Disclaimer: I'm not an electrical engineer, and rely on the information I can find when I need it.
Project: I have a heater controller I'm constructing. The heaters are 480, controlled by contactors. I have 480 3-phase coming in, as well as earth and neutral line. The controls (temperature controller, timer and contactor coils) are 240. Therefore, one leg of the 480 3-phase and the neutral line provide 240 VAC for the controls. On paper anyway.
Problem: Incoming voltage is high. My "480" line is 575 volts. The down-side of a complete brand-new transformer, panels and wiring from the street to my point of use I guess. Because of this, I have high voltage at my point of use (~330 volts).
Solution (?): Drop voltage to an acceptable level. Do search, find equations, purchase proper parts, test again, FAIL.
My math (since I'm no math genius):
AMPS= WATTS/VOLTS
In my case, I have 3W + 3W + 4VA for my initial calculation. I forgot the coils on the contactors in this but I'll get back to that later.
My amperage load came out to 0.042A
Resistor value= (volt drop)/AMPS
I need to drop ~110 volts, so that came out to be 2,619 Ohms
Power dissipation= (volt drop) X Amps
In my case I need to shed 4.62 Watts of heat
My parts: Went to the local supplier, and purchased two packages of 5-watt resistors. One is 2.2k Ohm; the other is 2.7k Ohm. I figured between the two, I could drop my voltage safely. Wattage seemed high enough to shed the heat.
Testing: "In God we trust; everyone else needs lots of data." So I test. Put the 2.2k in place, and test. No perceptible voltage drop. WTF, over? Tried second 2.2k from the package, in case I had a bad one. Same result. Test resistor directly with my (bottom of the line Fluke) and show ~1.something Ohm. WTF, Over? Test 2.7k resistor, see slightly higher resistance.
Thoughts: Getting back to the fact I forgot the two coils, I'm probably going to need to shed more heat. Maybe a 10-watt resistor is more appropriate. However, WHY do the resistors not test anywhere near spec? I presume the resistance will rise with heat build up, but if I over-volt the controllers (by more than 10%) I risk damage according to the manufacturer (Omega controllers by the way). I designed to use the single leg of 480 and neutral to simplify, and eliminate the need for a transformer, so I don't really want to go that route. A cheap switching power supply might work but I'm not sure how it will behave with the coils.
Anyway, smart people, help the idiot please.
Project: I have a heater controller I'm constructing. The heaters are 480, controlled by contactors. I have 480 3-phase coming in, as well as earth and neutral line. The controls (temperature controller, timer and contactor coils) are 240. Therefore, one leg of the 480 3-phase and the neutral line provide 240 VAC for the controls. On paper anyway.
Problem: Incoming voltage is high. My "480" line is 575 volts. The down-side of a complete brand-new transformer, panels and wiring from the street to my point of use I guess. Because of this, I have high voltage at my point of use (~330 volts).
Solution (?): Drop voltage to an acceptable level. Do search, find equations, purchase proper parts, test again, FAIL.
My math (since I'm no math genius):
AMPS= WATTS/VOLTS
In my case, I have 3W + 3W + 4VA for my initial calculation. I forgot the coils on the contactors in this but I'll get back to that later.
My amperage load came out to 0.042A
Resistor value= (volt drop)/AMPS
I need to drop ~110 volts, so that came out to be 2,619 Ohms
Power dissipation= (volt drop) X Amps
In my case I need to shed 4.62 Watts of heat
My parts: Went to the local supplier, and purchased two packages of 5-watt resistors. One is 2.2k Ohm; the other is 2.7k Ohm. I figured between the two, I could drop my voltage safely. Wattage seemed high enough to shed the heat.
Testing: "In God we trust; everyone else needs lots of data." So I test. Put the 2.2k in place, and test. No perceptible voltage drop. WTF, over? Tried second 2.2k from the package, in case I had a bad one. Same result. Test resistor directly with my (bottom of the line Fluke) and show ~1.something Ohm. WTF, Over? Test 2.7k resistor, see slightly higher resistance.
Thoughts: Getting back to the fact I forgot the two coils, I'm probably going to need to shed more heat. Maybe a 10-watt resistor is more appropriate. However, WHY do the resistors not test anywhere near spec? I presume the resistance will rise with heat build up, but if I over-volt the controllers (by more than 10%) I risk damage according to the manufacturer (Omega controllers by the way). I designed to use the single leg of 480 and neutral to simplify, and eliminate the need for a transformer, so I don't really want to go that route. A cheap switching power supply might work but I'm not sure how it will behave with the coils.
