Recently, I posted the Utterpower DIYer $20 Inter locking Transfer Switch. Following is a drawing of how it might be deployed in an off grid setup that can grow, and make use of wind, hydro, solar, or even pedal power if that’s all you got at the moment.
- Off grid Basic design
But There’s another topic we need touch on, and that be the Inverter Generator. We know it’s becoming popular, we know it will be available in diesel if it isn’t already. The diesel version would be somewhat of a contradiction as the inverter generators are normally an exercise in light weight.
Inverter Generator With Batteries ????
If we do consider adding batteries to the inverter’s bus, we’ll also need adequate air flow to cool inverter components, (maybe an electric fan?). We know the battery voltage will likely be higher voltage, and more dangerous than our typical 48V and lower Battery banks, so we’ll need covers, and adequate connectors to keep fingers out of the hazzard. Could this be a viable solution in the future for Off Gridders? redundancy you say? Buy two.. 🙂
Your input please.. Sometimes we see what we believe to be a natural step in the evolution of a product. We also know that if we thought of it, so have 10,000 others or more.
Will Inverter generators hit the market soon with another connector on them? One for a battery pack? And will that battery pack have another connector to hook in your solar array for charging?
GB
The inverter-generator option was unknown to me until I just read your post. I currently have a 15kW PTO generator for my backup that can run off my tractor (0.6+- gallons diesel per hour at 500 RPM on the PTO). However a handy portable inverter unit would be nice alternative to hook up quickly to run a few thing on a smaller power outage or out in the flield. I will have to look for one that can take a 240V plug to connect to my panel. I see some of the manufacturers like Honda make it possible to connect units for more power. I think the idea of using the inverter with other sources is a great idea and would make an inverter a handy tool.
If we look at the PTO driven Generator overall, from fuel in to power out, we should not expect efficiency, and I know you don’t Jack.. this is comment for those who may follow the thread.. Basically, we come out of the engine and through a set of reduction gears to meet one of our PTO standards (low RPM) we also note a need to run the engine at a higher rpm to meet the standard. Then we go thru the PTO drive shaft and hit a set of speed increaser gears to get back up to generator speed which is often 1800 rpm, and in a few cases 3600 RPMs..Lots of transmission losses for the sake of meeting a PTO standard, only to quickly divorce it. In other words, The PTO driven Generator is about as inefficient as a Pelosi Idea, sure it’s convenient for her at the time!
As for the need for 240 VAC to power a few circuits, I think there’s a way around that, and you’d do it with SPDT switches rated to do the job, you switch off the lead coming out of the main breaker and onto the generator supply. If you consider the fact that all the loads you normally need are 120VAC, the single unit works fine.
There is another way, but it is near the equivalent of the PTO situation, but in electrical terms. You simply use the 120VAC out of the Inverter-Generator, put it into an expensive autotransformer to step the voltage up, so you can use one side to power your 120 VAC loads.. extra losses and expensive included in the design. As for two inverters, I do wonder if there is an inverted clocking method available that might allow a smaller 240VAC deep well pump to be powered, and allow a pressure tank to be filled? The idea of adding batteries to the DC bus of an inverter is worth thinking about, we need see the potential, but need to toally engineer what we do. Can the Inverter Generator designed to be portable and light weight become part of a larger plan? Personally, I think it’s a natural, will the charge bus care that the power we give it came from another source? We may have a lot of interlocks, watch dog timers, and who knows what to sort if we attempt to do it ourselves. I’d bet there’s a battery pack and full line of other accessories at least in the R&D stage as we speak.
George, yes plenty aware that the PTO gen is inefficient but fairly cheap capital outlay to run the entire house in a pinch and take the mig welder out and about on occasion. I like the idea that I could put my solar panels (currently boxed) as part of a flex power package with the right inverter setup.
