Battery Capacity-Advice please

[sona]

I have a Sun Odyssey 24.2 with 1GM10 engine with standard 35A alternator and single battery of 70AH (6 years old but not giving problems).
When sailing I am using speed/depth instruments, vhf and chartplotter with the intention of installing a tiller pilot.
I an concerned that the battery will run down and cause engine starting problems. Should I install a second battery either in parallel or seperate with changeover switch (space would be a big problem), or replace the single battery with a larger capacity battery?

 

[sailorman]

1GM has a starting handle /forums/images/graemlins/confused.gif

 

[KenMcCulloch]

[ QUOTE ]
1GM has a starting handle /forums/images/graemlins/confused.gif

[/ QUOTE ]So it does but starting it by hand is some where between extremely difficult and impossible. I would go for a second battery as a dedicated starter supply with either a changeover switch or one of the various automatic systems for battery management (voltage sensing relay, diodes or whatever). You only need >200cca to start the engine so quite a small battery will do that.

 

[sailorman]

My Sons starts very easily perhaps depends on access.
i could hand start my old YSE 12 /forums/images/graemlins/ooo.gif

 

[charles_reed]

Well I did once

start my 2GM20 by hand, but only by dint of superhuman effort induced by total terror.

I'd agree a small dedicated engine battery is a prudent move - the starter motor on both 1 & 2 GM are the same a 2.5kW unit and a 28-35 ah cranking battery should be good for the job.

 

[RestlessL]

Re: Well I did once

You will probably be surprised at how small a suitable dedicated starter battery is.

John

 

[john_morris_uk]

Further to what the others have said, you have only 30 or 40 Ah (Amp-hours) or so of 'useable' capacity with your single battery. You might only have a few hours of sailing before you need to recharge with your current system. Check the current consumption of all the items you have mentioned. Chart plotters are often quite power hungry.

I remember a friend who ran out of power three quarters the way across the channel. He said, '... but the batteries must have been fully charged when we started - we'd motored down the Tamar.' Doh! (...as if motoring for half an hour or so is very likely to fully charge your batteries, even with a smart alternator controller!)

 

[pvb]

You have too little battery capacity. You should look at installing extra batteries - these can be some distance from your existing battery if necessary. It would be wise to have a separate engine starting battery; this need only be quite small.

I have an intense dislike of 1-2-Both switches. If you upgrade your system, consider having a voltage sensitive relay (VSR) between your starting battery and your domestic battery(ies). Your alternator output should go to the engine starting battery. This will ensure you can quickly start the engine.

 

[VicS]

Your service battery should be adequately large for you to never normally run it below about 50% of full capacity but you do not want one that is far larger than necessary as that will cost far more than necessary when you have to replace it.

A dedicated start battery may well be physically quite small. Only a small capacity is required, it just has to be able to supply the current required

With two similar batteries a <u>good quality</u> 1, 2, both, off switch is the most convenient isolating arrangement but separate isolating switches are preferred by many because there are so many rubbish 12both off switches around.

If you opt for a small engine start battery although it could be switched in the same way it might be better to make it purely an engine battery with some form of split charging circuit; diodes, VSR or X-split. Some alteration of wiring might be necessary to install it as a dedicated engine battery. Some switching will also be needed if is to be possible to start from the services battery. Personally I feel it should always be possible to start the engine from either battery if the need arises.

It would be possible to locate an engine start battery away from the services battery perhaps leaving space to increase the size of that if calculations indicate that the present one is undersized.

 

[William_H]

This is an excellent time to add a domestic battery. The start battery will die soon if it is 6 yo. Mount the domestic battery somewhere convenient. Connect the negative to the engine and start battery negative using heavy cable. Move all the power supplies for domestic services to the new battery via a switch. It can be relatively low current simply to carry the domestic load. ie 20 amps rating.

Run a cable via a switch from the engine +ve to the domestic positive. This switch should be rated at least 40 amps. If you have the cash this switch can be replaced by a VSR.
So after the engine is running you operate this switch to charge the domestic battery then turn off this switch when engine is stopped to isolate the domestic load from the engine battery. This function can be carried out very neatly by a VSR. That is a Voltage sensing relay which senses when the engine battery rises to usual charging voltage and so connects the domestic battery for some charge. it opens the circuit when the engine battery voltage falls to around 12.5 volts because it is not being charged.
Some VSR can make the connection domestic to engine battery to boost the engine battery in an emergency when engine battery dies.

If not get a single boost (jumper) cable heavy wire for that time when you need to boost the engine battery with the domestic battery. (don't go for 1,2,both switch although it will do the job)
good luck olewill

 

[sona]

Thank you all for your advice and will act on it.
I sail the west coast of Scotland single handed and need to be confident that my engine will start.
Thanks again

 

[Georgio]

Hi,
Another vote for practicing with the starting handle. I can start my 2GM just and I'm not a superhuman in any way. It's more of a knack thing rather than brute strength.

Alternativly you could swap your 85AH batt for a larger one (if you have the space).

Just my thoughts.

 

[PIGLETSDREAM]

Word of caution when hand starting. I used to hand start my Trapper 500 all the time, until one day the key attached to the end of the crank broke. Spoke to Yanmar who wanted to sell me a new crankshaft and implied that hand starting should be reserved for emergencies only as that is how it had been set up and that it was no suprise that it had broken as it was never designed to be always hand started.

 

[Tranona]

Good time to rethink your system. Definitely need a dedicated engine start battery and probably a larger service battery. For my 1GM I replaced 2 conventional 65 amp lead acid with a micro engine start and a 105 amp AGM in the same physical location. Switched and controlled by BEP Marine switch cluster that has a VSR and an emergency parallel. The beauty of the engine start is that not only is it small, but can be mounted in any orientation.

Merlin at www.power-store.com are very helpful and can make up an installation package with cables and bus bars etc.

Usual satisfied customer stuff!