Backup generator too large?

 I am working on getting a backup generator for a off grid system in Baja. I
have found a almost new (1hr runtime) 5000w 48v DC generator for a vary
reasonable price. However, I have one concern with getting this generator
vs. the 2.4k 48v PolarPower generator that I was originally looking at. The
battery bank I have is currently 32 US2200 225ah 6v batteries. US battery
says to charge the batteries at the 20hr rate / 10 amperes. If my
calculations are correct, I have a 900ah bank which should charge at 90a. A
5000 w generator could put out 104a if the batteries were at a flat 48v, how
worried should I be about harming the batteries?



System specs:
Outback VFX3600 inverter
Outback MX60 charge controller
900ah 48v battery bank
3120w array

 

Well, if you feed the generator through a charge controller, that should
not be a problem. The other one won't get close to the 90 amps. My
understanding of the DC generators is that you'll do best (and most fuel
efficient) with a smart controller which understands how to tweak the
generator directly for best output to charge batteries, rather than a
"dumb" voltage regulator. Look into suppliers for marine battery charge
controllers - a particularly well-thought of one was mentioned here in
the past year or so.

--
Cats, Coffee, Chocolate...vices to live by

 This is the generator I was looking at.
http://www.alpha.com/catalog/iFrameCatalog.asp?hdnSortID
010402&hdnAction=submit&CATID=3
It looks like it varies the engine speed according to the current draw. If
you think I need a charge controller, which one? The largest I know of is
the Outback MX60 which will only handle 70a.

 wrote:


http://www.amplepower.com/products/sarv3/

I think this is the one which was mentioned and well-regarded a while
ago either here or in homepower. I have no personal experience with it,
but it seems to be designed to do the job (charging batteries), wheras
the one you mention appears, from what I can see on the web site, to be
more of a "battery replacement" unit, without the brains of an adaptive
battery charge controller. Then again, perhaps they just write a dull
website, and actually have a product with brains.

--
Cats, Coffee, Chocolate...vices to live by

 That looks like a nice unit, but I don't think it will work as they only
have 12 and 24v versions.

The manufacturers website leaves much to be desired. I would have never
found them if it wasn't for finding one of there 5k units for about $1000usd
shipped.

I have been reading through the documentation on there website and found
this "The DC output of the APU connects directly to the inverter batteries
to recharge them when line power is lost and maintain an indefinite DC
supply to power supply inverter systems." (PG16
http://www.alpha.com/document/techmanuals/tm_alphagen50kwseries.pdf )

I think that this generator will work, I am just curious if going slightly
over the c/10 charge rate will harm my batteries. Aside from exercising the
generator monthly, it will probably only be used 5-10hrs/year. However, I am
not totally sure as I haven't yet added the two electric refrigerators to my
system which I will be doing soon.

I am also curious if anyone can recommend a circuit breaker and box to mount
next to my batteries for the generator. Outback makes a suitable breaker,
but I don't want to have to mount another costly PS2/DC box just for one
breaker.

TIA,
BIG