"..So, the refinement I would like to implement is a faster charge, since my
new AGMs can take it. Not sure how best to do that...."

To charge AGM's faster, you need to either run like chargers/regulators  in
parallel or charge different AGM banks from different chargers. Of course you
can always ditch the existing charger and double or triple it's size with a
single new one.

If you try to run different (brand) chargers together, in parallel, it's very
likely one will take over and suppress the other....Some work together, some
don't.
So adding another charger/regulator of the brand you now use is a logical
choice...you can always query the manufacturer to see if they work well in
parallel.

I run three Statpower 40 AMP chargers in parallel and they work well
together...only at the final stage of charging does one take over a
bit...which is fine...Arild noted in past posts that Xantrex has tested two in
parallel, not three, but I have found they work ok.

If I run the three Statpowers and a 130 AMP Freedom (Also Xantrex)
charger/inverter ALL together, 250 amps theoretical maximum, I sometimes get
to 170 maybe 190  or so amps briefly but my wet cells don't need that for
long...I don't let them get below about 50% maximum discharge....these
different units work together "bulking" ok but after perhaps twenty minutes
the Freedom begins to suppress the three Statpowers....I run my gen no more
than an hour daily to run a refrigerator, a bit over an hour when running a
frig plus a separate freezer on a second compressor.

I have six 8D's charging..in theory I designed for: 20% x 6 x 220 amp hours or
264 amps amps maximum bulk charge. (I figured 250 was close enough.) In fact,
they never take that 250 amps max ...maybe if I discharged them considerably
more they would, but that's not good for battery life. (Now I read wetcells
might take 25% but that seems unnecessarily high to me.)

No one should HAVE to run a genny FOUR hours daily for battery charging unless
they are powering a BIG, BIG frig and freezer in tropical temperatures along
with other accessories. Either the  battery bank is too small, the batteries
old and tired, or your charging system is undersized. For occassional use
perhaps it's not worth the trouble and expense to fix; for frequent travelers
away from dockside, it's a worthwhile upgrade.

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Rob's suggestion to add more chargers when using AGM is okay as far as it
goes  . . . BUT!
Consider this! It was mentioned that AGM can be charged at 50% or even 100%
of their A-H capacity.
Most people have a 600- 800 A-H bank and I have seen them as big as 2000 Amp
hours.

Taking this line of reasoning to its ultimate conclusion means you are
looking at a charging source of 300 - 1000 Amps.
Isn't that getting a little out of hand?  Its downright scary  thinking
about so much power running through your wiring.
Even a high capacity welder running at 100% duty cycle only delivers around
200-300 amps at approximately 24V

4/0 cable is only rated for 400 Amps. Contemplate running cables an inch and
a half in diameter. Consider the Cost!
You cannot get a 100A shore power fed charger for much less than $1000.  But
you need two or three or  . . . <grin>.
Have you priced out a 400 Amp Electrodyne or Balmar alternator lately? It
around $5000 plus install.

There is a trade off!
At what point does it stop making sense financially?
Especially if you continue to power things from a conventional AC genset.

Suggestions.
Cut back on your power consumption so you only use 150 A-H per 24 hour
period.

You do this by eliminating power wasting old design appliances.
You eliminate energy wasting habits. Get better lighting or go LED.
If you must cook electrically, explore other options than the old
conventional 4-6kw kitchen stove and oven.
Find an alternative to the wasteful electric hot water tank. Why heat water
if you are not using it now?
Insta-Hot and solar water heaters are two such possibilities. Engine waste
heat we all know about already.
If you are contemplating installing a heating system, use as hydronic system
that can double as a hot water system.

If you only use 150 amp hours per day you can replace that in an hour of
charging.
And if you replace the old AC genset with a Dc genset you can reduce your
fuel burn by almost 40% compared to the old standard. Why, you ask?  Look at
the fuel consumption curves.
A genset running at 1800 RPM is nowhere near the optimum point on the curve.
2800-3000 RPM is more like it.
A 4 kw DC genset will outperform a 6-8kW AC genset using an ordinary
inverter to charge the house bank.
The smaller engine of a DC genset is way more fuel efficient than the much
bigger sized engine driving the AC genset.

Cheers
Arild

Arild:

I take your point about DC gensets. Ample Power makes a few. Who else.

David

Here is a compilation of what I know based on my own research and public and
private emails on the manufacturers of DC gensets:

Ample Power Genie, 150 amp 12v DC- Looks kind of clunky and from reading
their website, it doesn't seem to be well supported for marine use. Anybody
have one?

Fischer-Panda- Expensive, but a nice compact package

MAS- Maybe they sell a DC version, not sure. Bill, please advise when you
hear back.

Polarpower- Expensive Lombardi engine based. I should stop by their shop and
see it. They are only a few miles from my office in SoCal.

I wish that Jack Rabbit Marine still made their DC genset. They used to buy
a NextGen package with our without the enclosure, less electronics and added
their own large frame alternator- Powerline I think. This looked like a nice
compact packgage. I wonder if NextGen could be persuaded to do it
themselves. Bill??

David

More thoughts on DC gensets:

If all of your loads are DC, ie battery charging, then a DC genset makes a
lot of sense. A large frame DC alternator of 150-200 amps or so at 12V,
driven by a modern 3 stage regulator, can put a lot of amps into a battery
bank quickly. These regulators are optimized for just that purpose, whereas
shorepower based chargers may not be.

But if you have any significant AC loads then an AC genset makes more sense.
On a prior boat I had a 5 kw Northern Lights AC genset. Each day or so I
would start it up and run it to supply AC to the Freedom 25, 100 amp
charger/2500 watt inverter. This loaded the genset to about 2 kw with
charging loads. Then when the charger started cutting back to about 1 kw
after 45 minutes, I would flip the water heater breaker on and load it back
up to 2 kw or better for another 45 minutes until the water heater
thermostat tripped. At that point the batteries had gotten about 100
amphours and I shut the genset down. I repeated the cycle the next day.

I could do the same while running a 16,000 BTU A/C, but only if I started
the A/C first. The AC would not restart with all of the other loads on the
genset.

If I were doing the same thing with a DC genset, the first 45 minutes or so
would charge the batteries at 150 or so amps. Then after the charging
current dropped, I would turn on the inverter to supply AC to the water
heater and it would draw about 100 amps to power the water heater coil.
Charging would be a bit faster, because of the first 45 minutes at 150+ amps
(assuming I had the right battery bank to accept it). But I couldn't run the
A/C at the same time that I was heating water. The A/C draws 16 amps and the
water heater draws at least 10amps and that is the more than most inverters
can supply. Plus it is more DC amps than some DC gensets can supply.

Efficiency of either scheme is about the same. DC gensets and DC power
distribution is less efficient than AC (high current and alternator
rectification losses), but you don't have the losses in the battery charger
to deal with on an AC system, but you do have them on the inverter side of
the equation. Again if most of your loads are DC then it probably is a wash.
If they are mostly AC loads then the advantage is with the AC genset.

So, I guess that is why 99.9% of all trawlers with a genset, have an AC
genset. Actually I have never seen or heard of a DC genset in a trawler and
have only heard about them in a sailboat.

David