Using Victron Battery Protect as solar shutoff relay

[hzcruiser]

I would consider a latching relay that might do just what you need.

[Oceanride007]

Switching DC current is problematic with Arc of current that would shorten the life of anything that is not designed for it, I don't believe any latching relay with itsy bitsy contacts would do it, you need huge silver contacts, the exception is with MOSFET technology that slowly throttles the current, like your Victron BP.

In the good old days we had huge knife switches, so its years since I dealt with it but the spike without BP could greatly upset whatever electronics are in circuit. I always use a blanket over panels before switching my panels, in my case, opening the MC4 connector.

[goboatingnow]

Originally Posted by Oceanride007

Switching DC current is problematic with Arc of current that would shorten the life of anything that is not designed for it, I don't believe any latching relay with itsy bitsy contacts would do it, you need huge silver contacts, the exception is with MOSFET technology that slowly throttles the current, like your Victron BP.



In the good old days we had huge knife switches, so its years since I dealt with it but the spike without BP could greatly upset whatever electronics are in circuit. I always use a blanket over panels before switching my panels, in my case, opening the MC4 connector.

Yep mosfets are best

[hzcruiser]

Originally Posted by Oceanride007

Switching DC current is problematic with Arc of current that would shorten the life of anything that is not designed for it, I don't believe any latching relay with itsy bitsy contacts would do it, you need huge silver contacts, the exception is with MOSFET technology that slowly throttles the current, like your Victron BP.

[...]

Maybe a bit of conjecture here? Last October a colleague of mine did a test with a latching relay rated at 50,000 cycles. The load was 40A (rating is 60A) and after a few days of cycling the 12V bus about every second or two he noticed a change in the clicking sound after 80,000 on-off cycles. At 100,000 we stopped the test and took the relay apart: some minor pitting but it still worked. The relay was due to be replaced now.

This could be an outlier, so we did the test again with a new relay and it also reached 100,000 without any failure.

Hence if you count the switching cycles in your system you're on the safe side for more than 50k cycles:

[PaulCrawhorn]

Originally Posted by hzcruiser

a colleague of mine did a test with a latching relay rated at 50,000 cycles. The load was 40A (rating is 60A)

Link to the unit tested please?

[goboatingnow]

Originally Posted by Oceanride007

Switching DC current is problematic with Arc of current that would shorten the life of anything that is not designed for it, I don't believe any latching relay with itsy bitsy contacts would do it, you need huge silver contacts, the exception is with MOSFET technology that slowly throttles the current, like your Victron BP.



In the good old days we had huge knife switches, so its years since I dealt with it but the spike without BP could greatly upset whatever electronics are in circuit. I always use a blanket over panels before switching my panels, in my case, opening the MC4 connector.

While what you say is true in the theoretical sense. In most cases the vast majority of disconnects will be when the battery is full and the solar is supplying small currents.

Hence the reality is a rated rehab will give good service in practice.

[fxykty]

Are you using a BMS that has trigger-based relays that send a low voltage signal when a trigger is activated? If yes, then run a relay to the battery protect and program the trigger to activate when SOC reaches your stop charge limit. Or instead of the battery protect unit a simple contactor will work as well.

The larger VE solar controllers do have a remote on/off terminal that can be controlled by low voltage relays - short circuit to allow charging and cut the circuit to stop charging.

If your BMS can output CANBUS then set up charging limits in CANBUS messages and send that to the Cerbo. The Cerbo will use the VE.Direct network to send charging commands (stop, or limit, or start).

Finally, don’t your solar controllers have Bluetooth? You don’t need any cables - just connect via Bluetooth (using the VictronConnect app). Bluetooth enables you to adjust settings and enable/disable charging for each controller individually.

[jordanbigel]

Originally Posted by fxykty

Are you using a BMS that has trigger-based relays that send a low voltage signal when a trigger is activated? If yes, then run a relay to the battery protect and program the trigger to activate when SOC reaches your stop charge limit. Or instead of the battery protect unit a simple contactor will work as well.

The larger VE solar controllers do have a remote on/off terminal that can be controlled by low voltage relays - short circuit to allow charging and cut the circuit to stop charging.

If your BMS can output CANBUS then set up charging limits in CANBUS messages and send that to the Cerbo. The Cerbo will use the VE.Direct network to send charging commands (stop, or limit, or start).

Finally, don’t your solar controllers have Bluetooth? You don’t need any cables - just connect via Bluetooth (using the VictronConnect app). Bluetooth enables you to adjust settings and enable/disable charging for each controller individually.

First, thanks very much for your feedback!

I do have LifePo4 batteries (which I am installing next week) with built-in BMS that have trigger-based relays that send low voltage signals. But, the signals are intended only for emergency conditions, the trigger points are not configurable, and they are not set at levels appropriate for controlling charging, only useful in a last ditch effort to allow a graceful shutdown and head off a BMS cutoff (they are Elec Car Parts Company BestGo batteries). They also have relay signals which can be used to signal a cooling/heating devices to activate when the battery is getting too warm or too cold.

I do not have BMS CANBUS capability.

I also have a BMV-700 which has a configurable relay that I could use for this purpose and I am considering wiring the relay to the BP between the MPPT and the battery charge bus along with the toggle switch. This way I can manually shut down the panels, but let the BMV control it when the switch is on - best of both worlds.

I am also planning to wire the BMV relay to the voltage regulator/alternator, to cut the ignition wire - this way I can use the BMV relay with a SOC trigger (say 80%) and the same relay will shut off the MPPT and the voltage regulator. I envision this being essential when motoring long distances.

Finally, I made a mistake and purchased a pair of Victron 75/15 MPPT without the Bluetooth. I bought them months ago. I was not aware at the time the BT version even existed, and by then it was too late to return or exchange them. I could sell them on eBay at a small loss, buy the BT versions, etc. etc., but for some reason, I feel like I would still want a hardware switch.

