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Fact-checked on Apr 7, 2026
The Redarc BCDC1280 has an 80A output and a built-in MPPT that accepts up to 520W of solar at 9–32V input — but there are at least five distinct reasons it can refuse to charge from solar, and most of them are not faults with the unit itself. I've chased this issue through three van builds. The fix is usually found in panel wiring, voltage thresholds, or a misunderstanding of how the MPPT start logic actually works.
The BCDC1280's solar MPPT has one hard rule that trips people up constantly: panel Voc must be at least 1V above the battery voltage to trigger a charge cycle. At 13V battery, that means your panel string needs to deliver at least 14V — not rated Vmp, actual measured Voc in current light conditions. A single 100W mono panel at Vmp is around 18–20V, so one panel is usually fine. But if you're running two 12V nominal panels in parallel rather than series, your Voc stays at roughly 20–21V, and the MPPT can start fine. Two panels in series doubles Voc to 40V+ — that's above the 32V maximum input and will either prevent charging or damage the controller. Parallel-only on this unit.
⚡ Expert tip
If the MPPT input shows correct voltage but the unit still won't charge, check the solar negative return path. I've seen installs where the solar negative was connected to a different ground bus than the battery negative — a 0.3V offset between grounds is enough to confuse the MPPT start logic. Always run solar negative directly back to the same bus bar as the BCDC1280 battery negative terminal, not to a chassis ground point.
Example calculation for your setup
Results based on a typical use case
| Appliance | Power | Usage/day | Wh/day |
|---|---|---|---|
| Compression fridge | 45W | 24h | 1080 |
| LED lighting | 20W | 4h | 80 |
| Water pump | 30W | 0.5h | 15 |
| Phone charging | 15W | 2h | 30 |
| Daily consumption | 1205 Wh | ||
Recommended solar panels
302 Wc
4h average sun hours
Adjust these values with the calculator below
VANPOWERCALC PROYOUR ENERGY PROFILE
YOUR ENERGY PROFILE.
This document contains the sizing of your future electrical installation, calculated based on your appliances.
Minimum Daily Consumption
0 WH / DAY
Inventory:
SYSTEM SIZINGPage 2
Battery
To guarantee 0WH without damaging your bank (80% max discharge):
0 AH
LiFePO4 12V
Solar
Minimum power required to recharge your consumption:
0 W
via MPPT
220V AC
Maximum power (with 25% safety margin).
0 W
No Need
Safety & CablingPage 3
12V Cable Sizing Guide
Use this professional reference table to select the correct gauge (mm²) for your cables. For 12V in a van, the maximum tolerated voltage drop is 3%. Always use multi-stranded flexible automotive wire.
| Current (A) | Round trip < 2m | Round trip 4m | Round trip 6m |
|---|---|---|---|
| 5A (LEDs, USB) | 1.5 mm² | 2.5 mm² | 4 mm² |
| 10A (Fridge, Pump) | 2.5 mm² | 4 mm² | 6 mm² |
| 20A (Heater) | 4 mm² | 10 mm² | 10 mm² |
| 50A (DC/DC Booster) | 10 mm² | 16 mm² | 25 mm² |
| 100A (Inverter) | 25 mm² | 35 mm² | 50 mm² |
Fuse Sizing
The fuse protects the wire, not the appliance. Always place it as close to the power source as possible (battery or busbar).
- Wire 1.5 mm² → Max fuse 10A
- Wire 2.5 mm² → Max fuse 20A
- Wire 4 mm² → Max fuse 30A
- Wire 6 mm² → Max fuse 40A
- Wire 10 mm² → Max fuse 60A
SCHÉMA ÉLECTRIQUE
PANNEAUX SOLAIRES
0W
RÉGULATEUR MPPT
BATTERIE AUXILIAIRE
0 Ah
Lithium LiFePO4
FUSIBLE
FUSIBLE
BOÎTE À FUSIBLES 12V
Pompe, Leds, Frigo...
CONVERTISSEUR 220V
NON REQUI
PRO GEARPage 4
SHOPPING LIST
Where to find this equipment? Here is the community-approved selection.
12V 6-way Fuse Box
Mandatory protection
Digital Multimeter
Test your connections
Heavy Duty Crimping Tool
For perfect lugs
Heat Shrink Tubing
Insulation and safety
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About this tool
Here's what I check, in order, every time a BCDC1280 won't charge from solar.
