A Guide to Battery Chargers for RC Modellers and Pilots

So, you've bought your first lithium polymer battery or your first pile of packs for your new racing quadcopter or RTF plane and they're sitting on your bench, intimidating you. Sooner or later you will need to charge them, balance them and even perform such wizardry as a storage charge. Further down the line you might find that a particular size of battery suits your models perfectly and decide to parallel charge a load of them in one charge, so you can fly for hours without charging. Let's get stuck in.

Maybe you already have a charger or something that said best charger in the description that you read the first paragraph of. If you already have a charger and you know how it works and what it will do, this article might help you choose a better one. This article is for those who bought the first charger they saw, or are looking for a new one. Battery chargers these days are usually capable of handling a multitude of different chemistries such as lithium ion, nimh, lead-acid and lithium polymer. This guide has a huge leaning towards using them with lithium polymer chemistries because that is what we use with our model planes and quadcopters.

lipo battery charger guide
We'll help you put the lipo battery charger jigsaw together

Things to know before looking for a charger

  • How fast do I want to charge my batteries?
  • How many cells will I be charging?
  • Do I want to use the charger at the field, in my workshop, or both?
  • Budget. Of course this is often hard to decide without a good understanding of what is available. Expect to pay more if you want to charge your batteries faster or need support for higher cell counts.
  • Connectors. Know the connectors on your existing packs, or the connectors typically used on the batteries you expect to buy in the near future. Modellers typically stick to one or two types of connector but it's handy to know if a charger includes charge leads that will support your existing packs (if any).

The different types of lipo battery charger?

Battery chargers for lipo batteries generally fall into one or more of a few categories: -

Mains powered chargers
AC or mains powered battery chargers are useful, because you can plug them in to your wall and start using them straight away in your garage, or your shed (and if you have mains power in your shed, we're jealous). These devices are basically two-in-one, in that they have a power supply integrated with the charger. A power supply or PSU is another device which takes your mains power (i.e. 110-240V AC) and turns it into usable DC power for the charger). Typically, AC powered chargers are relatively low in power output compared to their DC powered counterparts. We suspect the main reasons for this are to keep weight down and to keep the size of the thing manageable. The alert reader may have noticed we just mentioned power output, more on that shortly.
Tip: Do not leave a charger switched on or powered up, especially mains powered units as we have found this is a great way to shorten the lifespan of the internal power supply.
DC powered chargers
DC powered chargers rely on an external power source like a car battery, leisure battery or PSU. This type of device is often more convenient because they are usually lighter and thus more portable, but also more portable in the sense that they can be powered from your car if you're out flying at your club field. Another great advantage with this type is that you can even power them from another lipo battery, which is especially convenient if you are only flying mini quads with relatively small batteries. DC powered chargers typically support much higher power outputs than their AC powered counterparts. Of course it is up to you to supply the appropriate power source to achieve this, which is discussed in another section below!
AC/DC powered
Some chargers support both AC and DC power to provide the best of both worlds. Consider these if you want a charger to use in the shed that you can also take to the field with you. Some people already have a generator that they can use to power an AC charger and some prefer just to buy a smaller DC powered charger for portability.
Multi-channel or multi-port chargers
There are many convenient chargers on the market these days which have more than one output port. These allow you to charge multiple batteries simultaneously and normally independently, meaning you can charge for example a lipo battery on one port and a NiMH battery on another. These also allow charging for example packs with completely different configurations at the same time because each port or channel usually operates as if it is a completely separate charger.

Some great examples of these chargers can be found in our shop: -

What features to look for in a battery charger?

As well as complex specifications indicating the performance available, many chargers have slightly different features. At the very least, you should look for a charger with the following: -

Standard output ports
These are almost always 4mm banana jacks, but it's worth checking to be sure. You don't want to be buying charge leads and then doctoring them every time to fit your quirky charger.
Balance ports or support for balance charging boards
Smaller chargers often have integrated balance sockets to directly connect the battery but more accomplished devices usually have their own socket and include a separate balance board which can be swapped out depending on the manufacturer of the battery. Typically these days, most lipo manufacturers have standardised on the JST-XH/JST-XHR standard, which is a little white plug with an extra wire on top of the number of cells in the pack (e.g. a 3s pack will have 4 wires) so this makes life much easier.

chargers with standard features
Image showing various chargers with the standard charge output ports and balance sockets visible

Despite becoming more and more intelligent, power requirements during the last 10 years or so have actually dropped, with many people flying racing drones or small quadcopters which typically use something like a 1300mah 3s lipo, these only need about 20W to charge in an hour compared with your average 2200mah 3s pack which needs about 30W. Read on to understand more about your power requirements and try to find a charger that fits in your budget and hits or comes close to meeting your power requirements.

Charger specification gibberish, or what do all those numbers mean?

