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jhelms asked

Victron 100/50 Voltage / Current rise and fall cycle during bulk charging

Appreciate any help. I just picked up a victron 100/50. I have it paired with a 654W panel setup and via a switch a 10W panel is connected. I have it this way as my travel trailer sits under a large cover and the main panels do not get sun. The 10W panel is out in the sun to maintain the batteries (two 6v GC batteries).


I noticed that during charging with the 10W panel, voltage rises and falls every 30 seconds.

- Peak voltage and current I see is around 19.5v / 500mA ish

- Voltage and current then fall to 14.5v ish / 0mA


This rise and fall happens every 30 seconds or so which ends up looking like an exact waveform on the android app. And I see the wattage reading rise and fall exactly as with the graph.


Is this normal or is there an issue?

battery charging
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jhelms avatar image jhelms commented ·

Got in the second panel, charger is still acting totally odd. Says bulk charging but never goes off 12.8v on battery. Still seeing the peaks and valleys. Watched it for maybe an hour. A few times voltage and current would somewhat normalized but charging voltage was still 12.8 and after a bit, it would start bouncing again.

Getting frustrated with this controller - willing to accept I am doing something wrong, but I cannot figure out what it is.


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Mark avatar image Mark ♦♦ jhelms commented ·

The charge voltage is highly effected by the battery resting voltage, the battery SOC, the battery capacity & the MPPT charge current.

With so little solar power, I would expect it to take some hours or days for the MPPT to slowly raise the battery voltage to the absorption voltage set in the MPPT. So wouldn't worry too much about that aspect yet.

I agree that the oscillations are still an issue & that's a bit disappointing that they are still occurring with the 2nd 10w panel...

I don't think that your doing anything wrong or that the MPPT is faulty. I still just think that the sweep algorithm is too agresive to work properly with so little solar power.

As a next step, maybe try to wire the 2nd panel in parallel to double the current instead of voltage & see if the MPPT responds better to that.

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Mark answered ·

Are the other main panels still connected when the 10W is switched on, or does the switch automatically also disconnect them?

If they are they may be effecting the MPPTs ability to find the maximum power point & I would recommend to disconnect them as the next step.

I'm also thinking that 10W is a bit too small for the MPPT sweep algorithm to function correctly (to find the max power point) - when the MPPT increases the PV current the PV voltage drops (as it should), but it may be dropping so fast that it gets to the point that its around the current battery voltage (so ineffective). Because the 10W panel is so small it just may all be happening too fast for the MPPT to react in time & find the 'sweet spot'.

If possible maybe try to add a 2nd 10W panel in series with the 1st. This will bring the PV voltage well above battery voltage & also give the MPPT some more power to work with when finding the max power point.

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jhelms avatar image jhelms commented ·

I think you are spot on in theory. In the graph, I can see voltage being brought down as current peaks, but at that point, voltage sinks to low and it bounces the other direction like NOPE! Ordered in a 2nd panel and will series them. Betting this totally cures the problem. Little frustrating as no minimum voltage specs are listed that I have found but at the same time, having 20W worth of panels to keep the battery up is not a bad thing. I was rather skating a bit thin anyways with a single 10W but it did the job with my previous much smaller pwm setup.

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