BMV 712 Low voltage disconnect relay

[Surfsolar]

Building up my first solar system. So far I have 2 valence u27-12xp batteries giandel 1200w inverter, 400w solar, and a 100/50 victron mppt.

After watching Will’s video on the aili battery monitor being the same as Victron I added that to the list but doing some reading on the Victron BMV-712 says it having a relay that can be programmed for high and low voltage protection. Im just a bit confused or need to know if Im reading this right.

Will the BMV-712 actually disconnect loads from the battery in a HV/LV situation or does it just sound an alarm?

Are you able to do the same with the Aili or can you add a relay to it that will disconnect for Low voltage?

 

[RickP]

The BMV-712 receives its data via connection to a shunt, and does not control the battery itself. It does have an audible alarm, and a relay function that can respond to certain conditions, such as state of charge. Depending on your other equipment, this relay may be able to provide a disconnect signal. The manual is here: https://www.victronenergy.com/upload/documents/Manual-BMV-700-700H-702-712-EN-NL-FR-DE-ES-SE.pdf

 

[tictag]

Are you able to do the same with the Aili or can you add a relay to it that will disconnect for Low voltage?

No.

 

[Surfsolar]

The BMV-712 receives its data via connection to a shunt, and does not control the battery itself. It does have an audible alarm, and a relay function that can respond to certain conditions, such as state of charge. Depending on your other equipment, this relay may be able to provide a disconnect signal. The manual is here: https://www.victronenergy.com/upload/documents/Manual-BMV-700-700H-702-712-EN-NL-FR-DE-ES-SE.pdf

Alright I read through the manual and Im just as confused. In the manual and downloaded the app to use under demo. And you can program a relay for HV/LV and Hi/Lo Temp. But reading some other threads and watching videos makes it seem like its not capable of actually being a protective disconnect for High/Low voltage and Temp.

One on another forum was saying something about the relays inside the bmv-712 are just relays to control other relays that would actually disconnect the battery. Using the valence batteries I would really like the added monitor and if I can use the Victron BMV as a Voltage and Temp protection that would definitely be worth the extra cost over an Aili $40 monitor.

 

[RickP]

Yes, if I recall it has a common and one each normally closed/open. Some other units, Victron included, can use this signal to Open and close relays within the system. I may be using this function instead of using the AC Ignore functionality on my Multiplus, and will let you know exactly how I did it if I do. My system is all Victron/BattleBorn, so they work together to provide the basic things without added wiring. But there’s always something you find you need that isn’t there!

 

[Surfsolar]

Would I need to use like a 300-500 amp relay off the Positive side on battery going to everything? Or does the shunt actually do the disconnect but I need like a small relay to tell it when?

I’ve been researching like crazy and can not find much on people hooking a relay to the bmv for Hi/Lo voltage and temp protection.

 

[RickP]

Would I need to use like a 300-500 amp relay off the Positive side on battery going to everything? Or does the shunt actually do the disconnect but I need like a small relay to tell it when?

I’ve been researching like crazy and can not find much on people hooking a relay to the bmv for Hi/Lo voltage and temp protection.

Depending on what you are looking to protect the battery from, voltage-wise, there are several cheaper options. If you want to make sure it isn't being charged wrong, Victron makes something called a Smart Sense that gives all the relevant information to the SCC via BlueTooth. The Valence battery has a BMS that protects for low and high voltages, and over-current draw, internally as far as I know, so it should disconnect the load beyond it's own settings. Will did a battery tear down on these and the BMS was a massive, well-built unit. I'm no Valence expert, but from what I know, they are excellently engineered units, and it's unlikely such variables aren't already addressed internally.

 

[Surfsolar]

Depending on what you are looking to protect the battery from, voltage-wise, there are several cheaper options. If you want to make sure it isn't being charged wrong, Victron makes something called a Smart Sense that gives all the relevant information to the SCC via BlueTooth. The Valence battery has a BMS that protects for low and high voltages, and over-current draw, internally as far as I know, so it should disconnect the load beyond it's own settings. Will did a battery tear down on these and the BMS was a massive, well-built unit. I'm no Valence expert, but from what I know, they are excellently engineered units, and it's unlikely such variables aren't already addressed internally.

The XP series Valence batteries actually have no protection internally, To avoid a $600 valence specific bms I was planning on using the BMV to use the relays for High and Low voltage disconnect protection and for temperature protection. All while also having a precise monitor to watch them.

 

[Zil]

I have the Victron BMV-700. While the instructions seem to indicate the relay can be caused to open and close under various parameters, I have only used it for high voltage on. There is only one relay, open or closed. I am not sure but I read the maximum ampere on the contact is 1 amp. I used mine to control two fans at just less than 1 amp. There are many high ampere relays available that could be controlled with this small relay.

 

[Surfsolar]

There are many high ampere relays available that could be controlled with this small relay.

