Best Electric Generator For Back-Up Power.

[robert k]

The math is fairly simple I think. If you have two big marine batteries that that have 100 amp hours to contribute each. I would not run them dead so -10% leaves 180 amp hours. if you average 20 amps I would say it could last you 7 to 8 hours. Why not 9? because the inverter will not have perfect conversion efficiency. the lower the voltage, it will take more energy from the battery to maintain the same output dropping from 13.25 volts down to 11 or less will make a difference. The inverter's fan will also draw energy. It might only be 6 hours. I have an 800W inverter in my vehicle but they advertise it as only 88% efficient and I don't think that includes the inverters fan load.

[not so old china hand]

Hi, as a new member of the forum I hesitate to make such a long post but here is my ten-cents worth based on a steep and often expensive learning curve.

 

I lived aboard a junk in Hong Kong for four years. With no mains supply I was totally depandent on generators as my primary power supply. I used an inverter/charger to supply 240 volts during periods of low demand.

 

I had a 5kva diesel generator and a Honda 2kva petrol (gasoline) generator as backup. I also had a high capacity alternator on the main engine which could be used to recharge the battery bank more quckly than the two generators.

 

In my experience:

 

1) Dispite the repution of diesels for reliabity the diesel generator was tempramental: to say the least.

 

2) The Honda thrived on neglect and never once let me down. It lived on the foredeck with only an awning and an old sail-bag to protect it from Hon Kong's climate. A couple of gentle pulls on the starter cord to prime the carb (see below) and one firm pull and it would start every-time. It even started with a reduced cord length when I lent it to another boat owner and it was returned with the cord knotted together after they had broken it.

 

3) Petrol engines are easier to maintain than diesels. The only care the Honda ever received was regular oil changes and an occaisional cleaning and gapping of the spark plugs. It is important to check the oil regularly since Honda engines only have a small sump capacity.

 

4) I had no problems with the Honda's carb gumming up. Perhaps this was because I always stopped the engine by turning off the fuel supply, letting the engine run the carb empty and only then turning off the kill-switch (a trick I learnt from using 2-stroke outboards.)

 

5) If you go for an inverter/charger check the specifications carefully. If you want to run sensitive electronic devices check that the AC output is pure sine wave and not modified square wave.

 

6) The batteries for an inverter system need to be truely continuously rated (often referred to as automotive batteries). The batteries used for electic golf carts are a good example. Car batteries, and many so-called marine batteries rated for a continuous high current draw and don't like being deep -disharged.

 

7) Golf cart batteries are 6 volt. You need two connected in series to provide 12 volts, however two 6 volt batteries are a lot easier to move around than a single twelve volt battery.

 

Cheers Terry

[Jake]

Hi, as a new member of the forum I hesitate to make such a long post but here is my ten-cents worth based on a steep and often expensive learning curve.

 

I lived aboard a junk in Hong Kong for four years. With no mains supply I was totally depandent on generators as my primary power supply. I used an inverter/charger to supply 240 volts during periods of low demand.

 

I had a 5kva diesel generator and a Honda 2kva petrol (gasoline) generator as backup. I also had a high capacity alternator on the main engine which could be used to recharge the battery bank more quckly than the two generators.

 

Cheers Terry

Triple LIKE Terry, great advice especially about sinewave vs squarewave outputs.  Perhaps, at another time

with a new topic, I would love to hear more about living on board a Chinese junk.  You're the man!

 

Respectfully -- Jake (an avid sailor -- windsurfing and Hobie Cats)

[Dave Hounddriver]

Great report, China Hand.  I get the feeling, from your report, that many of us would be able to supply our needs from a combination of a small honda generator with a set of batteries and inverter.

 

Correct me if I am misunderstanding here, but in a totally off grid situation or extreme power failure you could run the generator for 4 hours, using that power supply while you recharge batteries, and then run off the batteries for the rest of the day?  Would you say the Honda Generator runs on about a liter of gas an hour?  So about a gallon a day using it for 4 hours?

 

I suspect this would keep a person with enough power for minimal use but would it run a fridge?

[not so old china hand]

Jake, Thanks for your kind words. (Blush)

 

Inevitably there is one glitch. In 6) I should have said "car batteries and many so-called heavy duty marine batteries AREN'T truely rated for deep discharge".

 

I need to learn how to edit posts post posting.

 

Cheers Terry

[not so old china hand]

Great report, China Hand.  I get the feeling, from your report, that many of us would be able to supply our needs from a combination of a small honda generator with a set of batteries and inverter.

