Download Optimizing 24 VDC Power Installation

OPTIMIZING 24 VDC POWER INSTALLATION
Jerry Wick, Advanced Energy Industries, Inc.
Proper wiring of AE products to the master 24 VDC
power supply can prevent a variety of problems. This
guide recommends specific wiring practices required
for consistent product performance. It assumes that the
relevant application has a main 24 VDC power supply
and the output voltage from this supply is distributed
to various devices located on or adjacent to the main
equipment. The tables on pages 9 and 10 provide
recommended wire gauge for various wire-length runs.
Table of Contents
Questions and Answers
2
General Wiring Recommendations
2
Wire Gauge and Voltage Drop
3
Wire Gauge Recommendations
4
Stray Signals
5
System Troubleshooting
6
Environmental Conditions
and Cooling
7
This is a guide to recommended practices. These
recommendations are not intended as mandates or
absolute requirements. Local and internal requirements
must take precedence as appropriate.
General System
Recommendations8
Products
Recommended Four-Wire Gauge
for Various Wire Length Runs
9
Recommended Two-Wire Gauge
for Various Wire Length Runs 10
• All AE power supplies
Applications
• Vacuum processing
Questions and Answers
The following section provides key questions and answers, assembled from numerous problem solving sessions and best-practice
recommendations.
Question
Question
How can electrical power problems impact production?
Why should product/system wiring be designed
for performance?
Answer
Some negative effects include:
Answer
• No production (system or site down)
Multiple power surveys indicate that approximately 80%
• Damaged output (product does not meet specification)
of all electrical problems originate within the facility. Only 20%
• Additional and unexpected maintenance costs
of electrical problems originate external to the facility.
General Wiring Recommendations
Question
Question
What overall wiring method does AE recommend between
Why does AE discourage the use of series-connected (daisy
the main 24 VDC power supply and the AE product?
chain) loads connected to the main power supply?
Answer
Answer
Each AE product should be individually connected to the
Series-connected equipment requires complex, detailed,
24 VDC power supply via dedicated wiring of appropriate
and careful load calculations. It would also require the use
gauge. Wiring in a “daisy chain” pattern can cause issues with
of multiple wire gauges. For example, if the site requirement
equipment performance.
were for eight 7 A loads, then:
Question
We use a common set of wires between the main power
supply and a distribution point. Individual wire sets then go to
each product. What wire gauges should we use?
Answer
Carefully sum the peak currents from each product. Use a
conservatively high current listing to determine an acceptable
wire gauge between the supply and the distribution point.
Use individual product peak currents to determine what wire
gauges should be used between the distribution point and
each specific load.
a)The wiring between load one and load two is calculated
for 7 A.
b)The wiring between load two and load three is calculated
for 14 A.
c)The wiring between load three and load four is calculated
for 21 A.
d)The wiring between load four and load five is calculated
for 28 A.
e)The wiring between load five and load six is calculated
for 35 A.
f) The wiring between load six and load seven is calculated
for 42 A.
g)The wiring between load seven and load eight is
calculated for 49 A.
h)The wiring between load eight and the power supply
is calculated for 56 A.
Thus, the appropriate wire gauge grew from reasonable
to very large. Finding a series of power connectors that
can accommodate this range in wire gauge would be
extremely difficult.
2
Wire Gauge and Voltage Drop
Question
Question
Why is it important to use the recommended wire gauge?
3% of 24 V is only 0.72 V. Why does such small voltage drop
matter?
Answer
Wiring without sufficient current-carrying capacity results in
excessive voltage drop. This reduced voltage, if even for a few
milliseconds, may cause the using device to report “low input
Answer
A 3% drop is 30% of the total 10% allowable drop, a significant
reduction in operating margin.
voltage” or not to operate as expected. Voltage drops can
cause anomalous product behavior.
Question
Can I gain any actual input voltage data from equipment that
Question
is already on my site?
What is the significance of the voltage lost between the power
supply and the AE product?
