running a battery charger off an inverter

[gladfish]

This is all good information, and as they say "there are many ways to skin a cat".
However its beginning to look like all i am going to end up with is a pretty f*#!ked up cat that's only doing half the job.
Between this thread and a couple of Bookface questions it looks like a definitive answer isn't going to present itself as the variables are too numerous.
A generator is not going to work due to space limitations and not wanting fumes in the boat.
An inverter has its fans but the numbers look shaky with my alternator size, however being able to run a CPAP machine onboard would make sleeping more appealing than it is currently.
The trollbridge looks interesting but I don't know anyone who has one so real data is not available. At least its fairly cheap so if it doesn't pan out its not such a big deal.
Solar isnt going to work as i dont yet have my hard top on, so nowhere to fit panels.
So even with everyones help I am not much closer to an answer and I think I have some trial and error in my future.

[NAGG]

As you mentioned before Chris...most of us, once we reach our starting destination, and begin fishing wont be travelling enough after that to add any significant charge via the alternator....

If I put a couple of 300w panels on the roof (subject to available space),

surely over the course of a day or 2 fishing that would add a useable amount of energy...it would also keep the batteries topped up while the boat is sitting around at home...

Can someone better explain about the house battery thing though...I have been boating for over 40 years now and with my parents when I was a kid and then me as an adult.... We have never owned a boat with more than one battery ever before....

600W of Solar would certainly put a good amount of juice back into your batteries - depending on the day ( bright & sunny) but remember that flat on the roof of a boat the efficiency will be pretty low …… & even with 600W you might only average 10amps / hr which from my experiences with spotlocking might be adequate on the best of conditions - but will still see your capacity going backwards …….. but hey at least you will be putting power back in .

As for the need for a house battery (dual system) it really depends on what you run …….. back in the day you might have had a sounder & a radio …….. the radio would be used infrequently & so you get away with a marine battery . . How often were these batteries replaced though?
Today ( looking at my boats) I run 2 (500W) sounders , live bait tank , deck wash , VHF & Stereo & much more lighting (low draw LEDs). …….. Now I have been caught out fishing on a dam - where over the course of 3 or 4 days I ended up with a flat battery (running a single Optima D31M …….. with 2 sounders going & only a short run to my fishing - I wasn't putting enough charge back into the battery compared to what my sounders were drawing down and ended up flat ………. eventually I went with a dual battery system with dedicated house battery managed via a VSR . Problem solved.

I've got a mate who has 3 sounders running plus uses a pie oven ….. along with the other stuff - As you could imagine his draw down would be significant ( He does run the motor when the pasta is warming up )

Chris

[scottar]

OK ….. that's the theoretical & depending on the size of your motor(s) your alternator could be only 40amps like my DF140

Reality is another story - With the exception of LiFePO4 batteries …… shouldn't deep cycle batteries only be charged at around 10-15% of the batteries capacity ? …… so what damage would 33 amps do to a 100/120 amp AGM / GEL ? (If you could pump in that much)

On the water - Realistically how far do people run between locations ? ……. most fishoes wouldn't move too far from their chosen destination - I certainly doubt that they would do too many 1 hour transits ( not for a trailer boat operator who will rely on an electric motor ) . Probably the exception would be boats fishing the big rivers in the NT .


Where I'm coming from is that depending on conditions (wind / tide … both) - you could be drawing anywhere from 20-50amps / hour spot locking ….. though I guess you could leave the motor running while spot locking.

The Trollbridge sounds wonderful but I'd like to see some realistic data on a trollbridge running off a 150hp outboard & maintaining the house battery & 2 x 100amp AGMs

Chris

Gels - yeah might be a problem. AGM should be fine. No one thinks twice about sticking one in a car with a 100 amp alternator. They usually die from the effects at the other end of the spectrum - over discharge or being left discharged and sulphating. Like I said - depends on usage pattern but even a cumulative total of short runs may mean the difference between a level of discharge that the battery is happy to tolerate and one that does damage. With solar going in all day, it would be even better. 10 amps over 6 hours is at least an hour extra use - maybe more. Whether the bit extra is going to be of use is up the individual and whether they think the outcome justifies the expenditure.

[scottar]

This is all good information, and as they say "there are many ways to skin a cat".
However its beginning to look like all i am going to end up with is a pretty f*#!ked up cat that's only doing half the job.
Between this thread and a couple of Bookface questions it looks like a definitive answer isn't going to present itself as the variables are too numerous.
A generator is not going to work due to space limitations and not wanting fumes in the boat.
An inverter has its fans but the numbers look shaky with my alternator size, however being able to run a CPAP machine onboard would make sleeping more appealing than it is currently.
The trollbridge looks interesting but I don't know anyone who has one so real data is not available. At least its fairly cheap so if it doesn't pan out its not such a big deal.
Solar isnt going to work as i dont yet have my hard top on, so nowhere to fit panels.
So even with everyones help I am not much closer to an answer and I think I have some trial and error in my future.

Definitive answer - using the inverter will not put as much into the batteries as the trollbridge without potentially putting more stress on your house supply. While inverters are getting better all the time as far as efficiency is concerned, they still consume power themselves. Something like the trollbridge that at a guess is simply switching relays will consume a lot less power to get power to your batteries than the inverter and then the battery charger. The downside of course is that the trollbridge is only working with "surplus supply" whereas the inverter charger will charge regardless of whether the rest of the boat is consuming power - at the possible detriment of your house bank. Personally I would be thinking trollbridge and a small inverter to run your CPAP assuming they don't have a DC option.