Low voltage disconnect for inverter

[cajunbill]

Been lurking here for a few days trying to read all I can regarding the above subject because of what may be a somewhat unique circumstance. The situation is that I recently built a houseboat that I will be using both a generator (when I'm there) and PV when I'm not. The only thing I'd like run on PV when I'm not there is a small fridge that operates on 110VAC so while I'd like to keep it running when I'm not there, it won't be a tragedy if the voltage gets too low to keep the fridge contents from spoiling. I tried several chinese LVD's with terrible results. It seems that the components are not robust enough to perform reliably. Keep in mind that the houseboat is presently in my backyard so I've had plenty of time to experiment. I previously had the PV system on my shop trying to run a freezer with mixed results so when we built the houseboat, I decided to move it there to try to utilize it more fully. The solar system consists of a Morningstar 45 solar controller tied to two 100W panels wired in series connected to two 110ah AGM batts wired in series for a 24V system. The inverter I'm utilizing is a 24V Samlex 1750W MSW, Model PSE-24175A and the inverter is connected to a switch that allows me to vary the feed from gen power to inverter power manually. While I'm using the batts on a separate circuit to power five LED RV ceiling lights in addition to the 12V bath exhaust fan, all the wall outlets are 110-120V and are set up to run a microwave, small AC and TV along with a couple for fans when needed. I experimented with running just the fridge exclusively and while it kept stuff frozen for 13 days, when we had 2-3 consecutive days of minimal sunshine, it didn't have enough "juice" to keep it going forever and ever amen. I carefully monitored the battery voltage and never allowed the voltage to get low enough to damage the batts, but if I hadn't been there, I feel sure that would have happened.

Here's my question: with the disappointing results of the chinese knockoff LVD's, I recently ordered a Victron 12-24V Battery Protect that I'd like to utilize to protect my batts from damage. I know what Victron says about using their LVD's with an inverter and I understand why that is so because of what happens electrically with my older inverter and the capacitors, but I only want to use it to disconnect the inverter, not to reconnect it. The inverter only has a remote that allows the pressing of a momentary on/off button to operate it so I'm not interested in doing that because (from what I read) I'd have to connect other devices that I do not feel comfortable in wiring up because I am somewhat of a newbie. Since the inverter is about 15 years old, it doesn't have the capability to utilize the remote relay aspects of the BatteryProtect device. From what I've read on this great forum, the answer seems to be to purchase a new programmable inverter, but I'm trying to get by cheaply at this point. (I do plan to upgrade where needed, just not now.) As I said, I have no DC load other than the separate circuity for the LED lights, etc. so I can't wire it up as Victron recommends to disconnect the DC load and use the remote to kill/connect the inverter. So more specifically, if I'm willing to sacrifice my fridge contents if we experience consecutive days of cloudy days, will the Victron unit work to kill the inverter only and then allow the PV system to recharge the batts so that when I return to the boat, I can manually reset the inverter and/or utilize gen power to run the other necessary 110VAC circuits?

 

[FilterGuy]

What are the specs on the Samlex inverter? What voltage does it cut out at?

Generally speaking, the inverter has it's own Low voltage disconnect and you only need low voltage disconnect on the DC loads.

 

[time2roll]

I would sooner cut the AC power upon low battery voltage. Then it is just the idle draw until the charge level can be restored.

 

[FilterGuy]

I would sooner cut the AC power upon low battery voltage. Then it is just the idle draw until the charge level can be restored.

That works too.

 

[FilterGuy]

BTW: Were you putting the Low Voltage disconnect between the inverter and the battery? I don't know what brand you were using but as I recall, Victron says that is not supported.

 

[cajunbill]

BTW: Were you putting the Low Voltage disconnect between the inverter and the battery? I don't know what brand you were using but as I recall, Victron says that is not supported.

Yes I was with the low cost chinese LVD's, but I was also trying to use them to reconnect after sufficient voltage returned. I don't intend to do that with the Victron, I was thinking just use it to disconnect solely to protect the batteries from being damaged.

 

[cajunbill]

I would sooner cut the AC power upon low battery voltage. Then it is just the idle draw until the charge level can be restored.

That makes sense. Any suggestions on a device to do that? Haven't searched for that yet.

 

[cajunbill]

What are the specs on the Samlex inverter? What voltage does it cut out at?

Generally speaking, the inverter has it's own Low voltage disconnect and you only need low voltage disconnect on the DC loads.

Hmmm, I'm not aware that the inverter has such a feature, but if it does and that is too low, then that won't protect the batts. I will try to determine that.

 

[cajunbill]

Hmmm, I'm not aware that the inverter has such a feature, but if it does and that is too low, then that won't protect the batts. I will try to determine that.

