Hi, I have a quick question regarding the behaviour of the 24V Mecer / Axpert solar charger / inverter.

I'm using this with LiFePO4 batteries and custom charge settings, however I only have 1500W of solar panels and 5.1kWh battery. I'm running a fridge, TV and some other DC powered items (router, lights etc off the battery - after converting to 12V DC). With all the rain and cloudiness, the charging started to decrease and not charge the battery up fully off solar so I moved my TV and then fridge onto mains and then put the inverter into sense mode (where it uses less power and will only turn on if there's a load). However I still had my DC loads running. Being LiFePO4 I wasn't too worried about the battery, but it got down to 23V in the early hours of the morning and the inverter powered off completely and pressing the buttons on the front of it didn't do anything. I was then worried about what would happen when the sun came up the next day. Was the battery now so low that the inverter/charger circuitry wouldn't switch on just with the solar power and start charging? Since my mains charging circuitry on the unit doesn't work anymore, I ended up getting out a lab power supply and charging the battery with a few amps until the voltage got a bit over 24V and then the inverter powered on by itself.

But I really would like to know, if it switches off and becomes unresponsive when the battery is below 23V, whether or not it will switch on again by itself when the sun comes up and start charging the battery? Or do I need to manually get the battery back past some threshold voltage first?

Thanks in advance!

4 minutes ago, Lindsay said:

Hi, I have a quick question regarding the behaviour of the 24V Mecer / Axpert solar charger / inverter.

I'm using this with LiFePO4 batteries and custom charge settings, however I only have 1500W of solar panels and 5.1kWh battery. I'm running a fridge, TV and some other DC powered items (router, lights etc off the battery - after converting to 12V DC). With all the rain and cloudiness, the charging started to decrease and not charge the battery up fully off solar so I moved my TV and then fridge onto mains and then put the inverter into sense mode (where it uses less power and will only turn on if there's a load). However I still had my DC loads running. Being LiFePO4 I wasn't too worried about the battery, but it got down to 23V in the early hours of the morning and the inverter powered off completely and pressing the buttons on the front of it didn't do anything. I was then worried about what would happen when the sun came up the next day. Was the battery now so low that the inverter/charger circuitry wouldn't switch on just with the solar power and start charging? Since my mains charging circuitry on the unit doesn't work anymore, I ended up getting out a lab power supply and charging the battery with a few amps until the voltage got a bit over 24V and then the inverter powered on by itself.

But I really would like to know, if it switches off and becomes unresponsive when the battery is below 23V, whether or not it will switch on again by itself when the sun comes up and start charging the battery? Or do I need to manually get the battery back past some threshold voltage first?

Thanks in advance!

Charging is controlled by setting 16 on my inverter. If AC and PV are on the inverter should use any of these sources to charge even with a hard switch off at the power switch. Read this with setting 16.

If PV is the only charger then AC will not charge. 

The same for AC. 

This is pretty standard that one would want to use any source available if activated. 

2 minutes ago, Scorp007 said:

Charging is controlled by setting 16 on my inverter. If AC and PV are on the inverter should use any of these sources to charge even with a hard switch off at the power switch. Read this with setting 16.

If PV is the only charger then AC will not charge. 

The same for AC. 

This is pretty standard that one would want to use any source available if activated. 

I'm afraid I don't understand what you mean, as I said, I know the AC will not be used as a charging source as that part of the unit no longer works and is not plugged in.

What I'm asking is If the unit has turned off (unresponsive to any button presses on the front panel) by itself due to low battery voltage overnight, when the sun comes up and the solar panels start producing power, will it switch on by itself despite the low battery voltage and start charging the batteries again?

1 hour ago, Lindsay said:

I'm afraid I don't understand what you mean, as I said, I know the AC will not be used as a charging source as that part of the unit no longer works and is not plugged in.

What I'm asking is If the unit has turned off (unresponsive to any button presses on the front panel) by itself due to low battery voltage overnight, when the sun comes up and the solar panels start producing power, will it switch on by itself despite the low battery voltage and start charging the batteries again?

Sorry. I misunderstood your question. 

34 minutes ago, Scorp007 said:

Sorry. I misunderstood your question.

Thanks for trying to help, hope someone else is able to help me out with an answer.

i wish i could answer your question. 

 

BUT. since you can switch the inverter off, and it will still charge with PV, it might be safe to assume that it could still charge even after the low battery cut off. 

are you going to attempt the scenario and give us feedback? 

2 minutes ago, Flouw said:

i wish i could answer your question. 

 

BUT. since you can switch the inverter off, and it will still charge with PV, it might be safe to assume that it could still charge even after the low battery cut off. 

are you going to attempt the scenario and give us feedback? 

Actually this time of the afternoon it must be known if it would switch on unless other parts of SA do not have as much sun as Gauteng. 

