The difference between lithium chargers and lead-acid chargers

As lead-acid battery chargers are generally set to two-stage or three-stage charging mode, the voltage levels of lithium batteries and lead-acid batteries are not matched. And there are also many kinds of lithium batteries, and the battery performance and battery protection plate parameters may be different. Therefore, lithium batteries do not have universal battery chargers like lead-acid batteries. Generally speaking, lithium batteries are shipped with a special charger. In order to protect lithium batteries, a special charger is required.

The difference between Lithium Battery Charger and lead-acid charger

At present, the chargers for electric vehicles in the market are mainly of the switching power supply type, which have the advantages of power saving, small size, light weight and mature technology. Only the lead-acid battery freight tricycle, but also use the frequency transformer type charger, simple, reliable, cheap, low requirements for the use of the environment.

Switching power supply type charger is essentially a can be called a regulated power supply. Specific fork points to pulse-width modulation chip TIA94 as the core of the half-bridge type and pulse-width modulation chip UC3842 as the core of the flyback type two types. The latter occupies more than 90% of the market because of the advantages of low cost, cycle-by-cycle protection. The specific circuit that follows is a specific analysis of these two types of typical circuits.

1, lead-acid charger three-stage charger

Nearly a century, the classic ordinary lead-acid charger for 0.1C charge J2-14 hours, very beneficial to the battery. Nowadays, people's life and work pace is accelerated, the electric car charger changed to 0.15C-0.2C charge 6-8 hours.

The so-called three stages refers to constant current, constant voltage, eddy current. Light-emitting diode is red means in constant current or constant voltage stage, becomes green means in trickle stage. Usually, turn green and then charge for several hours before the battery is really full.

(1) three important parameters of the three-stage charger

A. High constant voltage is a single cell hydrogen analysis voltage of 2.42V multiplied by the number of single cells of the battery pack, 36V Charger is 2.42Vx18 cells ≈ 43.56V, 48V Charger is 242Vx24 cells ≈ 58.08V.

This voltage is slightly higher is possible, in favor of a long constant current time, shorten the charging time: low will extend the time of the electric oil eaten.

Three-stage charger is essentially a regulated power supply with two output voltage values, this letter is that high output value.


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

This voltage requirement is strict, higher than this value will cause the electric oil loss of water: low battery can only eat 80% or 90% full. This value is the output value of that low voltage regulator.

C. Turning current (also turn light current). Charger has a real-time internal charging current detector, and a predetermined so-called "turning current"

Value for comparison, used to control the output value of the regulated power supply high or low: the charging current is greater than the value, and the output value of the regulated power supply low.

If the charging current is greater than this value, the control circuit is automatically switched to a high constant voltage output value and a red light is set to indicate that the charging current is less than the turning current value and is switched to a low constant voltage output value and a green light is set.

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

This value requirement is also strict, set a large dry empirical value, the battery should not be filled, but the electric oil sufficient time will be extended; set the value is less than the empirical value, the electric oil is easy to be charged bad deformation in summer. It is recommended that when adjusting the charger, large dry 50mA is appropriate.

Remember: it is possible to charge 10Ah battery with 20Ah charger. The other way around, it is not possible to charge a 20Ah battery with an IOAh charger!

Regarding the measurement of the three parameters, special instruments are required. Only with a digital multimeter can test the low constant voltage value, not connected to the battery (no load), with a multimeter DC voltage 200V block tour charger output value, read the value that the low constant voltage value. High constant voltage value generally can not be measured, to be connected to the battery charging situation, before the red light turns green a moment, with a multimeter DC voltage block can be measured.

Also need to add the negative temperature coefficient of lead-acid batteries related to the same issue. For every 1℃ rise in temperature, the terminal voltage per cell drops by 4mV. 24 cells of a 48V car, assuming a 10℃ rise in summer, the total terminal voltage drops by an approximate 1V.

If the charger output remains at the aforementioned regulated value, the battery may experience thermal runaway and water loss. The ideal charger boulder should have temperature compensation, the fact is that the vast majority do not.

Readers with hands-on skills can adjust the voltage lower in the summer and higher in the winter. The simplest way is to connect 1 to 2 6A10 diodes in series with the positive side of the output of the charger in the summer, and resume the original state in winter.

2.Lithium Battery Charger

Li-ion battery plate acceptance capacity is higher than lead-acid batteries, with IC current charging is also possible, may be the cost and reliability constraints, most of the chargers currently supporting with 48V hammer turtle moving car for 2A, only 36V lithium electric car charger supporting 5A. With 10Ah battery calculation, 5A is just 0.5c.

Lithium electric car users charging and lithium into when charging is much simpler, is a constant current limit voltage charge. The voltage limit value = single-center voltage limit value x the number of series connection of electric core. To now common 48V car with lithium tweeze-acid electric tunnels, or ternary electric core of 14 strings mostly, their voltage limit for 4.2Vx14 = 58.8V; 48V car with iron phosphate hammer electric core of 16 strings mostly, the voltage limit for 3.65VX16 = 58.4V. Early 36V car using drill acid fade electric core or lithium manganate electric core of 10 strings mostly, their sleep voltage for 42Vx10 = 42V.

Lithium charger also has the same internal charging current detection and comparison circuit, the charging indicator can also be from red to green.

Lithium battery chargers and lead-acid three-stage chargers have one 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. This means that there is one voltage before and after the light turn, i.e. the voltage limit value calculated earlier.

Therefore, the current setting value should be called "light current" is more accurate, about 0.02 C. Several manufacturers of lithium chargers tested, 10Ah lithium battery pack light current of about 240mA a 260mA. green light after continuing to charge for a period of time, the charging current will be close to zero. And lead-acid battery red to green light, because the high constant voltage to low constant voltage, charging current will soon approach zero.

Summary: Lead-acid batteries are limited by the ability to accept the pole plate, the charging current is limited to 0.15C or less is reasonable, taking into account the shortening of the charging time.