Answer
Most AE products are designed to function with a nominal
24 VDC ±10% input voltage. If there is excessive voltage
drop in the wiring, the product has insufficient voltage to
Answer
Possibly. Some AE products have an input voltage logging
function already in their software. Where available, this
monitor function can be accessed using AE Virtual Front Panel
(VFP) software.
correctly function. The lower voltage substantially decreases
the product’s ability to ride through any externally caused
24 VDC voltage reductions. Energy storage in a capacitor
Question
is calculated as 0.5CV2. Thus, seemingly small changes in
What maximum current is recommended for some common
voltage cause dramatic changes in total energy storage. The
wire gauges?
product typically reports an input voltage failure and likely will
not operate as desired when the voltage does drop below the
allowable minimum.
Answer
Please refer to the following table.
Table 1. Maximum current recommendations for common wire
gauges [1].
Wire Gauge
Max Recommended
Current
24
6
22
8
20
10
3
Wire Gauge Recommendations
Question
Question
What assumptions did AE make in providing the wire
What product current (peak, instantaneous, nominal,
gauge recommendation/run length distance tables
inrush, other) rating do I need to use with the tables
on pages 9 and 10?
on pages 9 and 10?
Answer
Answer
This guide assumes that the main supply output voltage
Use the peak or maximum current rating. Do NOT use
is 24.000 VDC measured at the output terminals of the
nominal or steady state values. You do not have to use
supply. The recommended wire gauge tables are based on
maximum inrush current rating.
an allowable 3% voltage drop. There are two sets of tables.
One set of tables is for cases in which there are two wires in
parallel for both the positive and negative conductors. The
Question
other set of tables is for cases in which there is just a single
My equipment voltage specification is 24 VDC ±5%. Can I use
wire for each polarity (positive and negative). No remote
the tables?
voltage sensing is assumed.
Answer
Yes. The tables are set up to provide a 3% voltage drop.
Question
Why do the wire gauge/run length distance tables, on pages
9 and 10, stop at approximately 30 m (100') length?
Answer
The 30 m distance accommodates the vast majority of actual
use at most installations.
Question
How does the AWG wire gauge listed in the tables compare in area to either circular mills or millimeter squared dimensions?
Answer
The following information is identical to that in Table 8 in the NEC® Handbook.
Table 2. Wire size equivalents [2]
4
Size in AWG
MM Squared
Circular Mills
18
0.823
1620
16
1.31
2580
14
2.08
4110
12
3.31
6530
10
5.261
10,380
8
8.367
16,510
6
13.30
26,240
4
21.15
41,740
3
26.67
52,620
2
33.62
66,360
1
42.41
83,690
Stray Signals
Question
Question
Does AE have any recommendations for situations in which
I observed excessive process-related signals on the 24 VDC
the 24 VDC wiring must pass near RF cables and products
power wiring. What solution does AE recommend?
(stray signal pickup defect)?
Answer
Answer
Do both pieces of equipment share either power or signal
Small-amplitude RF can be eliminated or greatly reduced
wiring? If moving power or signal wiring causes the observed
through the use of ferrite beads or cores. The power wiring is
signal to vary, the problem is caused by radiated emissions.
run through the center of the bead/clamp. Use steel conduit
Physically separating the wires is a low-cost aid to reduce
to shield the power wiring if RF coupling to the 24 VDC wires
the induced signal pickup. The following method to create
is an issue. Use of flexible conduit is not recommended as a
low-cost twisted-pair wire may help if the radiated noise has
solution. Please note that a key assumption is that the power
a frequency of less than 500 kHz.
and RF wiring is already separated from the 24 VDC wiring as
much as possible.
Twist the wire approximately four to six turns per foot to
create cables that can reduce stray AC or low-frequency
magnetic pickup. The wire twisting causes the noise to
Question
How can I tell if the electrician installed the desired type
of steel conduit?
Answer
Test with a small magnet. A magnet sticks to steel.
become common mode. Common mode noise is reduced
at the downstream transformer.
Wire shielding or other EMI reduction techniques provide
solutions if the two items share common I/O or power.
