Low Voltage Disconnect Suggestion

[JoshTheSolarBeginner]

I have EG4-Lifepower4 51.2V (48V) 100Ah batteries with a generic all-in-one inverter from a Chinese kit I purchased on Amazon. It was a mistake and I have learned a lot from it. The low voltage disconnect that is built-in to the inverter is set to 40V with no expressed way from the company or the manual to adjust it. The batteries have a factory recommended 44-47V low voltage disconnect. I have done research on options that I can place in between the batteries and the inverter and am struggling to find any distinct and clear answers as to whether the LVDs will actually protect my 51.2V batteries from over-drawing better than the built-in inverter's 40V disconnect setting.

FYI this is a completely off-grid setup.

 

[Daddy Tanuki]

40 volts on a normal 16s battery is 2.5 per cell… that’s pretty sketchy for long battery life. If the disconnects that allow for a 2.9 volt per cell cutoff are inexpensive I would jump on them. Otherwise buy a better inverter that can be adjusted

 

[MisterSandals]

40 volts on a normal 16s battery is 2.5 per cell… that’s pretty sketchy for long battery life.

It would be highly unlikely for all the cells to equally discharge to 2.5V at the same time. So your BMS would almost certainly be disconnecting well before your inverter ever sees 40V.

If your daily operation involves a hard disconnect on low voltage, your system will probably not last as long as it should.
You should consider getting enough batteries up front as opposed to having to buy a second, also insufficient set later.
There are other system design "opportunities" that would also help.

 

[Ampster]

There are voltage activated relay devices that can be set to disconnect at a specific voltage. You may need to add a heavy duty relay or contactor to that if your current is higher than the device is designed for. In the long run, I agree with the suggestion to do your research and save up for a better inverter that has the settings you need.

 

[time2roll]

Consider controlling the inverter load based on battery voltage. Much easier to stop alternating current. Then it is just the idle draw until the low battery voltage can be resolved.

 

[JoshTheSolarBeginner]

Consider controlling the inverter load based on battery voltage. Much easier to stop alternating current. Then it is just the idle draw until the low battery voltage can be resolved.

How would you suggest controlling the inverter load?

 

[Ampster]

How would you suggest controlling the inverter load?

You would put the relay contacts on the wires to the inverter load and the voltage sensor on the battery. If the load was 240 Volts you may need to use a separate two pole breaker.

 

[JoshTheSolarBeginner]

It’s only 120. I am a newbie to all of this, so I apologize if my questions seem reductive. I’m a little retarded.
To clarify what I think you are saying:
I would place a relay on the output wires from the inverter that is triggered to cut off the AC power when the batteries fall below a specified voltage. I assume this means that I would need a voltage sensor on my batteries that is capable of sending a signal to the relay to trigger it and that the relay would have to able to receive said communication.

Are there any products out there like this that you know of? Could you point me in the right direction?

 

[Ampster]

Could you point me in the right direction?

Use the search term, " voltage activated relay". There will be choices from Amazon and others. You will need to pick one with a DC voltage range that is near the value you want it to trigger. Then, if the relay is not rated for the loads you may need an additional relay big enough for that load that you want to control. As previously mentioned, long term the best plan would be an inverter that has that capability.

 

[JoshTheSolarBeginner]

Use the search term, " voltage activated relay". There will be choices from Amazon and others. You will need to pick one with a DC voltage range that is near the value you want it to trigger. Then, if the relay is not rated for the loads you may need an additional relay big enough for that load that you want to control. As previously mentioned, long term the best plan would be an inverter that has that capability.

Thank you for your continue help.

 

[JoshTheSolarBeginner]

Consider controlling the inverter load based on battery voltage. Much easier to stop alternating current. Then it is just the idle draw until the low battery voltage can be resolved.

Thank you for your help

 

[MisterSandals]

You would put the relay contacts on the wires to the inverter load and the voltage sensor on the battery.