Anyway, smart people, help the idiot please.
Not 100% sure what you are doing here, however...…
Are you testing the resistors out of circuit ? You can't measure them when connected.
Does the heater controller draw a constant current ? If it varies, for example if there is a relay that activates somewhere, then the current draw may be very variable. In a quiescent state it may draw very very little current and so that is why you see no volt drop across the resistor.
Do the controllers have a mains transformer in them (240 to something low) OR do they use what we call a watt less dropper which in reality is a cap.
Lots of variables here and we would really need to see the circuit if the controller (its power supply) to see what might be a suitable solution.
Are you testing the resistors out of circuit ? You can't measure them when connected.
Does the heater controller draw a constant current ? If it varies, for example if there is a relay that activates somewhere, then the current draw may be very variable. In a quiescent state it may draw very very little current and so that is why you see no volt drop across the resistor.
Do the controllers have a mains transformer in them (240 to something low) OR do they use what we call a watt less dropper which in reality is a cap.
Lots of variables here and we would really need to see the circuit if the controller (its power supply) to see what might be a suitable solution.
Yes, did that, as noted above
The controller is constant; however, it activates a dry contact, which activates the coil of the contactor. One controller per contactor- two controllers and two contactors.
No idea, but I suspect a switching PS is inside the box, since it can accept 100-240 volt input...
We're not going to get that schematic. Omega is in CT but the controller is made for them in China. If I can get the voltage down in the 200-260 range it will all work fine.
480V phase - Phase is NOT 240V P-N (Unless the 480V is really US style split phase, which while possible would I think be unexpected, that is usually a 120-0-120 domestic sort of thing).
480V Phase-Phase would be 277V Phase to neutral, which is a US industrial standard (Mostly seen in lighting industrial applications IIRC).
I would be straight onto the supply company to tell them that your supply voltage was fully 20% high and demand that they fix it, probably a tap changer has been left at maximum when it really needs cranking down a bit.
If I was in your position I would find a local industrial electrician to sort this out, large three phase supplies are nothing to monkey with, and you clearly don't know what you are doing (At least watch a few of the youtube 'arc flash' videos to understand what the stakes are and why CAT III 600V is a very good thing on a multimeter, also why 'In Fluke we trust' is a thing among industrial sparks).
That said a 'control panel' transformer is probably part of your solution, 277 to 120 or even 480 - 120 should be available from a decent trade supplies place.
Seriously get the power company to tap your supply down a bit, and find someone who knows what they are about, you may have a LOT of PSC in play.
Regards, Dan.
480V Phase-Phase would be 277V Phase to neutral, which is a US industrial standard (Mostly seen in lighting industrial applications IIRC).
I would be straight onto the supply company to tell them that your supply voltage was fully 20% high and demand that they fix it, probably a tap changer has been left at maximum when it really needs cranking down a bit.
If I was in your position I would find a local industrial electrician to sort this out, large three phase supplies are nothing to monkey with, and you clearly don't know what you are doing (At least watch a few of the youtube 'arc flash' videos to understand what the stakes are and why CAT III 600V is a very good thing on a multimeter, also why 'In Fluke we trust' is a thing among industrial sparks).
That said a 'control panel' transformer is probably part of your solution, 277 to 120 or even 480 - 120 should be available from a decent trade supplies place.
Seriously get the power company to tap your supply down a bit, and find someone who knows what they are about, you may have a LOT of PSC in play.
Regards, Dan.
I appreciate your notes of caution, particularly for those who have not have arc-flash training and do not understand the dangers.
I have had that training, and have been working with high current 3-phase power for a long time now. In that regard, I know exactly what I'm doing. My Father was also an electrician so I've been exposed to household stuff (110 and 220V over here) before getting into industrial stuff.
I agree, we probably should have the tap changed. I'm guessing the installation was done (about three years ago now) based on our total projected load. We have three large rectifiers installed currently for the plasma spray process but they don't run continually. Also three robots on line. We have tons of capacity for expansion...
We have power to spare here but this voltage is too high (I guess we are lucky nothing else has been damaged)... I will contact the VP and ask him his opinion. Once the main voltage is back in line, my single phase solution will work.
I have had that training, and have been working with high current 3-phase power for a long time now. In that regard, I know exactly what I'm doing. My Father was also an electrician so I've been exposed to household stuff (110 and 220V over here) before getting into industrial stuff.
