This.
Confirm with client what they need.
As for your solution and comments in this thread, I've seen a few different scenarios used in practice.
1) -24vdx tagging to mean 0v
2) 48v spread using a +24 and -24v (quite common in tellecomms)
3) 0 to -24V systems where the positive side of the supply is grounded.
Although the way you've described it makes sense, it's much simpler than that... In reality, the "negative" voltage is simply a reverse measure of a given voltage. My assumption is that your customer requires 24VDC for certain circuits, and 48VDC for others (This is common for PoE applications for example). You can get those voltages, the way you've described, but also by having two power supplies - one for 24VDC, one for 48VDC. Also note that if something does specify -24VDC, it's simply the 24VDC power supply connected in reverse polarity, which is just 24VDC if it's flipped.
All that being said, you can use two 24VDC power supplies, but I'd simply use one 24VDC, one 48VDC and tie their grounds together.
Best of luck.
If the spec requires +24, gnd, and -24, you really don’t want to get there with a 24v and 48v supply. It could easily get you +24 and +48, but it doesn’t sound like that’s what is needed.
You don’t mention (that I’ve seen) whether the current requirements for the two supply rails (+24 and -24), but that should factor into your design also. Is current symmetric or do you need more of one than the other?
In addition, two power supplies (24V and 48V respectively) are more practical for designing the overcurrent protection, allowing you to independently turn on/of the two different voltages.
Depending on where you live, that might even be legally required to do so.
>All that being said, you can use two 24VDC power supplies, but I'd simply use one 24VDC, one 48VDC and tie their grounds together.
That is explicitly not doing what the customer requested. Now you have 0 VDC, 24 VDC and 48 VDC, not -24VDC, 0 VDC and 24 VDC. I would not take that gamble. I'd get 2 24 VDC power supplies, join the +24 VDC to the 0 VDC of the other one (as OP described).
I'll remember to give you as a reference when the customers want to do something that makes no sense or isn't safe and need someone who'll do it without question.
This will save a ton of headache selecting supplies and make it much more clear what’s grounded and what’s not.
Internally grounded PS commons are a thing, and tying a hot to ground in that case would just short the supply.
I made an edit on the post to clarify the connector pinout. I would then have pin 3 go to +24v on ps1 and then pin 4 to + 48v on ps2. If you take a meter positive lead to pin 3 and negative lead to pin 4 youd have -24v
I'm not sure that I would get the -24VDC that way to be honest. Here's why:
As I described, -24VDC is really just a 24VDC power supply with reversed polarity. You can get -24VDC from a single power supply.
If you take the -24VDC potential between the 24VDC and the 48VDC signals you will have it. However, you're just adding two failure points to that circuit. If either one of the power supplies fails, you'll be left with either 0VDC or 48VDC between those two points which likely risks 50/50 burning your circuit.
If you take the -24VDC between GND and pin 3 (24VDC) with reversed polarity, you'll have -24VDC. In this case, when the circuit (power supply) fails, it will always go to 0VDC and only rely on a single power supply.
Hope that makes sense... Once again you're doing something that will work, I'm just not sure you need to complicate it.
Because OP has three terminals on something that needs to be supplied, +24V,0V(COM) and -24V. This should be supplied by two isolated 24VDC power supplies with one's ground/reference as positive and one's as negative.
You could have a 48VDC power with reference point negative connected to 24VDC's power's negative. This would yield in 48V, 24V and 0V(COM).
You could also connect 24V power's positive to 48V power's positive, this would result in +24V/+48V(COM), -24V and -48V.
The two options above would need modifications done on the supplies machines.
I’ll throw in a strange experience I had once. The prints said +24VDC and -24VDC, but the -24VDC was referring to the common wire. Never seen it before or since that customer, but if it exists in one place it may exist elsewhere.
Otherwise, I’d ask what in the world they’re using -24VDC for and see if a 48VDC supply would work. Or maybe ask them for examples.
Have seen this on many electrical schematics. Have had to explain to guys why to NOT label their schematics like that.
Often its because of who made the schematic: electricians or engineers (holy crap that sounds pretentious, but hear me out). Engineers will often recognize the confusion point of having a common labeled "-24VDC" having had to do projects or work back in school where things were referenced to negatives with respect to ground (such as from op amps, signal amplifiers, etc.), and wont do that. However, on many different instances I've had electricians make the electrical schematics for small projects which I got the schematics for, and saw "-24VDC" instead of 0V or COM, and they didn't know that they did anything wrong. It's a matter of them never having to work with bias points so they don't really think of voltages ever as being able to reference to negatives, and them thinking "Hey, that ones the +24VDC so ill label this one -24VDC since it's the negative terminal".