The portable ‘drive to’ ability of the PTO generator can’t be beat, especially on the ranch or farm.. Glad you got your panels 🙂
gas inverter generators are interesting, however for offgrid my thinking is to take what we can learn from them and apply them in a more open architecture scheme.
using my system as an example, and realizing it is not perfect and may not be even useful of others.
i use the changfa s195, and set the speed to 1800rpm (for reasons unimportant to this discussion). it drives two reapplied 110-555jho prestolite leece/neville alternators which started out life as 12volt native, and have been retasked to 24volt nominal operation. the result is a 3 step charging regime controlled by a marine regulator with a nominal output of 5.75kwatt DC (200 amps x 28.8vdc), and a peak output of 7.49kwatts (260 amps x 28.8vdc). the alternator efficiency is quite respectable at a touch over 80% .
i use a microcontroller system to do autostart, monitoring, shutdown, load management and a few other things, it computes the the generation capacity needed and sets the engine rpm to best address that level of need. i use two steps, 1200 and 1800rpm .
this generator system is used to both charge a battery bank and also provide additional DC power to the inverter system.
the end results are interesting in that i can provide for low load conditions with the batteries with a fair efficiency, actually much higher efficiency than if i provided for that level of power from what would be effectively too large a generator.
the generator only runs when the controller calculates that the load is sufficient to keep the generator operating within a predetermined window of maximum efficiency at either 1200 or 1800rpm
the system allows me to
1. limit generator run time
2. reduce noise
3. operate at or near peak efficiency
4. provide power efficiently over a wide range of loads
5. provide power at well under 2% thd
6. provide power at dead on 60hz
7. provide power at very tight voltage regulation.
8. and because of my inverters surge capacity and the batteries
ability to provide very heavy short term current capability, the system can provide easily twice the surge capacity of the genset on its own, and do it without voltage,hz droop or undue distortion.
9. best of all the unit burns less fuel per kwatt/hr electrical delivered to the load, than a similar unit running over a more or less continuous basis to provide for the same loads.
harvest and use the waste heat and you have a very competitive cogen system, that can compete favorably with what the big boys offer.
as previously stated, there are certainly other ways of doing an inverter generator, however i think for offgrid use, we need to include the battery bank and inverter system into the scheme. going further if we want to be responsible citizens and also reduce the cost of operation we ought to also recover and use the waste heat.
bob g
George,
Diesel inverter generators have been here for some time. The Onan “Quite Diesel” 7.5 kW generator we had on the 2000 Winnebago had one and it was a great genny. At low demand, i.e. charging batteries, running interior lights, it just idled along and you could hardly hear it. But turn on the hot water heater and/or the microwave and this and that, and it would throttle up in a stepwise manner. Powered by a 3-cylinder Kubota diesel. We put a couple thousand hours on it before we sold it. No problems. Nice genny, and a nice concept.
We need study exactly how the variable speed inverter gen works. variable speed constant voltage..
when you are making relatively high voltage DC for the front end of an inverter, you can produce this voltage over a fairly broad rpm range via a decent regulator.
case in point, the lowly automotive alternator, its ability to charge at engine idle is adequate, so we know that it exceeds approx 13.8volts, and it also will do so at full throttle engine rpm, which can be a range of 10 times idle speed or more. the only reason the alternator doesn’t produce more than the regulated voltage is the regulator.
if you lock the same level of excitation that produces 13.8vdc at engine idle and then spin it up to 5000rpm the voltage will go well over 100vdc the only thing keeping it from doing so is the battery which will quickly boil dry.
they do the inverter generator thing based on the same principle, they use a multipole alternator (12 to as many as 24poles or more) and set the buss voltage to something north of 200 volts dc at the lowest engine rpm they anticipate operating under, and then use the regulator to keep the voltage stable over the full design rpm window of the engine.
the ~200vdc is what the inverter needs in the front end to convert to 120vac 60hz sinewave.
unlike a typical inverter topology wherein the front end buss is a dc to dc converter, (12/24 or 48vdc is boosted to 200vdc or more) to go into the next stage, the inverter generator replaces that front end stage by simply making the high voltage dc to start with and do away with the efficiency loss of the dc to dc boost converter section… this saves ~5% of the inverter losses.
now as diy’ers i don’t see us building 200 vdc alternators with adequate rectifiers and regulators that are up to the task at hand, and we certainly don’t have access to inverters that allow us to opt out of the dc to dc converter front stage, so what do we do?
we go with what we can get our hands on, and adapt it to do at least most of what the inverter generator does.
we start with a multipole alternator, (12 or more poles) with dependable rectification, and a good regulator, both of which must also handle transients and load dump conditions. we probably ought to target 48vdc nominal because this is about the limit for off the shelf inverters.
