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  1. #11
    PeterB's Avatar
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    Quote Originally Posted by Donald Miller
    The second thing to recognize is that there are two types of electrical load. The first is inductive and is characterized by such devices as transformers, coils, and motors. The second type is resistive and it is characterized by such devices as resistance heating elements and incandescent lamps.
    Hi Donald,

    there are actually 3 types of AC component loads: resistive, inductive and capacitive. When analysing a circuit, these 3 components will exist to varying degrees. e.g. an AC motor has a high inductance, a moderate resistance and a small capacitance (between its windings). The complex electrical impedance (a.k.a. AC impedance) of the lumped combination of the components can be calculated. This AC impedance will have two parts to it - a resistive (or 'real') part and a reactive (or an 'imaginary') part. In the case of a motor the reactance will be 'inductive', and in the case of a fluorescent light the reactance can be 'capacitive'.

    The effect of inductive reactance is to cause the current to lag the voltage, while that of capacitive reactance is to cause the current to lead the voltage.

    Anyway, I posted this more just to correct a point rather than benefit the original question. So I should probably add something useful for foto-r3.

    regards
    Peter

  2. #12
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    Quote Originally Posted by foto-r3
    Thanks much, Monophoto, for your assessment of the situation. Yes, the head is an original. What we don't know yet is if the power company will remedy the situation, which, as it seems, is fairly widespread where we are, in a "rural" area. Apparently, if they boost the voltage for us, then this may create problems of over-voltage for houses closer to the transformer, or at least this is what they have told other users with similar problems.

    Another suggestion I received was buying an adjustable transformer that could be adjusted to the real voltage entering the transformer (to compensate for the fact that we are getting 184 instead of 220). Personally I have never seen one of these. What remains to be seen is if this voltage remains constant throughout the day. My friend suggested that at night when there is little consumption this might change, but I do recall using the enlarger at night with the same problem.
    You mentioned that you are using a solid state voltage stabiliser. These devices are designed to automatically switch between different taps on a transformer to comensate for changes on the input voltage. The issue you have may be that it is being operated out of its specified input range (e.g. they may be only designed to cope with voltage input ranging from say 200 to 260VAC). Try and find the specifications for the voltage stabiliser and see if it will cope with say 180V on the input (while still being able to convert the voltage to 220V)

    Your friend's suggestion is right, in that the voltage into your house WILL vary over a 24 hour period, it will increase at night time when less electrical load is on the distribution system. To solve this problem with an automatic solution is going to be expensive. Personally I would go for a manual option, and that is to buy a variac and an analog voltmeter. Get an electrician to permanently connect the voltmeter to the output of the variac so that you can manually adjust the voltage to be 220V whenever you need to (i.e. as it varies over the day). With this option you will also need to install an overvoltage cutout circuit (a.k.a. a crowbar circuit) which will prevent the voltage from going above say 230V.

    regards
    Peter

  3. #13

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    Quote Originally Posted by PeterB
    Hi Donald,

    there are actually 3 types of AC component loads: resistive, inductive and capacitive. When analysing a circuit, these 3 components will exist to varying degrees. e.g. an AC motor has a high inductance, a moderate resistance and a small capacitance (between its windings). The complex electrical impedance (a.k.a. AC impedance) of the lumped combination of the components can be calculated. This AC impedance will have two parts to it - a resistive (or 'real') part and a reactive (or an 'imaginary') part. In the case of a motor the reactance will be 'inductive', and in the case of a fluorescent light the reactance can be 'capacitive'.

    The effect of inductive reactance is to cause the current to lag the voltage, while that of capacitive reactance is to cause the current to lead the voltage.

    Anyway, I posted this more just to correct a point rather than benefit the original question. So I should probably add something useful for foto-r3.

    regards
    Peter
    Peter,

    Thanks for elaborating.

  4. #14
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    Thank you both, Donald and Peter, for your replies. This solid-state voltage stabiliser that we are using--purchased second hand from a different source--can handle input from 187 to 260 VAC. The reading we took midday Sat. was 184 -- probably a peak time, everyone in the kitchen and such. Yet I was using it today and it there was no apparent problem. The stabiliser in question has two fuses. The one that keeps popping was a 1,6 amp fuse. I don't know if this is the correct fuse size for the unit -- but it came with the unit when we bought it second hand. But perhaps a slightly higher fuse rating (as per an earlier post) would do the trick. But is there a way to calculate what would be the max. permissible fuse to ensure the safety of the voltage stabiliser?