Another point there is the setting at what battery level to go back to battery. It should stay off with the AC side out of order until this level is reached. 

Even if you switch off the power switch it should switch itself on in the morning and charge the battery from solar. Power should be available when the battery voltage is high enough. But I think something must be wrong for it to be unresponsive at literally 23.0 V battery voltage.

The battery's BMS may well be switching the battery off for discharging at that voltage. They must have something tricky in there that allows charging (e.g. from your bench power supply), yet not allow discharging (e.g. to allow the inverter to power up).

A 24 V LFP battery has to be 8S, and 23.0 V is an average of 2.875 V per cell. This really is very low. I would certainly not want my LFP battery to go any lower. So that's my guess.

1 hour ago, Coulomb said:

Even if you switch off the power switch it should switch itself on in the morning and charge the battery from solar. Power should be available when the battery voltage is high enough. But I think something must be wrong for it to be unresponsive at literally 23.0 V battery voltage.

The battery's BMS may well be switching the battery off for discharging at that voltage. They must have something tricky in there that allows charging (e.g. from your bench power supply), yet not allow discharging (e.g. to allow the inverter to power up).

A 24 V LFP battery has to be 8S, and 23.0 V is an average of 2.875 V per cell. This really is very low. I would certainly not want my LFP battery to go any lower. So that's my guess.

I am glad we think alike on the lower level of lithium drop in batteries. Most suppliers say low cut out is 10.5V. My own are set at 12.5V.

I did a few tests with a 12V 7Ah today. The manual and sticker on the battery shows cut out of 10.5V as mentioned above. Funny the manual shows charge current of 2A at 14.4V. The sticker mentions 3.5A @ 14.2V

9 hours ago, Lindsay said:

so I moved my TV and then fridge onto mains and then put the inverter into sense mode (where it uses less power and will only turn on if there's a load). However I still had my DC loads running.

How do you get to the sense mode?  I don't know of such a function or setting on Axperts.  I only know of Victron inverters that have a low power mode where they pulse the 50Hz at a 1/50 duty cycle and then measure the current.  If the current is over a certain threshold the inverter activates normal power mode.

I presume you use a 12V buck regulator connected straight to the 24V battery for your 12V DC loads?  I think you should use an isolated step-down regulator if you do that.  If one of your 12VDC loads inadvertently is connected to an earthed system, such as a mains powered PC, TV, HiFi, etc., the earth could find a path to the negative battery terminal.  As far as I know that is not permitted and could damage the HV DC/DC or one of the other converters.

2 hours ago, Modina said:

If one of your 12VDC loads inadvertently is connected to an earthed system, such as a mains powered PC, TV, HiFi, etc., the earth could find a path to the negative battery terminal.  As far as I know that is not permitted and could damage the HV DC/DC or one of the other converters.

The battery is isolated on the Axperts, so that should not be an issue. I can't speak to regulations, however.

Thanks all for the responses...

20 hours ago, Coulomb said:

The battery's BMS may well be switching the battery off for discharging at that voltage. They must have something tricky in there that allows charging (e.g. from your bench power supply), yet not allow discharging (e.g. to allow the inverter to power up).

It's definitely not the BMS as it was still powering my DC loads at the time, but maybe you are right and there is something odd with the Mecer, I can tell it switched off at exactly 22.99V and when I woke up and checked it half an hour later it was unresponsive to any button presses. Only after the battery voltage either got around 24.2V (from my charging) or because the solar panels were starting to get some sun (it was after 7am at this point) did the fans in the Mecer suddenly briefly spin up and it powered on by itself in sense mode.

20 hours ago, Coulomb said:

A 24 V LFP battery has to be 8S, and 23.0 V is an average of 2.875 V per cell. This really is very low. I would certainly not want my LFP battery to go any lower. So that's my guess.

Yeah, I'm not going to let it get so low in the future. Oddly I think the Daly BMS I got with the LBSA battery kit has cutoff set quite low, I think 2.5V per cell, maybe even lower.

It seemed to charge up ok yesterday, not full, but ran ok through last night, although only with DC loads and I left the inverter in sense mode and haven't put the fridge back on it.

13 hours ago, Modina said:

How do you get to the sense mode?  I don't know of such a function or setting on Axperts.  I only know of Victron inverters that have a low power mode where they pulse the 50Hz at a 1/50 duty cycle and then measure the current.  If the current is over a certain threshold the inverter activates normal power mode.

It's a Mecer, which I thought was an Axpert clone, it's one of the first settings in the menu on the inverter and works as you describe, can't really keep it in this mode though for TV's/fridges.

13 hours ago, Modina said:

I think you should use an isolated step-down regulator if you do that.  If one of your 12VDC loads inadvertently is connected to an earthed system, such as a mains powered PC, TV, HiFi, etc., the earth could find a path to the negative battery terminal.