everything is available off the shelf to put together such an alternator that can produce the requisite 48volts nominal, have tight regulation, handle transients and load dump, and also be able to do 3 stage temperature compensated charging of a battery bank,,, that is a nice plus.
this alternator can be driven at the appropriate speeds to enable operation over a fairly wide rpm range, more than adequate for operation on a diesel engine.
all we need to do then is couple this engine and alternator to our choice of 48vdc input inverter,
and if we also include a battery bank either as a buffer or as a surge enhancing option we have a very workable system that in many ways can be superior in operation to what the oem’s are producing and selling, at least in diesel powered units in this power range.
the last piece of the puzzle is the variable speed based on load controller, that too is much easier to do if we have a battery buffer or battery surge bank,,, the battery can cover the increased load while we are sampling and adjusting the rpm, so we don’t have to have instantaneous throttle response.
all we need then is a current transformer, to monitor the power going out to the load, the CT is monitored by a microcontroller which crunches the numbers based on the current demands of the load and adjusts up or down the engine rpm. or..
we can do it much simpler with a stepped control scheme, i use two steps, Quinn mentions a multi- step scheme on a motorhome? it all depends on what the specific needs are for the unit? my loads are such that two steps are more than adequate and in testing have proven to provide probably 90% of the fuel savings that a more sophisticated multstep or multivariable controller would provide.
bottom line is the fuel savings are significant, let alone the reduction of noise and wear on the engine.
in my opinion, based on what my experience is with the unit i have here, the inverter generator is probably one of the easiest to implement system of anything related to off grid power production.
we can build it to suit the class of work we need done, using the prime mover we want to use, we already have batteries and inverters as part of our offgrid installation. the rest is all off the shelf, incredibly well priced components because of the economies of scale in production,,
knowing what i know now, there is no way i would spend a significant amount of money for a oem gas powered inverter generator when i know i can do so much better with parts, that i know i can always source and repair myself, “and ” attain higher efficiencies as measured in gr/kw/hr produced (BSFC).
bob g
i would also like to add a bit more about the engine governor needed for an inverter generator
there is no need for fixed rpm operation that is dead nuts stable, the generator doesn’t need to produce 60hz power, and doesn’t even need to be very stable/repeatable,, it can also have a larger droop, all of which would not work well with a 60hz generator operation.
we can also retain the engine’s oem mechanical governor and use electronic bias of the governor…. this is not only simpler but safer in that there is no chance of an electronic failure leading to an overspeed condition.
one other note, i mentioned the use of a CT to monitor output current, we could just as easily monitor excitation current to determine the alternator loading and use that to adjust the engine speed. for example if the excitation current was to rise, the microcontroller would see that and raise the engine speed, any increase in engine speed will increase the alternators output voltage in which case the regulator will reduce the excitation and we have stable operation at higher rpm and output. the inverse is also true, the excitation current drops from a reduced load, the micro see’s that and reduces rpm.
we could accomplish very good operation via analog control as well, probably good enough to get the job done,, however use of a microcontroller allows for easy tweaking of the system.
bob g
did a little digging and came up with this
http://www.seindeo.com/power/pdfs/InverterGeneratorBasics.pdf
doesn’t go into as much detail as i would like, but gives one the basic theory of operation.
bob g
I have 2 Honda inverter generators; the 1KW and 2KW versions. Out of curiosity, I bought the full blown service manual. Quite interesting how it works. If memory serves, the crankshaft of the engine spins a PMG, which produces 300VAC which is then applied to the inverter (there’s a rectifier in there, so it’s basically a DC PMG). The controller senses the load, and ramps up or down the engine RPM as needed. The engine speed changes in discrete steps; not sure how many, but it seems as if there are 3 or 4 different RPM’s used.
It would be an interesting exercise to make a latter day Delco lighting plant with one of these Hondas. One would need a high voltage battery, equipped with a smart battery circuit to sense capacity. Also electric start for the engine. Then, the inverter could always be on, making AC available. Just like the old Delco plants, when the battery charge goes down, the engine starts, carries the user load, and charges the battery.
