Charging an growing old automotive lead-acid battery

“A small research reveals that automotive lead-acid batteries are totally different from deep-cycle or stationary batteries. Automotive batteries are designed to maximise cranking present capability and don't reply nicely to deep discharge or float cost (also called a stage 3 cost cycle). The plate construction of the starter battery maximizes floor space and has the next electrolyte particular gravity (SG) than different batteries to supply excessive start-up present. Like stationary batteries, automotive batteries which might be allowed to stay in a deep state of discharge endure everlasting sulfation, wherein small lead sulfate crystals produced throughout discharge remodel into secure crystalline kinds and deposit on the unfavourable plate.

“

A small research reveals that automotive lead-acid batteries are totally different from deep-cycle or stationary batteries. Automotive batteries are designed to maximise cranking present capability and don't reply nicely to deep discharge or float cost (also called a stage 3 cost cycle). The plate construction of the starter battery maximizes floor space and has the next electrolyte particular gravity (SG) than different batteries to supply excessive start-up present. Like stationary batteries, automotive batteries which might be allowed to stay in a deep state of discharge endure everlasting sulfation, wherein small lead sulfate crystals produced throughout discharge remodel into secure crystalline kinds and deposit on the unfavourable plate. Float charging, however, can simply trigger oversaturation in automotive batteries, which may result in oxidation of the optimistic plates and shorten battery life. Due to this fact, the cost voltage and cost cycle are crucial and are totally different for automotive and deep cycle varieties; moreover, the cost voltage ought to lower with ambient temperature at a charge of 3mV per diploma Celsius above 25ºC.

Determine 1 reveals the charging cycles for Part 1 and Part 2. Phases 1 and a couple of will be achieved with the circuit of Determine 2, in present limiting the cost present for stage 1 is comparatively fixed and because the cost present decreases under the present restrict for stage 2 fixed voltage mode. A superb rule of thumb right here is that the battery is absolutely charged when the present is not lowering.

Determine 1 Part 1 and Part 2 charging cycles

Determine 2 The uncooked energy provide unit (PSU) operates in fixed present mode (CCM) till the load present falls under the present restrict threshold. The adjustment sequence is: Modify the VR2 10k potentiometer to make Vout = 14.1V beneath no-load situation.

Exhausting or everlasting sulfation is a operate of time and state of discharge, so if the automobile just isn't in regular use it's advisable to have some technique of monitoring the battery voltage and restarting the charging course of if the voltage drops to some level under the total cost voltage. In Take the automobile’s discharge charge under consideration when setting the set level to provoke Part 1 charging.

Actual worth knowledge for cost charge, present, voltage, and float voltage varies by supply. Nevertheless, the primary takeaway from most sources is that to cost the battery optimally with out shortening its lifespan, don’t let it overheat, don’t onerous sulfate, don’t outgas, don’t oversaturate. This design concept makes an attempt to do that as simply as doable utilizing any gear aside from a soldering iron, screwdriver, and multimeter.

how does this work

Determine 3 reveals the entire circuit that gives fixed voltage present restrict operation to finish cost phases 1 and a couple of, as soon as the cost present has decreased to a gradual worth of roughly 200mA, the cost voltage is eliminated and the battery is discharged to some extent under 12.6V. Utilizing a trimmer potentiometer permits some freedom in establishing the charger in order that it could actually meet the charging necessities of most 12V automotive batteries.

D4 is a very optionally available try to cut back the charging voltage based mostly on ambient temperature. It labored nicely within the lab, however it stays to be seen the way it will carry out within the scorching Texas summer season! It's usually accepted that if the ambient temperature exceeds 49ºC/120ºF, it shouldn't be charged to extend the lifetime of the battery.

U1 and Q1 type a continuing voltage present limiting energy provide, VR2 units the utmost charging voltage, and VR4 units the present restrict. D4 gives some thermal derating at about 4mV/ºC.

