Im dimensioning a quadcopter,and from my math, everything will draw a maximum load of 58-63 A.
I need to choose Lipo batteries that can handle that current draw.
From what I know: Max current: Capacity*C-Rating.
For example, i cant use a 2200mAh 25C battery, because max current drawn will be 55A, but if I put 2 of those in parallel, I will maintain the 11.1V of 3S and will double the capacity. From that, my max current will be 4400*25=110A and I will be safe.
Is my thinking right? Can I do this?
Electronic – Can i double max current drawn, putting batteries in parallel
batterieslipoparallel
Related Solutions
An important question to ask yourself: Can I really not access the cells' individual wires?
Your best option is accessing the wires to all the cells, usually battery packs have balancing connectors, with in it wires to connect to the joints of each set of cells.
This is done, because LiPo cells are much more sensitive to cell-to-cell imbalance and will waste away much faster if you do not check the cell balancing regularly, preferably each time you charge and/or discharge. Alternatively you also should make sure no single cell ever discharges below a level of about 2.5V.
The 4 cell chips do all of that for you, if you choose an appropriate one. They will stop current flow when any one of the cells is depleted, in stead of when the entire pack reaches a lower limit, and they should be chosen to have some balancing feature, to alow you to fully charge all the cells.
A 1 cell device will only work with one single cell, because it expects the upper limit of 4.25V and lower limit of 2.5V, connecting a full pack of 4 cells to its terminals will at best just not work, but most likely turn it into a ball of smoke.
The weakest cells need to be recharged 1st then stopped.
Series cells fail due to weak link theory Overcharging it will reduce life and weakest cell determines overall capacity. So a balanced charger is essential.*
Matched cells ?
If you realize that flooded lead acid batteries are in every car made of 6 perfectly matched series cells. If they all aged at the same slow rate, they would all fail together, but this never happens.
It is always one or two cells due to the runaway factor that causes weaker cells to age faster when overcharged which amplifies the difference. From my past research, I recall cells are matched in attributes to <1% from quality sources and >2% is defective when new. This is for 6 and 12 cell batteries made in one batch, not the tolerance between batteries made in different batches.
The exact same analogy exists with putting parallel LEDs in tandem and running at highest current. From the same batch it runs fine, but from batch to batch, you can get thermal runaway at max current. The more LEDs in parallel, the lower the tolerance to mismatch for current hogging. THe same theory applies to series cells in charging batteries. The weakest cell gets over/under-charged first.
Max current?
Consider that cars can consume over 500A for 20 seconds in extreme cold weather with high engine friction and that may or may not start the car at -30 ~ -40'C (more Amps with V-8's).
Also your alternator matched to your engine size may be capable of fast charging from 60 t0 120A without any current limiting and only using Vbat sensing which is ideally 14.2V for desuplhating the battery without excessive electrolyte evaporation.
So when optimizing golf cart charger process ( or any motive power charger) due to a wide variance of aged cells in a series you must consider a charge balancer design.
[example]1
REferences
- https://www.google.ca/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&cad=rja&uact=8&ved=0ahUKEwjB0ra0lJnPAhXkz4MKHZxfArgQFggtMAI&url=http%3A%2F%2Fbatteryuniversity.com%2Flearn%2Farticle%2Fequalizing_charge&usg=AFQjCNHMxex6KZQPfMqahdMhVD-nZ_ybpg&sig2=UVf2i4GjokTOHN80AnwQPA&bvm=bv.133178914,d.amc
- www.chargetek.com/images/pdfs/equal.pdf
- www.jonathankimball.com/pdf/batteq_vppc.pdf
- http://www.rolls-battery.com/content/technical-downloads?q=node/47&phpMyAdmin=2eda4dec0bd69647b9e3cf0f71e01d23&phpMyAdmin=9dec4a269d70t7a63be7c
- important IEEE users > read here
Related Topic
- Electronic – Schematic for a lipo battery bleeder overcharge protector
- Electronic – Using capacitors to prevent surge current on lead-acid batteries
- Electrical – Powering up raspberry pi 3 b+ with one 11.1V 3S 2200mAH 30C Rechargeable LiPo Battery
- Electronic – 12V lead acid battery instead of 11.1V LiPo
Best Answer
Yes, this can and is commonly done in the RC modelling crowd with lithium polymer batteries. Just make sure that both batteries are at the same state of charge (voltage within 50mV) before hooking them up, or you might damage the less charged one by charging it out of spec.
You can even use batteries of different capacities in parallel (but never in series!) as long as they have the same cell count and battery chemistry.
It is also possible to charge multiple batteries in parallel. Again, make sure that the batteries are not too mismatched in voltage before connecting, and make sure that you connect the balance plugs in parallel when balancing (which you should do on every charge).
Your maximum current estimate is correct, but keep in mind that cheap LiPos often overstate the maximum discharge rate somewhat.