I’m another newbie starting out on my build and need a bit of advise on the electrics please.
I have been given a Waydoo Flyer mast and motor set so I am going to use this. From my research I see this motor is rated at 6000W. The original Waydoo WD-01 battery is rated at 7500W, 1776Wh, 40,000mAh.
I am building a battery so thought it best to make something as close in capacity as that of the original Waydoo battery. I am thinking of 2 x 6S13P that I will then connect in series when fitted in the board. I figured that two smaller batteries might be easier to charge, handle etc. What do you think?
6000W@44.4V = 135amps. With 12S that would be 11.25A per cell - correct? But that is only when the motor is going hard out. Do I need to select 18650 cells for this level of current or do you normally select for less current becasue I won’t be going hard out the whole time?
This then leads me to BMS selection - rating? Do I fit one to each battery?
What about ESC or VESC. Please can I have some advise on what current rating based on the above info?
Your needed ratings to get some headroom in your build would be about 100A continuous battery and bms with a 200A ESC. Since chinese ratings are normally wildly exaggerated this means a ”200A continuous” bms and a brand cell (samsung/LG/panasonic/sanyo etc) that can do 10A continuously with reasonable cooling (some battery discharge tests are done with infinite heatsinking potential whereas our waterproof boxes normally limit battery cooling a lot).
I would rather build a battery with 12s and not 2x6s (it will probably work if you really want to do it though). My reasoning for this recommendation is that a dual 6S has more possible fault modes for charging and balancing and more complexity.
-Two BMS that aren’t synced could lead to imbalanced voltages which will stress one of the 6S packs more, possibly leading to premature aging
-The voltage spike if one BMS breaks current could take out the other BMS.
I forgot one thing, what is the kV constant of the motor? If you don’t know then it can be measured with a drill press or even cordless drill and a multimeter. Some info and help here: bavaria-direct.co.za
If it’s kV 100-120 then above advice holds, if it’s a lot higher then i’d get a higher current esc like the ztw seal 300A or a 75300 VESC
If you split the batteries in two 6s packs as suggested, they can be charged with a rc charger (no bms needed). If the packs were discharched in series, the cell voltages should be more or less the same and the two packs can be charged in parallel. I use an iChargerx8 which can charge @ 30A and balance @ 2A, so 15A per pack. With 2 chargers you can charge @30A each. 2 server PSU’s in series serve as a 24V source for the chargers. See here: Lipo battery chargers - #21 by FacuO
If you split the batteries in two 6s packs as suggested, they can be charged with a rc charger (no bms needed
Plus you can get them to storage voltage easily and you can mopnitor each* cell voltage every time you charge them (if there is an issue with one of the cells, it might show a lower voltage befor you charge it)
*actually the 13 cells you have in parallel, but still way better than just having the complete package voltage
I agree, 2x6s without bms is a good solution if you can always stay conservative on the discharge voltage. Unfortunately sometimes i have too much fun, deplete almost entire battery and want to use rest of the pack to get home without damaging the weakest cell group, that’s where a bms solution can help.
I know it’s better to not end up there… but it still happens to me sometimes
Thank you all for your advice and suggestions. I think I will stick with the 2 x 6S and use two balance chargers.
I will fit an undervoltage alarm and display for each battery pack so I have some warning that low a voltage level is approaching.
Anyone got suggestions on what connectors to use on the battery packs? I have seen some battery packs in this forum using Marinco panel sockets and plugs but these appear to only be rated at 40amps from what I can see.
I would agree with sat_be: Skip the BMS and charge the batteries separately with an RC-charger (you need a balance cable @ each battery)
In my experience you will need ~100A only during startup for a relatively short time; when flying the current draw depending on wing, prop and weight is much lower at ~20-50A; myself (90kg + 35kg Board) fly at ~25A @ 25km/h.
Concerning battery capacity I would also recommend rather going lower:
With my first two builds I also built batteries in the 40-60Ah range which I very rarely use today because they are so heavy.
My current go-to battery has only 24Ah which is good for 45-60min ride depending on how often I need to start
For I newbee I would recomend to go for high-capacity 21700cells (e.g. LG INR21700-M50LT or Samsung INR 21700 40T or 50S) in an 6s8p x2 configuration - plenty of capacity at low (~8kg) weight.
Thanks for the additional advice. I think I will stick with the bigger battery on this build because it is my first build and I know there will be lots of people wanting to have a go, so the larger battery is proably a good thing. I can always build another smaller capacity battery at a later date.
I am pretty much committed to 18650 cells as I have got most of the hardware to build this battery now - except for the cells themselves.
Any thoughts on Panasonic NCR18650BD cells? I have seen them rated at 8amps in some literature while other literature says 10amps CDR.
I am also consider Samsung INR1 18650 30Q, which are rated at 15amps CDR. But I’m not sure that I really need 15amps CDR?
Funny, i just bought 50 of those to make a 12s4p light pack.
A couple of cells arrived dented (mistreated by the courier). The rest looked just like new. All cells were exactly at the same voltage
Nkon sent more and told me to get rid of the damaged ones. No questions asked. Very happy with ther customer support, especially since theyre reclaimed cells
I have an 12s12p pack with the Samsung 30Q cells as thse were the sells to have 2 years ago.
I can’t confirm issues with them: If you treat them well (Storage @3,7V, don’t over and under charge, balance with every charge) they should last. A lot of people in the german efoil group are using them without issues.
Same for me: After 2 years of heavy use the pack is just fine -Mine where even running in (sweet) water a couple of times thanks to a leak: Did not hurt them.