disconnecting batteries before charging?

[portvasgo]

In the process of gettng my head around 12v systems, batteries and charging. This is the frst time I've had a boat that requires me to know this stuff. Have followed many threads with interest and the search function has taught me loads.
One question. I understand from previous threads that I can attach a mains battery charger to my batteries without disconnecting the batteries from the boat. That the charger will charge the batteries whilst I still draw from them for lights etc.

However, my engine manual (nanni) states that 'you must disconnect the 2 battery cables when using a battery charger'
Also, the instuctions from the mains charger that I have (a car charger that I will probably replace in the future with a wired-in, designated marine charger), also tell you to disconnect the wiring before charging. Why would this be?

Thanks again in anticipation of your expertise.

 

[MoodySabre]

I don't disconnect the battery cables. My multistage charger is wired into the back of the 1-both-2 switch and I just point it at which battery I want to charge. In a marina I point it at the domestic battery and run the fridge and lights. Charge switches off when I disconnect the mains supply.

Been alright all last year - awaiting the doomsayers

Oh - you asked for expertise. I speak from successful experience not expertise.

 

[VicS]

Car manuals do tell you to disconnect the battery before charging. I cant think of a reason and I never do! (In fact one car has its battery on charge insitu and still connected as we speak)

Perhaps it's so that you cannot start the car and drive off with the charger connected but that does not explain it as far as your Nanni is concerned.

 

[fireball]

Our charger is built in and charges both sets of batteries - no need to disconnect anything from the engine for us - can't see why you would either - but that's not to say you don't need to ...

As for using lights etc whilst charging - YES!! This is absolutely fine ...
Think of your batteries as a watertank - you can fill the tank at the same time as drawing off water ... if you draw more than you're putting in then you'll eventually drain the batteries - but if you're just down on the boat and using it for lights etc then that occaisional use will be fine.

Going back to the engine - has your Nanni got Dynastart or Starter & Altenator?

 

[NormanS]

I have a wired in marine multi-stage charger, and don't disconnect anything when charging, or using battery power. I also have Adverc, and it has a select switch for either "Mains" or "Engine", but I think that that is so that I am charging from either the mains charger, or the alternator, and never both. Hopefully, someone will be along shortly who will be able to advise you (and me).

 

[lw395]

I think this advice probably dates back to the days of electro-mechanical 'cutout' dynamo regulators, where it can be a bad idea to charge with the dynamo in circuit but not going round?
also some mains chargers are very crudely regulated, and if the battery is totally duff, could put a lot of volts on the system as spikes.
I see no problem provided the battery is sound, the charger will be no worse than the alternator etc.

 

[portvasgo]

Thanks for all the advice. I was just nervous that I had missed something when reading through other threads, it had semeed to me that if you can use an alternatoar and draw from the baterries at the same time, then why not with a battery charger.

Fireball, good question! What's Dynastart? There is no mention of this in the engine manual that I have, I assumed that I had a 'normal' alternator and starter. Again, advise much appreciated.

 

[VicS]

I think this advice probably dates back to the days of electro-mechanical 'cutout' dynamo regulators, where it can be a bad idea to charge with the dynamo in circuit but not going round?

I wondered about that but a dynamo is disconnected by its cut out (until it is running and its output volts rises to the "cut in " setting,) and IIRC the output also goes (unlike an alternator) to the battery via the ignition switch.

Maybe your suggestion about spikes is more valid. Not from my old battery charger though, a stepdown transformer and an old fashioned metal rectifier.

Potvasgo.
A Dynasart or Dynastarter was a dynamo and a starter motor combined into one unit. Popular on small engines at one time.

 

[cimo]

disconnecting cables prior to charging is generally considered "good practice". From a equipment supplier perspective, your engine manufacturer has no control over what OEM charger you will use or what condition it is likely to be in. Your OEM charger supplier has no control over what your battery is connected to, or the health staus of the battery you're charging.

It's a common enough "disclaimer" type statement to include in product litrature. ~99% of the time we don't disconnect and things work out. It's the ~1% to which this statement is aimed at.

Although in the case of battery charging, I would agree that the precaution has some merit -

We all know that a wet cell battery will out gas when being charged (battery re-charging is a pretty violent process). Whatever the probability of sparking across live circuits may be, by disconnecting all aux. circuirty, the risk is greatly reduced.

Of course in the real would, "good practice" and being practicle don't always concur, but it's the same reason we don't check for gas leaks with a cigratte lighter (ahem?), the same reason we disconnect the mains before opening the up the DVD player - "good practise".

safe boating to all.

 

[rob2]

Yes, it was common practice to just hook on the charger when cars had dynamos. Early alternators proved somewhat vulnerable , though. IIRC the diode packs would burn out (was that to do with the excitation circuit being live?).

I believe it is once again considered normal to hook a charger to your car, although I've not put this to the test as my car is parked in the street! But it is a damned nuisance having to punch in codes to restart all the systems isn't it?

Rob.

 

[gasdave]

I too am in the process of redesigning my charging system (a simple 2 x 85Ah batteries set-up).

