David avatar image

Disable Multiplus & MPPT charger at low temp for lithium batteries

Hi All, (we have read Schnitzel's question from Feb 7 and found info/response valuable)

An off-grid installer customer of ours is preparing for a tinyhouse install (with self managed lithium) in an alpine area that will get snowed in over winter. I'm keen to offer him a couple of options for him to disable charging when batt temp drops below the nominated temp.

The installer will insulate battery cabinet and install a pad heater operated by a thermostat but we're keen to also disable charging if this pad heater fails or isn't sized appropriately.

The lithium battery he is using is an Australian made battery by PowerPlus which is self managed. (no comms cable) The battery has internal protection and self protect if charging is attempted below 0 deg C but we want to prevent system shut down as this would unnecessarily inconvenience the occupants. Australian battery standards prevent batteries being located in living areas so batteries will be on the towing frame in a foam constructed/lined cabinet with heat pad.

The site will have an auto start gen-set which we expect to come on frequently in winter when solar gain is low so we need to ensure charge from the Multi is disabled. Primary solar charging will be with a SmartVictron MPPT so this needs to be disabled also at low temp. Considering an Easysolar 48/5000 or Multi and MPPT and CCGX. VRM will be set up at this site.

QUESTION: We're keen to provide several options to the installer, from simple to complex. We see Schnitzel's option for BMV relay linked to the MultiPlus Aux 1 controlling the Charge Assistant. Keen to hear other options if any. Because the above example is only one of many similar installs we are seeing where we're keen to disable charge at low temp for self managed LiFeO4 we're keen to provide this to other installers. Apologies if there is a simple solution for this which we've missed. We know about Smart Batt Sense and disabling MPPT charge option but we prefer to have a CCGX at the site and understand potential conflict with SmartBattSense and CCGX from FAQ6 in the product manual.

Thank you.

VEConfigure 3PowerPlus
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1 Answer
ben avatar image
ben answered ·

(Option 1)

Well, the gold standard is to have separate charge and discharge busses, with separate isolation contactors on each, and a monitoring system that opens each as appropriate.

This won’t work with a combined inverter/charger; you have to buy two devices. But you did ask for options. :)

Another variant I have seen is for the battery itself to have two contactors built in, so a similar topology but implemented internally. I imagine your battery does not have this. (It also does not work very well with multiple batteries in parallel.)

(Option 2)

Use the charge control lines on each charger to disable the chargers. Install a temperature probe with a threshold output relay, and wire it up to your devices.

(Option 2b)

Better yet, add two of those, and set one to a higher threshold, and connect it to a relay that brings online an additional heating source, if you’re worried about it.

(Option 3)

Add a temperature probe to your GX device and write some custom logic to query the value and trigger the appropriate disable outputs. This is similar to option 2, but without a separate device and instead with some software. Victron doesn’t offer this feature today, of course, but it is a pretty open stack, and you asked for options. Someone who knows Venus OS could code this up in a few hours, I think.

I’m sure there are more approaches. Let us know what you end up doing.

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