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Installation of new batteries for Nancy

posted Feb 14, 2016, 3:26 PM by Posts Editor   [ updated Feb 14, 2016, 3:28 PM ]
Brian Marriot writes:
'Just letting people know where we're at with the changeover of the batteries on Nancy.
In summary, she is serviceable and can take tours but there are still some things to be done. 
Thanks to Brian Pain for all the help, and thanks, too, to Martin Krynen for the financial assistance.
In detail:
1) the new batteries are in place, wired to the standards, and propelling her along very nicely. The old batteries are there, but no longer used for propulsion. They'll serve as ballast till replaced with something more appropriate. We were able to re-use the original high-current cable because the new batteries are closer to the motor than the old ones.
2) we think we'll get about 4 hours running at 4kt (25-30A), with some reserve for emergencies and to minimise deep cycling of the batteries. (Even Li-ion batteries last much longer if they're not fully discharged. ) 
3) the new charger produces about 25A, so recharge time will be not much more than usage time. We'll presume 5-6hrs charging for 4hrs running, as a starting figure. 
4) the batteries have a Battery Control Unit (BCU) in the battery locker), which protects them from overcharging and over-discharging. I'll put together a set of instructions for it, but in the interim skippers and testers need to be aware that the if BCU cuts off the batteries, it will sound an alarm in the binnacle beforehand, and show a message on its display. If that happens, note the message and press the reset button on the top. If the error state recurs, isolate the batteries and don't try again, but do notify me asap. 
5) there are two new switches, one on the back of the battery locker (labelled "main switch") and one within it (labelled "battery isolator"). Both should normally remain on. If you need to work on the electrics, turn off the main switch; only if you're working on stuff within the battery locker (or if an error is reported, as above) should you turn off the isolator. 
6) work remaining to be done: 
a) 12V auxiliary and safety circuits (radio, bilge pump & alarm, lights and horn) . 
Previously these were supplied from the motor batteries via a 48-12V converter. The problem with this is that if we lose the 48V supply we can't work the safety gear. So, for the moment, I have that gear running directly from one of the old batteries. It has enough capacity to do that in the short term. 
This all needs fixing up to standard, which will involve an appropriately sized new battery with fuses and isolator, but before I do that I have to at least get it set up so that the 12V battery is charged from the motor 48V supply. 
b) thermal protection for the Li-ion batteries. 
Li-ion batteries have a reputation for catching fire.  It's actually quite rare, probably rarer than lead-acid batteries blowing up from hydrogen leakage, but we've been dealing with that one for the last 100+ years, so it doesn't make the news any more. 
Our batteries are LiFePO4, which don't emit flammable gases, making them safer than other Li-ion battery types, but they still should be protected from overheating. The BCU can do this, but it requires extra thermal sensors. I've ordered these and will fit them when they arrive. 
I'll keep you posted as the extra work is done.