I don't really have any of my 12V systems near anything that's mains, my lights run permanently on the 12V, some network equipment like the router as well. I guess if someone uses a mains powered laptop and plugged it into the LAN then that might be a concern? Do you have a suggestion for isolated step-down regulator? I do have the 24V wires fused at 3 amps before they get to the buck, but I know that really only protects against shorts.

 

1 hour ago, Lindsay said:

Thanks all for the responses...

It's definitely not the BMS as it was still powering my DC loads at the time, but maybe you are right and there is something odd with the Mecer, I can tell it switched off at exactly 22.99V and when I woke up and checked it half an hour later it was unresponsive to any button presses. Only after the battery voltage either got around 24.2V (from my charging) or because the solar panels were starting to get some sun (it was after 7am at this point) did the fans in the Mecer suddenly briefly spin up and it powered on by itself in sense mode.

Yeah, I'm not going to let it get so low in the future. Oddly I think the Daly BMS I got with the LBSA battery kit has cutoff set quite low, I think 2.5V per cell, maybe even lower.

It seemed to charge up ok yesterday, not full, but ran ok through last night, although only with DC loads and I left the inverter in sense mode and haven't put the fridge back on it.

It's a Mecer, which I thought was an Axpert clone, it's one of the first settings in the menu on the inverter and works as you describe, can't really keep it in this mode though for TV's/fridges.

I don't really have any of my 12V systems near anything that's mains, my lights run permanently on the 12V, some network equipment like the router as well. I guess if someone uses a mains powered laptop and plugged it into the LAN then that might be a concern? Do you have a suggestion for isolated step-down regulator? I do have the 24V wires fused at 3 amps before they get to the buck, but I know that really only protects against shorts.

 

For what it's worth I run my 12V stuff from 1 of the batteries with a balancer between them and I am happy the way they work. 

I find my lithiums work well at a 25V alarm level on a clone and they never reach cut out level as I rather switch off than to risk a hard cut out. 

 

Edited June 2, 20233 yr by Scorp007

1 hour ago, Lindsay said:

It's a Mecer, which I thought was an Axpert clone, it's one of the first settings in the menu on the inverter and works as you describe, can't really keep it in this mode though for TV's/fridges.

What is the setting menu number?
 

1 hour ago, Lindsay said:

I don't really have any of my 12V systems near anything that's mains, my lights run permanently on the 12V, some network equipment like the router as well. I guess if someone uses a mains powered laptop and plugged it into the LAN then that might be a concern? Do you have a suggestion for isolated step-down regulator? I do have the 24V wires fused at 3 amps before they get to the buck, but I know that really only protects against shorts.

@Coulomb said it's not a problem.  Seems that the Battery DC/DC step-up converter is fully isolated.  So you should be fine using a normal (un-isolated) buck regulator. 

LAN (ethernet) uses small isolation transformers.  They are always contained in one of these small black blocks close to the RJ45 connector.  Obviously they can't withstand hundreds of volts of isolation.  I don't know what they are specced at, my guess is that they should withstand at least 100V.  Battery voltages should not be an issue.

On 2023/06/02 at 2:52 PM, Modina said:

What is the setting menu number?
 

@Coulomb said it's not a problem.  Seems that the Battery DC/DC step-up converter is fully isolated.  So you should be fine using a normal (un-isolated) buck regulator. 

LAN (ethernet) uses small isolation transformers.  They are always contained in one of these small black blocks close to the RJ45 connector.  Obviously they can't withstand hundreds of volts of isolation.  I don't know what they are specced at, my guess is that they should withstand at least 100V.  Battery voltages should not be an issue.

 

the setting number 04 in some models. - Power saving mode enable/disable,, If enabled, the output of inverter will be off when connected load is pretty low or not detected.

Thanks @Flouw.  I had a look at various user manuals.  A lot of them (including Mecer) do not have that setting, but I found one Mecer model that indeed has it.  Good to know.

4 minutes ago, Modina said:

Thanks @Flouw.  I had a look at various user manuals.  A lot of them (including Mecer) do not have that setting, but I found one Mecer model that indeed has it.  Good to know.

Yes, I have the Mecer 3KVA 24V Plus and it's setting 04 in the menu, SdS: Savings mode disable (default) and SEN: Saving mode enabled. In savings mode it pulses about once a second and tries to sense a load, and as @Flouw says, the load has to be over a threshold for the inverter to turn on, about 100W in my experience.

3 hours ago, Modina said:

Thanks @Flouw.  I had a look at various user manuals.  A lot of them (including Mecer) do not have that setting, but I found one Mecer model that indeed has it.  Good to know.

It seems I have a good clone as mine does have the setting and my manual also shows it. 

If you get a manual that covers the Plus versions it should be shown. 

