Is my battery charging at all?

Had a similar head-scratch moment on the boat last summer with my PWM setup. Panel was rated at 5.5A but the controller kept showing barely 2-3A on a clear day and I was convinced something had died.

Turned out to be a few things worth checking:

Controller current rating vs panel output
A 5A PWM controller is going to clip anything your panel tries to push beyond that. Not ideal pairing if your panel can theoretically exceed it. Victron's own guidance is pretty clear on leaving some headroom.

PWM vs MPPT
This is the biggie for me. PWM essentially drags your panel voltage down to match battery voltage — so an 18V panel charging a 12V battery loses a chunk of potential straight away. I eventually swapped to a small Victron SmartSolar MPPT and immediately saw better numbers. Worth it even on a modest setup.

Battery state
If the AGM is nearly full, the controller should be tapering anyway. Easy to mistake absorption/float as "not charging."

What does the controller LED pattern show? Most Victron BlueSolar units give you a blink code that tells you exactly which stage you're in. Worth cross-referencing with the manual — they're all on Victron's site as free PDFs.

Anyone else running PWM on a boat or similar mobile setup? Curious whether people still find them reliable or whether MPPT is just the obvious choice now even at this scale. I've gone full MPPT but wondering if I'm being snobby about it 😄

@MandyGrant classic symptom of panel voltage being too close to battery voltage with a PWM controller — it just can't pull decent current because there's no real headroom to work with.

Worth checking a few things:

• Panel Voc vs Vmp — what's the actual spec?
• Battery state of charge at the time (a nearly-full battery will naturally throttle current)
• Cable run length and gauge — voltage drop kills PWM efficiency badly

Had exactly this with a Renogy 100W panel on my garden office build. Swapped to a Victron SmartSolar MPPT and went from ~2.8A to a consistent 5A+ on comparable days. PWM is genuinely inefficient once your panel voltage isn't significantly higher than battery voltage.

If your panel's Vmp is only ~18V feeding a 12V bank, that's your culprit right there.

@PennineVanLifer's cut off but they're onto something important there.

@MandyGrant I had almost the identical situation on my narrowboat a few years back — convinced the panel had given up the ghost, nearly ordered a replacement. Turns out my 12V nominal panel's Vmp was sitting around 17V which sounds fine on paper, but on a warm July afternoon panel temperature drags that down considerably. PWM just connects panel straight to battery, so whatever voltage headroom you've lost to heat, you've lost as usable current.

The real test I use now: check the Vmp figure on your panel's datasheet, then measure actual panel voltage mid-afternoon when it's warm. If it's dropped close to your battery voltage, that's your culprit.

Switching to MPPT on the boat transformed my charging figures — a Victron SmartSolar 75/15 paid for itself within one season in my case.

@MandyGrant yeah had this exact thing on the narrowboat. Switched from PWM to a Victron SmartSolar MPPT and suddenly the numbers made sense again. The difference on partial shade days especially was night and day.

Worth checking your panel's Voc vs battery voltage — if there's not enough headroom the PWM just throttles itself silly. MPPT handles it properly.

Also double-check your cable runs. I had a dodgy MC4 connector causing a similar drop that I chased for weeks before spotting it. Simple stuff but easily missed.

@MandyGrant what @PennineVanLifer was getting at before the cut-off, and what @HelenThompson discovered in practice, is the core PWM problem — but there's a quick diagnostic worth doing first.

Check your panel's open-circuit voltage against your battery voltage. If they're within ~5V of each other on a warm day (panels lose voltage with heat), a PWM controller is essentially starved. Mine was doing exactly this on the narrowboat before I switched.

The number that matters isn't your panel's rated current — it's whether your voltage differential gives the PWM anything to work with.

If you're seeing 2-3A consistently rather than zero, the controller is working, just poorly matched. A Victron SmartSolar 75/15 would likely recover most of that lost generation. Fogstar do decent budget options too if cost is the concern.

What's your panel's Voc rating?