Verify that you have correctly found the actual sources by
turning equipment off. You do not have the correct source
if the signal doesn't go away.
Question
What distance between products do you recommend,
with RS-232 wiring?
Question
Answer
Does AE recommend any wiring separation distance between
The original RS-232 standard (1962) states a maximum
wiring used for different functions?
15.2 m (50') distance. Today, longer distances are often used,
with some data integrity issues. Low-capacitance wire and
Answer
wire shielding, as well as attention to wire routing, often
A rule of thumb is that a separation of 2" (5.1 cm) or more
results in good performance. Very long runs may also use
often substantially reduces any signal cross coupling. This
electronic boosters to amplify the signal.
practice typically provides sufficient voltage reduction
for most AC and RF cables.
Question
I see stray RF or process signals when I monitor the RS-232
Question
wiring. What solutions do you recommend?
How do I arrange two different types of wires that need
to cross?
Answer
If wire separation hasn't reduced the signal pickup sufficiently,
Answer
use RS-232 cable equipped with an outer shield to reduce any
All wiring that needs to cross should do so at a right angle.
stray signal pickup. Connect the cable shield to earth ground
This minimizes stray signal pickup. Always follow the
at both ends if total cable is longer than 3 m (9.8').
2" (5.1 cm) minimum separation rule.
5
Question
We routinely place any extra cord or cable lengths behind a product. Is this a problem?
Answer
The cords/cables can couple energy simply due to being in close proximity. We suggest that you separate the cords/cables to reduce the
coupling effect. Arranging the wire coils at right angles also reduces any signal coupling. The 2" (5.1 cm) separation recommendation
generally reduces the coupled signal amplitude to less than a critical value.
You can electrically reduce the wire/wire coupling by coiling the wire in a figure eight arrangement. This cord pattern is commonly used
in product conducted interference testing.
System Troubleshooting
Question
Question
The system worked acceptably for a reasonable period of time.
We recently experienced inconsistent performance.
Suddenly, performance has been inconsistent. Any thoughts
Any thoughts on possible causes?
or suggestions?
Answer
Answer
Check to see if any periodic maintenance or cleanup was
Something has probably changed. What events happened
scheduled. Verify that all switches are fully on/off in the
at the date of the failure? A common problem is that an
correct position and all cables are fastened. Keep a list of
inadvertent change caused the failure. Has anything on the
settings or create physical marks to show the desired switch
tool, cables, or other nearby equipment been moved or
positions. Always verify that all inner and outer covers are
added? Did the system start running a different recipe? Were
installed using the proper number of screws.
any product or system covers removed or not installed using
all hardware?
Question
Use only known (measured) facts when troubleshooting. This
Several systems have what seem to be similar failures.
approach quickly leads to the true root cause. This structured
Any suggestions?
approach to problem solving may go by such names as
analytic trouble shooting or 8D, or another internal best-
Answer
practices term.
Is this a new failure mode? If the systems used to work
without defect, possibly some new or common factor is
causing problems. If different but identical systems have
near-simultaneous, identical issues, look for the common
factors. Verify both the AC and DC local power quality at a
point of concern. It's good practice to periodically measure
the delivered power quality at the point of use. If an anomaly
exists, it is important to know if this is a recent change or if
this parameter has always existed at this location.
6
Question
We measured large swings in DC voltage at the point of use. Suggestion?
Answer
Determine if the same voltage swing is present at the tool power supply. If it is, the supply either is defective or has excessive load.
Check carefully for any short-term peak current load. Has any new or different equipment been added to the supply load? If the supply
performed acceptably in the past, then a very common problem is that the cooling fan may be defective or turning slowly. Another
common problem is a blocked air cooling path that causes the supply to overheat. If the tool power supply is connected to a “low” mains
voltage, check to see if the voltage select switch (if present) was inadvertently set to the high-voltage position. Finally, check the supply
electrolytic capacitors to see if they have an acceptable capacitance value, as they have a finite lifetime. Capacitors that are worn out
cause excessive ripple on the output voltage or large swings as the supply regulation circuit attempts to create and hold a constant output.