I agree, we probably should have the tap changed. I'm guessing the installation was done (about three years ago now) based on our total projected load. We have three large rectifiers installed currently for the plasma spray process but they don't run continually. Also three robots on line. We have tons of capacity for expansion...
We have power to spare here but this voltage is too high (I guess we are lucky nothing else has been damaged)... I will contact the VP and ask him his opinion. Once the main voltage is back in line, my single phase solution will work.
Just checked the mains again, and it's reading 484... Where it should be.
No changes here. Perhaps the utility company was making changes at the sub station to accommodate increased demand they will see with A/C units running? I don't know, but things are normal today...
I may get a digital volt meter and put it on the panel so we can keep an eye on that.
Any input on my math in the first post, and why the resistors do not measure at value?
No changes here. Perhaps the utility company was making changes at the sub station to accommodate increased demand they will see with A/C units running? I don't know, but things are normal today...
I may get a digital volt meter and put it on the panel so we can keep an eye on that.
Any input on my math in the first post, and why the resistors do not measure at value?
Agree, had a friend with a similar problem the utility was required by ordinance to fix it.
Yep, a control panel transformer plus a suitably butch fuse given how stiff your supply sounds, is probably what you want, 277 or 480V to 110V, totally standard off the shelf thing in the US.
Resistive droppers almost always suck, especially as they would have to be scaled for your coil current in addition to the standby load, so the voltage will be all over the shop, do it right, use a transformer.
I may have called the OPs expertise wrong, I was basing on Phase-> Neutral NOT being 1/2 Phase-> Phase in a three phase system.
Regards, Dan.
Resistive droppers almost always suck, especially as they would have to be scaled for your coil current in addition to the standby load, so the voltage will be all over the shop, do it right, use a transformer.
I may have called the OPs expertise wrong, I was basing on Phase-> Neutral NOT being 1/2 Phase-> Phase in a three phase system.
Regards, Dan.
The maths is OK for a resistive load but as such it makes some assumptions on the power supply present in the unit. Just because its specified to work over 100 to 240 doesn't necessarily mean an SMPS, it could still be a watt less dropper followed by a voltage regulator of some sort. I also think the power factor of something like that could be really low.
If a resistor reads out of spec when out of circuit then its either faulty or marked incorrectly, or the meter is faulty. Resistors usually fail by going high in value and then open circuit. Try reading a standard carbon film or metal film resistor of around the desired value and see if you get the same odd result.
I checked some other resistors and none of them are measuring correctly...
On the plus side, I tried a low wattage 10M ohm resistor I had and I'm finally getting some "action"- I got it to drop to 87 volts. My meter measures this resistor as 'open circuit', so the meter needs to be carefully placed in the nearest wood chipper prior to being burned. (but in it's defense, it really is just for voltage at the plasma gun and other basic stuff)
I can tolerate voltage swing- I have a 10% overage allowance on the controllers (the sensitive things) so if I can get my steady state voltage around ~216 that should allow for safety margin if it spikes up the 20% I say yesterday, with the coils not pulled in- basically static.
I don't need "exact" voltage which would necessitate a power supply.
On the plus side, I tried a low wattage 10M ohm resistor I had and I'm finally getting some "action"- I got it to drop to 87 volts. My meter measures this resistor as 'open circuit', so the meter needs to be carefully placed in the nearest wood chipper prior to being burned. (but in it's defense, it really is just for voltage at the plasma gun and other basic stuff)
I can tolerate voltage swing- I have a 10% overage allowance on the controllers (the sensitive things) so if I can get my steady state voltage around ~216 that should allow for safety margin if it spikes up the 20% I say yesterday, with the coils not pulled in- basically static.
I don't need "exact" voltage which would necessitate a power supply.
Have you measured the voltages with another meter as this one seems very suspect.
10M (10 million ohms) is about as conductive as a couple of feet (edit, or couple of hundred feet... you get the idea
) of slightly damp cotton thread... it would only pass a peak current of 0.000044 amps when connected across 440 volts. Not even enough to light an LED.
10M (10 million ohms) is about as conductive as a couple of feet (edit, or couple of hundred feet... you get the idea
) of slightly damp cotton thread... it would only pass a peak current of 0.000044 amps when connected across 440 volts. Not even enough to light an LED.
Firstly there is no such thing as a low end Fluke. You get what you pay for. The more features the more it cost.
It sound like your Fluke meter needs a bit of service.
