Hi everyone.

I installed a Studer XPC-Compact inverter some 12-13 years ago as a standby inverter for a large marine aquarium that I had in the good old days before loadshedding became a serious problem. This unit was powered by 4x180Ah AGM lead-acid batteries connected 2S2P - thus 360Ah 24V - and connected to grid power only - no PV panels.

I replaced this unit in September 2024 (the original batteries were down to about 25%-30% of their original capacity - excellent performance for lead-acid batteries 😊) with a 12kW hybrid inverter, solar panels, and LiFePO4 batteries, and this old unit ended up in storage. My idea is to give it a second life on a farm that does not have any electricity, just to power some lights, a laptop, and some cellphone charging.

Some specs: Continuous power output = 1600VA, peak power (for 30 minutes) = 2200VA. Built-in "Battery charger" (that's what Studer called it... but it is actually two-way operation, both charging the battery and powering the inverter by discharging the battery...) max 37A x 28V end of bulk charge voltage with adjustable absorption time and 31.2V equalization voltage than can be disabled.

Now, for my questions:

1. Would it be possible/feasible to connect this old unit to a suitably sized lithium battery?

2. Would it be possible/feasible to charge the battery (lead-acid or LiFePO4) by connecting it directly to a MPPT controller with suitable (24V - 28V depending on the battery) voltage, and also have the inverter coupled to it via the battery so as to run the unit off PV directly during the day?

3. Anything else I should be asking...?

Thanks in advance for your input.

7 hours ago, HennieL said:

Hi everyone.

I installed a Studer XPC-Compact inverter some 12-13 years ago as a standby inverter for a large marine aquarium that I had in the good old days before loadshedding became a serious problem. This unit was powered by 4x180Ah AGM lead-acid batteries connected 2S2P - thus 360Ah 24V - and connected to grid power only - no PV panels.

I replaced this unit in September 2024 (the original batteries were down to about 25%-30% of their original capacity - excellent performance for lead-acid batteries 😊) with a 12kW hybrid inverter, solar panels, and LiFePO4 batteries, and this old unit ended up in storage. My idea is to give it a second life on a farm that does not have any electricity, just to power some lights, a laptop, and some cellphone charging.

Some specs: Continuous power output = 1600VA, peak power (for 30 minutes) = 2200VA. Built-in "Battery charger" (that's what Studer called it... but it is actually two-way operation, both charging the battery and powering the inverter by discharging the battery...) max 37A x 28V end of bulk charge voltage with adjustable absorption time and 31.2V equalization voltage than can be disabled.

Now, for my questions:

1. Would it be possible/feasible to connect this old unit to a suitably sized lithium battery?

2. Would it be possible/feasible to charge the battery (lead-acid or LiFePO4) by connecting it directly to a MPPT controller with suitable (24V - 28V depending on the battery) voltage, and also have the inverter coupled to it via the battery so as to run the unit off PV directly during the day?

3. Anything else I should be asking...?

Thanks in advance for your input.

Yes you can surely use it even for lithium. Just disable the equilization.

Yes you can get a MPPT like a Victron or Epever where you can set the correct settings for the battery used.

I and some other members have in fact used a external MPPT together with the inverter charger to increase the PV power that can be connected. 24V Axpert in my case.

Thanks for your input @Scorp007

@Energy-Jason Can you please suggest a suitable external MPPT and 24V battery (preferably with a larger capacity than my original)

@TaliaB and other electricians/installers: Keeping in mind that this unit will be fully off-grid, I will probably have to install a decent grounding rod to earth everything connected to the inverter - can anyone please advise on determining the correct length of rod, and also please comment on anything else required on the circuit: I'm planning to install a DC isolator between the solar panels and the MPPT, as well as between the battery and the inverter. Would an earth leakage (RCD) unit be needed on such a small device? Are there combination RCD and over-current isolators available in South Africa, and would such a device be preferable over a common RCD? Anything else ???

1 hour ago, HennieL said:

Thanks for your input @Scorp007

@Energy-Jason Can you please suggest a suitable external MPPT and 24V battery (preferably with a larger capacity than my original)

@TaliaB and other electricians/installers: Keeping in mind that this unit will be fully off-grid, I will probably have to install a decent grounding rod to earth everything connected to the inverter - can anyone please advise on determining the correct length of rod, and also please comment on anything else required on the circuit: I'm planning to install a DC isolator between the solar panels and the MPPT, as well as between the battery and the inverter. Would an earth leakage (RCD) unit be needed on such a small device? Are there combination RCD and over-current isolators available in South Africa, and would such a device be preferable over a common RCD? Anything else ???