Question
We measured large swings in AC voltage at the point of use. Suggestion?
Answer
Determine if the same voltage swing is present at the power panel. If it is, it’s likely that the supplying transformer is undersized or has
excessive load. Check for both peak and RMS loads at the transformer output. Insufficient peak current capability typically manifests as
waveform “flat topping.” Also check for new or unknown additional loads connected to the power panel.
Environmental Conditions and Cooling
Question
Question
The power supply will be located in a very warm environment.
How much room do I need to allow for airflow at the fan
The temperature might be close to the maximum ambient
intake and exhaust?
product temperature rating. Do you have any suggestions?
Answer
Answer
The individual product manual should define the minimum
Duct nearby cool air from an adjacent area to the air inlet
space required for airflow. A rule of thumb is that the gap for
of the product. Use a fan to force air to the product if the
both intake and exhaust airflow should be the same size as
product does not have a fan. If a product fan is present, it can
the fan diameter, to avoid unnecessary restriction.
pull the cool air via ducting.
A necessary assumption is that the air intake has access to
cool air. It also should not be located near the hot exhaust of
another product. The hotter the air is, the shorter the product
Question
lifetime is before failure or need for service.
My company doesn't want to add any air ducting to our
equipment. The local area ambient temperature will be
approximately 55°C (131°F). What are some possible effects
from this planned usage?
Answer
We recommend operating AE products in accordance with
their ambient temperature rating.
7
General System Recommendations
Question
Question
Does AE have any general recommendations for the 24 VDC
Why should the main power supply be plugged into
main power supply?
a “higher” voltage?
Answer
Answer
AE strongly recommends that any 24 VDC main power supply
The most common type of VAC power disturbance is a
be selected with “universal” auto-voltage VAC input capability
temporary voltage reduction. This lowered voltage condition
(85 to 264 VAC). Any power supply of this type should be
remains for a fraction of a second. The auto-voltage select
plugged into a 240 VAC nominal outlet when possible.
power supply automatically switches to the “lower” voltage
range during this anomaly. The power supply automatically
switches back to the “upper” voltage condition once the
problem is not present. Result: The connected load(s) see
Question
Must I always consider using an uninterruptible power supply
(UPS) for powering either critical equipment and/or processes?
Answer
No. Most installations can mitigate the majority of expected
AC power problems with a properly sized line conditioner
or constant voltage transformer along with thoughtful
attention to on-site installation practices. A UPS should only
be considered where absolute power quality is mandatory
(for example, for a data center).
8
a constant steady state voltage and function without error
during the external power defect.
Recommended Four-Wire Gauge for Various Wire Length Runs
These tables assume two wires in parallel for both positive and negative polarity. Run length refers to the one-way distance between the tool
power supply terminals and the product use terminals along the path where the wires will be located (not line of sight). All wire lengths are
rounded to the nearest whole number.
1 A Load
6 A Load
Wire Gauge
Wire Run Length
Wire Gauge
Wire Run Length
24
8 m (26')
22
2 m (7')
22
13 m (43')
20
3 m (11')
20
21 m (69')
18
6 m (18')
18
33 m (109')
16
9 m (29')
14
14 m (46')
12
22 m (71')
10
37 m (120')
2 A Load
Wire Gauge
Wire Run Length
24
4 m (13')
22
7 m (21')
7 A Load
20
10 m (34')
Wire Gauge
Wire Run Length
18
17 m (55')
20
3 m (10')
16
26 m (86')
18
5 m (16')
42 m (138')
16
7 m (24')
14
12 m (40')
12
18 m (61')
10
31 m (103')
14
3 A Load
Wire Gauge
Wire Run Length
24
3 m (9')
22
4 m (14')
8 A Load
20
7 m (23')
Wire Gauge
Wire Run Length
18
11 m (36')
20
3 m (9')
16
17 m (57')
18
4 m (14')
14
28 m (92')
16
7 m (21')
43 m (141')
14
11 m (35')
12
16 m (53')
10
27 m (90')
8
41 m (134')
12
4 A Load
Wire Gauge
Wire Run Length
24
2 m (7')
22
3 m (11')
9 A Load
20
5 m (17')
Wire Gauge
Wire Run Length
18
8 m (27')
18
4 m (12')
16
13 m (43')
16
6 m (16')
14
21 m (69')
14
9 m (31')
32 m (106')
12
14 m (47')
10
24 m (80')
8
36 m (119')
12
5 A Load
Wire Gauge
Wire Run Length
22
3 m (9')
10 A Load
20
4 m (14')
Wire Gauge
Wire Run Length
18
7 m (22')
18
2 m (7')
16
10 m (34')
16
5 m (17')
14
17 m (55')
14
8 m (28')
12
26 m (85')
12
13 m (42')
44 m (144')
10
22 m (72')
8
33 m (107')
10
9
Recommended Two-Wire Gauge for Various Wire Length Runs
These tables assume a single wire for both positive and negative polarity. Run length refers to the one-way distance between the tool power
supply terminals and the product use terminals along the path where the wires will be located (not line of sight). All wire lengths are rounded
to the nearest whole number.
