Plus and minus on the charger: how to determine the color of the wire and avoid mistakes

A broken charger for a car battery, laptop or smartphone is a problem that almost everyone has encountered. It is especially unpleasant when the wires are torn from the connector and there are no markings. How to determine which wire plus, and which one minus by color? It turns out that there is no single standard - it all depends on the type of device, manufacturer and even country of origin.

Many people mistakenly believe that red is always a plus, and black - minus. This rule works for most car chargers and consumer electronics, but not all. For example, in some Chinese devices or specialized equipment, the colors may be mixed up or absent altogether. A connection error is fraught short circuit, battery failure or even fire. Therefore, before repairing or connecting, it is worth understanding the nuances.

In this article we will look in detail at:

• 🔴 Standard color schemes for car and household chargers
• ⚡ Exceptions and Trapswhere the colors don't match expectations
• 🔧 Practical verification methods polarity without risk to equipment
• ⚠️ Consequences of incorrect connection and how to avoid them

Standard color marking of wires: what GOST and international standards say

In Russia and most countries there are general rules for marking wires by color, enshrined in GOST R 50462-2009 (for low voltage devices) and international standard IEC 60446. According to them:

• 🔴 Red (sometimes orange) - plus (+, positive pole)
• ⚫ Black — minus (–, negative pole or "ground")
• 🟡 Yellow - often used for plus in automotive electrical (for example, in standard wiring)
• 🔵 Blue - sometimes minus in European devices

However, these rules not mandatory for all manufacturers. For example, in laptop chargers Dell or HP white insulation can be used for the positive, and in some Chinese power supplies - green or gray for the negative. Car chargers (for example, from Bosch or Berkut) usually follow the standard, but even here there are exceptions.

One more nuance: in USB cables (for example, for charging phones) the color marking does not refer to the polarity, but to the purpose of the wires:

• 🔴 Red - +5V (food)
• ⚫ Black — GND (ground, minus)
• 🟢 Green and white - data (D+ and D–)

Here the polarity is clearly defined, but this does not apply to car chargers!

Exceptions: When Colors Are Deceiving

Even experienced electricians fall for manufacturers' tricks. Here are the most common cases when the wire color does not match polarity:

1. Chinese chargers. Many no-name power supplies (for example, for LED strips or car recorders) use white or gray wire for plus, and black is for minus. Sometimes both wires are the same color!
2. Old Soviet chargers. In devices from the times of the USSR (for example, ZU-75M) it could be used yellow for minus, and red is for positive, but with reverse logic for connecting to the battery terminals.
3. Chargers for lithium-ion batteries (for example, from screwdrivers Makita or DeWalt). Often used here balancing board, and the wires can be marked not by polarity, but by can numbers (for example, B1, B2).
4. Car chargers with "reverse polarity". Some devices (eg motorcycles) have polarity switch, and the wire colors do not match the actual positive/minus output.

It is especially dangerous to trust flowers in homemade chargers. For example, if someone resoldered the wires in the computer power supply (ATX), the red wire may not be +5V, and +12V, and black is not a minus, but a signal ground.

⚠️ Attention: In chargers for electric vehicles (for example, Tesla or Nissan Leaf) high-voltage orange wires are often used - touching them without special training is deadly!

How to determine polarity without a multimeter: 5 working methods

If you don’t have a tester at hand, you can use improvised means. Important: These methods are only suitable for low voltage devices (up to 24V)! For car chargers (12V/24V) they are safe, but for network power supplies (220V) they are deadly.

You will need a potato and two wires|Use an LED|Test on a neon lamp|Connect to a known source|Use salt water-->

• 🥔 Potato method. Cut a raw potato in half and stick the bare wires into it at a distance of 1-2 cm. After 5-10 minutes around positive wire a green spot will appear (reaction of starch with metal ions).
• 💡 LED. Connect red LED output (anode) to the supposed plus, and black (cathode) - to minus. If the LED lights up, the polarity is correct. If not, swap the wires.

  ⚠️ Attention: The LED must be 3V or 5V! For 12V charges, use a 1kΩ resistor to avoid burning the LED.

• 🌊 Salt water. Pour warm water into a glass, add salt and lower the ends of the wires (without touching each other). U negative wire active formation of bubbles (hydrogen evolution) will begin.

Another reliable way is to connect the charger to known source with clear markings. For example, to a battery with labeled terminals or to another known working power supply. If the device works, the polarity matches.

What to do if the wires are the same color?

If both wires are black or white, look for small markings on them:

- Plus can be marked +, V+, RED or stripe.

- Minus - –, GND, BLK or a dot.

If there is no marking, use a multimeter or one of the methods above. As a last resort, you can carefully cut the insulation - sometimes a colored wire is hidden under it.

Testing with a multimeter: step-by-step instructions for beginners

The most reliable way is to use digital multimeter (for example, DT-830B or Mastech MS8268). Even a cheap model for 300 rubles will cope with the task. Follow the algorithm:

1. Set the multimeter switch to measurement mode DC voltage (DCV or V–). Select limit 20V (for car chargers) or 200V (for network power supplies).
2. Connect black dipstick into the nest COM (minus), and red - into the nest VΩmA (plus).
3. Plug in the charger (if it is a mains charger) or connect it to the battery (if it is a booster).
4. Touch the bare ends of the wires with the probes:
   • If on the screen positive value (for example, +12.6V) - the red probe touches plus, black - minus.
   • If negative value (for example, –12.6V) - reverse polarity.

