Help make sense of generator numbers

[liandri]

Hi all,

Out of curiosity I was looking up generators to see what's out there. I'm still in the build-out phase but plan to run entirely off solar.

I was looking at this genny and the numbers don't quite make sense to me. I'm sure there's some sense to them, and I'll need that to eval other units. It says 1700W, but the output is only [email protected] DC. This would be only 100W. For 1700W@12V, it seems like this should be ~141A (whoa!). (Don't generators naturally produce DC?)

And given it's 9.5h runtime at 25%, that would be 2.375h at 100% utilization, which I'd assume I'd use to quickly boost the batteries, then turn the noise off. How does one control the output of a genny, and is 100% actually discouraged?

http://www.championpowerequipment.com/products/inverters/73536i-2000w-inverter/#product-specs

JFYI, my battery bank will be 12V 400Ah.

And does anybody know of generators that are JUST small generators without the inverter? I'lll already have in inverter in my system, no need for the redundancy/cost/extra-thing-to-break. With auto-start would be sweet

Thanks, all! I'm sure it's simple.

 

[MikeRuth]

I not the genny expert here but, if it is labeled or rated at 1700 Watts at 110 Volts, then it is offering about 15 amps at 110VAC and that's typical of one standard household outlet.
Many gen sets do have a DC output built in and that has essentially nothing to do with the AC output.

A 25% load would assume your pulling about 4.25 Amps or roughly 467 Watt load on the AC

 

[ViaVacavi]

As Mike said above, most generators have separate AC and DC circuits in the windings. Usually, the generators are used for running AC loads so that is where they have the higher power rating, and light battery charging on the DC side of things. Unfortunately you won't find much for commercial DC generators at any kind of high output, unless you're really wanting to spend some cash.

DIY DC generators are very easy and cheap to make out of scavenged lawn mower engines, a few pulleys and an old car alternator. You'll need about 1 horsepower for every 700 watts you want to produce (a little over 50A @ 12VDC).

 

[liandri]

Interesting! So generators actually don't produce just DC in order to convert to AC. So basically if you have a DC generator, you can get AC out of it "for free" or vice-versa (just speaking physics-wise)?

Cool idea about just DIYing your generator. The first one I posted must be a tiny motor then to make only 100W DC? This puny little model plane motor is 1.67hp, which would be 1246W... but I assume there would be decent losses in conversion to DC? https://www.amainhobbies.com/o.s.-max-.46axii-abl-airplane-engine-w-muffler-osmg0548/p234377. It'd be too easy if all I needed was that tiny little thing. I could just put a foot of insulation around it and it would just sound like a little bee caught in the cabinet (assuming proper cooling and intake/exhaust).

I think there's still something I'm not understanding.

Again, thanks for your guys' help!

 

[ViaVacavi]

Interesting! So generators actually don't produce just DC in order to convert to AC. So basically if you have a DC generator, you can get AC out of it "for free" or vice-versa (just speaking physics-wise)?

Cool idea about just DIYing your generator. The first one I posted must be a tiny motor then to make only 100W DC? This puny little model plane motor is 1.67hp, which would be 1246W... but I assume there would be decent losses in conversion to DC? https://www.amainhobbies.com/o.s.-max-.46axii-abl-airplane-engine-w-muffler-osmg0548/p234377. It'd be too easy if all I needed was that tiny little thing. I could just put a foot of insulation around it and it would just sound like a little bee caught in the cabinet (assuming proper cooling and intake/exhaust).

I think there's still something I'm not understanding.

Again, thanks for your guys' help!

it actually depends.  Some generators are nothing but alternators, where the alternating current is rectified with diodes to DC current.  Others are true DC generators.  Yet others are true alternators producing nothing but AC current.  Most Onan generators for example, have a large number of windings to produce AC, and they do a separate smaller winding which gets rectified for the DC charging circuit.  Other generators, such as inverter generators, generate DC power, which is then fed through an inverter for cleaner power output and more efficiency (since they can tune the engine to run at it's most efficient point in its power curve).

Technically speaking, 1 HP is about 747 watts equivalently.  You will have losses, for example friction and pulley losses in the DIY generator talked about above.  Regarding the model plane motor, there are probably a number of things contributing to the inefficiency.  The 1.67 HP rating is at a certain RPM, and the required torque to turn whatever generator it's turning may be bogging the engine down in the RPM ranges where power output is significantly less.  Similarly, alternators and generators have their power rating at a certain RPM.  Aside from whatever drive mechanism they are using, they are likely losing efficiency du to a mismatch in engine/generator RPM and torque requirements.  It can get pretty complicated, but those small engines simply don't have enough torque to push much useful power.  Finding the right combination and match is a bit of a crapshoot, but in general larger engines with more torque like seen in standard lawnmower engines will normally come out pretty well in the efficiency curve

 

[Mobilesport]

@ViaVacavi
So lets say a Honda 2000 generators inverter quit working ,  could you wire in a inverter to the honda ? 
Could you find the 12 volt output that powered the Hondas broken inverter and wire that 12 volts to a regular say Walmart inverter? 
Thanks for your time

 

[ViaVacavi]

@ViaVacavi
So lets say a Honda 2000 generators inverter quit working ,  could you wire in a inverter to the honda ? 
Could you find the 12 volt output that powered the Hondas broken inverter and wire that 12 volts to a regular say Walmart inverter? 
Thanks for your time

It probably depends on the make and  of the generator.  I've  never cracked one open, but I would imagine they vary from simple mechanical governors, all the way to feedback loops from the inverter that influence the rpm of the generator. If you're adventurous, crack it open and take some pictures. Of its a simple governor control, then the scenario you mention is probably possible. If you see electric actuators connected to the carburetor, it's probably a closed loop feedback system from the inverter. I'd be more than happy to try to help you decipher what's going on if you can get some good pictures.