I would start with a Qtip and, as close as you can find to 100%, isopropyl alcohol. Wet the Qtip and push it into the banana jack. If the Qtip won't fit easily then squeeze it down in width with a pair of pliers. Once you have the Qtip inserted rotate the Qtip back and forth. You will probaly see a lot of black stuff on the Qtip when you pull it out of the jack. Repeat until there is no more black deposit on the Qtip. Clean the probe's banana plugs as well.
It sound like your Fluke meter needs a bit of service.
I would start with a Qtip and, as close as you can find to 100%, isopropyl alcohol. Wet the Qtip and push it into the banana jack. If the Qtip won't fit easily then squeeze it down in width with a pair of pliers. Once you have the Qtip inserted rotate the Qtip back and forth. You will probaly see a lot of black stuff on the Qtip when you pull it out of the jack. Repeat until there is no more black deposit on the Qtip. Clean the probe's banana plugs as well.
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Update:
We have a line of dialogue with the local power utility. I sent them a mail with the details I had. Of course, they want to know "what other work was going on in the building"... (make sure to properly place blame before responding!!)
Anyway, it seems fine now. I'll presumably test further today with the heaters installed, which will have the whole system working and therefore I can monitor voltage drop when the coils pull in for the heater contactors.
It should be fine. But I'll keep you guys posted.
Thanks to everyone for the help, comments and suggestions.
We have a line of dialogue with the local power utility. I sent them a mail with the details I had. Of course, they want to know "what other work was going on in the building"... (make sure to properly place blame before responding!!)
Anyway, it seems fine now. I'll presumably test further today with the heaters installed, which will have the whole system working and therefore I can monitor voltage drop when the coils pull in for the heater contactors.
It should be fine. But I'll keep you guys posted.
Thanks to everyone for the help, comments and suggestions.
So much wrong with this thread that I doubt what to begin with.
1) this is a discussion involving DEADLY live voltages, with due respect the OP has no clue, it involves an Electrical, very high Voltage industrial inatallation and is well beyond the scope ow what DIY **AUDIO** handles.
AFAIK this is even forbidden or at least highly frown upon by Forum Rules.
2) that installation MUST be done by Registered/Licensed Professionals and not based on "something I read in the Internet".
Just a few notes, which anyway do not change what I wrote above:
Who also correctly suggested:
3) you claim:
**ANY** plain Electrician will know the relationship between phase-to-phase vs. phase-to-ground , it´s basic knowledge.
4)
Specially when he "measures" many from the same lot and "all are wrong" which is unheard of in modern commercially made resistors.
NO WAY a 2k2 or 2k7 resistor fresh from its package can measure "1 something".
Please save yourself a lot of headache (to put it lightly) and get a Registered Electrician or a properly trained and Licensed tech to do that job safely.
Take care.
1) this is a discussion involving DEADLY live voltages, with due respect the OP has no clue, it involves an Electrical, very high Voltage industrial inatallation and is well beyond the scope ow what DIY **AUDIO** handles.
AFAIK this is even forbidden or at least highly frown upon by Forum Rules.
2) that installation MUST be done by Registered/Licensed Professionals and not based on "something I read in the Internet".
Just a few notes, which anyway do not change what I wrote above:
No, it doesn´t. As duly noted by dmills .
Who also correctly suggested:
3) you claim:
does not match the knowledge level you are showing.
**ANY** plain Electrician will know the relationship between phase-to-phase vs. phase-to-ground , it´s basic knowledge.
4)
OR meter operator does not understand the meter or how to measure.
Specially when he "measures" many from the same lot and "all are wrong" which is unheard of in modern commercially made resistors.
Most probably you set the measuring Scale wrong, value is above maximum measurable/displayable and typicao over range indication is a digit "1" followed by blank spaces.
NO WAY a 2k2 or 2k7 resistor fresh from its package can measure "1 something".
See above comment.
Please save yourself a lot of headache (to put it lightly) and get a Registered Electrician or a properly trained and Licensed tech to do that job safely.
Take care.
Wow. Thanks for your input.
Meter is auto-ranging, simple meter. AC/DC volts, continuity and resistance. Fluke 10 is the model if I recall correctly (purchased decades ago, replaced by Fluke about one decade ago)
If it is a violation of forum rules to ask for assistance on checking mathematics, then I should be banned- along with the vast majority of members who have ever asked for assistance in that regard.
Clearly, I should have left out the background information to avoid being attacked. Since I'm so ignorant of high voltage that I was actually killed years ago doing this work, and this is actually my ghost posting now.
