Solar Panel / House Battery NC795

[ted415]

I had a rude awakening to how quickly my NC795 group 27 92ah AGM house battery depletes.

I got about 36 hours of refrigeration plus an engine raise in 65 degree weather. I guess it makes sense as AGM unlike lithium has a linear depletion with 50% cutoff. The little Dometic fridge did it in much faster than I'm used to with my camping lithiums.

Instead of upgrading boat to lithium now or adding batteries I'm more inclined to add a panel for situations at dock or anchor off shore power if it makes sense.

Any experience here would be appreciated.

[rene460]

Hi Ted, the battery capacity issue is not helped by the fact that only the best intelligent chargers get those lead acid batteries up to 100%, most top out at around 90%, so with a 50% cutoff, you can only use about 40% of the advertised capacity.  You did very well to get 36 hours of refrigeration from that, your fridge must be well insulated and very efficient.  I am assuming that you might have radio, instruments, some phones etc and lights in the evening that also draw on the battery capacity.

I would suggest that it is well worth while adding at least one more battery, or two if you can find room.  But you also need enough solar panels to replace what you draw each day.  Not hard on a sunny day in the tropics, but I am guessing that at 65 degrees, you may have had cloud cover which severely limits solar panel output.  But if you can find room for two to three hundred watt rated panel area, it will give you a good chance of covering what you use in the day time plus enough extra to store what is needed overnight.

There are lots of threads in the archives on panel and battery sizing worth browsing as your winter evenings approach.  Some of the forum members have built up truly amazing systems.  But on a smaller boat, battery weight is important, and there is more limited space for panels, so compromises are necessary.   The stock basic fit out of a single house battery really does not allow for much in the way of refrigeration or the other requirements for overnight stays, but overnight journeys are well worth the effort to make the necessary upgrade.

rene460

[Charlie-Bravo]

Rene is as always spot on with his advice.

As an intermediate measure, I found that a well insulated fridge keeps cold overnight even when switched off, ….. just remember to switch it back on first thing in the morning, so that keeps the battery consumption down quite a lot.

I survived this way for a year on my last boat , adding 400W of solar the next year really helped, and on the present boat I have less room for panels, but I fitted one 200W panel and it seems to keep up with the fridge , aided every now and again with the alternator when mooring or travelling under power when the wind is on the nose.

CB

[ted415]

Hypothetically can anyone guesstimate based on the 36 hours I got with the 92ah AGM how many more hours I'd get with current battery and a 100w solar panel at 80% performance vs a 100ah lithium?

[zaphod]

I find it quite amazing that you got 36 hours out of a single group 27 battery without running the battery down well below 50%. The refrigeration on my boat draws 5-7a and would consume the 45ah of usable power you have in less than a day!

Do you have an ammeter so you can see what your amp draw is when the fridge is running?

If you don't already have one, your first step should be to install a battery monitor. I recommend a Victron BMV712, which has Bluetooth connectivity and a mobile app that is a great window into your energy usage and battery health.

Figure out what your average daily electrical usage is, and that will help you decide how much battery capacity you need and what charging sources are best.

If you are spending a lot of time at anchor your goal should be to have your house bank fully charged every day, and run off your battery overnight. It is harmful to run a standard lead acid battery down below 50%, and keeping it at partial charge for long periods of time is just as bad. Both will cause the battery to sulfate, and result in permanent loss of capacity. It is better to have a larger bank and run off the top 25% of capacity.

[ted415]

Thanks for the info. The batteries are sealed maintenance free absorbed glass matt (AGM). For 95% of the year it's on shore power or charging from engine alternator.

I just want to direct the next $500 - $1,000 investment wisely. Solar or lithium or a 3rd AGM which might not fit the NC795 and add weight and I would prefer not to use three batteries since I don't overnight that often off shore power.

Thus the question of solar panel vs battery upgrade considering batteries are just a few years old.

I have a voltage meter and will check but it's it would have to be an average over time. I'm not going to upgrade the BMS. The 36 hours was a guess. Boat was left at 6:30 pm on a Friday and beers were probably 50 degrees 6:30 Sunday. The boat interior probably went to 75 degrees each day.

[zaphod]

Apr 16, 2023 5:44:44 GMT ted415 said:

Thanks for the info. The batteries are sealed maintenance free absorbed glass matt (AGM). For 95% of the year it's on shore power or charging from engine alternator.

I just want to direct the next $500 - $1,000 investment wisely. Solar or lithium or a 3rd AGM which might not fit the NC795 and add weight and I would prefer not to use three batteries since I don't overnight that often off shore power.

Thus the question of solar panel vs battery upgrade considering batteries are just a few years old.

I have a voltage meter and will check but it's it would have to be an average over time. I'm not going to upgrade the BMS. The 36 hours was a guess. Boat was left at 6:30 pm on a Friday and beers were probably 50 degrees 6:30 Sunday. The boat interior probably went to 75 degrees each day.

