Are modified sine wave inverters any good for anything?

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PDrill

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When ever it comes to inverters, the same thing always pops up; You need to have pure sine wave for XXXX

And it makes me wonder is a modified sine wave 'enough' for anything? Anything else than maybe classic household bulbs and as a torturing device.

It's just that over the years I've used almost anything and everything with the cheapest inverters with no problems. Desktop computers, portable computers (old 'laptops' which were powered only by AC), charged modern laptops, power tools, soldering iron, TV, fluorescent lights, coffee maker etc and everything has worked. Once I even ran a 600w blown air heater on an 600w inverter just to try it, and it also worked.

My friend runs a microwave by modified sine wave inverter and that makes a strange noise and it doesn't feel 100% powerfull, but that I can technically understand. And also an electric toothbrush with cordless charger may probably not work and I that I can also understand.

So, why is it that for anything one 'has to have' a pure sine wave? And can the modified sine wave be used for anything by any other than me 🙃
 
As you point out modified sine wave will run "some" things but not others, personally I wouldn't accept a power supply at home that would only run half of the stuff in the house;) when we bought our last van the previous owners used a modified sine wave inverter just for the TV off a AC to DC is my guess as it wouldn't run our microwave or coffee machine so guess what was the first job I did.
 
Have used both over the years.
last van relied on everything for ehu, it had a variable power microwave plus grill fitted.
I then put a 1500w psw inverter plus additional batteries.
Didn't use the grill off grid all OK.

The van before that had a Samsung junior M/W fitted plus 1000w modified inverter

That worked fine also for short burst on mw, boiled lw camping kettle, lw toaster.

This van came with 700w psw to run all off grid. But in the wrong place fo TV etc. (up front)
Fitted extra battery to run new diesel heater back of van at the same time a spare 1000w msw, to run TV kettle etc.
All working good.

Don't need hair dryer 😁

Sorry should have said good solar array on all vans
 
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PDrill said:
When ever it comes to inverters, the same thing always pops up; You need to have pure sine wave for XXXX

And it makes me wonder is a modified sine wave 'enough' for anything? Anything else than maybe classic household bulbs and as a torturing device.

It's just that over the years I've used almost anything and everything with the cheapest inverters with no problems. Desktop computers, portable computers (old 'laptops' which were powered only by AC), charged modern laptops, power tools, soldering iron, TV, fluorescent lights, coffee maker etc and everything has worked. Once I even ran a 600w blown air heater on an 600w inverter just to try it, and it also worked.

My friend runs a microwave by modified sine wave inverter and that makes a strange noise and it doesn't feel 100% powerfull, but that I can technically understand. And also an electric toothbrush with cordless charger may probably not work and I that I can also understand.

So, why is it that for anything one 'has to have' a pure sine wave? And can the modified sine wave be used for anything by any other than me 🙃
Click to expand...
Tricky as you don't want to buy something and find it doesn't do the job. I think it's a lot like other motorhome related stuff people say you must have X amount of solar X battery capacity a b2b etc etc quite often without asking what you actually want to use it for!
 
They are all I ever had in over 20 year's.
Never felt the need for anything better.
Although pure sign wave models are so cheap I would buy one now I ever need another inverter.

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Aot of modern electronic suff is so touchy its not worth the risk. You might save few hundred quid buying a cheap inverter it may cost you more in the long run.
I have a fairly low cost pure sine inverter it does what I want but I know the output is a bit noisy. Next time I buy one it will be a Victron or similar it will cost 2 or 300 more but better to be safe than sorry.

A lot of people overlook their batteries when installing inverters just remember if you have lead batteries you need 400 ah of batteries per 1000 Watts of inverter.
 
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We fitted the air con at the AVG offices in Newark. Their UPS inverters for the servers were modified sine wave. I suppose good regulated power supplies can handle it 👍
 
I found a modified square wave inverter would run everything except toothbrush chargers. Microwave was a simple model with knobs.
You can now get usb toothbrush chargers.
PSW inverters are now much cheaper so might as well get one of them.
 
I have a modified sine wave inverter and it always works perfectly for the only job I bought it for. That is running my wife's hair dryer. All other power needs are supplied by 12v electricity or gas.
 
Jev88 said:
Electric motors tend not to like modified sine wave.
Click to expand...
Even brush motors rather than induction motor?

