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when it breaks down....

Living off the grid,  generators have a place. There comes a time  when some backup power is needed.  In most cases  this means using an engine to turn some form of generator.

People living  in Vans, camping trailers or small cabins tend to view  a seperate engine driven  generator as a nuisance  to be tolerated  and  usually do  not wish to spend much money. Various alternatives  present themselves.
Running the Van motor to charge up  the battery is among the first  solutions  that  comes to mind.  Next is a small  stand alone portable genset and  a typical automotive charger  that plugs into the mains.
Clever  DIY  persons who are handy with tools  have even rigged up  utility or lawnmover engines  with  a surplus  belt driven  automotive alternator  and that is about as far as it goes. Few  people  delve into the subject  beyound this point.
In the boating field much greater  engineering effort has  been  made  because an anchored boat is also off grid and  must rely on the same  power sources  as an off-grid home ashore. Off-grid people  can benefit by borrowing  a few ideas from this.
First and foremost  there is the problem of noise.   This is easy to solve with  good mufflers and  sound  absorbing enclosures. It does cost money but  it can be done by  you if you are handy with tools.
Second is the concern  over  burning fossil fuels.   People who want to get off-grid also have a heightened awareness of  ecological impacts and environmental  issues.
When  running a fossil fuelled generator, getting the most  watts from the least amount of fuel burned should be a priority . This article will deal with this last  issue.
Conventional generators  run at a constant speed  regardless  of how big the load is.   If you are not using the full output  from the  genset, it is not as efficient  as when it is loaded to its full  rated output.
About the smallest  generator  you see nowadays is 1 kilowatt. Honda used to make an 800  watt model but it  did not  sell enough to justify  continuing production.
One kilowatt calculates into 70 amps charging current for a 12 V battery which is a pretty substantial  sized charger. Most people  tend to get a much smaller  charger.  Quite often  an automotive type that deliver  10 or 20 amps at most.   20 amps at 14.2 V  amounts to only 284 watts or 28 percent of the rated output from a 1000 watt generator.
A characteristic of  constant voltage  chargers  is the fact output current  steadily decreases  as the battery voltage  increases.
Prudent  people  begin  to recharge long before the battery is totally flat.  When using  a constant voltage charger,  this means  the charger is putting out even less than the possible maximum and now the genset has to run for a longer  period  of time burning more fuel and  creating more pollution.
So what is the answer you may ask?
Honda EU2000 offers one smart solution. The Generator  can vary the speed  according to the load. Light load = slow speed= less fuel burn and less pollution.
Another  solution is the ‘smart’ charger  often found  used on boats.
A smart charger  uses a microprosessor  to adjust the output   constantly for best results. During the  first  stage  the output is  held to a constant full current value until the battery reaches  about 75% of full charge. At that point the output is changed to constant  voltage  and the charge current  tapers off as the battery voltage  rises up to a maximum.  A third  stage  consist of a float voltage that finishes up the charge  to reverse all of the lead sulfate back into lead and sulphuric  acid. These  smart chargers are also called 3 stage  chargers. In recent years  four stage  chargers  have also emerged on the market.
Current capacities  range from 10 amps to as much as 100 amps.
An automotive  alternator  used to charge the car battery is  a fixed voltage  type and amounts to a terrible waste of engine power because so much of the time is spent putting out  less than the maximum possible.   Not only that,  except with  very small motors, the load placed on such an engine is so light the  engine never warms up  properly  and is even more polluting , not to mention inefficient in fuel consumption.   Idling a car engine  does not spin the alternator fast enough.
To  make  the most efficient  use  of engine driven  generators and alternators;  the  charging  in watts  should equal at least 70% of  the watts output produced  by the internal combustion engine.
And this output current must be adjusted to the size of the battery bank to avoid damage to the battery.
In all the articles,  websites, and even product offerings by companies  catering to the off grid market I have not  seen any indication this is  being given consideration.
Starting up a van and letting  the engine idle (even  a fast idle) to charge a battery is probably the most inefficient method.
Running an over sized  portable  genset  with an undersized charger is better but still pretty inefficient.
Getting something that is really efficient requires  a purpose built  charging  station.  Only a few  such  chargers are offered  for sale as a stock product.  The majority of such  generators are DIY built  to no particular design  or plan.
In the automotive world at least one manufacturer  offers what is described as a constant current regulator for alternators.  This is a better  choice  for a charging plant in off-grid  applications.  But is not available  for the typical consumer vehicle .  It is a specialized industrial applications device.
In my design work I have  investigated  various  battery charging solutions.  Microwave  and  telecommunications relay towers are equipped with battery systems and  motor driven generators to recharge  the battery banks.  Towers  located  on mountain tops have no other  means of powering their equipment. Running utility grid power  to some of these locations  is just not feasible.
Solar and wind power  cannot be relied on  during winter icing conditions.  A coating of ice  will render the solar panel array  useless until the ice melts away  and the same applies  to wind power if the wind turbine   blades are immobilized by a skin of ice.
Pretty much every communications tower is equipped with a genset  for recharging a battery bank.
Since  most of these locations are  inacessible  during the winter months  fuel efficient  operation is very  important.  They tend to use  generator sets that directly charge the battery and the genset is sized to exactly match the charging requirements  of the battery bank.  AC power for any  equipment  is derived from inverters.  This arrangement  has proven to be the most cost effective  approach  since it can use  off the shelf  products instead of custom designed equipment.
It also  means you are more likely to get a fast turnaround  if and when repairs are needed because  repair parts  can be ordered by part number instead of returning the entire piece of equipment  to the manufacturer for service.  The savings  in shipping charges alone will likely  justify the initial purchase  expense.  Although such  gensets are pricy  it is possible to build an equivalent  as a home built project.
I have seen several good examples while surfing the internet but forgot to bookmark them at the time.
In another article we will explore  the challenges  involved with installing and maintaining  a battery bank.  Believe me  there is more to this than  just connecting a couple of wires.  A properly used  and maintained  battery bank can last 8- 10 years.  A friend who was careful as well as a light  user got 12 years from  his batteries before they had to be replaced. And yet some careless or unknowing users  render a big bank useless in  less than 2 years, then complain  the batteries are no good.

