Re: Converting my Amel 54 to lithium batteries: what I did, what I like and what I don't like (after one year of full time live aboard use)

Paul Brown

Hey Scott,

What individual SOC do you read on each battery in respect to out of balance with each battery please once a month before you recharge to 100%?

As I have mentioned, my #1 battery is dropping approximately 30% lower the the other 3 after around 2 weeks while the balance with the other 3 batteries are almost the same SOC by 2-3%. I’m discussing this issue on Monday with a Mastervolt technician to hopefully shed light on it. I expect the batteries should not be out of balance by a large degree.

Regards Paul - Fortuna II A55/17

On 7 Sep 2019, at 1:53 pm, Scott SV Tengah <Scott.nguyen@...> wrote:


Thanks for the link. 

I think your charging takeaways are for extreme longevity. I'm curious what the data is with respect to how longevity is affected by high charge currents. I do know that cell imbalances are more likely to occur at very high charge rates. I think Delos has over 220amps of 230v chargers and only 400ah of battery capacity, so they're doing over .5C!

The 90% max charge makes sense for the "normal" charge. I do know that Victron requires 100% every once in a while to (1) reset the battery monitor and (2) allow for intra-battery cell balancing. My procedure is keep it below 80% except for the once a month or two 100% charge for reasons (1) and (2). Then once a year do the battery-by-battery rebalance with my little 1.5amp charger. Seems to work well so far, but then again I haven't done a full capacity test.

I don't think the requirement to have a buffer battery applies to Victron. On an over voltage condition, the VE.BUS BMS simply turns off chargers - it does not disconnect individual batteries. There are downsides to Victron's way of doing it, but it does remove the need for a buffer battery. 

Yes, lifepo4 is very intolerant of overcharging (over voltage) and taking the batteries too low (under voltage). One uncorrected fault and the battery could be dead. The BMS is supposed to monitor and trigger a response via the charge disconnect and load disconnect to stop that from happening. Of course, that means the disconnects need to work perfectly. I think an additional safety measure would be to rig up a cheap piezo alarm that goes off when the BMS detects a fault. That would require human intervention, but at least if you're around, you have a chance to fix the problem if your automatic fault correction systems fail. 

I thought for the Mastervolt 24/110 the reg-on wire WAS the voltage sense wire? So if it's disconnected, the alternator would stop charging. But perhaps your loose connection showed (true voltage - 5v) or something, making the alternator think the battery bank wasn't fully charged?

Again, all these complexities lead me to choosing a single brand, to the extent possible, with a good warranty. I would rather not invoke the warranty, but I installed the system per their engineer's recommendations and if something went wrong, hopefully they will take responsibility. Try that with a Chinese battery combined with Brand X charger!
2007 A54 #69
SV Tengah

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