I also have a dedicated ammeter (analog) for the solar panels, which I have not mentioned so far. Totally unnecessary now that I have the spiffy CerboGX, but it was there before, and who wants an empty hole in their panel?

[fxykty]

Originally Posted by jordanbigel

…
I also have a BMV-700 which has a configurable relay that I could use for this purpose and I am considering wiring the relay to the BP between the MPPT and the battery charge bus along with the toggle switch. This way I can manually shut down the panels, but let the BMV control it when the switch is on - best of both worlds.



I am also planning to wire the BMV relay to the voltage regulator/alternator, to cut the ignition wire - this way I can use the BMV relay with a SOC trigger (say 80%) and the same relay will shut off the MPPT and the voltage regulator. I envision this being essential when motoring long distances.



Finally, I made a mistake and purchased a pair of Victron 75/15 MPPT without the Bluetooth. I bought them months ago. I was not aware at the time the BT version even existed, and by then it was too late to return or exchange them. I could sell them on eBay at a small loss, buy the BT versions, etc. etc., but for some reason, I feel like I would still want a hardware switch.

…

Your plan to use the BMV’s relay to control a cut-off switch is a good idea given the limited functionality of the built-in BMS. Always better to automate the cut-off switch rather than rely solely on manual operation - mistakes and omissions can easily take place when humans are part of a process.

Regarding your solar controllers, you can get one of these for each controller: https://www.victronenergy.com/panel-...h-smart-dongle. Much cheaper than selling your controllers.

[hzcruiser]

Originally Posted by PaulCrawhorn

Link to the unit tested please?

Hello Paul,

We ordered them from the manufacturer through Alibaba but had them modified with copper leads, insulation and ring terminals.

[CatNewBee]

Originally Posted by jordanbigel

Yes, I hear this a lot - never connect the panels to the SCC without connecting the battery first (and conversely, never disconnect the battery first). A lot of people's anecdotal experience (including my own) seem to show this is not a real danger. But, I am not sure my own experience accidentally connecting panels before battery is really a valid test, compared to disconnecting the batteries while the panels are putting out. Maybe the damage is cumulative. I am no expert, clearly.

I guess the only complication in my scenario with disconnecting the panels is that there are 2 of them, each going to separate controllers, I would need 2 relays instead of 1. I have both MPPT's battery outputs going to a common positive stud, and from there to the charge bus-bar. So, it would be easier to "intercept" both in one place and cut battery power to both MPPTs with one relay. Real estate is tight and 2 relays take more space than one.

In the end, I will probably take the conservative route and follow conventional wisdom and go the 2 x relay route on the panel leads. I am not one to push the envelope, if this is a bad idea I am not going to pursue it.

Finally, can anyone reccomend an appropriate relay (my panels are only 195, so max 15 amps)?

Thanks for everyone's feedback.

Wrecked a SmartSolar 150/100 once by disconnecting it under load from the battery, not anecdotical, but you may be more lucky.

However you can use a SSR on the panels side to disconnect the solar panels instead or a simple relay contact and the remore input of the controllers, would be the easiest way.

The Victron BatteryProtect are just a SSR with a huge heat sink and some LED and some preset voltage triggers plus a timer.

[jordanbigel]

SO, the problem with both the bluetooth dongle suggestion (from fxykty), and the remote input on the controller (from Catnewbee) is they both require use of the one VE.Device port, which I really want to keep connected to the CerboGX.

Currently I am trying to find an appropriate SSR relay which I can use on the panel side instead of using the Victron BP on the battery side.

[CatNewBee]

Originally Posted by jordanbigel

SO, the problem with both the bluetooth dongle suggestion (from fxykty), and the remote input on the controller (from Catnewbee) is they both require use of the one VE.Device port, which I really want to keep connected to the CerboGX.

Currently I am trying to find an appropriate SSR relay which I can use on the panel side instead of using the Victron BP on the battery side.

No, the remote switch is a separate connector on some of the mppt controllers.

You can use the cerbo to deactivate the charger by the Ve.Direct interface by software (DVCC or customizing).

[jordanbigel]

Originally Posted by CatNewBee

No, the remote switch is a separate connector on some of the mppt controllers.

You can use the cerbo to deactivate the charger by the Ve.Direct interface by software (DVCC or customizing).

I'm trying to find out how to wire a remote switch to the BlueSolar MPPT 75/15, and I don't think there is a way other than via the VE.Direct port (via this cable https://www.victronenergy.com/access...e-on-off-cable).

A note on the web page for the above cable says:
Note that it's not necessary to use this cable on the larger SmartSolar models, as they feature an onboard Remote On/Off terminal.


From this I gather that the 75/15 is not one of the larger SmatSolar models, and as such, does not have a separate remote on/off terminal, only the VE.Direct port.

"You can use the cerbo to deactivate the charger by the Ve.Direct interface by software (DVCC or customizing)"

I am aware you know a lot about rPI programming and the VenusOS - can you give me some pointers to documentation, tips, or any leads on how exactly to to do this?

I have heard something about DVCC, but I don't even know what the letters stand for yet - I am going to research this now.

The whole reason for wanting a hardware solar cutoff is because there is a known limitation with the CerboGX. I found a dozen discussion threads about it (and now this one) all saying that it is not possible. This is the first clue I have seen which indicates it might be possible. But how exactly?

[goboatingnow]

Those Victron units either have a Remote on off line OR VE.direct as the serial line is multi tasked between the two options

There is no issue disconnecting the Victron mppt controller at the output, so if you want to keep Ve. Direct you could use an external disconnect.

I’m puzzled that Cerbo can’t issue ve.direct stop commands though