Although most off grid  applications  tend to go solar when it comes to getting  any electricty  for lights  and  sometimes other electrical equipment,  there comes a time  when something more is needed.
In most cases  this means using an engine to turn some form of generator.

People living  in Vans, camping trailers or small cabins tend to view  a seperate engine driven  generator as a nuisance  to be tolerated  and  usually do  not wish to spend any great amount of money for this particular project. Various alternatives  present themselves as ready made solutions. Running the Van  motor to charge up  the battery is among the first  solutions  that  comes to mind.  Next is a small  stand alone portable genset and  a typical automotive charger  that plugs into the mains.

Clever  DIY  persons who are handy with tools  have even rigged up  utility or lawnmover engines  with  a surplus  belt driven  automotive alternator  and that is about as far as it goes.
Very few  people  delve into the subject  beyound this point.
In the boating field much greater  engineering effort has  been  made  because an anchored boat is also off grid and  must rely on the same  power sources  as an off-grid home ashore. Off-grid people  can benefit by borrowing  a few ideas from this.

First and foremost  there is the problem of noise.   This is easy to solve with  good mufflers and  sound  absorbing enclosures. It does cost money but  it can be done by  you if you are handy with tools.

Second is the concern  over  burning fossil fuels.   People who want to get off-grid also have a heightened awareness of  ecological impacts and environmental  issues.
When  running a fossil fuelled generator, getting the most  watts from the least amount of fuel burned should be a priority . This article will deal with this last  issue.
Conventional generators  run at a constant speed  regardless  of how big the load is.   If you are not using the full output  from the  genset, it is not as efficient  as when it is loaded to its full  rated output.

About the smallest  generator  you see nowadays is 1 kilowatt. Honda used to make an 800  watt model but it  did not  sell enough to justify  continuing production.
One kilowatt calculates into 70 amps charging current for a 12 V battery which is a pretty substantial  sized charger. Most people  tend to get a much smaller  charger.  Quite often  an automotive type that deliver  10 or 20 amps at most.   20 amps at 14.2 V  amounts to only 284 watts or 28 percent of the rated output from a 1000 watt generator.
A characteristic of  constant voltage  chargers  is the fact output current  steadily decreases  as the battery voltage  increases.
Prudent  people  begin  to recharge long before the battery is totally flat.  When using  a constant voltage charger,  this means  the charger is putting out even less than the possible maximum and now the genset has to run for a longer  period  of time burning more fuel and  creating more pollution.
So what is the answer you may ask?
Honda EU2000 offers one smart solution. The Generator  can vary the speed  according to the load. Light load = slow speed= less fuel burn and less pollution.

