Redarc BCDC1240D Battery Charger Wiring Diagram
Typical setup
Solar and vehicle inputs, output to the auxiliary battery and setting wires.
Terminals and components · 8
- Solar
- Vehicle
- Output
- Ground
- Trigger (optional)
- LED
- Profile
- Loads
- Disconnect
Priority
The unit uses all available solar power first and tops up from the vehicle.
Wire size
Length Cross section 1-5 m 13,56 mm² (6 B&S) 5-9 m 20,28 mm² (4 B&S) Fuse
60 A near the battery; bolt-down MIDI fuses are recommended (Redarc FK60). Do not use blade fuses or self-resetting breakers.
Wire size
Length Cross section 1-5 m 13,56 mm² (6 B&S) 5-9 m 20,28 mm² (4 B&S) Splices
Join the heavy wires with crimped and soldered butt splices covered with heatshrink; do not use blade connectors.
Wire size
Length Cross section 1-5 m 13,56 mm² (6 B&S) 5-9 m 20,28 mm² (4 B&S) Fuse
60 A near the battery; bolt-down MIDI fuses are recommended (Redarc FK60). Do not use blade fuses or self-resetting breakers.
Wire size
Length Cross section 1-5 m 13,56 mm² (6 B&S) 5-9 m 20,28 mm² (4 B&S) Splices
Join the heavy wires with crimped and soldered butt splices covered with heatshrink; do not use blade connectors.
Caution
A «12 V» LED (3 V with a built-in resistor) will not work properly.
Lithium
Only LiFePO4 batteries with their own BMS, voltage protection and cell balancing. Do not install them in the engine bay.
Charge profile selection
How to connect the orange wire for each charge profile.
Terminals and components · 1
- Orange
- Red
- Green
Profiles
Profile Orange Max. Float A Not connected 14.6 V 13.3 V B To ground 15.0 V 13.3 V C To red 15.3 V 13.3 V Li To green 14.5 V 13.6 V Choosing
The profile's maximum voltage must not exceed the battery maker's maximum charging voltage. For an engine bay install, use a lower profile than in the cabin.
Vehicle input trigger
The blue wire selects when charging from the vehicle starts.
Terminals and components · 1
- Blue
Turn on / off
Mode 12 V: on / off 24 V: on / off Standard 13.2 V / 12.7 V 26.4 V / 25.4 V Low voltage 12.0 V / 11.9 V 24.0 V / 23.8 V With ignition
In low voltage mode, the ignition must also be on.
About This Diagram
These diagrams are redrawn from pages 8–9 and 11 of the Redarc BCDC1240D Battery Charger manual, and we offer them completely free and in English. We have also categorized it in the Batteries, BMS & Dual Battery (Solar & Batteries) section on Diagramverse, and it has been rated by 1 user with an average rating of 5.0. If you have any specific questions about the Redarc BCDC1240D Battery Charger Wiring Diagram, we suggest checking the Frequently Asked Questions (FAQs) section.
Printable Redarc BCDC1240D Wiring Diagrams
Wiring Instructions
Before you start
First pick the version of the drawing that matches your system Redarc BCDC1240D. Use the Complete tab with Lead acid for flooded, calcium, gel or AGM auxiliary batteries. Use LiFePO4 for a lithium battery with a built-in BMS that has under and over voltage protection plus cell balancing. The Profile tab shows how to set the Orange wire. The Trigger tab shows whether the Blue wire stays loose or goes to ignition.
- Tools: single-indent crimpers, soldering iron, heat gun, multimeter, cutters and strippers, plus a drill and screws for the four mounting tabs.
- Materials: butt splices, heatshrink, crimp lugs, MIDI bolt-down fuse kits (60 A, Redarc FK60 recommended), a load fuse and, for lithium, a low voltage disconnect.
- Cable size: for runs of 1-5 m (3-16 ft), use at least 13.56 mm² (6 AWG). For 5-9 m (16-30 ft), use at least 20.28 mm² (4 AWG). This applies to Red, Yellow, Black and Brown. Never go smaller, and check any vehicle codes that apply to you.
