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carl-erik-kopseng avatar image
carl-erik-kopseng asked

Charge controller (MPPT 75/15) lights not turning on

I recently chose to replace an older PWM controller with a Victron MPPT 75/15 charge controller, and yesterday I hooked them up to my fully charged battery bank (12.85 V before starting). I followed the instructions, that say that I was to hook up the cables in this order:

  1. Hook up the load
  2. Hook up the batteries
  3. Hook up the PV

Nothing happened on 1, but some leds flashed for a second or so when I connected the batteries. After that, it has seemed dead :-/ I disconnected the various cables to see if it happened again, but they all remained "dead" (no light). Yesterday was overcast/grey, so was getting 16.5-17V from the PV cables (two panels of 140W total max), and I wonder if this is the reason? The manual says it needs Vbat + 5V to start, and I guess that means it would need a minimum of 12.85+5=17.85V from the PV cables to get a starting power? Am I right in understanding this "Vbat+5V" terminology? The system is in a remote location, 3 hours from my home, so I am not able to hang around for sunshine to appear to verify ... Just had to leave and hope for the best :-/

One indication that something was happening is that the initial voltage of the batteries (same reading from the battery terminals as on the screws on the controller) increased after connecting them to the controller, from 12.85V to 13.2V, after a little while. This indicates they were being charged, but I do not understand how, if the controller was inactive/powered off. The LED overview in the manual did not show what "all leds off" indicated, so I assume that would imply a non-functional state.

I read some threads on the same topic for this controller, but could not really glean much info from them (conclusion: hw error).

Points where I have deviated from the manual

  • Did not connect a earth/ground wire, basically because I have no idea how to do that when I did not find any diagram or specific terminal marked "GND" or something
  • Connected everything while the controller was not yet mounted. The manual says it should be mounted vertically, which I did after connecting everything, but I cannot see how/why this should matter.

Debugging info:

  • Voltage reading from BATT screws on controller: 12.85V
  • Voltage reading from LOAD screws on controller: 12.85V
  • Voltage reading from PV screws on controller: 16.8V
  • 4 Concorde Sun Xtender 2580 batteries in parallel connected to bus bar
  • Charge controller connected to 100A busbar (one per polarity)
  • All battery cables of equal length (1m) and terminated with cable lugs or similar.
  • Sufficient cable thickness. 10mm2 for batteries, 6mm2 to load, 35mm2 to PV (long length).
error
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2 Answers
carl-erik-kopseng avatar image
carl-erik-kopseng answered ·

As suspected, this was all down to the regulator not turning on due to the Vbat+5V it needed to start. Once I get back to my cabin 4 weeks later, the batteries were fully charged and I could connect using the Bluetooth app.



I could even see from the overview it started charging the day after I left.


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JohnC avatar image
JohnC answered ·

Hi @Carl Erik Kopseng

Your understanding is pretty much correct re the +5V. Once it starts there's also a +1V requirement between Vbat and the tracked Vmp. But that can be very low in poor light, and panel specs go out the window.

It likely has been finding something while you're not watching it, stopping and starting as it thinks it's seeing sundown and a new day.

Wire your two panels in series, and that should fix it..

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carl-erik-kopseng avatar image carl-erik-kopseng commented ·

Thanks, John! These are two old panels from 1995 that I initially wanted to avoid fiddling with. I am not even sure old panels allow being connected in series?

I have bought three new panels that will be wired in series, but they are to be installed in a different location (with different snow/sun conditions) and a separate regulator, and I would like to keep this old one for redundancy.

if it is possible to cut the existing wires and then connect the old panels in series that would of course be a great option.

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Kevin Windrem avatar image Kevin Windrem carl-erik-kopseng commented ·

Series connection will certainly allow startup at lower light levels. However series connected panels need "blocking diodes" across them to allow current from cells in sun to flow around shaded cells. Many panels have blocking diodes built in but some do not.

You can check by connecting the panels in series then shading one panel. If you get usable power from the unshaded panel you are good to go. If not, you can add the blocking diodes externally.

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