Small starting batteries - motorcycle battery?

Ruffles

Ruffles

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26 Feb 2004
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Boat: Portsmouth, Us: Stewkley
www.soulbury.demon.co.uk
Thinking about fitting a small dedicated starting battery so I can increase the utility capacity. Took a car battery down to the boat and couldn't find anywhere sensible to mount it.

Now, I could buy one of these red-flash hugely expensive things

OR

I could try a motorcycle battery. What do you think? It has the cranking amps. It's cheap. And it can be topped up.
 
I use them on the Honda Pan (1300cc) and it's kept charged by an Ultimate battery charger. Excellent pice of kit. Now 3.5 years old.
 
The CCA spec is within requirements. And it is slim enough to attach to the wall of the engine compartment. If it starts your mc it should work with a 30hp diesel.

I believe the terminals are different on MC batteries but that's easily sorted.

I thought as step 1 I might just forget about VSRs and diodes and just wire the thing in. I have the old style 1,2,both switch and live in fear of my son switching to 'off' when the engine is running.
 
I used a battery from a Fiat Uno. They are much smaller than, say, a Ford Mondeo battery but were plenty big enough to start my Yanmar 2GM20.
 
I have a proper battery tester and a clamp meter so I know more about this than most. The cranking current on a Yanmar 2GM20 is anything up to 200A. I've tested motorcycle batteries on my tester which gives a direct readout of CCA and the two I tried give a suprising approx 250A from something about 1/4 the size of a small car battery. I've never tried starting a diesel engine on one but I would take great care not to melt the battery with the high current density. I think the smallest diesel car battery is as far as I'd want to go personally.
 
Thanks for that.

I've got a fast DVM with a peak hold facility. If I splash out on a current shunt I should be able to get some meaningful measurements. It's a fairly modern MD2030 so has a smaller flywheel than the older engines. Not sure if that reduces the peak current or increases it!

The volvo manual states the recommended capacity for the battery (70Ah). They rate the starter as 1200W so the battery needs to deliver up to 100A. What that means in actual use I've no idea....

Edit: Where did you get your DC clamp meter? Haven't been able to find one at sensible prices.
 
There's always something on ebay. Look for current probe, LEM or HEME. Make sure it's DC as well as AC and you want a 200A range or less as well as the usual higher ranges. I've got a probe which goes on a meter or scope as well as a self contained unit.
 
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I really don't think I could get any car battery to fit unless I put it low down near the stern gland which is far from ideal. MC batteries seem to be tall and flat. Ideal for fitting alongside the engine.

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Have a look at the Barden Batteries website. I was able to source a physically small 320CCA 12V battery to start my engine - they give the physical dimensions and the smallest size seems to be 175x175x190 mm 360CCA
 
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