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ted frater

wrote:
Hey folks, I've been having trouble getting an answer to my question
from off grid sites. I'm hoping someone can help me or point to the
right place. I am planning an off grid system. The house will be run
off of a bank of batteries with an inverter to supply AC power. My
question is on the charging of the batteries. In general, is it
better to supply the batteries with DC power generated consistently
over time or to supply AC through a charge controller for shorter
periods. I plan to use solar and wind but may have to rely on a
generator for some periods. The generator is the part that has me
stumped. Tho the generator will run off renewable fuels, I'm unsure
whether to run a large generator making AC for a short time, or run a
smaller generator making DC power for a long time. I had considered
an engine small enough to drive generators the size of those found in
wind generators. Any help or direction would be appreciated. Thanks,
Paul
Weve been off grid for some 38 yrs doing what you want to do.
Our initial power needs were small by other ac users ie folks on the
grid at that time
So we went for a 2.5kw Lister startamatic ac set 6hp single cyl diesel
running at 600 rpm. Alternator speed via v belt drive at 1500 rpm. These
were coming off farms for around $200.00 s/hand in 1971.. Weight around
1 ton.each flywheel is 6wt and 2ft 6in dia. times 2.
we ran this set from say 6pm to 10 pm when everyone was home and itgave
us ac for all our lighting and water pump anf television etc.
we had a waste oil co that removed red diesel from standby
installations that sold this perfectly good fuel for 1/10th the cost of
new. they were paid to remove the old ie in yrs fuel.
This was our cheapest option for some 20 yrs.
we had for our lighting system when the set was not running a 12 v dc
system throughout the house. running off a bankof 12v lead acid batteies.
Eash room has 2 sets of switches one ac and one dc.
we charge these batteries with a big ac to ac transformer then feed the
low voltage ac through a full wave rectifier from a welding set.
to control this charge rate we use a 5kva variac before the main
transformer.. This is a round variable transformer.
Works fine.These old design engines run perfectly well on waste
vegetable cooking oil which we get for free from our local recycling
center., tho we mix it in the winter with some mineral diesel fuel or
kerosene, or gasoline depending on whats available from our recycling
center.

to answer your question wether its better to generate low voltage dc
directly to charge your batteies or wether to have an ac plant at mains
voltage then convert to dc for battery charging.
I wouidnt hesitate going for an ac set.
There easier to maintain ie there are more of them around ,If you have a
breakdown you can hook up any ac plant till youve fixed your broken one.
weve several gen sets ,ranging from 2w,5kw yo to 25kw ac depending on
our needs.
What your needs are depends on where your planned home is going to be
and what you want to do there.
Weve recently bought a new 3kw Outback system that will run off a large
alkaline battery bank. thise batteies were ex railway signalling
standby , some 2 tons of them. Only 10 yrs old with a life of 40 yrs.

we still have our original gen set tho we dont use it. we nowuse daily
our 6kw 2cyl 1500 rpm direct drive ac set.
We have some 1000 gals of diesel put by . came by it when a big
engineering co closed recently and had to clear their fuel storage,
Planning your power needs is the 1st thing you have to do. then work out
how your going to get this,
Most female partners will want all mod cons , youll be liky to find one
that will settle for living on 2.5kw max available at any one time.
deep freezes are out, the compressor start loads are enough to trip out
your inverter system when they start up.

Hope this helps.