Just reviewed the manual and you are correct, there is a low voltage cutoff, but it is set for when the voltage drops below 20V and reconnects at 21.3V so thanks for bringing that to my attention. However, from what I've read, my batts will be damaged well before the inverter trips. If that is not the case, that would be great so maybe the "thrust" of this post can change to a discussion on whether my batts will be damaged or not if I use the inverter limits rather than having to rely on the Victron BP. Any and all thoughts would be greatly appreciated.

 

[mikefitz]

not aware that the inverter has such a feature,

It has but perhaps too low to be useful, 20 volts disconnect, 21.3 volts reconnect. These are fixed with no user modification.
The no load current is stated at 370 mA, around 9 Ah per day.

Using voltage levels to determine the point at which the inverter should be disabled, can be difficult due to the current surge when the fridge compressor starts up, as there will be a momentary voltage drop on the AGMs. The Victron battery protect has a disconnect delay of 90 seconds that will help, but there will be a voltage difference when the battery is loaded. Some experimental tests should determine suitable disconnect and reconnect voltage setting.

The battery connect cannot directly control the DC current to the inverter but could control a remote switch on the inverter or relays on the DC or AC side of the inverter. With additional circuits the momentary switch on the inverter could be activated.
A relay on the inverter output is an option, 12v DC operating coil, powered by the Victron protect output, example,

Ice Cube General Purpose Relay + Socket Choose Voltage, 8 Pin, 11 Pin, AC or DC | eBay

Ice Cube General Purpose Relay + Socket. YC-REP-2P10A Relay. YC-REP-3P10A Relay. Choice of AC or DC Coil. General Purpose Power Relay. 11 Pin Socket Included. 8 Pin Socket Included. Three Pole Double Throw 3PDT.

www.ebay.com

 

[cajunbill]

It has but perhaps too low to be useful, 20 volts disconnect, 21.3 volts reconnect. These are fixed with no user modification.
The no load current is stated at 370 mA, around 9 Ah per day.

Using voltage levels to determine the point at which the inverter should be disabled, can be difficult due to the current surge when the fridge compressor starts up, as there will be a momentary voltage drop on the AGMs. The Victron battery protect has a disconnect delay of 90 seconds that will help, but there will be a voltage difference when the battery is loaded. Some experimental tests should determine suitable disconnect and reconnect voltage setting.

The battery connect cannot directly control the DC current to the inverter but could control a remote switch on the inverter or relays on the DC or AC side of the inverter. With additional circuits the momentary switch on the inverter could be activated.
A relay on the inverter output is an option, 12v DC operating coil, powered by the Victron protect output, example,

Ice Cube General Purpose Relay + Socket Choose Voltage, 8 Pin, 11 Pin, AC or DC | eBay

Ice Cube General Purpose Relay + Socket. YC-REP-2P10A Relay. YC-REP-3P10A Relay. Choice of AC or DC Coil. General Purpose Power Relay. 11 Pin Socket Included. 8 Pin Socket Included. Three Pole Double Throw 3PDT.

www.ebay.com

I think the system could handle the no load current of the inverter at 9ah/day since I doubt the inverter would be in that condition for more than a day or so. So, maybe the relay on the output/AC side of the inverter might be a simpler solution? Would you guide me a little further regarding the ordering of the relay you suggested? For instance, 8 pin or 11 pin, etc.? While I'm not completely ignorant, it would help if you indicated which relay to purchase so that I can feel comfortable with it. thanks for your help.

 

[HarryN]

Usually the challenge is that the inverter standby power draw keeps going, even if the refrigerator is turned off.

So ideally the solution should be one that turns the inverter off, one way or another.

It is common for the inverter standby power to be just as much as the refrigerator itself draws, so it can be significant in low power situations.

 

[jdege]

A better solution would be to use a DC fridge.

 

[cajunbill]

A better solution would be to use a DC fridge.

Possibly, but I already have an AC fridge and if I was willing to do that, I suppose I could more easily spring for a programmable inverter that could be controlled by the Victron BP.

 

[cajunbill]

Usually the challenge is that the inverter standby power draw keeps going, even if the refrigerator is turned off.

So ideally the solution should be one that turns the inverter off, one way or another.

It is common for the inverter standby power to be just as much as the refrigerator itself draws, so it can be significant in low power situations.

So, can you or anyone else tell me how I could control the remote inverter switch with the Victron BP? What device/circuit/relay would I need?

 

[mikefitz]

ordering of the relay you suggested?

No problem. As pointed out by others, the ideal is to shut down the inverter. Since the inverter remote in momentary acting, its not a simple task to interface to the Victron protect.
The relay was chosen at random and a similar relay could be obtained from many suppliers. With the 8 pin base its an industry standard, easy to wire up, and easy to replace if needed.


