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guga avatar image
guga asked

SmartSolar 250/60 dropping current each few seconds

Hello,

My SmartSolar 250/60 keeps dropping solar and battery charging current every few seconds (screenshots below) and I can't get a stable charging current. I really appreciate your guidance to figure out what's happening. Below I describe my setup and the steps i've already gone through to troubleshoot following other topics posted in the forum.


Setup:

3x 160w panels in parallel (Resun RS6E160P). Vmp: 18.32V; Lmp: 8.85A; Voc: 23.6V; Lsc: 9A

1x SmartSolar 250/60 MPPT

4x 12v 220Ah Lead Acid Batteries in parallel

6mm2 solar cables rated for 65A

Main appliance consuming power: Dometic CRX refrigerator (65w nominal). It consumes an average of 2.5Ah in a tropical climate (i'm in south america).

MPPT Charging Behavior: can't get a stable charging current.


Troubleshooting Steps Done:

Fuses and circuit breakers check: i've read answered questions in the forum with the same behavior due to warm fuses/breakers. I've bypassed all of them between solar panels / MPPT and between MPPT and batteries. This behavior continues even with solar / mppt and batteries connected without any fuses/circuit breakers.


Changes in charging current: I can get stable charging behavior if I reduce the charging current between 10 and 20A, thus limiting a lot how much I harvest of wattage from solar panels. I noticed that if my battery bank is around 12-12.2v, a max charge current of 18-20A gives me a stable charging. Anything above 20A triggers the same up and down. If my batteries are near floating voltage (13-13.2v), I only get it stable by lowering charging current to nearly 10A.


Open Question before i try other steps:

1. Solar panels in parallel keep solar voltage around 18-20V and MPPT starts the charging cycle when PV is 5V above batteries. Not sure if i'm having trouble there, although I wonder if PV could drop reducing the difference below 1V between PV and battery, triggering a gap in charging (that's what the manual says). I see a voltage drop in the monitor (screenshots below) but the difference is still over 1V between PV and battery. If I connect solar panels in series, would this be solved? I want to avoid having all the work before checking with experts. :-)


2. Temperature: as I mentioned, i'm in the summer of south america. Temps are between 28/35C (really warm), and i've seen people saying that MPPT with temps above 40 become unpredictable. I'll try using a computer fan to lower temperature.


Any other Ideas are very welcome! And thanks in advance.

Gustavo Siqueira


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Screenshots:

Current drops to zero every few seconds.

1646655917325.png

Bat and solar voltage behavior

1646656018579.png





MPPT Controllers
1646655917325.png (534.5 KiB)
1646656018579.png (577.6 KiB)
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2 Answers
Paul B avatar image
Paul B answered ·

What I am seeing in the graphs is that the amps are dropping but the PV voltage is going high

Now it looks like the Panel voltage is dropping to under 1v diferance to the battery voltage - this will then cause the MPPT to turn off. so change the panels to series so the PV voltage is a lot higher. and It should solve your issue


Or try this

Please do these tests

1. discharge the battery to 70% or around 12.5v then does it still give the same issue if it does then do item 2. if not then its pointing to the not enough voltage diferance

2. Take the PV pos and Neg OUT of the MPPT unit and JOIN them togeather - yes this will short the panels . now put a clamp meter over the cable select DC amps's - you should then have a Steady current flow at about the panels rated amps when in good sunlight- if is still going up and down sthen you have a bad connection in one of the solar strings or a faulty panel.

( keep a eye on ALL PV connections and feel them and see if any are getting warn or hot)

once determined disconnected the wires again.


this should then rule out a panel issue -


3. then direct connect the mppt Bat + and - direct to the batteries without and fuses or inline connections.


4. Try another regulator to see if this still happens.

if it does then return the unit to your supplier for testing/ replacement



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guga avatar image guga commented ·
Thanks a lot for the comments. I'll follow the tips and will get back here with the results.
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guga avatar image
guga answered ·

Problem solved!

Followed the steps recommended and the switching the solar panels to series solved the problem I had with charging current dropping every few seconds.

Now I get a steady constant charging current.

1648810848475.png


Now I can move to the next challenge -- fine tune BMV700 SOC and current readings (but i'll post the issue in a separate topic/thread).

Thanks again for the help!


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