Can you list the symptoms that make your think the inverter is fried?

 

[Mobilesport]

It probably depends on the make and  of the generator.  I've  never cracked one open, but I would imagine they vary from simple mechanical governors, all the way to feedback loops from the inverter that influence the rpm of the generator.  If you're adventurous, crack it open and take some pictures.  Of its a simple governor control, then the scenario you mention is probably possible.  If you see electric actuators connected to the carburetor, it's probably a closed loop feedback system from the inverter.  I'd be more than happy to try to help you decipher what's going on if you can get some good pictures.

Can you list the symptoms that make your think the inverter is fried?

My Hondas inverter is' nt fried , just thinking for in the future
I do have a Honda 2000 electrical schemat if that will help

 

[ViaVacavi]

My Hondas inverter is' nt fried , just thinking for in the future
I do have a Honda 2000 electrical schemat if that will help

Excellent schematic, thank you

Ok, so this generator does indeed have a closed loop feedback.  As you can see, there are three windings - the first set of windings is a 3 phase set of windings wired in what they call "star" configuration.  This set of windings is at 180-200 VAC, and is known as wild AC, as both the voltage and frequency vary in proportion to the RPM.  The 2nd winding is a small AC winding that is rectified to DC for battery charging, and the 3rd "sub" winding is the feedback winding.  It's only purpose is to give the inverter logic a clean reference signal, which is used to control throttle.  Technically there is also a 4th coil, which is just a field coil that controls the current output of the other windings.

If the inverter were to go bad, there are other wild AC inverters on the market (Jacobs wind turbines are nearly identical in setup), though they normally aren't cheap and they wouldn't be a plug and play solution.  Personally, if it were me and the inverter went bad, it would be far easier and cheaper to convert the unit to a high current DC charging generator.  This could be done by passing the wind AC through a transformer to step down the voltage, then rectify that to DC, or even just rectify the wild AC directly and run that through a buck boost converter to step down the voltage.  This would be fairly cheap and easy to do and would leave you with a pretty nice DC charging unit

 

[Almost There]

If the inverter were to go bad, there are other wild AC inverters on the market (Jacobs wind turbines are nearly identical in setup), though they normally aren't cheap and they wouldn't be a plug and play solution.  Personally, if it were me and the inverter went bad, it would be far easier and cheaper to convert the unit to a high current DC charging generator.  This could be done by passing the wind AC through a transformer to step down the voltage, then rectify that to DC, or even just rectify the wild AC directly and run that through a buck boost converter to step down the voltage.  This would be fairly cheap and easy to do and would leave you with a pretty nice DC charging unit

Most of the above paragraph went way over my head and caused a bit of eye rolling...

But I did glean enough from it to ask if the opposite can be done. Can the DC wirings be used to boost the AC output?

I have a Honda 1000 that is a decade old and is now not producing the stated 900 watts continuous output. I found this out when not one but two good battery chargers caused it to brown out. When tested to see what load it would carry, it's somewhere around 600 watts now. Either charger ( I now have an Iota 55 amp) require in the range of 660 watts output to run.

Of course a Honda dealer suggested that I replace the unit and said that rebuilding the one I own was not going to be cost effective. I do have access to a couple of small engine mechanics who love to tinker with stuff but I'm not prepared to throw a bunch of money at the old one where the money could be better spent on buying a new unit.

Advice??

 

[ccbreder]

almostthere; There is most likely an electronic part failed and that is reducing the output. A "radio repair" type of mechanic would be needed rather than "small engine" shop. I would offer it for sale as is and buy a new Honda.
liandri; There are two basic types of generators for 120 volt ac operation. The ones that generate a direct 120 volt ac, the out put is adjusted by the rpm of the engine. Very loud, and inefficient. And then the Inverter type. They use an inverter to output a clean 120 volt wave. They can run slower and most can adjust their engine speed to the required output load. They generate a higher dc voltage than 12 volts so they can convert that to 120 volt ac. It is an efficiency thing. These generators are designed to out put the rated power as ac current. Therefore, the 1700 watts is at 120 volts. Most of these generators also have a tap for 12 volts labeled as battery charger. They don't output enough dc currant to be viable.
No it is impractical to do without the built-in generator inverter. Inverter generators are the state of the art in powering small loads. I use mine to charge the house bank by plugging my battery charger into the 120 volt outlet.

 

[Mobilesport]

@ Almost there
How many hours did you get out of the Honda before failure? 
I heard 2000 hours is about a average time of lifetime

 

[Almost There]

@ Almost there
How many hours did you get out of the Honda before failure? 
I heard 2000 hours is about a average time of lifetime

I have absolutely no idea.

It actually hasn't failed completely, it's just not putting out full power. I used it all winter but have to pair it with a 20 amp battery charger that takes forever and ever to get the battery bank up. It won't quite carry the 55 amp Iota charger.

I used it regularly at art/craft shows for several years and then it sat. It would probably be in much better shape if I had of followed maintenance instructions and exercised it regularly. It sat through several Canadian winters in a cargo trailer which meant it was cold AND damp. Surprisingly, when Justin showed me how to clean it up at the RTR the carb wasn't fouled, and with some SeaFoam and fresh gas it fired right up.

I blame me for it's problems, not Honda!