OneWheel Posted February 6, 2016 Share Posted February 6, 2016 I bought an external 156wh battery to attach to my 170wh unicycle. I found the external battery pack is too heavy and too big to attach to unicycle. Also, too dangerous to attach in case it falls! Question is lets say I have 1wh left in my unicycle and 156wh left in my external battery. I turn off my unicycle and attach the external battery, will the unicycle gain 156wh from the external battery? OR only gain half? Thanks. Link to comment Share on other sites More sharing options...
Keith Posted February 6, 2016 Share Posted February 6, 2016 1 hour ago, OneWheel said: I bought an external 156wh battery to attach to my 170wh unicycle. I found the external battery pack is too heavy and too big to attach to unicycle. Also, too dangerous to attach in case it falls! Question is lets say I have 1wh left in my unicycle and 156wh left in my external battery. I turn off my unicycle and attach the external battery, will the unicycle gain 156wh from the external battery? OR only gain half? Thanks. You will gain a small but quite impressive bomb!!!!!!!!!!!!!!!! There have been various discussions on this, the bottom line of which is NEVER, EVER, connect two batteries together unless they are at the same voltage (I.e. Same state of charge) If you are really lucky the BMS (battery management system) in one or other pack may limit the damage, if you are unlucky a massive charge current will flow from the charged battery into the discharged battery. This current will be limited by nothing other than the internal resistance of the charged battery pack and the resistance of the charging leads, Again if you are really lucky you will burn out the charging leads, if you are really unlucky the charge connector will weld and you will be unable to seperate them as they both heat up considerably until something blows. Link to comment Share on other sites More sharing options...
Cranium Posted February 6, 2016 Share Posted February 6, 2016 +1 with what @Keith said. Your options are: 1) Have the batteries connected in parallel all the time to keep them at the same voltage. This would result in a 326Wh effective battery size. 2) When one battery becomes drained, stop and swap batteries. This would also result in a 326Wh effective battery size. Link to comment Share on other sites More sharing options...
OneWheel Posted February 6, 2016 Author Share Posted February 6, 2016 keith ok got it Link to comment Share on other sites More sharing options...
OneWheel Posted February 7, 2016 Author Share Posted February 7, 2016 Good to have Charge Doctor, I can see the unicycle battery Voltage go up to 67.7 Voltage and Current of 0.07 after a few hours. Charging the External Battery bought from passiongadget, according to Charge Doctor started in the low 60's Voltage and Current in the 1.80's, Voltage slowing going up and current dropping slowly. Hopefully the Voltage will be at 67.7V after a few hours. Before 10km Ride 170wh EUC Charge Doctor Values 67.7-67.8V , 0.07A, 151.2wh 156wh External Battery Charge Doctor Values, 67.7-67.8V. 0.07A, 150.2wh ==================================================== After 10km ride, 4 degree celsius , multi small and medium hills 170wh EUC Charge Doctor Values 66.8V, 1.87A, 153.1wh. strange to see the EUC showing all 4 leds on indicating at least 75% battery left 156wh External Battery Charge Doctor Values, 66.0V, 1.87A, 152.7wh -------------------------------------------------------------------------------- Almost threw away the external battery, found away to put battery into camera pouch, wrap camera strap around handle and wrap 12ft velcro to secure it Link to comment Share on other sites More sharing options...
OneWheel Posted February 7, 2016 Author Share Posted February 7, 2016 Got the battery hook up, see pic above Wondering, should I be concern about the Charge Doctor Values after the 10km ride? Link to comment Share on other sites More sharing options...
zlymex Posted February 8, 2016 Share Posted February 8, 2016 As @Keith mentioned above that one should never attempt to parallel battery packs of different voltages. However, there are cases where late connection of external battery pack became necessary or required. For instance the rider just want to enjoy the freedom of not having to hookup to the external pack till the last moment, or one backup pack for several people and you really don't know who is the first one to drain out. The very simple way to parallel packs of different volts is thr a current limiting device, and the very simple current limiting device that I can thing of is a bulb. By some calculation and measurement, I select 12V 35W halogen lamps for this purpose. This is the device I made to be inserted in between the battery packs to be paralleled. There is a 3-way switch for off, bulb, and short. In my other implement, it is one bulb, two bulbs, and short. The max voltage difference at extreme will normally not exceed 12V(the drained pack will soon recovered to above 55V if stop ride) Link to comment Share on other sites More sharing options...
esaj Posted February 8, 2016 Share Posted February 8, 2016 6 minutes ago, zlymex said: There is a 3-way switch for off, bulb, and short. Hope you marked the switch clearly so that you won't accidentally put it in the "short"-position with two packs having wildly different voltages Link to comment Share on other sites More sharing options...
dmethvin Posted February 8, 2016 Share Posted February 8, 2016 Very sneaky! Those halogen bulbs get hot though, so be careful if you switch over when the two packs have different voltages and the bulb has to burn for a while. On the other hand it would make a nice hand warmer. Link to comment Share on other sites More sharing options...
Luca Morello Posted May 17, 2016 Share Posted May 17, 2016 Is there any smaller and cheaper model on the market ? 88wh ? Link to comment Share on other sites More sharing options...
Keith Posted May 17, 2016 Share Posted May 17, 2016 42 minutes ago, Luca Morello said: Is there any smaller and cheaper model on the market ? 88wh ? 88Wh for a 16 cell back would only be 1486mAh per cell. The smallest pack you can get is a single serial set of 16x18650 cells (or 15 for Ninebot) Since there is only a little weight difference and absolutely no size difference there is no advantage other than a small cost difference in buying smaller capacity cells. Since available capacity varies from around 2000mAh to 3500mAh that would mean you can buy a pack of from around 118Wh to 207Wh, typically 130 to 170Wh. Anything smaller would have to be a different type of cell, You could, of course always use 2 off 8 cell 1500mAh LiPos or 4 off 4 cell LiPos, but most would find charging and balancing them a pain and LiPos are easier to damage. Also there are smaller hard cased Lithium cells such as the 16650 but they are just a bit narrower, so wouldn't save much in physical size. Link to comment Share on other sites More sharing options...
WakefulTraveller Posted May 17, 2016 Share Posted May 17, 2016 I'm thinking of converting my old battery pack, once it's repaired, to an external battery / reserve battery. I wish that it was as simple as buying the right connectors, and maybe doing some soldering, but it looks like voltage will be an issue. Does anyone know if I can use the Charge Doctor V2 or something like it to protect the battery packs? Link to comment Share on other sites More sharing options...
Luca Morello Posted May 17, 2016 Share Posted May 17, 2016 I have samsung 132 wh in unicycle for motor of 350w. It arrive 1 hour of to use. I would arrive minimum 1 hour and half. Nothing craft solutions , partly because no circuit diagrams is not good . I prefer an external battery ready on the market Link to comment Share on other sites More sharing options...
Czestnut Posted May 23, 2016 Share Posted May 23, 2016 On 5/17/2016 at 5:19 PM, Luca Morello said: I have samsung 132 wh in unicycle for motor of 350w. It arrive 1 hour of to use. I would arrive minimum 1 hour and half. Nothing craft solutions , partly because no circuit diagrams is not good . I prefer an external battery ready on the market I have the same 132wh battery in my TG-T3, and use the same 156wh external battery as OP. Have it for a week now. Both 67.2V, and both seem to run well together. They seem to charge well in parallel as well. Link to comment Share on other sites More sharing options...
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