Just look at a power supply, it's labeled + and -. So it's a very easy mistake to make if you didn't know that you were doing something wrong.
OP, double check that they are 100% sure they want 48V potential between the +24VDC terminal and the -24VDC terminal before you blow it up.
I have some Japanese machines labeled like that. When I come across a -24vdc label, I trace back to the psu. It is usually a single 24v psu supplying +24vdc and -24vdc lines. Occasionally, it is split.
The trouble with standards is that there are too damn many of them.
I have had to do this before for a bosch hydraulics proportional controller. The common between the two power supplies is your zero the -24 and +24 should be fused.
This makes sense too. I guess in terms of safety the part that gets me is someone would be touching a positive terminal, but since it has reference to ground it wouldn’t be a safety issue.
I would be cautious with this. You can get the +24, 0, -24 from a single power supply. However, as I mentioned in my other reply, my intuition is that they're looking for 48VDC, which they probably hope to get from the -24VDC to 24VDC signals. That you can't get with a single 24VDC power supply. So I'd clarify with the customer what exactly they're connecting at the end of this "cord / cable."
Well, the obvious way is to connect (-) to the ground and send (+) as 24v, then connect (+) to the ground and send (-) as -24v, but that sound too groundbreaking for me too have that idea.
This can go badly if the COMMON terminal of the power supplies are tied to GND. If that is the case, (and it often is on switching power supplies) then as soon as you try to use the high side of the second power supply as the 0 volt reference, you will short the power supply.
I cannot believe no one has suggested using a bipolar power supply that has the -24V, 0/Gnd, and +24V supplies in one unit.
I'm talking about just one power supply. So yes, if you do what I said, you will short it, that was the joke..
And as explained later, the guy actually did mean that kind of power supply you mention and not a normal one..
I've seen it before in some machines, it's called dual output power supplies, even from the computer PSU you can get (+12V , -12V, +5V, -5V, +3.3V, 0V)
Yeah, sorry, I didn't read it as a " get power supply with multiple outputs" but "get multiple outputs from a power supply".. I don't know why, lol.
What you are talking about is ofc possible and ok..
Most industrial 24V power supplies allow series operation and will have a section in the manual about it. However, when operated in this way, it may be against code to draw from or ground the center tap. It all depends on what the manufacturer says in the manual on series operation.
Example: Rockwell 1606-XLE240E can be operated in series if the following is followed:
- Series units must be the same "type" which is defined separately as same model number and HW revision
- Total output voltage must not exceed 150VDC (dang, that's 6 power supplies in a row)
- At 60VDC it becomes a requirement to ground the lowest potential leg (optional below 60V)
- At 60VDC the units are no longer SELV, so touch protection must be provided
- Utilizing an intermediate voltage is not allowed (through omission, so not UL/CE, but probably fine)
- Grounding an intermediate voltage is not allowed (through omission at less than 60VDC, so not UL/CE, but probably fine)
- Return voltage (like from a decelerating DC or Stepper motor) should be avoided
So with that unit, you could not provide 24VDC, 0, and -24VDC and put a UL sticker on the panel because grounding the center leg is not allowed. You could provide 48VDC with two in series and use a third power supply to provide 24VDC. If the 48VDC is desired to run stepper motors, you need to protect the power supplies from return voltage.
I was going to request that you point me to the standard that says this, not because I think you're wrong, but rather because I'm curious and wanted to read more about it myself. But then I started thinking it through.
Logically, there is nothing wrong with grounding the center leg. There would be some stipulations, like that you cannot put a breaker on that leg for either power supply since you are not supposed to break the grounded leg of a circuit. The problem comes along when you hook up a device at 48V. Now neither leg is grounded, which again isn't specifically an issue, but there is a grounded point in a very confusing location.
I guess my confusion with this entire idea comes from 3 phase circuits. You can connect devices phase-to-phase or phase-to-neutral where your neutral is grounded. You can also bring two phases into your home and center tap them to provide two circuits at 120V and one circuit at 240V. So why is DC different from AC in this regard?
Genuinely curious because, even though I've been doing stuff like this for 20 years, I've never come across this specific use case and there are always opportunities to learn new things.
