Charging Batteries

[nova_castria]

Hi ,

Current set up is 2 batteries on domestic bank totalling 170 amps and 1 engine battery 70 amps , however when away crusing i always wake up to totally discharged domestic batteries. I reckon the fridge is pulling all the power (left on low all the time and turned up high when engine on ), I will run main engine if the heating is on . I always have to run the engine the following day for 2 hrs to recharge batteries and i wish to get away from this since the object is to sail ?

Batteries charge to 13.2 drop off to 12.8 then slow discharge to 11.6 . (when alternator is on voltage reads 14.2 volts )

Options

1 - increase battery bank - more amps to use (long to charge though)

2 - increase alternator size - charge back up quicker

3 - fit 4 stage smart regulator - put more amps in

4 - fit wind generator (not prefered option) will slow me down .

Thinking on increasing battery bank and installing smart regulator. Any views out there? Would appreciate any comments.

Andy

 

[Richard10002]

I have had a very similar experience, both during my trip across the Med. in 2007, and in the marina this year, (I was out of action for all of 2008).

Unfortunately, I have resigned myself to the fact that the batteries are knackered, ( 6 years old), and have just ordered 2 replacements, (2 x 125Ah). I replaced the engine start battery in March, (6 years old).

Sounds like yours are discharging way too fast for the size of your bank, (170Ah = approx. 85Ah useable). My fridge uses about 5 amps for about 15 minutes every hour so, overnight, it might use 10Ah.

 

[Chris_Robb]

Firstly, what kind of boat is it?
Then - look at the fridge and see how much insulation it has. Some standard production yachts from the 80 and 90 had hopelessly insulated fridges, and the only solution, as I have done, is to rip it out and start again! Ideal thickness is 3 to 4 inches.

As batteries do not like to be discharged below 50%, you may well have knackered the batteries, and they are now much reduced in capacity. So probably means new batteries.

You may want to add a Battery Monitor such as the Nasa BM, with which you will understand how much current is being taken by your equipment, and put in by the alternator.

Re the Alternator charging: Do you know whether the batteries are connected by a splitting diode, or manual switch (1, 2 or both) or a solid state switch. If the former (diode) then you will be loosing 0.5V at the battery which is significant in terms of rate of charge.

In broad terms, an alternator charging the battery at 13.8 will eventually charge it fully, but you might die waiting. at the other extreme, charging at 14.8 will charge much faster, but will boil water away, so you will need to replace water, so sealed batteries at this rate of charge iare not a good idea.

This link will give you a lot of help in understanding batteries and charging in general.
web page

They mention 14.4 as the norm for charging, which I think is due to the fact that they recommend sealed batteries, where as I prefer not sealed, and to charge faster at 14.8. I am not sure what the correct answer is - but it has worked for me.

What else..... Don't install a larger alternator until you have worked through the system. It may well be worth adding extra battery capacity, as you can then charge fater, and discharge less than 50%.

If you do not have one yet - get a digital multimeter - a thousand uses round the boat - will even (some) measure temperature in the fridge.....

 

[nova_castria]

Hi thanks for comprehensive answer .

Boat is a beneteau 33.7 , 1997 .

Don't think there is no split diode (or i haven't found it yet ) or 1/2 /both switch (I can switch off each bank independantly and normally have both banks on while motoring and switch engine battery off when engine is off ) , i am pressuming that both batteries are feed from alternator ?

andy

PS no shore power fitted use standalone battery charger on domestic when along side .

 

[Chris_Robb]

[ QUOTE ]
Hi thanks for comprehensive answer .

Boat is a beneteau 33.7 , 1997 .

Don't think there is no split diode (or i haven't found it yet ) or 1/2 /both switch (I can switch off each bank independantly and normally have both banks on while motoring and switch engine battery off when engine is off ) , i am pressuming that both batteries are feed from alternator ?

andy

PS no shore power fitted use standalone battery charger on domestic when along side .

[/ QUOTE ]

Others who know the Bene will be along soon....

The 2 individual switches would indicate that you will have some form of separating methd between the batteries.

We have eliminated the manual 1,2,both switch type, leaving the diode, or solid state switch. If the boat is a number of years old, it will most likely be a diode. This means that it is worth fitting an alternator controller if it is a splitting diode.

 

[Mrnotming]

fit the smart alternator controller, buy open lead acid batteries where you can check specific gravity if you suspect a bad cell, go for about 360AH of bats or more if you can find the space. None of your domestic batteries should even mention the word cold cranking amps, as these are not deep cycle types, Prepare to use about a gallon of distilled water a fortnight.Enjoy a higher charge of 14.8V or more. Fit solar panels of say 40watts and the fridge will not use any much power during the day. Fit a controller to the solar panels also to avoid any backdrain or (unlikely) overcharging. the solar panels will keep your batteries up during the winter too, and avoid spoiling them, as another poster says, if they go below 11.7 volts at any time.The key is to have enough capacity to avoid undue depletion.Good sailing to all. /forums/images/graemlins/cool.gif

 

[Mrnotming]

Caveat: If you have a yanmar engine, the alternators can be difficult to wire up for Smart Alternators, without snapping off the wires during disassembly, termed "splitting" by one vendor of battery enhancing gear.Suggest bringing the Alternator to a good Auto electrician to avoid a further bill for a replacement alternator!Good sailing to all.

 

[William_H]

You need to know if the batteries you have should be able to run the fridge overnight? Are they fully charged before you start ie is there diode stopping it being fully charged check with a voltmeter.

Is the fridge running too much? This can be caused by loss of gas. Most run something like 30% of the time ie with long off periods (unles you have one of those stupid peltier type electronic cool box which flatten batteries with very little cooling power.)

If the batteries should be able to cope with the drain ie drain is not so much and batteries are fully charged at start, then batteries are dead.
lack of capacity is a sure sign of age.

So if all is OK and correct and your drain is simply too much I would suggest another battery to increase capacity.

An amp meter is always good to confirm you are really charging the batteries at a useful rate. It can also be used to confirm that there is nothing else discharging the batteries that you havn't thought of.

good luck olewill

 

[James_Hortop]

In most installations, if the split charging system is set up appropriately, an alternator controller will have negligable impact.

I would always recommend in this case that you fit a battery monitor first, use it for a month and go from there. You can then approach this armed with a lot of information.

One word of caution, the Nasa BM was mentioned - good monitor - but it only comes with a 100A shunt which is undersized for your size of boat.

James