Re: Lithium Batteries under Consideration

Dean Gillies

Hi Courtney,
That's a tough lesson indeed.  Good luck with the Relion kit, that's a great amount of power for a good price. Unfortunately I cant get that kind of pricing in the UK.

Hi Scott/Brent,
Yes I've assumed I'll need to buy the Alpha Series 3 regulator if I proceed with Lithium.

Scott, regarding High Voltage Disconnect (HVD), the symptoms you have described are exactly what I'm hoping to avoid by using a 24V battery which is balanced end to end.  When a battery cell fades as you have described (increased resistance), and it's part of a series-connected string then the other cells and the other battery will be subjected to an overvoltage situation. If this overvoltage is sufficient to trigger a disconnect, then that string will be disconnected. If there are additional strings in parallel, then this should not cause too many problems since the other strings will assume the load and a significant voltage spike should not result. However, in this scenario I wonder how the battery with the faded cell will ever automatically recover, as logic dictates that the string with the faded battery will never be automatically re-balanced, and will shut down early on every full charge cycle.  What makes matters worse here is that the drop-in batteries have no mechanism to flag that this problem has occurred. The faded battery will just continue to fade, probably more and more quickly as time goes on. Having a system-level BMS like yours gives much more insight into such events and allows you to take action to restore the faded battery.

The high temperature disconnect is interesting. All the charging devices monitor their own temperature sensor, so the theory goes that they can self-protect.  However, the thing I've always had a problem with is where to locate the sensor.  If I've got 8 batteries and one temperature sensor, where do I put it? Near the top of the compartment is the likely sensible answer I suppose.  That would allow the chargers to react to a compartment-ambient temp inflicted disconnect where all batteries could possibly (unlikely) simultaneously disconnect. If one battery becomes hotter than the rest (most likely scenario), then that battery can dis-connect itself without causing system damage.  The high-temp cut-off for the RelIon 24V batteries is 80degC.

On the comparisons, my mind is still not made-up about life expectancy of the drop-ins. I know the theoretical cycle numbers look great, but we don't subject batteries to the theoretical cycling that the manufacturers test, so, for me, it remains to be seen.  I think the 12V drop-in pairs topology is particularly prone to earlier failure due to the hidden balancing problem.

As you say, personally my use-case for the boat derives no advantage from lesser gen-set usage, or overnight water-maker usage. In fact less gen-set usage in my case could well be classed as "under abuse".
Everyone has a different use-case for their boat, and if I was full-time liveaboard, I would go down the full-system path, maximise the solar, and certainly wouldn't be living aboard in Scotland lol. 

SV Stella A54-154


Join to automatically receive all group messages.