Last week while driving to work I wondered how the inverter would react if one exceeded the maximum discharge current when running in voltage mode. I have about 250 Ah 1C batteries in 3 banks. 2 x DIY (100 Ah) plus 1 normal battery (50 Ah)

I was running as per normal with the grid switched off and no PV as it was during the evening.

My setting is a low 50A discharge for 2.5 kW available. My charge current is set at a low 35A which works well for me.

The interesting thing which I would like to share is while running my induction plate, 1 kW spiral cooker and convection oven for a total load of about 3.3 kW (63A) the inverter just tripped and the error code was reported as F56 - DC Volt Low Fault. At the time of tripping the battery was at about 52.5V implying it was for sure not a low volt level but more an over current condition based on my 50A discharge. After a reset I still continued doing some weekly cooking for another 3 hrs.

As it is not common to run in voltage mode this could perhaps not be a common error picked up by many users.

I have never set up voltage mode for any of my clients, always lithium bms, but some of them still get the F56 low voltage trip ( without grid ), when they go over the discharge limits set up on the inverter or if it is a one battery set up

10 hours ago, Scorp007 said:

Last week while driving to work I wondered how the inverter would react if one exceeded the maximum discharge current when running in voltage mode. I have about 250 Ah 1C batteries in 3 banks. 2 x DIY (100 Ah) plus 1 normal battery (50 Ah)

I was running as per normal with the grid switched off and no PV as it was during the evening.

My setting is a low 50A discharge for 2.5 kW available. My charge current is set at a low 35A which works well for me.

The interesting thing which I would like to share is while running my induction plate, 1 kW spiral cooker and convection oven for a total load of about 3.3 kW (63A) the inverter just tripped and the error code was reported as F56 - DC Volt Low Fault. At the time of tripping the battery was at about 52.5V implying it was for sure not a low volt level but more an over current condition based on my 50A discharge. After a reset I still continued doing some weekly cooking for another 3 hrs.

As it is not common to run in voltage mode this could perhaps not be a common error picked up by many users.

I don't have Lithium batteries, so my SOC is determined by Voltage. But something that may be of interest, which would apply even if I had it set to voltage mode and had lithium, is that the inverter varies the cut-off voltage based on load. So, say at 1kw the cut off will be 24V, at 2kw load the cut off will be 23.6, etc. This is because of sag. It basically estimates what the sag would potentially be based on the load to avoid unnecessary switching off of the load, as a sag doesn't mean that the batteries are empty, as the voltage quickly recovers. Lithium sags also from what I have been told, so that might have been what happened.

I tripped my DC breaker this weekend for the first time in a year, as I had a load of 3.1kW and the sun completely disappeared due to a thick cloud, so the load was being supplied from the batteries alone. It is a 125A DC breaker, and I rated it so as to stay within the safe discharge current for my GEL batteries (5P2S config), so a little over 25A was pulled from each string before the breaker tripped.

Probably not related to your situation, but I thought I would share.

13 hours ago, Denns said:

I don't have Lithium batteries, so my SOC is determined by Voltage. But something that may be of interest, which would apply even if I had it set to voltage mode and had lithium, is that the inverter varies the cut-off voltage based on load. So, say at 1kw the cut off will be 24V, at 2kw load the cut off will be 23.6, etc. This is because of sag. It basically estimates what the sag would potentially be based on the load to avoid unnecessary switching off of the load, as a sag doesn't mean that the batteries are empty, as the voltage quickly recovers. Lithium sags also from what I have been told, so that might have been what happened.

I tripped my DC breaker this weekend for the first time in a year, as I had a load of 3.1kW and the sun completely disappeared due to a thick cloud, so the load was being supplied from the batteries alone. It is a 125A DC breaker, and I rated it so as to stay within the safe discharge current for my GEL batteries (5P2S config), so a little over 25A was pulled from each string before the breaker tripped.

Probably not related to your situation, but I thought I would share.

Thanks for sharing. In my case I know it was not due to sagging in voltage as I have a power meter which stores the accumulated Wh and Ah as well as the peak Watts and peak current and then the minimum voltage since last reset. Reset happens when the meter is disconnected from the battery supply.