Anyone know the ins and outs of high voltage battery packs? Lots of cells, but one would need lower A-Hr to get the desired W-Hr capacity.
once you get over 48volts your entering NEC domain, wherein the complete system will need to be fully enclosed so that no one but a qualified service technician can enter for purposes of repair or maintenance.
from experience, with a 240vdc battery bank that supplied a 15kva inverter system. when there is a short in one cell things get really bad in a very short time. the instantaneous power available is horrendous and fully capable of piercing multiple layers of 14gauge steel plates. the sound would be akin to a small explosion, and something i for one would want no part in.
i for one would want no part of such a project, even if an inverter was available to input the higher voltage DC.
me? i would stick with 48volts for a number of reasons, safety being one, availability of off the shelf components being another, and the ability to get very near the same efficiency overall if we use a gas engine as the prime mover.
i can see why honda, yamaha and others are drawn to high voltage dc inverter/generator designs, for one the dc amperage is quite low relatively speaking so the generator can be quite small. they need small and light weight to be successful for mobile use,,,
none of which is important to an offgrid application, we don’t need ease of mobility, small size or light weight.
honestly it is so easy to get the same result albeit heavier and larger, without resorting to high speed, light weight, and high voltage dc.
fwiw
bob g
Thanks for the comments regarding high voltage battery packs. I had thought that there would be potential problems with that many cells in series; upwards of 200 or so. I’d think charging would be problematic, either with constant voltage charging for lead acid or constant current types like NiMh. All the cells would have to be well matched in capacity, and would have to age at the same rate. Harder to do with 200 cells in series opposed to 24. I also appreciate your point about a single cell shorting.
In telco, we typically did use 130 volts for different things, and I will set the politics and saftety concerns aside in this post, as it’s too involved. I consider it a fact that we will see the use of higher dc voltages in near everything. If you’re curious, we used 130 volts dc from a wet cell string for range extenders and more.. You can only pull dial tone reliably on a loop of less than 1500-1600 ohms at 48 volts, then you need jack up the voltage to pull up that relay when the customer goes off hook. Imagine all the kids alive now that don’t know what dial tone is!
I say we should expect battery plants at much higher and more dangerous voltages in Cars, communications and more.
And old telco switch was/is a power hungy pile of energy conversions. Near countless power supplies converting to voltages the power individual circuit packs needed. All with heat sinks, and then a building full of large air handlers to carry that heat away. If you understand DC-DC converters, you got the bulk of a Central office figured. The switch itself.. an interesting community of entities with different jobs, and even some cross trained to do more than one job, yes a computer, but a very specialized one.
I always mention that we DIYers must look at power in, and power out. We can quickly acess the efficiency that way, and laugh at those who tell us it’s a free energy device. HHO is the prime example, and we ask… how is it we allow the believers to vote?
Jeff is right on.. (I think) but Bob is right on about the challenges as well. There will be covers, warnings, safety switches and more, but if the era of inexpensive energy is over (?Anti Nukers Winning the Argument?) we should expect all things to operate at the highest voltage reasonable.. One exception? ‘Kids Toys’ 🙂
We here have talked about off grid battery plants, and we know that 48 volts is twice as good as 24 volts, and 24 volts twice as good as 12 volts. But we say all this assuming we’ll draw some current. AND maybe even power conversion upwards to 120, 240 volts, and maybe attempt to make it look like a sine wave?
Let’s say.. all we are doing is running LED lighting, AND from the battery to the end of our longest run is 16 feet of generous gage wire, then it’s likely a single large 12 volt battery could meet our need. Putting batteries in parallel is done all the time, but I believe it’s something to avoid if possible because the cells are never perfectly identical, and no matter how small, current will attempt to flow between batteries, cells in that configuration. Constant float voltages can take care of the worry, but isn’t that just another way to waste a watt? Why engineer in the inefficiency IF you can avoid it?
With all this said, we need remember that simple SAE project of establishing the much needed new automotive standard. To move off 12 volts and upwards.. to reduce the wire size by half or better. (less cost, less weight, less emissions to make a car). To reduce the size of electric motors, for power windows, fans, and more.. Such a simple task and years later.. they’ve doen what ??? Nothing! Why??? Duh.. maybe it’s not so easy… here we go… we DIYers see these advances or lack of advance as an opp to learn something. A free luncher sees it as a reason to get the Government involved so they can really screw things up.