Differential amplifier U2 situations the sign on present sense Resistor R1 and applies the conditioned sign to the inverting enter of U3. U3 is linked as a comparator with its set level on the non-inverting enter offered by VR1. So long as the load (charging) present sign from U2 is above the set level, the output of U3 will probably be low, energizing RL1 and supplying charging present to the battery. The set level must be set to signify 3-5% of the utmost cost present. This may be finished with a resistive load or by monitoring the battery cost cycle and seeing at what present the charger flattens out (Determine 1). Relying on the cost present and preliminary state of cost, this technique can take as much as about 13 hours, however it’s a greater technique. As soon as the cost present falls under the set worth, the output of U3 will go excessive and reverse bias D1, turning off Q2 and thus de-energizing RL1.

Determine 3 Utterly modified PSU circuit

The PSU operates within the CCM mode described above till the load present drops under the present restrict threshold. When the battery voltage drops under 12.96V, the cost cycle begins, inflicting RL1 to show off. When the cost present falls under 200mA, the cost cycle ends, inflicting RL1 to open.

Modify the order

Step 1: Modify VR2 10k pot Set Vout = 14.1V Set fixed voltage beneath no load situation

Step 2: Modify the VR4a/b 1k potentiometer to set the present restrict to the specified worth beneath brief circuit situations

Step 3: Modify VR1 10k potentiometer to open Relay 1 (RL1), disconnect the battery, when the load present is decrease than 3-5% of the charging present (or saturation present)

Step 4: When the battery voltage drops under someplace between 12.5 and 12.6V, regulate the VR3 10k potentiometer to shut Relay 1 (RL1).

U4 screens the battery voltage and can be linked as a comparator; nonetheless, its set level is linked to the inverting enter, so when the battery voltage falls under the set level, U4’s output will go low, turning on Q2, energizing RL1 and apply charging present to the battery. When the battery voltage is increased than the set worth, the output of U4 will go excessive and reverse bias D2, thus turning off Q2 and de-energizing RL1. VR3 is used to regulate the battery voltage to the setpoint offered by VR1. Utilizing one set level for present and voltage saves a number of resistors!

The outputs of U3 and U4 are diode-OR’ed in order that U3, U4, D1, D2, Q2 and RL1 type a management loop with the battery to supply automated management of the cost cycle. The components within the circuit containing RL1 and Q2 must be adjusted to accommodate the coil resistance of RL1.

Part values ​​will be modified to go well with the state of affairs at hand, however resistor ratios must be maintained the place they work together to permit for the same vary of adjustment. A sensible choice for RL1 is any excessive present automotive relay, however the part values ​​round Q2 and RL1 will depend upon the coil resistance of RL1. The relay used is a 10A, 12V 1000Ω kind.

A single pole swap toggles the enter of U5 to Display present output or battery voltage on the meter.

Any op amp can be utilized so long as its output swing is inside about 200mV of both rail. The LM358 was used because the comparator for the U3 and U4 areas as they have been available and the roughness of the appliance allowed this, however any single provide comparator may very well be substituted if desired. The utmost present will be elevated if Q1 is a Darlington and the worth of R1 is decreased. The LT1413 used within the simulation is a alternative for the LM358 used on the board. U2 will be changed with an built-in present sensor such because the LTC6102.

The management circuit improve was initially simulated utilizing LTspice, then constructed on a solderless prototype board for analysis and is being added to current chargers.

It must be famous that totally different sources present considerably totally different values ​​for battery and charging voltage. Because the distinction between high and low voltages that trigger onerous sulfation or corrosion could be very small, it's value checking the battery producer’s knowledge on the particular battery being maintained. Completely different sources additionally give a rule of thumb for stopping charging at 0.1ºC or 3-5% of most cost present. When the proper charging voltage is utilized, the purpose at which the charging present tapers off and stops falling is one of the best ways to find out when to cease charging. One cost cycle ought to present the required measurements.