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The device bq24650 includes an advanced built-in MPPT Synchronous Switch-Mode Battery Charge Controller. It offers a high level of input voltage regulation, which prevents the charging current to the battery each time input voltage drops below a specified amount. Learn More:


Whenever the input is attached with a a solar panel, the supply stabilization loop pulls down the charging amp to ensure that the solar panel is enabled to produce maximum power output.

The bq24650 promises to provide a constant-frequency synchronous PWIVI controller with optimal level of accuracy with current and voltage stabilization, charge preconditioning, charge cut-off, and charging level checking.

The chip charges the battery in 3 discrete levels: pre-conditioning, constant current, and constant voltage.

Charging is is cut-off as soon as the amp level nears the 1/10 of the rapid charging rate. The pre-charge timer is set to be at 30 minutes.

The bq2465O without a manual intervention restarts the charging procedure in case the battery voltage reverts below an internally set limit or reaches a minimum quiescent amp sleep mode while the input voltage goes below the battery voltage.

The device is designed to charge a battery from 2.1V to 26V with VFB internally fixed to a 2.1V feedback point. The charging amp spec is preset internally by fixing a well matched sensing resistor.

The bq24650 can be procured with a 16 pin, 3.5 x 3.5 mm^2 thin QFN option.


 Courtesy: MPPT Synchronous Switch-Mode Battery Charge Controller Circuit

BATTERY VOLTAGE REGULATION 

The bq24G50 employs an extremely accurate voltage regulator for the deciding on the charging voltage. The charging voltage is preset by means of a a resistor divider from the battery to ground, with the midpoint hooked up the VFB pin.

The voltage at the VFB pin is clamped to 2.1V, in order to produce the following formula for the level of regulation voltage:

V(batt) = 2.1V x [1 + R2/R1]


where R2 is linked from VFB to the battery and R1 is connected from VFB to GND. Li-Ion, LiFePO4, as well as SMF lead acid batteries are ideally supported battery chemistries.

A majority of over the shelf Li-ion cells can now be effectively charged up to 4.2V/cell. A LiFePO4 battery supports the process of a substantially higher charge and discharge cycles, but the down side is that the the energy density is not too good. The recognized cell voltage is 3.6V.

The charge profile of the two cells Li-Ion and LiFePO4 is preconditioning, constant current, and constant voltage. For an effective charge/discharge life, the end-of-charge voltage limit may possibly be cut down to 4.1V/cell however it‘s energy density could become a lot lower compared to the Li-based chemical specification, lead acid continues to be much preferred battery because of its reduced production expenses as well as rapid discharge cycles.

The common voltage threshold is from 2.3V to 2.45V. After the battery is seen to be completely topped up, a float or trickle charge becomes mandatory in order make up for the self-discharge. The trickle charge threshold is 100mV-200mV below the constant voltage point.

INPUT VOLTAGE REGULATION 

A solar panel may have an exclusive level on the V-I or V-P curve, popularly known as the Maximum Power Point (MPP), wherein the complete photovoltaic (PV) system relies with optimum efficiency and generates the required maximum output power.

The constant voltage algorithm is the most easy Maximum Power Point Tracking (MPPT) option available. The bq2465O automatically shuts down the charging amp such that the maximum power point is is enabled for producing maximum efficiency.

Switch ON Condition

The chip bq2465O incorporates a "SLEEP" comparator to identify the means of supply voltage on the VCC pin, because of the fact that VCC may be terminated both from a battery or an external AC/DC adapter unit.

If the VCC voltage is more significant the SRN voltage, and the additional criteria are fulfilled for the charging procedures, the bq2465O subsequently begins making an attempt to charge a connected battery (please see the Enabling and Disabling Charging section).

lf SRN voltage is higher with respect to the VCC, symbolizing that a battery is the source from where the power is being acquired, the bq2465O is enabled for a lower quiescent current ( <15uA) SLEEP mode to prevent amperage leakage from the battery.

lf VCC is below the UVLO limit, the IC is cut-off, after which VREF LDO is switched off.

ENABLE AND DISABLE CHARGING

The following concerned aspects need to be ensured before the charging process of the proposed MPPT Synchronous Switch-Mode Battery Charge Controller Circuit  is initialized:

• Charging process is enabled (MPPSET > 175mV)
• The unit is not in Under-Voltage-Lock-Out (UVLO) functionality and VCC is above the VCCLOWV limit
• The IC is not in SLEEP functionality (i.e. VCC > SRN)
• VCC voltage is below the AC over-voltage limit (VCC < VACOV)
• 30ms time lapse is fulfilled after the first power-up
• REGN LDO and VREF LDO voltages are fixed at the specified junctures
• Thermal Shut (TSHUT) is not initialized
- TS bad is not identified
Any one of the following technical issues may inhibit the proceeding charging of the battery:
• Charging is is deactivated (MPPSET < 75mV)
• Adapter input is disconnected, provoking the IC to get into a VCCLOWV or SLEEP functionality
• Adapter input voltage is below the 100mV above battery mark
• Adapter is rated at higher voltage
• REGN or VREF LDO voltage is not as per the specs
• TSHUT IC warmth limit is identified
• TS voltage happens to move out of the specified range which may indicate that the battery temperature is extremely hot or alternatively much cooler

Self-Triggered In-built SOFT-START CHARGER CURRENT

The charger by irself soft-starts the charger power regulation current each time the charger moves into the fast-charge to establish that there is absolutely no overshoot or stressful conditions on the externally connected capacitors or the power converter.

