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hyperair

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About hyperair

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  1. hyperair

    V8 battery upgrade!!!

    This is a myth. Once all the cells are reconnected to the BMS and are above critical voltage (2.5V), the output will be switched on. To be safe, reconnect the cells in sequence (B1, B2, ..., B20) so that you don't prematurely reactivate the BMS and put it into a weird state. Keep in mind that batteries cannot be switched off so you will be working with live voltages. 84V starts to get a little dangerous so try not to complete the circuit with your body. Some USB power banks I've worked with have had their BMSes go into "sleep" mode when the cells are disconnected, and they don't immediately come back online when the fresh cells are connected. Plugging them into the charger will reactivate them though, so if your BMS doesn't seem to want to come back online, try charging it through the standard charge connector (small black JST SM connector). I have observed the V8 battery charging through the stock connector, and can confirm that the BMS does balance, but only near the full voltage, and very slowly. Same as the 16S generic BMS I've worked with in the past. Basically, when a cell hits about ~4.15V (or whatever the full voltage on that BMS is), it starts to draw current from that cell, venting out the energy as heat in the BMS PCB. You can feel this if you touch the BMS while it is in balancing mode, and it can hit around 40-50°C. The cells remain cool though. The heat dissipation of the PCB is fantastic -- if you disconnect the charger, it returns to room temperature in about 5 minutes. This suggests that the dissipated energy while balancing is of quite significant wattage as well in order to sustain that temperature. I did notice that if the cells were significantly out of balance (B18 was at 4.18V while the others were at 3.7-3.9V) , the BMS appears to continue grinding (feels warm to the touch), but also throttles the charging current (charger LED turns green, while battery indicator continues blinking), presumably to control the heat generation on the BMS so that it does not overheat and kill itself. Here are some photos I took while repairing my V8 pack. I left some details in the photo descriptions where relevant. It's not an upgrade, but the photos may help those who are planning an upgrade or repair of a V8 battery pack. https://www.facebook.com/media/set/?set=a.10161197629015104&type=1&l=230ec7d981
  2. If you say so. Between fire and faceplant, I choose faceplant. I understand if some people feel differently. The only thing that remains Gotway about my wheel is the shell. The motor and board are Microworks parts, and I've used two different battery packs on this -- one Victpower 16S1P which faceplanted me numerous times, mostly on ramps or sudden potholes, or when attempting to accelerate too quickly, and one self-built 16S2P pack from the BMS I linked above and Samsung 25R cells. I don't believe a Gotway has a BMS that can't cut power. It probably just has higher thresholds like the BMS I'm using with my 16S2P pack, and better 18650 cells with less internal resistance and hence less voltage sag at high currents. Having gone through a faceplant-prone wheel for a couple of months, I'll agree with you that it's very tiresome to deal with. But rather than shunting the pack, I'd replace it (which I did). I think this wheel got lucky, and that these Panasonic CGR18650CH cells are decent (they vent but don't spout flames). The same can't be said for the average generic wheel one finds on alibaba/aliexpress/taobao/ebay, especially the cheaper ones. If you want to see an actual 18650 fire caused by overcurrent, here's one: https://www.youtube.com/watch?v=08BoXebt_pk From what I can tell from various 18650 fire videos, 18650s tend to vent for 40-60 seconds before going up in flames, so that's how much time you have to work with if you see smoke.
  3. 1) is for short protection, IMO, which can happen if your wheel shorts out. Here's an old Gotway MCM 14" I received after it went into thermal runaway. https://www.facebook.com/hyperair/media_set?set=a.10156323229550104.1073741834.516720103&type=3. I'm not sure it actually hit 80A, but as you can see, it the motor leads got hot enough to melt the PTFE insulation. Since one of the motor bearings have completely seized up, I'm thinking that the bearing getting destroyed caused the motor to get stuck and turn into a short circuit (those motor windings have really low resistance), which in turn caused way too much current to go through the entire circuit. The Gotway battery pack, built with Panasonic CGR18650CH cells, has a couple of vented cells, and the BMS has some lifted traces. 2) Frankly speaking, I think unicycle vendors would be in for a much more severe lawsuit if caught running with BMSes that can't cut power. On my list of do-not-wants, fires and thermal runaways still rank higher than faceplants. Do you mean 18650?
  4. No I haven't. These are hypothetical, and under the assumption that the BMS uses that shunted MOSFET to disable the pack if any one cell drops below threshold voltage (see the row on overdischarge protection in http://www.aliexpress.com/item/16S-15A-59-2V-li-ion-unicycle-BMS-PCM-battery-protection-board-bms-pcm-with-balancing/32414515852.html). Cool. I didn't realize charge doctors worked without balancing leads. Do you have a link to the one you use? I ended up building a new 16S2P battery pack from a BMS with higher discharge current limits (80A, according to the specs in the link above) instead. It's not like they don't happen -- I saw a photo a couple of months ago of a burnt unicycle that had been left in a car trunk. The baby seat next to it was charred pretty bad. Probably not from voltage inversion though.
  5. I can see that being true for a healthy pack, but I'm uncertain about what happens as one of the cells approaches end-of-life. Does the cell still charge to 4.2V and simply discharge faster in such a scenario? If so, we're talking about a cell that will reach 0% SoC earlier than any of the other cells despite starting at 4.2V/cell. If one cell is at 0V and the other 15 cells need only be above 3V/cell to maintain a pack voltage above 45V. Voltage inversion can very well lead to a fire when attempting to charge that dead cell back up, and I'm more worried about that than a faceplant (having gone through a number of them myself, including one at the top speed of a Microworks wheel).
  6. Hi, I was just wondering if you considered the possibility of a voltage inversion in one or more of the cells when using a shunted BMS? http://liionbms.com/php/wp_lovtg_cutoff.php I'm thinking that it's not altogether unlikely if the user has had numerous cycles (not sure how many) not been balance-charging the battery (charging it all the way up to 100% and letting it sit for a while), since the cutoff voltage on the main board is 45V for unicycles using 16S, and 13 x 3.7V = 48.1V, i.e. you could have up to three cells at 0V and still not trigger the board's low voltage cutoff, which then leads to a voltage inversion in these dead cells as the board continues to discharge the pack.
  7. hyperair

    3D Printed 30km/h Electric Unicycle EUC

    Wow, this is cool. Is there any danger of your toes hitting the wheel while riding?
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