  5. #15

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    If your stabilizer had one fuse, it would be simple to estimate the fuse rating. You say that the stabilizer is rated at 600 VA. Assuing that a single fuse is in the 220 V line: 600 VA / 220 V = 2.7 A. A manufacturer would probably round up to give some margin. But your unit has two fuses, so I don't know what this particular fuse is doing. Is it supposed to be subjected to the full load? If you just willy-nilly replace a fuse with one that is too large, instead of the fuse blowing, the equipment may be damaged -- some semiconductor may become a fuse -- much more expensive.

    Since you have a 600 VA = 600 Watt stabilzer and a 250 Watt lamp, the unit is rated to handle the steady state load, but there is a the very large inrush current when the lamp is turned on. There will be ineffiencies from the step-down transformer etc. that raise the steady-state power consumption above 250 Watts, but it should even close to 600 Watts. Does the fuse blow at seemingly random times, or when you turn the enlarger on?

    If the full current is flowing through the fuse, then it is operating close to its rating: 1.6 A x 220 V = 350 W. The lamp power (250 W) plus power loss in the step-down transformer may be approaching this figure. Then when you turn on the lamp, the current will be briefly higher. Is it a slow or fast blow fuse?

    Frequently devices have written on them what fuse value to use.

  6. #16
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    Thanks, Michael, for your reply.

    This SALICRU brand stabiliser unit has two fuses: one with a 1A fuse (never blown) and another with a 1,4A fuse (which is the one that blows). We only recently set up the enlarger, and the fuse has only blown on us twice so far: the first time, during an exposure, during a session of using the enlarger (this was the fuse that the stabiliser came with originally -- who knows how long it was in disuse/use). Then, after that, we bought a 1,6A fuse because the electronics store does not carry the 1,4A variety. As soon as we replaced it, and turned on the lamp to focus for the first time, it popped. We replaced that fuse and have used it sparingly since (for a few days now) and no further blowing. The fuse we are using (I think) is a normal blow --neither fast nor slow--. I don't know whether slow/fast blow is something you can see on the fuse itself, since I can look to see what the original was. Unfortunately, nowhere on the unit itself is there any indication of what fuse rating to use. Would there be some advantage in using one or the other in this case?

    Maybe the thing to do would be to use it and see how long we go before another blow. If it occurs at long intervals maybe we can live with this, too. Fuses are cheap.

  7. #17

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    Is this the type of unit that you have: SALICRU Series RE2 or PLC2: http://www.salicru.com/estructura.as...esElectronicos. The specs look excellent. They also can handle high temporary overloads, e.g., even 1000% for 50 ms, so the lamp starting current shouldn't be a problem, particularly since your 600 VA unit has margin over the steady state load of 250 W plus inefficiencies.

    It is suspicious that neither fuse seems large enough for 600 VA. But I can't say what to do since I don't understand the role of the two fuses. Perhaps one is for the microprocessor and one for the current that goes to the load? I suggest trying to get a manual for the stabiliser -- try contacting the distributer or manufacturer.

    Slow versus fast on a fuse is the timescale of blowing: will the fuse tolerate a brief current above its rating.

  8. #18
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    Quote Originally Posted by foto-r3
    The fuse we are using (I think) is a normal blow --neither fast nor slow--. I don't know whether slow/fast blow is something you can see on the fuse itself, since I can look to see what the original was. Unfortunately, nowhere on the unit itself is there any indication of what fuse rating to use. Would there be some advantage in using one or the other in this case?

    Maybe the thing to do would be to use it and see how long we go before another blow. If it occurs at long intervals maybe we can live with this, too. Fuses are cheap.
    Firstly you should stick with the voltage stabiliser and not worry about a variac as I suggested, the voltage stabiliser will do what you are after given it is rated down to 187V, even if the input falls to 184V then this will not make a significant difference to the output for B&W work.

