That’s not correct, assume 10 X running current for 10 seconds during startup.
That’s 100 seconds of running current for startup versus 3,600 seconds of running current for an hours use….Regards, Rod
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That’s not correct, assume 10 X running current for 10 seconds during startup.
That’s 100 seconds of running current for startup versus 3,600 seconds of running current for an hours use….Regards, Rod
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This reminds me of my energy engineering days, when working with a team of energy engineers who all have different native languages. Of course, none fully fluent in English, although they always thought they were.The biggest challenge was never the engineering / math, but rather, understanding what the true question, or issue was trying to be solved. The engineering / math was always the easy part. Same in your example here, you tricked AI with your question. But in all fairness, AI still did a good job of answering considering the confusing nature of your question. So kudos to AI, its response was reasonable, and the details provided demonstrated the basis for its answer.
If you asked AIs how much per hour does it cost to run a 30HP motor, and nothing else, it's response is accurate based on its assumption of $.013 kwh charge, a variable you can alter to fit your cost basis. However, your question provided the actual load in Volts and Amperage, which is more specific than the nominal rated HP of the motor. Since V*A = watts (lets leave out Power Factor here for this simple example), the stated motor load you asked in your question would cost to operate per hour:
220 Volts
73 amps
16,060 watts
16 KW (*1, for 1 hr operation)
0.12 $/KWH
1.92 $/hour to operate at your stated load.
Of course, your 73amp value might be the FLA value, not the actual load during operation, so costs should be even less.
A fully loaded TRUE 30HP load on a motor at 220V would not draw 73amps, it would draw 102 amps. This is what AI based its answer on, i.e. theoretical load, not a practical load. Hence the much higher cost per hour it calculated.
30 HP
0.75 KW / HP
22.5 KW Total load
22500 Watts
220 Volts
102 Amps
However, its very rare (almost NEVER) does the nominal HP rating of a motor actually represent the FLA, Full Load Amps. Hence why the FLA is always listed on the motor nameplate. A more accurate method to determine actual cost, if possible, is to get an amp meter reading from one of the legs of an operational motor under load. If designed properly, a motor should be oversized.
Also, motor efficiency factor is already taken into consideration when taking a real world amp reading, or operating from % of FLA value. Many large motors I tested in commercial and industrial settings for energy audits would often operate at 40-60% of FLA when fully loaded.
And yes, inrush, is not even a glitch on the overall consumption, as it occurs in a fraction of a second, so when averaged over time, it a complete non issue in nearly all applications.
Last edited by Will Blick; 05-31-2023 at 9:45 AM. Reason: claifying
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Your reply is perhaps a more interesting commentary on AI than on the underlying question of motor energy consumption.Originally Posted by Will Blick
I'm amazed (humbled?) daily at how reasoned and accurate the answers are from AI on even the most technical and niche of subjects.
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Considering AI is at its infancy, at least to us, the general public, I fully agree with you. I have run a lot of AI searches, and sometimes I marvel at the responses, and other times, I notice the flaws. I would run AI queries on things I knew the answer to, and sometimes the responses were spot on, other times they were mostly right, and a smaller % of the time, the response missed the boat completely. Of course, that will change with learning. What I do like, as in the OP query, is how the response is delivered, i.e. detailed enough so you can ascertain the basis of the response, that is critical, vs. just giving an answer.
However, when the subject matter gets more technical and/or complex (beyond the scope of the OP question) of course the responses become much more limiting, and sometimes, the AI simply admits, it can not answer the question, which I prefer vs. an erroneous response. I consider AI a GREAT first pass on any query, and sometimes its all you need....but when critical decisions need to be made, a knowledgeable human is often required to decipher the response on more technical issues. This not being a good example, as the AI response was not wrong, but at the same time it was not accurate.... it struggled with a loaded question
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It did not mention that 220 volts is incorrect and therefor the motor will draw more amps in the brownout then it would at 240 volts.
My swimming pool motor is variable speed with a display that shows rpm,watts, etc. Watts at full load shows the motor is well under 100% efficient. Half speed is about 1/10 the watts. I assume the flow rate is roughly 1/2 to maybe 1/4 since output pressure ratio is around that.
