This isn’t really a question – it’s a strange problem and solution that might help someone in the future.
My existing system was a MultiPlus (MP) and 4 SmartSolar (MPPT). It worked wonderfully. I also had an option on the MP – a SmartDongle (SD). The SD is a small box, maybe 1.5" wide, 1" thick, and 4" long. It hooks to Battery +/- (on the terminals), and double-tapes to the battery. It also has a CAT5 to the MP. Once configured, it provides battery voltage to both the MP and the MPPT (the classic “battery sense” lead so you get battery voltage without drops), battery temp to the charge sources (for temperature compensation), and bluetooth insight into the MP. Works great.
LEAD IN TO PROBLEM
I am nearly complete with an upgrade to a DIY LFP battery. I am using an external contactor-based BMS that has an ATC output. To allow control of the MPPT (Victron is really sloppy with their MPPT and ATC), I have inserted a BP220 (220A) into the output of the MPPT. I also use this to interrupt two poorly regulated power supplies – a Watt and Sea and a Victron Centaur (50A output, input between 120 and 250AC, 50 or 60hz, or DC up to 450V – awesome flexibility!). My BMS can modulate the ATC lead, this is important becuase it allows me to let the battery back off after full charge, and also because the ATC limit is also the “reset SOC” limit – I MUST hit the ATC limit with at least one of my charge sources. So the BMS frequently turns off the BP (at least once a day, hopefully). Unfortunately, the BP won’t turn back on – it yields E1 “Short” and E4 “Over Voltage.”
THE PROBLEM
Here’s what happens. It’s undocumented. Victron manual talks about the “Short” with inverters, or some issue with wire length, or…well, none of it applies. The Victron Community is equally unhelpful. When the BP is “off” because the BMS has shut it off, the MPPT aren’t connected to the battery. They see a battery voltage (through the SD over bluetooth) that is too low, so they try and raise the volts. Nothing happens, so they keep going till they peg the system (around 16 or 17V at the input to the BP). This yields the E4, “Over Voltage.” When it tries to connect, it yields the erroneous E1, “Short Circuit.” A quick tap of a screwdriver across the BP terminals(with no sparks) gets it going, and battery charge of 10-20A commences.
THE SOLUTION
While slightly less than ideal, I’ve moved the power leads for the SD to the MPPT side of the BP. This allows the MPPT to regulate the voltage such that the MPPT sees 14V or so. The BP then happily connects the MPPT to the battery with no errors. This unfortunately isn’t quite ideal, as my sense point is separated from actual battery voltage by a BP, 5 feet of 4/0, a 400A fuse, a battery switch, and a handful of terminals. However, I’ve measured the total voltage drop at 20A of charge at about 20mv, insignificant. It’s higher at higher amps, of course – but if I’m pushing 100 or 150A, I’m ok with a bit of error.
The most important thing to realize is that if you have an E1 Short Circuit error on a Battery Protect (when used to control charge sources), it may be a result of an external voltage sense, and be unrelated to a short circuit.