The hard life of a Traction Battery.
Batteries are commercially classified according to their application:
- Starter batteries. For starting internal combustion engines
- Stationary Batteries. For powering static equipment: emergency lighting, alarms, UPS, telecommunications, etc.
- Traction batteries. To supply power to an electric motor that normally moves with the vehicle.
If we could make an analysis of the daily life of each of these batteries we could easily conclude that traction batteries are undoubtedly the ones that "have the worst life". Let me explain:
Starter BatteriesThey are sprint runners. High intensity peaks are demanded from them for short periods of time. Once the engine starts, the alternator starts to charge them. The 90%'s normal state of life is at rest at full load. Its design is oriented to increase the number of plates by decreasing their thickness, in order to increase the plate surface in contact with the electrolyte, which is the characteristic of the battery that facilitates high current peaks,
Stationary Batteries. These batteries operate with medium depth discharges and slow recharge. They normally serve alarms or emergency equipment that come into operation only once a month. Therefore they are constantly in float and at full charge. A stationary battery is supplying current in service only 3% of its useful life. Their design uses medium-thickness components providing for slow rate discharging and charging.
Traction batteries. This group of batteries normally works in working shifts of 4-8 hours. They are called cyclic because each of these cycles / shifts involves a complete discharge. In their construction thick plates are used to support the loss of active mass that entails the repeated deep discharges. Every manufacturer offers graphs relating useful life (number of cycles) with average depth of discharge. Deep discharges, which are always present, are harmful to battery life.
But what they do not tell us is that in addition to the fact that a traction battery is subjected to deep discharges every day, during its use it has the disadvantages of a starter battery. That is to say, it does not even have medium intensity discharges during relatively short periods of time. They have consumption peaks just like starter batteries.
If earlier we said that a starter battery is like a sprint runner, who then has a rest (rest) and an immediate treatment (alternator charge that does not allow deep discharge), in the case of traction batteries we could say that they are marathon runners "with drawbacks". It is as if a marathon runner were made to run the race in installments, with sprint starts and then slowing the pace to zero, to start again at sprint in the next installment. A marathon made up of successive sprints and stops/starts without eating or refueling for the entire shift. That is the daily life of a traction battery!
To illustrate this idea, we place a data logger that records current and voltage every second. Attached is the three-minute graph at the output of a golf baby carriage battery (36V). In red the current and in blue the voltage, peaks of 120A and average currents of 40A are recorded:
It is clear that the idea that traction batteries work with medium currents has to be put aside. The traction battery has all the disadvantages of a starter battery and receives a much more harmful treatment:
- Charges are done manually, the user, once the shift is over, connects the battery to the charger and completes (or not) the charge cycle. Partial charges are equally detrimental to battery life.
- Open lead-acid batteries need electrolyte replenishment, as gassing during charging causes losses. The correct level is not always maintained and this results in additional capacity loss.
So, let's keep in mind that traction batteries are "the hardest suffering of the party" and deserve consideration and proper treatment for that hard life given to them by their users. 😀