DIY "mobile supercharger"



  • @cr4p that is really innovative! Smaller and lighter than commercial batteries and doesn't need the ultra charger. Maybe fm can get inspired by your schematic and offer something for the rest of us. Even better, fm can hire your friend to make it for them. Congrats.



  • @jasont : i will have a look at the wiring to tell you.

    about the other questions. of course you could do the battery pack with a higher voltage - maybe this is a good idea, i am also open for suggestions on improvement, which i can also benefit from;-)
    but either you get the battery pack to exactly 58,4 V (or something very close too), or you will still need the step-up converter.
    it has been done like that, because we do not know how the OW exactly works inside and whats their battery and charging design looks like, so we wanted to stay on the safe side and make sure that the output voltage of the mobile supercharger is perfectly stabilized to avoid damaging of the onweheel.

    but of course you could design it to any voltage between - lets say 10 and 50 V, as long as it multiplies with 3,7V from the cells.
    but you have to keep the battery design in mind (required space and format, required wiring for serial/parallel, ...).

    yes the, charging circuit is in the onewheel. i can´t tell you if you really need the circuit on the battery, but we wanted to be on the safe side. the circuit on the battery pack prevents the battery from beeing damaged (undercharging, overpower, short circuit)...220Wh is a lot of power and the OW cunsumes a lot of power while charging in a short time, therefore the battery pack and the step-up converter do have some challenges while charging. we also didn´t want to risk anything here. if something goes wrong i don´t want the battery to explode or be damaged, so i am happy to have that circuit...



  • @cr4p it's interesting because the sticker on the Ultracharger claims to only put out 3.5amps per hour which at 60V is only 210W. So in a 20minute charge it's only putting around 70W/hr into it.

    I noticed that on the step-up transformer you bought, you can set the output amps. Do you know how many amps you have it set to?



  • @jasont I'm going to try building something similar. I think you could shed some weight and size by using flat packs of Lipo or LiFePo4 batteries instead of the round cells. Maybe one like this http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=74096



  • @jasont did u figure out the pinout for the XLR connector? I have my boosted converter outputting 58.4v but it won't initiate the charging. It won't draw more than .15A



  • @jasont Those packs are just over 3 pounds, significantly less than the 7 pound backup for sale on Amazon. Any idea how many charges you'd be able to get out of that?

    Be great if one of the electrical geniuses on here would produce one of these things and sell it. Not sure if I'd be able to make one without electrocuting myself.



  • Awesome info here.
    Where do I order the plug that goes into OW charging port?





  • @cr4p said in DIY "mobile supercharger":

    together with a friend of mine, we developed a mobile supercharger for my personal use.
    0_1461094709105_2.jpg

    i have to admit that i have no intentions to make a product out of it and i won´t sell any of these. however, i just wanted to inspire you, since i know that some of you were thinking about doing something similar.

    the reason why i did this was, that i needed something small and light-weight for the backcountry use, to extend my range to get more out of these perfect trails in my neighbourhood.

    the technical setup is simmilar to what i mentioned in the other thread (http://community.onewheel.com/topic/1076/extra-battery-backpack/16):

    therefore my friend has custom built a high power LIPO battery pack out of 24 high quality cells which are capable of delivering high current within a short time and are known for their stability. it wasn´t that easy to find some capable cells and they are a little bit expensive, but they work fine.
    0_1461094327219_IMG_20160302_211725.jpg
    (it would have also been possible to use LIFEPO4 cells, but this would have costs about 4-5€ more per cell and for a charging device I did not really need those advantages)

    he then added a circuit for overload- and undercharge-prevention and finished it.
    0_1461094729216_5.jpg

    after that, we were using an existing step-up converter to transform the 14V battery to stabilized 58V. some adjustments, measuring and testing and the thing was ready to go.
    0_1461094785668_1.jpg

    for a short-term solution i have added a 12V temperature controlled fan (to get rid of the heat when inside a housing) to it and put it all in a cheap plastic housing.
    0_1461094741064_3.jpg

    here are some technical details:
    the batterypack is 14,8V and has (useable) 220Wh. since the OW has 130Wh, you can charge it 1.5 times
    the (adjustable) step-up converter converts the 14,8V to 58,4V.
    the overall weight ist 1.6kg (3.5pounds) including battery pack, circuit and the housing with the fan. due to its size you can easily carry it within a very small backpack, so you do not feel it when cruising those offroad trails.
    since it already delivers those 58V you do not need the regular charger, but you can directly charge it and therefore get out more power of the battery (less energy waste)

    well, just to give you an idea of how something like this can work ...