1. Input voltage out of range. The MPPT input window is 9–32V Voc. Measure at the solar terminals with a multimeter — engine off, panels in direct sun, nothing connected. If you're above 32V, you've wired two panels in series. Re-wire in parallel. If you're below 14V (roughly), conditions are too poor or the panels are shaded. The unit won't attempt a charge cycle.
2. Battery already near full. The BCDC1280 reduces and eventually stops solar input when the house battery is above about 14.4–14.6V. This looks like "solar not working" but is actually correct absorption cutoff behaviour. Check the LED: a slow flashing green means absorption stage — the charger is backing off intentionally.
3. Flashing green but no measurable current. This is the frustrating one. The green LED flashes, the unit looks active, but a clamp meter on the solar cable shows 0A. Nine times out of ten: the panel cable connectors (MC4 or Amphenol) are not fully locked. Pull them apart and reconnect with an audible click. Also check that your solar cable fuse has not blown — a 15A inline fuse on the solar positive is standard, and a partial short can blow it without obvious signs.
4. Wrong panel type or degraded flexible panels. The BCDC1280 MPPT works correctly with standard crystalline panels. Some thin-film and flexible panels have unusual I-V curves that confuse budget MPPT controllers. Redarc's MPPT handles this well in my experience, but heavily degraded flexible panels — especially ones that have been baking on a dark roof without an air gap for 2–3 seasons — can output strange voltages under load. If your flexible panels are more than 3 years old, test them with a known-good rigid panel before assuming the charger is at fault.
5. Temperature-induced Voc spike. Cold morning, fresh panels in bright sun: Voc on a 200W mono panel can hit 25–26V. That is still within range. But if someone has wired two 24V nominal panels in parallel, cold-morning Voc can push toward 35–38V. Brief over-voltage events at startup can trigger the BCDC1280's protection mode, which requires a power cycle to clear. If the unit works fine in the afternoon but not in the morning, this is almost certainly the cause. Fix it by checking cold-weather Voc on your exact panel spec sheet — or switch to panels with lower Voc.
Frequently asked questions
Why does my Redarc BCDC1280 show a green light but not charge from solar?▼
A steady or slow-flashing green on the BCDC1280 can mean several things: the unit is in absorption or float (intentionally reducing current), or the MPPT has started a cycle but panel output is too low to show measurable current. First, check battery voltage — if it is already above 14.4V, the charger is backing off intentionally. If the battery is below 13V and you are still seeing no current, the MC4/Amphenol connector likely is not fully latched, or the solar cable inline fuse has blown.
Can I wire two solar panels in series to the BCDC1280?▼
No. The MPPT solar input is rated for a maximum of 32V Voc. Two standard 12V nominal monocrystalline panels in series will produce 40–44V Voc — well above the limit. Always wire panels in parallel on the BCDC1280. Two 200W panels in parallel gives you 400W at around 21V Voc, which sits comfortably inside the 9–32V window.
What is the maximum solar input for the Redarc BCDC1280?▼
Redarc rates the BCDC1280 solar input at 520W maximum, with a Voc range of 9–32V and a maximum input current of around 20A. In practice I have run 480W (two 240W panels in parallel) without issue. Trying to push more than 520W is possible in bright winter sun with high-efficiency panels — use a clamp meter on the solar cable to confirm you are not consistently exceeding 20A input.
The BCDC1280 charges fine from the alternator but not from solar — what is different?▼
The alternator and solar paths are separate circuits inside the unit. If alternator charging works, your BCDC1280 hardware is fine. The solar MPPT is a distinct subsystem. Start with the obvious: is the solar positive fuse intact? Is there voltage at the solar terminals (measure with a multimeter)? A blown inline fuse on the solar positive cable kills solar input without affecting alternator charging at all.
Does the BCDC1280 work with flexible solar panels?▼
Yes, in principle — the MPPT does not care about panel construction. But flexible panels degrade faster than rigid ones, especially when mounted flat on a dark roof with no air gap. After 2–3 years, a flexible panel can lose 15–25% of its output and develop unusual voltage curves under partial load. If your flexible panels are more than 3 years old and solar charging seems weak, test with a rigid panel to isolate whether the panel or the charger is the issue.
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