So would any high ampere relay work? How would you connect the BMV to the relay? Sorry if these are common electrical sense questions, this is my first time with solar and relays.

 

[Zil]

need hd relay that is rated to what you disconnect. ac or dc and the amount of amperes. The trigger of the hd relay must be dc <1 amp. My Victron has two connections for the relay. Some hd relays need to ground, some need a voltage current. The Victron is just a switch and can be wired as needed. Look at the installation manual for your Victron.

 

[tictag]

Will the BMV-712 actually disconnect loads from the battery in a HV/LV situation or does it just sound an alarm?

It does both.

One on another forum was saying something about the relays inside the bmv-712 are just relays to control other relays that would actually disconnect the battery.

Yes, exactly. They are just control relays. Most often used as remote control for some other device, such as a relay, but most often used to switch off an inverter or control something like a Victron BatteryProtect (other manufacturer are available) or other load control device such as the Argo or Cyrix battery isolator products, or both!

So would any high ampere relay work?

Yes, coil current must be <1A, which is quite common. The BMV's relay only draws 12mA.

To avoid a $600 valence specific bms I was planning on using the BMV to use the relays for High and Low voltage disconnect protection and for temperature protection.

Sounds reasonable.

 

[Zil]

The problem with that, you need to control high voltage while charging and low voltage while discharging. I can't do that with the one relay in the Victron BMV. I have a low voltage sensing relay to cut the discharge when battery voltage is low. Although not really necessary, I have a locking relay in partnership with it to keep it from reconnecting until I give permission. Next I work on a high voltage disconnect for charging, but think I can trick my SCC to handle that. Note, I still have a BMS as a last-stop-drop-dead individual cell protection that I hope is never tripped.

 

[Surfsolar]

Yes, exactly. They are just control relays. Most often used as remote control for some other device, such as a relay, but most often used to switch off an inverter or control something like a Victron BatteryProtect (other manufacturer are available) or other load control device such as the Argo or Cyrix battery isolator products, or both!

I have not heard of those products yet thank you for the links. Looking and reading the data sheets seems like the Cyrix would be what I would use.

Looking at the Cyrix wiring diagram I would be replacing the bms with the victron BMV. Correct?

Why would I not put the Cyrix straight off the battery then branch everything off?

Would you recommend a 230a or

Yes, coil current must be <1A, which is quite common. The BMV's relay only draws 12mA.

Is there one you would recommend or what/where I could search to find a specific one?

 

[tictag]

Looking at the Cyrix wiring diagram I would be replacing the bms with the victron BMV. Correct?

Exactly. Can you see in the wiring diagram how the relay (the Cyrix in this case) is powered? From a supply, through a small fuse to protect the circuit, through the BMS (or the BMV relay contacts in your case) then off to the Cyrix, then finding a return back to the supply. In your case, the BMV relay is switching a bigger relay that isolates the supply.

Why would I not put the Cyrix straight off the battery then branch everything off?

You would, that's how the above diagram is wired, although this diagram includes an inverter and 'a load', where I suspect your 'load' is actually the inverter. The inverter in the above case is depicted as being the 'emergency reconnect' because the MultiPlus has an in-built charger that, when grid/shore power is supplied, will provide a charge voltage that is used to reconnect the load. Your BMV has similar 'reconnect voltage' setting, though I suspect the charge voltage in your case will be from your SCC.

Would you recommend a 230a

I would recommend the model that best suits your load. You have a "giandel 1200w inverter", which would draw around 100A at 12V to deliver its rated output. Anything above that plus say 25% should be fine. Note: you might need to check with Victron about the ability of their product to support surge loads. My guess is that it will be fine as surge loads tend to be very short lived.

Is there one you would recommend or what/where I could search to find a specific one?

I have already provided suggested devices e.g. Cyrix, Argo etc. The Cyrix apparently draws 320mA (according to its user manual) so is well within the specs of the BMV relay contacts.


Other considerations:

1. As with all inverters, you should consider the surge current required to charge up their input capacitors on initial connection. Whilst in theory, you should never actually be activating this relay (because your system is designed to avoid discharging your battery below 50% SoC!), this relay will be carrying the inverter's initial surge on re-connection if it does activate. Is this a problem for the Cyrix? I don't know.
2. Victron have both Cyrix-ct and Cyrix-li models. I am not sure of the difference. Be sure to check.
3. I have no experience using these devices - please do your research to make sure this product is right for you/your system.
4. Be sure to connect your SCC to your battery before you connect your PV array - it needs to determine your battery system voltage. After doing so, in my experience with Victron SCCs, it will be fine to subsequently disconnect the battery.

 

[Zil]

With Li battery, must monitor each cell in a series bank. A BMS is doing that. Monitoring the bank total voltage can lead to things going well out of balance. My BMS is the last defense if any cell goes high or low. But the overall bank voltage is measured by a separate system that shuts discharge if bank overall voltage goes low. The BMV along with a HD relay can do that.