Do I have to charge both of them?

[steve]

Two questions:
1. I've got two 88Ah sealed batteries, one for starting and one for domestics. I'm looking into buying a Sterling charger and it's occurred to me that maybe I only have to worry about charging one of the batteries. If I only use the starting battery to start the engine, it should charge back up immediately, right? Sealed batteries lose their charge very slowly and I can always use the selector to give it a shot if it's been sitting around for a long time. Am I making a mistake here?
2. Will a more powerful charger (more than 10% of the capacity of the battery(ies)) charge it (them) faster and if so, how powerful should it be?

Thanks in advance.

 

[ccscott49]

1. If you buy the sterling smart charger, you dont have to worry about either battery, it will take care of both of them, without having to worry about, topping one off etc. It will do it all and incorportates a splitter.
2. As a rule of thumb, an 88 ah hour battery will take 8.8 amps for 10 hours to be fully charged, that is a very loose calculation, but if you have a bigger output charger, it will take less time to charge the battery. I would however go for a proper marine charger, with a new type charge regime built in, again a smart charger. This will charge the batteries properly without danger of overcharging and overgassing.

 

[pvb]

A more cost-effective solution...

...would be to spend the money on a second domestic battery, and then buy a cheapish automatic charger (Halfords do one for about £30). By doubling your domestic battery capacity, you'll gain valuable extra endurance. And, because the 2 domestic batteries will normally suffer a lower percentage discharge than a single battery, they'll last much longer.

You're right to suppose that the engine starting battery recharges almost immediately when the engine's running - starting a marine diesel typically uses less than 1Ah.

 

[yachtbits]

why not to buy a cheap "Halfords" Charger

problem with using a cheap automotive type charger is they are transformer based. They require close to 240vac to work properly due to the step down ratio of the transformer. Shore supplies can often be at the end of long cables running lengths of pontoons which is where volt drops can occur.
Low input volts = Low output volts.
Sterling chargers are switched mode non-transformer types, so can run on a very wide input voltage range.

Additionally, transformers are not very efficient. If your marina charges you by the unit for electricity, then it will cost you more to run the cheap charger due to the reduced efficiency.

kev
yes, we do sell Sterling chargers!

www.yachtbits.co.uk
sales@yachtbits.co.uk
marine electrical/electronics specialists

 

[Guest]

There seems to be some confusion here. When you say a Sterling charger do you mean an independent charger powered from the mains or do you mean the unit that they sell which replaces the alternator regulator.

If you mean the independent type, modern chargers (whether from Sterling or from Halfords) are switched mode (not the older type which uses a transformer).
Switched mode chargers can cope with a much wider range of input voltage.

Alternator regulators and transformer type battery chargers charge batteries using the constant voltage system ie the output voltage of regulator and charger is maintained at a fixed level, which is higher than the highest voltage that can be reached by the battery. As the battery charges, the voltage at its terminals increases and hence the charging current decreases. This means that it can take a long time to charge a battery fully. The pundits claim that with this system, batteries only reach around 75% of charge.

Units ('smart regulators') which replace the alternator regulator, and switched mode chargers work on a different principle, entailing what they call multi stage charging. Initially, the charger/smart regulator drives a constant current into the battery until the battery terminal voltage reaches a pre-determined level. The charger/smart regulator then switches to a constant voltage mode and supplies a trickle/maintenance charge to the battery. A battery in good condition can reach almost a full state of charge.

The answer to your question about the relative size of charger to battery is that a bigger switched mode charger will charge the battery faster. There is a limit and the charger manufacturer stipulates the minimum size of battery that can be safely charged. Similarly, a bigger alternator combined with a smart regulator will charge batteries faster.

If you intend to fit a Sterling regulator, it will take care of both banks of batteries automatically.

 

[Guest]

Re: why not to buy a cheap \"Halfords\" Charger

Mathematics dispells the first part of the argument about voltage drop .....

Reduction of 240 to 14.4 = 16.66666 factor
therefore should voltage available at charger be reduced to 200 volts then resulting output will be : 12.0V

The likelihood of losse to 200, considering that the 240V supplies often exceed 230-240 anyway is surely unlikely and not so important. Generally Marina's etc. use reasonable size cable to reduce Voltage losses etc.
I berth in a marina where I have about 150m run of cable that I supplied from the distribution 'shed' at the head of the pontoon ... it is normal 'caravan' type cable and I run all from this and have absolutely no problem with losses ....

