Why have a dedicated starter battery?

pvb said:
They can't be that knowledgeable, you could spend less on a starter battery than that magic device costs!
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But you should also factor in the cost of a the split charge system and additional wiring and fuses. Low loss splitters – sometimes recommended here – are not cheap.....
 
PetiteFleur said:
I know the current thinking is to have dedicated starter and leisure batteries, but I have two 110ah leisure batteries controlled by an (old fashioned) 1 both 2 switch, so you can choose whichever for engine starting/leisure and combine the two if one goes flat. In practice I use them alternatively and have rarely had to use both. I'm a fan of the KISS principle.
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Keeping it simple is actually much more complicated! I had exactly the same system as you requiring a fair degree of mindfulness about switching. My system is now more complex (separate starter battery, Sterling A2B charger, independently switched house and starting circuits with emergency linking) but is functionally much simpler. When I arrive at the boat I switch on house and engine start circuits and when I leave the boat (up to a month later) I switch them both off.
 
Engines use a lot of amps in a very short time, household uses less amps, but for extended period. That’s why you normally use deep cycle batteries for household and a starter battery for your engine.
 
Poey50 said:
Keeping it simple is actually much more complicated! I had exactly the same system as you requiring a fair degree of mindfulness about switching. My system is now more complex (separate starter battery, Sterling A2B charger, independently switched house and starting circuits with emergency linking) but is functionally much simpler. When I arrive at the boat I switch on house and engine start circuits and when I leave the boat (up to a month later) I switch them both off.
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One of the most sensible post i've read on here for a while :encouragement:

KISS is great, but keep it for the operator, let the system do the work.
 
PaulRainbow said:
One of the most sensible post i've read on here for a while :encouragement:

KISS is great, but keep it for the operator, let the system do the work.
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Unless you sail off the beaten track and it is better to either not rely on sophisticated systems or have a back up system you can employ when it all goes wrong.
 
Poey50 said:
Keeping it simple is actually much more complicated! I had exactly the same system as you requiring a fair degree of mindfulness about switching. My system is now more complex (separate starter battery, Sterling A2B charger, independently switched house and starting circuits with emergency linking) but is functionally much simpler. When I arrive at the boat I switch on house and engine start circuits and when I leave the boat (up to a month later) I switch them both off.
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I've got almost the same set-up and I consider it simpler than the dreaded 1-2-Both switch.

I turn on the domestics when I get onboard. I turn on the engine battery when I want to run the engine. And I've the 'link' switch to start the engine from the domestics if ever needed in an emergency.

You could argue the A2B charger isn't in itself simple but it does simplify the usage of the system. For example if I ever had to start the engine from the domestics the A2B would still charge the engine battery as well as the domestics.
 
Sandy said:
this is almost as good as an anchor tread.

P.S. I know people who have sailed from France to South Georgia and back without a fridge or air conditioning or even a TV!
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There are a couple of them in my club.... still using paraffin lamps and fathom charts.
Their mantra? "Don't fix what ain't broke!"
 
geem said:
Unless you sail off the beaten track and it is better to either not rely on sophisticated systems or have a back up system you can employ when it all goes wrong.
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Or indeed a system with some built in redundancy and components that fail safe.
 
geem said:
Unless you sail off the beaten track and it is better to either not rely on sophisticated systems or have a back up system you can employ when it all goes wrong.
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Nothing complicated or sophisticated about what was described. The addition of a parallel switch to use the house bank for starting in the unlikely event of the engine start battery failing is a useful backup. The important thing is that it avoids flattening the engine start battery which could arise if you rely on human intervention to select what battery is used. The small diesels used by most here only need a small dedicated start battery which is not suitable for use as a house battery so best to keep it separate.
 
geem said:
Unless you sail off the beaten track and it is better to either not rely on sophisticated systems or have a back up system you can employ when it all goes wrong.
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I completely agree. This is why i'd say fit separate switches and battery banks designed for purpose. There is nothing particularly technically sophisticated about that, just some on-off switches. Add a third switch for emergency starting and you have your backup system. If you were sailing off the beaten track you would likely have a sizeable domestic bank, but still only need a relatively small engine starter battery, so separate circuits make even more sense.

Split charging doesn't have to be complicated and can be arranged to fail safe. The simple VSR, with the alternator connected to the engine battery, will fail safe, leaving the alternator charging the engine battery and the option to use the emergency switch to allow domestic charging. Most of the Sterling devices fail safe, leaving basic charging. A FET based low loss splitter does not fail safe, but if located in an accessible place it's a very simple job to move the alternator cable to the engine battery terminal and have basic charging.
 
Tranona said:
The small diesels used by most here only need a small dedicated start battery which is not suitable for use as a house battery so best to keep it separate.
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Indeed. Mine is a small 28AHr AGM which, somewhat incongruously, arrived labelled up as a snowmobile battery. It sits above one of the main batteries, the other main has the charger sitting in the same place. This battery is quite sufficient to start a 30hp diesel.

Pete
 
Mataji said:
On a sailing boat with space for 2 batteries, why not have 2 leisure batteries rather than 1 leisure battery and 1 dedicated starter battery?
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Ignoring the usual arguments about 1-2-both and VSR that arise whenever somebody types 'batteries', I use the system already described by Tranona. My boat has moulded in compartments for three batteries, which originally contained 2 x 110 Ah for the domestic circuit, one similar for starting. I run a refrigerator full time for half the year and it seemed much more sensible to have three identical domestic batteries but there was nowhere obvious to put a starter battery. I managed to squeeze a small Red Flash AGM battery alongside the gearbox, which is quite adequate to start a small engine. I know someone who uses a similar battery to start a bigger engine, in this case lying on its side in the bilge beneath the sump.
 
>Engines use a lot of amps in a very short time, household uses less amps, but for extended period. That’s why you normally use deep cycle batteries for household and a starter battery for your engine.

Yes, deep cycle batteries, such as Trojan, should be use for domestic batteries and cold cranking amp batteries for start batteries. They are both designed to do different things.
 
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