Batteries (making funy buzzing noise),chargers,and separators

[georgesoilis]

Hi all
I got a B31ft sailing sloop that has a 12hp yanmar diesel .2 batteries ,starter non maintenance battery 75ah,and domestics wet (isnt that the proper name \) 75 Ah .
they are conected through a key switch (the main battery switch not the key for the engine),a separator?? ( maybe its not the english name but this is what the swedish plans say) ,that is supossed to isolate the starter battery from the domestic when using power the 12v system (??)like lights etc i guess....or so that it doesnt empty the domestic during starting???And then when charging from the engine generator ,the current goes directly to the starter battery?Or does it go through a regulator maybe,i m not sure.
I would like if anyone can verify that what i am describing makes some sense to the more experienced and also if you can say if the 4A battery charger that came with the boat is enough for these batteries and how they should be connected when charging.I think the idea is to connect to the domestics pos and neg terminals and from there the current goes to the starter battery when the domestic is full?????????It doesnt make sense .or it s of no importance if the charger is connectedto the one or the other ,as it will charge continiously anyway and i just need to observe the indication on an ampmeter and stop the charging at some point (in which case please tell me what should this point be and by the way can i use a voltometer (the cheap argos ones) to measure the Volts directly on the battery terminals or someother way?And there is also a battery test for both batteries on the mains board ,but with not very accurate indications as it is only color coded.should i be using this instead or can i do what i said with the other Voltmeter ?

Also something that i noticed is that when conecting tha charger now to the domestics battery it makes a buzzing noise and i now it needs changing from the previous owner ,but is it dangerous?I refilled it,checked the level in all compartments to be not more than 2 mm over the plates,but it seems the battery has had it as it goes up to a certain level of charging and then just empties in 10 minutes (after hours of charging...The starter battery is still fine ,starting with first go at every time my engine ,which is well preserved so far and with water cooling system(YSE12,1978 built ,imagine that ...

Sorry a load of xmas questions but i have to get it up and running in the next 2 weeks as my marina fees are running out and i need to move her ........heeeeeeelp>>>>>>>>>

cheers
Mari /forums/images/graemlins/confused.gif

 

[William_H]

I am guessing that the "separator" is a switch to connect the engine battery to the domestic battery so that it will be charged when the engine is running. If this is a robust switch it can also be used to put the domestic battery in paralell with the engine battery to assist the engine start if the engine battery is tired or discharged. Normally this switch is only connected when the engine is running as if it is left connected when you arer living on board with the engine not running you could discharge the engine battery as well as the domestic battery. You might consider a voltage sensing relay to replace or bypass this switch which will automatically connect when the engine battery is on charge. (and automatically disconnect when engine stops)
Now I think you are saying that after charge your domestic battery dies after 10 minutes (presumably with some lights turned on) In that case have a new battery. The buzzing I imagine is coming from the charger (the transformer is vibrating with the magnetic field in the iron) not a problem except that transformers sometimes buzz when there is an excessive load on the charger. (check for a buzz when charging the good engine battery alone. If it has an ampmeter this will indicate the load.
The dead battery may be causing the excessive load. Check the battery voltage when on the charger if it is in the range around 14 volts that is OK if the voltage is less than 12 you could cook the charger. The charger 4amp rating should be fine but of course will be slow to recharge the batteries needing one or 2 days to recharge from discharged state. Hope you enjoy Christmas think of us poor folks had 41.5 degrees max last week forcast 35 for Christmas day. will

 

[oldharry]

Sounds as though the domestic battery is dead, if it discharges in 10 minutes. If it has an internal short then it could be overloading the charger, which would make the buzzing noise worse. I think your 'separator' is probably a diode arranged to prevent one battery discharging into the other.

Firstly I suggest you take the batteries out to an auto electrician for heavy discharge testing. This will establish whether they are still in good condition. They need to be fully charged for this test.

Second, you should replace the charger with an automatic one, of higher capacity. Your 4 amp unit would take up to 48 hours to charge both batteries from flat, (i.e. 2x75ah = 150ah @ 4ah = 36 hours + at least 25% for charging losses.)

A 10 amp automatic charger should bring them up to charge in 24 hours. There are some quite decent reasonably priced ones around nowadays, with a 'full charge' and 'float charge' switch - the latter being useful because it means you can leave the charger permanently on without damage to the batteries.

The charging circuit should be as follows: The alternator will have either an internal or external regulator; it doesnt make a lot of odds which. Its function is to control the alternator output to the correct levels for charging the batteries according to the state of charge they are in. If the regulator is external never connect anything between it and the alternator - it will upset the charging output of the alt, and the voltages will be wrong and likely to damage electronics.

The regulated output should always feed to the starter battery, and normal practice is to give that priority over everything. The domestic battery will have a diode or relay (the separator in your circuit diagram) to prevent the domestic circuits from draining the starter battery; it is common however for the domestic battery to be able to support the starter battery if it is low.

As to testing, as you have already noticed the voltmeter is not very accurate. It will vary according quite a bit according to whether the batteries are being charged or discharged, or are idle. There is no reason why you should not use a small multimeter - many of us do! Accurate readings are only obtained when the batteries have not been used for a mimum of 10 minutes (i.e. everything switched off - ideally when arriving on board and before switching anything on)

The following approximate voltages should be observed:

Charging: after 10 minutes 13.8 - 14.2 Volts (any higher will damage the batteries, lower means the alternator output is down.)

Quiescent battery voltage 12 - 12.8 volts

Part charged 11.5 - 12 volts

Below 11.5 - effectively flat! (Never drop below 11.2 volts, as damage ensues, and below 10.5 volts the battery capacity will be seriously impaired permanently)

Note that these readings ONLY apply to batteries that have stood for at least 10 minutes without being charged or discharged in any way: Anything drawing current from the battery from a light bulb to the starter motor will cause a degree of voltage drop - the starter motor for example will run at around 9 volts. this is normal!

Finally, if the starter battery is in good condtion, it can be used for domestics. Many smaller boats do this - you just have to be careful not to stay up with the lights on too late and flatten the battery! /forums/images/graemlins/wink.gif

Have a nice Christmas!

 

[Talbot]

A dying battery is a nuisance and causes all sorts of other problems, a replacement from a caravan shop is less than £50 and will solve most of your problems. If you can fit one, go for a 110amp/hr rather than the 75 as 75 for a 31ft boat is very small. The battery charger is very small and will only provide a trickle charge to keep the battery up. For such a small battery installation, I would expect a 25 amp charger on my boat I have a 45 amp charger that chares both banks simultaneously.