question

Ingo Pfeiffer avatar image

Buck boost on/off via ATC-signal from Lynx Smart BMS - yes or no?

Hi Community

I have the following setup to charge my Smart Lithium Batteries while driving my van:

  • Buck-boost switches on via vibration sensor
  • Charge is applied to Lynx Distributor positive bar (from which also all DC-loads are powered)
  • Smart Lynx BMS connected to Lynx Distributor
  • Batteries (2x200Ah in parallel) connected to Smart Lynx BMS

Now, during winter, the batteries are regularly too cold to charge and Smart Lynx BMS shows "Not allowed to charge".

Usually, I check the situation before I start the van and keep the BMS in Standby mode if Victron Connect App for the batteries shows low temp alarm (i.e. main contactor is open, so batteries are disconnected).

Recently, I had the BMS in operation while parking so the contactor was closed, and when I turned on the engine and the Buck Boost switched through for charging, the BMS opened the contactor due to "Not allowed to charge", thus disconnecting the batteries AND, as charge voltage still reaches the Distributor, all my DC-appliances still work while driving (e.g. lights, USB-chargers and the audio system.)

My questions are the following:

1) Are there any reasons to not use the buck-boost & BMS-auto-disconnect at low battery temps in the way explained above while driving?

2) If this should not be used in that way (according to answer with some reasons under 1)...), there seem to be several ways to prevent the Buck Boost from becoming operational in such situations e.g. not using vibration sensor but Pin 1 with e.g. input for the ATC-signal from the BMS. In the "help-text" in TSConfig point 50 states "Attention, when using pin 1 as an input, connect a 1k-10k resistor in series.

  • Is this really needed for the ATC-signal coming from the Smart Lynx BMS (I recall reading somewhere it's 1,5A only...)?

Thanks for reply and explanations. If a resistor is needed on Pin1, it would be also helpful with a link where to purchase an applicable such (I do not find "range"-specific resistors and only such that are intended for circuitboard welding).

Ingo

BMSOrion DC-DC Converters not smart
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Hi Community - still no answer here :-(... @Stefanie @Matthias Lange - DE you have been so active in answering, I see... any feedback to my questions?
I've never had a buck-boost, thus I cannot help you there. Sorry.

Thx @Stefanie for quick response :-)

1 Answer
Matthias Lange - DE avatar image
Matthias Lange - DE answered ·

I would recommend to use the ATC signal.
Opening the contractor should always be the very last security step and not normal operation.

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