The soft-start is featured with of stepping-up the chaging stabilization amp into eight uniformly executed operational steps next to the prefixed charging current level. All the assigned steps carry on for around 1.6ms, for a specified Up period of 13ms. Not a single external parts are called for enabling the discussed operational
function.

CONVERTER OPERATION

The synchronous buck PWM converter employs a predetermined frequency voltage mode with feed-forvvard control strategy.

A version III compensation configuration lets the system to incorporate ceramic capacitors at the output stage of the converter. The compensation
input stage is associated internally between the feedback output (FBO) along with an error amplifier input (EAI).

The feedback compensation stage is rigged between the error amplifier input (EAI) and error amplifier output (EAO). The LC output filter stage needs to be determined to enable a resonant frequency of around 12 kHz - 17 kHz for the device, for which the resonant frequency, fo, is formulated as:


fo = 1 / 2 ? ?LoCo

An integrated saw-tooth ramp is allowed to compare the internal EAO error control input to alter the duty-cycle of the converter.

The ramp amplitude is 7% of the input adapter voltage enabling it to be permanently and completely proportional to the input supply of the adapter voltage.

This cancels away any sort of loop gain alterations on account of a variation in the input voltage and simplifies the loop compensation procedures. The ramp is balanced out by 300mV so that a zero percent duty-cycIe is achieved when the EAO signal is below the ramp.

The EAO signal is likewise qualified to outnumber the saw-tooth ramp signal with a purpose to achieve a 100% duty cycIe PWM demand.

Built in gate drive logic makes it possible accomplishing 99.98% duty-cycle at the same time confirming the
N-channel upper device consistently carries as much as necessary voltage to always be 100 % on.

In the event the BTST pin to PH pin voltage reduces below 4.2V for longer than three intervals, in that case the high-side n-channeI power MOSFET is switched off while the low-side n-channe| power MOSFET is triggered to draw the PH node down and charge-up the BTST capacitor.

After that the high-side driver normalizes to 100% duty-cycle procedure until the (BTST-PH) voltage is observed to decline low yet again, on account of outflow current depleting the BTST capacitor below 4.2 V, as well as reset pulse is reissued.

The predetermined frequency oscillator maintains rigid command over the switching frequency under most circumstances of input voltage, battery voltage, charge current, and temperature, simplifying output filter layout and retaining it away from the audible disturbances state.

 In this post we learn how to use an exercise bike or a treadmill for charging a battery through a simple shunt regulator circuit with full charge cut-off feature. The idea was proposed by Mr. Peter Jaffe.




The Request

Swagatam,

Hi. I have been following your circuit tips for a little while. Very helpful and informative!
I was wondering if you can help me out.

This is the deal. I have a beautiful recumbent exercise bike I inherited from my dad. Its a TRUE PS/100. It has a three phase induction AC motor. 250watts at 1amp.

I also have a small solar system. 5 X 38wah Lithium Ion Batteries 12V in parallel. They are hooked up to two 245 watt 10amp (each) Poly Panels. The solar system works great...getting 18-19amps at peak sun...more than enough to charge the system.

Now..on cloudy or rainy days..and obviously at night I am not getting any power into my lithium battery bank. So.... heres the question.... I have wanted to utilize my exercise bike to install a bridge rectifier..(which I did)...three phase AC to single phase DC...the problem is...its still too much voltage to charge my 12 volt battery bank with.... how can I step down the voltage to 24volts (from @150-200 Rectified DC) to lessen the Back EMF coming into the bike which makes it difficult to peddle...and lower the voltage so I dont blow the batteries??... What type of circuit do you suggest? Resistors? 400volt caps? a transistor perhaps?? Im not formally trained in circuit..design. Please help! Thanks!

Regards,

Peter Jaffe


The Design

Initially it appeared to me that the request was regarding operating the bike from alternative source but after reading it the second time I realized that actually its regarding using the exercise bike for charging batteries by generating electricity from the bike motor.

The easiest way to use a treadmill as a battery charger is by reducing its voltage through a shunt regulator circuit.

I have already discussed a few shunt regulator circuits in this website, which can be viewed through the following relevant links: