Voltage adds in series. For connections, this means you start at the negative of one component (a battery in this case), go through to its positive, and then connect that to the negative of the next one. Voltage gets higher and higher for each battery it goes through, but the current still only has one path through so it doesn’t change.
Current adds in parallel. All the battery voltages are the same, but the current can flow through multiple paths at the same time so current capabilities increases with every extra parallel connection you make. You can see on the left here all the negatives are tied together, and all the positives are tied together.
If you’ve got two 5S 4.5Ah 30C batteries and you put them in series, you get 2x the voltage at 10S, but the rest stays the same. 30C at 4.5Ah gives 145A. You don’t have any extra places for current to flow so the C doesn’t change.
If you put them in parallel, you don’t get any extra voltage because you have to tie the terminals together, but you do get extra current. So you have a 5S 9Ah 6̶0̶C̶ 30C battery. 30C at 9Ah gives 270A. Amps are real current, C is roughly “current as a proportion of the total capacity”, so it confused me there. Absolute current doubles, but current as a proportion of capacity doesn’t
again I’m being a bit loose but I think it’s appropriate, two things here:
First is if you have two batteries it doesn’t really matter how you connect them, the capacity will be the exact same and the mileage will be roughly the same. Pretend it’s the same.
The other: Voltage is roughly proportional to speed. You want higher top speed, you need more voltage, more series connections. Torque is roughly proportional to acceleration. You want to push hard to get off the line, you need more parallel connections, more P groups
This is part of the issue here. You’ve got this idea of mileage and speed, when in reality those are tertiary to what a build should focus on. First is safety, second is reliability.
If your board can go whatever speed for however many miles, but it’ll be broken in a month or be at risk of burning out, what good was the project?
30mph on any board is dangerous. On a cheaply constructed board loaded with compromises in the wrong spots, even more so.
LiPos are fine for many people, but if you’re currently not sure of how a VESC is programmed or how current limits work, then LiPos may not be the safest option.
Any lithium battery can have a catastrophic failure. LiPos tend to have the most animated failures, and I don’t believe that’s a risk you’re currently equipped to take on.
What’s the actual top end of your battery budget? Because the Meepo pack is a non starter. Don’t buy that, it’ll cost you money to replace fairly soon. The M36 cell is a fairly low discharge cell, you’ll likely get bad voltage sag and it won’t be a battery that can grow with the build should you ever choose to replace the ESC with a better one.
His vesc is best run around 25-30a. The battery its self will only do 30a. So tell me how that battery is not safer for the vesc he has compared to using say hummie’s.
Ok, sorry I read @mr.shiteside ’s comment wrong, ok I’m slowly understanding this. Now correct me if I’m wrong, amp hours is how long the battery lasts. I gotta spend this night just researching information about this but it’s better then when I really had no clue
yeah I should probably have included this, I just didn’t want to add another unit and a conversion in when the specs of batteries are usually described by sellers in voltage and Ah and S and P groups and stuff. Watt-hours are energy, that’s why it doesn’t really matter how you arrange them, the energy and therefore range is largely the same.
Long answer is: The battery isn’t the main thing that determines speed, but if you’re keeping everything else the same (same gears, wheels, motor) then this is roughly right
Bit more engineering basics: mechanical power is torque x speed. You can adjust gearing to increase one or the other. This is why first gear in a car takes off quickly but can’t hit top speed, even though it’s got the same engine.
Electrical power is voltage x current. If you have a fixed power source, you can pick high current or high voltage but not both.
The job of the motor (and sort of the ESC) is to convert electrical power in the battery to mechanical power in the wheels, efficiently.
I’d personally just pick whatever battery configuration is easy or standard as a starting point and adjust other stuff from there. Low enough that it fits the voltage limit of the ESC, high enough that it doesn’t use mountains of current and burn the ESC (power = voltage x current, if you want to keep the voltage low and still have power you need high current). Basically, use 10S because it’s as high as the ESC can reliably handle, and use whatever current it can handle, then adjust your wheel size and gears to get more torque or more top speed.
yeah to be fair we have been focusing on steering away from a meepo deathtrap, and keeping the ESC settings to favour reliability rather than speed but
may have missed this a bit. I personally don’t think lipos are thaat far from a safe choice in this scenario, and we have been emphasising that everything be done slowly and with pictures in a thread, but yes there’s still risk of stuff going tits up
