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Generators and Power factor
Recently took delivery of the Wolf 800 Generator, at just under a 100 notes
I thought it would come in handy for our all too common power cuts, not much output at 650 watts but will run the gas central heating and the tele! Reasonabale little genny set it up runs fine does the job i want, however looking thru the instruction booklet I came accross the following table, http://www.stuartstuart.fsnet.co.uk/misc/gen1.jpg and I am clueless to what it is going on about, maybe someone on this group can explain. Lighting, Power Factor = 1 Load = ~650W Power Tools Power Factor = 0.8 ~ 0.95 Load = 520W Electric Motors Power Factor =0.4 ~ 0.75 Load = 220W The first bit seems reasonable enough, use lighting up to its max output of 650W The next two bits is where I am getting confused. Is there some difference between a power tool and an electic motor, after all I can't think of a power tool that dosn't have an electric motor! (maybe a Soldering Iron ?) So what does it all mean? Presumably the power factor is a percentage, so power tools 80 - 95% of 650Watts. does this mean that the (80% 0f 650=) 520W is a minimun, if it is the maximun then what does the 95% represent? Anyway, I have plugged it all in and it does what I want, but I am curious as to what that table is all about, I have emailed the manufacturers but I won' hold my breath for their reply! Another Question, can these types of generators ever damage TVs, Videos or computers? should I use a surge protector? |
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"Stuart" wrote in message ... Another Question, can these types of generators ever damage TVs, Videos or computers? Yes if you start them with the equipmet plugged in. should I use a surge protector? A good one may help but just unplug first. I would suggest instead getting a battery driven UPS for the computer or TV and keep the generator for the lights and central heating. |
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Stuart wrote:
Recently took delivery of the Wolf 800 Generator, at just under a 100 notes I thought it would come in handy for our all too common power cuts, not much output at 650 watts but will run the gas central heating and the tele! You will probably find in the small print it says an output of 650 VA rather than watts, of which more anon... Reasonabale little genny set it up runs fine does the job i want, however looking thru the instruction booklet I came accross the following table, http://www.stuartstuart.fsnet.co.uk/misc/gen1.jpg and I am clueless to what it is going on about, maybe someone on this group can explain. Lighting, Power Factor = 1 Load = ~650W OK this one is easy enough. What they are saying is the load is a plain resistive one. For an incandescent bulb this is true (however it is not true for many fluorescent lights). When you are dealing with loads that look like a resistor, then you can treat AC circuits pretty much like you would a DC one. All the normal formula apply; so 650 VA (or volt amps) is exactly the same as 650W. Power Tools Power Factor = 0.8 ~ 0.95 Load = 520W Electric Motors Power Factor =0.4 ~ 0.75 Load = 220W Now things get a bit more interesting. When you start talking about loads that have some capacitive or inductive elements as well as a resistive one, you no longer have a simple load, but a complex one. This is now more correctly called an impedance. Inductors (i.e. things with windings) will exhibit no resistance (other than that of the wire from which they are made) when passing DC. Inductors like steady state current flow, but will "fight" changes of current (by releasing energy stored as a magnetic field in its coil). This will result in the alternating current flow to no longer be aligned with the alternating voltage. The current flow is now delayed (or phase shifted) by 90 degrees for a perfect inductor. Capacitors show a similar effect, but in the opposite way, they will block DC, but pass AC ever more readily as the frequency rises. In a perfect capacitor the current waveform will lead the voltage one by 90 degrees. So to arrive at the total impedance you need to do a sum which adds the capacitive and inductive reactance to the DC resistance. To complicate matters, the phase shift involved with the AC reactive components means the sum must be done in the complex number domain to allow for the magnitude and angle componets of the reactance to be taken into account (i.e. you are adding vectors and not scalars) The result will usualy not be a simple numeric answer either, but a vector which has a phase angle component. The first bit seems reasonable enough, use lighting up to its max output of 650W Yup, just like DC. Unless the lights are fluorescent in which case they will have a capacitive element to their load as well. The next two bits is where I am getting confused. Is there some difference between a power tool and an electic motor, after all I can't think of a power tool that dosn't have an electric motor! (maybe a