Topic: Battery charging question

Glen_Mist    -- Sep-25-2009 @ 8:28 PM
  Hi all

      Silly question time.

I'm looking at getting a battery charger to attatch to shore power at the marina, just to keep the batteries healthy when i can't get down to my boat.

My question is this;

As i have 4 batteries (1 engine start and 3 domestic with a split charge relay and single 85 amp alternator), will the one charger suffice, or will i need 2 (one for the engine/1 for the 3 domestic connected in parallel), or even 4 (one per battery).

As i said, a silly qustion that i should probably know the answer to but after a week of night shifts the old thinking matter isn't firing on all 4 cylinders.

Many thanks in advance

Chris J

Anybody want to buy a Birchwood 22?

Pandora-3    -- Sep-25-2009 @ 9:28 PM
  Can't you just connect the battery charger where the positive and
negative of the alternator connect? Assuming that this one
alternator does actually charge all the batteries.

Glen_Mist    -- Sep-25-2009 @ 9:32 PM
  I had thought of that as well, but i'm worried about possible ramifications (damage to the alternator?), also the charger would possibly have to be a bit of a beast to be able to handle 440Ah of batteries.

Chris J

Anybody want to buy a Birchwood 22?

shortfeed    -- Sep-25-2009 @ 11:50 PM
  cheapest way Chris .... keep borrowing ours until they are all charged! Wink

I wish you would tell me you were comming aboard dear ...that coffee was realy hot! Ruth

Glen_Mist    -- Sep-26-2009 @ 4:14 AM
  Hi Mum

    I know that, but i was thinking aboust those rare occasions that you might need it at the same time  Smile

Chris J

Anybody want to buy a Birchwood 22?

kfurbank    -- Sep-26-2009 @ 8:23 AM

If you place a battery charger just after the alternator you are going to have a voltage drop across the split charge relay of around 0.7V plus a drop for the rest of the cable run to the batteries. A charger should always be placed as close to the batteries as possible. Ideally connected straight to the batteries. The split charge relay is used to enable the one alternator to charge multiple batteries without them needing to be physically connected to each other and therefore isolating a bad battery from draining a good battery, or domestic usage from draining an engine battery etc. Therefore is you were to use a single charger to connect all the batteries to charge them, you would negate the isolation and potentially end up with a bad battery draining a good one.

Therefore you need a charger per battery bank, or a charger such as the Sterling charger that has multiple isolated outputs allowing you to charge up to three different battery banks at the same time. I am assuming that your three domestic batteries are in parallel, therefore you need either two chargers or a Sterling charger, or similar, with multiple charge outputs. As well as providing upto three isolated outputs, the Sterling charger also uses four step charging to ensure that the batteries are conditioned.


VetChugger    -- Sep-26-2009 @ 4:15 PM
  I have a very similar setup Chris. My engine battery (i'm touching wood) has no problem holding its charge. The engine starts very readily so it doesn't pull much out and it obviously gets a good charge during running from the alternator. Its my domestics that need the occasioinal boost or top up. I'd be tempted to concentrate on those with your charger. Keith is right about what you would need to charge both sets, what he fails to mention is the kings ransom that Sterling charge for that sort of euipment! That is not a criticism of Keith I hasten to add! As it is, we need something like a 20/25amp charger at least to cope with the big domestic batteries and these are not free with a packet of crisps either!

Just as an aside, was there no electric on your pontoon mooring at Brundall Gardens?


Glen_Mist    -- Sep-26-2009 @ 4:20 PM
  Hi Keith

       Thanks for that info, i was aware of the need for the charger to be ass close to the batteries possible, it's the number of chargers i was unaware of.

I'll probably just stick to the one charger for now (for economy reasons rather than anything else) connected to the bank of domestic batteries (yes they are in parallel) as i can jump the engine start from them if need be   Playful   or use my boost pack (not that they in a bad way, but it's always good to have a contingency plan).

I had also though about solar panels (but decent ones are not cheap), or even hooking up an alternator to my excercise bike and getting 'The Brat' to earn her keep   Evil Grin

Thanks again

Chris J

Anybody want to buy a Birchwood 22?

Glen_Mist    -- Sep-26-2009 @ 4:30 PM
  Hi trevor

       Nope, no electricity on the pontoons where we were (and where you are now as you are in my old spot, it was me that put down the non slip patches), which is one of the reasons why we moved across to where you were, and with the new Seamaster there is much less of an issue with tide levels there.

As an aside, i have seen 6 amp Stirling chargers on Fleabay for £35 plus P&P

Also a rather nice looking 10amp Black and Decker for £26 plus P&P

Chris J

Anybody want to buy a Birchwood 22?

kfurbank    -- Sep-26-2009 @ 4:44 PM

A word of caution. If you do not use an intelligent battery charger, make sure your batteries are in good condition and well topped up with water, otherwise they will boil very quickly and soon be consigned to the scrap heap. My batteries are currently approaching 4 years old and good as the day they went on the boat. One other thing to consider is that for a 330AH battery bank, you should really be looking at something like a 25 - 30A charger. Most chargers in a car accessory shop are designed for car batteries up to 85A and will output 6 - 10A.


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