No Load output current sensing

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Michael Vesovic asked Nov 20, '19

No Load output current sensing

Hi all,

We are employing the SmartSolar MPPT 75/15 in a number of remotely located instrument cabinets that will eventually be inaccessible to people. To remotely monitor the SmartSolar device, we are utilizing a Serial to Ethernet bridge. This device also allows us to also perform any mandatory firmware updates remotely, but with a caveat.

In order for us to be able to take advantage of the SmartSolar’s load current sensing, our load (‘Ethernet Devices’) needs to be connected to the LOAD output. However, during a firmware update, the LOAD output switches off at the 4% mark, thereby causing the firmware update to stop indefinitely. D1 solves this issue by sourcing power directly from the battery (Batt) when the LOAD output switches off (during a firmware update). The side effect of connecting the Batt terminal to the LOAD via D1 is that the LOAD output never comes back on, despite VictronConnect stating that the LOAD is ON. Instead current continues to flow through D1, therefore current sensing on the LOAD terminal never takes place. Only by utilizing D2 does the load current flow through the LOAD terminal and reported in VictronConnect.

Our question: Before we invest time in building a low-power-loss device (FET in place of D2) to circumvent this issue, is Victron able to provide a firmware update that ensures that either the SmartSolar LOAD output always stays on during a firmware update, or at least a firmware update that would allows us to omit D2? And failing a response here, how can we contact Victron directly with this request?

Thanks in advance,

Michael

MPPT Controllers firmware update current limit

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klim8skeptic ♦ commented · Nov 22, 2019 at 12:06 AM

Question, Why do you want load current sensing?

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Answer 1 · 2019-11-20T08:26:42Z

wkirby answered · Nov 20, 2019 at 08:26 AM

It is not possible to update firmware on the microcontroller without is going into reset at some point. When the microcontroller goes into reset, the output which drives the MOSFET at the Load Output goes low and therefore the MOSFET sitches off.

You want D1 to stop conducting when the Load Ouput switches on, ie. you want the Voltage at the Cathode terminal of D1 to be less than ~0.6V lower than its Anode.
This is difficult to acheive when D2 is presenting a similar Voltage drop to that node of the circuit.
So, you could increase the turn on threshold of D1 by adding another one in series with it. This will mean that the two diodes, D1 and (D3) would present a 1.2V drop which is probably OK for your Serial - Ethernet bridge to operate during a firmware update, but when the Load Output is On, the Voltage at the Cathode of (D3) will be less than 1.2V below the Anode of D1 (D1 and D3 in series).
With the D1 and (D3) network unable to conduct, all the current for your equipment must flow through Load and D2.

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Michael Vesovic commented · Nov 20, 2019 at 07:43 PM

Thanks, WKirby.

To minimise power loss and to lower the voltage drop across D2 (the diode which will be conducting full-time) we will try replacing it with an 'ideal diode' with a suitable low RdsOn FET.

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Answer 2 · 2019-11-20T20:28:10Z

Robert answered · Nov 20, 2019 at 08:28 PM

if a system is working satisfactorily, why do any firmware updates on the MPPT?

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Michael Vesovic commented · Nov 21, 2019 at 10:29 PM

According to Victron, mandatory firmware updates are required to fix serious bugs.

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