Design and application of a solar-powered vehicle-mounted electronic tag OBU

Considering that the non-stop toll collection system implemented in China uses a dual-chip on-board electronic tag, the on-board electronic tag needs to have a strong power module to provide sufficient power for the working module (card reader module, DSRC receiving and transmitting module, etc.). Traditional on-board electronic tags generally use 3.7V high-performance lithium batteries, which are generally used for about two years. Since the on-board electronic tag is fixed on the vehicle once, it is not allowed to be disassembled privately. After the battery is exhausted, it needs to be replaced at a designated maintenance agency, which is very inconvenient. For this reason, Shanghai Donghai Computer is the first in China to launch a solar charging on-board electronic tag, which uses a rechargeable lithium-ion battery + strong light solar charging module + external charger to extend the service life of the electronic tag to more than 5 years, greatly reducing the burden on issuing service outlets and car owners.

1. Solar energy Schematic diagram of electronic tag function module

2. Description of solar electronic tag power supply method

1. Adopt 4.2V 270mAH (or 650mAH) rechargeable lithium-ion battery + strong light solar charging module + external charger mode;

2. The rechargeable lithium battery can be fully charged more than 500 times and has a service life of more than 7 years;

3. Strong light type Solar cell Panel: Power 0.048W, current 10mA±1 mA, open circuit voltage 4.8V, chip conversion rate 15%, service life more than 10 years;

4. It has a "HOLD" function for overcurrent, overtemperature, undervoltage, overcharge, and short circuit protection. This makes the protection action extremely reliable. It completely avoids the battery from being damaged by overcharging, completely avoids shortening the battery life due to overdischarge or short circuit, and completely avoids the possibility of repeated shutdowns damaging the protection board;

5. With low battery alarm module;

6. The calculation of the solar charging efficiency of the electronic tag is as follows:

① The 4.2V rechargeable lithium battery can be used for at least 1~2 years once it is fully charged before the electronic tag leaves the factory;

② The maximum current of 4.8V solar charging can reach 10mA (generally 2mA), which is much larger than the self-discharge current of the electronic tag (<5μA);

③ According to the national standard, the electronic tag meets the requirement of 10 transactions per day:

The average working current of the contactless CPU card is about 60mA, the transaction time is about 250ms, the working current of the 50ms pre-reading IC card information time is about 50mA, and the working current of the 1s waiting time is about 10mA. The total power consumption in one day is calculated as follows:

10×60mA×0.25s + 10×50mA×0.05s + 10×10mA×1s + 5μA×24×3600s ≈ 0.2 mAH

Power consumption of transaction work Power consumption of pre-reading card Power consumption of transaction waiting Power consumption of 1 day Self-discharge of 1 day Total power consumption

The average working current of the contact CPU card is about 30mA, the transaction time is about 250ms, the working current of the 50ms pre-reading IC card information time is about 50mA, and the working current of the 1s waiting time is about 10mA. The total power consumption in one day is calculated as follows:

10×30mA×0.25s + 10×50mA×0.05s + 10×10mA×1s + 5μA×24×3600s ≈ 0.18 mAH

Power consumption of transaction work Power consumption of pre-reading card Power consumption of transaction waiting Power consumption of 1 day Self-discharge of 1 day Total power consumption

④ The solar micro-current charging time is about 8~10 hours with sunlight exposure. The power is 16mAH~20mAH;

⑤ Calculation based on 10 transactions per day: If there is sufficient sunlight to ensure a 2mA charging current, 0.2mAH/2mA≈360s, that is, 6 minutes can meet the power demand for one day's work; when the charging current is 1mA, 12 minutes can meet the power demand for one day's work; when the charging current is 200μA under ordinary light, 1 hour can meet the power demand for one day's work;

⑥ Calculation for 50 transactions per day: If there is sufficient sunlight to ensure a 2mA charging current, 0.5mAH/2mA≈900s, that is, 15 minutes can meet the power demand for one day's work; 30 minutes can meet the power demand for one day's work when the charging current is 1mA; 2.5 hours can meet the power demand for one day's work when the charging current is 200μA under normal light;

⑦ Added an external portable charger to charge the electronic tag. If you encounter special climate, such as long-term rainy days (rainy season), you can use this charger to charge. The external portable charger has short circuit protection and overload protection functions, and has anti-surge protection function.

3. Testing and application of solar electronic tags

Donghai solar electronic tag (model: TQXS6-SD-OBU-II) has passed the physical layer test and protocol interoperability test of the National Traffic Safety Facilities Quality Supervision and Inspection Center.

Recently, in the ETC equipment bidding test organized by Jiangsu Province, a special solar charging test was conducted on Donghai Solar Electronic Tags. The test method was to consume the power of the electronic tag until it could not be traded, and then charge it in ordinary sunlight for 8 hours, and then conduct continuous transactions with contactless CPU cards, with the number of transactions exceeding 1,000 times, achieving the designed effect of solar charging.