Soldering Iron ?) So what does it all mean? Presumably the power factor is a percentage, so power tools 80 - 95% of 650Watts. does this mean that the (80% 0f 650=) 520W is a minimun, if it is the maximun then what does the 95% represent? The power factor simply the ratio of "real" to "apparent" power. The apparent power is what your generator "sees" as the load. The "real" power is what is actually gets transferred into the load to do real work, rather than that used to overcome the reactive effects of the inductors and capacitors in the load. There is a nice description he- http://en.wikipedia.org/wiki/Power_factor Anyway, I have plugged it all in and it does what I want, but I am curious as to what that table is all about, I have emailed the manufacturers but I won' hold my breath for their reply! Its one of those simple questions where the answer starts to get quite complex (pun not intended) quite quickly! Another Question, can these types of generators ever damage TVs, Videos or computers? should I use a surge protector? Once it is up and running it ought to have a reasonably decent sine wave output so long as you are not loading it near the limit. You would need to be careful as loads switch in and our however as this could mess up the output of the genny briefly. -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
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On Wed, 12 Jan 2005 04:35:22 +0000, John Rumm wrote:
snip Now that was a pretty fair - and accurate - description of power factor and its ramifications. Wonder how many others will read the OP and jump straight in with *their* interpetation, instead of reading the replies first? :-) -- the dot wanderer at tesco dot net |
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On Wed, 12 Jan 2005 07:33:25 UTC, Wanderer wrote:
On Wed, 12 Jan 2005 04:35:22 +0000, John Rumm wrote: snip Now that was a pretty fair - and accurate - description of power factor and its ramifications. It was...but didn't answer the question about the difference between power tools and electric motors...! -- Bob Eager begin a new life...dump Windows! |
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"Bob Eager" wrote in message ... On Wed, 12 Jan 2005 07:33:25 UTC, Wanderer wrote: On Wed, 12 Jan 2005 04:35:22 +0000, John Rumm wrote: snip Now that was a pretty fair - and accurate - description of power factor and its ramifications. It was...but didn't answer the question about the difference between power tools and electric motors...! No, and although it all sounded very clever it failed to answer any of the questions! OK it did answer the one about lights but then again I answered that myself! So, Power Tools - "0.8 - 0.95" If the 520Watts equates to 0.8 (80%) Is that a min or max, what is the 0.95? And is this only power tools without electric motors? Such as an incredibly big soldering iron? Just out of interest I connected my 750watt jig saw and it worked just fine, even under load! It also works the water pump at the low setting which is 40watts, so what exactly is "Electric Motors" (0.4 - 0.75) 220W represent. |
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On Wed, 12 Jan 2005 08:27:33 UTC, "Stuart" wrote:
Now that was a pretty fair - and accurate - description of power factor and its ramifications. It was...but didn't answer the question about the difference between power tools and electric motors...! So, Power Tools - "0.8 - 0.95" If the 520Watts equates to 0.8 (80%) Is that a min or max, what is the 0.95? A max of between 0.8 and 0.95, depending on the power factor of the actual load being used. These will vary. And is this only power tools without electric motors? Such as an incredibly big soldering iron? That's pretty well a resistive load. I've never heard of a soldering iron being called a 'power tool' although I guess that one could argue that technically it is. Just out of interest I connected my 750watt jig saw and it worked just fine, even under load! It also works the water pump at the low setting which is 40watts, so what exactly is "Electric Motors" (0.4 - 0.75) 220W represent. The maximum safe load without possible damage to the generator. You can connect more for various reasons; the power factor may be a bit 'better' in some cases, and most things will stand an overload for a while without melting, burning out or catching fire! I'm not sure of what they're getting at with the 'power tools' or 'electric motors' bit...except that perhaps power tools uses motors with a better power factor. Sometimes I wish I'd studied proper electrical engineering! -- Bob Eager begin a new life...dump Windows! |
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In article ,
