one battery or two that is the question

stepheneyre · 16 April 2009, 00:08

hi all i have just fitted a 150 hp engine to my rib and find the battery struggles to start the engine (had the battery tested its ok and fully charged)

i am thinking do i get a bigger 1 with a higher cranking power or do i put twin batterys on

i have room at the front in the console to do this

if i do twin up do the batterys do i need the same power or can i just connect 2 together + to + and - to -

would 2 affect the electric,s

thanks for looking

any advice would b helpull

steve

BogMonster · 16 April 2009, 00:25

How big is the battery? Unless it is a bit weedy I don't think it should have a problem spinning over what is only I think around a 2.6L engine.

Anything decent that will provide say 600 amps plus of cranking power shouldn't have a problem at all - that will start a diesel of that displacement never mind a petrol. What CCA and Ah is printed on the battery? If its 70Ah and 600 amps CCA or more then I think you need to look at other causes e.g. faulty connection, bad earth, dodgy starter motor etc.

Unless you have twin engines and separate electrical systems or some sort of split charge arrangement I can't see any real benefit in having two batteries rather than one big one so one big one would be my suggestion. I have heard (on vehicle installations) that two batteries permanently connected + to + and - to - can self discharge due to current cycling between the two when everything is switched off, but I don't know if it is even common or even true - I've not seen it.

Just my 2p, I'm no expert on boat systems but I do spend a fair amount of time peering at vehicle electrics which is much the same as a boat but without the complication of salt water

codprawn · 16 April 2009, 03:17

My Discovery has a pretty weedy battery - about 75a/hr but it starts a 2.5 diesel even in cold weather = there should be no probs with a big outboard.

IF the battery is fine - and the tests don't always work - then check the cables - either too long or too much resistance etc.

chewy · 16 April 2009, 06:58

What size cable have you got fitted, welding cable works well!

dougcrock · 16 April 2009, 09:23

I had probs on previous rib where water had turned copper black and caused loss of power volts to engine every thing looked ok and battery was good had to replace complete starter cables

PeterM · 16 April 2009, 09:53

I have 2 - one runs the auto bilge pumps & after heavy rain for a few days will struggle to start the motor . So hence having the other one to be sure I have a 'full' battery to start with.

I have also had probs where corrosion of the wiring dropped the voltage to the point of not being able to start the motor - and you only can see/ measure the drop when the battery is underload - again cables replaced & no problems. Cut the sheilding off the cable & you could see the corrosion.

jambo · 16 April 2009, 10:36

HI Steve, like Blackroady I have two fitted. I use my boat on the wset of scotland and sometimes it maybe 2 weeks in between visits so with rain and natural discharge I have found thru experience that two is best with a battery switch. I have 2 120ah's squadron marines and they work fine. I found last year I was not starting well and my engineer spotted the problem my negative cable from batteries to engine was more than 60% corroded and therefore not enough charge was getting thru to turn my 150 2st mariner. So do achech on your cables especially if there is a long run from consul to engine under deck.
Hope this helps

J

Downhilldai · 16 April 2009, 13:00

Check the MCA/CCA requirement of your DF150 and, as you have the space, I'd suggest you fit 2 batteries of at least that rating, connected via a changeover switch (batt 1/batt 2/both/off).

Also check the cabling, as mentioned above. The installer of the motor should have done this.

codprawn · 16 April 2009, 13:05

Quote:

Originally Posted by Blackroady

I have 2 - one runs the auto bilge pumps & after heavy rain for a few days will struggle to start the motor . So hence having the other one to be sure I have a 'full' battery to start with.

I have also had probs where corrosion of the wiring dropped the voltage to the point of not being able to start the motor - and you only can see/ measure the drop when the battery is underload - again cables replaced & no problems. Cut the sheilding off the cable & you could see the corrosion.

My single 120a/hr battery will start the engine after 2 months of heavy rain and there is no cover on the boat - and Wales is pretty wet!!!

jambo · 16 April 2009, 13:12

Quote:

Originally Posted by codprawn

My single 120a/hr battery will start the engine after 2 months of heavy rain and there is no cover on the boat - and Wales is pretty wet!!!

