Still Required?
Ever since we published my thought that lithium batteries had come of age, I have been pondering whether or not they have reached a point of reliability that would make me comfortable installing them on an offshore boat without the lead acid serial backup we have recommended for years.
After all, we now have systems from Victron and Mastervolt that have, or at least can have if coinfigured properly, redundancy with two or more BMSs. So surely the time has come?
After giving it a lot of thought, I’m not convinced and would still install a serial lead acid backup to support critical loads while upgrading to lithium on an offshore boat of mine
Here’s why:
I would suggest another reason for a lead acid backup—lightning. I would assume that the lithium BMS’s are more susceptible to a lightning strike than their lead acid counterparts. While the other components in charging system are also susceptible, having an analog battery backup may provide the time to jury rig some charging until back to port.
Hi John and all,
I am putting together a lithium system, basically with Victron components and using 2 of my grp 31 gel batteries as starter batteries and, possibly, use as an emergency bank . They will be charged by a DC-DC charger off the lithium house bank.
In controlling my system, I do not have the usual off/on/both switch but rather separate on/off switches for house/parallel/starter.
This has been fine for combining similar chemistry battery banks, but I know the parallel switch will become useless and even dangerous as it would put lithium together with gel. But it seems to me, that there may be a possibility of using the parallel switch to bring my 2 gel starter batteries on line to power essential equipment were the lithium bank to have become unusable.
Three things jump out at me:
one would be ensuring that the lithium bank did not “pop” back into action and get into catastrophic mischief with the gels. Possibly accomplished by an isolation switch for the lithium house bank.
The second would be to be able to quickly change the charging algorithm, probably easily done with a Wakespeed regulator.
The third is that I would have to be diligent in monitoring the gel cell single bank with combined duties to ensure the engine would always be able to be started.
I am wondering what other considerations should be jumping out at me? And/or what designs others have put together.
My best, Dick Stevenson, s/v Alchemy