Stuart wrote: Lighting, Power Factor = 1 Load = ~650W Power Tools Power Factor = 0.8 ~ 0.95 Load = 520W Electric Motors Power Factor =0.4 ~ 0.75 Load = 220W The next two bits is where I am getting confused. Is there some difference between a power tool and an electic motor, after all I can't think of a power tool that dosn't have an electric motor! Most power tools use a series-wound universal motor, and this type of motor can have a high power factor. But an induction motor (such as in a fridge, or blower motor in a c/h boiler) can have an awful power factor. ...................... So what does it all mean? Presumably the power factor is a percentage, so power tools 80 - 95% of 650Watts. does this mean that the (80% 0f 650=) 520W is a minimun, if it is the maximun then what does the 95% represent? You've sussed it. Real Power, in Watts = Volt*Amps*PF. Another Question, can these types of generators ever damage TVs, Videos or computers? should I use a surge protector? Possibly, but I don't think I would chance it.... too much to lose just for a bit of rubbishy telly during a power cut. Might be safer to use a UPS and let the generator float-charge the battery. -- Tony Williams. |
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Recently took delivery of the Wolf 800 Generator, at just under a 100
notes no offence, but you were robbed... I bought one (a rebranded version) for £43+vat at Makro The next two bits is where I am getting confused. Is there some difference between a power tool and an electic motor, no idea, but I "tried" to use an angle grinder (500w motor) hooked up to the genie and it failed miserably, however, a 1300watt pressure washer worked fine... weird LJ |
#10
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In an earlier contribution to this discussion,
Stuart wrote: Recently took delivery of the Wolf 800 Generator, at just under a 100 notes I thought it would come in handy for our all too common power cuts, not much output at 650 watts but will run the gas central heating and the tele! Reasonabale little genny set it up runs fine does the job i want, however looking thru the instruction booklet I came accross the following table, http://www.stuartstuart.fsnet.co.uk/misc/gen1.jpg and I am clueless to what it is going on about, maybe someone on this group can explain. Lighting, Power Factor = 1 Load = ~650W Power Tools Power Factor = 0.8 ~ 0.95 Load = 520W Electric Motors Power Factor =0.4 ~ 0.75 Load = 220W The first bit seems reasonable enough, use lighting up to its max output of 650W The next two bits is where I am getting confused. Is there some difference between a power tool and an electic motor, after all I can't think of a power tool that dosn't have an electric motor! (maybe a Soldering Iron ?) So what does it all mean? Presumably the power factor is a percentage, so power tools 80 - 95% of 650Watts. does this mean that the (80% 0f 650=) 520W is a minimun, if it is the maximun then what does the 95% represent? Anyway, I have plugged it all in and it does what I want, but I am curious as to what that table is all about, I have emailed the manufacturers but I won' hold my breath for their reply! Another Question, can these types of generators ever damage TVs, Videos or computers? should I use a surge protector? Let me have a go at a simplified version of John Rumm's explanation. For any AC device, the voltage and current are not constant - but vary sinusoidally (as in a sine wave) 50 times per second. When the load is purely resistive - as in a normal light bulb, or soldering iron - the current is exactly in phase with the voltage - i.e. the phase angle is zero. When the load is reactive - as in electric motors etc. with capacitance and/or inductance - there is a phase shift so that the current is no longer in phase with the voltage, but leads it or lags behind it by a phase angle, which varies from device to device. In all cases, the power consumed is calculated by multiplying the RMS (Root Mean Square) Voltage by the RMS Current by the Power Factor - where the Power Factor is the cosine of the phase angle. Your generator is apparently capable of delivering 650 watts for resistive loads (where the phase angle is zero, and the power factor is 1). So, at 240v, it can deliver a current of 650/240 = 2.7 amps. But it can *still* only deliver 2.7 amps when reactive loads are used. So if you have a device with a power factor of 0.4 (phase angle 66 degrees), you only get a power output of 240 x 2.7 x 0.4 = 260 watts rather than the original 650. As someone else said, the generator has an output of 650 VA rather than 650 watts. This is a measure of volts x amps (ignoring phase angle) and only equates to 650 watts for purely resistive loads. HTH. -- Cheers, Set Square ______ Please reply to newsgroup. Reply address is invalid. |
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"Bob Eager" wrote in message ... On Wed, 12 Jan 2005 07:33:25 UTC, Wanderer wrote: On Wed, 12 Jan 2005 04:35:22 +0000, John Rumm wrote: snip Now that was a pretty fair - and accurate - description of power factor and its ramifications. It was...but didn't answer the question about the difference between power tools and electric motors...! Bob Eager It's the difference with some electric motors have carbon brushes and some which use inductive electric motors. The "Electric Motor" part of the table is motors without carbon brushes (Inductive motors). The "Power Tools" part of the table is for electric motors with carbon brushes fitted (Reactive motors). |