    There are generally two types of fuses fast or slow (there is no 'normal' , but because fast blow are more common they could be considered 'normal' !). Don't assume that the fuse which came with the unit is correctly rated. As Michael suggests, get a copy of the manual, by going to the link he found and requesting it. That will tell you straight away the correct rating and type of fuse you need.
    A fast blow fuse has a straight filament of wire in it, whereas a slow blow fuse will have the wire coiled at some or all of its length http://www.microfuse.co.kr/4fuse%20g...%20guide06.htm (this site names the fuses normal, medium slow-blow and time-lag. Normal is 'fast blow' and the 2nd two are slow blow)
    here's a close up piccy of a slow blow fuse http://www.marcucci.it/prodotti/imm_comp/3004646.JPG
    If the fuse case is glass then you will be able to see this for yourself.

    regards
    Peter

  9. #19
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    You really need to heed the advice about looking to the manufacturer of the voltage stabilizer to determine the rating of the fuse. The reason is that the stabilizer is limited by both an overvoltage constraint and an overcurrent current constraint. As long as the maximum voltage at the receptacle in your home is less than the maximum voltage rating on the stabilizer nameplate, you don't need to worry about the overvoltage limit.

    But the overcurrent limit is different. As some others have noted, there are a different kinds of electrical loads. Another way of parsing these loads is into those that are constant impedance (such as lamps) and those that are constant power (such as motors). There are also constant current loads, but none of the components in your enlarger system will have that characteristic.

    The fan wants to absorb constant mechanical power (measured in kw in Europe, or horsepower here in the US where our political leaders force us to use an archaic system of measurements). Constant mechanical power into the fan means constant electrical power into its motor. But as the voltage drops (for the reasons we now understand), the current drawn by the motor will increase - electrical power is equal to the product of voltage and current. But if that current flows through a device that is temperature-limited, the concern is that a reduction in voltage could result in excess thermal stress on the voltage stabilizer.

    The manufacturer should specify a fuse rating based on his knowlege of the thermal withstand capabilities of the components in the stabilizer. That knowlege should include both the maximum current and the duration - and hence the manufacturer should specify both a current rating (in amperes) and a time rating (slow, fast or something more elaborate) for the fuse.

    The point you will need to be aware of is that it is possible that the fuse that you have is the appropriate fuse, and the fact that it is blowing could be telling you a critical bit of information - that the rreduced voltage from the power supplier is below the minimum voltage that the stabilizer is rated to withstand and deliver rated power output. Actually, that relates to one of the questions you asked - is it possible to use a smaller lamp in the enlarger. Switching to a smaller lamp would eliminate the fuse blowing problem, but it would also affect the printing time with your enlarger.

    The analogy that I like to use is to think of that distribution circuit as a rod that you are holding in your hand. If you wiggle your hand a little, the end of the rod at your hand moves up and down a little - but the far end of the rod moves a lot more. That's exactly what is happening on that distribution circuit - as the voltage varies a little back at the utility source, the variation out at the remote end (where you live) is a lot more. The ideal solution for you is one that is dynamic and that can maintain a constant supply voltage to your enlarger (or any other appliance in your home) as the input voltage from the utility varies over the entire range. If the range of variation is too large, it may be too expensive to try to solve the problem for a small load like your enlarger.

    The problem you are experiencing with your enlarger is affecting every other appliance in your home, and also all electrical appliances owned by your neighbors. Perhaps a better solution is to revisit the notion that the utility could do something to improve voltage regulation on the circuit.


    The explanation from your power supplier that because you are in a rural area, they cannot boost the voltage to you without causing an overvoltage at other customers is bogus. I suspect they are being lazy and trying to avoid having to solve the problem. There are several possible solutions they could apply - some as simple as locating power factor capacitors at various points along the distribution feeder, while others include installing an automatic voltage regulator part-way down the feeder to boost the voltage for those customers further away from their source while leaving the voltage closer to the source unchanged. Other solutions include distribution series capacitors and various forms of static compensation devices.

    In the US, distribution utilities are required to satisfy performance standards that include (among other things) the tolerable range of voltage delivered to the consumer. If there is an equivalent regulatory body in Spain, they may be able to help you (and your neighbors) put some pressure on the utilty supplier to correct his problem. As a minimum, you should determine if the low voltage you have measured is considered an acceptable delivery voltage under local standards.

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