Watts vs Volt-Amps - huh ??

[Sunny Solar]

Sunking its not the point if there is only one step or 2,376 steps The inverter is first designed??to produce a SQUARE WAVE. Because thats the cheapest way to make an inverter.
So after the square wave gets modified you could call it a stair wave a step wave or anything similar but the fact remains the first conversion from DC to AC is done with a square wave.

And no matter how you cut and slice it its ALWAYS going to be wrong to call it a Modified Sine Wave.
IE You cant have a modified Ford vehicle unless you first start with a Ford vehicle.

Beanyboy its not always easy to recommend items by brand or even by a particular model as to what is best or "worstest"
Very often an item made for one countries market can be very different to the "same" model marketed in another country.
Another problem can occur if some one on here buys a very early version and it has problems ,and they say its c..p but the second version many be great.And you would not be buying it because of reading on here it was a so so product.
Also some of us in this industry get pre production items that may have features that dont end up on the retail version. Then you will be complaining we gave bad advice. This certainly applies to me I get to test many panels,batteries ,charge controllers and inverters that in many cases dont have the same features as the final versions will. And could never give results on here as all testing is highly confidential. Much as I would like to tell you some of the real shonky items that never come close to their claimed specs. This holds especially true for many MPPT controllers.Many cant even equal let alone beat a good PWM controller .
Mabe there are some others that will give you some advices as to what to buy.. But it usually comes down to MONEY you buy rubbish 10 times you buy good once.

[Beanyboy57]

With that said I need to make sure the small frig I want to get is efficient and does not have a poor PF. Too bad I didn't know enough about the difference between a TSW and MSW inverter before I purchased my Whistler. At least I know I have to stay below the 2500watt rating.

I gotta read more of the posts in here so I can learn as much as possible about building my own PV system

In trying to figure out why some appliances or motors have a poor PF and others do not I have formed the idea that PF is related to the design, construction and quality of the components. Is this a correct assumption? If so the old adage, "you get what you pay for" certainly rings true once again but as per everything that I read on this site the respondents will show me that its not that simple!
Further to the last comment made in the above quote, do the contributors to this site have a page where they might recommend certain products or brands for use in an renewable energy System?

[Sunking]

John along those lines you could call it Modified Stair Wave as that is a more accurate description of what it looks like on a scope. However the question becomes how many STEPS are used. Really cheap inverters is just a plain ole square wave and more robust units may be several hundred steps.

[Sunny Solar]

Why the persistence in using the totally incorrect term MSW to mean Modified Sine Wave?? No one in their right mind or left mind would ever modify a sine wave to get a Modified Sinewave.

The correct term is MSW .Modified Square Wave.

[Sunking]

SunEagle do not get to wrapped up into it. It only becomes a problem when you are pushing the inverter to the limits.

[SunEagle]

Well here is the deal. You had better know if you sell the stuff and fully understand the subject.

You need to know a TSW = True Sine Wave Inverter., and MSW = Modified Sine Wave Inverter.

TSW inverters can run Motors loads (reactive) and Non Linear loads (switch mode electronic power supplies) up to a limit.

MSW may but not likely to do so.

It matters.

LOL. Care to make me an offer for my whistler? The good thing is that I don't sell inverters. I am just trying to build a personnel portable solar power system.

It's funny that I have a number of years experience in the electrical engineering field for industrial and commercial complexes as well as studying the design and fabrication of Cadmium-Sulfide Solar cells back in the 70's but when it comes to these DYI solar power systems I am still learning and really appreciate your advise as well as the other experts on this website.

I will pay attention and learn as much as I can. That is why I am asking for help with the purchase of a 30A Charge Controller. Right now I have learned that MPPT is better than PMW and that going less expensive gets you less quality. I just don't know which charger I need to get since there are so many different manufacturers as well as knock-offs that sound and look as good as the real thing. If someone can point me to the right brand and model I would really appreciate it. Thank you.

Vince

[Sunking]

Sunking. Thanks. I didn't know about the difference between a TSW and MSW inverter.

You are also correct about the non linear switching loads. They cause harmonics which increases both Voltage and Current distortion which can cause bigger losses than a low PF.

Actually that is my job to help our customers eliminate these harmonics by installing HMI type transformers. By putting in transformers with higher efficiencies that also mitigates the triplet harmonics there is a good change of reducing their electric bills by 4 to 6% as well as eliminate issues caused by the harmonics.

Well here is the deal. You had better know if you sell the stuff and fully understand the subject.

You need to know a TSW = True Sine Wave Inverter., and MSW = Modified Sine Wave Inverter.

TSW inverters can run Motors loads (reactive) and Non Linear loads (switch mode electronic power supplies) up to a limit.

MSW may but not likely to do so.

It matters.

[SunEagle]

Which unfortunately gives the individual homeowner no economic incentive to reduce their PF.

