Using Victron Battery Protect as solar shutoff relay

[jordanbigel]

Good afternoon!

So, I just installed 2 Victron MPPT controllers for my 2 solar panels. I want to be able to have a hardware shutoff switch and I'm looking for the best way to do this.

One approach I read about which appeals to me is to use a Victron Battery Protect (https://www.victronenergy.com/batter...attery-protect) which would be wired between the MPPT(s) and the battery charge bus. The BP device has a remote switch connection which I could wire to a toggle switch inside the boat (at the nav desk). Seems like a simple, cost effective approach ($40).

I can't recall where I read about using this device, in this manner, but I recall reading that this also has positive benefits in terms of actually protecting the battery, although I cannot remember the reason stated in the thread/article.

The one question I can't answer so far - assuming this is a good idea - is how to program the low-voltage shutdown.

Has anyone used this device for this purpose?

Is this a good idea?

What are the pros and cons?

THANKS !

[Stu Jackson]

I would re-read what you think your source was. In most cases, controllers require the panels be disconnected before the batteries are.

[PaulCrawhorn]

Yes, a simple switch between panels an SC will do.

Only then disconnect the SC from the bank

[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.

[jordanbigel]

PS. Here is the article I was reading last week - finally found it. From the Victron support forum. The "Accepted Answer" seems to be from a Victron distributor in Australia, but and several other people in this thread indicate they use the BP the same way. But, as you would expect, there are also counter-opinions who say NEVER DO THIS. Sigh. I think the question comes down to does this allow current to flow backwards and damage the BP? Beats me. Anecdotal experience, seems to say no. Also, Victron seems to say this is okay (not in this post, see below).

https://community.victronenergy.com/...interrupt.html

Then there is this fellow who is describing the exact conundrum I face (the damn CerboGX cannot turn the MPPT on/off, unless you have internet access of course - yes, if you did not already know this, I hope you are as shocked as I was when I found out). You can use the Cerbo to turn the MultiPlus on and off, but not the MPPTs. Sigh.

I do have the ability to connect my laptop directly to each MPPT (one at a time) with a USB/VE.Direct cable when I need to (minor PITA) but the MPPTs are plugged into the Cerbo, and isn't that what the CerboGX is supposed to be for?

https://seabits.com/correcting-the-l...system-design/

Anyway, this guy wrote:
The solar panels are two 100W flexible panels mounted on my bimini, connected to the BlueSolar MPPT 75/15 solar controller. The solar controller is connected to the Color Control GX via VE.Direct, but it cannot command it off – another strange compatibility limitation, likely due to the bus type. As a result, I have a BatteryProtect 65 between the charging leads from the MPPT controller and the LiFePO4 bus. This allows the VE.Bus BMS to completely disconnect the solar panels in the event that the battery is being overcharged. The controller also has Bluetooth, and can be configured using the Victron app. You can also see a wealth of information on solar performance, charging, and historical data via Bluetooth.

In the above scenario, Seabits guy has a BMS signal turning the BP on/off, and cutting the battery to the MPPT. In my case I would use a simple switch. Same result.

Finally, there is THIS from the Victron product page for the BP itself. The relevant comment is terse and lacks detail, but, seems to indicate this is a normal use-case for this product.

https://www.victronenergy.com/batter...attery-protect

The BatteryProtect is a uni-directional device. It can only deal with current in one direction, so either current to a load, or current from a charger, but not both currents at the same time. In addition to this, current only can only flow from the Battery terminal to the Load terminal. In case of use with a load, the battery connects to the Battery terminal, and in case of use with a charger, the charger connects to the Battery terminal.


*Note bolded section.

[goboatingnow]

Originally Posted by Stu Jackson

I would re-read what you think your source was. In most cases, controllers require the panels be disconnected before the batteries are.

No they don’t

[goboatingnow]

Originally Posted by jordanbigel

PS. Here is the article I was reading last week - finally found it. From the Victron support forum. The "Accepted Answer" seems to be from a Victron distributor in Australia, but and several other people in this thread indicate they use the BP the same way. But, as you would expect, there are also counter-opinions who say NEVER DO THIS. Sigh. I think the question comes down to does this allow current to flow backwards and damage the BP? Beats me. Anecdotal experience, seems to say no. Also, Victron seems to say this is okay (not in this post, see below).



https://community.victronenergy.com/...interrupt.html



Then there is this fellow who is describing the exact conundrum I face (the damn CerboGX cannot turn the MPPT on/off, unless you have internet access of course - yes, if you did not already know this, I hope you are as shocked as I was when I found out). You can use the Cerbo to turn the MultiPlus on and off, but not the MPPTs. Sigh.