Take care when wiring up the base, the DC and AC connections are colose to each other. The relay coil is connected to the Victron connect output, pin 2 and battery negative, pin7.
Conect AC supply input to pins 1 and 8, output to fridge, pins 3 and 6.
With power applied to the coil the contacts connect 1 to 3 and 8 to 6. When power is removed these contacts open.
Order optios are, pins 8, relay plus socket, DC , 24v
These relays are offered with different coil operating voltages, so for the 24v system a 24v coil.
There are other styles of relay available, this style chosen for easy connecting up

 

[cajunbill]

No problem. As pointed out by others, the ideal is to shut down the inverter. Since the inverter remote in momentary acting, its not a simple task to interface to the Victron protect.
The relay was chosen at random and a similar relay could be obtained from many suppliers. With the 8 pin base its an industry standard, easy to wire up, and easy to replace if needed.

View attachment 272239
Take care when wiring up the base, the DC and AC connections are colose to each other. The relay coil is connected to the Victron connect output, pin 2 and battery negative, pin7.
Conect AC supply input to pins 1 and 8, output to fridge, pins 3 and 6.
With power applied to the coil the contacts connect 1 to 3 and 8 to 6. When power is removed these contacts open.
Order optios are, pins 8, relay plus socket, DC , 24v
These relays are offered with different coil operating voltages, so for the 24v system a 24v coil.
There are other styles of relay available, this style chosen for easy connecting up

Thanks, even I can understand that. lol Guess I have to decide if I want to go halfway and do this and run the risk of the having the inverter standby AH ruining the batts or just pull the trigger on a new inverter that the BP can control. Since the Samlex is pretty old and is a MSW, a Pure SW would be nice to have. Do you have any recommendations? I was thinking of this if I decide to do it although it is only 1200W continuous:

https://www.amazon.com/Victron-Energy-Phoenix-Inverter-VE-Direct/dp/B076TP3MCP/ref=sr_1_6?crid=15WIMF5MU7QD5&dib=eyJ2IjoiMSJ9.Q3s0OteVcnj80XVRd0m4gYHsEIi-4DDPSB8LG2EdXRhp7nbhWDpKnc85PjZmOopphN5qGr__6i7lTFC6FgyOLwNHEa9OWW6G9adhuqME81L8ULD3SM5EvaXEmavQ_P7jkyOYWNUyHxiKKL9R2vI14dClASVyMkQgHGFVkhtEDqEAwltPW1EJMFJnBT86yUZ6-fHI2b-64bmeDKb8_dOrdREQZIWm3R8o996JyBOeZodLX-Cl4Ttqb0wP7YpPrC1HrQOPHRFl-RSM6Ev7CCjrx0Hg6CLzXv3CVvyV4ghxQZC5wt2-8UPoqM41Cm1xdpVxECYs3RfeKrCP-tLP8pNEX9vXBzm1rb7h8yrQWjik3VQTwlXS3lgM-iR8z6Ej6emztQTfGCyj7WB75iilicg6vJMZfC3jZMGUZaJozsGJt1Sz3fWPVxLkPySCBVQ2MtUM.Yymz-lqKWt7gvZAtDVTSlo8_SipnW_ez9d_3Mz9kMzU&dib_tag=se&keywords=victron%2Binverter&qid=1737586421&sprefix=%2Caps%2C118&sr=8-6&th=1

 

[FilterGuy]

What kind of batteries do you have? All LiFePO4 batteries that I know of also have a low voltage disconnect.

 

[HarryN]

So, can you or anyone else tell me how I could control the remote inverter switch with the Victron BP? What device/circuit/relay would I need?

On some inverters, there is a terminal pair for signaling on / off. The inverter that I have uses this as a remote on / off, and it is just TTL logic. So any switch will operate it. I am not sure about your exact unit.

I have not used it yet, but the victron display unit ( BV series ) has an built in relay that can be programmed to switch on / off with a voltage setting. In theory, this can work.

There is another approach, which is to put a timer on the inverter on signal. A refrigerator operates in cycles, example turns on every 20 or 30 minutes for 10 ish minutes. So in theory you could turn the inverter "off" for 20 minutes, and then turn it on to allow the fridge to cycle. This would cut out a lot of inverter standby power use.

@RV8R and some others have posted related info on how their 120 vac refrigerator worked in a cabin, which is not so different than what you are doing.

 

[cajunbill]

What kind of batteries do you have? All LiFePO4 batteries that I know of also have a low voltage disconnect.

AGM lead/acid

 

[Q-Dog]

The Victron Phoenix 1200 inverter is rated in VA, not watts, so it is really 1000 watts continuous, but it can surge to 2000 watts. and it does have a remote port to turn it on/off, but the low voltage disconnect can also be programmed to whatever voltage you wnat. You will need a way to program it ... I use the VE Direct bluetooth dongle.