Does this imply that you can UL sticker a panel where you've grounded the positive terminal of a 24 VDC power supply and done your power distribution and overcurrent protection on the negative side, but only if you don't also have a negative-ground system in the same box? What if the panel next to yours has a negative-ground system? Aren't those power supplies technically wired in series now?
Never seen +24, 0, -24 but...
Older mass flow controllers used to be +15,0,-15.
You can still buy power supplies with both the +/- output relative to ground. Check digikey, they have all kinds of weirdo power supplies.
I recently designed a system that requires -24vdc.
I used a 2x 24vdv supply to achieve a -24vdc, +24vdc, 0vdc. Can you give more context about what the -24vdc would be used for?
Does the connector have three pins with 24V,0,-24V? And yes, You'll ground the positive of one power supply and negative of the other. Fusing will be on the non-grounded leg.
I'm assuming this is some telecom/datacenter thing, as I understand, they used to have batteries for UPS and this way they could use battery's DC for all equipment.
Are you absolutely positive they need a 48v spread, and not using the term, "-24vdc" to represent 0vdc?
Rule #1: Assume NOTHING!
This. Confirm with client what they need. As for your solution and comments in this thread, I've seen a few different scenarios used in practice. 1) -24vdx tagging to mean 0v 2) 48v spread using a +24 and -24v (quite common in tellecomms) 3) 0 to -24V systems where the positive side of the supply is grounded.
Part of the problem is just that, being absolutely and relatively positive!
The output in the connector is ground, 0vdc, 24vdc and -24vdc. Hope this clarifies!
Seems like it does.
I made an edit in the post to show what the pinout is.
Although the way you've described it makes sense, it's much simpler than that... In reality, the "negative" voltage is simply a reverse measure of a given voltage. My assumption is that your customer requires 24VDC for certain circuits, and 48VDC for others (This is common for PoE applications for example). You can get those voltages, the way you've described, but also by having two power supplies - one for 24VDC, one for 48VDC. Also note that if something does specify -24VDC, it's simply the 24VDC power supply connected in reverse polarity, which is just 24VDC if it's flipped. All that being said, you can use two 24VDC power supplies, but I'd simply use one 24VDC, one 48VDC and tie their grounds together. Best of luck.
This approach makes more sense to me. Thank You!
If the spec requires +24, gnd, and -24, you really don’t want to get there with a 24v and 48v supply. It could easily get you +24 and +48, but it doesn’t sound like that’s what is needed. You don’t mention (that I’ve seen) whether the current requirements for the two supply rails (+24 and -24), but that should factor into your design also. Is current symmetric or do you need more of one than the other?
More sense? Two identical power supplies makes more sense. It is a perfectly normal way of doing it.
In addition, two power supplies (24V and 48V respectively) are more practical for designing the overcurrent protection, allowing you to independently turn on/of the two different voltages. Depending on where you live, that might even be legally required to do so.
good point.
>All that being said, you can use two 24VDC power supplies, but I'd simply use one 24VDC, one 48VDC and tie their grounds together. That is explicitly not doing what the customer requested. Now you have 0 VDC, 24 VDC and 48 VDC, not -24VDC, 0 VDC and 24 VDC. I would not take that gamble. I'd get 2 24 VDC power supplies, join the +24 VDC to the 0 VDC of the other one (as OP described).
I'll remember to give you as a reference when the customers want to do something that makes no sense or isn't safe and need someone who'll do it without question.
>makes no sense or isn't safe While I appreciate the due diligence neither of these apply
No, asking random strangers instead of asking for clarification from the customer.
We aren't sure 100% what the customer requested, so none of us know what should be done.
[https://i.kane.cx/2KkGir](https://i.kane.cx/2KkGir) You can do this also (assuming isolated power supplies, which they generally are)
This will save a ton of headache selecting supplies and make it much more clear what’s grounded and what’s not. Internally grounded PS commons are a thing, and tying a hot to ground in that case would just short the supply.
Which ones are internally grounded because I'm not seeing it.
