Popular Post tvu213 Posted May 15, 2021 Popular Post Share Posted May 15, 2021 Hi everybody. I am looking for help to build a 84V battery pack for my wheel(Gotway MCM5). I found this board from ewheels.com. and also found another wiring instruction from this forum So my question is what is the connector with 4 wires coming out from HV area for? Are they for balancing battery from different battery packs? That way, I will just buy (or make some Y connector, so that I can connect the two battery packs together, right? Thank you for your time reading my post. 4 Quote Link to comment Share on other sites More sharing options...
Camenbert Posted May 15, 2021 Share Posted May 15, 2021 (edited) What MCM5 is yours exactly (battery size)? Wont you re-use the BMS? From how it looks, these 4 wires are in fact 2. Your guess seems correct, to balance 2 pack in //. As on MCM5 you have one on top, one on side - this would mean each have their own BMS, no? I must say the wires on the XT60 looks very small. AWG14 it should be (in fact thicker-better, as DIY you dont have to cut cost!) Edited May 15, 2021 by Camenbert 2 Quote Link to comment Share on other sites More sharing options...
tvu213 Posted May 15, 2021 Author Share Posted May 15, 2021 I actually will build another battery pack to use along with the original one 'cause the original one is still very good (I just have the wheel 1 month and directly from the store). There is only one battery pack in my wheel 'cause it is the 460Wh version (not the 800Wh one) with only one battery pack (as in images) And the thing is this, there are just two pair of wires come out of the battery pack: one is connected with mainboard through XT60 connector and one connect directly to the charging board. So I think if I build another battery pack at 84V with a 20S bms, I don't need the balance wire. I just think so. 3 Quote Link to comment Share on other sites More sharing options...
Camenbert Posted May 15, 2021 Share Posted May 15, 2021 (edited) Sound good, "unicycle" bms are a bit specific: no protection on discharge, yet allowing regen (braking), their task is for balancing/charging essentially. As far as you have one of these, one is connected with mainboard through XT60 connector and one connect directly to the charging board is correct, just adding "Y". Here is a subject on this forum about available space, you might be able to fit 20S2P : On 12/19/2019 at 4:41 PM, Traveller said: For maximum battery size you would be better off with 18650s as you will be able to fit 2p in the side location where as with 21700s you can only fit 1p. Edited May 15, 2021 by Camenbert 1 Quote Link to comment Share on other sites More sharing options...
tvu213 Posted May 15, 2021 Author Share Posted May 15, 2021 Thank you for suggesting a topic related to what I am looking for. Do you think it is ok if I use the bms that is sold on amazon instead of the one from ewheels? Like this one? Quote Link to comment Share on other sites More sharing options...
Camenbert Posted May 15, 2021 Share Posted May 15, 2021 (edited) I cannot say for sure, but : It must have separate charging port - you dont want all the amps available at the wheel charging connector. It must allow regen - some bms block the way back (especially the one with separate charging port). There should be no protection on discharge even if your main pack will always stay "live". Once these clear, you dont specifically need a gotway bms, but if you dont have the info, you better buy from ewheel Edited May 15, 2021 by Camenbert Quote Link to comment Share on other sites More sharing options...
tvu213 Posted May 15, 2021 Author Share Posted May 15, 2021 It is really a good advice. I will be noticed. Thank you so much. And because the gotway bms is not really expensive, so I think I will go for it. 1 Quote Link to comment Share on other sites More sharing options...
Chriull Posted May 15, 2021 Share Posted May 15, 2021 3 hours ago, tvu213 said: So I think if I build another battery pack at 84V with a 20S bms, I don't need the balance wire. I just think so. Unfortionately this balance wire is extremely important. Once one pack gets out of balance without this sync wire single cell groups get overcharged. Which will not end nicrly 1 Quote Link to comment Share on other sites More sharing options...
tvu213 Posted May 16, 2021 Author Share Posted May 16, 2021 1 hour ago, Chriull said: Unfortionately this balance wire is extremely important. Once one pack gets out of balance without this sync wire single cell groups get overcharged. Which will not end nicrly Thank you for pointing out the point. The original battery pack in my wheel doesn't have the balancing wires (I just saw the one with XT60 connector and the one for charging. Do I have to unpack the original one and add the balancing wires? 1 Quote Link to comment Share on other sites More sharing options...
