First post here.
We currently have a couple of Seahopper folding dinghies (8' / 10') that we can sail, row or outboard. We don't live on the water so only get out when we get the chance, when the weather is nice (in the UK?) and have the time etc.
I have a Yamaha badged Minn Kota (M12) that is the baby of the line-up and draws a maximum of 30A on speed 5 of 5 and ~15A on speed 3, which is about as fast as we are allowed to go on many UK rivers and canals. We aren't interested in the sea as it's bad enough trying to plan a trip as it is, let alone having to deal with tides etc. ;-(
I picked up a nearly new MK 60Ah traction battery quite cheap that is rated at 1000 cycles with a DOD of 50% so at 15A so I'm looking at around 2 hours cruising. I'm also going to run some tests with a PWM controller as I understand the 'speed coils' these outboards ('trolling motors') use to give the lower speeds are very inefficient. The only real problem with our current setup is the weight of the LA battery (around 17.5kgs, about the same weight as my 2.5hp 4/ Mariner outboard). ;-(
Now, I've looked into alternative battery chemistries and can get a 96Ah worth of LiPo 'battery' (4S12P) at around 10kgs (with a suitable box etc) but I'm really not sure the cost, effort and attention needed, really justify the result / usage? ;-(
Like, with two or three 36Ah LA batteries I can reduce the weight of each battery to something manageable by the Mrs and don't really have any weight issues once they are in the boat. I wouldn't have to buy any special high current and sophisticated chargers (or fireproof enclosures) as the LA battery can be charged and left at 100% charge 24/7 (Optimate). This is handy in case we decide at the last second that we want to go boating.
Soft pack LiPo on the other hand would give us say 96Ah (6 x 16,000 mAh) with an 80% DOD but would need to be kept at a 'storage voltage' and charged to 100% prior to use, requiring some serious charge power (I only have an iCharger 1010B+ ATM) and 'attended' charging, plus careful monitoring of the cell voltages in use, not just to prevent over-discharges from ruining the capacity but to minimise the risk of worse. Not maintaining a LA between uses just risks the battery, I'm not sure that is the case with Lithium?
I could fit such LiPo packs with a suitable BMS but the other risks from Lithium based batteries are still present that I'm not sure exist at anything like the same levels with say LA (or even Nicad or NiMh etc).
So would LiIon be a suitable compromise (safety over capacity / price) as they seem to be more commonly used in EVs but are still more 'needy' when it comes to charge / discharge voltages (again, when compared with LA).
I understand that if weight and performance are paramount (eBikes / scooters), then Lithium batteries are the only real option and make more sense when high cycle counts are also required. If we were to go boating 10 times a year and discharge a good traction battery to 50% it will still probably outlast us! ;-(
So, am I being over cautious re the risks (and obligations) when running Lithium based batteries in this sort of role (not to mention the mix of Lithium and water) or is there a Lithium based solution that really would just be a straight replacement for a LA traction battery?
What about these 'drop-in replacement' ~12V Lithium monoblocks (with built in BMS's) that you can now get for golf buggies and the like? A 60Ah would still be much lighter than my current LA and as long as the BMS could cope with 30A continuous (worst case) ... could that work?
Cheers, T i m