Re: Alternator charging a Lithium bank


Doug Smith
 

Great feedback Scott, Dominique and Dean. I feel like I am in a “masterclass”.

I was thinking of the Sterling APD, in the same way you use fuses for the batteries.  It is unlikely that the 450 fuses would blow, but having the APD installed gives protection to the alternator, if there is a disconnect of the batteries for any reason.  Not just cutoff of the BMS, but a disconnect for other reasons like a blown fuse on the Cerbo, or BMS, or even the main battery fuses while the engine is running.  Maybe overkill, and that is why I am putting this out there. Trying to learn from those who are already doing the installation and living with it, while I am buying pieces. 

 

Doug Smith

S/V Aventura, Amel 54-113

Patuxent River, MD USA

 

From: <main@AmelYachtOwners.groups.io> on behalf of Scott SV Tengah <Scott.nguyen@...>
Reply-To: <main@AmelYachtOwners.groups.io>
Date: Thursday, February 18, 2021 at 3:29 AM
To: <main@AmelYachtOwners.groups.io>
Subject: Re: [AmelYachtOwners] Alternator charging a Lithium bank

 

[Edited Message Follows]
[Reason: correction: cerbo vs. cyrix confusion on my part]

Doug/all,

That Cerbo GX is pretty powerful! I just skimmed the manual and it certainly provides a lot of cool features. If I was building a system from scratch, I would possibly consider adding it, although the parasitic draw of it and the DMC (which you are required to have if you have the Ve-bus BMS and want to also be able to turn off your inverter - see manual) starts to add up. I went down this road to minimize generator usage, so I am willing to give up some cool features to achieve my primary goal. 

That said, I agree with Dean on minimizing the number of devices/connections that need to work perfectly to keep my expensive Victron batteries alive. One single connection/device failure, ONE TIME, could kill a battery. Not great when you're in the middle of the Pacific. My caveman relay system was "designed" so that if they fail open, the worst case is that the alternator stops charging prematurely. If they fail closed, the MV Alpha Pro II will still stop charging at 27.4v or thereabouts. A low enough absorption voltage that you're well out of the knees of the voltage curve, so per Victron techs, the likelihood of a cell over voltage that is masked by the bank voltage is very very low. If you go the Cerbo route, I suggest you do the same with respect to MV absorption voltages. 

Maybe I am missing something important, but why is the Sterling APD necessary on a mostly Victron system? The over volt/overtemp is dealt with by turning off the MPPT,Quattro,Skylla,MV Alternator and ceasing charging - you will not have a hard disconnect event with the alternator pumping out full output. On a low cell voltage event, the Victron solution is to cut off the loads. The batteries are still connected to the charging side if I recall correctly so the alternator will not experience a hard disconnect. In any event, low voltage disconnect is a missing piece on my system, as I mentioned in previous posts. My installation of the Victron BP-220 was unsuccessful and I intend to wire my system so that the Onan starts if SOC gets below say 30% or possibly if cell voltage is below 3v. To be continued.

Dominique - you can adjust the charging voltages on the MV if that helps. Start with the Lithium profile and adjust as you feel appropriate. That said, I personally think the LiCT and the Li Charge are adding unnecessary complexity. For reasons mentioned above, if I can achieve the same functional result, I would rather go simpler vs. more complex.

Dean - I think that without the BMV-712,  the Cerbo wouldn't know how many AH the MV alternator is putting into the batteries? Maybe it gets that value from its own shunt?


--
Scott 
2007 A54 #69
SV Tengah
http://www.svtengah.com

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