Are you suggesting to add the (AC) relay after the inverter because the amps will be much lower?
For my own setup, I would have added (DC) relay before the inverter to stop that from continuing to draw power.

Asking because i suspect i will learn something...

 

[Ampster]

Are you suggesting to add the (AC) relay after the inverter because the amps will be much lower?

No I was just following up on another suggestion to cut off the AC load. The only advantage is that an AC load is easier to switch when loaded.

For my own setup, I would have added (DC) relay before the inverter to stop that from continuing to draw power.

Yes, that would be the preferred setup because it would stop any drain. The above approach still leaves inverter overhead as a drain that could ultimately destroy the battery if not corrected.

 

[JoshTheSolarBeginner]

No I was just following up on another suggestion to cut off the AC load. The only advantage is that an AC load is easier to switch when loaded.

Yes, that would be the preferred setup because it would stop any drain. The above approach still leaves inverter overhead as a drain that could ultimately destroy the battery if not corrected.

I am having a hard time finding a relay that can detect the 44-47v low range on my batteries to trigger the relay and that would also allow the 50A and 110V AC output from the inverter to flow without any noticeable loss. Do you know if any exist that fit those constraints?

You mentioned another option being the same basic thing but it would be a DC relay between my 51.2V/100ah batteries and the inverter. Are there any DC relays you can think of that would work in this scenario

FYI I totally agree that I need more batteries VS allowing them to drain on a regular basis. I also totally agree I will need a better inverter. I just don't have the thousands of dollars that will require at the moment, but it is definitely next on our priority list.

 

[time2roll]

For my own setup, I would have added (DC) relay before the inverter to stop that from continuing to draw power..

Not sure the DC current but is there a DC relay or contactor that is recommended?

 

[JoshTheSolarBeginner]

chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/https://www.victronenergy.com/upload/documents/Datasheet-Battery-Protect-48-V-100-A-EN.pdf

does this seem like it would work to prevent the batteries from over-drawing/draining? It seems like it does based on its data sheet. Could I not just install this between my batteries and the inverter so that it stops drawing completely from the batteries at any Voltage that I set?

 

[Daddy Tanuki]

i really think that a better inverter would be cheaper in the long run. any inverter that does not allow you to specify(adjust) low battery cutoff is going to cause you problems in the future... to what degree is unknown, but it will.

 

[HRTKD]

chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/https://www.victronenergy.com/upload/documents/Datasheet-Battery-Protect-48-V-100-A-EN.pdf

does this seem like it would work to prevent the batteries from over-drawing/draining? It seems like it does based on its data sheet. Could I not just install this between my batteries and the inverter so that it stops drawing completely from the batteries at any Voltage that I set?

No. Victron says that the BatteryProtect device is not to be used between a battery and an inverter/charger because the BatteryProtect is designed for current going one-way.

I agree that a better inverter is the better solution.

 

[MisterSandals]

I am having a hard time finding a relay that can detect the 44-47v low range on my batteries to trigger the relay

The relay does not detect the voltage, it is simply the connect/disconnect mechanism.

The load output from many SCCs can be programmed based on voltage. When the load is "on", it closes the relay/contactor which powers the inverter. Its fairly simple.

There are quite a few different DC contractors. Many on ebay an online retailers. The DC voltage and amps are the primary characteristics to shop for. The amount of power it uses to hold the contactor closed can be another issue.

Just some examples of what's available:

High Voltage DC Contactor Relays - Littelfuse

www.littelfuse.com

 

[Rocketman]

Does your inverter have a switch or input that the Victron battery protect could trigger to shut it down?

I use the Victron Battery Protects (BP) to orderly slow down the draw my system in low battery situations.

If you want the Battery Protect to shut down the inverter…. Put a heavy duty relay/contactor like a kilovolt EV200AAANA (except for 48v instead of 12v). Then the BP runs the contactor. If too low voltage it shuts the contactor down - which kills power to the inverter.

Set the BP at a high enough setting that if it shuts down the BMS Doesn’t shutdown yet - and the solar can get the batteries out of the critical zone.