If you look beyond the initial quagmire of seemingly meaningless numbers associated with any chargers you see while shopping, there are 4 important attributes that will almost immediately indicate its capability to you. Let's look at these attributes now: -

Power supply type
This refers to the type of power input the charger needs to work its magic. Either AC, DC or both
Maximum power output
Measured in Watts. Also referred to as "maximum charge power output". This is often abbreviated to things like "100W battery charger" but usually incorporated in the name of the device, e.g. the “SkyRC D100” is capable of 100W output. Various manufacturers tackle this attribute differently, iCharger for example name their chargers using the supported charge current and maximum cell count, for example the iCharger 106 can charge at up to 10 amps and supports up to 6s packs.
Maximum charge current
Measured in amps. This is usually something like 2 amps or even 10 amps (Some, like the iCharger 4010 will go up to 40 amps with the right power supply!). Just note that the maximum current will be limited by the maximum power output. More on this later, but if we assume 100% efficiency, a charger with a maximum power output of 40W (40 watts) and a maximum charge current of 5 amps is only going to charge a 3s pack at a maximum of around 3 amps. (3 multiplied by 12.6V is about 40 watts. Conversely, this same setup would only charge a single cell lipo at a maximum of 5 amps, because it will not exceed this, despite there being headroom in the power output to get nearer 10 amps.
Maximum cells or voltage
Most chargers will charge packs up to 4s or 6s but some will do up to 8s and 10s. This is usually measured in "s" referring to the number of cells in series. Referring to the the Junsi iCharger range, for example, the 306b can charge up to 6s lipos up at up to 30 amps. Always refer to individual charger specifications to be certain.

How to choose a power supply for my charger?

If you are using a DC powered charger (One that needs a leisure/car battery or generator to power it) you should be aware that most DC powered chargers are only around 80% efficient at converting their input power into power that will go into your batteries. To get the most from a 100 watt charger for example, you should look to employ a power supply with an output power of at least 125 watts (100W / 80% = 125W) to compensate for this inefficiency.

Do's and Don'ts for taking care of your charging equipment

If you take care of the circuits in your charger (and power supply) they will provide you with many hours of trouble-free operation. Over the years we have learned a good bit about dealing with these devices, in summary: -

  • SAFETY FIRST – ALWAYS be aware of your surroundings and your equipment. If in doubt, ask someone more experienced.
  • ALWAYS power up your charger BEFORE connecting a battery or batteries for charging
  • ALWAYS use good quality charge leads with no exposed contacts or breaks in the wire
  • ALWAYS connect the main battery pos/neg wires to your charger and then connect the balance connector to the balance board or appropriate socket on the charger
  • ALWAYS get into the habit of double-checking your battery cell voltages before and after a charge and before/after you fly
  • ALWAYS take care of your batteries, for example don't leave lithium polymer batteries fully charged as this has been shown to be detrimental to their useful lifespan
  • ALWAYS familiarise yourself with the safety features of your charger (e.g. capacity cut-off or maximum charge time cut-offs)
  • NEVER charge lithium batteries unattended
  • NEVER leave your charger powered up after use

Frequently asked questions

What is a parallel charging board?
A special board, usually with integrated charge ports and balance sockets so that you can connect one or more of your lipo batteries directly to the board. The idea is that this board is then connected to your charger as if it were itself a single battery with a total capacity equal to the capacity of all the packs connected to the board. Special care should be taken to understand the correct way to use these boards and ensure you keep you and your equipment safe.
What is a balancing board?
A balancing board or balance board is where you connect the so-called balance tap or balance connector of your battery to the charger. Many chargers include balance boards but some, such as the B6 Mini have the balance sockets on the side of the charger. Separating the sockets from the charger via a balance board is a handy way for manufacturers to support different types of balance connector. In recent years, many lipo manufacturers have standardised on the JST-XH type connector although these boards are still prevalent.
What does JST-XH or JST-XHR mean?
JST stands for Japanese Solderless Terminal. The XH part of this term refers to the typical, now almost standard type of little white balance connector on the majority of battery packs. Historically there were about three different types of balance connector: Multiplex/ThunderPower/Enerland, Graupner/Kokam and ‘Everything else’. If you had batteries from these different manufacturers, you ended up with quite a few different balance boards and headaches if you went to the field with the wrong one. These days, thankfully JST-XH is almost the norm among batteries.
What is a storage charge?
Storage charging lipo batteries is the process of hooking them up to your charger and charging or discharging them so that they are at around 3.85V per cell. This is considered the best resting voltage that does not harm the useful lifespan of the battery. Storing lipo batteries at full charge or depleted below this voltage is considered detrimental to the performance and longevity of the pack. Many chargers these days have a special setting to perform a storage charge automatically and will charge or discharge and balance the pack appropriately in order to bring each cell to this 3.85 volts.
What is parallel charging?
Parallel charging can be a time-saving process where by your lithium batteries with the same cell count and capacity are connected in parallel and then charged together at the same time. Packs connected in this way are seen by your charger as a single battery with a capacity equal to that of all the individual battery capacities added together. There are various caveats to this process and we won't go into detail here. Parallel charging boards are available which help signficantly with this process and we find it very convenient when flying with the same packs to charge 2 or more at the same time, this is especially advantageous for higher power chargers where the packs can be charged in the same time that it takes to charge a single pack.
Read more about parallel charging
Can any charger do parallel charging?
Yes! Almost any charger can charge packs in parallel, ultimately your charger is only aware of there being a potential difference between the positive and negative connections on its output ports, so it doesn't really care what is there. Even the humble Imax B6 Mini is capable of parallel charging despite its relatively low charging power. How effective your charger is at charging packs in parallel is generally down to its maximum output power and/or charge current. You can use our handy little calculator below to see how much power you need to charge a given number of batteries in parallel. Many people prefer the simplicity of using a multi-port (often refered to as multi-channel) charger for simplicity, for example the SkyRC Q200 has 4 ports and splits its 200W output power between them.

parallel charging board example
Image showing an example parallel charging board

Calculator for parallel charging

charge rate (C)
Required charger power:

Further Reading

Here are some useful links to help you understand more and get the best from your batteries and chargers

email: info@electricwingman.com
© 2008-2020 electricwingman Ltd, United Kingdom