A quick explanation of the importance of using the best charge algorithm for your batteries
In simplest terms, a charge algorithm (or charge profile) contains all of the logic used to accurately recharge your batteries. Delta-Q develops algorithms by working closely with battery manufacturers to meet their charging recommendations for each battery model. Our battery testing lab includes more than 20 test channels and a temperature chamber to simulate charging in different ambient environments.
Different battery types, batteries from different manufacturers, and even different capacity batteries from the same manufacturer should be charged differently to maximize run-time and battery lifetime. This requires a deep understanding of the battery chemistry and how the manufacturer wants to see their batteries charged.
Battery chemistries have varying levels of efficiency. Flooded lead-acid batteries are typically 80% efficient, sealed lead-acid batteries (gel and AGM) are 85% efficient, and lithium batteries are 95% efficient. This efficiency is seen during charge and discharge and is inherent in the chemistry.
Flooded Lead-Acid Algorithms
Flooded lead-acid batteries have a liquid electrolyte between the positive and negative plates. It is important to provide a level of over-charge to the batteries to stir this electrolyte and balance the individual cells in the battery pack. A lead-acid charge algorithm contains the logic used to execute a multi-stage charging process, including bulk, absorption, and finish phases.
The bulk phase is used to return most of the energy to the batteries and is usually set to maximize the output power of the charger. However, lead-acid batteries should be charged at approximately 10% (and not more than 13%) of the C/20 capacity (a 200 Amp-hour battery should not be charged at more than 26 Amps). It is important to ensure that your selected algorithm and charger combination do not put energy into the battery too quickly in this phase as more heating will occur. Charge algorithms exit from the bulk phase when the battery voltage reaches a specified (usually conservative) voltage.
Next, the absorption phase holds the battery voltage constant, and gradually allows the battery current to naturally taper down, or “absorb” the current until its needs are reduced. Energy is returned at a gradually slower rate until the battery essentially reaches a 100% state of charge, when the charge profile transitions to finish. While 100% state of charge may seem sufficient, lead-acid batteries require a certain amount of overcharge to remain healthy and extend battery lifetime – as much as 20% for some battery manufacturers.
The finish phase delivers constant current to the battery to lightly stir the electrolyte. Batteries could be left to taper down to no current, but a modest finish current safely shortens overall charge time. The finish current should be very well tailored to the capacity of the battery pack (ranging from 1% to 3% of the C/20 capacity). There are many different methods to determine the over-charge in the finish phase to maximize batteries’ lifetimes, and the machine use case should be considered when choosing an algorithm – Delta-Q uses two main methods.
- Amp-hour Counting: Amp-hour counting algorithms are more precise and therefore use less water. To be effective, they require a temperature sensor to adjust target voltages based on ambient temperature. They are generally more specific to the battery they are designed for and are ideal for applications with long life requirements, occasional shallow discharges, and regular, daily charging.
- dV/dt: Algorithms that use a dV/dt finish criteria, where the change in voltage over time is used to terminate the finish phase, will continue to apply current until the batteries are no longer accepting charge. These algorithms are best used when the use case involves deep discharges, frequent use, and less regimented charging. These algorithms do not require a temperature sensor and are more generic for use with different flooded batteries. Because dV/dt algorithms require a minimum amount of time in finish to confirm that the limit is met, they will likely result in more water usage.
Sealed Lead-Acid Algorithms
Two types of sealed lead-acid batteries are widely used in floor care. Gel and AGM (Absorbed Glass Mat) batteries capture electrolyte in a way that requires less over-charge, since the liquid does not need to be stirred as much. Overall, sealed lead-acid batteries are more efficient during discharge and charge.
The charge profiles are generally similar to a flooded lead-acid algorithm. Sealed lead-acid batteries can accept a higher bulk charge current – even 30% of the C/20 rate is acceptable. In many cases, sealed lead-acid algorithms use gentler finish currents, or apply other unique approaches to keep from overheating or excessively venting the batteries. These methods can lead to slightly longer overall charge times. Most gel and AGM battery manufacturers request temperature compensation in their algorithms to prevent significant under- or over-charging.
Lithium batteries are the most efficient and can be discharged and charged at substantially higher rates, with minimal loss of capacity when discharged quickly. Lithium battery packs need to be controlled by a Battery Management System (BMS) that monitors voltages and temperatures—and distributes energy among the cells. Lithium algorithms are significantly simpler than lead-acid algorithms. Due to the efficiency and lack of an electrolyte to be stirred, they are generally charged at a constant current until a target voltage is reached. This charge rate can be equal to or even higher than 100% of the capacity. However, increased heating and reduced lifetime would result from this approach. The use case should help determine what charge rate is used.
To ensure that the battery is safe, there are three different control methods available within Delta-Q lithium chargers. The algorithm only method is used where the BMS and the battery charger do not communicate—the charger simply operates a charge algorithm as specified by the lithium battery or BMS manufacturer to return energy until a target voltage is reached. The BMS can close or open a contact to signal the charger to enable or disable charging. This method relies on the charger to control the output to maximize safety.
The remote-control method requires CAN bus communication between the BMS and charger. The battery charger in this instance becomes dependent on the decisions made by the BMS and can be commanded to operate to its maximum voltage and current.
The mixed control method offers the benefits of remote control but within some tighter safety restrictions that are resident in the lithium charge algorithm. This helps prevent problems should the BMS fail or face similar issues.
Future Proofing Your Floor Care Machine
Delta-Q has recently upgraded the software in our chargers to be able to easily switch between lead-acid and lithium charge algorithms. Many floor care OEMs are offering lithium battery options on their machines. Previously, OEMs would have to order unique part numbers for their chargers to delineate lead-acid or advanced lithium charging. Now, a single CAN bus enabled charger can be installed at the factory and configured to charge lead-acid or advanced lithium batteries. If customers wish to change their battery chemistry in the field, they simply need to send a CAN command to the charger to toggle between the two operating modes at any time.
There are many other advantages to CAN bus enabled chargers, as well.