More Computer Probs.

[bsrlee]

Reason they go 'all twitchy' when you mention 'computer' is that they are liable for any damage they cause due to poor/fault electrical supply. Ditto any other household goods damaged, but computers going belly up may have associated 'buisness losses' if it screws the hard drive.

If they have the system set up to turn on different users in blocks, you may be 'lucky' enough to have been assigned to a block with some huge user, like the local water pumping station, which causes a temporary brown/blackout. Oh. and I beleive it is also illegal to supply less than 240 volts to a metered customer - this was an old trick by some Sydney suppliers before they all got taken out a few years ago - they supplied >180 volts in some areas, which pushed apparent usage up, hence more profit.

If you are worried about the P.C., and/or use it for work, get a 'UPS' - Uninteruptable Power Supply - this will give you, say, 30 seconds of panic while everything crashes in slow motion, but they are the big brother of 'surge busters' and you'll only loose a bit or work instead of everything.

[Peter R]

. Oh. and I beleive it is also illegal to supply less than 240 volts to a metered customer - this was an old trick by some Sydney suppliers before they all got taken out a few years ago - they supplied >180 volts in some areas, which pushed apparent usage up, hence more profit. (bsrlee)

The rule on that is actually must not supply at less than - 4% and no more than +6% of rated supply be it 240V or 415V.

If you put a voltmeter into your power points and watch it at around 6 in the evening it will almost surely will drop below 240V. If the loading gets too heavy it will be automatically boosted which may cause a spike. This is difficult for the suppliers to control because it is all about maximun demand and that is variable.

180V volts on a 240v motor would cause great damage especially under load.

I can't follow the more usage bit. All that would happen is that motors and appliances would work at low voltage. the wiring in the motors and appliance would not become bigger and draw more current. But I guess you might be right in so far as a toaster would have to be on longer to toast as would a jug to boil, but even then the voltage drop would drop the current, which is what you are charged for, not the voltage.
More comment??

Peter R.

[CHJ]

. All that would happen is that motors and appliances would work at low voltage. the wiring in the motors and appliance would not become bigger and draw more current.
Peter R.

An increase in current and hence heat on Motors if the back EMF is reduced because of lower torque reducing rotor speed may not be desireable for long periods.

.
But I guess you might be right in so far as a toaster would have to be on longer to toast as would a jug to boil, but even then the voltage drop would drop the current, which is what you are charged for, not the voltage.
More comment??

Peter R.

As far as I am aware all AC power supplies are monitored by wattmeters.
So charge is based on Voltage X Amperage so units charged should remain the same regardless of voltage.
They are however calibrated assuming a Power Factor is met (something like 98%) if this power factor goes astray because of unballanced loads then you could be charged for AC power that is not providing useable energy.
Power Factor correction is usually built into induction motors and the like in the form of a large capacitor (to compensate for the winding induction) in order not to skew the supply. Any appliance with a large capactive load will have a compensating choke (inductor) fitted.

See a standard starter triggered flourescent light unit which will have both a choke to control the current and a capacitor to re-align the power factor, if you removed the capacitor you would most likely see a reduction in brightness. (as well as skew the supply a little)

The last workshop I controlled used in excess of 4 megawatt at peak so even the design of the bus bars had to compensate for the capacitance of their runs and the furnaces were designed to have non inductive heater windings (A one megawatt load can seriously skew a power supply if not ballanced)

Hope I remembered it correctly.

Chas

[ozwinner]

Wrong!!!!!
When the voltage drops, the amps increase.

Al

[echnidna]

Give it to em Oz

[Peter R]

Wrong!!!!!
When the voltage drops, the amps increase.

Al

It has been a long time but......

E over IXR = E 240v (say) 10 ohms = 24 amps
E 140v 10 ohms = 14amps

The windings remain at 10 ohmns, no change. If the amps increased it would be a great boon for power cables. As the voltage dropped the amperage would increase so it would be better to run cable over a long distance with lower voltages, Yes? No!

If you increase the voltage the amperage increases but it will still flow at the 24amps of the 10 ohms resistance until a too high voltage causes an overload.

WADGYAREKON?

Peter R.

What about that,Bob? You can be the umpire.

[johnmc]

If I operate my 1200W GMC router at 240V, based on the formula P = IE where P is power, I is current and E is voltage, it will draw 5 amps. If the voltage is dropped to say 120V, it will draw 10 amps. Ergo, volts drop, amps increase.

Ohm's Law: E = IR and P = EI

[Cliff Rogers]

It has been a long time but......

E over IXR = E 240v (say) 10 ohms = 24 amps
E 140v 10 ohms = 14amps

....

On a purely resistive load only, a motor is an inductive load & it is even more complicated if it has a capicitor coupled start winding.

In a perfect world the formula above works fine for DC theory.
When you move on to AC theory, resistance R becomes impeadance & it can be inductive or capacitive. :eek: It gets messy.

[Cliff Rogers]

If I operate my 1200W GMC router at 240V, based on the formula P = IE where P is power, I is current and E is voltage, it will draw 5 amps. If the voltage is dropped to say 120V, it will draw 10 amps. Ergo, volts drop, amps increase.

Ohm's Law: E = IR and P = EI

Not nessecelery, see my other post, in AC theory, R is no longer purely resistive, it is impedance, not resistance.... messy, yuky argument, stop now.

[CHJ]

Wrong!!!!!
When the voltage drops, the amps increase.

Al

Its possible on an AC motor, particularly a universal series wound one that the current may increase due to reduced back EMF (motor acts as generator partialy balancing input current).

But on a plain resistive load the current will fall (Ellectric Fire for instance).

I (amps) = V (voltage) / R (resistance)

As Cliff says it can get very messy if you slow an induction or universal motor down to much with a mechanical load because it responds more as a resistive load and will allow considerably more current to flow. (that is why they draw a lot more current at startup when armature is not up to speed)

Chas

[outback]

I have watched this very carefully. If I understand all you experts, what your saying is there ain't no little hamster goin' hell for leather in me router.

I thought when ya plugged it in it just fed him a bit, so he'd work.

[Cliff Rogers]

Yeah outback, they gave up using hamsters in routers years ago.

The problem was the life span of the hamster.
They would outlive the crappy models & not the good models so the owner had to take the router back for a new hamster every couple of years.
Some of the router maintenance people got onto this lurk & they were putting recycled hampsters out of dead crappy models into the better models.

[echnidna]

If you increase the voltage the amperage increases but it will still flow at the 24amps of the 10 ohms resistance until a too high voltage causes an overload.

WADGYAREKON?

Peter R.

What about that,Bob? You can be the umpire.

Well me 9 volt Black and Decker cordless drill goes hell for leather when I put an 18 volt GMC battery in it.

Which just goes to prove that elcheapo crap can work well.
(Hows that for a Hijack PeterR ?)

[outback]

Thanks Cliff for that concise easy to follow answer.
Much better than the drivel everyone else is spouting.

[echnidna]

So I put the 18 volt battery in me Arlec Cordless drill and it let the smoke out of the drill!
bum!