How to / DIY > Generators
Slow speed alternative fuel engine + battery bank = powerful option
mike90045:
Battery bank voltage is determined by the AC system load.
1kw = 12V
2kw = 24V
+2kw = 48V.
This is because of the DC amps thru cables to power the inverter. 12v into a 3KW load needs massive cables to carry 250amps, and if you really believe the inverter has heavy enough cables inside to not burn up in 10 minutes, have fun with it. (only 62A at 48V battery)
If your loads are only a couple hundred watts, 12V and a small 500w inverter would be fine.
Welderherup:
Hi, this is exactly what I’m doing. I bought 2 130ah 12v batteries and a £120 4000w inverter. Hooked them up and they run my freezer for about 2 days. Then I fire up the genny and charge the batteries. This worked the first time but on test number 2 I ran into problems. Genny only making 70v. Fettled it today and got her up to 230v but she still seems low on grunt to me. I’m new to all this kaper so I’m learning as I go. I am in Ireland. I have an LT1 genny.
mihit:
Batteries are the weakest link in any off-grid system. Ideally you generate what you use, as you use it. Run the washing machine in the middle of the day, etc.
Batteries are ultimately consumable. But you also have a wasteful double conversion of energy, and storage loss.
You yanks are unfortunate with the 110V systems, as pointed out above, lower voltage demands higher current. 240 is way cooler.
24V would be the minimum bank voltage I'd consider. 36, 48 or 72 even better if you can find the gear (inverter etc) to run with it. Telco backup suppliers would be the people to contact.
The less conversion of energy, the better. You have a rotating engine, first look should be what can you spin straight off that (compressor, lathe, drill press)
Then if you need to charge batteries, a DC generator head (rather than generating 110 to feed a charger, to rectify and transform it to LVDC to go into the batteries, to be drawn out, inverted and feed the house...)
Diesel engines beat petrol IMO. Both for fuel storage, and tolerance. They'll generally run on any cleaned oil, waste motor oil, veg oil etc.
Petrols can be run on gassified wood, LPG/CNG, methanol, so there's a bit of resilience there but not as straight forward.
mobile_bob:
"Batteries are the weakest link in any off-grid system."
+1
i couldn't agree more!
years ago, on this very forum, and on the sister forum we got into the weeds on this topic and i among others sang the song over and over again
"if" one is in the planning stages, of house and power system, and "if" one is flexible to changing his/her lifestyle to one that is more frugal the options widen dramatically.
anyone starting out with a clean sheet paper approach to home and power system design he could do far worse than learning from the yachting and nasa boys.
learn how to limit your needs, and control those needs, and the cost of success goes down to something quite manageable.
producing power to charge a battery bank to use later to convert via an inverter to supply poorly managed loads, gets spendy in a hurry. far better to use the power as it is generated than to go through various stages of conversion, let alone the cost of the battery bank.
every watt saved or trimmed from the need column is a watt you don't have to generate, and probably more like 2 or more watts if you plan on storage and conversion.
that is the main reason the whole tiny house movement has captured my imagination, if there was ever a way to make a very efficient offgrid power system, starting with a well designed tiny home makes things very easy.
bob g
mikenash:
--- Quote from: mobile_bob on October 26, 2021, 10:36:34 PM ---"Batteries are the weakest link in any off-grid system."
+1
i couldn't agree more!
years ago, on this very forum, and on the sister forum we got into the weeds on this topic and i among others sang the song over and over again
"if" one is in the planning stages, of house and power system, and "if" one is flexible to changing his/her lifestyle to one that is more frugal the options widen dramatically.
anyone starting out with a clean sheet paper approach to home and power system design he could do far worse than learning from the yachting and nasa boys.
learn how to limit your needs, and control those needs, and the cost of success goes down to something quite manageable.
producing power to charge a battery bank to use later to convert via an inverter to supply poorly managed loads, gets spendy in a hurry. far better to use the power as it is generated than to go through various stages of conversion, let alone the cost of the battery bank.
every watt saved or trimmed from the need column is a watt you don't have to generate, and probably more like 2 or more watts if you plan on storage and conversion.
that is the main reason the whole tiny house movement has captured my imagination, if there was ever a way to make a very efficient offgrid power system, starting with a well designed tiny home makes things very easy.
bob g
--- End quote ---
Interesting you say that Bob. I recently moved from where I lived for the last five or so years - sharing a 130-year-old, timber-framed, high-ceilinged, half-insulated, drafty 5-bedroom farmhouse with an old friend - to a professionally-built "tiny-ish" house made from two insulated containers with a whole bunch of sun-trap glass areas. Can't believe how little energy it takes to heat the place. Something of a revelation :)
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