Wow so many great posts and interesting over the last few days. So here is my 2 Cents worth on a lot of different subjects.
First off again my system.
Lagoon 410 E
144V twin Electric Drives
12 - 210ah AGM’s in Series for the Propulsion bank
4 – AGM’s for the House bank at 120ah (480ah total)
16KW Genset Rectified to 144V DC (variable output up to 165V savely)
No solar
So first off, like Capt. Mike, I’m pleased with the service of the AGM’s for the Propulsion bank and to date I have 8 years on them. The boat came with LA’s and those lasted about 2 years before needing replacement but Lagoon is known for having shitty batteries from the factory. The AGM’s are Northstar and heavily used in the telecommunications industry as battery backups. I have a Balancing system as well as the PakTrakr monitoring system and maintain the batteries as best as I can.
With that said I would jump on a set of LiFePo4’s in a heart beat if I knew when these AGM’s where going to go bad.
Eric’s analysis of the different batteries out there is spot on. I’ve read a lot of posts and a lot of papers on them and with out a doubt these are the latest and greatest SAFE Lithium’s out there. There are a lot of even higher bred’s when it comes to Lithiums but as far as I can tell the LiFePo4’s meet all the requirements that we need to run EB’s.
Now I know this is a statement from someone most of you have no idea who I am and someone who doesn’t have LI’s installed so take it for what it’s worth.
Second running electric motors from a genset.
Do it all the time. Since my genset is variable output I can set the voltage to whatever I want it to be. If I need to charge the batteries while running the motors I can set the output to say 160V (or higher) at 80A and run the motors at 60A (total). The rest goes to the batteries. Once I get close I can reduce the output of the genset to the Motor load only. Nothing goes through a charger.
I saw one post about charging the batteries with the Alternator being a source of problems.
It’s amazing what some people are doing to their motors when it comes to oversized Alternators. Double pulleys, external regulators, modified mounting frames. Since I have a healthy Genset to start with I have 1 dedicated, maintenance free, high Cranking Amp battery with a stock, ready off the shelf, dedicated Alternator, nothing else to screw it up system. O, and a set of jumper cables to reach the house bank and 1 spare auto charger in case I somehow drain it anyway.
Here’s what I do know about LiFePo4’s vs all other older tech bats.
AGM’s and LA’s
Can be charged to 100% and then trickle charged.
50% discharge then Recharge
Will self discharge over time with no load.
Life expectancy about 5 years if cared for. Seems to be the main cause of death is undercharging.
LiFePo4’s
SAFELY discharge to 90%. That’s an increase in run time of at least 30%.
Charge to 90% (or 95% with no known issues).
Maintain their charge indefinitely with no load.
Charge to max 95% then SHUT THE CHARGER OFF! Never trickle charge. The worst thing you can do to these batteries is overcharge them. I’ve seen reports and studies of drawing the LiFePo4’s down to 0% and brought back to life with no known issues. Note that the life expectancy is the only thing we are not sure of when doing this to often.
Bottom Balance the pack. A lot of controversy on this still but I’ll go with Jack on EVTV on this one.
Some one said ”I think Li’s need to be charged faster”. In fact they can be charged faster at a higher rate than LA’s but they don’t have to be. I plan on using my Brusa charger for charging at 16A my 144V pack of 48 bats (when I get them). It’s done all the time, the EV crowd wants to pull into a station and charge at ungodly amounts of power quickly. See Tesla charging stations.
To BMS OR NOT TO BMS:
Another controversial subject where “M” is either “Management” or “Monitoring”. For me Monitoring is a must. Management is a byproduct of Monitoring therefore not required.
John,
“From the BatteryUniversity.com site, it sounds like charging Li batteries to 4.1V per cell, and stopping there will extend the life of the battery bank, and provide a bit more guard band to avoid problems.”
4.1V sounds way too high. From what I’ve seen 3.8seems to be the going number but YMMV. Each battery manufacture has a different number so double check the max V number! This may also be old info…
My unknowns:
I’m not an electrical wizard like a number of people here. I don’t quite understand the use of relays to control the charging of the batteries. I have an issue wit the Brusa charger shutting off all together for no reason I can come up with other than it’s been on charge for an extended period (14+days) in trickle charge. Something we as boaters tend to do if we are weekend cruisers. Brusa tells me it’s a safety issue but the charger has a 999 hour run time built in. I assume that most of the other chargers mentioned over the last few days, Elcon, Victron, and such don’t have an issue with this. But with Li batteries there is no Trickle charge. The Relay would be what would control the on/off cycle. I just don’t get the “how to do it” thinking. Also most charger profiles with Li’s don’t have the multistage charging. Bang it in until a set point shuts it off.
Some good reading:
This is a string in the Cruisers Forum on House banks but most of the info would apply to propulsion banks as well. Very looooong but interesting.
Also a well written tech article from Jens Groote “State of health Estimation of Lithium Batteries”
http://webfiles.portal.chalmers.se/et/Lic/JensGroot.pdf
And finally I wish we could save info like the “DIY Electric Car Forums” do but for boats. Yahoo is such a pain when it comes to searching. Having specific “pages” dealing with specific issues would be such a help.
Steve in Solomons MD
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