Another  solution is the ‘smart’ charger  often found  used on boats.
A smart charger  uses a microprosessor  to adjust the output   constantly for best results. During the  first  stage  the output is  held to a constant full current value until the battery reaches  about 75% of full charge. At that point the output is changed to constant  voltage  and the charge current  tapers off as the battery voltage  rises up to a maximum.  A third  stage  consist of a float voltage that finishes up the charge  to reverse all of the lead sulfate back into lead and sulphuric  acid. These  smart chargers are also called 3 stage  chargers. In recent years  four stage  chargers  have also emerged on the market.
Current capacities  range from 10 amps to as much as 100 amps.

An automotive  alternator  used to charge the car battery is  a fixed voltage  type and amounts to a terrible waste of engine power because so much of the time is spent putting out  less than the maximum possible.   Not only that,  except with  very small motors, the load placed on such an engine is so light the  engine never warms up  properly  and is even more polluting , not to mention inefficient in fuel consumption.   Idling a car engine  does not spin the alternator fast enough.

To  make  the most efficient  use  of engine driven  generators and alternators;  the  charging  in watts  should equal at least 70% of  the watts output produced  by the internal combustion engine.
And this output current must be adjusted to the size of the battery bank to avoid damage to the battery.
In all the articles,  websites, and even product offerings by companies  catering to the off grid market I have not  seen any indication this is  being given consideration.

Starting up a van and letting  the engine idle (even  a fast idle) to charge a battery is probably the most inefficient method.
Running an over sized  portable  genset  with an undersized charger is better but still pretty inefficient.
Getting something that is really efficient requires  a purpose built  charging  station.  Only a few  such  chargers are offered  for sale as a stock product.  The majority of such  generators are DIY built  to no particular design  or plan.

In the automotive world at least one manufacturer  offers what is described as a constant current regulator for alternators.  This is a better  choice  for a charging plant in off-grid  applications.  But is not available  for the typical consumer vehicle .  It is a specialized industrial applications device.

In my design work I have  investigated  various  battery charging solutions.  Microwave  and  telecommunications relay towers are equipped with battery systems and  motor driven generators to recharge  the battery banks.  Towers  located  on mountain tops have no other  means of powering their equipment. Running utility grid power  to some of these locations  is just not feasible.

Solar and wind power  cannot be relied on  during winter icing conditions.  A coating of ice  will render the solar panel array  useless until the ice melts away  and the same applies  to wind power if the wind turbine   blades are immobilized by a skin of ice.
Pretty much every communications tower is equipped with a genset  for recharging a battery bank.
Since  most of these locations are  inacessible  during the winter months  fuel efficient  operation is very  important.  They tend to use  generator sets that directly charge the battery and the genset is sized to exactly match the charging requirements  of the battery bank.  AC power for any  equipment  is derived from inverters.  This arrangement  has proven to be the most cost effective  approach  since it can use  off the shelf  products instead of custom designed equipment.
It also  means you are more likely to get a fast turnaround  if and when repairs are needed because  repair parts  can be ordered by part number instead of returning the entire piece of equipment  to the manufacturer for service.  The savings  in shipping charges alone will likely  justify the initial purchase  expense.  Although such  gensets are pricy  it is possible to build an equivalent  as a home built project.
I have seen several good examples while surfing the internet.

In another article we will explore  the challenges  involved with installing and maintaining  a battery bank.  Believe me  there is more to this than  just connecting a couple of wires.  A properly used  and maintained  battery bank can last 8- 10 years.  A friend who was careful as well as a light  user got 12 years from  his batteries before they had to be replaced. And yet some careless or unknowing users  render a big bank useless in  less than 2 years, then complain  the batteries are no good.

Buy our book - OFF THE GRID - a tour of American off-grid places and people written by Nick Rosen, editor of the off-grid.net web site

11 Responses to “Emergency Power: engine-driven generators”

  1. Nazir Ahmed

    In subject article none of the participants has even touched question asked. My question was whether three phase alternator being driven by a gas engine as prim-mover, operating off load/<25% of rated load may become a motor resulting either resisting or fastening its prim mover , resulting damage of engine?. Please reply if any body has such experience . Regards and thanks.

