Nice I’m sure you would wreck me on the drones I just tinker around with mine at the park nothing too serious, been flying on and off over a couple of years but not really regularly ever and still getting used to FPV. You can go either way with it, if you have the cash and want the slimmer profile and want to wire up a BMS and switch then would go 18650. If you want to go more minimal (I have a web/software engineering background so in my mind less things = less things breaking) then LiPos, a loop-key, and a decent charger and you’re all set.
Believe most people actually do it as packs of cells in parallel with each other because easier to spot weld (or solder) the tabs across a set of positives with a block of cells and negatives on the other side and they are effectively in parallel, then wire those blocks of cells that are in parallel, in series to get the 12S. Regarding amperage you multiply the amps supplied by number in parallel (15A flow from each set of cells in parallel, each one of the cells in parallel is feeding into the positive and negative it isn’t flowing through all the cells as is the case when connecting in series).
When you hook up cells in parallel they are effectively going to charge/discharge each other until they are level so be sure the cells are close to the same charge before connecting them, once connected they will self balance but if too much charge is quickly dumped into a cell it will overheat it.
Regarding 15A per cell if you have 4 in parallel you have 60A max discharge without causing a problem, and at around 45-50V you could be drawing 3000W which I think is pretty unlikely (unless you’re racing up a hill perhaps and have huge motors). That said in the case of max discharge and current in general leaving some buffer is always a good thing.
If you don’t plan on buying or making a spot welder though your options are limited on how to get this done safely. There are these packs http://vruzend.com/ believe they’ve posted on some threads here too but would have to search around and find those to see how that turned out.
Lots of places to get them premade as well, miami electric, diy, believe psychotiller, and longhairdboy may do them too.
When thinking about batteries in series and parallel, like your earlier “4p” example, if there isn’t a separate “S” number with it, you can assume it’s 1s, or one cell in series. So a “4p” pack would be four cells, connected so that all their positive terminals are together, and all their negative terminals are together.
If you run across “12S” with no parallel number with it, you can assume it’s 1p, or 12 cells end to end, the positive of the first going to the negative of the next, and so on.
“12s4p” means you take 4 batteries and put them in parallel, then take 12 sets like that and put them all in series.
Batteries in series add voltage, but not capacity. So a 12s1p pack of 3000mah cells will still be 3000mah.
Batteries in parallel add capacity, but not voltage. So a 1s4p pack will have the same voltage as a single cell, but 4 times the capacity (and 4 times the current too).
Add them together, and you have 12 times the voltage and 4 times the capacity.
Yup you got it so if you made a 12S4P pack out of those Samsung 30Q cells which are 3.6V and 3Ah, you’d end up with an overall battery pack rating of 43.2V and 12Ah which works out to 518Wh.
And because the pack is 4P, you’d have a total discharge rating of 4*15A = 60A, which as long as you’re not building a mountainboard etc, is fine.
Keep in mind thought that just because each cell might be rated at 15A discharge, ideally you don’t want to be pushing that much current very often if you want to get the most out of them as they’ll generate less heat and be less stressed.
In general, the less current you’re regularly drawing from your battery, the longer the cells are gonna last and the more charge cycles you’ll get out them, so if you’re on a budget, keep in mind that if you spend a bit extra now, they’ll last you longer.
Also, when comparing cells, don’t just go by their manufacturer rating as these values aren’t particularly reliable. Try and find discharge curve charts that people having created from testing, such as this one:
Wow. This is a wealth of information! I really thank you all for taking the time to share and educate me on this.
I would rather purchase a spot welder than to solder, even though I am very good at soldering, it just seem a bit too risky to solder these kinds of batteries.
Michaelcpg: I’m curious as to why you said this:
“And because the pack is 4P, you’d have a total discharge rating of 4*15A = 60A, which as long as you’re not building a mountainboard etc, is fine”
Is that too much power? I have a trampa mtb running 2 low kv motors for good torque. Would 60a be too much draw of power? I’m in Florida going over fields and pavement. Flat lands.
WaffleJock: I’m using these lipos:
On 60xx 118kv motors. Reason I chose low kv is because I’m a big guy. 6’2" and about 230lbs built with a Lil belly, lol. So I need some torque to carry this big body.