I do have the ability to connect my laptop directly to each MPPT (one at a time) with a USB/VE.Direct cable when I need to (minor PITA) but the MPPTs are plugged into the Cerbo, and isn't that what the CerboGX is supposed to be for?



https://seabits.com/correcting-the-l...system-design/



Anyway, this guy wrote:

The solar panels are two 100W flexible panels mounted on my bimini, connected to the BlueSolar MPPT 75/15 solar controller. The solar controller is connected to the Color Control GX via VE.Direct, but it cannot command it off – another strange compatibility limitation, likely due to the bus type. As a result, I have a BatteryProtect 65 between the charging leads from the MPPT controller and the LiFePO4 bus. This allows the VE.Bus BMS to completely disconnect the solar panels in the event that the battery is being overcharged. The controller also has Bluetooth, and can be configured using the Victron app. You can also see a wealth of information on solar performance, charging, and historical data via Bluetooth.



In the above scenario, Seabits guy has a BMS signal turning the BP on/off, and cutting the battery to the MPPT. In my case I would use a simple switch. Same result.



Finally, there is THIS from the Victron product page for the BP itself. The relevant comment is terse and lacks detail, but, seems to indicate this is a normal use-case for this product.



https://www.victronenergy.com/batter...attery-protect



The BatteryProtect is a uni-directional device. It can only deal with current in one direction, so either current to a load, or current from a charger, but not both currents at the same time. In addition to this, current only can only flow from the Battery terminal to the Load terminal. In case of use with a load, the battery connects to the Battery terminal, and in case of use with a charger, the charger connects to the Battery terminal.





*Note bolded section.

Solar is of course one way currents ( these disconnects are MOSFET based so unidirectional

There are no intended circumstances where reverse currents flow and the MOSFET body diode that conducts is actually quite big and robust anyway so , it would require considerable reverse currents to damage it.

The OP could indeed use them as per his idea.

Ps. Ve. Direct hex protocol for mppt has remote on off control and you can also program the RX pin of the serial interface to act as a remote on off of your don’t use ve.direct

[noelex 77]

Why do you want to disconnect the solar panel input?

[goboatingnow]

Originally Posted by noelex 77

Why do you want to disconnect the solar panel input?

He’s not , he’s switching the output of the Victron mppt controller

[noelex 77]

Originally Posted by goboatingnow

He’s not , he’s switching the output of the Victron mppt controller

Which disconnects the solar panel input into the batteries and loads, hence my question.

[jordanbigel]

Originally Posted by noelex 77

Why do you want to disconnect the solar panel input?

1- so I can see at-rest state of (parasitic) loads
2- so I can see how much load is being used at any given time without doing math for any given piece of equipment (by turning off everything else)
3- to let the LifePo bank rest at storage voltage while we are away from the boat
4- because I don't like being restricted from being able to turn stuff on and off
5- because it's a hassle to disconnect the Cerbo and plug in the VE.Direct USB adapter and use the computer to access the MPPT via VEConnect (one at a time).

While it may be the case that some of these reasons are very low-priority and may not be compelling to everyone, I think there are enough reasons that most people should want the same ability, and I am curious and surprised to even find someone who would ask this question, who (I assume) does not feel the ability to do this is useful. Why not?

[PaulCrawhorn]

Most people just set and forget their solar.

But otherwise, just using the built-in SC switch to turn off the unit is most common.

For long term "storage mode" accounting for parasitic loads, an HVC/LVC switch set to cycle between 3.2 and 3.1Vpc would IMO be ideal.

[noelex 77]

Originally Posted by jordanbigel

While it may be the case that some of these reasons are very low-priority and may not be compelling to everyone, I think there are enough reasons that most people should want the same ability, and I am curious and surprised to even find someone who would ask this question, who (I assume) does not feel the ability to do this is useful. Why not?

I was not implying that it was not useful, but what you are hoping to achieve influences how it would be best to implement the disconnection.

Given your aims, the simplest would be circuit breakers (or switches if you prefer) between the solar panels and the controller. If you are leaving the boat for a long time you can also switch the connection between the controller and the batteries (or just pull the fuse) although the parasitc load of modern controllers tends to be very small.

If you want a remote switch all that is needed is a relay.

Given your goals it may also be useful to install a seperate ammeter to permanently show the solar panel input, battery input, or both.

[goboatingnow]

It all depends on what you want

If you want automatic disconnect of the mppr controller from the battery bus then the Victron batter disconnect can be used on the output of the mppt controller. Set the disconnect voltage etc.

Alternatively you can trigger the disconnect of the mppt controller via the Ve . Direct hex command or use the disconnect option of the Rx serial line option. But to my knowledge CERBO can’t direct a shutdown of the solar system

The method you suggest is probably the simplest given your setup. There’s no issue with using it so.

[Oceanride007]

Well I wouldn't use this method of isolation just so that you can monitor the load current. May be better to install a separate BMV on the load side.

LFP doesn't need to rest, you got to have faith in your MPPT settings and keep well below the knee, my float mode is about 13.3V I get no higher than 86% SOC.

But if you must do a isolation and real estate is a premium, I see nothing wrong in joining the 2 Negatives, and mounting your single Isolating devise there.