1 A Load
6 A Load
Wire Gauge
Wire Run Length
Wire Gauge
Wire Run Length
24
4 m (13')
22
1 m (4')
22
7 m (22')
20
2 m (6')
20
11 m (35')
18
3 m (9')
18
17 m (55')
16
5 m (15')
14
7 m (23')
12
11 m (36')
10
19 m (60')
2 A Load
Wire Gauge
Wire Run Length
24
2 m (7')
22
4 m (11')
7 A Load
20
5 m (17’)
Wire Gauge
Wire Run Length
18
9 m (28')
20
2 m (5')
16
13 m (43')
18
3 m (8')
14
21 m (69')
16
4 m (12')
14
6 m (20')
12
9 m (31')
10
16 m (52')
3 A Load
Wire Gauge
Wire Run Length
24
2 m (5')
22
2 m (7')
8 A Load
20
4 m (12')
Wire Gauge
Wire Run Length
18
6 m (18')
20
2 m (5')
16
9 m (29')
18
3 m (7')
14
14 m (46')
16
4 m (11')
12
22 m (72')
14
6 m (18')
12
8 m (27')
10
14 m (45')
8
21 m (67')
4 A Load
Wire Gauge
Wire Run Length
24
1 m (4')
22
2 m (6')
9 A Load
20
3 m (9')
Wire Gauge
Wire Run Length
18
4 m (14')
18
2 m (6')
16
7 m (22')
16
3 m (8')
14
14 m (35')
14
5 m (16')
12
16 m (53')
12
7 m (24')
10
12 m (40')
8
18 m (60')
5 A Load
10
Wire Gauge
Wire Run Length
22
2 m (5')
10 A Load
20
3 m (7')
Wire Gauge
Wire Run Length
18
4 m (11')
18
2 m (4')
16
5 m (17')
16
3 m (9')
14
9 m (28')
14
4 m (14')
12
13 m (43')
12
7 m (21')
10
22 m (72')
10
11 m (36')
8
17 m (54')
References
[1] Alpha Wire, Alpha Wire Catalog, Master Catalog Version 3A , Elizabeth, NJ: Alpha Wire Company, 1997.
[2] National Fire Protection Association, National Electrical Code® (NEC®) 2011 Handbook, Quincy, MA: NFPA, 2010.
11
To view AE’s complete product portfolio, visit:
www.advanced-energy.com/en/Products.html
Advanced Energy Industries, Inc.
1625 Sharp Point Drive
Fort Collins, Colorado 80525 U.S.A.
T: 800.446.9167
F: +1.970.221.4670
www.advanced-energy.com
Specifications are subject to change without notice.
©2013 Advanced Energy Industries, Inc. All rights reserved. Advanced Energy®, and A Powerful Advantage™ are U.S.
trademarks of Advanced Energy Industries, Inc. National Electrical Code® and NEC® are trademarks of National Fire
Protection Association {NFPA).
ENG-24VDCInstallation-260-01 0M 12.13