Hah all good. Think you’re mixed up in a common way though. The max discharge isn’t how much will go through the circuit you apply the voltage to it’s the maximum you should ever draw (really you should never draw that much ideally). How much gets drawn is dependent on how much on time (duty cycle) the speed controller is opening the gates to let power flow to the coils of the motor. Basically the ESC ramps up the power it lets flow through the coils until there is enough current (amperage) flowing in the coils to turn the motor then when it detects the motor is turning it fires the next set of gates (MOSFETs) to let the current flow through the next set of coils. It’s a little more complicated than this but that’s a general picture.
So the amps we’re talking about with the battery supply you want to be much higher than what the system will ever actually use. It’s not as though the battery is “pushing x amps” the battery is just charged with y voltage potential and the circuit has z resistance in ohms then the x amps you need the battery to supply (calculated as y voltage over z ohms y/z = x, or more commonly V/R = I) should be under the “max amps” the cells can safely supply. So increasing the number in parallel increases the buckets you have to draw the total current from and you want the current from any given bucket to be below the max rating for that bucket.
Think this visual series is helpful in getting a picture in your head of how things work if you don’t have a lot of background in electrical circuits or batteries:
The batteries all have “internal resistance” just resistance like any other component but in the battery itself so if that is too high the battery cooks itself inside out. Max amperage ratings are in a round about way telling you the internal resistance of the cells and the heat dissipation capability of the cells.
The discharge current (amperage) through a circuit is always equal to the voltage divided by the resistance so say you hook your battery up to a high resistance load (say a bunch of light bulbs) if their resistance is high enough the current will stay low but if they have very low resistance then the current is high. In our case the load is more complicated since we have chips that open and close gates/switches at a high speed the current flow to be regulated but the same basic rules apply.
The chart @michaelcpg linked is showing that if you have higher discharge rated (lower internal resistance) cells then you get more mAh out of them if you draw the power at a lower current, basically less you are stressing the cell with heat the more power you actually get out of them and the less you’ll damage them in the long run. The long story short is more in parallel can’t really be bad aside from weight/volume issues more in series and you can end up with voltage potential that is higher than the components you’re using are rated to handle
Amperage causes loss as heat (I^2R = power loss, so delivering power [Watts=AmpsVolts] at as high a voltage your components can support and doesn’t kill you is ideal).
That almost got a little confusing on the last 2 post, not gonna lie, lol. But I get the gist of it.
Best way I can compare it as a Drone Racing guy, is pretty much the same. Not one number is good. There are variables that need to be considered.
Foe example; a
500g racing drone,
with 2207 2600kv motors
with 30a esc for each motor
on 5 inch 50 pitch propellers
= a power house, powered by a 4s 1300mah 100c.
Too much power for a light drone. The 30a esc’s are basically overkill. I would be fine with a 20a with my skill level, but with a pro, 30a isn’t enough, they would need a 35a otherwise risk of burning out the esc’s.
If I change it up with a 4s 1500mah 90c instead of 1400mah 100c
5 inch 40 pitch propellers
I would lessened the aggressiveness of the power by adding weight from the Lipo and toning down on the propeller pitch. Much easier to tame for me.
The heavier the drone, the more mAh I need, less c rating, bigger propellers and lower kv motors to keep it efficient. Maybe get a higher esc amps, like a 40.
This is more my language, but it is the same concept. Everything is accounted for based on weight. Does that make any sense? Lol. I’m rambling now…
not sure I understood that but I think it might be wrong
Max discharge is the amperage a battery CAN discharge continuosly, the vesc (or esc) will determine how many amps it needs to draw from the batteries. At most times on street boards that is only about 40a on hard accelerations, once you get up to speed and start cruising the motor will need less amps since the load on the motor is decreased because it is already spinning (normally 1-2a). For mountainboard I recommend you get batteries with a bit more discharge rating (not sure if you posted your weight but that plays a big role too). Mountainboards require more amps to turn the motor becuase the pulleys on the wheels are much bigger and the wheels are also much bigger, which leads to bigger rolling resistance. Hope this helped