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I want to stop charging my e-scooter at around 85% because this will increase the battery life. To avoid always having to pull the plug at the right level, I made a stop circuit that goes between charging brick and e-scooter.

There's no processor involved, just a CMOS 555 used as inverting Schmitt Trigger which controls a power mosfet. Also two status LEDs and a start switch. The poti adjusts the cut-off level. Worked on first try, with only manual voltage and tolerance calculations beforehand!

Comments
  • 5
    Niiiice :) You don't happen to have a schematic? Just curious of the workings ☺️

    Edit: Are those leads for debugging?
  • 12
    @ScriptCoded I have only made an ASCII drawing, but here it is. The leads are for soldering the cables to them (LEDs, switch, battery and charging brick).
  • 7
    @ScriptCoded Here also the dimensions of the electric parts:

    R1 10k
    RP 2k
    R2a 1.3k
    R2b 100
    R3 100k
    R4 1.5k
    R5 2.5k
    R6 5.1k
    R7 5.2k

    C1 10µ
    C2 100n
    C3 100n
    C4 10µ

    Lr LED red, 1.7V, 2mA
    Lg LED green, 1.9V, 2mA

    Z1 Zener 12V

    T1 IRFZ44 VPbF (Mosfet N-Ch)

    555 TLC555 (inv. Schmitt-Trigger)

    The details for the 555 Schmitt Trigger are like this: https://petervis.com/dictionary-of-...
  • 4
    Nice job man!
  • 1
    @Fast-Nop Haha, thanks 😁 Looks good
  • 2
    I have no idea how it works but that is frickin cool man!
  • 3
    Could you explain why charging to max 85% increases lifespan? Is that for lead irin batteries or lithium? And why wouldnt manifacturers build in that feature by default
  • 2
    @Angry The basic idea is that the 555 chip puts "high" on its output when the input voltage goes below the ON-threshold (at 4V), and "low" on the output when the input is above the OFF-threshold (at 8V).
  • 7
    @jareish Because the last 10% or so stress out lithium batteries the most. That's why good smartphones and good electric cars don't charge until 100%.

    See the Tesla picture below. 100% would be charging up to the right border, but the car will instead stop at the dashed white line.

    Battery manufacturers don't put that into the batteries because that's the job of the charging electronics. It's the user or device manufacturer who has to choose between maximum battery range right now or maximum battery life in the long run.
  • 3
    @jareish li-ion will wear out faster the higher you keep its voltage. It will also get damaged if voltage goes too low. It's common practice to stop charging early on products designed for long life. On consumer electronics long life doesn't matter as products should last only a couple years anyway. Also better battery life when the device is new means a lot to consumers.
  • 1
    @electrineer what's considered long life? This always confuses me and I'm planning on getting a new laptop by the end of the year as my daily driver. I'd like to not shred the battery.
  • 2
    @electrineer I'm not sure I'd agree that consumer electronics products *should* just last a couple of years, but the manufacturers certainly go for that on the basis of profit...
  • 4
    @kingcodra li ion batteries have a life that is counted in charging cycles. One charging cycle means pumping 100% of the battery capacity into it.

    So charging it from 0% to 100% is a full charging cycle. Charging it from 30% to 80% two times is also one full charging cycle although you charge it two different times, but 50% each, and 2*50%=100%.

    Li ion batteries have a datasheet which tells you how many full cycles from 0% to 100% they can do, typically only around 500-1000.

    If however you use the 30%-80% method, you will get two or three times as many full cycles.

    Another thing is, don't store li ion batteries at 100% charge state for a long time (like, weeks). Also, don't discharge them down to 0%, they don't like that either.

