Bad Military Surplus Generator Advice Online

johnray13 · Aug 21, 2013

I know what you mean.

On a RV forum I frequent, a constant recommendation is to only buy inverter generators, as they produce "clean" power for all your electronic devices. This drives me nuts. For one thing, most modern electronics (including the computer I am typing on the the monitor I am looking at) have a rated input of 50-60hz @100-250 volts.

Secondly, I have yet to figure how an inverter is going to produce a better sine wave than an a AC generator.

But this magical "clean" power is all the rage.

storeman · Aug 21, 2013

johnray13

You are right and if you research inverters, some are pure sine and some are modified sine.

glassk · Aug 21, 2013

[h=2]Some recommendations.[/h]For those on a very tight budget, the Harbor Freight 800W or similar is a decent little entry-level generator for those needing a small, portable unit. On sale now and then at Harbor Freight for $89 from its regular $129 price tag, it’s hard to beat when it’s on sale. Grab a 20% off coupon out of your American Rifleman magazine or Google “Harbor Freight 20% off coupon” images on the internet (and print out said coupon) for an even better bargain

http://www.gunssavelife.com/?p=1925

Looks like the Mep's may have some Competition ,..

..

Hey Marcus,
You might be scratching your head about the “what kind of electricity” mentioned a moment ago. Cheaper generators and inverters produce a “modified” sine-wave alternating current (AC) electricity. This will work in a pinch but it causes motors and transformers to run hot and some electronics may not run at all with modified sine-wave AC.

MarcusOReallyus · Aug 22, 2013

glassk said:
Hey Marcus,
You might be scratching your head about the “what kind of electricity” mentioned a moment ago. Cheaper generators and inverters produce a “modified” sine-wave alternating current (AC) electricity.

Actually, the cheapest inverters produce a square wave (but I doubt there are many of those on the market). That's the natural result of most DC-AC techniques, and then other circuitry is added to modify that square wave to something resembling a sine wave. The more you fuss with it, the closer you can get it to a sine wave, but every bit of extra circuitry adds expense. That's why the cheaper the inverter, the "dirtier" the power. It's closer to that original square wave.

But like I said, I don't even know HOW you could possibly build a GENERATOR that puts out a "modified sine wave". That's just not how a generator works. It's natural output is a sine wave. You'd have to TRY to make it anything other than a sine wave. The difference between cheap generators and expensive generators (other than durability) is how well they regulate the output in terms of voltage and frequency, but even a poorly regulated sine wave is still a sine wave.

This is Generator 101.

steelypip · Aug 22, 2013

MarcusOReallyus said:
But like I said, I don't even know HOW you could possibly build a GENERATOR that puts out a "modified sine wave". That's just not how a generator works. It's natural output is a sine wave. You'd have to TRY to make it anything other than a sine wave. The difference between cheap generators and expensive generators (other than durability) is how well they regulate the output in terms of voltage and frequency, but even a poorly regulated sine wave is still a sine wave.

This is Generator 101.

True as far as it goes, but you're confusing a generator (which is a device which creates an alternating electric current by means of moving a magnetic field past windings) with a generator, which is a consumer appliance, often in a box, which makes house current when supplied with some fuel.

There are lots of the nicer sort of appliance generators which use a permanent magnet gen head and a variable speed engine to make variable voltage and frequency AC which is rectified into DC and then fed to an inverter to make some quality of AC for use by consumer electric appliances. The Honda EX series are probably the most popular and well-known. They have good noise characteristics and good fuel consumption because the engine runs only fast enough as needed to make the amount of power required for the load at that moment.

The electronics do exact an efficiency penalty, but the high efficiency of the PM generator in combination with the low idling fuel consumption gives them a better average fuel consumption number per WH generated versus a traditional constant RPM system up to about 80% of rated load.

Because there is indeed an inverter in the circuit, you have all the traditional inverter design issues to deal with. So you're both right and wrong, depending on which meaning of the word 'generator' you use.