- Battery data: confirm your auxiliary battery's maximum charging voltage, and check that it accepts 40 A of charge current.
Mount the unit as close as possible to the auxiliary battery. It can go in the cabin, on a chassis rail or in the engine bay, away from hot spots, mud and debris. Lithium batteries do not suit engine bay installs. Location also affects the profile: in the engine bay, a battery rated 15.0 V maximum uses profile A and one rated 15.3 V uses profile B. Work with the engine off, the key removed and the solar panel covered or disconnected. Redarc recommends a qualified installer. If you are not confident making high-current connections, hire an auto electrician.
Step-by-step wiring
- Mount the charger with the front decal visible, using all four mounting tabs. A metal surface helps it shed heat.
- Run the Black: ground wire to a clean, bare chassis earth point. Make sure the auxiliary battery negative and the solar panel negative also reach chassis ground.
- Set the Orange: charge profile wire. Leave it disconnected for A (14.6 V), connect it to ground for B (15.0 V), to the Red wire for C (15.3 V), or to the Green wire for Li (14.5 V). Insulate the end if it stays loose.
- Set the Blue: input trigger wire. Leave it unconnected and insulated for a fixed voltage or temperature compensating alternator. Connect it to an ignition-switched feed for a variable voltage alternator.
- Connect the Brown: output to the auxiliary battery wire to the auxiliary battery positive through a MIDI fuse mounted close to that battery. Leave the fuse out for now.
- Connect the Red: vehicle input wire straight to the start battery positive (12 or 24 V) through a 60 A MIDI fuse close to the start battery. Leave this fuse out too. Never feed the Red wire from a fuse box or accessory circuit.
- If you use solar, connect the Yellow: solar input wire to the positive of an unregulated 12 V panel array. Do not add a separate solar regulator: the charger has its own MPPT.
- For remote status, wire a basic 3 V LED from the Green: optional external LED wire to ground. A "12V" LED with a built-in resistor will not work properly.
- Feed your loads from the auxiliary battery through their own load fuse. On a LiFePO4 system, route them through the low voltage disconnect.
- Make every heavy joint with a crimped and soldered butt splice under heatshrink. Secure the cables away from sharp edges and hot parts.
Testing and start-up
Before fitting fuses, measure the auxiliary battery: it must be above 4.2 V for the charger to recognize it. Check polarity at each positive with your meter. Fit the Brown output fuse first, then the Red input fuse.
- Allow up to 20 seconds for the charger to start whenever a source appears. Solar can take up to 2 minutes to be recognized.
- With the engine running, the Vehicle LED should come on. In standard mode, the Red wire must read above 13.2 V on a 12 V system or 26.4 V on a 24 V system. In low voltage mode, the ignition must be on and the Red wire above 12.0 V or 24.0 V.
- In daylight, the Solar LED lights once the Yellow wire sees more than 9 V open circuit.
- The selected profile LED stays solid while charging, and flashing means standby. If all LEDs flash in a repeating count, that is an error code.
- At the auxiliary battery, voltage should rise toward the profile maximum, then settle at about 13.3 V float (13.6 V for LiFePO4).
Safety notes
- Lead-acid batteries give off explosive gas. No smoking, sparks or flames. Fit the fuses last so any spark happens at the fuse holder, not at the battery.
- Wear eye protection. Wash acid off skin with soap and water. If acid gets in your eyes, flush them with running cold water for at least 10 minutes and get medical help.
- A battery can push a very large current into a short. An unfused positive touching the chassis can melt cable and start a fire, so fuse every positive close to its battery.
- Never choose a profile whose maximum voltage is higher than the battery maker's limit.
- Do not open or modify the unit. Use it only to charge a battery, not to power a system directly.
- Solar panels produce voltage whenever light reaches them. Cover them before handling the Yellow wire.