    Don't charge them when they are below 0°C, and don't discharge them below -20°C. On the other end, don't let them heat up to more than 50°C, i.e. don't leave the laptop in your car during summer.
  • 1
    @AlmondSauce that's what consumers buy. That's the reality at the moment.
  • 1
    I am amazed! I wouldnt have even considered doing this without an mcu as they are literally dirt cheap and easy to work with. Props to you doing it in analog!
  • 2
    @JFK422 That's because I studied EE back then, not CS. :-) This 555 IC is one of the oldest ones still around, it dates from 1971. It's so superb because you can use it to hack a lot of different things together.

    @RantSomeWhere Especially with a Dremel and soldering iron. It has become a bit difficult because I struggle to actually see what I'm soldering. But when it has the right smell, it works. ^^
  • 1
    Gotta love the 555, versatile as fuck, probably one of my favourite 8pin ICs (others would be LM386 and 741 I guess)
  • 1
    @M1sf3t The device is even compatible with the very popular Xiaomi M365 e-scooter which has the same charging brick data.

    For a product, small series production has de facto been outlawed in the EU due to the electronic waste directive. The EU tries hard to crack down on anything besides big corporations.

    @gogokun I'm happy that it spurred your curiosity. :-) There's a lot of interesting hardware stuff to learn through small projects like this. In case you should have questions about how this works, I can give you a walkthrough.

    @RememberMe Ah yeah the amplifiers, I remember them in early radio assembly kits.
  • 1
    @Fast-Nop I built several guitar amplifiers and effects (well tbh mostly OD/distortion because I wanted good tones out of my bass and Big Muff Pi/Boss Bass Distortion etc. are too expensive) in college, lots of 386 (and other stuff) usage there. Good times.

    I also really respect folks who do power electronics now (amp output stage to speakers etc.), that shit gets real complex very fast.
  • 1
    That's really cool! I made something like that before, but my knowledge about eletronics is too basic yet, so it is full eletronic (Arduino), with a webserver. My phone turns it off with a http request.

    Someday I will try to create a new version, more similar to your model.
  • 0
    @gogokun It's still enough for just a posting or two. ^^

    Depending on how familiar you already are with electronics, there's a nice YT introduction on basic electronic components. You'll get an easy overview within just 38 minutes, and it's even subtitled: https://youtube.com/watch/...

    Ok, back to the circuit. The resistors R1, RP, R2a and R2b divide the measured voltage down to about 8V. You could put RP and R2a into one potentiometer, but splitting them up allows using a smaller potentiometer resistor which gives more adjustment precision.

    The capacitors C1 and C4 deal with possible ripple voltage of the charging brick. When S1 is pressed, the sensed voltage goes down to about 0.4V which is below the 555's ON-threshold of 4V. Since this also discharges C4, R2b limits its discharge current to about 80mA as not to damage the switch.
  • 0
    @gogokun In the left, the Zener diode Z1 has always about 12V in the adjusted current range. R5 makes sure that the current range is limited to what Z1 can take. The green power LED Lg is always on, and R6 limits the current through Lg.

    The 12V of Z1 source the 555 chip, and the switching thresholds are at 1/3 and 2/3 of 12V, i.e. 4V and 8V. When the input is below 4V, the 555 changes its output to high (i.e. 12V), and when the input goes above 8V, the output changes to low (i.e. 0V). The potentiometer RP adjusts the exact measured voltage level where the 8V are provided to the 555. C2 and C3 are small stabilising capacitors.

    Only when the 555 output is high, the red charging LED Lr is on, and R7 limits the current through Lr. Also, the gate (control input) of the transistor T1 is set to 12V so that the transistor lets current flow and the battery gets charged. R4 limits the current from the 555 to T1 gate in the moment of switching. R3 is for static discharge of T1.
  • 1
    Really something useful πŸ‘πŸ‘
  • 1
    πŸ“Œ

    Also: my electronics is a bit rusty, but if you use the 555 as a gate, couldn't you use a PNP instead?
  • 1
    @react-guy In principle I think so, but I prefer a mosfet. Mosfets are easier to use as switches, don't need base current (except when switching) and have lower losses.
  • 1
    That's very cool!
  • 1
    Ah yes German engineering
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