The green toggle RCDs are only RCD and the white includes overload. The imported common RCD will show on the legend of the unit if it is only an isolator or if it includes the overload. A symbol which looks like a T junction is only isolator. As soon as it has a X on the switch level then it is a circuit breaker as well.

Even if the system is only say 250W at over 100V one can still be killed during a shock. One would thus always use a RCD that can trip if one had to touch any live wire. Plug sockets is a MUST to be protected. Even as small as the system if it feeds multiple circuits one needs to do it according to SANS.

15 hours ago, HennieL said:

Some specs: Continuous power output = 1600VA, peak power (for 30 minutes) = 2200VA. Built-in "Battery charger" (that's what Studer called it... but it is actually two-way operation, both charging the battery and powering the inverter by discharging the battery...) max 37A x 28V end of bulk charge voltage with adjustable absorption time and 31.2V equalization voltage than can be disabled.

1.Should be fine with lifep04 batteries.

2. I would suggest using a Victron SmartSolar Mppt.

3. Earth rods are standard 1.2m. It will depend on the soil resistivity as how many earth rods to use you are aiming for 5 ohms for the Rcd to function. I= 230/5= 46ma would flow in the case an earth fault high enough for the RCD to discconect. Always use a RCD on any ac source as >40ma is hazardous. Remember to measure the output voltage from the inverter between neutral and earth as i doubt that it would have a internal bonding relay. You could do a permanent bond between neutral/earth for off grid applications. Also the RCD @Scorp007 described that provides overcurrent implemented within the RCD is quite expensive so what i normally use is a mcb before the RCD(no overload) that is much cheaper and works well. Also use a double pole isolator as a main switch(inverter output connected) that is a Sans10142 requirement. Would you consider a small inverter generator for redundancy during lengthy cloud cover. Should you use the RCD with overload no need for an isolator as the RCD can be used as a main switch

Should you need spesific calculations on mcb sizing and wire gauges feel free to ask as there it plenty of forum members that could assist.

Thanks for everyone's advice - much appreciated.

21 hours ago, TaliaB said:

Would you consider a small inverter generator for redundancy during lengthy cloud cover. Should you use the RCD with overload no need for an isolator as the RCD can be used as a main switch

This farm is really in the outbacks and has never had electricity - still using paraffin lamps etc. Also, no cellphone reception on most of the farm - heaven on earth 😁

This is a weekend farm, with only one labourer staying there full time. A 2kW portable "power bank" is currently used over the weekends, and recharged in town during the week.

I do have a 5kVA generator that can be used for backup if needed. This Studer inverter has separate "AC In" and "AC Out" circuits, and back when I used it as a backup for my aquarium I simply had a 3-point plug on the "AC In" cable, plugged into a 15A plug socket. Whenever the batteries became exhausted during prolonged power outages I simply plugged a 3-core extension lead into this generator, and plugged the inverter's "AC In" plug into the lead. Given that there is no grid power on the farm, I plan to do the same there if really needed, although the new battery should last for two nights over the weekend, and be fully recharged during the week when there is no consumption.

23 hours ago, TaliaB said:

1.Should be fine with lifep04 batteries.

2. I would suggest using a Victron SmartSolar Mppt.

3. Earth rods are standard 1.2m. It will depend on the soil resistivity as how many earth rods to use you are aiming for 5 ohms for the Rcd to function. I= 230/5= 46ma would flow in the case an earth fault high enough for the RCD to discconect. Always use a RCD on any ac source as >40ma is hazardous. Remember to measure the output voltage from the inverter between neutral and earth as i doubt that it would have a internal bonding relay. You could do a permanent bond between neutral/earth for off grid applications. Also the RCD @Scorp007 described that provides overcurrent implemented within the RCD is quite expensive so what i normally use is a mcb before the RCD(no overload) that is much cheaper and works well. Also use a double pole isolator as a main switch(inverter output connected) that is a Sans10142 requirement. Would you consider a small inverter generator for redundancy during lengthy cloud cover. Should you use the RCD with overload no need for an isolator as the RCD can be used as a main switch

Should you need spesific calculations on mcb sizing and wire gauges feel free to ask as there it plenty of forum members that could assist.

Thanks for the detail input. For the once off safe install I think spending just over R300 on these type of RCD with overload as a main switch as per this installation is not too dear. These are also available as a 40A current version ideal for smaller inverters. ABB also market a similar RCD combined unit as well as so many imports. I am happy with my ABB brand.

Just a question on the SANS556 quoted in this picture. Could you perhaps expand a bit on what is contained in this set of regulations/requirements.

50 minutes ago, Scorp007 said:

Just a question on the SANS556 quoted in this picture. Could you perhaps expand a bit on what is contained in this set of regulations/requirements.

That the manufacturer adhere to the spesifications in this standard.