2x 200 amp alternator?

[drousy88]

will i have any problems putting 400 ah back into my 1000 ah battery bank? is there a limit as to how fast you can put energy back in batterys?

2x 200 amp = 4800 watts
if i drain a 1000 ah battery bank down to 600 ah will it take my 2 alternators 1 hour to be fully recharged?

[rcmpegasus]

Conventional flooded lead acid can be charged at up to 20% of 20 hr capacity. So, a 1000 amp hr bank can take 200 amps. Agm and ultra pure lead thin plate can take more than 50%.

[btrayfors]

So long as charging voltage is controlled and appropriate, batteries are going to accept only a certain amount of amperage, no matter how large the charging capacity.

Flooded batteries which are 50% discharged will take approximately 25% of their AH rating, so your 1,000AH bank would accept a maximum of about 250A. And, this is only for a relatively short time. After the state of charge (SOC) increases, the amperage acceptance will cut back.

Unfortunately, no matter how large your charging source, you're not going to reach full charge in 1 hour. As the SOC gets above 80-85%, the amperage acceptance goes WAY down, and in the last 5-10% of charging it will be very low. Bottom line: it takes several hours to reach full charge, no matter the size of the charging source.

As was noted above, AGMs and Gels can accept more amperage and can cut charging times significantly.

Bill

[S/V Alchemy]

This is precisely the logic behind my decision to go with a larger "conventional" bank and smaller charge sources. I am thinking two externally regulated 90 amp alts (I have a double PTO), plus 4 x 135 w panels, plus a 400 w wind genny should mean I get a small but continuous top-up as determined by MPPT set-points. Multiple ways to skin the amp-creation cat.

I like AGMs for start batteries and windlass batteries. I prefer rugged and cheaper 6V golf cart batteries for making a 1000 Ah house bank. Unlike some, I have room for it low in the middle of the boat. I can understand the allure of laying telecom-type long and flat AGMs on their side in fin keelers.

[btrayfors]

That sounds like a nice setup. I agree with your logic and choices :-)

You can save a bit more $$$ by using flooded batteries for starting (I use a Group 31 start battery) and for your windlass (I have used two T-105s for many years). They're a bit more rugged and not so fussy as AGMs.

Depending on the type of cruising you do -- and on your onboard charging capacity -- AGMs may be the worst choice for house batteries and even other applications aboard.

By contrast, for many cruisers gelled batteries are a pretty good choice, given their longevity and relatively low self-discharge rate. Just gotta be careful to control the charging voltages properly.

When choosing onboard power systems, it's definitely not a one-size-fits-all solution!

Bill

[S/V Alchemy]

No, I agree, and I went through a lot of research and reasoning before I decided that "old school" was the way to go.

I had two T-105s as the house batteries when I bought the boat. They lasted a remarkable 18 years (from the boat's launch in '88 to when I bought it in '06...a remarkable run.

I'm moving the house batteries to mid-boat, and I have yet to decide between L-16s or T-145s, but I want it to add up to 1,000 Ah so I can make ice at anchor for five cloudy and windless days. I'm fairly strong on big capacity/small draws. Having a full keeler helps that decision. It's got to work (ideally!) for five years, so dollars aren't as big a consideration as getting a strong battery that can take a lot of cycles but rarely face a 50% discharge...that's one of the reasons I want a big house bank, to stay above 75%.

A Group 31 makes sense for a start. Not sure how I'll do the windlass battery yet, but your suggestion is good as that area's going to be tossed around more than amidships.

[Shanaly]

I haven't tried them but Sterling electronics of the uk does some pretty advanced marine charger and regulators. Well worth a look!

[S/V Alchemy]

I saw the Sterling booth at the boat show, but I have yet to review their "big picture". I agree they seem worth a look. North Americans seem to favour Victrons and Mastervolt, as far as I can tell.