AC vs DC Ampere calculation

Hi guys,

I'm doing some current consumption for a panel, hope to get some advice from you guys here.

My control panel will be supplying 24V DC to 60 field instruments at 1 Amp each. So total 24V DC for field is 60 Amp & panel about 5 Amp. Total is 65Amp.

Thus, I'll be using 4 units of 1606-XL480E (giving 18Amps/unit) & 1 unit 1606-XL480E for backup. Each 1606-XL480E will be working with a 1606-XLRED20-30 for N + 1 redundancy function. Each 240V AC for 1606-XL480E input is 5Amp, total is 25 Amps. Additional 5 Amps for other panel components.
1) Total is 30 Amps (is my calculation correct)?.

I've another 13 Amp, 3 pin socket in the panel for notebook use. Notebook consumption only 1.5Amp.

2) So my request for the single phase 240V AC incoming to the panel shall be 30+1.5Amps or 43 Amps?

OK so here are the numbers as I understand them.
60 units at 1 amp on a 24VDC line
Panel at 5 amp on 24 VDC.
Total load is 65 amps

You intend to supply load with 4 1606-XL480E units rated at 18 amp at 24 volt. This totals to 72 amp total capacity. Now if mine I would load to 80% which is 57.6 amps supply - so I would use a fifth unit for total capacity of 90 amp which would be 72 amp at 80% derated load. I think you do have a very good idea of having one more for a spare.

I suggest this because based on your country's flag I surmise it may be a little warm and you may not be able to fully load your power supplies thus you need to reduce each ones load to 80% and maybe even more depending on ******t (ho kceh A M B I E N T) temperatures.

Dan Bentler

i'll second that. i would keep an eye on temperature.

with 20A rated output we are talking about 20A*24V=480W while input is about 230V*5A=1150W. the difference is 1150W-480W=670W which is a lot to waste in heat (efficiency only some 42%, most units nowdays should do at least 65%). this only for one unit and you will be several of them inside same cabinet... (some 3kW in loses)

Also, do yourself and everyone else down the line from you a favor:

Do not wire all the power supply outputs in parallel. "Cut" the machine up into sections and put them on seperate supplys (You can make the '-' terminals common, but please keep the + seperate!)

Tharon said:

Also, do yourself and everyone else down the line from you a favor:

Do not wire all the power supply outputs in parallel. "Cut" the machine up into sections and put them on seperate supplys (You can make the '-' terminals common, but please keep the + seperate!)

Click to expand...

+1 On this reply !

2) So my request for the single phase 240V AC incoming to the panel shall be 30+1.5Amps or 43 Amps?

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It appears that 30 + 1.5 = 31.5 Amps

Does the laptop also use 240 volts? If so, the total should be 31.5 Amps load on a 240 volt power line.

Thanks guys, I'll go with 31.5Amp with labelled the SSO for notebook only

Tharon said:

Also, do yourself and everyone else down the line from you a favor:

Do not wire all the power supply outputs in parallel. "Cut" the machine up into sections and put them on seperate supplys (You can make the '-' terminals common, but please keep the + seperate!)

Click to expand...

Hi Tharon,

May I know any particular reason for doing this?

As you know I've 60 field instruments powered from the panel 24V DC power supplies. These are divided into 4 groups (4 different locations). Some groups has more, some has lesser than other. If I were to divided the power supplies into different groups, some power supplies will be more loaded than the other. If i link all these power supplies together, they can share the load, so each of the power supplies will be 'working' equal hard. Another unit for backup, any of these 'working' power supplies failed, the backup will kicks in.

Do you foreseen any problem for this setup?

Tying multiple power supplies in parallel seems to be OK on paper and may just work. However they may not be regulated power supplies and even if so the regulation may not be designed to operate in parallel.
The other reason is that a major fault will cause all in parallel to trip. I would not do it. Connect one power supply to X of these units such that power supply is loaded to 80% to allow for cooling. Connect 2nd power supply to another set of X etc etc.

Dan Bentler

flyers said:

Hi Tharon,

May I know any particular reason for doing this?

As you know I've 60 field instruments powered from the panel 24V DC power supplies. These are divided into 4 groups (4 different locations). Some groups has more, some has lesser than other. If I were to divided the power supplies into different groups, some power supplies will be more loaded than the other. If i link all these power supplies together, they can share the load, so each of the power supplies will be 'working' equal hard. Another unit for backup, any of these 'working' power supplies failed, the backup will kicks in.

Do you foreseen any problem for this setup?

Click to expand...

Well, we have one fairly large machine that has 3 20A 24V power supplies wired in parallel.

We did not build this machine, it was built for us. Each power supply is fused separately, but they all come back to one main terminal block. There are indicator lights on the fuses to let you know when they are blown.

But, we have had times when one fuse is blown. The indicator does not light because there is 24V potential on both sides of the block. So one power supply drops off the system and you do not notice until it overloads the next, etc. (I myself can notice, but offshift maintenance just goes by lights.)

Also, think about what happens when you put a 23.5V supply in parallel with a 25.6V supply? I'm sure if they are built for parallel operation, they can handle it, but I still think it causes unnecessary heat.

I've opened up the panel to this machine to check other things, and notice that one of the supplys are running really hot, like 190F+, and check around and it turns out one of the other supplys have had a fuse blow and go unnoticed.

It's just so much easier from a troubleshooting point of view. Also, think of the wire gauge requirement for 20A vs 80A.

Tharon,

I see your point, thx for explaining. The AB power supply 1606-RED comes with a signal output to SCADA when there is a faulty. The reason I've to parallel all the 24V DC power supplies is to share the load and minimize the qty of power supplies in the panel. Currently 6 units is consider a lot for a panel. I'll check with Rockwell to see if I can separate the power supplies to supply to different segments of the field instruments and the 6th unit will act as the backup for the rest.
Till now they still can't confirm with me if the 6th unit (backup unit) is also supplying when I power ON the panel or it's just sitting there doing nothing until a failure occured at the other power supplies.
Do you think I need diode & fuse in each of the power supplies output?
Hope to hear from you soon. Thanks.

If you are intending to use the socket for laptop use, are you going to limit the current to it by using a fuse or mcb. It doesn't matter how you label it, someone later down the line will see it as a convenient point to plug any kind of load into it, possibly taking out the whole panel by overloading your 230V supply.

flyers said:

Do you think I need diode & fuse in each of the power supplies output?

Click to expand...

I cannot say. I just don't know.

My comments are from a troubleshooting point of view, not design. I've never personally built or designed anything that required more than a single power supply.

I do have 2 large machines, both with multiple power supplies. One runs with them in parallel, the other runs with just a shared common. We have never had a power supply issue with the machine with shared commons, but have had many supply issues with our parallel supply machine.