And interesting read? you be the judge… http://www.danmcmenamin.com/What_Does_A_Telco_Need_For_400VDC_To_Find_A_Place_In_The_Central_Office_INTELEC2010_Orlando_Florida.pdf
Forgive the naive question, but anyone know why inverter generators seem to be in the 1-3kW range, and nothing higher (i.e. 6-7kw)?
Theodore,
Survival of an entity like a (company) demands that they accurately acess demand when building a product and investing a large amount to build and market it. I’d bet that 98% of market demand is between the numbers you mention, and many years of my personal study show that buying a portable generator too large (for the general public) is a regrettable mistake, there are many sales made in attempts to buy the smaller and more desirable generator.
Large is far heavier, less portable, and less appealing. After some study of the market, the principal players (those who build these inverter generators) have adoped the strategy of ganging together two or more sets for the moments (?minutes?) when you need more power. Playing the numbers game, a significant number of those who demand more power than one portable have special needs, OR they are unaware of the smarter ways to get their work done.. yes yes, opinions always vary.. but I think these folks know and understand their market. Two smaller sets should have high resale value, the larger one.. not so much..
Survival of a country demands the same diciplines, you can’t keep spending money on ideas where there is no real return on investment.
I completely follow your point, George B.
I think what I’m asking is that it’s unfortunate that I can’t seem to find an inverter generator that can power a whole house. My regular gen is 5.5kw with 8kpeak; which runs the fridge, boiler, well pump, and some lights. These inverter generators appear to be fantastic because they vary engine power (and noise and gas usage) with load. It’s a shame to hear my gen chugging along continuously (during a power outage) even though the kids have already showered and the house is warm and all we want is a few hours of power to read or clean up after dinner without panicking that someone flushed twice and the water tank will run out soon. And to satisfy the peak motor load I calculated, I’d need 3 of those smaller inverter gens tied together, so that’s not practical.
Theodore.. I don’t claim you haven’t thought this out.. but the term you use (whole house), it’s like an alarm bell to my ears. It usually means a guy wants something that can handle the WORST case condition one can imagine, and the odds of this happening could be very low.. Furthermore, it’s all too easy to assure it never happens.
So called whole house generators can burn a lot fuel… you are far more likely to run out before the power returns. Fuel storage with our present gasoline is a LARGE problem for most, the more fuel you burn the larger the problem..
You may have thought of all of this.. do note Quinn’s post, he says they make larger units for RVs, maybe you investigate?
We’ve had many discussions here about load management.. maybe a simple example might be a set of make/break relay contacts on your well pump pressure switch.. In order to run the pump, other loads might be automatically stripped, they also automatically return.
Our design starts out with discovering your largest load, or the one hardest to start.. and what you need to start it.. as you clearly know, starting two motors at he same time is a killer.
IF your well pump is the larger challenge, it is sometimes cheaper to consider adding an 80 gallon water tank with air bladder, you basically store a lot of water and can ‘schedule’ the well pump runs to charge the tank, OR build the the relay(s) to kill one while the other runs.
Houses are different, 240 VAC well pumps are somethign we typically need to design around.
Load magmt can save a lot of money initally, and it allows the use of a smaller generator that normally makes more KWHs fo rthe fuel burned than a larger and partially loaded gen set capable of handling a few major events at the same time..
I am a ex-owner of a eu3000is from Honda. Very nice piece of equipment, and it could provide most of my power needs. I loved it.
Evidently someone else did too, as they walked off with it and two other generators from my personal power generation array.
The downside of that generator, however, was that it could not start my 240VAC well, which only pulls 6 amps at full load. However, being a Franklin pump with a split phase motor and BIAC switch for controlling the starter winding, it pulled 32 Amps to start. None of the single cylinder listeroids or the even the 10hp china diesels can safely start that load, if I am interpreting most of the technical data available correctly.
To do that, I had another generator (also stolen) that had a big loud B&S 11hp motor and a 6.3KW alternator. I just replaced that unit with a Ridgid gas unit. WOnderful running with a Chinese Yamaha engine, but loud as all get out.
Some of us have this conundrum on generators… ie., a small unit can supply most of the power we need, except for the all important well head (my well is 290ft deep).
