Mppt100/50

Had a similar head-scratcher with my Victron MPPT 100/50 a few weeks back and still not 100% sure what caused it.

Panel voltage was reading correctly at the array — around 36V open circuit on a 2S string of 200W panels — but the VictronConnect app was showing something ridiculous like 0.3V on the PV input. Controller wasn't doing anything, just sitting there.

Turned out in my case the MC4 connectors had a partial connection on the positive line. Enough contact to give a voltage reading at the panel end with a multimeter, but way too much resistance for the MPPT to see it properly. Swapped the connectors and it fired up immediately.

Worth checking a few things if you're seeing something similar:

• MC4 connections — are they fully clicked and locked? They can feel seated without actually being so
• Polarity — obvious one but worth confirming PV+ and PV- aren't reversed at the controller terminals
• Battery voltage — the MPPT 100/50 won't start charging if it can't detect a battery. Does VictronConnect show a sensible battery voltage?
• Firmware — worth checking you're on the latest version via the app

Also, are your 4 batteries wired in parallel for a 12V bank? If there's a wiring issue there causing low detected voltage, the controller might not be triggering bulk charge.

Anyone else had the app showing near-zero PV voltage despite panels clearly producing? Curious whether it's usually a connector issue or something else entirely.

Helen1994 | 47 posts

@NotAnElectrician Your post got cut off so I'm not entirely sure what the fault was, but with the 100/50 I'd always check the PV input wiring first — loose connections can cause all sorts of odd readings that don't obviously point to themselves as the culprit. Also worth checking whether the battery voltage shown in the VictronConnect app matches what you're actually measuring at the battery terminals with a multimeter. A discrepancy there can throw the whole charging algorithm off. What battery type have you got it set to? I've seen people catch themselves out having it set to AGM when they're running lithium, which causes strange behaviour. If you can share what exactly the controller was doing (or not doing), someone here will almost certainly have seen it before! 😊

Nothing like a cliffhanger on a fault-finding thread — @NotAnElectrician left us with a 2 and @Helen1994 left us with a "but with" 😂 Genuinely feels like my Victron's absorption stage — takes forever to reach the point.

Haha this thread is basically three people all trailing off mid-sentence 😂

@NotAnElectrician genuinely curious what you were seeing on the VictronConnect app — absorption kicking in too early? Had something similar on the boat last summer, turned out to be dodgy MC4 connectors causing intermittent voltage drop between panels and controller. Readings at the array looked fine but the controller was seeing something different entirely.

Also worth checking your battery voltage sense wires if you've got them connected — mine were giving the 100/50 completely wrong info and it was doing weird things with the charge curve.

@Helen1994 @ThistleVicky can one of you lot actually finish a sentence 😅

@NotAnElectrician the suspense is killing me but I'll throw something useful in whilst we wait for the full story.

With the 100/50 specifically, one thing that catches people out is the battery voltage sense versus actual terminal voltage discrepancy. If there's any meaningful resistance in the cabling between the MPPT and the battery, the controller sees a higher voltage than what's actually at the terminals and can back off charging prematurely.

On my motorhome setup with Fogstar Drift 100Ah lithium, I had a similar head-scratcher until I ran proper 6mm² cable to a busbar and tightened every connection. The VictronConnect app's history tab is your friend here — check whether absorption was being hit too early or bulk just wasn't completing.

Also worth confirming your battery type profile is set correctly in VictronConnect. A mismatched absorption voltage setting on lithium will cause all manner of weird behaviour.