And on-topic: yes there are people saying stupid things about Mil Surp generators on the internet. Great! they're too expensive in surplus right now anyway.

trukhead · Aug 22, 2013

MarcusOReallyus said:
Actually, the cheapest inverters produce a square wave (but I doubt there are many of those on the market). That's the natural result of most DC-AC techniques, and then other circuitry is added to modify that square wave to something resembling a sine wave. The more you fuss with it, the closer you can get it to a sine wave, but every bit of extra circuitry adds expense. That's why the cheaper the inverter, the "dirtier" the power. It's closer to that original square wave.

But like I said, I don't even know HOW you could possibly build a GENERATOR that puts out a "modified sine wave". That's just not how a generator works. It's natural output is a sine wave. You'd have to TRY to make it anything other than a sine wave. The difference between cheap generators and expensive generators (other than durability) is how well they regulate the output in terms of voltage and frequency, but even a poorly regulated sine wave is still a sine wave.

This is Generator 101.

steelypip said:
True as far as it goes, but you're confusing a generator (which is a device which creates an alternating electric current by means of moving a magnetic field past windings) with a generator, which is a consumer appliance, often in a box, which makes house current when supplied with some fuel.

There are lots of the nicer sort of appliance generators which use a permanent magnet gen head and a variable speed engine to make variable voltage and frequency AC which is rectified into DC and then fed to an inverter to make some quality of AC for use by consumer electric appliances. The Honda EX series are probably the most popular and well-known. They have good noise characteristics and good fuel consumption because the engine runs only fast enough as needed to make the amount of power required for the load at that moment.

The electronics do exact an efficiency penalty, but the high efficiency of the PM generator in combination with the low idling fuel consumption gives them a better average fuel consumption number per WH generated versus a traditional constant RPM system up to about 80% of rated load.

Because there is indeed an inverter in the circuit, you have all the traditional inverter design issues to deal with. So you're both right and wrong, depending on which meaning of the word 'generator' you use.

And on-topic: yes there are people saying stupid things about Mil Surp generators on the internet. Great! they're too expensive in surplus right now anyway.

glassk said:
Some recommendations.

For those on a very tight budget, the Harbor Freight 800W or similar is a decent little entry-level generator for those needing a small, portable unit. On sale now and then at Harbor Freight for $89 from its regular $129 price tag, it’s hard to beat when it’s on sale. Grab a 20% off coupon out of your American Rifleman magazine or Google “Harbor Freight 20% off coupon” images on the internet (and print out said coupon) for an even better bargain

http://www.gunssavelife.com/?p=1925

Looks like the Mep's may have some Competition ,....

Hey Marcus,
You might be scratching your head about the “what kind of electricity” mentioned a moment ago. Cheaper generators and inverters produce a “modified” sine-wave alternating current (AC) electricity. This will work in a pinch but it causes motors and transformers to run hot and some electronics may not run at all with modified sine-wave AC.

Very interesting, so:

Does the peak amplitude of the modified sine wave inticate the actual voltage output?

In a sine wave producing AC generator, the very peak of the sine wave is way way higher than the rated, stated output of the generator (peak or about 176 volts for a 110 volt output), and, is the actual AC output is a result of the RMS (Root Mean Square) or averaging of the area under the sine wave compared to the area under a square wave curve?

tow2gunner · Aug 22, 2013

I just saw an article on a CAR site - saying how much better generators from car engines (gas) were so much better and more reliable and fuel efficient.
Hard to find diesel , cant find anyone to work on the MEP generators, parts hard to find.....

blatant diesel hatred!!!

Isaac-1 · Aug 22, 2013

Steelypip: I think you mean Honda EU series being inverters, not EX which I think is one of their traditional generator series. I have a little Honda EU-1000 inverter generator, it is great for many things, 1,000 (well 950 watts) ultra quiet (quieter than a modern small car at idle), and weighs under 30 pounds.

glassk · Aug 22, 2013

MarcusOReallyus said:
Actually, the cheapest inverters produce a square wave (but I doubt there are many of those on the market). That's the natural result of most DC-AC techniques, and then other circuitry is added to modify that square wave to something resembling a sine wave. The more you fuss with it, the closer you can get it to a sine wave, but every bit of extra circuitry adds expense. That's why the cheaper the inverter, the "dirtier" the power. It's closer to that original square wave.

