House lights flickering with HDD

[v-600]

I have an unusual problem. Living in Kathmandu we have regular load shedding of mains electricity (currently about 12 hours a day, roll on the monsoon), so I have an inverter attached to the mains in my house.

When the mains is on, all is well, all my electrical equipment runs fine and the inverter charges the battery.

When the power goes, the inverter powers everything (minus the heavy draw stuff in the kitchen). Normally this is the lights in the house, hifi, laptop (on charge in a wall socket), various little odds and sods/routers/phonechargers, and occasionally the TV.

I've noticed that my house lights flicker on occasion, and through a slow process of elimination put the blame on the laptop, specifically the hard drive. As it spins up and down, the lights flicker. Its really annoying. My best guess is that as the power requirements of the laptop vary the inverter can't adjust its output fast enough to keep up, but I don't have a an advanced knowledge of electronics.

I already run the laptop through a surge protector and thought this would have helped dampen out the effects, but to no avail.

I think it happens less when I'm gaming (or at least I notice it less as my attention is more focussed on the computer), possibly because the discrete graphics and CPU all power up, the whole computer draws more power and the HD stays spinning longer, or the difference between idle and spinning is less as a percentage of the total power used by the laptop.

Solution at present, unplug laptop and run off battery = no flickering.

I would your thoughts on what else there could be to limit this effect or come up with a better solution.

Muchos gracios

 

[Automaticman]

Maybe get a small UPS instead of just a surge protector, I would think that would provide a bit of buffer between the laptop with its own dedicated battery and the rest of the house.

Maybe something small like this:

http://www.newegg.com/Product/Produc...82E16842102135

Check how much draw your laptop's power supply is rated at.

 

[nonymoosee]

And also if possible you might want to switch to a SSD if possible, they use a lot less power.

 

[Automaticman]

And also if possible you might want to switch to a SSD if possible, they use a lot less power.

That is a good point as well.

 

[v-600]

Maybe get a small UPS instead of just a surge protector, I would think that would provide a bit of buffer between the laptop with its own dedicated battery and the rest of the house.

Maybe something small like this:

http://www.newegg.com/Product/Produc...82E16842102135

Check how much draw your laptop's power supply is rated at.

Thanks. I hadn't considered a UPS at all. It might work well and I know work have loads. I might be able to buy an old one from them.

I had also thought about adding an SSD to the laptop, replacing the DVD drive with an external one. I can't replace the main drive purely due to the gigs of stuff on there, and the cost of a large SSD in relation to the value of the laptop.

 

[westom]

I had also thought about adding an SSD to the laptop, replacing the DVD drive with an external one. I can't replace the main drive purely due to the gigs of stuff on there, and the cost of a large SSD in relation to the value of the laptop.

You have assumed a reason that is unjustified by numbers. Find a six watt nightlight. That tiny bulb (load) is also so large as to power maybe three disk drives. Numbers make it obvious. Disk drive is consuming near zero power; does not cause lights to flicker.

So why would an inverter do short power cutoffs? Among a long list of reasons include noise. Apparently you suspect that noise is generated by a laptop. It shouldn't. But if it is, even the UPS would not avert that noise. UPS was recommended to address something different.

Examples of line filters are at:
http://www.westek.com.au/rfi-emi-filters/emi-powerline-filters/

But again, this assumes noise causes a power source to be temporarily confused. Other possible reasons require other possible solutions. But we know this much. A drive could never consume enough power to cause lights to flicker. Numbers make that woefully obvious.

 

[PowerEngineer]

If I understand you correctly, your household loads are only fed by the inverter when the utility power is lost. The power provided by the inverter is almost certainly of much poorer power quality (lots of harmonics and magnitude fluctuations). I suppose it's possible that harmonics fed back to the inverter from rectifying loads (like your laptop) might confuse its firing circuitry, but that's a stretch. Are your lights fluorescent or incandescent? If fluorescent, these are rectifying loads too. In any event, I agree with westom that the size of the load change caused by a hard drive spinning up (or down) can't be the cause.

 

[Automaticman]

If I understand you correctly, your household loads are only fed by the inverter when the utility power is lost. The power provided by the inverter is almost certainly of much poorer power quality (lots of harmonics and magnitude fluctuations). I suppose it's possible that harmonics fed back to the inverter from rectifying loads (like your laptop) might confuse its firing circuitry, but that's a stretch. Are your lights fluorescent or incandescent? If fluorescent, these are rectifying loads too. In any event, I agree with westom that the size of the load change caused by a hard drive spinning up (or down) can't be the cause.

While I agree that the hard drive itself is a highly unlikely source of the issue, my original thought was that something else associated with the laptop could still be, and that might also be associated with the times the HDD spins up. Specifically, I was thinking that maybe the CPU may be rapidly changing states/clocks/usage load, and that can draw significantly more power than a HDD and change very quickly.

