Constant Voltage Transformer
- Thread starter Pitt123
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ELA
Senior Member
- Occupation
- Electrical Test Engineer
Yes it will help with dips:
Here is a link that provides some good info.
http://www.solahd.com/products/powerconditioning/cvs.htm
Click on specifications for more
Here is a link that provides some good info.
http://www.solahd.com/products/powerconditioning/cvs.htm
Click on specifications for more
dbuckley
Senior Member
- Location
- Canterbury, New Zealand
Just a word of caution about the old-school ferromagnetic constant voltage transformers - they dont like non-linear loads like computers...
ghostbuster
Senior Member
- Location
- Great White North
They also have a high output impedance and reflect electrical noise between all common secondary loads.
TxEngr
Senior Member
- Location
- North Florida
The threshold will vary by manufacturer for the processors and will sometimes vary by component of a manufacturer. Take a look at the literature for your devices. That said, as a rule of thumb, I typically use 90VAC as a minimum. Don't forget about components such as interposing relays as well as the driven devices. They may have a lower rating than the PLC system and still cause you problems.
ELA
Senior Member
- Occupation
- Electrical Test Engineer
If there is an assumption that it is a voltage problem , have you monitored the AC line? Is there a AC/DC power supply involved?
What type of "voltage" problem is assumed? Brown outs or transients?
I would not accept any assumptions without having done line voltage monitoring.
What are the symptoms of the failures? Are the PLCs being reset?
What type of "voltage" problem is assumed? Brown outs or transients?
I would not accept any assumptions without having done line voltage monitoring.
What are the symptoms of the failures? Are the PLCs being reset?
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
100115-1440 EST
My design criteria is generally 95 to 135 V. In the last 25 years I have gone to a constant voltage transformer at the input and greatly reduced the problems of tolerating this wide voltage variation.
In the early 60s I designed a proportional capacitance gage for liquid level measurement (an unbalanced bridge circuit) that without DC or AC voltage regulation had stability of 1% of full scale with an input variation of 95 to 135 V. Available integrated circuits did not exist at that time.
One of the problems with brute force series pass regulators is the very large amount of power that must be dissipated in the regulator in over-voltage conditions.
Suppose on a required 5 V output that you need a minimum input of 8 V to the series pass regulator at 95 V. Then approximately at 135 V the 8 V becomes 11.4 V. Suppose the load current at 5 V is 5 A. At the low end the series pass is dissipating (8-5)*5 = 15 W, and at the high end (11.4-5)*5 = 32 W. Note the output power is 5*5 = 25 W.
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My design criteria is generally 95 to 135 V. In the last 25 years I have gone to a constant voltage transformer at the input and greatly reduced the problems of tolerating this wide voltage variation.
In the early 60s I designed a proportional capacitance gage for liquid level measurement (an unbalanced bridge circuit) that without DC or AC voltage regulation had stability of 1% of full scale with an input variation of 95 to 135 V. Available integrated circuits did not exist at that time.
One of the problems with brute force series pass regulators is the very large amount of power that must be dissipated in the regulator in over-voltage conditions.
Suppose on a required 5 V output that you need a minimum input of 8 V to the series pass regulator at 95 V. Then approximately at 135 V the 8 V becomes 11.4 V. Suppose the load current at 5 V is 5 A. At the low end the series pass is dissipating (8-5)*5 = 15 W, and at the high end (11.4-5)*5 = 32 W. Note the output power is 5*5 = 25 W.
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We are currently measuring line voltage. The symptoms are PLC's loosing communication with the network.
I looked up the specification for the particular PLC and found it has a listed "input voltage range" of 85V AC to 265V AC. It has a "nominal input voltage" of 120/220V AC.
Does this mean that the PLC power supply should be able to handle voltage dips as low as 85V and still operate normally?
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
100117-2142 EST
Yes.
Some people are referring to these as a universal supply. Basically it is a wide input voltage range switching regulator and has high efficiency.
You are implying the PLCs are working fine except loose communication with the network. Does anything else loose network communication?
You might want to determine if network switches might be the problem, or the central computer or computers.
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Yes.
Some people are referring to these as a universal supply. Basically it is a wide input voltage range switching regulator and has high efficiency.
You are implying the PLCs are working fine except loose communication with the network. Does anything else loose network communication?
You might want to determine if network switches might be the problem, or the central computer or computers.
.