For network power supplies (for example, from a laptop) the algorithm is the same, but be careful: some models only produce voltage when the load is connected. In this case, connect a 10kΩ resistor parallel to the wires.

Device type	Expected Voltage	Polarity by color (standard)	Exceptions
Car charger (12V)	12.6V – 14.4V	🔴 Plus, ⚫ Minus	Yellow instead of red (for example, in Ctek)
Laptop charger	19V – 20V	🔴 Plus, ⚫ Minus	White plus (for example, in Lenovo)
USB cable (5V)	5V	🔴 Plus, ⚫ Minus	In non-standard cables the opposite may be true.
Charger for screwdriver (Li-ion)	10.8V – 21.6V	🔴 Plus, ⚫ Minus	The colors depend on the number of cans (e.g. DeWalt uses gray for minus)

1) Is the charger plugged in?

2) Are there any breaks in the wires?

3) Is the load connected (if required)?-->

What happens if you confuse plus and minus: consequences and how to avoid them

Polarity error is one of the most common causes of electronic failure. The consequences depend on the type of device:

• 🔋 Car battery. If the charger is connected incorrectly:
  • The protection in the memory is triggered (if there is one) - the device simply will not turn on.
  • If there is no protection, the battery starts discharge instead of charging, which leads to sulfation of the plates.
  • In the worst case - battery explosion due to overheating (especially with older lead-acid batteries).
• 📱 Phone/laptop charger. Modern devices (eg iPhone or MacBook) have reverse polarity protection, but cheap Chinese gadgets can burn out.
• 🔌 Power supply. If you reverse the polarity at the output (for example, when soldering a connector), either the device itself or the equipment connected to it will burn out.

How to avoid problems:

1. Always check polarity with a multimeter, even if the wire colors seem standard.
2. Use keyed connectors (for example, XLR or Deans), which will physically prevent you from connecting the device incorrectly.
3. Stick on the wires marking (for example, red tape on the plus) after checking.
4. For critical devices (such as charging for LiPo batteries) use balancing boards with reverse polarity protection.

⚠️ Attention: If, after connecting incorrectly, the charger begins to smoke or smell of burning, it's impossible turn it on again! This is a sign of a short circuit and requires repair or replacement.

Features of determining polarity in car chargers

Car chargers (chargers) have their own nuances. Here's what you need to know:

• 🚗 "Crocodiles" on wires. In most memories (for example, Vympel-55 or Orion PW-700) red crocodile - that's a plus black - minus. But check the markings on the case!
• 🔌 Chargers with polarity switch. Some models (eg Berkut Smart Power SP-8N) have a switch 6V/12V or 12V/24V. When changing modes, the polarity on the terminals may also change!
• ⚡ Starter chargers (boosters). They often use yellow wire for positive, and black is for minus (for example, in Carku E-Power-3).
• 🔋 Charger for AGM/GEL batteries. May apply here blue wire for minus (for example, in Optimate) to avoid confusion with conventional lead batteries.

Particular attention should be paid homemade chargers from computer power supplies (AT/ATX). In them:

• 🟢 Green wire - this is PS-ON (inclusion), not a plus!
• 🔴 Red — +5V, but it cannot be directly connected to the battery (a stabilizer is needed).
• 🟡 Yellow — +12V (suitable for charging, but current is limited).

To convert an ATX power supply into a charger, you need finalization of the scheme (adding a resistor to PS-ON and current limiter). Without this, there is a risk of burning the battery or power supply.

Frequently asked questions and mistakes when determining polarity

❓ Is it possible to determine plus and minus by the thickness of the wire?

No, the thickness of the wire depends on the maximum current, not on the polarity. For example, in laptop chargers, the negative wire may be thicker, since more current flows through it (due to the features of the circuit).

❓ Why are both wires black in my charger?

This is typical for cheap Chinese devices. In this case:

1. Check the wires with a multimeter.
2. If the device shows 0V, perhaps the charger requires a load (connect a 12V light bulb).
3. If there is voltage but the polarity is unclear, use the LED method.

❓ What to do if after checking the multimeter shows negative voltage?

This means that you have mixed up the probes:

• If on the screen –12.6V, then black dipstick concerns the plus, and red - minus.
• Simply swap the probes or label the wires accordingly.

❓ Is it possible to use a charger with reversed polarity if it turns on?

Absolutely not! Even if the device turns on, this does not mean that it is working correctly. For example:

• The battery will discharge, rather than charging.
• Lithium-ion batteries will be protected and will no longer accept a charge.
• Diodes or capacitors in the power supply may fail.

Always double check polarity before extended use!

❓ Why do some chargers have three wires and not two?

The third wire is usually used for:

• 🔹 Temperature control (thermistor in batteries Makita).
• 🔹 Alarms (for example, in chargers DeWalt to indicate the charge level).
• 🔹 Balancing (in Li-ion batteries to equalize the voltage on the banks).

In this case, the polarity is determined by only two main wires (usually red and black), and the third is the signal wire.