I wonder if what is really happening is that the laptop is doing indexing in the background, or maybe an AV scan, some thing that might both spin the drive and increase other load.

To the OP - before we get any more carried away, have you really left the laptop unplugged for a long enough time to truly rule out that the flickering is only coincidental to the laptop being plugged in?

In other words, leave the laptop unplugged or don't use it for an entire 12hr blackout to really verify that you still don't get flickering from an entirely different source.

 

[v-600]

Thanks for the input. So if I rule out the power draw of the HDD, them something else is going on. Three lights are stable without the laptop on, or unplugged. I've noticed this for the last few months, and been checking fairly consistently. Two cuts come twice a day so it's never twelve hours in one block. Ive never intentionally not used it through a whole load shedding, so that might be the next step.

All the lightbulbs downstairs are florescent ones. The inverter is rated to produce 500W and having 4 60w incandescent bulbs in my living room alone it seemed the sensible choice.

What made me think it was hdd was that it seems to happen when the drive activity light flickers (and that led uses even less power so we can rule that out �&#56861.

 

[v-600]

Just got back from Easter hols, but I can now add that throughout a load shedding period with the laptop not plugged in at all there is no flickering. I'm certain something about the laptop is causing it, but still not sure what yet (if not variation in power use).

 

[westom]

... throughout a load shedding period with the laptop not plugged in at all there is no flickering. I'm certain something about the laptop is causing it, ...

Define load shedding. Is AC power disconnected and power then comes from an inverter and battery? What is this inverter?

 

[Red Squirrel]

Definitely get a UPS. If the spikes are bad enough to be noticable through the hard drive, you're hurting your equipment, especially the hard drive itself.

Even a cheap <$100 one will do, just make sure it's a half decent wattage. Typically I don't buy anything lower than 1000VA (600w) but you can probably get by with lower. 1000 is a safe bet though and not that expensive.

 

[Mark R]

Definitely get a UPS. If the spikes are bad enough to be noticable through the hard drive, you're hurting your equipment, especially the hard drive itself.

He's GOT a UPS (effectively an inverter/battery combo). The house lights flicker when the mains is out, and he is running the lights and laptop from the inverter. UPS power is the dirtiest, noisiest power that you can get, generally far worse than even poor quality mains power.

Basically, the issue is a poor quality inverter. When the laptop CPU kicks in, then the extra load it takes makes the inverter voltage sag, and this causes the lights to flicker. Basically, when the laptop is thrashing the HD, the CPU is intermittently idle -waiting for data from HDD. So the power consumption of the CPU fluctuates wildly as it goes from idle (while waiting for the HDD), then to full load, when the HDD delivers, then idle when the CPU has processed that batch of data.

Options to mitigate the flicker are:
1. Use a more powerful inverter
2. Use lights which aren't as susceptible to voltage fluctuations (electronically ballasted LED or CFL, or low voltage halogen).

 

[v-600]

Definitely get a UPS. If the spikes are bad enough to be noticeable through the hard drive, you're hurting your equipment, especially the hard drive itself.

I think its the other way round, the spikes causes by the computer, not affecting it.

Basically, the issue is a poor quality inverter. When the laptop CPU kicks in, then the extra load it takes makes the inverter voltage sag, and this causes the lights to flicker. Basically, when the laptop is thrashing the HD, the CPU is intermittently idle -waiting for data from HDD. So the power consumption of the CPU fluctuates wildly as it goes from idle (while waiting for the HDD), then to full load, when the HDD delivers, then idle when the CPU has processed that batch of data./QUOTE]

I thought the consensus was that variations in the laptops power draw were too inconsequential to consider, unless I misunderstood the previous comments

Options to mitigate the flicker are:
1. Use a more powerful inverter
2. Use lights which aren't as susceptible to voltage fluctuations (electronically ballasted LED or CFL, or low voltage halogen).

Not sure the increasing the available power output of the inverter would change things, as i'm already well under its output.

Different lights might be the best/only solution, unless I can find a way of smoothing the electrical noise coming from the laptop.

 

[v-600]

I realise this thread has been a bit dead. I'm heading back to the UK for a bit and thought I would try and pick up some different bulbs there. There doesn't seem to be a shop near me that seems to sell anything different from normal fluorescent. I've not heard of electronically ballasted before Is there anything specific to look for when buying?

We've had more rain so the power is on more at the mo (only off for about 8 hours a day) so I've not noticed as much. I also thought to try and video the effect. In this case when I scroll the webpage it causes a flicker in the lights. I don't think the camera is particularly sensitive and the effect is more noticeable in real life, but still observable. With the laptop unplugged they're fine. Kind of rules out the HD though as the light stayed off the whole time.

https://www.dropbox.com/s/7t4s4tjot6uw7ci/2014-06-16 13.54.27.mp4

 

[BrightCandle]

Its far more likely to be the CPU since that could be a significant amount of power depending on the laptop in use. You are already pulling 240W just with the lights so a 120-200W extra from a powerful laptop could cause a drop in voltage on a 500W UPS. Even minor adjustments in voltage would produce a flickering effect which is noticeable. You can't cause any significant impact to a big source like a hydra-dam but to a little UPS pulling on and off the power of a CPU which could be 50W + drive + RAM etc could certainly be enough temporary load.