BTW, since the problems an inverter has with low PF loads are most noticeable near full rated output, the thing you have to watch is the PF of your largest (usually motor) loads. If the only thing you are powering is CFLs and computer power supplies, you are probably nowhere near the full output of your inverter unless that is the entire load that you have planned for.

With that said I need to make sure the small frig I want to get is efficient and does not have a poor PF. Too bad I didn't know enough about the difference between a TSW and MSW inverter before I purchased my Whistler. At least I know I have to stay below the 2500watt rating.

I gotta read more of the posts in here so I can learn as much as possible about building my own PV system

[russ]

Which unfortunately gives the individual homeowner no economic incentive to reduce their PF.

BTW, since the problems an inverter has with low PF loads are most noticeable near full rated output, the thing you have to watch is the PF of your largest (usually motor) loads. If the only thing you are powering is CFLs and computer power supplies, you are probably nowhere near the full output of your inverter unless that is the entire load that you have planned for.

There is so much BS surrounding the PF - urban myths supported by loony sites and all the average homeowner is screwed anyway. I have written to manufacturers asking for the info for CFL lamps and been told they don't give that information out.

That would be one place regulation would be useful - even if just a penalty for the abusing lamp/fridge or whatever - make it cost more upfront to make the crao less attractive.

[inetdog]

Not really true - the costs, including losses due to poor power factor, are paid by the customer - it is just averaged out and tacked on to all bills. In the event all power factors were 1 the utility costs would be less.

Which unfortunately gives the individual homeowner no economic incentive to reduce their PF.

BTW, since the problems an inverter has with low PF loads are most noticeable near full rated output, the thing you have to watch is the PF of your largest (usually motor) loads. If the only thing you are powering is CFLs and computer power supplies, you are probably nowhere near the full output of your inverter unless that is the entire load that you have planned for.

[russ]

The only way a residential customer would end up paying more for a high PF is if the utility-supplied meter reads incorrectly in the presence of higher harmonics in the current waveform. And as far as I know, none do, but I am open to a counterexample.

A commercial meter can be configured to record either average or worst case PF in addition to recording the real power (watts) consumed.

Not really true - the costs, including losses due to poor power factor, are paid by the customer - it is just averaged out and tacked on to all bills. In the event all power factors were 1 the utility costs would be less.

[SunEagle]

Playing with words? Where on the residential bill does it specify a penalty for poor power factor? What utility anywhere around points out a charge to the residential customer a penalty for poor power factor? None that I know of. Of course the end customer always pays.

For commercial use it is standard to have a penalty clearly charged.

Not playing with words. Just not trying to be too definitive by saying no residential bill has a power factor penalty added to it. Since I do not have direct knowledge of all resident tariffs I felt if there were any at all then by saying most do not I was being as truthful as possible.

You are also correct when you say the customer always pays one way or the other. Utilities will find a way to pass on the costs to all customers.

[inetdog]

Playing with words? Where on the residential bill does it specify a penalty for poor power factor? What utility anywhere around points out a charge to the residential customer a penalty for poor power factor? None that I know of. Of course the end customer always pays.

For commercial use it is standard to have a penalty clearly charged.

The only way a residential customer would end up paying more for a high PF is if the utility-supplied meter reads incorrectly in the presence of higher harmonics in the current waveform. And as far as I know, none do, but I am open to a counterexample.

A commercial meter can be configured to record either average or worst case PF in addition to recording the real power (watts) consumed.

[russ]

A bad or low Power Factor is no good for either the utility or the homeowner. Utilities charge a PF penalty to customers to help them reduce waste on their distribution system.

While a residential connection does not usually have a PF penalty added to their bill by the Utility, a low PF means they have losses in their electrical system. These losses will use up some of the total available kva of their transformer capacity in their inverter.

Playing with words? Where on the residential bill does it specify a penalty for poor power factor? What utility anywhere around points out a charge to the residential customer a penalty for poor power factor? None that I know of. Of course the end customer always pays.

For commercial use it is standard to have a penalty clearly charged.

[SunEagle]

PF is no ta huge problem for TSW inverters, but can be a major problem for MSW inverters. However even TSW inverters can have a problem for example running a lot on non linear loads like switching power supplies found in Desktop computers and cheap CFL light bulbs where PF can be .6 or even less. Most TSW inverters can only handle .8 PF at full power.

Sunking. Thanks. I didn't know about the difference between a TSW and MSW inverter.

You are also correct about the non linear switching loads. They cause harmonics which increases both Voltage and Current distortion which can cause bigger losses than a low PF.

Actually that is my job to help our customers eliminate these harmonics by installing HMI type transformers. By putting in transformers with higher efficiencies that also mitigates the triplet harmonics there is a good change of reducing their electric bills by 4 to 6% as well as eliminate issues caused by the harmonics.