disconnecting batteries before charging?

You are so fortunate to have a modern set up in your boat, perhaps if you had an older power plant like the rest of us you would take the advice offered here.
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We used to have an older vessel with older powerplant ... didn't change how we charged!
It may be that advice given when alternators became common was to disconnect them before charging - but as that advice doesn't stand for newer kit it would be sensible to consider the advice and see what fits your particular circumstance...
As you don't understand the electronics of it all we can only assume you're just regurgiating advice given to you - and thus it may have no application in the OPs circumstance - your original post gave no hint of your knowledge (or lack thereof) and could quite easily be taken as gospel by those also in the dark ... perhaps you should clarify why you're giving the advice you're offering in the future.
 
I never disconnect the battery cabling before charging my two Beta 20's, and as Vic says, I also cant think of a reason to do so. You dont disconnect when jump starting so why do so when charging?
Willie
 
William_H said:
A modern charger thanks to cheap electronics takes the pulsing DC from the rectifier applies it to large value capacitors then via series regulator transistors to give a very precise steady and accurate voltage set to the desired voltage.
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What is modern ? over 25 years ago we bought out a multi-stage charger, controlled current. to maitain a given voltage to 0.01 of a volt.

The end of the day, a battery charger is not there to start the engine, they are not designed to supply 300 amp. It may work, it may not, but over the last 30 years I have seen more chargers killed than alternators, from starting with the charger on.

It is like switching batteries with the alternator running will distroy diodes. I have come across yachts that have motor sailed for hours with the batteries isolated. No damage to alternator, reconnect batteries, and away they went.

It is just down to good pratice, you should not start with the battery charger switch on, you should not isolate batteries with engine running. One day may work, next day may be a big bang, just because it worked for Joe, it may not work for you, you do not have his boat.

Brian
 
The only problem I've had with charging and batteries is somebody turned (mistakenly) the house batteries off while while they were being charged. It blew our SSB and Icom (who repaired it) said it had been exposed to a 24 volt spike.
 
William_H said:
A modern charger thanks to cheap electronics takes the pulsing DC from the rectifier applies it to large value capacitors then via series regulator transistors to give a very precise steady and accurate voltage set to the desired voltage. This may be 14v for trickle charge or higher for limited periods with a stepped charger. The higher voltage however is not usually so much as to cause damage ie a bit above 15v.
So even with a dud battery it is unlikely to cause damage. olewill
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Not all chargers have a smooth output. A spiky output is supposedly better to help 'desulphate' the battery. Don't know whether it's deliberate design or just the price of big capacitors, but many fairly 'good' chargers are quite spiky as seen on my Tektronix 'scope.

I think the people who advocate not starting the engine with the charger connected have a good point. If the starter motor does not disengage instantly as the engine catches, it can generate a lot of volts, possibly damaging the charger.
Some equipment for vehicles is specified to withstand voltage spikes up to 4x the nominal in both polarities.
As with all electronics, failure from abuse may not be instant, every time you take a semiconductor outside its 'safe operating area' you potentially reduce its reliability. Failure may follow months later.
 
perhaps the following link may enlighten (or give you cause for pause). Describes procedure for charging in situ (car battery).

http://www.battery-chargers.com/charging_instructions.htm

I personally know of two battery explosions onboard local fishing vessels growing up. One incident was fatal. Had to deal with a boiling battery onboard once myself - not a nice problem. When it comes to deep cycling (i.e. electrical stressing), best advice I ever got was to treat your batteries as if they were bombs!

have to agree with you halcyon & lw395.
 
fireball said:
perhaps you should clarify why you're giving the advice you're offering in the future.
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I think it was perfectly clear why I was giving that advice, I was speaking from personal experience and was trying to prevent some other unfortunate from frying their alternator, but I was certainly not alarmist.
 
Well we'll have to disagree there. You made a statement with nothing to suggest you were not speaking aurhoritively.
 
"Also remember that the VSR is always live, so if not running 24/7 charge, you are draining the batteries.

Brian"

I am going to show my embryonic (but improving I hope!) level of knowledge on these matters!:o

If the VSR is the only live connection from the batteries (everything else is switched out), how great is this drain?
As I described earlier my plan was to include such a set-up - see the attached diagram.
 
Thanks for all your replies. I think that I will charge without disconnecting - in fact I did so over the weekend without any problems afetr reading the above replies. I did wonder whether the warnings in the charger instruction book were there as a way of covering themselves in the event of a problem.

This leads me to other questionsas. I have been doing a lot of learning over the last few months with my newly bought boat. It will probably be best if I post the questions as a new thread.
Thanks again to everyone for taking the time to answer my question.
 
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