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I am working on a project that is effectively just a battery powered reticulation system. It is charged through a solar array and cheap MPPT charger, which connects into the battery via the BMS. The BMS output goes into voltage regulators (in series, 5v and 12v respectively) to power an Arduino and a solenoid valve.

My issue is that when I connect the valve to my output wires (from the voltage regulator) it turns on for less than half a second, then snaps back shut. I then have to reset the BMS (by connecting the battery + to the BMS out +) in order to have power again. If I bypass the BMS, this does not happen and the solenoid stays open whilst it is connected. Why is this happening?

Notes:

This is the BMS: https://www.ebay.com.au/itm/1S-2S-3S-4S-5S-6S-BMS-PCB-Protection-Board-For-18650-Li-ion-Lithium-Battery-Cell/142415496988 (the 4s 20A option)

The battery pack is salvaged from an old laptop (conveniently already assembled how I needed it)

The wire I am using is a combination of 26AWG (yes I know that is very thin, but it is plenty for the max current this will have to handle) and 9AWG wire. No length of wire (in the relevant area) is longer than 5cm. The BMS is directly on top of the battery pack (separated by some thin plastic).

The solenoid I am using is 12V and 7W (0.58A)/(0.44A at the 16V battery once converted)

I am just manually connecting the valve when I test this setup, it will eventually be used with a MOSFET. It also has a reverse biased diode connected, if that is at all relevant.

EDIT: Sorry for the (really long) delay, I've been busy.

Here is the (rough and messy, I tried to not overlap wires and failed, sorry) schematic for the system, the cells represent the batteries and BMS whilst the voltage source represents the solar panels and charger: Schematic

The batteries are connected to the BMS like this: BMS connections

I've also done a few tests very recently and found some very confusing things:

  • Occasionally (once every few tries), it will work fine, but when I come back a few minutes later to test it again it has the issue mentioned above
  • Using some resistors, I've confirmed that the BMS can supply the required amount of current (more than the solenoid draws)
  • I know the solenoid works as it functions properly on other power sources
  • The battery pack powers other things just fine such as a 12v 0.2A fan

Could my BMS be broken or am I doing something wrong?

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  • \$\begingroup\$ Show a schematic proposal with all details. \$\endgroup\$ – Andy aka Aug 2 '20 at 8:43
  • \$\begingroup\$ flyback diode missing? \$\endgroup\$ – dandavis Aug 3 '20 at 8:08
  • \$\begingroup\$ dandavis there is a flyback diode on the solenoid. \$\endgroup\$ – Command-Alt-Escape Aug 5 '20 at 6:17
  • \$\begingroup\$ I'm voting to close this because it is an abandoned usage question. An engineering treatment would start with measuring the actual current drawn by the solenoid. Note also that increasing the voltage will increase the current as the solenoid is being overpowered; you don't have a switch mode power supply here which would allow you to design in terms of the intended power consumption. \$\endgroup\$ – Chris Stratton Sep 18 '20 at 16:19

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