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diy solar

Low voltage disconnect

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Red Squirrel

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Jan 1, 2020
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Curious what everyone does for low voltage disconnect on your systems, in order to preserve the batteries. My train of thought is to mod the inverter so it can be turned on/off via a relay (by modifying the on/off switch which is usually a soft switch) and then having a microcontroller that monitors the battery voltage. Could also make it monitor the solar voltage so that when it does turn off, it will only turn back on when it sees solar voltage (in case the battery voltage creeps back up naturally).

But wondering if there are solutions already for this that I just don't know about?
 
Sterling ProLatch R has a battery protection option. However, take a look at the use manual before you decide to jump in. It's listed at the bottom of the linked page.


Features:

Charging mode - Uni / bidirectional - When the ProLatch R is installed between 2 batteries (e.g. engine starter and auxiliary) it works as a bidirectional voltage sensitive relay (i.e. The trigger voltage on the input or output will activate the relay). The ProLatch R will latch when the alternator is active allowing current to flow from the starter to the auxiliary via the ProLatch R. In contrast, if there is a solar cell / wind gen / other charging source on the auxiliary battery bank it will also activate the relay and allow charge to flow to the starter battery. The unidirectional setting triggers the activation of the relay by the voltage on the input stud only.

Battery protection mode - The ProLatch R prevents the over charging or over discharging of batteries. In order to prevent over charging, the relay disengages at a preset voltage or a voltage you specify (e.g. 14.4V). Therefore the battery will disconnect from the charging source. Conversely, to prevent battery depletion beyond a certain voltage, the relay will prevent charge from being drawn by the draining source (appliance). The device alerts the user by switching the power 'off' for 10 seconds and then back 'on' for 1 minute..



ProLatch R Programmable Latching Relay - 80 Amp

The ProLatch-R is designed to 'lock into position' and will not consume power once in position. The only current drawn is to run the internal software which amounts to about 0.5mA. This makes the ProLatch-R ideal for use with solar or wind sources.
baymarinesupply.com baymarinesupply.com
 
Also the Victron Battery Protect works with certain inverters that have a remote on/off feature, such as the Victron inverters. It should not be connected directly between the battery and inverter however. Linked below with verbiage from the user manual. User manual also has a view diagrams regarding connections.

4. The short circuit protection of the BP will be activated if you try to directly connect loads with capacitors on their input (eg inverters). For that use case, please use the BP to control the remote on/off switch on the inverter, instead of disconnecting the higher power DC line.

 
Wow that's not cheap. Might stick to my original plan then. Just figured maybe there was something I was overlooking so did not want to reinvent the wheel.
 
I have my Victron SCC set up to control the inverter with an arduino board being the intermediary between the on/off from the Victron and button pushing on the inverter. To date it hasn't actually gone into action but it's nice to have it there rather than let the system fly into a wall and have the BMS step in. Ideally I would set up to monitor power in / out of the battery but watching the voltage is good enough for me.
 
Will did a couple of videos on controlling an inverter that doesn't have a remote on/off feature. If memory serves, the first one he used a high-power contactor, in the second he used an opto-relay to control the on/off switch. It would definitely be, imho, better to control the on/off function rather than switch the supply circuit.

I personally use the SoC calculation from my battery monitor (Victron BMV700) to remotely switch off my inverter (Victron MultiPlus) as the two are digitally linked.
 
A voltage activated relay ($40 or less) and a KiloVac contactor (approx $100) might be an alternative. I have no idea what the Victon solutions cost.
I use a KiloVac held in closed position by a Ready to Charge signal from my BMS (Orion Jr.)
 
Red Squirrel said:
Curious what everyone does for low voltage disconnect on your systems, in order to preserve the batteries. My train of thought is to mod the inverter so it can be turned on/off via a relay (by modifying the on/off switch which is usually a soft switch) and then having a microcontroller that monitors the battery voltage. Could also make it monitor the solar voltage so that when it does turn off, it will only turn back on when it sees solar voltage (in case the battery voltage creeps back up naturally).

But wondering if there are solutions already for this that I just don't know about?
Click to expand...
I do what you describe with a Victron Battery protect and a samlex inverter that has provision for external switching.
 
tictag said:
Will did a couple of videos on controlling an inverter that doesn't have a remote on/off feature. If memory serves, the first one he used a high-power contactor, in the second he used an opto-relay to control the on/off switch. It would definitely be, imho, better to control the on/off function rather than switch the supply circuit.

I personally use the SoC calculation from my battery monitor (Victron BMV700) to remotely switch off my inverter (Victron MultiPlus) as the two are digitally linked.
Click to expand...
@tictag Hello, I'msearching the same kind of control on a Multiplus 2 48/3000 35/50 to allow charge/discharge by using the Aux I/O or Temp Sens relay. Can you describe to my how you link the BMV700 SoC calculation and the Multiplus relay?
 
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