 

Correct me if I am misunderstanding here, but in a totally off grid situation or extreme power failure you could run the generator for 4 hours, using that power supply while you recharge batteries, and then run off the batteries for the rest of the day?  Would you say the Honda Generator runs on about a liter of gas an hour?  So about a gallon a day using it for 4 hours?

 

I suspect this would keep a person with enough power for minimal use but would it run a fridge?

Hi Dave

 

Yes you are correct. One advantage of inverters is that they can handle heavy start up loads for a short period. If your fridge is kept full (use bottles of water for example) the motor is not running that much but there is a heavy load for a short time each time it needs to cool down.

 

If you are on the grid you could do without a generator at all if you only need the back-up for a short time or for a small load for a long time. RV's (motorhomes to us Brits) do this - pulling into a campsite every few days to recharge the batteries and running off the batteries the rest of the time.

 

If you go for this solution the battery bank needs to be sized carefully. An earlier poster touched on this although if I were using a system all the time I would not discharge the batteries below 50%: even with automotive batteries.

 

If you need a to support a heavy ac load for many hours eg air conditioning (kWatts rather than a few hundred watts) then a generator plus charger/inverter is the way to go.

 

A gallon for four hours would be about right for 2kVA petrol gennie.

 

Cheers Terry

 

[Jake]

 

Great report, China Hand.  I get the feeling, from your report, that many of us would be able to supply our needs from a combination of a small honda generator with a set of batteries and inverter.

 

Correct me if I am misunderstanding here, but in a totally off grid situation or extreme power failure you could run the generator for 4 hours, using that power supply while you recharge batteries, and then run off the batteries for the rest of the day?  Would you say the Honda Generator runs on about a liter of gas an hour?  So about a gallon a day using it for 4 hours?

 

I suspect this would keep a person with enough power for minimal use but would it run a fridge?

Hi Dave

 

Yes you are correct. One advantage of inverters is that they can handle heavy start up loads for a short period. If your fridge is kept full (use bottles of water for example) the motor is not running that much but there is a heavy load for a short time each time it needs to cool down.

 

If you are on the grid you could do without a generator at all if you only need the back-up for a short time or for a small load for a long time. RV's (motorhomes to us Brits) do this - pulling into a campsite every few days to recharge the batteries and running off the batteries the rest of the time.

 

If you go for this solution the battery bank needs to be sized carefully. An earlier poster touched on this although if I were using a system all the time I would not discharge the batteries below 50%: even with automotive batteries.

 

If you need a to support a heavy ac load for many hours eg air conditioning (kWatts rather than a few hundred watts) then a generator plus charger/inverter is the way to go.

 

A gallon for four hours would be about right for 2kVA petrol gennie.

 

Cheers Terry

 

Keep going guys.....I love this chit!

[not so old china hand]

I need to go offline for a bit now. My original reply was more focussed on using a gennie (or inverter) for back-up during brownouts.

 

Going off the grid is potentially a hugh topic, but one close to my heart since sailors do it everytime they leave harbour. Or in my case even when I was in harbour...

 

Is this best covered here or in a new thread.

 

Cheers Terry.

 

PS I answered the questions posed without looking to see if this topic has been covered elsewhere on this forum. Will do what all newbies should and look through old posts.

[Jake]

I need to go offline for a bit now. My original reply was more focussed on using a gennie (or inverter) for back-up during brownouts.

 

Going off the grid is potentially a hugh topic, but one close to my heart since sailors do it everytime they leave harbour. Or in my case even when I was in harbour...

 

Is this best covered here or in a new thread.

 

Cheers Terry.

 

PS I answered the questions posed without looking to see if this topic has been covered elsewhere on this forum. Will do what all newbies should and look through old posts.

Hey Terry,

 

I think the notion of a backup generator is of a temporary nature.  However, off the grid usually means

total independence from any power grid.  Whenever you're ready, go ahead and start a new topic.  I

believe you will be first one describing that type of lifestyle.  And living on a junk boat would be an icing

on the cake.  My favorite playground has always been in or near the water.  

 

Respectfully -- Jake 

[Thomas]

Hi, as a new member of the forum I hesitate to make such a long post but here is my ten-cents worth based on a steep and often expensive learning curve.

Good you stoped hesitating  :)  No reason for that. We want MORE people to post, and it DON'T need to be as good posts as yours, which is a candidate to the best post this year  :thumbsup: :thumbsup: :thumbsup:  

If we would have demand for such standard as minimum to post, then we would have very few posts   :)

Edited May 13, 2014 by Thomas