The more I have read around this subject now the more I am being persuaded to go down the route of separating the charging circuitry from the power distribution circuitry (as recently desciribed in other threads here). In other words, using a Smartbank VSR across the two batteries to take care of charge distribution, connecting the alternator to Battery 1 and maintaining my 1/2/B switch to select which battery power comes from (rather than also using it to determine where charge is distributed to). The idea is to mostly use Battery 1 for everything in the knowledge that Battery 2will always have enough charge to cover emergencies.
This set-up also protects the alternator diodes from accidental switching off during engine running.

By using the SmartBank I can connect a 240V charger (I am using a CTEK Multi XS25000) and/or a solar panel and/or wind generator to Battery 1 (in addition to the alternator) and both batteries will be charged. There is no need to disconnect the batteries for charging. CTEK state in their literature that batteries can safely be left in place during charging and that the unit can double as a power supply.

I have used a similar charging system on my bike for a while (smaller CTEK) - the cables are permanently connected to the bike battery and fed out to a socket tucked under the frame. Simply plug in or out as necessary without the hassle of lifting the seat every time.

However I would stress that mains charging in this way does depend on the type of charger you are using and matching it appropriately to your battery. You need a "smart" multi-stage charger.

 

[GrahamHR]

Quick fix for the code problem for radios etc if a car battery has to be disconnected for charging; buy a plug that fits in the cigarette lighter socket. Fit a 12V battery to it ( the sort that is used for alarm remote controls/ cigarette lighters). Plug it in before you remove the car battery.

 

[VicS]

Quick fix for the code problem for radios etc

whether or not your suggestion will work depends upon whether or not the socket is normally live when the ignition is off.

 

[halcyon]

However I would stress that mains charging in this way does depend on the type of charger you are using and matching it appropriately to your battery. You need a "smart" multi-stage charger.

Will it work ? Yes

We introduced multi-stage mains chargers interfaced to our VSR system back in 1983/84, these were connected direct to the batteries, and there are 1000's still running. Why they should tell you to disconnect the battery, I can give you no good reason, bar covering themselves from a charger fault.

Re the posts about 1,2, both switches, one big reason two seperate battery banks became populer back in the 70's / 80's was the growth in electronics. Having the power supply, and engine start on the same battery, you get spikes and low voltage, causing problems with the electronics. This is still a problem that modern power cruiser builders meet when using the same battery bank for power and engine supply.
If using a VSR across a 1, 2, both switch, and fitting solar panel / wind gen, make sure the cable between VSR and batteries is large. If you start the engine with the VSR engaged it can take a high current till it drops out.

Brian

 

[gasdave]

make sure the cable between VSR and batteries is large. If you start the engine with the VSR engaged it can take a high current till it drops out.

Brian

How large do you suggest, Brian?

 

[SAMYL]

By all means connect your charger to batteries and run your lights etc. but DO NOT turn on your engine ignition - depending on what circuit and built in protection you have, you could wreck your alternator.

 

[halcyon]

How large do you suggest, Brian?

You have to allow for the link taking full alternator output. You cannot assume you will have the second battery always full, and it only taking a few amp. Depends on alternator, but 10 - 15 sq mm is on the safe side.
Also remember that the VSR is always live, so if not running 24/7 charge, you are draining the batteries.

Brian

 

[William_H]

Battery chargers

Old fashioned battery chargers consisted of a transformer rectifier and some amount of series resistance. In some cases this was effectively in the transformer itself. The voltage out of the rectifier was a pulsed voltage rising from 0 to perhaps 18 volts then diminishing again to zero and rising again at 50 times per second. (or 100 times for full wave rectifier) The battery would take a current depending on the voltage of the charger (above that of the battery) This current higher at the peak of the cycle would reduce the charger output voltage because of the internal resistance of the charger. So battery voltage which is also charger o/p voltage is reasonably steady at about 14v. The high pulses could be described as being absorbed by the battery. This kind of charger can be described as near to a constant current charger. As the battery voltage rises there is always an excess of voltage above the battery voltage to push some more current though obviously the average charge current diminishes with battery charge.

If left 24/7 this kind of charger if of sufficient power will destroy the battery but on the other hand will put in the best amount of charge for a limited time. You have to remember to turn it off.

Now one mode of failure of a battery is where it becomes a high resistance itself. it will not deliver output but also will not accept a charge. If this kind of charger is connected to a battery also connected to operating systems then the system voltage will rise with large peaks. Systems may be destroyed.
I remember my father did exactly that and destroyed the clock on his old car. Fortunately it was so old there was no other electronics.
Hence i believe the warning about disconnecting all services when charging.

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

 

[fireball]

By all means connect your charger to batteries and run your lights etc. but DO NOT turn on your engine ignition - depending on what circuit and built in protection you have, you could wreck your alternator.

That's a bit alarmist ... I know I've got a modern boat/charger/engine - but we can start the engine with the battery charger on .... no problems at all ...

What circuit and built in protection are you talking about?

 

[SAMYL]

That's a bit alarmist ... I know I've got a modern boat/charger/engine - but we can start the engine with the battery charger on .... no problems at all ...

What circuit and built in protection are you talking about?

Alarmist I may be but if it saves someones alternator then it is good advice. This was always the case years ago when alternators became common as ROB2 quotes above. It was the advice I was always given and habits die hard so I still disconnect the electrics from the batteries when mains charging. I don't understand the electronics of it all so cannot comment on what the protection devices are, I have been told that modern systems are better controlled.
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.