From your video it certainly looks like the momentary movements are causing the issue. When you do a longer scroll I notice the light level stays even so its hit the new level. The voltage is sagging under the load.

One thing you could try is to pick up some LED light bulbs. You can get similar light output for around 7W of draw. The main reason for getting them is reduced electricity use. They tend to be higher temperature white so think more office colour than the homely orange. But more importantly they will reduce the load on the Invertor which in theory should reduce the effect. But I doubt it will eliminate it completely and could in theory make it worse! The problem is that relative to the bulbs right now your laptop is a small load, if you reduce the bulbs down to 28W in total the laptop could very well be more load and that could cause a more distinct flicker if its not actually struggling with the load but instead failing to respond to the power draw in time.

The only reliably way I can think to fix it is to isolate the lights from the laptop. That is use a UPS for the laptop on its own and leave the lights on the existing setup. You ideally need a plug that isn't through the invertor for the UPS/laptop to go through so it can detect the lack of mains supply. The cost of the two solutions (UPS v 4 LED bulbs) is pretty similar so I would tend to suggest a separate power loop just for the laptop is prudent.

 

[sm625]

What you need is a big capacitor:

Cut open the power lines that go from your AC adapter to the notebook and wire the capacitor in there.

 

[v-600]

Just an update to this. I got some LED lightbulbs which don't flicker. Everything appears to be resolved.

 

[Hones]

The problem is of EMC. With electronic gear (ballast) , light will not flicker as is also the case with LED lights.
The electromagnetic inerference comes in mains by radiation of other electrical equipments (e.g. mobile phone) or from mains from say electric motor.

 

[alkemyst]

If you get a UPS, get one with AVR. However; this may still cause flickering if the UPS has to adjust power often.

 

[mindless1]

I

Not sure the increasing the available power output of the inverter would change things, as i'm already well under its output.

Different lights might be the best/only solution, unless I can find a way of smoothing the electrical noise coming from the laptop.

1) It has not been established that there is any significant noise coming from the laptop. On the contrary it is not at all a likely problem. The laptop is merely a dynamic load.

2) The closer you get to the output rating of the inverter, the longer a sag time there will be with an increase in load, unless you add sufficient capacitance to buffer it.

What you need is a big capacitor:

Cut open the power lines that go from your AC adapter to the notebook and wire the capacitor in there.

A capacitor that large would probably destabilize the laptop AC adapter, as well as cause a long, high inrush current. To make it work it could be necessary to put a current limiting resistor in series with the cap +, and a schotty diode in series after it to prevent reverse charging of the cap, AND a direct lead from the PSU to the laptop in parallel with that. It might also be prudent to put a schottky diode in series on the direct lead depending on the design of the PSU.

Along with that it would be useful to have a larger capacitor on the high voltage DC side of the AC adapter, though then it becomes an issue of safely isolating something connected to high voltage.

What is the voltage of the battery bank supplying the inverter? To some extent it could make as much sense to compare that battery voltage to the input voltage requirement of the laptop. Supposing it might be a 12V or 24V battery bank, it may be a bit too high or low for the laptop to use directly, BUT it might not be.

Perhaps a basic laptop automobile (lighter outlet type) adapter would work to directly supply power from the battery bank to the laptop and avoid the losses converting from battery DC to inverter AC then AC adapter back to DC while doing so. That would isolate the laptop from everything else as much as you're going to be able to unless you also have an independent battery just for it.

 

[BrightCandle]

Just an update to this. I got some LED lightbulbs which don't flicker. Everything appears to be resolved.

Hmm well I am surprised my first instinct was right and the second guess was wrong. Glad to hear it was resolved.

 

[westom]

Just an update to this. I got some LED lightbulbs which don't flicker. Everything appears to be resolved.

Your laptop contains a power supply (a regulator) so that voltages on each semiconductor vary by zero when AC voltages vary massively. Your LEDs contain a power supply (a regulator) so that voltages on each LED vary by zero when AC voltages vary massively.

Was concern for AC voltage regulation? Or just stop lights from dimming? Voltages still vary significantly probably due to a weak or defective inverter design. A problem maybe made obvious by changing reactive power. A problem that would be ignored by capacitors, every surge protector or most UPSes. Magic boxex do not solve the defect. A defect / design compromise probably remains unresolved inside the inverter.

Does a defect remain? Connect an incandescent bulb. If that bulb intensity varies significantly, then inverter's voltage regulation remains poor.