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"Set Square" wrote in message ... In an earlier contribution to this discussion, Stuart wrote: Recently took delivery of the Wolf 800 Generator, at just under a 100 notes I thought it would come in handy for our all too common power cuts, not much output at 650 watts but will run the gas central heating and the tele! Reasonabale little genny set it up runs fine does the job i want, however looking thru the instruction booklet I came accross the following table, http://www.stuartstuart.fsnet.co.uk/misc/gen1.jpg and I am clueless to what it is going on about, maybe someone on this group can explain. Lighting, Power Factor = 1 Load = ~650W Power Tools Power Factor = 0.8 ~ 0.95 Load = 520W Electric Motors Power Factor =0.4 ~ 0.75 Load = 220W The first bit seems reasonable enough, use lighting up to its max output of 650W The next two bits is where I am getting confused. Is there some difference between a power tool and an electic motor, after all I can't think of a power tool that dosn't have an electric motor! (maybe a Soldering Iron ?) So what does it all mean? Presumably the power factor is a percentage, so power tools 80 - 95% of 650Watts. does this mean that the (80% 0f 650=) 520W is a minimun, if it is the maximun then what does the 95% represent? Anyway, I have plugged it all in and it does what I want, but I am curious as to what that table is all about, I have emailed the manufacturers but I won' hold my breath for their reply! Another Question, can these types of generators ever damage TVs, Videos or computers? should I use a surge protector? Let me have a go at a simplified version of John Rumm's explanation. Or even more simplified. There are two different types of Electric Motor, Inductive, which doesn't use carbon brushes to make it work, and Power Tool Electric Motors that do use carbon brushes to make it work. Inductive loads have a huge variation in the voltage and current they draw from a gennie, and cause the output to swing positive and negative a lot more, especially on start up, than an electric motor that uses carbon brushes to send the voltage and current through the winding coils. The table seperates them into two catagories of "Electic Motors" and "Power Tools" and that's the only difference. Simple. For any AC device, the voltage and current are not constant - but vary sinusoidally (as in a sine wave) 50 times per second. When the load is purely resistive - as in a normal light bulb, or soldering iron - the current is exactly in phase with the voltage - i.e. the phase angle is zero. When the load is reactive - as in electric motors etc. with capacitance and/or inductance - there is a phase shift so that the current is no longer in phase with the voltage, but leads it or lags behind it by a phase angle, which varies from device to device. In all cases, the power consumed is calculated by multiplying the RMS (Root Mean Square) Voltage by the RMS Current by the Power Factor - where the Power Factor is the cosine of the phase angle. Your generator is apparently capable of delivering 650 watts for resistive loads (where the phase angle is zero, and the power factor is 1). So, at 240v, it can deliver a current of 650/240 = 2.7 amps. But it can *still* only deliver 2.7 amps when reactive loads are used. So if you have a device with a power factor of 0.4 (phase angle 66 degrees), you only get a power output of 240 x 2.7 x 0.4 = 260 watts rather than the original 650. As someone else said, the generator has an output of 650 VA rather than 650 watts. This is a measure of volts x amps (ignoring phase angle) and only equates to 650 watts for purely resistive loads. HTH. -- Cheers, Set Square ______ Please reply to newsgroup. Reply address is invalid. |
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in2minds wrote:
Recently took delivery of the Wolf 800 Generator, at just under a 100 notes no offence, but you were robbed... I bought one (a rebranded version) for £43+vat at Makro The next two bits is where I am getting confused. Is there some difference between a power tool and an electic motor, no idea, but I "tried" to use an angle grinder (500w motor) hooked up to the genie and it failed miserably, however, a 1300watt pressure washer worked fine... weird Starting current versus running current. A very high efficiency motor can draw HUGE startup currents quite out of proportion to its actual running current, and its also instructivce to see whether its input or output ower being quoted. A cheap electriv motor may lose up to 40% of the power - or more. A good one can be 95% efficient. LJ |
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On Wed, 12 Jan 2005 11:09:16 UTC, "BigWallop"
wrote: It was...but didn't answer the question about the difference between power tools and electric motors...! It's the difference with some electric motors have carbon brushes and some which use inductive electric motors. Ah, thanks...thought it might be something like that...! -- Bob Eager begin a new life...dump Windows! |
