Re: Always check your contractors' work


 Hmmm, I still don’t quite follow your explanation, Scott.
  If you have big enough cables from the batteries to the main 24V posts (ie no resistance at high amps), connecting at the post or the battery shouldn’t make any difference.  If they connected to one of the batteries in a series pair that is NOT connected to the main 24v post,  then the charge would almost certainly go to that battery preferentially.  If the cables are not big enough to give zero resistance, the charge would go preferentially to the closest battery.

If you mean that the + output cable from the MPPPs should be on the boat (load) side of the main battery switch, you would have to leave the switch “on” (“Marche”) to charge the batteries.  On Kristy with Victron Skylla-i Charger and wet cell lead acid batteries the output is to the + and - posts where all for pairs of batteries are connected in parallel.  The 3 MPPPs for the three pairs of solar panels are likewise connected to the same posts.  I can turn off the battery switch and still let the solar panels charge when I’m away from the boat.  The output can be monitored on remote panels, or by using the Bluetooth dongle on the MPPPs, but cannot be monitored with the primary 24V monitor which is on the boat side of the switch.  It’s not ideal because the four pairs are not completely balance-charged, but correcting that seems a lot more complicated.  So far this is working well for me.

Kent Robertson
S/V Kristy
SM 243

On Aug 20, 2019, at 2:42 PM, Scott SV Tengah <Scott.nguyen@...> wrote:

[Edited Message Follows]

I learned this through monitoring my batteries. 

The electrician connected the positive lead from the MPPT to the positive post of ONE of the batteries. His thought was that it would be like a bunch of interconnected cups. Once this first battery one got some charge, it would overflow the current into the next battery and so forth. I am no electrician so it sort of made sense at the time.

Well, monitoring showed me that this does not actually occur. The Battery1 that was directly connected to the MPPT was always higher voltage than the rest. The further away from the MPPT-Battery1 connection, the lower the voltage. The entire bank was being actively imbalanced!

Now I have the positive attached to the post where all the battery positives join. The batteries have remained balanced over the past year.

I can't remember where I read it, but a marine electrician stated that "in case it wasn't obvious, you connect the MPPT output to the load." I don't quite have it perfect as it's where all the batteries join, but I'm going to relocate the MPPT anyways, so I'll connect it to the load then.

Sorry, if my explanation isn't precise enough as I never studied engineering. Just lots of reading, lots of testing and lots of monitoring.

2007 A54 #69
SV Tengah

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