Smart BMS features in the KS Energy Super series range of batteries

Introduction

Since lithium batteries deliver the bulk of their power over a flat voltage range, conventional voltage based charge gauges are rendered redundant. This makes it very difficult to determine remaining power. Our smart Bluetooth technology easily provides you with this valuable information. It consists of a smart BMS built into the Super Series range of KS Energy batteries and a free to download Android® or Apple© app.

It gives an indication of the state of charge (SOC) of the battery and allows the user to see other helpful or interesting data such as power usage, operational status, even the battery model and serial number. Here we cover some of the features and the operations relating to these features in more technical detail.

State of Charge (SOC) – App page 1

The SOC indicates a percentage (%) approximation of remaining charge. It self-calibrates during cyclic use over time by noting the low voltage cut-off (under discharge) activation point and then gauging the total accumulated charge to a factor where the nominal charge voltage is reached and its tail current falls to a few percent of capacity (Over charge). In addition, the changing impedance over time is also noted. It then uses these parameters to maintain its accuracy. In detail, our BMS uses the Texas Instruments® BQ series fuel gauge chip, current is detected by a hall sensor. The data on the BMS is collected by a UART and sent from the Bluetooth transceiver to the app. The UART is “write protected”. Therefore, the entire operation of the BMS is fully automated. The KS Energy application as well as the fuel gauge have absolutely no input to the operation of the battery. To be clear, everything is performed purely automatically and requires no external user monitoring at all regardless to whether the app is connected, or its owner is monitoring the battery or not!

Once you are connected, the application consists of four pages which you can scroll through by left swiping:



KS Energy Bluetooth battery monitor appThe KS Energy Battery monitor app for Android and Apple Bluetooth 4.0 devices

Voltage - Page 1

This indicates the total battery voltage by internally measuring the combined cells, as opposed to battery terminals, it is accurate to hundredth of a volt. The normal voltage parameters of the battery can be between 10V (under discharged) and 14.6V (over charged). Typical service values during discharge are likely to be between 12.5V and 13.2V and the journey of discharge from 12.5V is likely to be comparatively fast since the battery by then will be approaching a low state of charge.

Capacity – Page 1

This is fixed and indicates the original design capacity of the battery as new, along with the batteries serial number both are fixed at the point of manufacture.

Status – Page 1

This parameter will update during normal operation, the statuses are as follows: Standby – there is no charge or discharge current flowing in the battery and it is ready for operation. Discharge – the battery has a discharge load and current is flowing out of the battery. Charge – the battery is accepting a charge load and current is flowing into the battery. Over Discharge – the battery is fully exhausted and has switched itself off to protect itself from complete discharge to prevent damage. Over Charge – the battery has fully charged and switched itself to charge protect so that it cannot receive further charge current that could cause damage. Short Circuit – the battery has experienced a dangerous and sudden demand of current (a fault condition) and senses a short circuit across its terminals which must first be removed to restore normal operation.

Health – Page 1

This indicates the battery cell banks are all correctly operating and working to their maximum given efficiency

V – Page 2

This is an identical displayed parameter to that as described in “Voltage – page 1” above, except in addition this screen also has an easy to read analogue voltage meter dial display.

A – Page 2

This is an analogue easy to read and digital Amper meter displaying current in Amps flowing into or out of the battery. If the current is flowing out and the battery, the battery is discharging at the indicated current. In this instance it will be displayed as a minus (-) integer. If the battery is charging, it displays the charge current in amps as a positive integer.

Temperature – Page 2

This displays the internal temperature of the battery cells numerically in degrees Celsius (ºC), also displaying the temperature as an easy to read bar graph from left and increasing to right. High temperatures should be avoided where possible since battery aging considerably accelerates at higher temperatures. Ideally comfortable ambient (22) plus 10 would be a good ceiling. That aside, for safety the BMS will switch itself into a self-protect mode if the internal temperature rises to far.

Cycle Life – Page 2

This is a numerical count of the number of charge and discharge cycles the battery has experience since it was new, much like a mileometer on a vehicle. A single cycle is counted as a complete discharge and charge of its designed capacity from a given point and is purely automatic and read only, it cannot be altered or reset.

Page 3 – Cell Status

This is a matrix display of the individual voltage levels of the separate banks of cells that make the battery. There are four banks in the 12V lithium-Iron Phosphate battery, eight in the 24V and sixteen in the 48V formats. Thus, in a 12V battery just four of the cell banks will be displayed as active. Cell banks are automatically balanced during normal operation. Generally, most of the balancing takes place when the battery is at or near a fully charged status. This is when voltage levels may be allowed to independently rise, whilst the cells that have not quite reached maximum continue to absorb charge. Again, this display is purely indicative, the operation of which is wholly automatically controlled within the batteries BMS. If any of the cells were to reach a level where damage could occur (4.2V), the BMS will cut out. You may have already noted that the current battery voltage is an addition of all four banks.

Page 3 – Disconnect

To disconnect the application from the battery, press the disconnect button on this page. (Shutting the app will automatically perform a similar function). The battery will switch its Bluetooth transceiver into ultra-low power receive/hibernate mode and draw near zero current. If you have two or more batteries, you must disconnect from one battery to connect to another using the same app. It is not possible to connect to more than one battery at a time with a single device.

Page 4 – Information

This page is purely for KS Energy contact information and performs no other function.

Important considerations for successful use of the app with parallel and series configurations

Where two or more batteries are connected in parallel to increase your total capacity there are several considerations to be aware of. Safety: ● Before attempting to connect any battery in parallel or series configuration, you must ensure both batteries are of the same make and model. ● Before attempting to connect any battery, ensure that the batteries are all fully charged first, (ideally cycled at least once) and fully charged before connecting. This ensures that the impedance of each battery is very much equal and that there cannot be an excess flow of current transferred from one battery to the other. ● Where batteries are configured in series to increase the voltage, ensuring both batteries are fully balanced prior to putting into service. Imbalanced pairs will not self-correct whilst imbalances may exacerbate over time causing premature ageing.

Parallel battery banks

As highlighted under “Disconnect – page 3” above, it is only possible to connect to a single battery at a time with a single app and device. However, in practice it will prove only necessary to connect to a single battery to gain an indication of the total state of charge of both batteries.

This is because, when correctly paralleled, both batteries over time will begin to charge and discharge at near identical rates as they age, and their impedances settle down and begin to closely match. As this process begins, the voltage indicators mirror as will temperatures. Do however bear in mind that the current indicator will be shown as a division of the total number of batteries paralleled. For example, where two batteries are paralleled, a current draw of 5 will in fact be a multiple of two so that the total current draw is in fact 10.

Series battery banks

As covered above, since the state of charge (SOC) is presented as a percentage, over time it will begin to match its counterpart more closely (providing balance is maintained). The current reading of a single battery will also be valid for the bank; however, the voltage reading will be a division of the total voltage.