On 05/11/2011 10:56 PM, graeme bird wrote:
> sounds good, I have an Odyssey PC310 fitted which is 2.7kg, its 8Ah
> and has a cranking current of 310 Amps.
Yep, I have two of these babies in my Europa. I have two fully separated
electrical systems (two alternators, two batteries) but use only one
system for starting. I have added a cross-over switch to tie both buses
(and batteries) together but I have never needed it. 8Ah is good enough
for starting.
However, if you have a 914 (like I have) you need the battery to keep
the fuel pump running in case of an alternator failure. In that case 8Ah
is way too small. So either you have to get a larger battery or
eliminate the single failure point by installing an additional
alternator. The latter is what I did and needless to say that both fuel
pumps are fed from a seaparate electrical bus.
When I designed this system I looked into the Lithium thing, but at that
time I decided that it was not reliable enough. Problem is the difficult
way of charging a Lithium battery, you can not just connect it to the
electrical bus like a lead-acid battery but need a very sophisticated
charge controller. Charge it wrong (a charger failure will do), and the
battery will explode or catch fire. This also happens if you puncture
the battery (like during a crash landing) There are plenty of you-tube
movies showing exploding lithium batteries.
Common advice is to keep Lithium batteries in a safety shell. But of
course this compromises the weight savings. With the dedicated charge
controller plus safety shell there might not be much weight saving left.
So I would recommend to use a PC310. It is safe, reliable, uncomplicated
and well tested.
Frans
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