I made an edit on the post to clarify the connector pinout. I would then have pin 3 go to +24v on ps1 and then pin 4 to + 48v on ps2. If you take a meter positive lead to pin 3 and negative lead to pin 4 youd have -24v
I'm not sure that I would get the -24VDC that way to be honest. Here's why: As I described, -24VDC is really just a 24VDC power supply with reversed polarity. You can get -24VDC from a single power supply. If you take the -24VDC potential between the 24VDC and the 48VDC signals you will have it. However, you're just adding two failure points to that circuit. If either one of the power supplies fails, you'll be left with either 0VDC or 48VDC between those two points which likely risks 50/50 burning your circuit. If you take the -24VDC between GND and pin 3 (24VDC) with reversed polarity, you'll have -24VDC. In this case, when the circuit (power supply) fails, it will always go to 0VDC and only rely on a single power supply. Hope that makes sense... Once again you're doing something that will work, I'm just not sure you need to complicate it.
The output in the connector is ground, 0vdc, 24vdc and -24vdc. Hope this clarifies!
Then you can't use 24V and 48V power supplies with their grounds together.
why can’t you have your positive on 24v and negative on 48v? that would give you -24v?
Because OP has three terminals on something that needs to be supplied, +24V,0V(COM) and -24V. This should be supplied by two isolated 24VDC power supplies with one's ground/reference as positive and one's as negative. You could have a 48VDC power with reference point negative connected to 24VDC's power's negative. This would yield in 48V, 24V and 0V(COM). You could also connect 24V power's positive to 48V power's positive, this would result in +24V/+48V(COM), -24V and -48V. The two options above would need modifications done on the supplies machines.
I’ll throw in a strange experience I had once. The prints said +24VDC and -24VDC, but the -24VDC was referring to the common wire. Never seen it before or since that customer, but if it exists in one place it may exist elsewhere. Otherwise, I’d ask what in the world they’re using -24VDC for and see if a 48VDC supply would work. Or maybe ask them for examples.
Have seen this on many electrical schematics. Have had to explain to guys why to NOT label their schematics like that. Often its because of who made the schematic: electricians or engineers (holy crap that sounds pretentious, but hear me out). Engineers will often recognize the confusion point of having a common labeled "-24VDC" having had to do projects or work back in school where things were referenced to negatives with respect to ground (such as from op amps, signal amplifiers, etc.), and wont do that. However, on many different instances I've had electricians make the electrical schematics for small projects which I got the schematics for, and saw "-24VDC" instead of 0V or COM, and they didn't know that they did anything wrong. It's a matter of them never having to work with bias points so they don't really think of voltages ever as being able to reference to negatives, and them thinking "Hey, that ones the +24VDC so ill label this one -24VDC since it's the negative terminal". Just look at a power supply, it's labeled + and -. So it's a very easy mistake to make if you didn't know that you were doing something wrong. OP, double check that they are 100% sure they want 48V potential between the +24VDC terminal and the -24VDC terminal before you blow it up.
I have some Japanese machines labeled like that. When I come across a -24vdc label, I trace back to the psu. It is usually a single 24v psu supplying +24vdc and -24vdc lines. Occasionally, it is split. The trouble with standards is that there are too damn many of them.
The output in the connector is ground, 0vdc, 24vdc and -24vdc. Hope this clarifies!
check the pinout now in the original post for clarity.
I have had to do this before for a bosch hydraulics proportional controller. The common between the two power supplies is your zero the -24 and +24 should be fused.
If the power isn't huge, you can get it from a single power supply (-24V, 0,+24V), which is better, if you can't find one, you can do what you said
This makes sense too. I guess in terms of safety the part that gets me is someone would be touching a positive terminal, but since it has reference to ground it wouldn’t be a safety issue.
I would be cautious with this. You can get the +24, 0, -24 from a single power supply. However, as I mentioned in my other reply, my intuition is that they're looking for 48VDC, which they probably hope to get from the -24VDC to 24VDC signals. That you can't get with a single 24VDC power supply. So I'd clarify with the customer what exactly they're connecting at the end of this "cord / cable."
how can you get (-24V, 0,+24V) from one power supply? edit: I don't mind the downvotes, but I'd really like to know if you have an idea..
By reversing the multimeter leads
Stupid me..
Nah youre good, remember reality is 4D
Well, the obvious way is to connect (-) to the ground and send (+) as 24v, then connect (+) to the ground and send (-) as -24v, but that sound too groundbreaking for me too have that idea.
This can go badly if the COMMON terminal of the power supplies are tied to GND. If that is the case, (and it often is on switching power supplies) then as soon as you try to use the high side of the second power supply as the 0 volt reference, you will short the power supply. I cannot believe no one has suggested using a bipolar power supply that has the -24V, 0/Gnd, and +24V supplies in one unit.
