My mower battery is three times cheaper than the original battery, and its capacity is twice as large. Conducted field tests - mowed six hundred square meters of tall grass on a single charge.
Last year I bought a Makita DLM380Z cordless mower at a sale for 3990 rubles (https://ammo1.livejournal.com/1069589.html). Now such a mower costs 6990 rubles. The letter "Z" in the model name means no batteries and charger included. DLM380PM2 with 4 Ah batteries and charging is sold for 19,600 rubles.
The mower accepts two standard Makita BL18 series 18-volt power tool batteries. They are available in capacities from 1.5 to 6 Ah. A set of two 5 Ah batteries and charging costs 14,300 rubles. But I went the other way. :)
My battery contains 30 cells 18650 2.5 Ah according to the 10S3P scheme. Its total capacity is 277.5 Wh (36V 7.5Ah).
I bought 40 cans on Aliexpress Liitokala INR1865025R (https://ammo1.livejournal.com/1083162.html), but only 30 of them were perfect. I opened a dispute and received a refund for 10 batteries.
The 30 best batteries (voltage after storage not lower than 4.072 V, internal resistance not higher than 20 mΩ) I used for assembly. I had to measure the parameters of each battery, enter them into the table and select for each of the 10 cells three batteries that are closest to each other in terms of parameters.
Of course, it would be more correct to connect the batteries by welding, but I soldered them to speed up, using them for tinning contacts with soldering acid (this was not the best solution, then I had to re-solder a dozen of contacts). For the connection I used a 1.5 mm² stranded wire.
On one side, the batteries are inserted into plastic holder 6x5 (two connected 3x5).
Used for charge protection and control 35 amp BMS 10S board.
For some reason, almost all sellers have a connection diagram with several errors. With difficulty I found the correct scheme.
Genuine Makita batteries have normally closed thermal protection elements connected between the positive and the third contact. Of course, such protection could have been neglected, but I still bought thermal switch 60 degrees and installed it between the batteries.
You could use the charger from my electric scooter to charge the battery, but it only gives 1.7 A and the battery would take more than 5 hours to charge. I bought 5-amp chargingcharging my battery in less than two hours. The plug chose the standard 5.5x2.1mm round.
In this charging there is a small and rather noisy fan, but you get a "sound indication" - when the battery is fully charged, the fan turns off and you can immediately hear that the process is over.
Five wires come out of my battery: +, -, protection, two charging wires with a 5.5x2.1 mm socket.
I removed the panel with connectors for standard batteries from the mower (they are connected with flat "car" terminals), connected the minus of the first connector with the plus of the second and connected the protection contact of the second battery. Plus the first, minus the second and extended the protection of the first through the same contacts, so as not to lose the warranty on the mower.
Instead of a panel, I installed a plastic insert on which a homemade battery will be placed. Of Velcro tapes made the mount, screwing them in with self-tapping screws holding the panel with the standard battery connectors.
These are the tapes.
At the top and bottom of the battery, just in case, there are gaskets made of porous packing material (so that as if nothing has closed), the battery is wrapped in cling film (so you can quickly unpack and pack it back).
Wago 221 32-amp connectors are used to connect three wires. The battery can be charged without removing it from the mower.
The battery compartment is tightly closed with a lid so that no grass gets inside.
The voltage across a fully charged battery was 41.06 V. It was enough for 49 minutes of continuous operation of the mower in difficult conditions (tall grass, stops every 1.5-2 minutes to empty the container). It may seem that 49 minutes is not enough. In fact, this is a lot - in fact, it is more than 2.5 hours of work and about 6 hectares of mowing with uneven terrain and many obstacles.
About ten minutes before the end of work, the right low battery indicator on the windrower began to flash. At the end, the mower stopped and did not start again (internal protection prevents the engine from starting). The battery voltage was exactly 35 volts.
I measured the voltage on each cell of the three batteries immediately after use and then after charging.
I'm not sure if the BMS is working correctly: 4.238V on the first cell is too much. But I don't know how to check its work.
Batteries are designed to discharge up to 2.5 V, so when discharged to 3.5 V, they give less energy than they could (however, under load, the voltage is probably much lower).
Nevertheless, the battery is working and the site has been successfully cut.
The battery and charger cost me $ 75 including discounts and coupons (about 5000 rubles when I paid). This is three times cheaper than the original Makita battery and charger kit, and my battery capacity is almost double.
Now all the parts cost about $ 93 (today ~ 6800 rubles), which is still half the price of the original battery and charger.
© 2020, Alexey Nadezhin
The main topic of my blog is technology in human life. I write reviews, share experiences, talk about all sorts of interesting things. My second project - lamptest.ru. I test LED bulbs and help figure out which ones are good and which are not so good.