Bill D
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220 V is not incorrect. It's much less common than 240V, but still exists for various reasons in the USA. It's just a function of the hot leg (hot to neutral), which in USA we still see, 110V (the old norm from the 50's and prior, but very uncommon today), 115V, 120V (most common) and 125V. This is why motors have tolerances of incoming operating voltages. In the past 30yrs, I have lived in places where my incoming voltage was as low as 112V, and as high as 124V. From memory, I think the current standard in USA is 114V to 126V.
But yes, amp draw would increase proportionally as voltage drops, but total energy (watts) remains unchanged, as the load determines total energy draw (Ohm's law). Significant brownouts can be very problematic, as the voltage can drop below a devices min. voltage requirement. Many higher end machines have brown protection set at a level that will prevent damage to any downstream devices vulnerable to a voltage below the set point level.
Efficiency is can of worms beyond the scope of this thread
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Just to add a complexity in case anyone puts an ampmeter on their table saw motor. When a motor is not loaded, it acts like a big inductor. It will draw a fair amount of amps but the amps will be out of phase with the voltage. That phase difference is known as "power factor". When the motor is loaded, the power factor is close to one. When it's unloaded, the power factor is low, maybe 0.4.
The only thing you get charged for is watts, and watts are not just the amps times the voltage. It's the amps times the voltage, times the power factor.
Let's take a small motor, maybe a 3HP on a table saw. It might be rated at 10 amps at 240 volts, and that's for full loading (3HP). When unloaded, it may be pulling 6 amps but those amps will not be in phase with the voltage.
Anyway, if you measure the amps on an idling motor, you'll get a higher reading than you might expect.
Mike
Go into the world and do well. But more importantly, go into the world and do good.
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A few years back the local utility (city owned/operated) replaced our old dumb electro-mechanical meters with the latest and greatest smart meter. One of the reasons for that was that they were purchasing more bulk electricity from the provider than was being metered. That and labor-free reading were the reasons given for the swap.
Coincident with the change-out, everyone complained about an increase in bills. There was no rate increase, just an increase in measured usage. I've always suspected that the smart meters see the inrush of all the motors, (A/c, refrigerators, compressors, saws, etc) as billable usage while the inertia of the electro-mechanical version never registered it.
The techs working on the system agree, off the record, but will not say so publicly.
What do the experts think?
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I am certainly no expert, as I retired 25 yrs ago, technology changes fast on everything. OTOH, some basic issues remain fundamentally the same.
You mentioned the rates stayed the same, only the consumption has increased. Be sure the billing tariff did not change, to be certain they did not change the billing model in addition to the consumption.
As for your suspicion of added consumption, this is very commonplace. It's rare an old meter and new meter will read the same. Considering the utility was buying more power than it was selling, might be a result of old, under-reporting meters. I assume its a very small utility from your description. Has the utility found with new meters installed, the net buying / selling KWH's are more in parity now, so the problem resolved itself? If its a small utility, these things can often be found out with a phone call, which is not the case with a $20B a year utility
I was an expert witness in several of these cases, where the meter was over recording consumption, which equated to million$ in excess charges over many years. To determine this, we hire 3rd party certified metering companies whose data and testimony stands up in court. They install transducers on the incoming lines as well as the grounds, searching for ground leaks as well. They have sophisticated computers on site which report back to their offices. This is done for at least 3 months, if over recording is noticed, it is typically left on for 6 months. When the variance is noticed, not in your favor, then you call the utility, or if enough money is at stake such as the industrial facilities I was involved with... legal gets involved before contacting the utility.
If the extra billing is significant enough, you can all split the cost of 3rd party monitoring of a few of the meters to see if you are now being billed fairly, or the new meters are in fact, over recording. Just beware, there will never be perfect parity between the two, but if you are within a couple %, that's the best that can be expected. If the dollar amount is marginal, prob. not worth all this effort, and just try an old fashion phone call...maybe the utility will do their own checks, as I am pretty certain there goal is not to intentionally over charge you. Hope this helps...
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Start up energy use isn’t significant, it’s more likely that the new meters are more accurate…….Regards, Rod
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