Interesting one this — I've been down a similar rabbit hole with a small solar setup powering a water feature pump at my shepherd's hut, so hopefully some of this is useful.
The core issue with pairing a Victron BlueSolar PWM controller with a Battery Protect is sequencing. The Battery Protect must sit on the load side, between the battery and the pump — never between the panel and the controller. I've seen people wire it incorrectly and wonder why their controller throws fits or the BP keeps tripping.
A few things worth checking:
- Charge profile — make sure your PWM controller is set to the correct battery chemistry. AGM, gel, and lithium all need different absorption/float voltages. Get this wrong and you'll either undercharge or cook the battery.
- Battery Protect threshold — I'd set the low-voltage disconnect around 11.8V for a 12V lead-acid setup, with reconnect at roughly 12.8V. This gives the battery a fighting chance before the pump starves it flat.
- Pump inrush current — pond pumps can draw 3–5x their rated current at startup. Worth checking your BP model's current rating handles that surge.
For a 55W panel, you're not dealing with massive power budgets here, so a decent Fogstar or similar AGM in the 50–100Ah range would complement it well.
What's the pump's rated wattage and the battery capacity you're working with? That'd help narrow down whether the system is actually sized correctly before worrying about configuration settings.
Would be good to hear from others who've run similar setups — particularly anyone using PWM rather than MPPT on small feature pumps.
