Help understanding "overcharge"



  • @sam said in Help understanding "overcharge":

    I'm reading the OW+ manual and the section that talks about charging advises never to undercharge or overcharge your board. The same manual also says to occasionally leave your OW plugged in overnight.... huh? Would leaving your OW plugged in all night after it is fully charged not be considered overcharging?
    I know that you shouldn't ride down a steep hill after a fresh charge as the regenerative battery would already be at 100% and explode or something, however, this is mentioned in a different part of the manual and doesn't use the word overcharge anywhere so I'm not making the connection.
    Any thoughts? Thank in advance!

    Hey Sam,

    Sorry I didn't in the last post. To actually answer your questions here we go:

    The battery is lithium ion, so you don't really have to worry too much about not fully charging it and riding it, or "overcharging" it. That being said, it's just not a good practice to leave a battery charging overnight, when it only takes 20-30 minutes to charge. Also, the charger gets pretty warm. The reason you should not immediately ride downhill when your board is at 100% charge is because of regenerative braking. Your battery will not explode, but it can't accept anymore charge, so the Onewheel will simply shut off. So lets say your house is on a hill and you've left with 100% charge. Just ride around on flat ground a bit to burn off a bit of charge before you begin your journey. Hope this helps!

    --Max



  • @lighten_lens It's not a lithium ion battery, it's lithium iron phosphate.



  • Why not just switch (from regenerative breaking) to active breaking instead of shutting of? Looks like a design flaw to me...



  • @djinn ?? Active Breaking (btw it is braking)? You mean like friction braking? I would like to see the mechanical design to address that. In fact I have haven't seen an elegant mechanical brake design in any skateboard or even rollerblade product to date. The regen braking (assuming the battery is not at 100%) is very effective, efficient and elegant - no parts to wear out and it puts juice back into the battery. Brilliant!



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  • @gadgetrider No i mean active electrical braking: use the battery power to apply negative torque (and counter the rotating motion).



  • @djinn With most motor systems, that is precisely regenerative braking -- the amount of battery power to apply negative torque is negative, so you get regeneration for free with braking. The only limit is your ability to sink that power, which is why heavy vehicles with regen brakes also have a "brake chopper" (a huge resistor bank) to sink more power than the battery can take (and then a huge heat sink to dump the resulting heat).



  • @craiger123 my mistake! I had a feeling I was off, think I got confused with my drone batteries. Thanks for the correction haha.



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  • @ggould: What kind of motor does the OW use? Can't we just reverse the phase sequence of the motor in order to brake?



  • @ggould The resistor bank with heat sink could be an interesting solution and allow the braking effect to continue well past the battery's ability to accept the current. However, the overcharge condition is pretty rare as in most cases the battery should be more than happy to accept some regen charging. Since the occurrence is so rare, FM probably accepted this as a design limitation and moved on.

    The one exception that has puzzled me was a Youtube video that I saw about someone climbing up a mountainous road. It looked like it took him a long time with multiple charges to get up to the top. My question is "how did he get down"? Did he have to stop part-way down and expend that battery somehow?

    Also, would it be a fair assessment that the faster I zip down a hill, the less charge I take on? Basic physics would dictate that the conversion from potential energy to kinetic energy (which converts to electrical energy) is independent of speed. However, intuition tells me that the braking effort to go down a hill slowly may create more of a charge than if I descend quickly with minimal braking effort.



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  • @gadgetrider The last brake chopper I worked with (on an agricultural robot) weighed five hundred pounds and needed a separate radiator to keep from melting, so my knowledge of such things has little application to the OW.

    In general the OW design seems to be working near the limits of practical heat dissipation, so I am confident that FM's engineers have considered this.



  • @sam

    Check out this page, tons of answers and guidance

    http://onewheel.wiki/Riding_technique#Regeneration_Pushback:



  • @skyman88 oh wow that's a great site! never thought to look for a onewheel wiki page, thanks for sharing



  • @lighten_lens I see... I guess all we can do is ignore him and hope he gets bored and goes away. He clarified further down the thread that it was indeed meant to be a joke... but last I heard jokes were meant to be funny...



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  • My electric car does it the best - whenever it's charged to over 100%, regeneration is disabled. It's a little eerie, because the car will coast like it's in neutral for the first few miles (or, like all cars with an internal combustion engine). Then, regeneration will return.



  • The difference is that an electric vehicle also has friction brakes and a Onewheel does not. I usually do a few laps of the car port before descending our driveway when the battery is fully charged.



  • The Onewheel uses a the Constant Current/Constant Voltage charge technique (CCCV) its pretty common for quick charging. So what happens is when you plug into the board the charger will start giving max current which is 3.5A on this charger. Then at 80% charge the board BMS will start dropping current while maintaining 58V and finish the charge. At this point your trickle charging and the BMS won't allow the board to go above 58.4v. LiFePO4 battery chemistry is very resilient to overcharge and can safely be overcharged to 4.2v per cell. I would not worry about over current at all when it comes to damaging. However the BMS is another story and can shut down the board if it thinks it's overcharging. I'm guessing they play it safe and shut it down way earlier than necessary. Regenerative braking is just a by product of the way the Onewheel is designed. The energy has to go somewhere and it makes it's way back to the battery.


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