question

mihlit avatar image
mihlit asked

Negative MPPT power in node red and MQTT

Right now, Cerbo shows pv production jumping between 0 and -5.3 W. I guess that negative value means there is some wrong formula in the sw that should be fixed.

I get the negative value both in Node-red
node "Venus system | MPPTs - power (W)" and MQTT at

N/<id>/system/0/Dc/Pv/Power

Venus OS version is v3.00~42

MQTT history log:

07/17/2023 8:44:29 PM(-2.02 seconds) 

{"value": -5.256000215649607}

07/17/2023 8:44:23 PM(-6.03 seconds) 

{"value": 0.0}

07/17/2023 8:44:21 PM(-1.98 seconds) 

{"value": -5.258000261455777}

07/17/2023 8:44:07 PM(-14.03 seconds) 

{"value": 0.0}


Note: During the day, when there was enough sun, values were correct - matching expectation. On the other hand, I can spot 0 jumping to -5 easily, but would not notice 5 W jumps on high values.

cerbo gxMQTTbug report
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smallsolar avatar image smallsolar commented ·
Are you using the load outputs on the mppt or are they on? Mine shows the same, but I have some loads on the load outputs of the mppts and the load is always on.
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mihlit avatar image mihlit smallsolar commented ·
No, I don't use load output.
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2 Answers
d-ferdi avatar image
d-ferdi answered ·

hello,

what mppt does you use?

i have this only with mppts with a connected load or mppts which are powered from accu.

is this the power from pv or from accu?

goodby

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mihlit avatar image mihlit commented ·

I'd say usual 48V setup. First MPPT is SmartSolar 100/20 with 2p2s 1.16kWp, second one SmartSolar 150/85 ve with 1p3s 1.18kWp atm, both connected to LFP battery, nothing on 100/20 load terminals (150/85 does not have those) and no other DC load except MPII inverter.

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d-ferdi avatar image d-ferdi mihlit commented ·
hello,

i think, that you have no load on the system and you accu is full, then this can happen.

in this case the mppt shut off, because it cannot load energie to the accu and there is no need to transfer energie to any other devices.

i see only a negative pv power on my system, if i don't have enouth pv-power for my load at the load-port of the mppts or my old mppt 150/70 is powered from accu with 0,2-0,3A per mppt.

which system-voltage have you, if this happens ? and which is the maximum voltage set in the mppts?

it can be possible that the mppt 150/85 use power from accu for a short time, if it is off because you have reached the max voltage.

some of my old mppt 75/50 can't be powered from accu, but all mppts which can be powered from accu need a powersuply connected to the accu and one connected to the pv-input to get the needed power. if the mppt is on, it tranfer energie from pv to accu-side and if it is off, it can't transfer the energie which the second power-suply needs.

i have no circuit diagram of the mppts, but i think, this can be a reason for you negativ pv-power.

i have powered some of my old mppt 75/50 with a resistor from accu and it need very less power, but the big 150/85 with can-bus needs more power for itself as the smaller mppt-controllers.

goodby

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mihlit avatar image mihlit d-ferdi commented ·
Checking the logs, battery SOC was 50.8 %, so far from full. Both MPPTs were in BULK state. Battery was 52.57V, DVCC max is set to 55.5 V, so also not near that limit (and battery was discharging at that time anyway).
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d-ferdi avatar image
d-ferdi answered ·

hello,

which pv-voltage have you? is the mppt in off-state ?

get you power from mppt if you remove the data-connection to the gx-device?

if you have bms connected to the gx, check the bms-parameters. this can prevent the system from charging. my bms set the charge current to 0 if accu is full. but this can also happens, if something is wrong like a very unbalanced accu.

bulk is ok, but which charge current do you have. in this case the mppt should transfer the hole pv-power to the system. if not, there must be a current-limit active.

i think, you can check that with the victronconnect-app and check the batterie settings. normaly the gx will overwrite this, but it can only overwrite the voltage with a hight value, not the current!

the only way to get the actual parameters is with an own program or terminal-program over a vedirect-connection. you must read registers 2001 voltage and 2015 current. some samples are in the vedirect hex docu.

goodby

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