Q. At what rate should I charge my LiIon pack?
A. In general, don't exceed 5C, and best practice is charge at 1C.
Look, teaching you everything you need to know about battery charging
is beyond the scope of this website. We'll share some examples to try
and help guide you, but don't for a minute believe this is a
comprehensive explanation. Point being, it's on you to learn enough to
be safe and the charger manufacturer will also have information to use
in safely charging your battery pack.
To begin, you need to be aware of a bit of math. Like how the 'm' in mAh
means mili, or 1/1000. Regarding the A, that means Amperes (or amps),
and h=hours. So the capacity of the pack is measured amps delivered in
one hour, or Ah (A*h or A x h), but since packs for models are often
measured in fractions of an ampere, then they're also often expressed in
terms of milliamps, or 1/1000th of amp. As for time, since the time
frame is always based one hour, then . . .
- 5000mAh = 5Ah - meaning it'll deliver 5A of current for one hour
- 2000mAh = 2Ah
- 850mAh = 0.85Ah
. . . understand?
Further to this, C (capacity) of a 5Ah pack is 5A for an hour, 2.5A
for two hours. Similarly, 2A of consumption for an hour from a 2Ah pack,
So charging at 1C (meaning 1xC) it means a 5Ah pack can be charged at
5A, and if the same pack is being charged at 2C (meaning 2xC or 2x5=10)
it means it can be charged at 10A and since we're dealing with full
hours, this means it'll charge in 1/2 that much time, or 1/2 an hour.
Confused? Continue reading.
Let's switch to a 2Ah pack (same-same as a 2000mAh pack). Charging a
fully discharged 2Ah pack at 1C means hitting it with the charger at 2A
for one hour. Hit it at 2C (4A) means it takes half that much time
(1h/2=1/2h or 30-minutes) Ditto, charging at 3C takes 1/3 of an hour or
20 minutes (60min/3=20minutes), or at 4C takes 1/4th of an hour, or 15
minutes. Get it? If not, review and consider learning about this
material in other places until it clicks because if you screw up you're
putting your life at risk.
We're not kidding so please consider yourself warned!
Note; all this is in theory because it's never a good idea to
discharge below 20% capacity. Point being, a 5000mAh pack in practice
should be considered 80% of 5ooomA (0.8 x 5000=4000), or 4000mAh instead
of 5000mAh. This is important!
There's more to learn, and it's not really rocket science, but it's
on you to go learn about it before charging batteries. We're sharing
some some rules of thumb that will for the most part keep you out of
trouble - but - you can burn your house down by being stupid so don't go
trying to blame us because a) we're telling you battery charging can be
dangerous, and b) that what we're sharing isn't everything you need to
know. The major point being, you should go learn how to do it safely
before you begin!
Q. My charger has a LiPo charge-cycle instead of LiIon. May I still use it?
In general, chargers expressly made to charge LiIon packs are set to
similar cell-voltages for LiPo-chemistry and thus, won't damage the
pack. Basically, the difference internally is the LiIon cell has a
liquid electrolyte while the LiPo, which is also a lithium-ion
technology, uses a gel for the electrolyte. Anyway, always use a charger
designed for the appropriate chemistry. Note; chargers are available to
charge multiple chemistries.
Q. My charger has a LiFe charge-cycle instead LiIon. May I still use it?
A. In general, no because a LiFe-charge cycle is going to charge at a lower level than for LiIon.
Q. Can I charge my 2S LiIon pack with a NiCd charger for 7-cells since that's designed to charge 7.2V packs?
A. No. Hell no! Don't do it.
The reason is the NiCd charger makes no provision to monitor the cell
voltage of the individual cells the way a charger designed for LiIon
packs will. This is the inherent advantage of the LiIon technology in
that each cell is wired to the little white balance-connector so the
charger can monitor the voltage of each cell as it charges. Be careful
because this is a good way to start a fire and burn down your house!
You've been warned!
Q. I'm Canadian and fly year around, sometimes in sub-zero temperatures. Is it OK to charge my LiIon pack in these conditions?
A. Yes, but be careful. Capacity is reduced maybe 20-30% at
freezing. And at lower temperatures the data is inconsistent. Look,
batteries basically like to 'live' at similar temperatures where 'we'
like to live. Fortunately, in practice, what most folks do is charge
their packs whilst in their car!
That said, if you do charge in below
freezing temperatures, reduce the rate of charge to 0.1C . . . e.g. 10% of
the battery capacity.
Q. I'm confused, isn't LiIon the same as LiPo? Also, why don't
you recommend LiPo packs? I like that they're cheap so what's wrong
A. Yes, LiIon and LiPo are similar. But critical differences aren't so much in their chemistry (they're actually very
similar) but in their methods of construction. This is the key to understanding our recommendation for LiIon versus LiPo.
This is because the LiPo is built in a poylmer
bag. This gives it the characteristic brick shape as the
individual cells are flat-rectangles, which are overlaid upon one another. The shape is also the giveaway for
the LiPo vs. LiIon where these packs are built within cylindrical metal shells (typically aluminum).
Note; the Po in LiPo refers to the polymer in it's construction
(aluminized polymer bags). Anyway, the individual cylindrical
shells, because they're made of metal instead of thin polymer bags
means they're more resistant to physical damage. By the way, this metal
shell is the same technology used in old school NiCds and
NiMH (and alkaline cells, for that matter). It's been around forever
because it works!
There are downsides to these metal shells. First, the metal is a bit heavier than the plastic bag use in LiPos. Second, simple
geometry dictates two cylinders contain less volume than two flat cells
(capacity). Third, they're more expensive to produce.
disadvantages are upsides. Like metal shell is FAR more sturdy. This
turns out to be a crucial advantage because metal protects better
against inadvertent damage (like a pack shifting during a
maneuver and bumping up against the hard edge of a former). If this
happens to polymer style packs, the dent may result in it puffing. Or in
a fire. Need I mention our models are constructed of
flammable materials like balsa, foam, and fiberglass?
Bottom line? For an engineer, part of the remit is looking not at when
going right, but when things are going wrong. Look, nobody sets out to
their pack so it's dented due to shifting during a maneuver, but . . .
shit happens, right? So it's when things go pear shape that a good
engineer earns his pay.
Our deciding against continuing to offer 'Po' style packs for control
avionics is a direct result of data indicating it might sound good in
theory, but in practice, leaves something to be desired. This reminds of the immortal words of a wise wag of baseball.
way, when the data changes, we change our mind! This is why our control
avionic pack recommendation is to use durable LiIon instead of more
fragile and less costly alternatives like LiPo brick style packs.
Note; for propulsion, the weight and package volume
(capacity) give an overwhelming advantage to polymer bag construction.
This is why LiPo packs are used for powering RC models. But also know
this, these packs are removed prior to charging (or should be), so the
risk profile is somewhat different.