Inverter Type Question

[guardian]

Can someone give me an idea of which type of things can be safely run with a regular inverter and which are best run with a pure sine wave inverter? Thanks!

[inetdog]

Can someone give me an idea of which type of things can be safely run with a regular inverter and which are best run with a pure sine wave inverter? Thanks!

I first take issue with your categorization of a Modified Square Wave (MSW) inverter as "regular". It is not inherently more regular than PSW. It is generally less expensive though.
Motors, especially induction motors, will vibrate more and run hotter on MSW. Whether the motor has enough design reserve to operate well and have a normal life span depends on the individual motor.
Power supplies, especially capacitor input rectifiers on switching power supplies, can overload their input diode bridges when driven by MSW. The biggest problems will be with inexpensive (cheap) power supplies including typical USB chargers.
Incandescent light bulb filaments will vibrate more than normal and this may affect the bulb life as well as causing audible noise.
Resistive heating appliances should be fine on MSW, but it is not a good idea to drive resistive heat from PV if there is any alternative.

P.S. Transformers can be a problem too. Noise and severe overheating among other problems. As well as the output voltage being off.

[Logan005]

Almost everything you think you need an inverter for can be powered directly from battery. In a true off grid situation, the inverter may use more power than your devices. in a 24X7 operating scenario, your inverter will require more panels and more batteries. Unless you are running an air compressor or deep well pump, I would stay away from an inverter. especially for 24X7 off grid operation.

[guardian]

I first take issue with your categorization of a Modified Square Wave (MSW) inverter as "regular".

No need to take issue. I don't really know the difference yet between any of these inverters. I'm just learning. Unfortunately, I started out being mis-advised (by an outside source, not here on the forum). I bought a Bestek 1000 inverter to run 2 - 50 watt small 386gph water pumps used in my Tower Gardens. At that time, I didn't know there was more than one type of inverter. The pumps run on 110 v, so I figured they could not run directly from battery, and I blindly followed the incorrect advice.

Later, I learned here on the forum to replace that Bestek 1000 with a 300 watt pure sign wave inverter, which I did, and this works with less battery drain. So, I asked my question here because I wanted to know if the Bestek would be useful for anything else down the line. I do not know if it is a modified sign wave inverter, so I thought there was just a regular inverter (the box says PWM) that is neither modified or pure sign wave. If I'm wrong about that, I'd like to know. In the meantime, I'm still wondering whether my Bestek will have any practical use, or would it be best to sell it on eBay.

Thank you!

[inetdog]

Later, I learned here on the forum to replace that Bestek 1000 with a 300 watt pure sign wave inverter, which I did, and this works with less battery drain. So, I asked my question here because I wanted to know if the Bestek would be useful for anything else down the line. I do not know if it is a modified sign wave inverter, so I thought there was just a regular inverter (the box says PWM) that is neither modified or pure sign wave. If I'm wrong about that, I'd like to know.

Thank you!

Ask and....

A pure sine wave (PSW) inverter or true sine wave (TSW) inverter is the same thing. The output voltage is a mathematical sine wave, a smooth curve whose shape is what is produced by a simple coil of wire turning in a constant magnetic field. That is what an ideal generator produces and what a utility tries to provide.
The bulk of electrical and electronic equipment is either designed to operate
1. off this smooth voltage,
2. off smooth DC or
3. off pulses of DC delivered by a controller.

The simplest way to produce alternating current from a DC supply is to simply switch the polarity of the two leads 120 times per second. This produces a wave form called a square wave. This waveform causes serious problems with most loads designed to operate off the same voltage sine wave. Either the average is too high or the peak is too low for the AC equipment, depending on what that equipment does.
The next better alternative is what most people call Modified Sine Wave (MSW). I choose to call it Modified Square Wave (MSW) instead because it is closer in many ways (including the problems it causes) to square wave than to sine wave.
Imagine zero volts for 1/4 of the cycle, a high positive voltage for 1/4 of the cycle, then zero for 1/4 and finally the opposite high negative voltage. Repeat sixty times per second.
This causes fewer problems, but is still only an approximation. ]
The next step up, rarely found in practice, is the stepped square wave which goes up to the high positive voltage in two or more equal voltage steps, and the same for coming back down and going negative.
If you add enough smaller ad smaller steps that the steps are not easily visible you get what is very hard to distinguish from a sine wave. Some PSW/TSW inverters actually take this approach and that is fine too.
Type 1 devices operate best off PSW but may work acceptably on MSW or even SW.
Type 2 devices avoid the inverter completely and you just have to match their voltage requirement.
Type 3 devices, such as most modern electric vehicle traction motors and some DC lighting, can get their high voltage DC source directly from the battery or from a power supply run off AC.

