The first step: Preparation and planning

1. Tool List:

Soldering iron and solder wire: used for reliable connection of wires.

Multimeter: A must-have! It is used for measuring voltage, determining positive and negative poles, and conducting on-off tests.

Hot melt glue gun & silicone sealant: Used for fixation and sealing. Silicone sealant has better elasticity and is more recommended.

Heat shrink tubing or electrical tape: used for insulation and protection of solder joints.

Electric hand drill & appropriate size drill bit/hole opener: used for making holes in the housing.

Screwdriver set: For disassembling audio equipment.

Wire strippers, pointed-nose pliers, scissors

Cable ties: Used for internal wiring fixation.

2. List of Materials

DC power socket: It is recommended to use the 5521 type (also known as DC-005) socket, which is the most versatile model. Ensure its quality is reliable.

The matching DC power cord: One end is a 5521 plug, and the other end has exposed wire cores. The recommended wire diameter is 18AWG or thicker to carry sufficient current.

Wire: A small section is used for internal connection, and the wire diameter matches that of the power cord.

Step 2: Determine the internal power supply plan for the audio system

This is the most crucial step, which determines how you connect the wires.

Disassemble the audio system: Carefully unscrew all the screws and slowly open the audio system casing. Note that there might be hidden clasps. Remember the internal structure for restoration.

Find the power supply point (choose one of the three) :

Option A (Best) : Connect to the battery compartment contacts.

Find the metal spring connecting the positive and negative terminals of the battery.

Use the DC voltage range of a multimeter to confirm the positive and negative terminals (insert the battery, touch one point with the red test lead and the other point with the black test lead. If the voltage shows a positive value, the red test lead is the positive terminal).

Advantages: The simplest and most direct, no need to solder the mainboard, and low risk. When direct current is inserted, the battery will be automatically disconnected (physically).

Option B (Commonly used) : After connecting to the charging circuit.

If the audio system comes with a built-in lithium battery and USB charging function, you can find the output terminal of the charging module.

Usually, the charging module has the pad markings of "B+" and "B-", which are the positive and negative terminals connected to the battery.

Confirm with a multimeter! When charging, measure which two points have the same voltage as the battery (such as 3.7V or 7.4V, etc.).

Advantages: It can utilize the charging and discharging management circuit inside the audio system, making it safer to charge the battery.

Solution C (for experts) : Directly connect to the power input terminal of the motherboard.

If the above two points cannot be found, the main power input point on the motherboard needs to be located. This may be close to the power switch or the DC-IN interface (if any).

Risk: Extreme caution is required. Connecting the wrong voltage or positive and negative poles can easily burn out the motherboard.

Step 3: Install the DC socket

Select the opening position

Choose a flat position on the audio equipment casing that has sufficient internal space and does not affect the original structure or the reinstallation process.

The ideal position is on the side or at the bottom of the rear to avoid direct water dripping.

Hole opening

Choose the appropriate drill bit or hole opener based on the outer diameter of the DC socket you purchased.

Drill slowly to ensure that the holes are smooth and the dimensions are accurate.

Fixed socket

Insert the DC socket into the hole from the outside of the housing.

Insert the gasket and nut from the inside and tighten and fix them with a wrench.

Key point: Apply sufficient silicone sealant to the contact surface between the socket and the housing (both the inner and outer sides are acceptable) to form a complete waterproof sealing ring. Wait for it to cure.

Step 4: Internal wiring

Be sure to operate when the power is off (remove all batteries)!

Prepare the wires

Tin the pins of the DC socket and the wires to be connected.

Cut two pieces of heat shrink tubing of appropriate length and put them over the wire for later use.

Determine polarity

The polarity of a DC socket is usually as follows: the center hole is the positive pole (+), and the outer wall is the negative pole (-). Be sure to confirm with the "on/off" or "resistance" range of a multimeter!

Welding

Solder the positive terminal of the DC socket to the power supply positive terminal you found in the second step.

Solder the negative terminal of the DC socket to the negative terminal of the power supply.

The welding action should be fast, and the weld points should be round and firm to avoid false welding.

Insulation and fixation

Push the heat shrink tube that was previously put on onto the solder joint and heat it with a hot air gun or a lighter (be careful) to make it shrink and completely wrap around the solder joint.

Use cable ties to properly secure the internal wires to prevent them from shaking and short-circuiting with other components on the motherboard.

Step 5: Sealing and testing

Final sealing

Before closing the casing, check again whether all connections are firm and whether the insulation is good.

Apply a uniform layer of silicone sealant at the joint of the shell.

Carefully close the shell and tighten all the screws. Wipe off the spilled glue.

Let it stand for at least 12 to 24 hours to wait for the silicone to fully cure.

Step-by-step testing (extremely important!) :

Step 1 (short-circuit test) : Do not install the battery for now. Set the multimeter to the "on/off" or "Resistance" range and measure whether there is a short circuit between the positive and negative poles of the DC socket. If the buzzer sounds, it indicates a serious short circuit. Check it immediately!

Step 2 (Voltage testing) : Insert the vehicle power adapter (or use an adjustable power supply), and use the DC voltage range of a multimeter to measure at the internal solder joints to confirm whether the voltage is correct and the polarity is correct.

Step 3 (Functional Test) : Ensure that the silicone is dry. First, do not install the battery. Just connect the modified audio system directly to the car power supply or a power bank. Turn on the machine for a test to see if it can work normally. If it can, it indicates that the DC power supply is successful.

Step 4 (Battery Test) : Install the battery and test whether the battery power supply is still normal.

Step 5 (Charging Test - If Applicable) : If a charging circuit is connected, test whether the battery can charge normally when powered by DC.

Summary and precautions

Safety first: Always keep in mind the safety of electricity usage. Confirming the polarity is the key of keys.

Waterproofing is the core: The sealing of openings and seams determines whether the waterproof performance of the modified audio system will be compromised.

Voltage matching: Ensure that your external power supply (such as a 12V car) matches the working voltage of the audio system. If the audio system is 5V, you need a voltage reduction module and cannot directly connect it to 12V.

Installing a fuse: For absolute safety, a fuse slightly larger than the working current of the audio system can be connected in series in the positive circuit (for example, if the working current of the audio system is 1A, a 2A fuse can be used).

After completing all the above steps, your waterproof audio system will successfully have a reliable DC power supply interface, allowing you to enjoy music to your heart's content during your travels! Wish you a smooth modification!