But like I said, I don't even know HOW you could possibly build a GENERATOR that puts out a "modified sine wave". That's just not how a generator works. It's natural output is a sine wave. You'd have to TRY to make it anything other than a sine wave. The difference between cheap generators and expensive generators (other than durability) is how well they regulate the output in terms of voltage and frequency, but even a poorly regulated sine wave is still a sine wave.

This is Generator 101.

This was from a "GUNSIGHT" and a play on scratching your Head,

:smile:

Triple Jim · Aug 22, 2013

trukhead said:
Very interesting, so:

Does the peak amplitude of the modified sine wave inticate the actual voltage output?

Only for square wave AC. Modified sine wave AC is usually square pulses with some time at zero volts in between, so peak voltage is greater than RMS.

In a sine wave producing AC generator, the very peak of the sine wave is way way higher than the rated, stated output of the generator (peak or about 176 volts for a 110 volt output), and, is the actual AC output is a result of the RMS (Root Mean Square) or averaging of the area under the sine wave compared to the area under a square wave curve?

For a sine wave, V(peak)=V(rms)(√2), so for 120V AC, the peak voltage is 169.7V, and peak to peak is 339.4V. AC voltage is almost always defined as the RMS voltage. It just happens that with a square wave RMS voltage is the same as peak voltage. Other wave forms have lower RMS values than peak values.

glassk · Aug 22, 2013

trukhead said:
Very interesting, so:

Does the peak amplitude of the modified sine wave inticate the actual voltage output?

In a sine wave producing AC generator, the very peak of the sine wave is way way higher than the rated, stated output of the generator (peak or about 176 volts for a 110 volt output), and, is the actual AC output is a result of the RMS (Root Mean Square) or averaging of the area under the sine wave compared to the area under a square wave curve?

isn't Vpeak X 0.707 a short cut to RMS? and think you have to divide by duty cycle for modifed wave

Isaac-1 · Aug 22, 2013

It can be a shortcut estimation assuming you have a symmetric wave form

Triple Jim · Aug 22, 2013

Specifically it has to be a sine wave for the √2 (approx. .707) factor to apply. For example, triangular waves, even if symmetrical, use √3 instead.

Edit: As stated below, √2 is approx. 1.414!

LuckyDog · Aug 23, 2013

Yea, I caugt a mistake!!!!! :razz:

√2 ≈ 1.414 ≈ 1/0.707

But otherwise - Yea, what 3xJim said.

Triple Jim · Aug 23, 2013

Absolutely, sorry for the goof, and thanks for fixing it! For sine waves, multiply RMS voltage by √2 to get peak voltage. Divide peak voltage by √2 (or multiply it by 1/√2 =approx .707) to get RMS voltage.

glassk · Aug 23, 2013

Doesn't That square root of three 1.73 do some three phase stuff too,...??

Triple Jim · Aug 23, 2013

It sure does. As an example, the 3-phase line to line voltage is √3 x the line to neutral voltage. 120v x √3 = approx 208v

trukhead · Aug 23, 2013

Amazing, all this for describing movement of electrons (volume and pressure of little things you can't even see) through a conductor! :idea:

bsorcs · Aug 23, 2013

Re Ike's start of this thread, one of my Dad's favorite aphorisms was from Ben Franklin: "Believe none of what you hear, and only half of what you see." Re the previous post, to be absolutely correct, it's the electron potential, not pressure. Only reason I can comfortably write this is because of a similar commonly and long-held, but equally incorrect, perception in the field of groundwater flow [previous life experience], the equations for which are identical to those for electric fields and heat flow.

Triple Jim · Aug 23, 2013

When I was going to school at the U of MD, I would sometimes browse the stacks of the engineering library, mainly when I should have been studying. I was amazed to see complicated analyses of electric motors and generators, including calculus and differential equations, in journals dated from the late 1800s.

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