As I understand it the 400v PV input is converted to battery input levels by the MPPT, please correct me if I'm wrong. Apparently 400v PV input models do not send the 400v to the bus side after the DC to DC circuit,

12 minutes ago, AndrewF said:

As I understand it the 400v PV input is converted to battery input levels by the MPPT, please correct me if I'm wrong. Apparently 400v PV input models do not send the 400v to the bus side after the DC to DC circuit,

@Coulomb may want to also add his comments, but essentially the 400V PV models save you money on copper, not sure if you checked out copper pricing recently, I nearly soiled my shorts... anyway, to run, lets say 3kW's worth of PV power at 300V, will only require 10 to 15A on the cable capacity side, whereas if it were at battery Voltages, you'd be looking at 60A or so and thus a somewhat LARGER cable diameter...

are there losses converting 400v to 48-50v battery levels input of inverter, if so what is the loss % down converting 400v PV input to battery levels

Only low voltage (145V) models convert PV input to battery levels. On high voltage (500V) models, PV input goes to the high voltage side. Check the schematic here:

https://powerforum.co.za/topic/14666-repair-of-axpert-inverters-a-journey-started/#findComment-138439

edit: Or better this one:

The first one doesn't have a PV input, actually.

Edited August 20, 2025Aug 20 by kuba.cz

On 2025/08/20 at 11:56 PM, kuba.cz said:

Only low voltage (145V) models convert PV input to battery levels. On high voltage (500V) models, PV input goes to the high voltage side. Check the schematic here:

https://powerforum.co.za/topic/14666-repair-of-axpert-inverters-a-journey-started/#findComment-138439

edit: Or better this one:

The first one doesn't have a PV input, actually.

Do all high PV Input (500V) Hybrid Inverters follow this block diagram where PV input is connected to the HV bus..

9 hours ago, AndrewF said:

Do all high PV Input (500V) Hybrid Inverters follow this block diagram where PV input is connected to the HV bus

No. Most of the all-in-one's do, as they can and it makes sense. Including Axpert, InfiniSolar, Deye. But when comes to modular systems they always convert PV to the battery voltage first, even when using high-voltage PV strings. For example:

• Victron RS450 (450V)

• Studer VS120 (900V)

Anyway, for smaller systems it's advisable to stay with low-voltage PV strings. But when you go for let's say 40kWp and above then the low-voltage strings will start to be a real complication. For example, having roughly 40kWp with 520V per string (13S) needs just 6 strings. But with 120V (3S) you will need 26 strings. Not to mention that you need SPDs and fuse disconnects for all of these. And once you try to lower the amount of these components by paralelling more and more strings together, then you end up with extreme currents on the PV side, that will need thick cables and will have voltage drop losses due to cable length and resistance.

Long story short - each use case needs a different approach. Sometimes LV PV is the best, sometimes HV PV is. And that is the reason why the portfolio of available products is so broad.

Edited September 2, 2025Sep 2 by Youda

On 2025/08/18 at 6:24 PM, AndrewF said:

As I understand it the 400v PV input is converted to battery input levels by the MPPT, please correct me if I'm wrong. Apparently 400v PV input models do not send the 400v to the bus side after the DC to DC circuit,

Sorry for the very late reply.

No, the Voltronic high PV voltage models (450-500 V max PV) boost the PV voltage (if needed, else pass through) and it's used as the DC bus voltage. To charge the battery from PV, this power is then pushed back to the battery by running the DC-AC converter in reverse (effectively making it an AC to DC converter). It also runs the DC-DC stage (bus to/from battery voltage) in reverse. The power flow can change dynamically as loads and available PV power go up and down. If necessary, the buck stage will reduce the voltage to the DC-DC converter stage when charging the battery.

Only the 145 V max (and lower) Voltronic models buck directly to the battery voltage.

The reason for this disparity is efficiency. Transformerless power converters (which in an Axpert is all of them except for the DC-DC stage) work more efficiently when the ratio of input to output voltage isn't too large. So bucking directly from say 400 VDC panels to 50 VDC battery is an 8:1 difference; it would not be efficient. 130 V bucking down to 50 V (2.6:1) or 120 V up to 360 V (1:3) is acceptable, but you get better performance when bucking down from 80 V or boosting up from 320 V.

On 2025/09/26 at 6:38 AM, Coulomb said:

Sorry for the very late reply.

No, the Voltronic high PV voltage models (450-500 V max PV) boost the PV voltage (if needed, else pass through) and it's used as the DC bus voltage. To charge the battery from PV, this power is then pushed back to the battery by running the DC-AC converter in reverse (effectively making it an AC to DC converter). It also runs the DC-DC stage (bus to/from battery voltage) in reverse. The power flow can change dynamically as loads and available PV power go up and down. If necessary, the buck stage will reduce the voltage to the DC-DC converter stage when charging the battery.

Only the 145 V max (and lower) Voltronic models buck directly to the battery voltage.

The reason for this disparity is efficiency. Transformerless power converters (which in an Axpert is all of them except for the DC-DC stage) work more efficiently when the ratio of input to output voltage isn't too large. So bucking directly from say 400 VDC panels to 50 VDC battery is an 8:1 difference; it would not be efficient. 130 V bucking down to 50 V (2.6:1) or 120 V up to 360 V (1:3) is acceptable, but you get better performance when bucking down from 80 V or boosting up from 320 V.

Based on this explanation will a 145v max model voltronic buck say 40-45v up to 49v for battery input it there is enough current supplied by panels(direct sun exposure)

Just now, AndrewF said:

Based on this explanation will a 145v max model voltronic buck say 40-45v up to 49v for battery input it there is enough current supplied by panels(direct sun exposure)

Which brands do this form of bucking the solar input voltage to acceptable bus voltage for 400V versions and buck solar input voltage to battery input voltage for the 145v versions..

On 2025/10/25 at 9:59 PM, AndrewF said:

Based on this explanation will a 145v max model voltronic buck say 40-45v up to 49v for battery input it there is enough current supplied by panels

I very much doubt it, that's a very low voltage. Also, the high PV voltage models require pulses from the DSP, and it would be trying to regulate bus voltage, not battery voltage. So almost certainly you can't use the "wrong" type of solar charger.

As for which models do which, just check the PV charging specs. The voltages will tell the story.

Edited October 29, 2025Oct 29 by Coulomb

On 9/26/2025 at 7:38 AM, Coulomb said:

work more efficiently when the ratio of input to output voltage isn't too large

So is this why there’s an MPPT voltage range, and the PV never starts working before reaching the minimum threshold? I’ve seen some cheap cloned Voltronic models that were modified at dealers’ request to start at 30 V — those exact units produce noise and interfere with TVs and ADSL routers whenever the PV is active ؟

On 2025/12/21 at 6:17 PM, esmail-kassir said:

So is this why there’s an MPPT voltage range, and the PV never starts working before reaching the minimum threshold?

That's part of it. The high PV voltage models vary with their minimum MPPT voltage: some are 120V, others 90V, and others have 60V. The start voltage is often higher than the minimum MPPT voltage. So for example the start voltage could be 150V; once this is reached, it could be dragged down to say 90V by load and/or light conditions, yet keep working. If low light dropped the panel voltage below the minimum MPPT voltage, then the PV will switch off until the start voltage (150V in this example) is seen again.

I'm amazed that the minimum MPPT voltage could be (semi officially?) set as low as 30V. This would indeed be very inefficient, so the solar converter would work hard, but I would not have expected that to cause excessive interference.