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

Just one small piece of the puzzle for you. If you're using lead/sulfuric
acid batteries, they quickly degrade if allowed below 80% charge for long
periods of time. its called sulfating. batteries of this style for forklifts
are probably your cheapest power storage

Karl

On Tue, 15 Sep 2009 15:52:35 -0700 (PDT), "
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

If I read your post correctly you are asking whether to charge your
battery with AC or DC? If that is your question the answer is that you
should use DC to charge your battery.

The question of what amperage you should charge your batteries at is
best answered by the battery manufacturer as different types of lead
acid batteries can be charged at different rates. Trojan deep cycle
batteries have (if I remember correctly) a maximum charging rate
recommendation of 20% of capacity.

On Sep 15, 5:13*pm, wrote:
On Tue, 15 Sep 2009 15:52:35 -0700 (PDT), "





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

If I read your post correctly you are asking whether to charge your
battery with AC or DC? If that is your question the answer is that you
should use DC to charge your battery.

The question of what amperage you should charge your batteries at is
best answered by the battery manufacturer as different types of lead
acid batteries can be charged at different rates. Trojan deep cycle
batteries have (if I remember correctly) a maximum charging rate
recommendation of 20% of capacity.- Hide quoted text -

- Show quoted text -

Some systems use AC power to run the house while supplying a charge
controller to feed DC to the battery pack

In article
,
" wrote:
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

Well, first off, price out everything (not just the big obvious
components). I did, and given that I'm running a shop and house, not
merely a house with no tools (as is typically assumed) my system cost
for doing a good job off grid came to $25K, minimum (parts only, me
doing all the labor). When I started, the power company was tossing
about similar figures, but I revisited once it came time to spend money
(no borrowing, took a few years, during which I rehashed what and how to
do it off-grid a lot), and once I get done filling the trench, will be
connected to grid at 400 amps for about $5K less, in the end, as opposed
to off-grid at about 50 amps and having to do a little dance of what
runs when to make tools work. That includes hiring in a master
electrician to keep the power company happy with it - given that I've
done a lot of wiring on the other side of the box, but never a service
entrance, that kept me happy too.

You want a charge rate of at least C/20 (and perhaps greater) your
battery bank size, so don't go too low on the "tiny little thing." ie,
if you have an 800 amp-hour bank, you want a minumum of 40 amps DC
available to charge it. You get issues with the acid stratifying if the
charge is too slow, among other reasons - some of the reasons touted
seem a bit funky, but the practical fact is that rules of thumb come
into being because of actual behavior, even when we may not have the
correct understanding of the underlying cause, so don't go too far down
into tiny charging land or your battery will not be happy.

Depending on what inverter you use, there can be a lot less trouble with
a fuel-DC DC-Inverter-AC setup, as most inverters use the same parts for
charging the batteries as they do for making DC into AC, so an AC
generator (usually) has to be able to run all your loads and provide
power to charge batteries, while a DC generator can be sized to charge
the bank, without having to be big enough to run your largest loads (if
they come on, the generator will contribute, but the battery will be
discharging while they are on, if the generator is not that big). You
also miss one step of less-than-perfect-efficiency conversion from fuel
to charged battery. You may well still want an AC generator set for
further backup, but it can be a little less robust than you'll want if
it's your primary, perhaps. Also, a good DC generator setup can actually
be throttled by its controller when producing less than full power
rather than running at constant speed as typical AC generators do to
make 60 (or 50) Hz. AC generators that don't run constant speed are
actually DC generators with an inverter as part of the generator. On the
third hand, unless you have a lot of spare power from the system, it
might make more sense for something like an air compressor to simply be
hung off the diesel directly rather than powered by electricity in an
off-grid setting. And then you can get into antique machine tools and
lineshafts also driven by diesel.

If your system is still open to design, 48VDC offers many advantages,
not least of which is surplus cell-phone equipment, such as 48V DC
diesel generator sets...