    we are still trying to improve this thing. currently we are working on a custom circuit with improved power consumption and heat emmission and i will work on an aluminium housing with a smaller size. but for now, this allready works and i am using it on my rides!!

    McGyver!? ;)



  • So, I built one of these, thanks to this thread (thanks @cr4p ) and this great instruction guide: http://onewheel.wiki/Charging_on-the-go

    I've attached a few pictures below.
    I've tried two methods:

    1. 12v/10Ah (120Wh) LifePo4 battery + 300Watt power inverter + Onewheel supercharger
      Total Weight (including Onewheel charger): 5lbs, 8oz
      Results: Charge Onewheel 65% in 30min

    2. 12v/10Ah (120Wh) LifePo4 battery + 58v up-converter
      Total Weight (no Onewheel charger needed): 3lbs, 15oz
      Results: Charge Onewheel 72% in 90min

    Needless to say, I'm disappointed with my results using setup #2 (basically the setup described in this thread) both in terms of the minimal charge improvement over the 120v inverter method but also/mostly in terms of the 90min charge time.

    The thing I don't understand (which is probably why the charge time was so long) is that I programmed the up-converter to deliver 58v and 3.5a but it only actually was delivering at 1.1a. Did I do something wrong? Do I need a different kind of battery? Any suggestions would be appreciated.

    Method 1:
    0_1498144389352_IMG_3114.jpg

    Method 2:
    0_1498144412601_IMG_3115.jpg

    Charging display during 90min/72% charge session, showing only 1.1a draw:
    0_1498144580574_IMG_3119.jpg
    0_1498144592573_IMG_3120.jpg



  • @kbern Your battery is only 12V. I think you will need at least 24V.





  • @JacoNZ Thanks. Yeah, I think so too, though I'm still confused about why the 12V battery can't output 3.5A, but I will try a higher voltage battery and see what happens.



  • @kbern and @cr4p

    The my volt meter is reading power supply xlr jack as: pin 1 as negative, and ping 2 and 3 are positive. Do you wire this the same? or just use pin 2 as positive and pin 3 blank?



  • @SkyPilot 2 and 3 need +



  • @SkyPilot @wr420 yup, pin 2 & 3 are both "+", per the instruction page (though that tidbit is easy to miss):
    http://onewheel.wiki/Charging_on-the-go
    and I tested both + pins with a voltmeter to make sure they both had good connections.
    Thanks for brainstorming. Let me know if you can think of any other potential issues.



  • since the question with the pins is already answered I just like to add another thing:
    if you guys are using the (very comfortable) MPT-7210A, I THINK that you it would be a good idea to use a battery pack/configuration with a higher voltage. altough the spec/user manual of the solar charger says it´s capable of 12 to 60V, it seems like on the lower voltage side it limits the current output which leads to longer charging times. so if this theory is correct, the more towards the 58.4V you go, the better (also the efficiency would improve I guess). As an alternative you might find a better step-up-converter which is really capable of delivering the required output current with 12V inputs.

    as mentioned, that´s just a guess - has yet to be confirmed;-)



  • @kbern have you attempted to hook this up via power supply, and did you get the same results? If the power supply was faster, then it maybe related to the battery's discharge rate. The inverter combined with the output rate may be exceeding the max discharge rate of the battery.

    I'm thinking the MPT-7210a may have more overhead than everyone thinks when up converting 12v to 58v. I suggest increasing the battery voltage to 24 or 48 volts and see if there's an improvement (adjustable voltage power supply is ideal for testing.)

    As I type this I'm realizing the problem may be combined in both the loss in up converting and the max discharge of the battery.

    Just some suggestions, getting late here please forgive my rambling.