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In an earlier contribution to this discussion,
BigWallop wrote: Or even more simplified. There are two different types of Electric Motor, Inductive, which doesn't use carbon brushes to make it work, and Power Tool Electric Motors that do use carbon brushes to make it work. Inductive loads have a huge variation in the voltage and current they draw from a gennie, and cause the output to swing positive and negative a lot more, especially on start up, than an electric motor that uses carbon brushes to send the voltage and current through the winding coils. The table seperates them into two catagories of "Electic Motors" and "Power Tools" and that's the only difference. Simple. It may be simple, but it totally fails to address the question about power factor! Nowhere have you made any reference to phase angle between volts and current - which is fundamental to the whole thing. Startup current vs running current is an entirely different issue. Whilst it needs to be taken into consideration, it has nothing to do with the question which the OP asked - which was why the Power Factor was different for different types of device. -- Cheers, Set Square ______ Please reply to newsgroup. Reply address is invalid. |
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On Wed, 12 Jan 2005 00:30:13 -0000, "Stuart" wrote:
The next two bits is where I am getting confused. Is there some difference between a power tool and an electic motor, They're assuming "power tool" is a brushed motor (most hand-held tools) and "electric motor" is an induction motor (bigger stationary machines). Unless you're a woodwork shop, assume "power tool" for all. If you _really_ care, the electrical FAQs at www.owwm.com are good on power tool motors. -- Smert' spamionam |
#17
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Stuart wrote:
No, and although it all sounded very clever it failed [...] A simpler way to think about it is to think of your genny as having a current rating rather than a power rating. Since the power rating at unity power factor is given as 650 watts, we can deduce that the current rating is 650 watts divided by 230 volts, which is about 2.8 amps. Most (or at least "many") appliance rating plates give a full-load current rating. If this is 2.8 A or less, the genny should be able to run the appliance OK (although it might struggle to start some things with 'larger' motors). -- Andy |
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Tony Williams wrote:
In article , Stuart wrote: Lighting, Power Factor = 1 Load = ~650W Power Tools Power Factor = 0.8 ~ 0.95 Load = 520W Electric Motors Power Factor =0.4 ~ 0.75 Load = 220W The next two bits is where I am getting confused. Is there some difference between a power tool and an electic motor, after all I can't think of a power tool that dosn't have an electric motor! Most power tools use a series-wound universal motor, and this type of motor can have a high power factor. But an induction motor (such as in a fridge, or blower motor in a c/h boiler) can have an awful power factor. ...................... So what does it all mean? Presumably the power factor is a percentage, so power tools 80 - 95% of 650Watts. does this mean that the (80% 0f 650=) 520W is a minimun, if it is the maximun then what does the 95% represent? You've sussed it. Real Power, in Watts = Volt*Amps*PF. Another Question, can these types of generators ever damage TVs, Videos or computers? should I use a surge protector? Possibly, but I don't think I would chance it.... too much to lose just for a bit of rubbishy telly during a power cut. The only bit of te telly at risk from voltage surges is teh swtched mode PSU. Most are ramarkably tolerant. Might be safer to use a UPS and let the generator float-charge the battery. SAafer, but arguable as to how necessary. Worth putting a meter on the gennie and seeing how high the voltage goes. Most mains side TV stuff is rated at 400v = peak voltage of 280vAC. |
#19
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Set Square wrote:
In an earlier contribution to this discussion, BigWallop wrote: Or even more simplified. There are two different types of Electric Motor, Inductive, which doesn't use carbon brushes to make it work, and Power Tool Electric Motors that do use carbon brushes to make it work. Inductive loads have a huge variation in the voltage and current they draw from a gennie, and cause the output to swing positive and negative a lot more, especially on start up, than an electric motor that uses carbon brushes to send the voltage and current through the winding coils. The table seperates them into two catagories of "Electic Motors" and "Power Tools" and that's the only difference. Simple. It may be simple, but it totally fails to address the question about power factor! Nowhere have you made any reference to phase angle between volts and current - which is fundamental to the whole thing. Startup current vs running current is an entirely different issue. Whilst it needs to be taken into consideration, it has nothing to do with the question which the OP asked - which was why the Power Factor was different for different types of device. 'Leakeage' inductance. |