Edited June 5, 20233 yr by Scorp007

11 hours ago, Scorp007 said:

It seems I have a good clone as mine does have the setting and my manual also shows it. 

If you get a manual that covers the Plus versions it should be shown. 

i dont have the Plus model, but have the setting, and mine is not a Clone, its the Mecer unit

4 hours ago, Flouw said:

i dont have the Plus model, but have the setting, and mine is not a Clone, its the Mecer unit

Good to know. I just thought that's why Modina has never seen setting 04.

Setting 04 also "disappears" if you have paralleled inverters, or even if your settings say that you have (even if you only have the one inverter).

This is the answer from ChatGPT:

 

Axpert is a brand of inverters commonly used in off-grid and hybrid solar power systems. When you mention "battery cut-off voltage" in the context of an Axpert inverter, you are likely referring to a feature called "low voltage disconnect" or "LVD."

The low voltage disconnect (LVD) is a critical safety feature in solar power systems that use batteries. It is designed to protect the batteries from over-discharge, which can lead to permanent damage and reduced battery lifespan. Here's what typically happens when the Axpert inverter reaches the battery cut-off voltage:

1. Voltage Threshold: The Axpert inverter is programmed with a specific voltage threshold (battery cut-off voltage), which is typically set slightly above the minimum safe voltage for the connected batteries. This threshold is often user-configurable.

2. Monitoring: As the batteries discharge during normal operation, the Axpert inverter continuously monitors the battery voltage.

3. Voltage Drop: When the battery voltage drops to or below the pre-set cut-off voltage, the inverter takes action.

4. Load Disconnect: The inverter will disconnect or cut off power to the connected loads (appliances, devices, etc.). This is done to prevent further discharge of the batteries, which could damage them.

5. Alarm/Notification: Some Axpert inverters may provide an audible or visual alarm when the low voltage disconnect is triggered. This serves as a warning to the user that the system is running on battery power and that action may be needed.

6. Reconnection: Once the batteries have been protected and the voltage rises back above the cut-off threshold (typically due to solar panel charging or other power sources), the inverter will automatically reconnect power to the loads.

This feature is essential for preventing deep discharge of batteries, which can shorten their lifespan and render them unusable. It ensures that there is always a reserve of charge in the batteries to provide backup power when needed.

Keep in mind that the specific operation and settings of an Axpert inverter may vary depending on the model and manufacturer, so it's important to consult the user manual or documentation provided with your particular inverter for precise details on how the low voltage disconnect function operates and how it can be configured to suit your needs.

 

 

 

This is the answer from ChatGPT:

 

Axpert is a brand of inverters commonly used in off-grid and hybrid solar power systems. When you mention "battery cut-off voltage" in the context of an Axpert inverter, you are likely referring to a feature called "low voltage disconnect" or "LVD."

The low voltage disconnect (LVD) is a critical safety feature in solar power systems that use batteries. It is designed to protect the batteries from over-discharge, which can lead to permanent damage and reduced battery lifespan. Here's what typically happens when the Axpert inverter reaches the battery cut-off voltage:

1. Voltage Threshold: The Axpert inverter is programmed with a specific voltage threshold (battery cut-off voltage), which is typically set slightly above the minimum safe voltage for the connected batteries. This threshold is often user-configurable.

2. Monitoring: As the batteries discharge during normal operation, the Axpert inverter continuously monitors the battery voltage.

3. Voltage Drop: When the battery voltage drops to or below the pre-set cut-off voltage, the inverter takes action.

4. Load Disconnect: The inverter will disconnect or cut off power to the connected loads (appliances, devices, etc.). This is done to prevent further discharge of the batteries, which could damage them.

5. Alarm/Notification: Some Axpert inverters may provide an audible or visual alarm when the low voltage disconnect is triggered. This serves as a warning to the user that the system is running on battery power and that action may be needed.

6. Reconnection: Once the batteries have been protected and the voltage rises back above the cut-off threshold (typically due to solar panel charging or other power sources), the inverter will automatically reconnect power to the loads.

This feature is essential for preventing deep discharge of batteries, which can shorten their lifespan and render them unusable. It ensures that there is always a reserve of charge in the batteries to provide backup power when needed.

Keep in mind that the specific operation and settings of an Axpert inverter may vary depending on the model and manufacturer, so it's important to consult the user manual or documentation provided with your particular inverter for precise details on how the low voltage disconnect function operates and how it can be configured to suit your needs.

 

 

 

We could perhaps expand on point 5 that the notification with alatm 04 on screen is given prior to reaching the cut off point. In 2 years I have only reached a cut off twice. 

Also one can use the N/O contact to drive a light or buzzer to earn of the cut off will be reached soon from this level. This condition will be reset if the load is reduced and the voltage recovers to above this trigger point. I reach this on a regular basis when using my microwave on a 24V Axpert. I use a 2W LED for this purpose clearly visible in the kitchen.