When I used a 24V 2.4 kW Axpert inverter I had quite a number of trips as my Solarwise 125A DC MCB started tripping at just over 60A. The breaker itself also got quite hot and at times ran up to 80 degrees around the current tripping coil. Funny that it never tripped during surge starting current but always while the inverter had a constant load current used.

10 hours ago, Scorp007 said:

When I used a 24V 2.4 kW Axpert inverter I had quite a number of trips as my Solarwise 125A DC MCB started tripping at just over 60A. The breaker itself also got quite hot and at times ran up to 80 degrees around the current tripping coil. Funny that it never tripped during surge starting current but always while the inverter had a constant load current used.

That’s a sign of thermal derating or poor breaker design. Continuous load at high DC current caused internal heat buildup. Many “DC breakers” are rebranded AC types that can’t handle continuous high DC current properly. Poor terminal torque or contact resistance a common cause of localized heating and premature trips. Ambient heat rise 80 °C coil temperature suggests >50 °C case temperature, which can easily derate trip current to around 50–60% of nominal.

With that said any quality dc breakers are very expensive like the saying goes you get what you pay for. I use Noark as far as possible being very reliable and accurate also bi-directional for use on inverter battery systems.

Below a link to one supplier of these dc mcb and the average cost of a 200A mcb.

EasyPower Solar

Noark PV DC Disconnector 2P 1500V 10KA 200A

Noark PV DC Disconnector 2P 1500V 10KA 200A

Edited October 15, 2025Oct 15 by TaliaB
Added context

23 minutes ago, TaliaB said:

That’s a sign of thermal derating or poor breaker design. Continuous load at high DC current caused internal heat bubuild. Many “DC breakers” are rebranded AC types that can’t handle continuous high DC current properly. Poor terminal torque or contact resistance a common cause of localized heating and premature trips. Ambient heat rise 80 °C coil temperature suggests >50 °C case temperature, which can easily derate trip current to around 50–60% of nominal.

With that said any quality dc breakers are very expensive like the saying goes you get what you pay for. I use Noark as far as possible being very reliable and accurate also bi-directional for use on inverter battery systems.

Below a link to one supplier of these dc mcb and the average cost of a 200A mcb.

EasyPower Solar

Noark PV DC Disconnector 2P 1500V 10KA 200A

Noark PV DC Disconnector 2P 1500V 10KA 200A

That is quite a price, I must say. I have a Fivestar 125A DC breaker rated to 1000VDC. It costs 250 rand. I have never had issues with random trips, and when things like the microwave and airfryer run at night, I am pulling between 70 and 100A for about 5 to 15 minutes with no trips.

The battery cable is a 35mm2 one, and I used an HX-50B crimper to crimp those heavy-duty pin lugs to it, which go into the breaker. There is a chance he might have just had a bare copper end cable connected directly to the breaker. That may have made a poor connection. I had done it like this temporarily while waiting for the crimper and lugs to get delivered, and I must say the voltage drop was pretty high with just a 1kW load. After crimping, it improved considerably.

6 hours ago, TaliaB said:

That’s a sign of thermal derating or poor breaker design. Continuous load at high DC current caused internal heat buildup. Many “DC breakers” are rebranded AC types that can’t handle continuous high DC current properly. Poor terminal torque or contact resistance a common cause of localized heating and premature trips. Ambient heat rise 80 °C coil temperature suggests >50 °C case temperature, which can easily derate trip current to around 50–60% of nominal.

With that said any quality dc breakers are very expensive like the saying goes you get what you pay for. I use Noark as far as possible being very reliable and accurate also bi-directional for use on inverter battery systems.

Below a link to one supplier of these dc mcb and the average cost of a 200A mcb.

EasyPower Solar

Noark PV DC Disconnector 2P 1500V 10KA 200A

Noark PV DC Disconnector 2P 1500V 10KA 200A

As a old hand I do regular checks for tight connections. This comes from one of my tasks during an annual shutdown at a factory I worked decades ago.

The temp was measured on the plastic around the actual coil as the temp did vary quite a bit on different spots on the outside. I have comfort in the fact that it will trip when needed. Now that I run on a ceiling set on the Deye of 50A my system will not reach this level as this MCB only protects the cable to one of my 3 batteries from a busbar on my main disconnect/fuse carrier.