Meter is auto-ranging, simple meter. AC/DC volts, continuity and resistance. Fluke 10 is the model if I recall correctly (purchased decades ago, replaced by Fluke about one decade ago)
If it is a violation of forum rules to ask for assistance on checking mathematics, then I should be banned- along with the vast majority of members who have ever asked for assistance in that regard.
Clearly, I should have left out the background information to avoid being attacked. Since I'm so ignorant of high voltage that I was actually killed years ago doing this work, and this is actually my ghost posting now.
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Please review the forum rules. They have changed regarding high voltage line level postings.
> I tried a low wattage 10M ohm resistor I had and I'm finally getting some "action"- I got it to drop to 87 volts. My meter measures this resistor as 'open circuit', so the meter needs to be carefully placed in the nearest wood chipper
Series resistor *needs* a LOAD to "sag". No load, no sag.
If you are trying to measure "voltage" withOUT the relays loading your resistor, then it will read high until your *meter* loading approaches the resistor value. DMMs are often 1Meg to 10Meg. 482V to 87V suggests 2.2Megs in the meter, which is not an unlikely value for a Power (opposed to Electronics) DMM.
Many DMMs will NOT read resistances much higher than a Meg. That requires real-low input current. My Fluke will go 50Meg but that cost me (and is Electronics-trade). Another says "OL" for anything over 1.99Meg. Who the heck needs values that big? Not electricians.
Your relay seems to be ~~5K load. Indeed ~~2K *feeding a 5K load* should get your voltage down. 2K feeding a 2Meg meter, you will get 99.9% of the source voltage, "no drop". (And 10Meg feeding a 5K resistor/relay gets you 0.24V, which aint what you need.)
Yes, 2.5K at 10Watts "should" get your ON condition down more like what you want. Note that the OFF condition leaves full too-high line voltage across the switch that controls this relay-- is it good for that? Wiring also?
The 5 Watts waste heat won't break the budget, but will be heat you don't really want. There are autotransformers and isolation transformers for "any" likely need. And it is fairly common to tap 230V 370V 437V down to 24VAC and use 24V contactors.
Don't get side-tracked in hacks. You know what you need to do. Get the Line Voltage to be what it is supposed to be; otherwise is insanity and excess stress. If the "over-voltage" is a measurement problem, figure it out. Many DMMs get goofy when their batteries get weak. 3-phase comes wYe and Delta, which you know better than me, but is still confusable. And of course the Company guys have different blind-spots and political pressures.
Series resistor *needs* a LOAD to "sag". No load, no sag.
If you are trying to measure "voltage" withOUT the relays loading your resistor, then it will read high until your *meter* loading approaches the resistor value. DMMs are often 1Meg to 10Meg. 482V to 87V suggests 2.2Megs in the meter, which is not an unlikely value for a Power (opposed to Electronics) DMM.
Many DMMs will NOT read resistances much higher than a Meg. That requires real-low input current. My Fluke will go 50Meg but that cost me (and is Electronics-trade). Another says "OL" for anything over 1.99Meg. Who the heck needs values that big? Not electricians.
Your relay seems to be ~~5K load. Indeed ~~2K *feeding a 5K load* should get your voltage down. 2K feeding a 2Meg meter, you will get 99.9% of the source voltage, "no drop". (And 10Meg feeding a 5K resistor/relay gets you 0.24V, which aint what you need.)
Yes, 2.5K at 10Watts "should" get your ON condition down more like what you want. Note that the OFF condition leaves full too-high line voltage across the switch that controls this relay-- is it good for that? Wiring also?
The 5 Watts waste heat won't break the budget, but will be heat you don't really want. There are autotransformers and isolation transformers for "any" likely need. And it is fairly common to tap 230V 370V 437V down to 24VAC and use 24V contactors.
Don't get side-tracked in hacks. You know what you need to do. Get the Line Voltage to be what it is supposed to be; otherwise is insanity and excess stress. If the "over-voltage" is a measurement problem, figure it out. Many DMMs get goofy when their batteries get weak. 3-phase comes wYe and Delta, which you know better than me, but is still confusable. And of course the Company guys have different blind-spots and political pressures.
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I might suggest looking up kirchhoff's current law and kirchhoff's voltage law.
It's not difficult to understand and for the most is applicable to ac as well. Of course ac is more complex when dealing with reactive components but it's the same deal with account of the phase shift. kirchhoff''s laws are an extension and application of Ohm's law.
It's not difficult to understand and for the most is applicable to ac as well. Of course ac is more complex when dealing with reactive components but it's the same deal with account of the phase shift. kirchhoff''s laws are an extension and application of Ohm's law.
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