I recently installed a Victron MPPT 100/20 controller fed by two, identical 185W, 12V panels wired in series. Battery is a Fogstar 105Ah LiFe PO4 (with it’s own BMS and self-heater). Intallation is remote, off-grid.
All has been working as expected with battery usually showing 100% charge upon arrival at the site. However, yesterday and today the charging remained resolutely “off” in spite of drawing a load (10w- 25w) to run lighting. At first I assumed this was because the battery was fully charged and had ‘told’ the charge controller that it did not need charged. However, having left the lighting on all day which reduced the battery capacity to 81%, the controller is still showing tha state; "Charging is off’.
Weather is beautifully sunny. I would normally expect to see 40v - 50v from the panels in such weather but the displayed voltage from them has been hovering around 13 volts all day and no current, regardless of how much sun is shining on them. I didn’t have my multi-meter with me, so I wasn’t able to check the actual voltage being produced by the panels when disconnected from the controller. Because the system is still new to me, I’m not sure if the solar panel voltage displayed on the Victron app is the actual voltage produced in the panels or the modulated voltage that the controller has set for them?
There was a brief period yesterday evening when the charger displayed “Bulk” and the display values were what I would expect, but it was shortly before sunset and the charger was back to being ‘off’ again as darkness came.
I’m assuming that the Forgstar battery will take priority over the charge controller and will only accept charging power when it requires it? Given that it has been sitting fully charged for over a week in sunny weather, perhaps it is in some kind of maintenance mode, where it wishes to discharge significantly before allowing a recharge?
I’ll be back at the site in a couple of days armed with my multi-meter. What should I be checking for? Thanks for any help.
Your panels at 12V each will generate a maximum of 24ish Volts.
Your panels in that pic are producing 10V the battery is at 13V. The PV needs to get above 18V to start the mppt.
You either have poor connections or your PV is insufficient to reliably charge the battery.
Thank you very much for your reply Nick, but you have perhaps missed some of what I wrote? For example:
“All has been working as expected with battery usually showing 100% charge upon arrival at the site” (Until now. Something has changed)
“Weather is beautifully sunny. I would normally expect to see 40v - 50v from the panels in such weather”
“I’m not sure if the solar panel voltage displayed on the Victron app is the actual voltage produced in the panels or the modulated voltage that the controller has set for them?”
I am aware that the panel voltage needs to be +5V relative to battery voltage to initiate charging, but as I said, I would expect the voltage to have been much higher than 10V in such sunny weather (see screenshot below from early March on a less sunny day). The panels face due south and were in full sunshine under a clear blue sky at mid-day. Something is reducing the voltage from the panels and I’m wondering if it is the controller doing this?
If the charger is reporting 10V then you have an issue on what seems to be the PV side.
I would check that carefully.
If this mppt has an external fuse, then check that also.
If the solar does not register battery voltage plus 5V it won’t start. As simple as that.
Thank you Nick. I shall carefully check all the PV connections when I next visit. I’ll also rig up a substitute cable from PV to controller to check & rule out whether the existing wiring is faulty. Panels are brand new Victron models and should have sound MC4s, but I’ll double check them to be certain.
If the controller is throttling the power output from the panels, I would have expected it’s heat-sink to get warm or even fairly hot. This was not happening, so perhaps this indicates the fault is in the supply side. Cables are 4mm2 and should be operating within their rated value.
I’m not sure if this unit ( MPPT 100/20) has an external fuse or not. I’ll check the manual.
Fuse on the controller was OK. Up onto the roof, to check the MC4 connectors from (brand new) panels to existing cable leading down to the controller. One of the new MC4 conectors from the panel had a ‘burnt’ looking apperance and it’s female counterpart on the existing wiring looked corroded. All other connector pins were shiny and silver. So I reckoned this was a bad joint. Panel voltages open-circuit were all good.
I tested the ‘bad-joint’ theory by plugging in a substitute cable to the controller and this brought back normal operation. So I cut off the ‘bad’ connector and fitted a new one. Cleaned the ‘burnt’ looking pin with fine emery paper, blasted all connectors with silicone lube and re-fitted back together. System now happy and displaying a health 280 watts and 37 volts. battery was charged from 81% to 100% in 90 minutes or less. All good.
Reading through this forum, I can see that my experience is a very common one; assuming that there is a fault with the electronics before suspecting and checking the very basic stuff like connectors & joints. Thanks for all the help.
What I would like now is to find a source for good-quality, long-lasting MC4 connectors and replace them all. There is so much equipment available nowadays that it is hard to be sure if one is buying properly made gear. The joint that failed was only two years old.
Can anyone recommend a source of high-quality connectors (and fuses please) from UK suppliers?
Glad you came right. There was a topic lurking somewhere about poor quality connectors and rather sourcing from the original manufacturer.
Connections wear with time. Always good to inspect regularly but I suspect the reason electronics is always the first target is simply because its harder to get the ladder out