A but prawn you get 'special' rain in wales!!

J

codprawn · 16 April 2009, 14:13

Quote:

Originally Posted by jambo

A but prawn you get 'special' rain in wales!!

J

Oh it's special alright - you can have as much as you like!!! in fairness it's been pretty good for the last few weeks save for a couple of bad days.

the weather forecasts seem to have been totally wrong for the whole of the Easter bank holiday - thank god!!!

jambo · 16 April 2009, 14:17

Quote:

Originally Posted by codprawn

Oh it's special alright - you can have as much as you like!!! in fairness it's been pretty good for the last few weeks save for a couple of bad days.

the weather forecasts seem to have been totally wrong for the whole of the Easter bank holiday - thank god!!!

Yea I am just back from an other famous wet area Argyll and had a wonderful rain free sunny easter w/end! Unfortunatly I was antifouling!!
Never mind as long as there long range 4cast for the 'hottest@ summer comes true.

J

codprawn · 16 April 2009, 14:22

i think it might - the last time Swansea marina froze over we had one of our hottest summers ever and it froze over again this year!!!

PeterM · 16 April 2009, 15:51

Quote:

Originally Posted by codprawn

My single 120a/hr battery will start the engine after 2 months of heavy rain and there is no cover on the boat - and Wales is pretty wet!!!

Thanks Cod - but us Opti owners need special electricity for our sensitive motors

. Seriously something still isn't 100% but its being reliable at the mo ( rather than not starting at all like times during last summer ) so I dont want to disturb anything .

I forked out for 2 new batteries, switches & cabling over the winter so need a break before I try & find the real problems ! Have also gone down from 2 x 110Ah to 2 x 85Ah - so that cant help !

m chappelow · 16 April 2009, 17:07

my old fishing boat had 2 batterys even though it was a 12 volt system owing to the fact they were crap batterys in the first place ,i changed them for one decent battery and had never any problems ,if you do decide to put 2 together and its a 12 volt system they need to be wired right otherwise you will get 24 volts ,

chewy · 16 April 2009, 19:07

Sorry if I'm stating the obvious to some people but two 12v batteries in series will create 24v and in parallel 12v but will last twice as long.

http://www.nyc-arecs.org/Connecting_...d_Parallel.pdf

HUMBER P4VWL · 16 April 2009, 21:24

might sound stupid, but we recently went from a 90 3 cylinder opti where one battery turned it over very rapidly. We now have the v6 2.5ltre 175 which is the same block as the 150, this has two batteries but importantly it sounds like it is hardly turning over when you start it, and i have heard 3 engines like this. It sounds like it only turns over twice before starting, wheareas the 90 turned over like a car. Also, it sounds the same with one battery isolated, so you dont need two to turn it over.

Hope this helps.

Erin · 16 April 2009, 22:23

If you are going to replace your starter cables, I strongly recommend using the Ancor Lifetime cable. It's tinned so it won't suffer corrosion like normal auto cable. This way you can really fit and forget. If you've got good cables, and the power can get through to the engine, there really isn't any need for a second battery, unless you have a lot of electronics that are used when the engine is off. In which case a dedicated 'domestic' circuit is a good idea so you don't drain your start battery.

jyasaki · 17 April 2009, 16:53

Quote:

Originally Posted by Erin

there really isn't any need for a second battery, unless you have a lot of electronics that are used when the engine is off. In which case a dedicated 'domestic' circuit is a good idea so you don't drain your start battery.

I have two batteries, both wired up identically, but through a selector switch. Just have to remember to switch it occasionally to charge the non-selected one. Bottom line is that I run the motor, lights, and electronics off whatever is selected, and have the second battery (theoretically) fresh in case the first is depleted.

How you wire up a pair of batteries is not as important as understanding the system and using it appropriately.

jky

BruceB · 17 April 2009, 18:20

I ended up fitting two batteries but fed through a VSR with switch. The switch gives off-batt1-batt2-both but when left in either batt1 or batt2 will isolate and auto charge the other battery whichever one this is.
Always gives me a spare battery no matter what I do, has worked well since installed.
The battery management is automatic and doesn't rely on making sure the second battery is kept charged by switching etc