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"Stuart" wrote in message ... Recently took delivery of the Wolf 800 Generator, at just under a 100 notes I thought it would come in handy for our all too common power cuts, not much output at 650 watts but will run the gas central heating and the tele! Reasonabale little genny set it up runs fine does the job i want, however looking thru the instruction booklet I came accross the following table, http://www.stuartstuart.fsnet.co.uk/misc/gen1.jpg and I am clueless to what it is going on about, maybe someone on this group can explain. Lighting, Power Factor = 1 Load = ~650W Power Tools Power Factor = 0.8 ~ 0.95 Load = 520W Electric Motors Power Factor =0.4 ~ 0.75 Load = 220W The first bit seems reasonable enough, use lighting up to its max output of 650W The next two bits is where I am getting confused. Is there some difference between a power tool and an electic motor, after all I can't think of a power tool that dosn't have an electric motor! (maybe a Soldering Iron ?) So what does it all mean? Presumably the power factor is a percentage, so power tools 80 - 95% of 650Watts. does this mean that the (80% 0f 650=) 520W is a minimun, if it is the maximun then what does the 95% represent? Anyway, I have plugged it all in and it does what I want, but I am curious as to what that table is all about, I have emailed the manufacturers but I won' hold my breath for their reply! Another Question, can these types of generators ever damage TVs, Videos or computers? should I use a surge protector? There have been enough discussions about power factor but I feel none are likely to be helpful to the lay man. Generators are rugged beast and can cope with a great deal of abuse. You can typically draw more than the rated power though the engine will start to struggle. It is the power which determines whether the engine can cope or not where power factor will have little effect. When a load with a poor power factor is used the "useful" current is higher than indicated by power alone. These give rise to copper losses in the generator part itself and creates heat. If you can get a true RMS meter reading Amps then it becomes easy to determine whether if the VA loading is exceeded. If the load is intermittent then internal heating effects are unlikely to be a problem. For the purists, current phase lag or lead is not the only cause of reduced power factor. Many power supplies draw a non sinusoidal current and reduce power factor accordingly. Old PCs would have this characteristic! My experience is that I have never damaged electrical stuff using a generator. To be honest I'm not convinced a surge protector is going to do much and have never used one! |
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The Natural Philosopher wrote:
A very high efficiency motor can draw HUGE startup currents quite out of proportion to its actual running current, and its also instructivce to see whether its input or output ower being quoted. A cheap electriv motor may lose up to 40% of the power - or more. A good one can be 95% efficient. Something to bear in mind next time someone starts a cheap power tool thread! It is not only the motor losses that add up, there are also the mechanical ones in poorly made gearboxes etc. The upshot of which is that if input power is being quoted, the tool may perform way below the expectation that would be given from the numbers alone (PPPoo tools anyone?). If it is the output power being quoted (far less common on cheap tools), then you can expect it to draw more power than you would otherwise expect. -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
#22
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In article , John
Rumm writes The Natural Philosopher wrote: A very high efficiency motor can draw HUGE startup currents quite out of proportion to its actual running current, and its also instructivce to see whether its input or output ower being quoted. A cheap electriv motor may lose up to 40% of the power - or more. A good one can be 95% efficient. Something to bear in mind next time someone starts a cheap power tool thread! It is not only the motor losses that add up, there are also the mechanical ones in poorly made gearboxes etc. The upshot of which is that if input power is being quoted, the tool may perform way below the expectation that would be given from the numbers alone (PPPoo tools anyone?). Yes and what a heap of dung they are. Never buying another one;((( -- Tony Sayer |
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Stuart wrote:
No, and although it all sounded very clever it failed to answer any of the questions! OK it did answer the one about lights but then again I answered that myself! Cheeky sod ;-) The only "question" not directly addressed that I can see, was the varying power factor attributable to different types of electric motor. So, Power Tools - "0.8 - 0.95" If the 520Watts equates to 0.8 (80%) Is that a min or max, what is the 0.95? And is this only power tools without electric motors? Such as an incredibly big soldering iron? This will be most common tools with universal motors. Things with heaters can be somewhat inductive, so even your soldering iron may not have a power factor of 1. Just out of interest I connected my 750watt jig saw and it worked just fine, even under load! It also works the water pump at the low setting which is 40watts, so what exactly is "Electric Motors" (0.4 - 0.75) 220W represent. Try this one: http://en.wikipedia.org/wiki/Induction_motor As you can see there are in fact a large number of permutations of "electric motor" - not just "with brushes", and "induction". As you can imagine, as you start adding field coils to the load in addition to the motor windings, the electrical load starts getting ever more complex. Add to that the fact that many induction motors have a capacitor used to help them start which is switched out when running, you get a load that will have a dynamic power factor that changes as the motor starts, and runs, and also changes with (mechanical) load. There is also the separate issue of the inrush current required by your appliance at switch on. If the generator is not able to meet the demands for that, then you may never get the thing running in the first place, even if in theory the generator should be able to supply it once it is up and running. -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
#24
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"in2minds" wrote in message ... Recently took delivery of the Wolf 800 Generator, at just under a 100 notes no offence, but you were robbed... I bought one (a rebranded version) for £43+vat at Makro Ours has the Wolf at not much more either. |
#25
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In article ,
Tony Williams wrote: In article , Stuart wrote: The next two bits is where I am getting confused. Is there some difference between a power tool and an electic motor, after all I can't think of a power tool that dosn't have an electric motor! Most power tools use a series-wound universal motor, and this type of motor can have a high power factor. But an induction motor (such as in a fridge, or blower motor in a c/h boiler) can have an awful power factor. While in maplin the other day I picked up one of these: http://www.maplin.co.uk/Module.aspx?... ID=&doy=12m1 This measures volt, current (and can show watts etc) as well as keeping track of kwh etc. One thing that surprised me was that it has a PF option that shows you the power factor of whatever is plugged into it. For 12quid it seemed a bargain so I picked one up. Haven't a clue how accurate it really is but its a gadget :-) The manual that comes with it is not exactly great either - nice engrish. It seems to return about the correct values for my kettle and a couple of smaller appliances. Also, it shows the kettle to have a PF of 1 near as dammit (as I would expect) right down to my cordless drill charger which it claims has a PF of .25. Its a cheapy wickes cordless with a 1hr charger - I guess its plausible. Not tried it on the fridge yet as that requires effort moving the fridge Darren |
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John Rumm wrote:
The Natural Philosopher wrote: A very high efficiency motor can draw HUGE startup currents quite out of proportion to its actual running current, and its also instructivce to see whether its input or output ower being quoted. A cheap electriv motor may lose up to 40% of the power - or more. A good one can be 95% efficient. Something to bear in mind next time someone starts a cheap power tool thread! It is not only the motor losses that add up, there are also the mechanical ones in poorly made gearboxes etc. The upshot of which is that if input power is being quoted, the tool may perform way below the expectation that would be given from the numbers alone (PPPoo tools anyone?). If it is the output power being quoted (far less common on cheap tools), then you can expect it to draw more power than you would otherwise expect. The motors used in cordless power tools are at best 55% efficient. Even the best ones. |
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Andy Dingley wrote:
On Wed, 12 Jan 05 19:41:41 GMT, (dmc) wrote: While in maplin the other day I picked up one of these: http://www.maplin.co.uk/Module.aspx?...1&source=15&Wo rldID=&doy=12m1 This measures volt, current (and can show watts etc) as well as keeping track of kwh etc. It also measures watts, volt-amps and power factor, so you can find out for yourself about all those different motors. I was curious about that, but the Maplin list (and the salesdroid) seemed to imply that it only measured immediate power. Can I set it off counting for a week and come back to a tally of kWh ? I want to track a dehumidifer that runs intermittently. Although the product description doesn't mention kWh, the FAQ tab does. The specific questions and the answers are very muddled about the difference between "power" and "energy" but overall it seems fairly clear - clear enough to take a punt for £12.50, so thanks for the tip! -- Ian White Abingdon, England |