The thing about lithium batteries is that they have a very high acceptance rate and will suck up all the power an alternator will put out. Stock alternators with basic internal regulators often burn out from the load. Because of this, when upgrading to lithium, people end up upgrading to an externally regulated alternator as well. It may not be as big an issue on a small bank like yours, but it is something to be aware of.

You can extend the staying power of your agm with a fairly inexpensive solar system. I initially put a 160w flexible panel on my boat, and it was able to run all my loads during the day and charge the battery while at anchor, so the batteries only discharged overnight. We stay off grid for weeks at a time, so I added a second 160w panel, but 1 would probably do for your purposes.

[Charlie-Bravo]

Amp meter is the only device to see what your fridge draws, you also need to figure out how long it runs for before it switches off and back on again for an accurate assessment of its power needs.
As you asked for a guesstimate……. let’s say it draws an average of 5 amps (mine runs at 3 amps ) 5 amp x 12 volts = 60Watts.
the 100W panel will keep up with the fridge use as the fridge cycles on and off with about 30% on ….. very rough guess, so in theory needs about 20W to top up the battery, ….. but then a 100W panel doesn’t work giving you 100W full time, and nothing at night, a reasonable guess is , having established the actual power draw, is to double the solar power requirement and you won’t be too far off.

I would squeeze in another AGM , mount as much solar as you can (you can easily join smaller panels together ) and you may well find that the fridge keeps going, and whilst you are not using the boat, the solar will keep the batteries charged ready for your next trip.

Buy a cheap amp meter.

CB

[ted415]

That's an awesome answer. Thanks. I will probably go solar and let the marine lithium battery tech develop to where an afforable battery doesn't need a lithium optimized charger. These exist now but are ultra premium as far as I have experienced with my trailer Battleborn, Dakota Lithium and Renogy (and these brand need optimized charger as far as I know). By the time my AGMs are ready for replacemnt price point should be $500 instead of over $1k. As for third AGM, not a lotta space to work with.....(wide angle lens)

photos.app.goo.gl/YUDMzRgtctSXDi1K8


Now the question looms where to put panels. I'm inclined to not hardwire and store a folder in the battery compartment for the rare occasions it's needed....

[zaphod]

Apr 17, 2023 1:52:40 GMT ted415 said:

That's an awesome answer. Thanks. I will probably go solar and let the marine lithium battery tech develop to where an afforable battery doesn't need a lithium optimized charger. These exist now but are ultra premium as far as I have experienced with my trailer Battleborn, Dakota Lithium and Renogy (and these brand need optimized charger as far as I know). By the time my AGMs are ready for replacemnt price point should be $500 instead of over $1k. As for third AGM, not a lotta space to work with.....(wide angle lens)

photos.app.goo.gl/YUDMzRgtctSXDi1K8


Now the question looms where to put panels. I'm inclined to not hardwire and store a folder in the battery compartment for the rare occasions it's needed....

Yes, for your purposes, a suitcase solar panel might be the most economical solution. I would be inclined to run wire to a spot on deck with a plug rather than rely on alligator clips for the battery connection.

[ted415]

Good advice/agreed. I guess I would put an SAE port in this area......

photos.app.goo.gl/KgwHR96AvsqUxvFz9

[ihsan]

We have placed a second lead acid house battery in our 795,  in the empty space, which is actually under the port side sitting place. This place is reachable from where your standart house battery is.  You only need to cut the neighbouring fiber wall there big enough to push in the battery. It rests tied on a wooden platform inside a plastic cover positioned in line with the first one. It was not easy to work there, but finally we did it. This new second house battery is almost adjacent to the first house battery, with the same position and separeted partly by a small piece of fiber wall remaining there, cable distance is acceptable. In this way, the rest of this new place towards the stern may still be used for storage of secondary items.
In our case house batteries are 2x105 amp. for their a bit smaller



 110 amp. Crank battery is 110 amp. The below picture shows the location but recently it is much wider now and the hatch has been removed for easy access. 

[Mikeh]

Do you have a switch between those house batteries or are they constantly connected in parallel? Can the standard outboard alternator handle all three large batteries?

[ihsan]

Jun 5, 2023 12:44:12 GMT Mikeh said:

Do you have a switch between those house batteries or are they constantly connected in parallel? Can the standard outboard alternator handle all three large batteries?

                          To start with its better to emphasize that all electrical alterations must be carried out by a competant person. In our case the factory set up of the electrical system of the 795 S1, 2020 was kept as it is.  The system handles well the extra lead acid service battery which we installed.   There was no need for a switch between batteries. As for an outboard alternator's handling the extra battery, we did not feel any difference before or after.  Anyway, I think, even with one service battery, the outboard assist is not to be relied on, because the engine working time is usually limited. I hope this answer helps.