Inverters for Computers

[MrEnergy]

The computer will run on any waveform that reaches a high enough voltage, but over time modified sine wave inverters will usually destroy the capacitors in the computer power supply. Sometimes this can take months, sometimes a few weeks, and in some cases even a few days. People have run computers from modified sine wave inverters for years, but it all depends on how well the power supply was made, how good the components are that they built the supply with, etc.

In my case I have seen my desktop power supplies go bad within one year. I have also lost DirectTV receivers within one year. If the power supply is made as a DC converter with high quality components and is engineered well then they can last for years with no problems on modified sine.

Running straight filtered DC from panels etc directly into the device (if it is a dc-dc converter) would be easier on it than modified sine wave.

 

Tad

[Dustoffer]

I have had no problem with the high quality modified sine wave inverters running the computer for 15 years.

What has damaged them is surges from lightning through the cable or phone line welding and pitting the mother board.

So now, when severe storms are coming I unplug from the wall the DSL/telephone connection in addition to turning off the power strip.   I have had no problems with most electric motors, but a few cheapies can’t take it or make noise.

For my guitar amps, I have a selectable pure sine wave inverter.   The home stereo runs fine on modified sine wave, as does the well pump, heater fan, TV and DVD/VHS players.  When I was building, modified sine wave (twin DR2424s) ran Skilsaw, drill, jig saw, router, table saw, and cement mixer with no problem.  I haven’t even had the problems that are supposed to happen with adapters or AC to DC chargers for cordless equipment.

[MrEnergy]

Yup. It all depends on the harshness of the waveform. The shape of the waveform makes a huge difference. Let’s see an oscilloscope shot of your output and that will tell us why. Or the model number of the inverter, I may have one here. Are they all DR2424’s? All motors will be about 10-15 percent less efficient on modified, and that power loss will show up as heat, but in general they should run fine.

Nowadays the sinewave inverters are so inexpensive that it’s no longer as much of a cost savings to go with modified, but back in the day it was for sure. I still run a small DR12 series on job sites once in a while, but the house has been changed over to a SW4024 since I got it for free damaged and repaired the circuit boards.

[JP Huie]

How about powering “wall wart” transformers with a MSW inverter?  Like for a modem or charger for a tablet…  do the same power-supply risks apply?

Thanks.

[MrEnergy]

They should work fine but will buzz. It’s harder on the internal capacitors, and they will use a little more power than on pure sine.

 

Tad

[lorenzop]

some good information here, but I’d like to add some myself. don’t be fooled by what you think an UPS does. they are good to have, and can help protect your computer hardware and unsaved files, but they wont necessarily change the characteristics of your AC power. normally, an UPS will power a computer straight from the wall, using a relay inside it, which you can usually hear click if you listen for it. if power from the wall fails or the voltage dips low, the relay will click over and it’ll start using the battery to produce power and keep the computer running. the device you’re thinking of is called a power conditioner. it can be used as an UPS, with a built in battery as well, but the difference is there’s no relay, and it’s always producing its own clean sine wave power. basically, you could say you’re taking the DC from your battery banks, into the MSW inverter, converting to DC in the conditioner then back to AC a second time with a pure sine wave, and into the computer. power conditioners also have the down side of some power loss due to the conversions to DC and back to AC. simply put, save yourself time and money and get a PSW inverter, even a cheap one.

for my own use, I do plan on using a PSW inverter and an UPS for my desktop. I’m a programmer, so a desktop is important to me. there is a little extra power used by an UPS to keep the internal battery charged, but it’ll protect your computer from unstable power and allow you to shutdown properly. a laptop basically does this internally, because it has a battery, however it’s still possible a MSW inverter could harm the power supply for your laptop. these and wall warts can also overheat and burn out just like motors.

MrEnergy, your video has me thinking. when you’re testing on the bench, do you have a load on the inverter, or is only the oscilloscope connected? putting a small load on it may change the wave you’re seeing. it’s possible the squaring could be very low current. I don’t have as much knowledge of the internal workings as I’d like, but maybe it’s possible there are noise filters at the output of the inverter which are acting as tinny capacitors, and throwing off the scope. just a theory. try putting a 100 watt incandescent lamp on the inverter while testing it. let me know what you find.

[MrEnergy]

The video was shown with no load, but with a load such as a drill or small vacuum it does change the waveform a bit. I am designing an inverter that will take a high voltage DC bank of batteries and convert directly to pure sine wave with no step-up. This should increase efficiency and allow a much smaller footprint for the inverter, and also be much easier on the batteries since they wont have to supply but more than 10 amps per 120VAC leg (double stacked). Charging will change to a simple digitally controlled converter and then into the battery bank. I.E. rectified 240VAC into a 180VDC battery bank digitally controlled by two triacs (phase control).

This setup should simplify power conversion, increase efficiency and greatly increase the life of the battery bank. Basic testing of this system shows a set of 30 Trojan T-105’s that barely have to do any work (10-20amp max load and 5 amps constant) so it looks promising so far. Charging from the panels will be simple since we just take a high voltage string of panels and use a PID control loop to handle direct charging of the bank of batteries from the panels without step-up or step-down. This also allows me to run my 240VAC welders from the source instead of firing up a generator.

My desktop is required for my work as well since I design circuitry, program microcontrollers and make simple communication apps in CSharp for them. I use the UPS’s for power outage situations only, but I would never go back to modified sine wave to run this system and the rest of the house. It’s just not financially worth it for me to run anything but pure sine wave.

<span style=”line-height: 1.5em;”>Tad</span>

[lorenzop]

I’m sure you know of the dangers with 180 volt DC. the entire system running at such high voltage means the entire thing must be designed very safe. don’t cut any corners and don’t work on a live system, ever. drain capacitors, air gap equipment, use ground fault interrupters, avoid all possible risks, put equipment under lock and key to avoid unfamiliar hands.

[MrEnergy]

480 is a common voltage I work with daily on three phase equipment. And 2400 VDC systems for ionizers. It’s really the same safety precautions when working with 240VAC. It’s certainly not fun to get hit with higher voltages, though I have only been hit once with 2400VDC and once with 480VAC. I use lineman’s gloves (which are good for up to 5KV) for working on the ionizers these days. Of course 180VDC is not much different than 240VAC shock wise and so you are right about the safety precautions.

Many years ago I was on a job site where a man who was breaking up an old concrete slab punctured a ~10KV main line with a jackhammer and killed him instantly. His friend was running over to push him away from the jackhammer when the foreman yelled “Don’t touch him!”.

Tad

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