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Eli Hunter avatar image
Eli Hunter asked

Multiplus 2 with Lynx shunt brief voltage drops

I've had this system intalled for a bit over 3 years now for our house. I'd left it disconnected for about 2 weeks while we were away and when I started running off the battery again I got several DC ripple warnings followed by low voltage warnings several times per hour. There is no corresponding current draw when the voltage drop occurs. It happens with and without load on AC output and with AC input connected or disconnected.

The battery is made up of 2xTesla modules with SimpBMS connected to a VenusGX. There's also a Lynx Shunt in line between the batteries and Multiplus units (split phase setup).

I found Victron is reading down to about 11V for several seconds while the BMS is reporting normal voltages the entire time. I've inspected the wires and terminals. I also removed wires between the battery and Lynx shunt, cleaned terminals, and reconnected. If it matters I'm pulling data from /battery/DC/0/Voltage (shows voltage drop) and /battery/system/MinCellVoltage (no voltage drop).

I'm suspecting the Lynx or Multiplus is having trouble determining the voltage. Anything else I should be checking?

Multiplus-IIHelp
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3 Answers
JohnC avatar image
JohnC answered ·

@Eli Hunter

If you have a battery isolator switch, check it internally for damaged contacts caused by arcing.

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Eli Hunter avatar image
Eli Hunter answered ·

Thanks John, finally got around to working on this and decided to just replace the contactor in my BMS just in case. Within a couple hours of connecting things back the Lynx shunt showed a voltage spike while the Multiplus and SimpBMS both show normal voltage. I'm suspecting an issue with the Lynx shunt reliably reading the voltage.

Can anyone confirm I'm monitoring the correct voltages?
1) battery/Dc/0/Voltage - Lynx Shunt
2) battery/System/MinCellVoltage * 6 - SimpBMS minimum cell voltage * 6
3) system/Dc/Battery/Voltage - Multiplus DC voltage

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Eli Hunter answered ·

I figured this out, it was stupid. In case anybody else runs across this the BMS is powered through a battery protect module. When I left on vacation I disconnected the leads from the battery protect. I forgot it's directional when hooking the battery protect back up which I suspect was causing the BMS to lose power briefly under certain circumstances.

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