The power ground, logic ground and the the power supply reference usually. If you don't have a loop, your fine.

I did get to think about trying to make a high side sense. One would need to determine:

1. the input Z of the shunt input.
2. The percent change with the voltage calibration pot A pot is an abbreviation for a potentiometer.
3. The percent change with the current calibration pot.
4. Measure some voltages and resistances to get an idea how things are interconnected.
5. Determine if the decimal point can be changed.

These are basic specs that are missing. There should always be an equivalent circuit like the DATEL meters have. That meter is everywhere, including Amazon. I tried chat with Aliexpress. Nothing worthwhile.

I'd probably start with one of these https://www.pololu.com/search/compare/118 except the unipolar one and the 5 A one.
The 5A one could probably be used if you could move the decimal point. The device itself gives a 2.5 to zero and 2.5 to 5 V output. i.e. zero current is the center of the 5 V supply. The output is inherently isolated from the input.

The meter doesn't look like it has a negative sign, but they used a motor. Tha's a bad example because a motor could charge a battery resulting in a negative current.

The only reason not to use the 5 Amp sensor is the decimal point, 50.0 could represent 5.00 Amps if you can't change the decimal point.

The voltage is too high and the filter pin should be used. A capacitor can be added to that board. Pads are provided.

So, we can power this with another 5 V supply and get isolation on both sides.

But, the voltage is too high. Like 2.5 V. So, we can take a couple of resistors and knowing the current range and the calibration range get it below 75 MV @ 50.0 displayed. Now, see why it would be useful if we could know that one could get say 20 to 100 displayed at full scale?

We might want to consider clamping negative currents at some point just in case.

Now, let't think of it in terms of 75 mV/2,5V = X% of FS, where FS is Full Scale or 50 or whatever the calibration pot allows.

So, we figure out the two resistors to use and the total resistance has to be bigger than about 5,000 ohms.

Now, here is the trick. Take an IC called a rail splitter. This would take the second 5V supply and create a low impeadace point (an artificial ground) at half the supply voltage.

Read 2.5 as mid supply. So, if we connect the virtual ground created by the splitter, the output would be 0 to 2.5 at the output of the current sensor, and when suitably divided, -50 to 50 mV unless we can clamp the negative direction, The 50 depends on the full scale calibration that can be achieved. A negative voltage may or may not harm the meter,

An AD8220 Instrumentation amp has some peculiarities we can exploit. It can be powered from a single 5V supply, so it can BUFFER the 2.5 - 50 mV and the 2.5 + 50 mV signal. With the IA, we can easily offset the output to mid supply made by the rail splitter. So, we can connect, that point to whatever is considered 0V for the shunt.

So, you have the meter and it's 5V supply.
You have the hall effect sensor as a module.

And you have a small PCB with 2 active parts on it and maybe a dozen passives and connectors.

I don't really like the two supplies, but we have no intimate knowledge of the meter, Using a DC-DC to get the second 5V would be advantageous. Issues might occur if the meter wasn't powered and got voltage, Again, no intimate knowledge.

 

[oskar270]

And I thought the video was good – was planning to do the same, lol

Yes I want to measure only the Volts /Amps from a single power supply unit but the negative is grounded

So reading your last email I think we are wasting our time because as I explained in my first post I'm not knowledgeable enough in electronics and therefore I decided to just use a simple Voltmeter on my cnc and forget the Ampmeter (for now).

What you described to do is a project by itself (for me) and perhaps I can tackle it after I finish building my cnc which is taking too much of my free time

I'm sorry and I thank you for your time very much

Nicolas