    Reply
  2. elnav

    Mobile_Bob, thanks for the comment pointing to the Micro-co generation forum. Great stuff! This is what serious off-gridders should be looking at not some techno fable that requires support from the very thing they claim they want to get away from . I once ran a manufacturing facility making electronics equipment so I have an inkling what is involved in a silicon ingot foundry and the subsequent process steps needed to make solar panels. Methane digestion is the complete opposite. It can be done with low level technology and if the worst comes to pass and our industrial base is totally incapacitated this would survive whereas a photocell manufacturing facility would not.

    Reply
  3. elnav

    Absolutely. In fact the ultimate setup is a homestead farm with a methane digester. The digester can generate methane gas to be used as fuel for the generator and the waste heat in turn can be diverted to either keep the digester going in subarctic conditions in winter or heat the house and hot wash water.

    Reply
  4. mobile_bob

    we take a different view to engine driven gensets, where we harness
    the waste heat and develop control strategies to limit run time and maximize efficiency.

    anyone interested is welcome to come take a look, and apply as you see fit.

    if you are going to run a genset, you may as well learn how to build an efficient unit and use it in a responsible and efficient manner.

    microcogen.info

    Reply
  5. elnav

    It would be helpful if readers could provide links to their favourite website providing data for regions of the world outside the US of A. How about it people, care to contribute?

    Reply
  6. elnav

    Jim, you wrote:
    You may contact the US Solar Institute for more information.

    But what happens if you live outside the United States? Their data charts and maps are cut off at the border. This website is based in the UK and we have people from all over the world reading the forums and posting comments. Your horizons need broadening.

    Reply
  7. elnav

    The comment about a true solar home reminds me that some but not all installations have a considerable reserve in their battery bank. Unfortunately this can ssometimes work against you. If you do have a week’s worth of capacity and you do end up with cloudy bad weather for the duration no matter how big the reserve is eventually you will have exhausted it. The downside I spoke of is that as any lead acid battery discharges it forms lead sulfate. When lead sulfate has sat around for several days it is harder to reverse back to sulphuric acid and lead oxide. there is always some residue. The longer until you recharge the harder this resssidue becomes and will not revert back. In addition many solar panel installations are finite in charging capacity . The strenght of charge current these panels can produce is not always enough to revert 100% of all the lead sulfate that has accumulated.
    The net result, being over time lead sulfate accumulates and chokes the battery and in effect reduces the storage capacity. There is a solution however. It does cost money. A product called a desulfator can be installed on the batteries and it will electronically assist in reversing the lead sulfate during the charging process. The original patents were issued back in 1987 but by now clone products are showing up in many countries. This would not be happening if the technique did not work. There are also liquid additives you can mix into the electrolyte but my experience with this is that it may not work quite as expected. On one badly sulfated battery it literally ate away the plate material. I cut apart the battery for a close up look to study the failure mode. However I have had good success with the electronic modules. It has been estimated by industry exxperts that approximately 80% of so called dead batteries only suffer from sulfated plated so badly they can no longer accept a charge. The remaining batteries suffer from various plate damage that is not reversible.

    Reply
  8. elnav

    Jim I’m not sure exactly what you call a ‘true off-grid solar system” but when you have 7 days straight cloud cover and maybe also a thick layer of frozen rain or ice or just plain old snow fall as much as 24 ” deep the solar panels do not work very well at all. At some point the battery bank does get depleted. Sooner or later.
    Freezing rain in particular poses problems in removal. Unlike snow you can’t simply brush it off. Scraping and chopping as you would do on a roof is not recommended. I hear the glass cover over solar cells can break. At least my brother in law tells me so after he finished crying about his shattered PV panels. (sigh)
    I was talking to an off -grid dealer with customers in the Yukon and he tells me they use solar panels half the year then a generator during the six months of arctic winter night. At my latitude we get maybe 4 hours of sunlight in the winter. The sun never comes above 30 degrees over the horizon and there is a 2 hour delay after official dawn before we see the sun due to high cliffs to the east of us.

    Reply
  9. Jim

    Fokes if a true off grid solar system is installed you do not need a back up generator. You may contact the US Solar Institute for more information. Our company Off Grid Solar Inc. has been developing, designing and installing off grid solar electric applications of over 40 years now. To us it is simple and very cost affective.

    Reply
  10. Elnav

    A friend used his 800 watt Honda for over 10 years. I had one at work that never let me down. If I ever see another one (used in any condition) at a flea market or garage sale its sold!

    Reply
  11. Jason Smith

    Informative… Honda also produced a 600 watt generator in 83… best damn little work horse they made, I still use ours to run an evaporative cooler in the summer, runs 12 hrs on half a gallon of gas…

    Reply

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