[guardian]

Thanks! If I'm reading this correctly, best to sell my Bestek 1000 on ebay.

[inetdog]

Thanks! If I'm reading this correctly, best to sell my Bestek 1000 on ebay.

Let me see:
1. 1000W inverter for $70
2. Car power plug and battery clip cable for 100A peak current
3. No UL or other regulatory agency approval

Yup, that's enough. Get rid of it if you are comfortable inflicting it on someone else.

[Mike90250]

Almost everything you think you need an inverter for can be powered directly from battery. In a true off grid situation, the inverter may use more power than your devices. in a 24X7 operating scenario, your inverter will require more panels and more batteries. Unless you are running an air compressor or deep well pump, I would stay away from an inverter. especially for 24X7 off grid operation.

This seems to be a favorite anti-inverter meme. There is a alternative view to it. A very good inverter does not have too awful of standby loss. if you are a hermit living in the woods, it's not a big thing, go 12V. But when you get to an average house, with wiring runs more than a couple feet, the low voltage/high amp copper loss, starts getting real bad.
And the efficient DC fridges go for over $1K , with limited storage space. Compared with a modern energy star 22cf fridge for a household, that goes for the same price or less, and has modern shelving. Lighting, unless you go to an RV shop, you have limited lighting choices, along with standard switches with no DC ratings, appliance outlets, a 12VDC cabin is not a house. Sadly, my water system base loads (ozonater, deep water air pumps, uV lights) 900' up the hill from the battery shed/inverter, need AC power. Along with the well pump, welder and garage door opener. Too many things the wife relies on to not have an inverter.

[Sunking]

Got a boat?. You can use it for a boat anchor. Or if you have someone you do not like much and want to see disappear, use the Inverter for a pair of cement shoes to walk on water with.

The correct size Inverter is one that powers all the connected loads you intend to run at the same time plus an extra 25 to 30% headroom. Total your connected load that will be on at the same time, and add 25 to 30 % more. Say 200 watts and divide it by .75. So 200 watts / .75 = 266 watts. So you go shopping for a 250 to 300 watt Inverter.

There is one exception, if your load is a MOTOR. Then you need to know the starting current required. When you power a motor from an Inverter it is critical you se a motor with SOFT START. Some Motors starting current is some 4 to 8 times running current So if that Motor were say 500 watts running might have 4000 watts to start. In that case you would need a good 2000 watt continuous, 4000 watt intermittent for 5 second. Huge diferenc in cost using a 750 watt inverter with a SOFT START Motor vs a 2000/4000 watt Inverter.

[guardian]

Good info - thanks boys. I also have too many cool things that will require inverters to go pure DC. As I work my way up, my goal is to spend wisely. Clearly, I'm off to a bad start. I already have to sell back my first inverter and my first charger (too small). But, with a place like this for advice, and working through the learning curve, I will get myself situated. And, of course, there's eBay to try to cut some of my losses.

Great board you have here. Again thanks!

[J.P.M.]

Good info - thanks boys. I also have too many cool things that will require inverters to go pure DC. As I work my way up, my goal is to spend wisely. Clearly, I'm off to a bad start. I already have to sell back my first inverter and my first charger (too small). But, with a place like this for advice, and working through the learning curve, I will get myself situated. And, of course, there's eBay to try to cut some of my losses.

Great board you have here. Again thanks!

And so cut some of your losses by selling the stuff to some other equally ignorant soul. Nice touch. Smart to let the word out too.Thanx for the head's up.