If you are in a cold climate, use liquid-cooled generator and make use
of the engine waste heat in the building heat/hot water - maximum return
on your fuel money.

I don't know what groups you have been trying - I have not seen anything
in alt.energy.homepower or alt.solar.photovoltaic, or if I have the
subject line has not caught my eye amid the spam and trolls. The
homepower magazine website is also worth browsing through. There's a
pretty good webforum (I don't really like them, but traffic in the
newsgroups is down with servers being dropped by so many providers) at

http://www.wind-sun.com/ForumVB/index.php

Though I have not really been there since my project flipped from
off-grid to on-grid. Xantrex has one that's useless, Outback has one
that's sort-of OK, but this one is better (with a bit less of a
one-maker slant to it.)

--
Cats, coffee, chocolate...vices to live by

Almost all of the current crop of DC generators are 3 phase alternators
with 6 big diodes. The alternator form is usually more efficient in
terms of heat losses and such plus the cost to build it is much less
than the incremental cost of the diodes.

Which brings one to the issue of genset efficiency: You want to
optimize electricity out for fuel in. I went looking for a bookmarked
set of fuel economy tests on small generators, couldn't find it. IIRC,
you need to be at about 2/3rds of the rated hp converted to the
equivalent kw output to get the best efficiency in the single cylinder
engines up to perhaps 10 hp.

I did find some other sites with outlandish comments. This fellow claims
that a small generator is better, then has a table that shows the kwh
per gallon of gas is much higher for the larger generators. Go figure!
http://www.endtimesreport.com/Generators.html

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

On Tue, 15 Sep 2009 15:52:35 -0700 (PDT), "
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

Generally, you size your renewable supply (solar or wind or whatever)
to keep up with your consumption, plus some reserve charging capacity
to get recharged in a reasonable period after discharging your
batteries. Then you size the backup generator to charge at a similar
rate. For example, at my place www.citlink.net/~wmbjk/solar100.htm,
solar is 2000W nameplate, and wind is 1000W. Charge rates vary
considerably depending on whether one or the other or both sources are
generating, and how much load is concurrent. There's really no such
thing as average, but I'd say that the normal charging rate we see is
about 40A after loads. Our primary backup generator produces about
70A. We rarely discharge below about 70%, and that generator can get
us back up to about 90% in 3 or 4 hours, depending on loads. For a
while I used a 140A generator, but that was too much. You'd need to
supply a lot of information to get a good recommendation on the best
balance for your application, and even then opinions will vary. But in
general, you want the *smallest* generator that will do the job. I
suggest that you post your info at alt.energy.homepower, or at the
Outback forum. Either way, lots of knowledgeable folks will offer
real-world experience.

Wayne

On Wed, 16 Sep 2009 07:13:36 +0700, wrote:

On Tue, 15 Sep 2009 15:52:35 -0700 (PDT), "
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

If I read your post correctly you are asking whether to charge your
battery with AC or DC? If that is your question the answer is that you
should use DC to charge your battery.

The question of what amperage you should charge your batteries at is
best answered by the battery manufacturer as different types of lead
acid batteries can be charged at different rates. Trojan deep cycle
batteries have (if I remember correctly) a maximum charging rate
recommendation of 20% of capacity.
I THINK the question is whether to use a DC generator or an AC
gernerator and a battery charger.
GENERALLY a DC generator directly is more efficient.
It depends a bit what your system voltage is. 12 and 24 volt DC
generators are VERY easy to come across - 36 and up gets a bit more
difficult.

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.

The best way is to run the house off the batteries all of the time.
Have the external supply - can change as needed - charge and supply
load current when strong generation is available.

So when the wind stops or the furnace cools after midnight - you run
on batteries until you get power - or you run out of batteries.

The batteries can supply DC for some lights. inverters from batteries
cover all the rest.

Just like a large UPS - no switching in and out just always run.

Martin

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