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On Thu, 13 Jan 2005 03:30:18 +0000, Andy Dingley wrote:
I was curious about that, but the Maplin list (and the salesdroid) seemed to imply that it only measured immediate power. Can I set it off counting for a week and come back to a tally of kWh ? Tried following the link in OP and then the FAQ button? -- Cheers Dave. pam is missing e-mail |
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In article ,
Andy Dingley wrote: I was curious about that, but the Maplin list (and the salesdroid) seemed to imply that it only measured immediate power. Can I set it off counting for a week and come back to a tally of kWh ? I want to track a dehumidifer that runs intermittently. Yes it can. Ok, I have it in front of me at the moment. (I appear to have lost the manual - no great loss though ). It has options for Volt Amp Watt VA Hz PF KWH and hour KWH would do exactly what you want - the hour option shows you how many hours it has been measuring for. It seems to be a fairly neat little bit of kit. As I say, I'm not too sure how accurate it is but its good enough for most things. Darren |
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In article , dmc wrote:
Ok, I have it in front of me at the moment. (I appear to have lost the manual - no great loss though ). Ok, found the bit of paper now. According the the manual it can do: quote Item Range Accuracy RMS Volt 180-250 Vrms (Max 1% typical 0.2%) RMS current 0-15 Arms (Max 1% typ 0.3%) Active Power 0-3750 Watts (Max 2% typ 0.5%) Apparant Power 0-3750 VA (Max 2% typ 0.5%) Line Frequency 0-63.0 Hz (Max 2% typ +/- 0.1Hz) Power Factor 0-1.00 (Max 0.03 typ 0.01) Energy Quantity 0-9999 KWh (Max 2% typ 0.5%) KWH hour 0:00-9999 (30 ppm) Note: The typical accuracy for Volt is in the range 190V-250V and for current is in the range 0.2A to 15A Press KWH shows the energy consumption then press key to display the time (hour) and active power for 1 second each automatically. KWH/Hour is a toggle function key, the LCD will show the sequence of KWH - Hour - KWH. Kilo-watt- hour is electronic energy. Hour is the duration time after poweron (ie from 1 minute to 9999hour) /quote Not sure that helps you much though ;-) Darren |
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On Thu, 13 Jan 2005 09:17:09 +0000 (GMT), "Dave Liquorice"
wrote: Tried following the link in OP and then the FAQ button? No, I hadn't noticed that ! I was looking at a paper cat in Maplin's last week. Kevin the teenager was quite clear that it didn't do kWh and it wasn't clearly discernible without opening the package. -- Smert' spamionam |
#34
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In article ,
Andrew Gabriel wrote: Try it with a compact fluorescent with integral electronic control gear. The Brennenstuhl was wrong by a factor of 3 on such a load. Ok. Not sure what I would expect from this so can't really tell if this shows the same problems as the one you have but.... A GE compact flourescent marked BIAX(tm)Electronic 11W gives reading of 11W, 0.07A, 18VA and a power factor of 0.64-0.65. Does that sound plausable? Voltage is currently 244.0V for completeness Darren |
#35
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dmc wrote:
A GE compact flourescent marked BIAX(tm)Electronic 11W gives reading of 11W, 0.07A, 18VA and a power factor of 0.64-0.65. Does that sound plausable? Fairly, yes. 11/18 is nearer to 0.61 than 0.64 but it's (just) within the 0.03 accuracy limit you quoted in an earlier post. Nothing would appear to be out by a factor of 3. I'll go and get one of these at the weekend if the local Maplin have got any. It seems too good to be true for the price... -- Andy |
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#37
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In article ,
Andrew Gabriel wrote: Does the unit say on it who makes it, what model it is, etc? The box is marked with maplin logos but the actual unit is labelled as model 2000MU made by Prodigit Electronics 5 seconds with google points to http://www.prodigit.com/e2000m.htm and indeed, the second image on that page is pretty much the beasty. http://www.prodigit.com/e2000m.pdf is the same manual as I have - well, the first page of it is anyway. Page two seems to be about a split unit. HTH, Darren |
#38
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In article ,
Andy Wade wrote: I'll go and get one of these at the weekend if the local Maplin have got any. It seems too good to be true for the price... Well, maplin maidstone had hundreds of the things on Tuesday. If you do get one I'd be interested in your opinion of it. Cheers, Darren |
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