12V DC Genset

sarabande said:
the only proviso I have is whether a diesel generator engine running at a maximum of 2/3 capacity for - say - half the time, and much less than that when the charge to the batteries levels off, is going to be happy and long-lifed. There are issues such bore -glazing especially at light load and extended tickover.

If you can add extra 240v load when the charger moves into float mode, that would give the engine more work to do and make it run well. Perhaps something as simple as a fan heater would do.
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I agree the principles Sarabande but 2 things:

1. all this "glazing the bores" is treating gensets like they are Faberge eggs. They're just a box you buy with a cr card and yep sure if the bores are glazed in 6 years then chuck the thing in the bin. But don't compromise your life in the meantime! :D

2. As mentioned above I just switch the genset off if the batteries are approaching float mode and I have no other 230v loads. There is no need to bother charging them the last 10 % or whatever. sure they will get down to very discharged sooner, but then you flick the genset back on. Your total genset hours are smaller if you do it this way
 
perhaps, jfm, battery and battery charger makers have a view that most people have a different objective, i.e. battery life ? The two different objectives are both valid, and will require different specification of the battery and charging system.


Trojan suggest between 10 and 13 %
http://www.trojanbattery.com/BatteryMaintenance/ChargerSelection.aspx

and the figure crops up in other places, too.


OP might do well to read the Battery University's views on charging regimes for a start

http://batteryuniversity.com/learn/article/charging_the_lead_acid_battery


There are lots of technical articles on dis-charging rates, but nowhere near as many on charging rates, and the "10% of capacity" figure feels like a convenient peg on which to hang a generalisation will be adequate for most installations, but which for high tech battery environments is likely to need substantial modification.

I agree with your " near-Pareto" principle of not going for the last few Amp-hours of charge. It gives you more than enough capacity set against the benefits of a good night's sleep for owner and guests.


EDIT

I am intrigued by your empirical observation about 1500 rpm being a nice sound and not affecting the brain/body. ( I cannot offer an opinion on it as I have do not have comparable experience) I did some very minor research years ago on visceral and visual disturbance from leaf-sprung tractor seats, using the venerable Perkins 3 cylinder diesel engine. It was found that some revs produced optical disturbance, and others almost made people sick. Adding a metal slab of IIRC 3lbs altered the response frequency of the seat and damped out the effects.

1500rpm is about 25 Hz, at the lower end of human hearing. Not quite infrasound, which can be quite painful. 3000rpm is 50HZ, definitely audible to most humans. It is almost G sharp, and thus not a 'nice' musical note.
 
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For reference, with my battery bank of 440AH discharged to about 60% of capacity, I can initially pump in 110A. This is as much as my alterator can manage. With a bigger alternator I might be able to do marginally better, but probably not by much. This tails off over time. It takes about 4 hours to get the batteries "full".

These are normal lead/acid.

The objective with a generator would be to load the generator as much as possible and run it for as little time as possible to get the most kWH per liter of fuel (and to avoid the noise nuisance as much as possible).

With a well set up AGM bank you can pump a lot more amps in.

From the Lifeline website:-

Lifeline Website said:
A 100AH GPL-27 battery can be charged at 500 amps, and will be done in under 30 minutes, without getting too hot. We recommend chargers no larger than 5x the capacity of the battery, but no other manufacturer even comes close. (100 ah x 5 = 500 amp charger max).
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@Sarabande #24:
Yup, and I think both your links are written from POV of being uber kind to the batteries - one of them says so explicitly. The problem is that this isn't kind to gensets, genset service costs and depreciation, guest comfort, fuel burn and the folks who smell the diesel exhaust. Those factors together if not individually will surely outweigh battery life for a rational boat owner, who has to cut through this single-POV stuff and get the best all round answer

I haven't time to google hard but here is a contrasting page that says (3rd and 4th paras) you can give the batteries a good hiding in the bulk charge phase, ie up to 70% charged, as a matter of physics and chemistry. This is just saying what you can do, and makes no allowances for being kind to the batteries
http://www.evdl.org/pages/hartcharge.html
 
michaelchapman said:
For reference, with my battery bank of 440AH discharged to about 60% of capacity, I can initially pump in 110A. This is as much as my alterator can manage. With a bigger alternator I might be able to do marginally better, but probably not by much. This tails off over time. It takes about 4 hours to get the batteries "full".

These are normal lead/acid.

The objective with a generator would be to load the generator as much as possible and run it for as little time as possible to get the most kWH per liter of fuel (and to avoid the noise nuisance as much as possible).

With a well set up AGM bank you can pump a lot more amps in.

From the Lifeline website:-
Click to expand...

Thanks Michael. I think I have 440AH as well (@24v) for the house batteries - ie 4 x 220AH batteries). When they're well discharged I put 180Amps worth of mastervolt charger onto them (with temperature feedback gizmos). I don't recall exactly what they'll take but I'll look on the instruments later this week and report back.

When my lead acids are busted (likely this winter - 2 seasons of abuse) I might look at your Lifelines or similar, if I can get that much faster charge into them. Currently in hot weather on anchor my genset autostarts at around 5am when batteiries get low (due to the fridge load mostly) and it charges for 45mins (timer), but I could set that to say 20mins with AGMs and get them much more % charged.

BTW the genset also serves a/c load at this time so has a decent demand of 50Amps@230v on it
 
Alright then, will go for an ac gen. Since I have cummins and cover for a few years and the genset falls into it, will go with cummins. Now I need to size it, which will depend from the water maker. Will start a new thread for water makers!

Thanks everyone for your insights and advice.
 
Thanks Rob for pointing me the read. I clearly fall into the dc concept. The doc has thrown doubts on having an ac genset. And clearly because my boat is new and nothing runs on 220, it makes even less sense having an ac gen. Clearly they know what they are talking about and clearly they aknowledge dc gens in the dc concept. I don't think I'll do any rush decision on this one :ambivalence:
 
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