Most low speed electric vehicles use 60V or 48V power, but we have also seen 64V and 72V power. Most motors are permanent magnet motors Hall, and there are also series excitation motors with carbon brushes. There are many power types such as 2KW, 3KW, 4KW, etc. Let's take a 60V3KW motor as an example with Hall to talk about several key points in the selection of a lithium iron phosphate battery.
1. First select the number of channels. As we all know, the rated working voltage of lithium iron phosphate battery is 3.2V. 60V requires 60/3.2 strings, which is about 19 strings. I recommend choosing 20 skewers. Why ? If you assemble the battery yourself, you can arrange it in two rows of 10 and 10 depending on the condition of the battery compartment, or you can arrange it in four rows of 5 and 5 and5 and 5. Because they are neat and uniform, it is easy to fix and install the battery.
Car battery
2. Once the number of channels is selected, capacity must be considered. To ensure long-term vehicle mileage, it is recommended to select a larger capacity. What size is appropriate? Personally, I think this should be determined based on my scope of work and economic conditions. If the daily journey is less than 30 km, it must be considered that the battery must be sufficient for a range of 100 km: on the one hand, as the battery capacity increases, the battery discharge rate decreases. This helps extend battery life; on the other hand, the battery capacity will decrease after a few years of use. If you just pick it at the beginning, it will be like Song Dandan's sketch in a few years. years (when yous young, the front legs are lifted here and the hind legs are lifted here. Now that I'm old, I can't put my shoes on my feet, but I have more energy than I can afford, and I can no longer meet the demands of traveling. At that time, the battery will become child's play for Cao Cao - it is tasteless to eat and a shame to throw it away. If you buy it again, you have to spend money. If you don't buy it, you won't be able to meet the requirements.
So I think an investment should be fundamentally in place. Another practical advantage of this method is that the battery utilization rate is high: for example, the original car has a 50 Ah battery. After three years, the capacity drops to 60% of the original, the mileage decreases and it can no longer be used. If you choose 100AH battery at first, it will still have 60AH capacity three years plus later, and the old one will have a greater capacity than your new one. It will not be a problem to use it for another 3 years.
Car batteries
3. Selection and calculation of battery capacity. First, calculate the operating current under normal working conditions: 3KW/60V=50A. Secondly, you have to consider mileage: the maximum speed of a 3 kW vehicle is around 60 km/h. If you want to travel 100 km, and taking into account the decrease in battery capacity from year to year and the poor discharge in winter, the capacity. should ensure that the vehicle can travel for at least two hours. 2 hours × 50A = 100AH. In this way, the new battery can theoretically travel 120 kilometers. Even if it decreases by 10%, it can still meet the 100km requirement.
Car batteries
4. Estimated cost of batteries. At present, the price of genuine d cellshe lithium iron phosphate battery on the market is about 2.5 yuan/AH. Once disassembled, depending on the quality and number of cycles, the price varies from 1.36 to 1.8 yuan/AH. Taking a 20-cell 100Ah lithium iron battery as an example, the price of cells ranges from 2.5 × 100 × 20 to 1.5x. Between 100x20, plus 20 strings of 150A protection boards (about 250 to 380 yuan), 73V30-50A lithium battery chargers (the price is about 1,000 yuan, if you modify it yourself, let's talk separately) and auxiliary materials about 50 yuan (such as panel epoxy resin, heat shrinkable material, welding wire, copper connecting piece, etc.), that's it.
First, you need to find a way to connect all these batteries in parallel, then find a 4.2V charger to fully charge all the batteries. After making sure that all batteries are in good condition. charged to 4.2 V, then cSeparate them, let them sit for a day or two, then find a multimeter to measure their voltages. Since these are second-hand batteries, your requirements cannot be too high. whose voltage is still higher than 4.1 V after two days of rest. See how many there are. If there aren't enough, get a few that are close to 4.1V and make a multiple of 13 strings. of batteries is 4.1 or higher, that would be better. Anyway, just do it up to a multiple of 13. How many times can you make multiple parallel connections~ So don't you have an internal resistance meter? of these piles one by one. Find a pen and write it on the pile. After writing everything down, roughly divide them into 13 parts and try to make the total internal resistance of each part equal. these 13 pieces in parallel, then connect them in series to form a 13-string drum, then connect yourtre 13-string protection board, connect the charging port and output port, then package it to be waterproof and shock-absorbing, then get a case and install it, then you can put it in the car and use it ~ It's a waste to buy an internal resistance meter more than 300 yuan, you should buy a discharge meter ~ 18650 A better capacity tester is less than 50. If you have a 18650 with about 2.5AH, your discharge parameters can be set as follows: discharge current 2A, cut-off voltage 2.8V, and test the ones with the lowest voltage after leaving it alone for two days. Then compare. the average and highest voltage and measure them separately. If the difference is big, eliminate the smallest capacity, keep them all. If you want to connect to 18650, you need to find them. a place. You can buy a welding machine for more than 200 yuan, which is more convenient than an internal resistance meter. . .