Experimental Aircraft Battery Management System - (BMS)

 

Others always talk about having a BMS, but you never see it!  

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Ask if their BMS is a simple analog type with a simple fault detector blinky light that leaves you guessing... or a digital programmable type with individual cell monitoring in real-time as in Aerolithium batteries.

 

Experimental Aircraft Battery Management System

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Heavy Duty BMS made specifically for for Aviation use. Dual low voltage protections mean your Aerolithium battery will never die, even if you leave the master on.

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Battery Management System Protections

 

For Peace of Mind - when you need it the most!

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• Balancing - continuous

• OverVoltage from charging, no crowbar needed

• OverCurrent from charging

• Under Voltage from discharge - UVP - 9.8V

• Parasitic drain auto shut off - LVD - 13.0V

• Low Voltage engine start reserve

• Short Circuit protection

• Thermal: over/under temp - dual sensors

• LED Battery status indicator

• "Wakeup" button - saves energy in non-use

• Heat sink AL plate- keeping Mosfets cool

• Remote Panel Digital display option

 

Aerolithium Battery Management System Specifications and Unique Features

 

Click Here for 13V BMS SPECS

Click Here for 28V BMS SPECS

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• Dual Low Voltage / over-discharge protection levels in which load sensors signal activation thresholds for LVC. Cells must be kept in balance, any over voltage from over charging will damage the cell as well as letting a cell sit in an undercharged (<2V ) state.

• First level protection for accidental "master switch-left on" situations, ensuring reserve power for engine starting. Returning to a dead battery is a thing of the past.

• Second Level protection for in-flight alternator or generator failure, allowing the battery to support your aircraft electrical system with stable power at a constant voltage down to its minimum recoverable charge, thus maximizing flight time on battery power alone.

• NOTE: for those wanting to do a "cranking test"... please watch this first; https://www.youtube.com/watch?v=uvnrbUrPy8Y

 

What method of internal balancing does your lithium battery use?

 

The basic method of balancing lithium cells hasn't changed in years.
 

The two types can be divided into Passive cell balancing and and the newer Active balancing type.
 

Passive balancing drains charge from cells with excess charge and dissipates the drained energy as heat. Active balancing on the other hand transfers charge from  higher charged cells to lesser charged cells.
 

Cell balancing is not only important for improving the performance and life cycles of a lithium battery, it also improves safety of the lithium battery.
 

Both Active and Passive cell balancing are ways to improve system health by monitoring and matching each cells SOC. But, unlike passive cell balancing which simply dissipates the charge during the charge cycle, Active balancing redistributes the charge during charge and discharge cycles.
 

Therefore, Active cell balancing increases system run time and improves charging efficiency without generating the internal heat of a Passive resistor system.
Passive balancing is the method most used today to keep costs down at the expense of battery efficiency. A cheaper type of BMS is used in all lithium batteries seen in the market today using the Passive method where battery performance is not critical or safety dependent.
 

These cheaper BMS's may try to add other features like alleged redundancy or fault indicators to compensate for the inevitable early demise of the battery due to the imbalanced state of the cell pack.

 

 

 

 

The faster the charging, the greater the imbalance that is occurring.

It is a common weakness with all lithium batteries that cell imbalance is a liability in every battery system. If lithium batteries are overheated or overcharged, those conditions will accelerate battery degradation and quickly shorten the batteries lifespan. Just as there are no two identical snowflakes, so too are there no two identical cells. There are always subtle differences in SOC, self-discharge rate, capacity, impedance and temperature characteristics. This is the case even if the cells are the same model, same manufacturer or same production batch.

Without a robust balancing ability the results are a large difference in voltage over time decreasing capacity.

In Passive balancing, the practical goal is to achieve capacity balance at the end of charge. However, due to the typical low balancing current, if the cells begin to diverge in SOC, it is virtually impossible to correct the charge imbalance at the end of charging. In other words, Passive balancing, while avoiding overcharging of the strongest cells does not allow a full charge of the weaker cells because extra energy is wasted in shunt resisters as heat... a LOT of heat!

With Active type balancing, 2 goals - achieving voltage parity at the end of charge and minimizing V differences among cells can be achieved at the same time. Energy is conserved and transferred to the less charged cells which results in increased safety, discharge capacity and life of the battery.

Unless the cells are well balanced, a ' weaker ' cell in the pack will limit the overall performance of the battery and eventually render the battery unusable. To avoid this, the cells should be balancing at all times  not just while being charged so that the differences between cells are as small as possible.

Operational wise; the Passive method is simple and straightforward - the BMS uses resisters to dissipate energy. It is cost effective and this method is used for all low cost applications. However, since 100% of the excess energy is turned into heat inside the battery, and it is incapable of keeping up with the incoming charging current, imbalance is assured and runtimes are diminished.

A typical BMS with Passive balancing comes with 50 - 200milliamps capability. When the charging current is high - such as from an alternator - the resisters are overwhelmed and the heat generated by them degrades the cell pack over time.
Active balancing on the other hand utilizes capacitive or inductive charge shuttling to deliver energy where it is most needed with minimal loss and heat generation.
 

It is significantly more efficient because energy is diverted to where it is most needed, rather than turned into heat. Of course, the trade-off for this higher efficiency is a slightly higher battery cost.

Active balancing can happen during any battery operation - charging, discharging or at rest. Compared to Passive balancing, almost no energy is lost to heat.

 

 

 

 

 

This method can extend battery life by as much as 50%, maximizing
the capacity of the battery ensuring that all its energy is available.

Aerolithium has already started phasing in Active balancing in all
its batteries.
 

Take the Guess-Work out of Flying!

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A visual display is an essential requirement for an aircraft battery. You will absolutely need a visual reference in order to determine battery health. 

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Cell voltage monitor and early warning indicator of each cell and total battery overvoltage, undervoltage, and cell balance condition. Also has a low voltage audible alarm.

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​These Safety Features engage automatically:

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• Overcharge / Over voltage Protection from a regulator Failure which may result in excess voltage and current.

• Aerolithiums heavy duty circuitry needs no external regulator ( crowbar ) assistance.

• Max. charge 100 amps protection

• Over current protection limits maximum charging current to battery from any size alternator / generator.

• Thermal Protection - 2 sensors automatically adjust charging and discharging limits per environmental temperature conditions.

• AC Ripple Protection - circuit of coils and capacitors to filter this out. Smaller engines really need this feature.

• Short Circuit Protection - 2 ms

• Cell Balancing - Smart Float type activated by 0.015ma differential at 40 - 300 ma

• Sleep Mode - BMS will not drain battery when not in use, < 1 ua

• Mosfet Management Proprietary redundant design equalizes MOSFET impedance preventing overheating under extreme loads.

• Conducted Protection circuitry to abate damage from Back EMF at the alternator. No other competitors BMS, have this important safety feature.

• Dual Core MCU based system redundancy - monitors cell sensing circuity, sensing wires and thermal sensors against, out of limit variation

• Heat sink plate for Mosfets - to dissipate excess heat from all that power!