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Why do Axperts run hot in Hybrid (SUB) mode, but cool in SBU?

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I have something curious on my Axpert VMIII 3KW (2019):


The temperature remains constant around 40 degrees when in SUB mode.

When I switch to SBU mode (Solar is powering the loads by this time), then it drops off pretty close to ambient temperature.

The load is under 500W here, for the duration of this graph.

I'm curious if anybody can explain why this is the case.

Edited by Ben Harper
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5 hours ago, Ben Harper said:

I'm curious if anybody can explain why this is the case.

My wild guess is that as the PV starts generating power, the fans (or at least one of them) runs faster, cooling the heatsinks. Voltronic attempt to have the fans run more often in the daytime (when PV is generating), so it's quieter at night.

At night, the constant 40°C will be the equilibrium of the waste heat with the ability of the heatsinks to dissipate heat with little or no fan cooling. The reported temperature is the maximum of several temperature measurements; the heatsink running the loads (which will probably be varying even at night, as the fridge(s) and/or freezer(s) switch on and off) might be cycling up and down in temperature, but always less than some other heatsink or the transformer, which has a fairly constant (mostly self consumption) load. As I type this, it's not very convincing to myself, but I don't know the VM models well.

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Thanks.. I guess what I'd really love to know is precisely how the "hybrid" circuit works.

I clearly recall seeing in my telemetry a while ago that the load on the inverter was a sustained 4KW for many minutes (it's a 3KW model), and the inverter's overload protection clearly didn't kick in. I have no reason to believe that the overload circuitry is broken, because I often get the "beep beep" for a second or two as the washing machine element kicks in, but before my automated switchover has sent the washing machine back to grid power.

So what I'm wondering is if the design of the hybrid circuity somehow allows more than the rated power to be safely utilized.

This is not something I intend to make a habit of!

But it did make me curious.

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Hi Ben

Not sure about your VM3, but I know with my King 5kVA it has an option to Enable Bypass on Overload. Basically just switches a relay that connects input AC directly to output if we try to draw more than 5kW (usually a visitor who doesn't know not to put a kettle on while the geyser is heating!). In bypass mode the inverter can easily sustain more than 5kW (I expect they've got at least a 40A relay in there), but it does complain about it the whole time. There shouldn't be excess heating from this, since it's not having to do any sort of rectification or inversion.

I'd also be interested to know if this is similar on your unit :)


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