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Old August 8th, 2018, 09:54 PM   #16
seth350
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I only use a transformer if I have to for some special device. Other than that, it’s 3 phase and 24VDC. No problems here. Although, 120V in the panel is purdy handy for laptop charging.

Here’s a thought....install a small outlet that steps the 24 VDC down to your laptops charge voltage. I think mine is 18V or 16V. It would get rid of that big brick PSU that converts 120VAC to DC. Just would need a cable. I thought of it first Graceport.
I would install them everywhere.
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Old August 9th, 2018, 04:45 AM   #17
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We have used Siemens 3-phase-to-24VDC PSUs for almost 20 years now. Barely any problems.
Even when we have a control transformer to get single phase AC, we still use the 3-phase PSU.
Back in the days, there were "programming devices" that absolutely needed an AC outlet to run. Today it is a nice-to-have rather than a must-have because of laptops.
Also, these single phase control transformers generate a lot of heat.
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Old August 9th, 2018, 05:14 AM   #18
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Even when I do put 120V in cabinets for lighting and convenience outlets, I don't use a transformer. Just have a feed run from the nearest 120V distribution panel. That also saves the line when someone inevitably opens the door and plugs in a vacuum or heavy power tool!
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Old August 9th, 2018, 05:37 AM   #19
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Quote:
Originally Posted by rdrast View Post
Even when I do put 120V in cabinets for lighting and convenience outlets, I don't use a transformer. Just have a feed run from the nearest 120V distribution panel. That also saves the line when someone inevitably opens the door and plugs in a vacuum or heavy power tool!
Oh yes. Had a complete plant shutdown because an external fitter couldnt find an outlet, until he walked into the control room and the cabinet door was open.

Today, we do the same as you. In addition to using 3ph PSUs we arrange for lighting and outlets to be supplied separately. So there will be lighting and power outlets available even if the main switch is off. Convenient for maintenance or modifications on the panels.
The wiring, terminals etc. are labelled prominently that they may powered even when the main switch is off.
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Old August 9th, 2018, 06:18 AM   #20
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I hear you on outside contractors plugging in and tripping breakers . . .

We use 480 VAC to 24 Vdc supplies in a lot of different places.
Works well with few problems.

I'm looking at one of my spares - A SOLA SDN 5-24-480.
Input power requirements are listed as '3PH 380/500 VAC'. Looks like it can accept
a wide range of input volts. As I said, many years very few problems.
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Old August 9th, 2018, 09:22 AM   #21
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Thank you everybody for the feedback!
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Old August 9th, 2018, 10:49 AM   #22
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All my Electrical cabinets are numbered and pad locked, Only Maintenance has a key and it is a violation of company policy to leave one unlocked, let alone open.
I do agree with outside power (labeled)I use this for the cabinet light, outlet and Ethernet switch,
480vac to 24 dc is great
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Old August 9th, 2018, 04:04 PM   #23
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We use the 480 volt power supplies almost exclusively nowadays. With all of our PLC/HMI equipment on a separate-from-anything-else network, I can connect to all that I need to on my laptop or PC from anywhere in the building(s) so I'm not tied to a cable into a panel. This once eliminated the need for 120VAC in our control panels.
However, on our panels that require a managed ethernet switch (our IT dept mandates Cisco units) we have to have 12 volts to power the switch. This is usually easiest done by putting a receptacle back into the MCP and using the managed switches power supply. The receptacle is powered from a breaker panel like any other receptacle in the building.

Win some--lose some.
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Old August 10th, 2018, 05:17 AM   #24
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I've had a few failures of a 480 to 24dc PS. However, the plant generator had a tendency
to lose a phase from time to time. The machines were also in a 100% humidity environment. The SOP was to wait for a motor to hit a ground fault, explode, then replace.
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Old August 10th, 2018, 05:20 PM   #25
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Quote:
Originally Posted by NetNathan View Post
Phoenix will do competitive costing. Send them the info on the PULS and price.
Usually they will beat it by a few bucks.
I keep them inline by sending them pricing from Automation direct.
Off topic question, is it allowed to send the quote from one company to a different company in order to reduce pricing? At my work, I am not allowed to do this in order to keep the market competitive on it's own. I'm unsure about other companies.

Thanks.
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Old August 10th, 2018, 07:32 PM   #26
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Quote:
Originally Posted by alive15 View Post
Off topic question, is it allowed to send the quote from one company to a different company in order to reduce pricing? At my work, I am not allowed to do this in order to keep the market competitive on it's own. I'm unsure about other companies.

Thanks.
It's not illegal but probably not the best practice for your benefit. If you tell someone what their competitors are charging, they may beat the price by 5%, but if they didn't already know, they may have been able to beat it by 10%
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Old August 11th, 2018, 01:32 AM   #27
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Actually my Phoenix Rep. requested the pricing and the information sheet on the competitive product.
I understand part of it..the competitive DC supply has to meet or exceed the specs of the Phoenix unit.

As far as a lot of components go, I spend about 35 grand a year at Automation Direct (control components, no PLCs or HMI...yet). I have a lot of companies that will compete with their pricing.
BUT... 90% of the time, the ease of ordering from A/D is what makes me stay...not to mention their website is very well setup.
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Old August 14th, 2018, 12:22 PM   #28
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Keep in mind that the efficiency of the transformer is 90-something percent. For a 500 VA transformer (which is pretty standard for us in smaller cabinets), that is a considerable heat source.
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