I would like to run cheap power tools of a decent sized inverter.

Cheers James
 
I've ran a power drill, grinder and a jigsaw on an msw inverter just fine. Don't know about brushes, but everything has been old (~20yrs) and then cheapest :-D

The 700w grinder took half a second to start with a 600w inverter but ran fine.
 
Nearly all handheld power tools are brush motors. Most cheap static tools are too.
 
Price difference between PSW and MSW inverters is such that it makes sense to get the PSW ones for extra flexibility. Be aware that many cheap "Pure Sine Wave" inverters do not have a very clean waveform and it is a matter of getting what you pay for. The best way to tell is with a Scope or Multimeter with display, but most people don't have access to those so have to accept what they are told from the description.
The Victron Inverters are superb in that respect and I have found are actually cleaner then the grid supply :)

The idea that you need 400Ah of Lead Acid per 1000W of inverter I would definately not agree with. Maybe it is a "nice to have" but certainly not a requirement to be able to use. On my last self-build I used a Victron 12/3000 Multiplus (so a 2400W inverter) with a 400Ah Lead Acid AGM Bank and it worked perfectly with the 2kW water heater and the 2kW Induction Hob (not at the same time of course). I switched to 645Ah of Lead Carbon AGM around a year later, but solely as I got them for a very good price. 2 of the old AGMs went into another VW camper upgrade with another inverter - 200Ah running a 1500W inverter for occasional use and that has been fine for the last couple of years. My current Motorhome was running the 1300W inverter (Multiplus 12/1600 in this case) with 300Ah of Lead Carbon AGMs without any issues (although that now has a 100Ah Lithium to be a 400Ah Hybrid - done because I could).
If someone wants to use that calculation to be 'safe' then great, but not a necessity (IMO)

Something that needs to be remembered with Inverters and LITHIUM BATTERIES is to not exceed the BMS currently capability. The typical 100Ah Lithium has a BMS of 100A which is just about on the limit for a 1000W at full power. Some Lithiums have lower rated BMSes - some as low as 30A for a 100Ah! If you want to use an Inverter with Lithium it can be a good idea to have paralleled batteries as that allows load sharing of course and so the current per battery is significantly reduced.
Also don't rely on the "Battery Gauge" on some Inverters remote control. that is purely a voltage indication and because the Lithium voltage stays fairly level across its State of Charge, plus it sags less under load, it gives a very poor indication of capacity. (It is not much use with Lead Acid either in fact).

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I’m having a hard time to believe that a 400ah delivering 170a it’s a good thing. That if it can. The plates inside must boil the mat. That’s a C/ 2,5 rate. Any prolonged load at that rate will wear the lead prematurely. Even the pure lead agm that delivers 1C, it’s for short bursts, and not to be abused. I do not condone the brute use of lead batteries. A C/10 rate it’s what I would recommend max, and up to C/5 on heavy stationary with thick 5mm and above plates.
There is a safety reason to, as the discharge is just reverse of charge, the same thermal runway applies to discharge as well. Do few cycles knackered the plates, then short inside, and you got a hot situation.
 
Been using an 1800watt MSW inverter in the RV for 15 odd years, it's run everything I have plugged in to it. TV, phones, water heater, kettle etc.
 
Hoovie said:
The idea that you need 400Ah of Lead Acid per 1000W of inverter I would definately not agree with.
Click to expand...
It is if you value your batteries and want them to last.
You should limit the max current discharge to the C5 rate which on a 100ah battery is 20 amps so really for a 1000 Watts you need 450ah, I was being generous in my eairler post.
 
Whilst considering size of battery bank you need remember the Peukert exponent. If you hammer your batteries at a C2 rate the capacity is very much less than at the C5 rate. In other words you get far fewer Ah out of your battery if you drain it quickly.

8. Battery capacity and Peukert exponent

www.victronenergy.com www.victronenergy.com
If you have LiFePO4 batteries you can just about ignore the Peukert exponent but it has a significant effect on most lead acid types.
 
Pausim said:
Whilst considering size of battery bank you need remember the Peukert exponent. If you hammer your batteries at a C2 rate the capacity is very much less than at the C5 rate. In other words you get far fewer Ah out of your battery if you drain it quickly.