Nigel L

 

[charles_reed]

Re: why not to buy a cheap "Halfords" Charger

However the message is the same - save money on charger spend more on batteries.

The quickest way to destroy batteries is to leave them on a transformer trickle charger past their full charge situation.

I'd also query whether ALL Halfords chargers are switch mode.

Nigel, I'd suggest you carry out a voltage drop survey before assuming anything - my experience is that 210v is commonplace and I've even found 185 v in one place.
The one thing that won't change is the cycle rate.

 

[Guest]

Re: why not to buy a cheap \"Halfords\" Charger

I am not arguing that my way is better. or the other suggestion are wrong etc. In fact I agree with them ...... its just that I haven't had any problem ....... now that I've said that - I'll probably end up with the biggest problem ever !!!!

The only hassle I have with my marina ..... is that there are only 8 outlets and a lot more boats that want to connect !!!! Its on a meter and you stick a coin in, connect your lead ... go back next day and find your lead OUT, anothers in. Thats where I lose my money .... not on the batterys because of cheap chargers !!!!! Anyway I survive thats the important bit !!

 

[ccscott49]

Re: why not to buy a cheap \"Halfords\" Charger

Why not just do the job properly in the first place? Sterling alternator controller and sterling mains charger, or equivalents. Then you have no worries and can sleep soundly without having to go through all this!

 

[boatone]

steve - see post on MBC forum - 12volts on boats. may be some useful info for you

boatone@boatsonthethames.co.uk

 

[pvb]

Because...

That's total overkill when there's only 88Ah of domestic battery capacity. Much better to spend money on increasing the battery capacity first.

 

[ccscott49]

Re: Because...

No problem, I do understand, just like to do things right, lets me sleep safe and sound, as a liveaboard.

 

[steve]

Thanks for your replies, but...

let me explain more clearly. I asked the question for the following reasons:

1. I burned out one set of batteries using the trickle charger that was on board when I bought my boat.
2. I burned out another battery using another trickle charger with a supposed automatic cut-off and exploded a third (luckily I was on board (steel boat) but not in the engine compartment).

So, as you may imagine, I'm a little suspicious of battery chargers. I was thinking that:

1. If I don't put the starter battery on the charger, I'll always be able to start the engine whatever happens. (Last time it took me five days to go a hundred miles and I practically lost my job).
2. If I only charge the domestics, I can get away with a smaller (cheaper) charger.

At the moment I only use running lights and instruments on the batteries while at sea, so 88Ah is enough. I also figure that if I get a fridge, for instance, I can add another battery to the domestic bank and still use the smaller charger.

In light of all this, can you add anything more?

 

[pvb]

Oh, yes...

Well, sounds like you've been unlucky! Perhaps you had some faulty trickle chargers. However, I maintain that your main problem is insufficient domestic battery capacity. The usable battery capacity is between, say, 50% and 80% of theoretical capacity. That equates to 30% of theoretical capacity. With only 88Ah of domestic battery capacity, you have only about 26Ah of real capacity! That's just not enough for real world conditions.

So your first priority should be to increase the domestic battery capacity by adding extra batteries connected in parallel. I have 6 domestic batteries (total 630Ah) and NEVER have any problems with batteries. You don't have to have this much capacity, but the principle holds true - the greater the capacity; the smaller the problem.

In terms of your choice of charger, a small charger should cope adequately with your domestic battery (or battery bank). The engine starting battery should recharge automatically with no problems whenever you start the engine. If you're hooked up to shorepower, there's hours to charge the domestic battery/bank. A smallish charger will do this quite adequately.

 

[VMALLOWS]

Re: why not to buy a cheap \"Halfords\" Charger

Nigel, know the problem! Only solution I found was to spend the night on the boat.
Then it's a case of who gets out of bed to put the next 10p in the meter!

Solved it by moving to a swinging mooring. Can now afford to replace the batteries
that don't get charged as much as they would like.