Battery Choices (House vs Start)

[kmclemore]

FYI, I was researching battery info for other reasons tonight and came across this nifty battery capacity calculator....

http://www.lifelinebatteries.com/marinesizing.php

Nicely done.

They also have an AC from DC calculator, too:

http://www.lifelinebatteries.com/marinesizingac.php

[Boblee]

Those tables are great for the layman Frank, it is fairly simple but there can be heaps of variations that cause complications eg making sure the battery is fully charged to start with.
The lifeline batteries are supposed to be pretty good and they are available here now.
One of the biggest problems I have encountered seems to be what is required to recharge or maintain full charge.
I struck a fellow camper who was running a 240 v generator all day and part of the night to try and keep two fridges cold, the generator was running an 8 amp battery charger.
His whole camper was set up by an auto electrician at great cost and yes it would do it if run 24 hrs or helped by the vehicle alternator while travelling.
With recharging you have to pump an extra 25% in, plus the amount required to top up.
As a battery charger senses higher voltage it cuts back the charge and so while it may be capable of charging 8 amps it may actually only deliver 2-4 amps for the last 25-30% of capacity.
Couple this with this blokes fridges running flat out and taking 6-8 amps he had no hope even with two batteries especially as his supply leads to the fridges were too long.
This meant he could only take the top 25% of the batteries anyway due to voltage drop as they cut out at 11.2v on the fridge terminals.
So much for the expert who wired it and assured him it would work.
The AGM batteries are great because they will accept high charge rates, with our honda driven alternator we can pump in 50 amps for two hours which means our fridge can run for approx 20-30 hrs depending on setting.
The bloke above would only be able to maintain his two fridges for 10 hr's even with our setup

[Boblee]

Kelly
If your emergency list says to take a battery topside I would still do it as while the battery terminals may not short out, it doesn't mean one of your other circuits won't blow the fuse supplying accessible power to where your radio is.
We have one battery under the v berth that is just strapped in and on a 50amp plugin connector but would still not like to try and get it out in an emergency.
Bob

[Frank C]

My 26X installation of two large batteries is under the galley-aft seat. It's not practical to remove either of them in emergency conditions. However, that's why my earlier comment ... wire direct from the battery to a VHF high-up in the cabin, fused only at the radio.

Leaving a long wire run 'unfused' until at the VHF is a violation of wiring SOPs. But with a "submersible" AGM, it gives reasonable assurance that the radio should work in an emergency, even after the cabin becomes flooded. Since I now have just marine-deep wet cells, they probably wouldn't survive a flooding, so the special wiring has no benefit.

[kziadie]

My batteries are in the conventional spot on the M, in the compartment under the companionway ladder. The batteries are held in by rubber straps which are easily removed and the terminal wires are connected by wing nuts so an easy removal is not unthinkable. I also keep in the battery compartment a 10 foot length of twin 10 gauge wire with alligator clips on one end and unterminated copper at the other to help with emergency jury rigging.

Hopefully I will never have to execute any of this, but it was just my paranoid mind at work when I was planning this stuff.

Kelly