Chriull Posted May 16, 2021 Share Posted May 16, 2021 8 hours ago, tvu213 said: Thank you for pointing out the point. The original battery pack in my wheel doesn't have the balancing wires (I just saw the one with XT60 connector and the one for charging. Do I have to unpack the original one and add the balancing wires? Yes! This topic is looking at 2015 GW BMS, but maybe still can give you some ideas/hints: Quote Link to comment Share on other sites More sharing options...
Camenbert Posted May 16, 2021 Share Posted May 16, 2021 (edited) 9 hours ago, Chriull said: Unfortionately this balance wire is extremely important. Thx for the link that explain Edited May 16, 2021 by Camenbert 1 Quote Link to comment Share on other sites More sharing options...
yuweng Posted May 16, 2021 Share Posted May 16, 2021 (edited) Afaik, all gotway wheels year 2020 & later doesn't use this 4 wire balance anymore even though the pcb does have it. Whoops, my bad Spoiler Edited May 16, 2021 by yuweng wrong info 1 Quote Link to comment Share on other sites More sharing options...
tvu213 Posted May 17, 2021 Author Share Posted May 17, 2021 10 hours ago, yuweng said: Afaik, all gotway wheels year 2020 & later doesn't use this 4 wire balance anymore even though the pcb does have it. Whoops, my bad Reveal hidden contents I don't see the four balancing wire in the battery pack of my wheel either. It is the Gotway MCM5. And just a quick question. IS the balancing wire used to connect the two battery packs together only? Does it need to be connected to the mainboard? Quote Link to comment Share on other sites More sharing options...
tvu213 Posted May 17, 2021 Author Share Posted May 17, 2021 19 hours ago, Chriull said: Yes! This topic is looking at 2015 GW BMS, but maybe still can give you some ideas/hints: So, the HV of the two battery packs must be connected? And it will not be connected to the mainboard? 2 Quote Link to comment Share on other sites More sharing options...
Chriull Posted May 17, 2021 Share Posted May 17, 2021 2 hours ago, tvu213 said: So, the HV of the two battery packs must be connected? And it will not be connected to the mainboard? Sorry - i never looked in detail how these sync wires have to be connected. Quote Link to comment Share on other sites More sharing options...
yuweng Posted May 18, 2021 Share Posted May 18, 2021 (edited) On 5/17/2021 at 12:00 PM, tvu213 said: I don't see the four balancing wire in the battery pack of my wheel either. <= as mentioned, pcb input is there, they don't provide it if its a single pack It is the Gotway MCM5. And just a quick question. IS the balancing wire used to connect the two battery packs together only? <=Yes Does it need to be connected to the mainboard? <= No Though i've help/ seen fellow riders tear down their wheels but never got to opened up their battery pack since both packs are ok (no point in tearing up the heat shrink) so never got to see exactly how it was wired. mcm5 uses two different BMS, 2 piece BMS for the top(40cell) & single piece at the side(20cell). You can't fit 40 cell to the side together with this BMS or you won't be able to close the shell ! If you're interested in using back the existing top BMS... Spoiler You can wired the 2nd pack balance wire directly to each resistor correspondingly B1 to B20 & the negative to this existing top BMS. Use a multimeter to check it. You can use 40 cell for this mod. Best to use the same capacity as top pack. Eg. Yours should be 3100mah. If you intend to use this side BMS then my best educated guess is wired the sync wire back to the top pack as what you've post on your 1st post below. But better you double check before anything blows up unexpectedly Good Luck Edited May 18, 2021 by yuweng Update info 1 Quote Link to comment Share on other sites More sharing options...
Camenbert Posted May 18, 2021 Share Posted May 18, 2021 On 5/17/2021 at 6:00 AM, tvu213 said: I don't see the four balancing wire in the battery pack of my wheel either. The vid of yuweng answer this. It's a direct connection from one pack to another. You might have to solder these wire on the BMS. I'm still wonder how crucial is this, is it to protect when you plug together 2 pack with different state of charge or if necessary on daily base. As I'm also planning to add a side battery pack (and keep the 2A charger), i might end using a bms that use main wire to charge, so as slave : The charger charge the main pack, as the voltage increase, the secondary pack get charged by the xt60. 1 Quote Link to comment Share on other sites More sharing options...
Hansolo Posted May 18, 2021 Share Posted May 18, 2021 The connector with 4 wires (2 black and 2 red) on the Begode BMS is for the interconnection between the BMS. If there is a problem with one battery pack during charging, a signal is sent to the other pack to stop charging. 3 Quote Link to comment Share on other sites More sharing options...
