Boiling Batteries

[harrytom 642]

IT, what size would you recommend for a house battery that is primary used for lighting and fridge (waeco cfx 40)?

 

when not using yacht bring it home and trickle it??

[wheels 543]

Was the battery size you had, OK for keeping everything running without discharging too far? If yes, then replace with the same size. I see that Supercheap are now stocking Optima. A very very good Battery. But damn expensive. However, so are most very good Deep Cycles, so the same capacity may not be a lot different between comparable makes. There are certainly cheap Deep Cycles out there. You certainly get what you pay for.

When not using yacht, do you have any form of trickle charging on board? such as a Solar panel? If not, then yes, take home and trickle.Lead Acid of any kind do not like sitting uncharged for any length of time.
Basically, as soon as a Battery starts to discharge, they start a slow process of dying. The greater the discharge and the longer it is left that way, the more the damage done. The faster you can restore the charge to full capacity, the faster you get it up away from the damage being done to the plates.
 

[Island Time 1,235]

What wheels said.

Plus, what does the fridge draw. Plus how long does it run on an average summer day. We are after how many amp hours consumed each day. Then we look at recharge, and how you put those amp hours back. Then how many days you wish to run without recharge.

Remember that a lead acid based battery should not be reduced by more than 50%. Can calculate required battery size from that.

I can supply batts if you like, but as I said before, I'm not back until 19 jan

[harrytom 642]

Thanks for the replies and advice.Will look at solar in the future,meantime will replace and bring home,not that much trouble to do.

no idea what fridge draws but very efficient unit. Waeco.

[Island Time 1,235]

Measure it, what's it draw when it's on, how long does it run before switching off, how long gone till it switches on again...

You can do that at home.....

[Chloe 7]

Thanks for the replies and advice.Will look at solar in the future,meantime will replace and bring home,not that much trouble to do.

no idea what fridge draws but very efficient unit. Waeco.

Your Model use's about 0.78amp per hour. 

[wheels 543]

Even a little portable Solar panel for trickle charging would be fine on the boat when you are not aboard. Providing the battery is fully charged before you leave. They have no show of charging the battery, but can happily keep one topped up.

Re the 50% comment. It is important to understand that as soon as a LA battery starts to discharge, it also starts to deteriorate. The speed it does so increases with the depth of discharge. The 50% rule of thumb came about as a Sum of Battery Cost/length of life.  If you consistently discharge below 50%, then the battery will not last long. Replacement is expensive. If you never discharge below a few percent, the battery may last much longer, but you never really needed the capacity, so it was a waste of money. 50% is considered the best efficiency in Amps produced over it's life to Cost ratio.
Something to watch out for in Warranties when purchasing a cheaper Deep Cycle. They often on warrant a Deep Cycle for X many years providing the Battery has never been discharged below 20%. And that has to be able to be proven. For many boat installs, that is not possible, because only the really expensive regulators have that facility. So you need to ask the supplier what the Warranty entails and do need proof of discharge floors, or your warranty may be void.

[Island Time 1,235]

OK, so a (very) rough calculation then, fridge 25 amp hour, lights say 3 hours, 3 amps total draw say 10 amp hours. That's 35 amp hours per day. So that's a min 70 amp hour battery - I'd go for a 100, provided it will fit in your battery box.

Also, consider your charging - the last 20 percent of charging takes hours. Many cruisers only ever charge to 80% for this reason, unless on shore power. The 100amp hour battery gives you that ability.

[harrytom 642]

OK, so a (very) rough calculation then, fridge 25 amp hour, lights say 3 hours, 3 amps total draw say 10 amp hours. That's 35 amp hours per day. So that's a min 70 amp hour battery - I'd go for a 100, provided it will fit in your battery box.

Also, consider your charging - the last 20 percent of charging takes hours. Many cruisers only ever charge to 80% for this reason, unless on shore power. The 100amp hour battery gives you that ability.

got a new 120ah battery today ,so will be taking care of it,no cranking,have a good crank onboard.

[Vivaldi 53]

I'd like to add that the battery computer needs to be correctly installed -, the shunt being the first connection on the negative lead - NO other wires direct to battery negative. Then it needs to be correctly programmed - battery type and capacity, reset current (circa 1% of capacity), proper purkets factor for that battery etc.

The purkets factor for that battery and the correct charging voltages will be given on the product data sheet, and sometimes on the side of the battery.

