Maybe get in on the focbox (Vesc updated in a case) group buy 115 shipped. I am still on the fence because I don’t need them but will probably buy because it’s a great price.
Ok so just don’t go to fast down the hills to avoid damaging the components, got it. 10000 mah should be good for 8s set up right? Also thanks for the lengthy explanation about the brakes.
No problem just lessons learned in real use. Short answer is yes… details are below.
10Ah is just the capacity, for the batteries you basically need to know 3 parameters, capacity (expressed in Ah or mAh), energy potential (voltage, 8S in this case), and max amperage (current expressed in Amps A or as a C rating on LiPo packs).
10Ah means you could draw 10A from it for 1 hour continuously (or 5A for 2hrs). Basically more Ah capacity means more volume/weight for batteries and longer range. Personally I have a 10S 5Ah battery setup (2 5S 5Ah in series) and can get 12+ miles out of it (I draw about 5A on average, ride for about an hour including little stops). To compare different battery capacities that have different voltages it’s useful to look at them in terms of Watt Hours or Wh which you just calculate by multiplying the nominal voltage of the batteries by the Ah, so 10S3.7V5Ah = 185Wh, compare with 8S3.7V10Ah = 296Wh. So you would get killer range with 10Ah but keep in mind if you stack 2 5Ah batteries in series it is still just 5Ah because the current flows through both batteries at the same time/rate (as opposed to if they are in parallel where you would add the capacity and max current throughput, but get no additional voltage).
The 20C on the battery is the max current rating and tells you how much you can “safely” draw from the batteries without rapidly killing them (due to their own internal resistance and overheating). For example 20C * 5Ah = 100A max discharge, in reality having higher C rating helps to avoid voltage sag while the batteries are delivering power and will allow you to get a bit more range most likely (discharge graphs if you search google images can see how A draw on different C batteries affects how many mAh you can get out before the voltage dives). Real world difference between say 20C or 30C or 40C though your guess is as good as mine, been using 20C 5Ah for a while without issue but imagine it could deliver more (unnecessary) power if I went with 30 or 40C.
Realize that was already a lot but a few other things to sort of keep in the back of your mind about all this, I’m drawing somewhere between 10-20A on accelerating and 3-6A (based on crappy ammeter measurements, getting a metr.at module soon hopefully) usually when riding continuously but these numbers will vary especially when you reduce voltage (it will need more amps to get the same kind of power/acceleration). Also going faster means more wind resistance and overall more load on the components so they will run more/less efficiently depending on how/where you ride.
So if I hook up my batteries in series, then I will get more voltage (the full 8s), But in parallel, I will get the full Ah (10Ah) but only 4s of power. So you have two 5s 5aH batts, but they have 5Ah capacity since they are is series, but still supply 37V of electricity? Therefore I assume that I should hook my batteries in series to achieve the 29.6V of energy potential the calc says? (I have same Ah as you now yet more range because I use less voltage) Did I get that all right?
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Yup all sounded right to me.
Sweet! Can’t wait to get the parts and start building! I will post pictures and problems I encounter here. (Probably mostly with the VESC) I will stick to the 20C batteries since you use them without issue and I don’t need the “unnecessary power” of 30C and 40C.
Yeah I don’t mean to downplay the benefit of higher C rated batteries when you are drawing a lot of amps, say a big guy trying to go fast up pretty big hills or a sizeable helicopter built for 3D acrobatics, but I just haven’t ever seen a time I actually draw that many amps personally.
Again take with a small grain of salt since you have slightly lower voltage at 8S you’ll have slightly higher amps to get the same Watts power to the motor. Seeing as how I’ve never actually seen my board draw that much current in any measurement I’ve done so far and my batteries seem to be doing fine after about a year I think it’s fine.
soooo…All the parts are arriving now, but I realized that I accidentally ordered a 5200 mah battery 4s, but it only has 10c discharge. How will this effect my board? Should I try to return it and get new batteries?
However, I plan to set my motor max at only 40A, so it should be ok since I calculated the max discharge of my 5.2A 10c battery to be 104A?
Check lipo discharge charts to see for yourself but basically lower C means higher internal resistance in the cells so you consequently get more heat build up and voltage sag with lower C batteries and will likely shorten the number of cycles you can really use the batteries. I use 20C 5Ah but really that’s considered the low end of acceptable typically keep in mind manufacturers will rate their components in ideal situations (controlled pressure and temperature etc)
If your cells are in series they all experience the same continuous amperage flow and you only add voltage the Ah capacity doesn’t get added since you are drawing electricity through both at the same rate. Also C rating is per battery based on it’s Ah in that scenario, if you instead put them in parallel the Ah and the C rating from both batteries get added since you’re only drawing half the circuits total current from each battery when in parallel. In series you’re looking at 52A max rating which is still above what you’ll probably ever draw (can do Volts*Amps=watts or watts/volts = amps to work backwards from your motor max power to the max amperage given a voltage). All that said higher is better.
Ok, so my question is if I can run it on 10c by setting max motor to 40A without frying anything . I will switch to 10s with higher c in the future.
Pretty sure you can limit amperage both on the motor side and on the battery side so yeah basically as long as they aren’t severely overheating should be fine (probably wouldn’t do too much hill climbing and just monitor the battery temp on the first few runs keep in mind the heat builds up on longer cruises)
Ok, so how would I limit amperage on the battery side? I know I can limit motor amperage through bldc for vesc . Also only the battery is in danger here right? Because I have insurance for my batteries if they break.
Yeah basically the ESC can deal with some max amperage but it will only draw as much power as it needs to drive the motor around. So basically only issue here is the batteries can’t really consistently supply that current without starting to get warmer (due to their internal resistance, also the warmth creates more resistance which isn’t ideal).
The components on the ESC (MOSFETs are mostly dealing with delivering the power from the battery to the motor) have some max limit, pretty sure for the VESC the MOSFETs are rated for 50-60A continuous and 240A peak bursts but the higher amps it is drawing for any amount of time equals more heat build up in those components… this is mainly why higher voltage is better, since power is Volts*Amps if you can increase the voltage you can reduce the amps and keep the same power output (and by reducing the amps you reduce the heat loss and consequent voltage sag).
Soooo, I finished the board and it works really well!!! However, I am having issues once I reach top speeds. I was riding the board and I pulled the remote trigger as far back as I could, reaching top speed. However, around 10 seconds after reaching the top, there was a sudden jolt in which the board went even faster and almost threw me off the board. Does someone know what it going on? I can send pictures of the programming and what not.
Not sure might be a loose connection between the receiver and ESC try to be sure everything is either soldered and/or mechanically secured with hot glue or whatever else so no connections can vibrate loose easily. Check the ppm high and low values in the display after you’re sure the connections are solid, you can disable control mode and still use the display to adjust the min and Max Ms values for the ppm input.