Chriull Posted May 18, 2021 Share Posted May 18, 2021 (edited) 53 minutes ago, Camenbert said: I'm still wonder how crucial is this, is it to protect when you plug together 2 pack with different state of charge or if necessary on daily base. The sync ("balancing") wire does not prevent the fireworks happening if one connects two packs with too different state of charge. Edit: just to avoid misunderstanding - with firework no sparking connectors are meant, but venting and burning li ion cells... Quote As I'm also planning to add a side battery pack (and keep the 2A charger), i might end using a bms that use main wire to charge, so as slave : The charger charge the main pack, as the voltage increase, the secondary pack get charged by the xt60. This was done in the beginning and changed to paralleling with sync wires. There are too many disadvantages from this "daisy chaining". Edited May 18, 2021 by Chriull 1 Quote Link to comment Share on other sites More sharing options...
Camenbert Posted May 18, 2021 Share Posted May 18, 2021 14 minutes ago, Chriull said: This was done in the beginning and changed to paralleling with sync wires. There are too many disadvantages from this "daisy chaining". Please go ahead and tell us Quote Link to comment Share on other sites More sharing options...
Chriull Posted May 18, 2021 Share Posted May 18, 2021 3 minutes ago, Camenbert said: Please go ahead and tell us Imagine during charging the second pack engages the charge protection due to single cell overvoltage. The first pack will go on charging and once the overvoltage cell from the second pack is discharged again and charge protection disabled again an "uncontrolled" charge current will flow from pack 1 to pack 2. A big part of the output current (almost about 1/2?) will flow through the charge protection circuitry (mosfet(s)) of the second pack, which is not designed to take such currents. Reverse input voltage protection rauses some other issues, bit afaik/r this is not used with gw bms? 1 Quote Link to comment Share on other sites More sharing options...
Camenbert Posted May 18, 2021 Share Posted May 18, 2021 By where to start, 20 minutes ago, Chriull said: charging and once the overvoltage cell from the second pack is discharged again and charge protection disabled again This usually happen in such a short period of time that the delta wont be significant, it's a 2A charger, meaning 2wh per minute... About high current, have you see what regen braking was sending ? What you don't say is that not all BMS will be compatible to the task (cant find gotway 16S BMS anyway), this is way more critical than daisy chaining or not. Last as EUC have no room for any failure, I do not plan to keep my battery pack long enough for such trouble to happen... 1 Quote Link to comment Share on other sites More sharing options...
tvu213 Posted May 21, 2021 Author Share Posted May 21, 2021 On 5/18/2021 at 2:23 PM, Camenbert said: "I'm still wonder how crucial is this, is it to protect when you plug together 2 pack with different state of charge or if necessary on daily base. As I'm also planning to add a side battery pack (and keep the 2A charger), i might end using a bms that use main wire to charge, so as slave : The charger charge the main pack, as the voltage increase, the secondary pack get charged by the xt60." So, do you mean the two battery pack (original one and the new one) should be parallelly connected? this means if I parallelly connect the two battery pack (when they are at the same voltage), parallelly connect the charging port => both will be charged at the same time when I plug in the charger. I couldn't order the bms for Gotway MCM5 (the seller told me they don't have one for MCM5 460Wh right now), so will it be ok if I use the other smart bms? Quote Link to comment Share on other sites More sharing options...
tvu213 Posted May 21, 2021 Author Share Posted May 21, 2021 On 5/18/2021 at 3:15 PM, Chriull said: The sync ("balancing") wire does not prevent the fireworks happening if one connects two packs with too different state of charge. Edit: just to avoid misunderstanding - with firework no sparking connectors are meant, but venting and burning li ion cells... It sounds dangerous... This was done in the beginning and changed to paralleling with sync wires. There are too many disadvantages from this "daisy chaining". Quote Link to comment Share on other sites More sharing options...
Camenbert Posted May 21, 2021 Share Posted May 21, 2021 I think you need a Gotway 20S BMS, not specifically one for MCM5 460Wh. They must know this, ask when next batch comes in? 17 minutes ago, tvu213 said: so will it be ok if I use the other smart bms? I don't know what exactly the other bms you are referring to. On my side I'll advise a bms only once I finish and test my secondary battery, so not in immediate future. How good are you with making a battery? How will you weld? Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.