I have read that Grundfos has a brushless model 1/2hp submerged pump that can provide softer starts and much lower starting current requirements. But they have silly high prices!
There is the cistern + pressure pump idea, but I live in a subdivision, where my yard is narrow but deep. Any water storage would have to be downhill from the pump, which means my house would be uphill from the cistern. And worse, cisterns seem to be a maintenance nightmare, and I automatically have to add a second pump to the system to use one, reducing overall reliability of my water system, to be able to cope with the occasional extended outage.
I am looking into building a inverter plant at the moment,and just use the loud unit to keep the batteries topped off for a inverter. However, the highest voltage inverters available usually run on a 48V string. This helps the current demands, but doesn’t solve all the battery balancing issues, and batteries have worse expiration dates than modern gasoline, even when properly maintained, just by virtue of the extreme currents involved to produce a high AC voltage from a low DC voltage. A 240VAC inverter using a DC bus near the proper voltage would take minimally 29 batteries in series.
If the prices of the super caps come down soon, it may be plausible at some point to use a capacitor string to provide the voltage required, and just a small inverter generator to keep the caps topped off.
Have I written a hundred pages about the well pump being the key in deciding what you need? There are some three phase pumps run by controllers that are similar to VFDs.. always worth a look.. they have a buss, no reason you couldn’t add more Caps if you use protection to assure none achieve too high of voltage across them..
The listers.. like the old start o matics, had a huge flywheel mass, they might make 3.x KW flat out continuous, but that stored energy in the flywheel can get a pump’s rotor spinning, and shut off that high current..
Sorry about the thieves, Ozzies should at least be able to own shot guns and rock salt. You got spiders and snakes down there, maybe you train them to look after your gennies?
Not an Ozzie, I am in the US mainland, North Carolina to be exact 🙂
On the subject of VFD units, that is a possible solution. However, according to Franklin Eelectric, who makes my current 2 wire pump unit, a 3 phase submerged well pump can pull up to 15 amps per phase at start time. Hopefully a VFD could draw that demand down by a bit. Still, hard to justify the expense, when 98% of the year, 32Amps is not a big deal!
I will go the 3 phase/VFD route when I have to pull the current unit out of the well, though. Of course, the desire is to not be in the place by the time that 2 wire unit fails. The removal of generating equipment has accelerated my look for a dwelling a bit different from the current one.
But in tribute to the Franklin Electric 2 wire that is the bain of my electrical existence when off grid power, the hard water here has eaten through most of the plumbing, which I personally replaced by necessity, that pump has gone on for 13 years! I am probably cursing it by talking about it, but Franklin makes a good pump, even if it has a horrible power factor during startup 🙂
Ohhh No! I made another mistake.. I should have recognized the accent! My apologies.. as for the Draw, hopefully you’d tender it with the DC buss, but there are other pumps who claim a very soft start, maybe someone here will tell you about it.. ?
Let me see if I can explain this clearly.
I have been thinking about this well pump thing, because I just finished a complete water system rebuild out at the farm house. New pex lines, new faucets, all new, except the water heater tank. Toilet fill valve, pump, down hole, etc. everything is new.
I’m set up for 120 only on the genny. The well pump is on 110, as it is only about 45ft deep and a 1hp jet-pump does just fine. It is an old hand dug well so the down hole stuff is just dropped down in the well and the pump is top side.
But I’m still concerned with the surge when starting the pump.
What if?
When the grid power goes down—
Make your generator hardware connections/disconnections as you normally would.
Start the well pump by itself before anything else is started.
Have a bypass/return line to the well that would just put the water back in the well.
Using one of these CycleStopValves, you could bypass 1 gal per minute, and let the pump run continuously, at the lower 3 or so amps?.
http://www.cyclestopvalves.com/index2.html
By what I’m reading on their website, this recommended 1 gal( probably dependent? ) would be enough to keep the pump cool.
When the family opens a tap and calls for water the CSV would open up and supply the open tap demand, in addition to the 1 gal per minute bypass that you are putting back down the well or maybe pumping out to the cattle tank.
Would this be easier to live with as long as the genny is happy?
Can we afford a constant 3 or whatever amps you measure at the running pump?
I’m seeing this might be better than VFD?
Just a thought
Randall
I forgot.
I’m not associated with these guys
Randall