8. Battery capacity and Peukert exponent

www.victronenergy.com www.victronenergy.com
If you have LiFePO4 batteries you can just about ignore the Peukert exponent but it has a significant effect on most lead acid types.
Click to expand...
Indeed, a tipical 100Ah battery is expressed at a common C/20 rate, at C/5 is allot less than 100ah. Some even give the capacity at C/100 as it looks better for marketing. Worth knowing the capacity declared at what rate is given.
As for the MSW inverter vs PSW is efficiency for starters and type of load. Most loads are ok, inductive capacitive difficult, resistive not a problem. Resistive doesn’t care if you feed DC or AC, it works but at different efficiency. When the load is difficult, results in loads of reactive power returning back, giving a very low power factor. That, can be corrected to some degree with large capacitors. Hence some MSW with good capacitors fair better with some loads. Change the load that’s not compatible with the capacitors delivery, and you’re in a pickle. Inefficiency is heat and lost power, you will see a MSW running hotter than a PSW. Also the PSW will always have a lower stand by consumption, most are microprocessor controlled high frequency fets. The fets will switch at a very high rate simulating a perfect sine wave, producing a 8-10v AC, then feeding it to a transformer to up it up to 230v. A toroidal transformer that’s found in PSW inverters, is much more efficient at this job compared to the old type, resulting in less heat, less hamming, and better surge capability.
The MSW are also better and worse, the square wave is awful, the trapezoidal wave better, as its closer to the sine wave. The later is also known as quassy wave. The sine wave also can be better or worse, it can go trough 0 to fast squeaking the wave, and becomes like a sawtooth under load. You need the sine wave switching perfectly at 180 deg and have some compensation under load. This is given in the THD total harmonic distortion in the inverter datasheet. All inverters that connect and synchronise to the grid, have a tight tolerance due to regulations, 3-5THD, resulting a high quality inverter to be able to be accredited for that use.
Many stand alone inverters that have no accreditation’s, are PSW with no load, but not so clean under load, but, miles better than MSW.

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Raul said:
I’m having a hard time to believe that a 400ah delivering 170a it’s a good thing. That if it can. The plates inside must boil the mat. That’s a C/ 2,5 rate. Any prolonged load at that rate will wear the lead prematurely. Even the pure lead agm that delivers 1C, it’s for short bursts, and not to be abused. I do not condone the brute use of lead batteries. A C/10 rate it’s what I would recommend max, and up to C/5 on heavy stationary with thick 5mm and above plates.
There is a safety reason to, as the discharge is just reverse of charge, the same thermal runway applies to discharge as well. Do few cycles knackered the plates, then short inside, and you got a hot situation.
Click to expand...
Well it certainly can - and did. (Not 170A though. It was touching 200A in fact with inverter overhead and voltage drop under the load).
With paralleled batteries, I also do a fully disconnect and individual check of each battery each 6 months and the batteries were as good then as when new.
So I guess we are going to have to disagree on what is possible.
 
Hoovie said:
Well it certainly can - and did.
With paralleled batteries, I also do a fully disconnect and individual check of each battery each 6 months and the batteries were as good then as when new.
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I don’t contradict you, they must be damn good batteries, and you must found their limitations to use them at their max. 👍
 
GHD hair stuff didnt work on my mates basic inverter, he had to buy an expensive one
The cheap one I had in my previous van and the one I fitted in current van (different brands) work everything I need and the bosses hairdryer, on low heat because it's only 1000w inverter
 