Not to do all this means the battery computer will not be accurate, possibly by so much its useless. In my experience 90 odd percent of them are not set up correctly.

Personally I use VRSLA batts (sealed) so I don't have to worry about electolye levels.

Remember, never discharge below 50%,recharge asap to full, use float charge systems, and you'll get 10years or more from your batts. .

Don't do this and you'll kill them early.

Hi IT,

I have a BEP Matrix on mine and it appears to be wired up as you describe (negative lead to the shunt first), with the exception that the wires from the solar panel regulator go direct to the battery terminals (so it still charges when the batteries are isolated). should the negative from the solar panel battery go to the shunt instead of the terminal? And if so which side of the shunt?

Cheers

Paul

[Island Time 1,235]

Hi Paul, absolutely yes.

But isn’t the matrix a tank monitor? Did you mean a dcm 600?

In your setup as is, the computer does not know about the solar panel. They should be wired to the load side of the shunt ( not battery side), and they should be fused. The power for the meter should also be on full time.

The new draft electrical standards for nz boats (not -yet- law) require batteries to be fused with ignition protected fuses, so a fuse is also ok as first thing from + terminal, and the solar + to the load side of that.

That’s what I have + terminal to fuse to always on bus distribution ( solar, wind gen, bilge pumps, battery computer ) then to mains switch ... all the things on the always on bus also have their own fuses of course, that battery fuse is way to big and slow to blow for them!

[Vivaldi 53]

Hi,

The monitor is a BEP Matrix DC monitor - so not a computer - monitors voltage for house and engine batteries, shows amps charge or discharge, and shows a percentage of remaining capacity. The solar panel has a MPPT Controller then to the battery. Seems to work okay, but I’ll move the negative to the shunt.

The shunt seems to have a negative from the house battery on one side and a negative from the engine on the other side of it, with a smaller wire heading up to the monitor - does that sound right?

[Island Time 1,235]

OK, that is a dcm600, and it is a battery monitor computer. What I said above stands.

Move the engine neg to the load side of the shunt, There should be NO other connections on the battery side of the shunt, except the main cable to the battery, and, on the small screw terminal, the neg sense wire for the meter. Nothing else to the terminal either. Loads must pass thru the shunt to be seen by the monitor.

So your battery monitor, like most, wasn't installed correctly, and was telling you lies!

Once the wiring is fixed, check the programming!

[Vivaldi 53]

Thanks, just checked - engine battery is on load side, house negative is on the battery side. So I just need to put the solar neg on the load side to have it seen by the monitor, is that correct?

[Island Time 1,235]

That and move house neg to load side too.

Again, battery neg to shunt. NOTHING ELSE ON THE BATTERY TERMINAL, OR BATTERY SIDE OF SHUNT. The only exception is the neg sense wire on the little screw terminal for that purpose on the battery side of shunt.

[Vivaldi 53]

Thanks- one more question if you don’t mind. I’ve been looking at the VSR and noticed that the wires going from the VSR to the battery isolator switches are quite small in diameter - about 6mm, certainly not battery cable size. Could this affect charging efficiency when the motor is running?

[Island Time 1,235]

Yes. Vsrs should have cable appropriately sized for their rated throughput and length. What amp rating is the VSR, and how long are the cables (battery isolator to VSR to the other battery isolator)?

Sometimes, if one battery is full and the other low, a lot of current can flow via the VSR.

[Vivaldi 53]

Only about 600mm. It’s a 140 amp model

[Island Time 1,235]

That would put best cable size at 35mm2....

[wheels 543]

IT has it all excellently covered.
I would just like to add, for all and any Battery cable, ALWAYS keep the runs as short as possible. If practicable, I like to go one size up on any cable that is also providing charging. Using a table or calculation to work out the size of cable is fine for when it is supplying a load only, but when any charging current is being sent down it too the Bank, it is always best to have the least resistance as possible. It is NOT a good idea to place any charger or regulator right beside a Battery, these things usually end up being some distance away from the battery, so the cable run can often be longer that desired. So keeping the cable larger aids in accurate charge monitoring.
Also, a Shunt needs to be isolated from anything that can ignite, just as a precaution. Just a simple piece of anything that will not support combustion placed behind it is all that is required. They should never get hot in normal use, but in the event of something going wrong, they can do.