Can lithium battery charger charge lead-acid battery?

Lead-acid battery charger adopts three-stage charging, excellent quality, good performance, high charging saturation, can improve the service life of the battery. Lithium battery charger is a charger specially used to charge lithium ion batteries. Lithium-ion batteries have higher requirements for chargers and require protection circuits, so lithium battery chargers usually have higher control precision and can charge lithium-ion batteries with constant current and constant voltage. So the lithium battery charger can charge lead-acid battery? Let's take a closer look at it.

Is the charger for lead-acid batteries and lithium batteries common?

Since the lead-acid battery charger is generally set to a two-stage or three-stage charging mode, the voltage levels of the lithium battery and the lead-acid battery are not matched. There are many kinds of lithium batteries, and the battery performance and battery protection board parameters may be different. Therefore, lithium batteries are not like lead-acid batteries, and there are universal battery chargers. Generally speaking, lithium batteries are equipped with special chargers when they leave the factory. In order to protect the lithium battery, a special charger is required.

The difference between lithium battery charger and lead-acid charger

At present, the chargers for electric vehicles on the market are mainly switching power supplies, which have the advantages of power saving, small size, light weight, and mature technology. Freight tricycles with only lead-acid batteries also use power frequency transformer chargers, which are simple, reliable, cheap, and have low requirements for the use of the environment.

Switching power supply charger is essentially a regulated power supply. Specifically, the pulse width modulation chip TIA94 as the core of the half-bridge and pulse width modulation chip UC3842 as the core of the two types of flyback. The latter occupies more than 90% of the market due to its low cost and cycle-by-cycle protection. Behind the specific circuit, are based on these two types of typical circuit for specific analysis.

1. Lead-acid charger three-stage charger

For nearly a hundred years, the classic ordinary lead-acid charger is 0.1C for J2-14 hours, which is very beneficial to the battery. Now the pace of people's life and work is accelerated, and the electric car charger has been changed to 0.15C-0.2C for 6-8 hours.

The so-called three stages refer to constant current, constant voltage and eddy current. The red color of the light-emitting diode indicates that it is in the constant current or constant voltage stage, and the green color indicates that it is in the trickle phase. Usually, the battery can be really full only after a few hours of charging after the green light.

(1) Three important parameters of three-stage charger

A, high constant voltage is understood as single cell hydrogen evolution voltage 2.42V multiplied by the number of cells in the battery pack, 36V charger is 2.42V x 18 cell ≈ 43.56V,48V charger is 242V x 24 cell ≈ 58.08V.

It is possible to have a slightly higher voltage, which is beneficial to the long constant current time and shorten the charging time: lower voltage will prolong the time for the electric oil to eat.

The three-stage charger is essentially a regulated power supply with two output voltage values. This letter is the high output value.

B, the low constant voltage value is the single cell chlorine evolution voltage of 2.35V multiplied by the number of cells in the battery pack, the 36V charger is 2.35VX18=423V, and the 48V charger is 2.35Vx24=56.4V.

This voltage requirement is strict, higher than this value will cause electric oil water loss: low battery can only eat 89% full. This value is the low output value of the regulated power supply.

C, turning current (also turn lamp current). There is a real-time detector of charging current inside the charger, and a predetermined so-called "turning current"

The value is compared to control the output value of the regulated power supply:

If the charging current is large enough to dry this value, the control circuit will automatically switch to the output high constant voltage value, and at the same time set to red light to prompt: the charging current is less than the turning current value, switch to the output low constant voltage value, and set to green light.

The setting of the turning current value is related to the ampere hours of lead-acid batteries. The empirical value is about 350mA for electric oil of about 10Ah, about 500-550mA for batteries of about 17Ah, and so on.

This value requirement is also strict. If you set a large dry experience value, the battery should not be fully charged, but the time for sufficient electric oil will be prolonged. The set value is less than the experience value, and the electric oil is easy to be damaged and deformed in summer. It is recommended to adjust the charger, large dry 50mA is appropriate.

Remember: it is possible to charge 10Ah battery with 20Ah charger. In turn, it is not possible to charge 20Ah battery with IOAh charger!

With regard to the measurement of the three parameters, specialized instruments are required. The low constant voltage value can be tested only with a digital multimeter. Under the condition of not connecting the battery (no load), the output value of the charger with a multimeter DC voltage of 200V is used, and the read value is the low constant voltage value. The high constant voltage value cannot be measured generally. It can only be measured with the DC voltage block of a multimeter before the red light turns green when the battery is charged.

It is also necessary to supplement the negative temperature coefficient of lead-acid batteries. The terminal voltage of each cell drops by 4mV for every 1 ℃ increase in temperature. A 48V car has 24 cells, assuming that the total terminal voltage drops by approximately 1V when it rises by 10 ℃ in summer.

If the charger output is still the aforementioned regulated value, the battery may have thermal runaway and water loss. The ideal charger should have temperature compensation, the truth is that most do not.

Readers with hands-on skills can turn the voltage down in the summer and up in the winter. The simplest method is to connect 1~2 6A10 diodes in series along the positive pole of the charger output in summer and restore them to their original state in winter.

2. Lithium battery charger

The acceptance capacity of lithium battery plate is higher than that of lead-acid battery, and it is also possible to charge with IC current, which may be a constraint of cost and reliability. At present, most chargers matched with 48V hammer turtle motor cars are 2A, and only chargers matched with 36V lithium electric cars are 5A. In terms of 10Ah battery, 5A is only 0.5c.

The charging of lithium-ion electric vehicles is much simpler than that of lithium-ion electric vehicles, that is, constant current and voltage limiting charging. Voltage limiting value = single-core voltage limiting value x number of electric cores in series. Most of the common 48V vehicle tweezers lithium acid batteries or 14 strings of ternary cores have a voltage limit of 4.2Vx14=58.8V; Most of the 16 strings of 48V vehicle phosphoric acid hammer cores are limited to 3.65VX16=58.4V. Most of the early 36V cars used 10 strings of drill acid fading cores or lithium manganate cores, and their sleeping pressure was 42Vx10=42V.

The lithium battery charger also has a charging current detection and comparison circuit inside, and the charging indicator can also be changed from red to green.

Lithium battery charger and lead-acid three-stage charger has a major difference:

When the charging current is greater than the set value, only the charging indicator turns red without changing the output voltage; when the charging current is less than the set value, the charging indicator turns green without changing the output voltage. That is to say, there is a voltage before and after turning the lamp, that is, the voltage limit value calculated in front.

Therefore, this current set point should be referred to as the "turn lamp current" to be more precise, about 0.02C. The measured lithium battery chargers matched by several manufacturers, 10Ah lithium battery pack turn lamp current is about 240mA to 260mA. After the green light continues to charge for a period of time, the charging current will be close to zero. After the lead-acid battery turns green, the charging current will soon be close to zero because the high constant voltage becomes low constant voltage.

Summary: Lead-acid batteries are limited by the plate acceptance capacity, and it is reasonable to limit the charging current below 0.15C, taking into account the shortening of the charging time.