Raul said:
Indeed, a tipical 100Ah battery is expressed at a common C/20 rate, at C/5 is allot less than 100ah. Some even give the capacity at C/100 as it looks better for marketing. Worth knowing the capacity declared at what rate is given.
As for the MSW inverter vs PSW is efficiency for starters and type of load. Most loads are ok, inductive capacitive difficult, resistive not a problem. Resistive doesn’t care if you feed DC or AC, it works but at different efficiency. When the load is difficult, results in loads of reactive power returning back, giving a very low power factor. That, can be corrected to some degree with large capacitors. Hence some MSW with good capacitors fair better with some loads. Change the load that’s not compatible with the capacitors delivery, and you’re in a pickle. Inefficiency is heat and lost power, you will see a MSW running hotter than a PSW. Also the PSW will always have a lower stand by consumption, most are microprocessor controlled high frequency fets. The fets will switch at a very high rate simulating a perfect sine wave, producing a 8-10v AC, then feeding it to a transformer to up it up to 230v. A toroidal transformer that’s found in PSW inverters, is much more efficient at this job compared to the old type, resulting in less heat, less hamming, and better surge capability.
The MSW are also better and worse, the square wave is awful, the trapezoidal wave better, as its closer to the sine wave. The later is also known as quassy wave. The sine wave also can be better or worse, it can go trough 0 to fast squeaking the wave, and becomes like a sawtooth under load. You need the sine wave switching perfectly at 180 deg and have some compensation under load. This is given in the THD total harmonic distortion in the inverter datasheet. All inverters that connect and synchronise to the grid, have a tight tolerance due to regulations, 3-5THD, resulting a high quality inverter to be able to be accredited for that use.
Many stand alone inverters that have no accreditation’s, are PSW with no load, but not so clean under load, but, miles better than MSW.
Click to expand...
Do they still use toroidal transformers, I thought they were all switch mode.
 
They certainly do, you can tell by the weight, and surge capability. If you refer to grid tie, some do some don’t. The ones with, have galvanic protection to.
Most grid tie don’t need that, so transformerless can be approved if meets the test. But, standalone hybrid or battery inverters, all have a transformer, to up the voltage. There is no buck boost in battery inverters. It has DC max min in, and the rest is done by transformer. The grid inv does buck boost as the array can supply 80- 600vdc and gets chopped to 230 or boosted. Doesn’t need a transformer. The battery inverter is fed by lower voltage, hence the need for that transformer to up it up.

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Ref the comments about having a max C10 or C5 current draw... In general use, I would absolutely agree and you don't want to hammering your batteries constantly as that will do them no good, but for occasional high power use for genuinely decent batteries, there is no reason why you should not draw at a higher rate for short periods.

If you go on a basis of 400Ah bank if you have a 1000W inverter, so let us make that a 600Ah battery bank if you have a 1500W inverter (which is quite often the case for some one who uses one of those Nespresso machines or maybe has a hairdryer that must be used).
So in that situation, someone who runs their coffee machine or hairdryer for 10 minutes a day MUST have a 600Ah battery bank??
To go back to my examp!e, my last self-build was deliberately gas-free. I had electric cooking and electric hot water (not electric heating mind, had a diesel heater) and with that setup, in that case my 645Ah (@C20), would have apparently been insufficient to support my 2400W inverter (which I did use to power 2kW devices).
Well, out of interest, I decided to check my overall "C" usage rating over a winter's weekend parked up at the Green Frog in Moffat, off grid of course, and my calculated "C" rating (using data logged by the Victron BMV on a minute by minute basis over a 48 hour period) was C120.
If someone has a battery bank as recommended to support a large (but very minimally used) inverter, they will have so much excess battery capacity they will not know what to do with it! If they are a heavy inverter user, maybe they need the capacity, but for most ... Nah.

PS. The batteries (Lead Carbon AGM) In the "Green Frog" van had a datasheet that detailed the available capacities at different C load ratings right down to C1, so clearly they are tested and validated down to that level.
 
Raul said:
I don’t contradict you, they must be damn good batteries, and you must found their limitations to use them at their max. 👍
Click to expand...
Well, I do know one thing ... I would not be doing what I did if I had something like the typical motorhome fitment of Banner Bull Wet batteries (although I would say they make excellent doorstops).
 
Raul said:
I don’t contradict you, they must be damn good batteries, and you must found their limitations to use them at their max. 👍
Click to expand...
Maybe that is the big variable in different installations, for many years I had 320ah of Exide Gel running a 3kw inverter but typically around 50% capacity so under 200 A draw and never for long periods.

Actually when we bought the van it had only 2x80ah Gel but still ran the 3kw inverter at 50% capacity, I added two more batteries after two or three years.

As you might guess I don't go for the 400ah/1000watts of inverter but maybe I would if I had experience with crap batteries.
 
And to add to that variable, even a crap cheap starter battery is capable of 3C for a short period of time. The think is, define that short period. To some can be seconds, minutes, and some if it’s there I will use it.
Design limitations are there to protect the inexperienced. Certainly you can push if you know what you are doing.
 

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