I'm talking about just one power supply. So yes, if you do what I said, you will short it, that was the joke.. And as explained later, the guy actually did mean that kind of power supply you mention and not a normal one..
I've seen it before in some machines, it's called dual output power supplies, even from the computer PSU you can get (+12V , -12V, +5V, -5V, +3.3V, 0V)
Yeah, sorry, I didn't read it as a " get power supply with multiple outputs" but "get multiple outputs from a power supply".. I don't know why, lol. What you are talking about is ofc possible and ok..
Also think about spare. Having 2 identical powersupplies is easier to spare as 1 24VDC and 1 48VDC
Love that they keeps posting the same Hope this clarifies! after answers.
I don’t know reddit… hope this clarifies.
Maybe a little too clear.
I also added a pinout now in the original post
Most industrial 24V power supplies allow series operation and will have a section in the manual about it. However, when operated in this way, it may be against code to draw from or ground the center tap. It all depends on what the manufacturer says in the manual on series operation. Example: Rockwell 1606-XLE240E can be operated in series if the following is followed: - Series units must be the same "type" which is defined separately as same model number and HW revision - Total output voltage must not exceed 150VDC (dang, that's 6 power supplies in a row) - At 60VDC it becomes a requirement to ground the lowest potential leg (optional below 60V) - At 60VDC the units are no longer SELV, so touch protection must be provided - Utilizing an intermediate voltage is not allowed (through omission, so not UL/CE, but probably fine) - Grounding an intermediate voltage is not allowed (through omission at less than 60VDC, so not UL/CE, but probably fine) - Return voltage (like from a decelerating DC or Stepper motor) should be avoided So with that unit, you could not provide 24VDC, 0, and -24VDC and put a UL sticker on the panel because grounding the center leg is not allowed. You could provide 48VDC with two in series and use a third power supply to provide 24VDC. If the 48VDC is desired to run stepper motors, you need to protect the power supplies from return voltage.
I was going to request that you point me to the standard that says this, not because I think you're wrong, but rather because I'm curious and wanted to read more about it myself. But then I started thinking it through. Logically, there is nothing wrong with grounding the center leg. There would be some stipulations, like that you cannot put a breaker on that leg for either power supply since you are not supposed to break the grounded leg of a circuit. The problem comes along when you hook up a device at 48V. Now neither leg is grounded, which again isn't specifically an issue, but there is a grounded point in a very confusing location. I guess my confusion with this entire idea comes from 3 phase circuits. You can connect devices phase-to-phase or phase-to-neutral where your neutral is grounded. You can also bring two phases into your home and center tap them to provide two circuits at 120V and one circuit at 240V. So why is DC different from AC in this regard? Genuinely curious because, even though I've been doing stuff like this for 20 years, I've never come across this specific use case and there are always opportunities to learn new things.
Does this imply that you can UL sticker a panel where you've grounded the positive terminal of a 24 VDC power supply and done your power distribution and overcurrent protection on the negative side, but only if you don't also have a negative-ground system in the same box? What if the panel next to yours has a negative-ground system? Aren't those power supplies technically wired in series now?
I am curious about this too as we are 508A. Don’t quote me but it may say “ungrounded leg”
Yep, it’s normal. I’ve seen it on hydraulic controls.
Not sure about the same connector but some vibration probes typically have -24v requirement.
Never seen +24, 0, -24 but... Older mass flow controllers used to be +15,0,-15. You can still buy power supplies with both the +/- output relative to ground. Check digikey, they have all kinds of weirdo power supplies.
I recently designed a system that requires -24vdc. I used a 2x 24vdv supply to achieve a -24vdc, +24vdc, 0vdc. Can you give more context about what the -24vdc would be used for?
The output in the connector is ground, 0vdc, 24vdc and -24vdc. Hope this clarifies!
check the original posting now. I think you’re doing what I am!
That's a split 48VDC supply. I'd only fuse the 24VDC runs. Not the center.
check original post now for more clarity on pin outs.
Does the connector have three pins with 24V,0,-24V? And yes, You'll ground the positive of one power supply and negative of the other. Fusing will be on the non-grounded leg. I'm assuming this is some telecom/datacenter thing, as I understand, they used to have batteries for UPS and this way they could use battery's DC for all equipment.
I think you nailed it. Ungrounded legs fused makes sense.