Battery bank charging.

[Rick_A]

Hey guys.
After reading the solar/wind power thread, it seems that these are fine for trickle chraging unless you go for an unsightly size of wind gen and a huge solar panel.
At the moment on our boat we have 2 batteries, a 100ah and a 85ah. Plans are to increase the battery bank to having one 100ah battery for starting the engine and anchor winch, and running anything that is used when underway. And having a 300+ah battery bank for tv/dvd, lights, radios, laptop ect. There is no fridge or any constant draws from the batterys. Solar and wind gen will also be added for charging, but we dont have enough room for a big solar panel so will hopefully they will top up the battery bank for each trip.
The only charging that the batteries currently get is when the engine is on and its one at a time, the batteries are never fully charged unless i take them home. I have the intention to add a second alternator to the engine that has a high output. But what size would be ideal for charging a 300ah or greater battery bank? Would a 100a alternator suffice or would it need to be a greater one. Unfortunately the current alternator is as big as it can go as there is not enough room to fit a bigger one to our perkins engine.
Engine is normally used for around an hour a day when we are onboard.
How does everyone keep their electrics topped up without using shore power. Shore power is not an option as we rarely visit marinas.

 

[charles_reed]

No problem, using solar and the engine every 10 days.

However there is no answer to your problem if you aren't prepared to spoil the outline of your boat.

Regarding the alternator - a standard short alternator will, in the same external dimensions, put out 35 amps to 150 amps. So a more sensible idea, than excluding all possible solutions, might be:-
1. Check your alternator output and if it's more than 85 amp have it modified so the field can be led to an external smart controller such as the Adverc or Sterling.
2. Work out your daily usage - your 1 hr a day will put about 40% of the maximum alternator amps back into the batteries.
3. If that's nor enough, get a larger output alternator, beef up wiring and belt and see if that does the job.
4. If that doesn't meet your needs look at, preferably both, solar and wind generators

OR give up using something that needs electric power.

 

[mitiempo]

If your batteries are flooded they will only accept 25% of the bank size in amps. And that only in bulk charging mode, in other words from 50% state of charge to 80% state of charge. After that they will accept less and less - the last 20% charge takes as much as 8 hours if using engine alone. This is the reason long term cruisers use a bank down to 50% and charge to 80% only, any additional coming from solar or wind.

For your 300 AH proposed bank that means much over 75 amps output in an alternator is wasted, as long as the reg actually gives you max. Another issue is that any alt over 100 amps needs a double belt.

Probably the best solution is an alt of say 90 amps and a good reg that lets you dial the alt back a bit for cooler running, like the Balmar MC-612.

Rather than add a second alt I would replace the current one with a small frame one with good output. Keep your current alt for a spare.

 

[Rick_A]

Thanks guys.
A small wind gen, most likely the rutland 504 and as big a solar panel as i can fit on the dog house roof will be fitted but these will only top up the charge when we are not onboard meaning we should have well charged batterys to come back too.
They will be deep cycle batteries that are going to be bought.
I dont want to give up anything electrical, but there is usually only one item used at a time, and i feel a 300ah bank should have no problems running them.
I just wondered how a single alternator would charge the 3 batteries connected in parallel, surely it will take 3 times as long to charge the same as it would one battery? And would for example a 50 amp (no idea what size is on mine just know it was a small output one) alternator manage to charge the batteries?

 

[pvb]

I just wondered how a single alternator would charge the 3 batteries connected in parallel, surely it will take 3 times as long to charge the same as it would one battery?

It wouldn't take 3 times as long. Bigger battery banks can absorb charge quicker.

 

[ukmctc]

Thats like saying it takes an egg 3 mins to boil and ask how long it would take 10 eggs?
The other way to help the alternator if using a bigger one is to make the wheel size bigger so the alternator is producing at tickover, this I have seen this year not but a couple of weeks ago. I think, as I recall it was a 3-1 size. The Rutland 504 is purely for weekend sailing, trickles all week for the engine start, The R913 or 914i are for more serious charging and daily use.

 

[vyv_cox]

I have 3 x 110Ah domestic batteries which, discounting my solar panels, are charged by a 55 Amp alternator regulated by a Sterling unit. This seems to be perfectly adequate to get them up to a high charge level. My 125 watts of solar panel are used almost exclusively to keep the fridge running.

Your proposal of 300 Ah of battery to run services that don't include a fridge, assuming your laptop is not running 24 hours per day, seems to be very generous. My camper van has 200 Ah of domestic batteries and will run a TV, lights, water pump for 3 -4 hours with barely any discernable effect on the batteries.

 

[Rick_A]

I have 3 x 110Ah domestic batteries which, discounting my solar panels, are charged by a 55 Amp alternator regulated by a Sterling unit. This seems to be perfectly adequate to get them up to a high charge level. My 125 watts of solar panel are used almost exclusively to keep the fridge running.

Your proposal of 300 Ah of battery to run services that don't include a fridge, assuming your laptop is not running 24 hours per day, seems to be very generous. My camper van has 200 Ah of domestic batteries and will run a TV, lights, water pump for 3 -4 hours with barely any discernable effect on the batteries.

Excellent, this is what i wanted to hear. It may be generous, but its better to have too much power than not enough. A fridge is something that would be good to have but not essential to me yet.

 

[Tranona]

Excellent, this is what i wanted to hear. It may be generous, but its better to have too much power than not enough. A fridge is something that would be good to have but not essential to me yet.

Can't really see the need for all that capacity if you are not using heavy consumers like fridge and lap top. You need perhaps to look more at improving your existing system with a VSR for splitting the charge automatically and possibly some form of charge controller. This, plus a solar panel to top up when you are not using the boat should be more than adequate.

 

[mitiempo]

A larger bank makes sense for several reasons. You will discharge them less than a smaller bank so they will last longer - battery life is shortened with deeper discharges. If you are unable to charge or don't want to for a few days you can.
When you get that fridge you are ready for it.

300 ah bank will give you 150 ah usable if they are fully charged. If you are using the engine for charging 80% is max charge without engine running for hours. From 50% to 80% is 90 ah usable so it definitely is not excessive.

 

[Stu Jackson]

Excellent, this is what i wanted to hear. It may be generous, but its better to have too much power than not enough. A fridge is something that would be good to have but not essential to me yet.

Rather than guessing, do an Energy Budget.