Troubleshooting
| Symptom | Probable Cause | What to Check |
|---|---|---|
| No LEDs light up at all | No auxiliary battery is detected on the Brown wire, or that battery is below 4.2 V, and no input is connected. A missing ground or a blown fuse can also cause this. | Measure the auxiliary battery: it must be above 4.2 V. Check the Black ground at the chassis, then check that both MIDI fuses are intact and tight. |
| The profile LED keeps flashing and nothing charges | Either there is no valid charging source, or the auxiliary battery is disconnected or at an unsuitable voltage. | Confirm that the Red wire goes straight to the start battery positive through its fuse and the Yellow wire to the panel positive. Check that Black reaches the chassis, the auxiliary negative and the panel negative. |
| Engine is running but the Vehicle LED stays off | The Red wire voltage is below the turn-on threshold, often on a smart alternator with the Blue wire left unconnected | Measure at the Red wire. Standard mode needs above 13.2 V (12 V system) or 26.4 V (24 V system). If your alternator is variable voltage, connect Blue to ignition. It then needs above 12.0 V or 24.0 V. |
| Blue wire is on ignition but the vehicle input never starts | Blue is tapped to a feed that is not live with the ignition on, or the connection is poor | With the key on, measure the voltage at the Blue wire. Move it to a true ignition-switched circuit if it reads 0 V. |
| Panel is in full sun but the Solar LED is off | The open circuit voltage at the Yellow wire is below 9 V, the panel has its own regulator, or the panel negative is not grounded | Measure the Yellow wire close to the charger: it should be above 9 V. Remove any regulator between the panel and the charger, check that the panel negative reaches ground, and wait 2 minutes. |
| All LEDs flash 6 times, pause, and repeat | Input over voltage, for example a panel array above 32 V or a wrong supply on the Red wire | Measure the Red and Yellow inputs. Both must stay within 9-32 V. Use only a 12 V nominal unregulated panel array. |
| All LEDs flash 5 times, pause, and repeat | Input under voltage, caused by a weak start battery or voltage drop on a long, thin or poorly joined Red cable | Measure the voltage at the start battery and at the Red wire under load. A big difference points to undersized cable or a bad splice. Use 6 AWG up to 5 m or 4 AWG up to 9 m. |
| All LEDs flash 4 times, pause, and repeat | Output battery voltage is too high, often because another charger is feeding the auxiliary battery or the profile is wrong | Measure the auxiliary battery with other chargers off. Check that the Orange wire setting matches the battery's maximum voltage. |
| Auxiliary battery gets hot or gasses heavily | The profile voltage is too high for the battery, or the battery cannot accept 40 A | Compare the battery maker's maximum voltage and current with the profile you chose on the Orange wire. In the engine bay, drop one profile. |
| Output fuse or splice gets hot or blows | Blade fuse, undersized cable, or a crimp-only or loose joint creating high resistance | Replace blade fuses or circuit breakers with MIDI bolt-down fuses. Redo the joints as crimped and soldered butt splices, and check the cable gauge against its length. |
| Remote LED stays off or acts erratically | A "12V" LED with a built-in resistor was used, or its return is not grounded | Fit a basic 3 V LED between the Green wire and ground. If you selected the Li profile, the Orange wire must stay joined to Green. |
| 12 V vehicle setup will not start even though wiring checks out | The unit has latched into 24 V mode | Remove the Red wire fuse, wait, then refit it so the charger re-detects the input voltage. |
Frequently Asked Questions (FAQs)
Which charge profile should I choose for my battery?
Choose the profile whose maximum voltage does not exceed your battery maker's recommended maximum charging voltage. Profile A gives 14.6 V, B 15.0 V, C 15.3 V and Li 14.5 V for LiFePO4. Location matters too. In the engine bay, a battery rated 15.0 V uses profile A and one rated 15.3 V uses profile B, because heat lowers the voltage a battery can take. Lithium is not recommended in the engine bay. If you are unsure, check your battery's datasheet before you connect the Orange wire.
Do I connect the Blue wire or leave it unconnected?
Leave the Blue wire unconnected if your alternator holds a fixed voltage or is temperature compensating, and connect it to ignition if you have a variable voltage, or smart, alternator. Standard mode turns on above 13.2 V on a 12 V system. Smart alternators often sit lower than that, so low voltage mode turns on above 12.0 V when the ignition is live. In a 24 V vehicle, the thresholds are 26.4 V and 24.0 V.
