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Battery Talk: What a Numbers Mean

Every now and afterwards we get a doubt from someone during an RC field, and it’s scarcely always a same question: “How many milliamps is that battery?” The initial time we listened that, we didn’t know how to respond since a doubt didn’t make clarity to me. So my “What do we mean?” response resulted in another doubt about how large a battery was or how many ability it had. That we could answer.

The lithium polymer (LiPo) batteries that we use currently in a electric RC aircraft are typically described regulating several customary electrical terms: “voltage” or “cell count”; “storage capacity”; and “current” or “discharge rate limits.” Take a demeanour during any LiPo tag and you’ll see during slightest these 3 items. These terms aren’t singular to a batteries we use in RC; they’re terms that are used in all electrical fields, so it’s critical to know what they meant and to use them properly. TEXT PHOTOS BY JOHN KAUK

VOLTAGE

A battery is stoical of cells, that are connected in array and/or together to make adult a battery. The voltage of any battery is dynamic by a chemical combination of a element within a battery’s cells. Nickel cadmium (Ni-Cd) batteries have a reference, or nominal, voltage of 1.2 volts per cell. Lead-acid batteries have a favoured voltage of 2.0 volts per cell. A customary LiPo dungeon has a favoured voltage of 3.7 volts per cell.

A battery’s sum voltage is given as a mixed of a dungeon voltage, so 6 lead-acid cells make adult a 12-volt battery we lift in a cars. A three-cell series-connected (3S) LiPo is labeled “11.1 volts,” and a 6S battery’s tag is “22.2 volts.” At a state of full charge, a LiPo battery’s voltage will be nearby 4.2 volts per cell, and a cutoff, or smallest allowable, voltage is 3.0 volts per cell.

 

Two 5000mAh battery labels uncover opposite C-rates. The Pulse battery shows a singular 45C rate, while a Turnigy shows a operation from 25C to 50C. While it’s not settled explicitly, I’d yield a reduce as a continual rating and a aloft as a 30-second rating. Note that conjunction tag specifies a assign rate.

The labels for these batteries both uncover appetite ability in watt-hours in further to a storage ability in amp-hours. The E-flite tag specifies a charging voltage, while a ElectriFly specs a assign current.

STORAGE CAPACITY

A battery’s storage ability (C) is described as a volume of assign that it can broach over a duration of time while staying above a cutoff voltage, and is fundamentally dynamic by a distance of a battery. In general, bigger LiPo batteries have some-more capacity, as do bigger Ni-Cds. Capacity is totalled in amp-hours (Ah) or milliamp-hours (mAh), and those are tangible by a series of hours that a battery can yield a given liberate current. This means that a battery with a ability of 1Ah is able of providing a stream of one amp for one hour before it gets to a cutoff voltage. It can also yield 500mA of stream for dual hours, or dual amps for half an hour. Josh Barker of MaxAmps arguable for me that a attention customary for labeled ability is a one-hour liberate rate.

Storage ability varies; it isn’t a constant. Increasing liberate stream will diminution a battery’s ability as will heat extremes. It’s also value observant that we frequency use a battery’s full ability anyway as doing so competence means repairs to it and digest a lifespan. we time my flights so that we land when a battery is nearby storage voltage: 3.8 volts per cell. That leaves about 45 percent of a ability unused, though it allows a reserve domain for unsuccessful alighting attempts and it’s easy on a batteries. It’s also easy on me since we don’t have to assign or liberate to storage levels once I’m finished flying.

USES OF “C”

In all batteries, ability is used to conclude several other rates, such as assign and liberate rates, and this is where things can get a tiny confusing.

Charging a battery wrongly can repairs it, so manufacturers mention a protected limit assign rate in multiples of C. With a LiPos we use, a 1C assign rate is roughly always protected and easy on a batteries. Some manufacturers mention aloft assign rates. For instance, Pulse Batteries and MaxAmps mention a 5C assign rate, so I’d be gentle regulating that rate from time to time. For slight charging, we hang to a gentler 1C rate since we consider that it helps a batteries final longer.

The tenure “C-rate” is used to conclude a liberate stream for a battery. As with assign rates, this series is specified as a mixed of C, such as 20C. Sometimes a tag will uncover a range, like 25–50C, and infrequently it will uncover continual and pulse, or 30-second rates. A continual C-rate is a limit liberate stream that a battery can yield for a full discharge, from full assign down to a cutoff voltage, but deleterious a battery. The 30-second C-rate is a liberate stream that a battery can supply for short-term pulses adult to 30 seconds but deleterious a battery. For a 5000mAh 25-45C battery, that means a continual stream of 125 amps and a beat stream of 225 amps.

This aged Astro Flight Whattmeter has served a author good over a years. Knowing current, voltage, and energy allows a modeler to endorse that a energy complement is within a battery’s specs to equivocate damage. Watt meters are accessible during many RC vendors.

How these limit liberate currents are dynamic is a bit of a poser to me. I’ve talked with people during several companies about it, and there isn’t a unchanging answer. In many cases, a boundary are tangible by a dungeon manufacturer to demarcate excessively high currents that would repairs a battery. Things like dungeon chemistry, dungeon construction, intercell connections, inner resistance, and handle distance all have an impact on a final limit stream rating for a battery.

This information record from a Castle Creations Edge HV 120 in a author’s Top Flight Corsair shows voltage and stream graphs for a initial flight. A limit stream of about 58 amps and limit energy reduction than 3000W meant that a energy complement is good within a boundary on this flight.

I try to set my models adult with assuage stream demands, for reasons I’ve discussed before. An advantage of doing this is that we don’t have to worry about illusory C-rates causing problems for me. If we keep my limit stream to 75 amps or less, a battery rated during 25C is sufficient for incomparable planes. They’re reduction costly and final a prolonged time since we don’t highlight them much.

If you’re meddlesome in some-more ubiquitous information about batteries, there are copiousness of arguable sources on a Internet. One that I’ve found useful from time to time is batteryuniversity.com, and MIT’s Electric Vehicle Team has a good beam to battery definitions as good (web.mit.edu/evt/summary_battery_specifications.pdf). A some-more in-depth contention of LiPo science that relies heavily on Internet forum sources is “Learning About LiPo Batteries” by Ken Myers, accessible during theampeer.org.

BuddyRC AB Clips

One of a many irritating things about charging batteries is removing a JST-XH change lead plugged into and out of a change board. The block bodies are tiny and sincerely thin, and when they’re stranded in a socket, they can infrequently be tough to hold good adequate to lift out easily. Resorting to a organisation lift on a wires risks pulling them out of a cosmetic block and causing a brief circuit in a change leads. Trust me, I’ve finished it and it’s no fun.

BuddyRC’s AB Clips solve that problem, and they do it cost effectively. The one-piece molded polypropylene shave snaps firmly around a change block and a wires, combining a incomparable square that’s many easier to grip. That creates it easier to bond and undo a change leads with no risk of damage. I’ve got them on all of my batteries now, and we haven’t pulled a handle out of a block in a prolonged time.

Available to fit 2S by 6S change plugs, a AB Clips come in packages of 5 for a unchanging cost of $1.95. buddyrc.com

BY JOHN KAUK

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