ELA
Senior Member
- Occupation
- Electrical Test Engineer
If the PLCs are losing communications but not resetting then I would not suspect the AC power (especially with such a wide input range).
Sounds like you need to do some network monitoring to see what is happening with network traffic.
For all you know at this point it could even be software?
Sounds like you need to do some network monitoring to see what is happening with network traffic.
For all you know at this point it could even be software?
This PLC in question is communicating to the network over a wireless connection. It is suspected that the voltage in put to the wireless transmitter is dipping and causing the wireless communication to drop out. I do not have the spec on the wireless unit, however is has a plug which plugs into an outlet and converts to 24V inside the plug. I'm not sure if this regulates as well as a power supply.
We put a power meter on this outlet and saw dips down to 112V when a large motor in the area was started. These dip times seemed to corrospond with the wireless communication being lost.
I wouldn't think 112V would be enough of a drop to cause issues, but I could be wrong. We are going to put a power supply on this wireless unit. Others have questioned frequency of the 120V during these disturbances.
We put a power meter on this outlet and saw dips down to 112V when a large motor in the area was started. These dip times seemed to corrospond with the wireless communication being lost.
I wouldn't think 112V would be enough of a drop to cause issues, but I could be wrong. We are going to put a power supply on this wireless unit. Others have questioned frequency of the 120V during these disturbances.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
100118-2101 EST
Pit123:
Assuming these wireless devices are your problem, then you could use a rechargeable battery, a lead-acid gel cell, as the power source, and float a charger across the battery. That charger might be your current power supply. Might need a current limiting resistor between the supply and the battery.
What is a power meter that reads voltage? What is its response time? Are you merely watching the meter to see the voltage drop to 112, or does it have a minimum reading capability?
Your plug-in supply simply may be a transformer, rectifier, and filter capacitor. This will have an output voltage proportional to input voltage with some small lag. Or it may be a semi-regulated switching supply; or a full regulated switching supply.
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Pit123:
Assuming these wireless devices are your problem, then you could use a rechargeable battery, a lead-acid gel cell, as the power source, and float a charger across the battery. That charger might be your current power supply. Might need a current limiting resistor between the supply and the battery.
What is a power meter that reads voltage? What is its response time? Are you merely watching the meter to see the voltage drop to 112, or does it have a minimum reading capability?
Your plug-in supply simply may be a transformer, rectifier, and filter capacitor. This will have an output voltage proportional to input voltage with some small lag. Or it may be a semi-regulated switching supply; or a full regulated switching supply.
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The power meter is a Fluke 1735 power meter. Not sure about response time. We are using the event capture feature, and I know that the event must be at least 1/2 cycle to trigger an event. We set the event capture to trigger +/- 5% of 120V and for each trigger it records voltage for 4 min. During each trigger we see volage dip to 120V and then recover after aprox 1s. The event waveform shows a max and min waveform which I'm assuming are the max and mins for any given sampling interval.
RETRAINDAILY
Senior Member
- Location
- PHX, arizona
what kind of network IP,data highway
ELA
Senior Member
- Occupation
- Electrical Test Engineer
It is interesting how information about your issue is slowly uncovered and how the landscape changes with the new information.
Now that we know we are talking about a wireless network could it possibly be RF interference with other RF devices?
Now that we know we are talking about a wireless network could it possibly be RF interference with other RF devices?
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
100118-2217 EST
Pitt123:
I do not have personal experience with that meter, but it should be adequate for your purpose.
Thus, the voltage drop you have mentioned I would not expect to have caused a problem with the power supply to your RF units.
Maybe try a Variac on the input to the supply and lower the input voltage until the RF link fails and see what voltage that is.
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Pitt123:
I do not have personal experience with that meter, but it should be adequate for your purpose.
Thus, the voltage drop you have mentioned I would not expect to have caused a problem with the power supply to your RF units.
Maybe try a Variac on the input to the supply and lower the input voltage until the RF link fails and see what voltage that is.
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RETRAINDAILY
Senior Member
- Location
- PHX, arizona
That big motor is on a drive?
all your network wires are well away?
we don't put the cables in the pundit we sticky back them to the front corner as far as possible from the drives and mount the wireless device well away from the cabinet.
all your network wires are well away?
we don't put the cables in the pundit we sticky back them to the front corner as far as possible from the drives and mount the wireless device well away from the cabinet.
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