Can I use the BCDC1240D in a 24 V truck?
Yes. The Red vehicle input accepts a 12 V or 24 V start battery within the 9-32 V range, and the charger still outputs a 12 V charge to the auxiliary battery. The auxiliary battery must always be 12 V. The unit detects the input voltage on its own, and the Blue wire trigger works the same way, with 24 V thresholds of 26.4 V standard or 24.0 V low voltage.
Can I connect a solar panel that already has its own regulator?
No. The Yellow solar input accepts only an unregulated 12 V nominal panel array, because the charger has a built-in MPPT regulator. A regulator in between interferes with power tracking, and the Solar LED may never turn on. Connect the panel positive straight to the Yellow wire and the panel negative to ground. Keep the panel's open circuit voltage within 9-32 V, and check the rating label on your panel.
Can it charge from solar and the alternator at the same time?
Yes. The charger always draws as much as it can from the Yellow solar input first, then tops up from the Red vehicle input to reach its 40 A, 600 W output or whatever the battery needs. Both the Solar and Vehicle LEDs light when both sources are in use. It also works with only one source connected. With solar alone it acts as a stand-alone solar regulator, and with the vehicle alone it acts as a DC-DC charger.
Do I still need a battery isolator or VSR?
No. The BCDC1240D already does the isolator's job. It turns on when it senses the vehicle running and turns off when the start battery voltage drops, so the start battery is not drained by the auxiliary system. It does not link the two batteries the way an isolator does. It is a charger, so the start and auxiliary batteries can be different chemistries without any problem.
What wire size do I need for the BCDC1240D?
Use at least 6 AWG (13.56 mm²) for runs of 1-5 m (3-16 ft) and at least 4 AWG (20.28 mm²) for runs of 5-9 m (16-30 ft). This applies to the Red, Yellow, Black and Brown circuits. The ground must be the same size as the positives. These heavy wires carry peaks of up to 50 A, so going bigger is always fine and going smaller is not. Also check any codes that apply to your vehicle type.
What fuses should I use, and where do they go?
Use 60 A MIDI-style bolt-down fuses, such as the Redarc FK60 kit, close to each battery on the positive runs. One goes near the start battery on the Red wire and one near the auxiliary battery on the Brown wire. Blade fuses are not recommended because their resistance causes heat. Self-resetting circuit breakers can trip early from heat. Your loads need their own separate load fuse.
Can I charge a lithium battery with this charger?
Yes, as long as it is a LiFePO4 battery with a built-in BMS that provides under and over voltage protection and cell balancing. Select the Li profile by joining the Orange wire to the Green wire, which gives a 14.5 V maximum and 13.6 V float. Mount the battery and charger in the cabin rather than the engine bay. Add a low voltage disconnect on the loads so the battery is not over-discharged.
Can I run my fridge or lights directly from the charger output?
No. The BCDC1240D is designed only to charge a battery, not to power a 12 V system on its own. The Brown output must go to the auxiliary battery positive through its fuse, and your loads should run from that battery through their own load fuse. The charger also checks for a battery every 100 seconds and shuts down if it finds none, so loads without a battery would cut in and out.
Why does the charger switch off briefly every 100 seconds?
This is normal: the charger pauses every 100 seconds to test its input and confirm that a battery is present on the output. While it is off, no current flows, so it can read the true start battery voltage without cable voltage drop. If that voltage is below the turn-off threshold of 12.7 V (11.9 V in low voltage mode), it stops charging. In float the test can take up to 60 seconds.
Where is the best place to mount the BCDC1240D?
Mount it as close as possible to the auxiliary battery it charges, because that keeps the output run short and the charge voltage accurate. In a camper or trailer, the battery compartment is usually best. Under the hood, put it on the inner guard, behind a headlight or beside the radiator, away from engine heat and mud. It works best below 130°F with good airflow, and a metal surface helps it cool.
