How to choose an RC LiPo charger

TLDR – This article went on long than I planned.  If all you want is a short rule of thumb here is it –  You need 25W of charge power for each LiPo cell, for a 5amp charge rate.  One 2s = 50w, one 3s = 75w, two 3s at the same time (or one 6s) needs 150w, and if you want to charge 2 6s at the same time, plan on at least 300w.  Why 25w per cell, and why 5amp charge rates? Read on to find out!

So, you just got your first RTR RC car! It had everything you needed in the Box including a basic charger, but now three days later, you are sick of waiting all day to recharge the battery. Or maybe you bought an RTR that did not come with a charger, and now you are searching for that “just right charger” to go with your new RC. Either way, all the available choices can leave your head spinning, if you don't know what is important.

In this article, I am going to look at some important factors to take into consideration when choosing a new charger. Primary, I will be addressing the New Guy, but if you have been in the hobby for a few years and are looking to upgrade your charging station, there will be some good info in here for you too. Also, I'll take a quick look at a few Chargers on the market, to show in which situations they would be useful in real life.

So how do we start this journey of looking for a new charger? First, we must address a few key questions:

  1. What batteries do you currently have now?
  2. What kind of future needs will you have?
  3. Lastly, maybe most importantly, what is your budget?

Once we've answered these three questions, we'll can a look at a few popular Chargers on the market today and see how they fit various requirements.

What batteries do you currently have now?

What kind of batteries do you currently have? With most of the modern chargers, can you charge a wide variety of chemistries, so this is not normally a huge issue. However, it does need watching, as some basic chargers can only charge one chemistry type. Note down your battery chemistry – Nickel Metal (NiMh), Nicad, LiPo, LiHV? What is the capacity of the batteries (in milliamp hours or mAh). This can be very important, as larger capacity batteries will need a more powerful charger. Also, what is the cell count and total voltage of your battery? Again, the higher the voltage, or cell count, the more powerful charger you will need.

Last – take note of any special battery types you may have. This could include loose cells (AA’s or 18650 cells), or batteries with non-standard connectors. Charging of loose cells is mostly outside the scope of this document, but it still needs to be noted and addressed when choosing a charger. For non-standard plugs, you can often have a Local Hobby Shop (LHS) solder up a special charge lead for you, but in many cases, it is better to change the plug on your batteries and car over to a more standard plug.

What kind of future needs will you have?

Future Needs. Take some time thinking about this. Do you see yourself simply sticking with this one RC and it’s included battery, playing happily with it for years to come? Do you see yourself dropping the Hobby in 6 months?

If either of these are true, then you probably will only need a very basic charger. On the other hand – do you see yourself, like so many of the rest of us, expanding your RC garage over the next year or three?

A charger is one of the few pieces of RC equipment that should really be looked at as an investment into your future RC hobby. A good charger with sufficient power and multiple channels will support your Hobby Habit for many years to come. But a weaker powered charger that lacks some basic features will need to be replaced in a few months, essentially wasting your money now. This leads right into Point Number Three.

What is your budget?

I know, the standard response to this question is always “as little as possible”. But give this question some real thought and try to attach a dollar sign with it. You can buy a basic single channel 50 watt charger with full features for about $50. You can get them for a bit less, if you are willing to buy an off-brand or cloned charger. However, with the clone, you will often lack the warranty support if something goes wrong down the road.

If item number two (Future Needs) comes true, and you begin buying more RC cars and more batteries over the next year or two, that basic charger will quickly not be able to fulfill your needs. Especially if you are a parent, you should really think hard about buying a charger that can charge more than one battery at the same time, as you will quickly want to get a second car so that you and your children can run together.

When this happens, you will either need another $50 charger, or spend half the day waiting on your batteries to charge so you can all run together. Also, if you later decide to get a car that needs two batteries (like a 1/8 scale monster truck), having a 2-channel or 4 channel charger will make charging the large amount of batteries you need much quicker.

More channels, more power, adds up to more money. There is no getting around that. However, as a secondary effect, these higher power multi-channel chargers often have a pretty good resale on these use RC marketing. If you decide to get out of the hobby, you will be able to get it some if not most of your money for that nice charger back.

Now on to some Nuts and Bolts. So how do we go about figuring out how much charger we need for our batteries? The short answer is math – but this is easy math, so don’t worry.  The basic formula is Volts times Amps equals Watts (V * A = W). Take the battery pack voltage, and multiply it by the desire charging amps, and you get the wattage needed to charge that pack. So, to charge a 2s lipo (7.4v) at 5amps you need 7.4v * 5a = 37watts, while a 4s battery would need 74watts for the same 5 amp charge rate.  

If all you want is a short rule of thumb here it is – You need 25W of charge power for each LiPo cell, for a 5amp charge rate.

How do you know the proper charge amps rate, though? For this, it is a fairly simple rule of thumb. Unless you know your battery is rated otherwise, use the 1C charge rate rule. 1C is equal to 1 times the batteries capacity in amp hours.

Most batteries have milliamp hours listed on the label, so divide that number by 1000 to get amp hours. A 5000 milliamp hour battery is equal to 5 amp hours. So a 1C charge rate for this battery would be 5 amps. Some batteries will allow a 2C or even 5c charge rate. To find this charge rate, again multiply amp hours times the C rating, and you get the maximum amps to charge the battery with. So with that same 5000 milliamp hour battery, a 2C charge rate would be 10 amps, and a 5c charge rate would be 25 amps.

With chargers, watts = money, so why would we want to charge at more than 1C?  The short answer is Time. 1C charging will normally charge a battery in about one hour.  2C will charge twice as fast – 30 minutes, and 4c charging can have your batteries ready in 15 minutes!  Also, the same is true on the flip side. If your charge only has the wattage to charge your battery at 0.5C, it will take about 2 hours to charge.  Slow charging your batteries will not hurt them, but if you need to charge several packs at .5C, you may forced to charge all your batteries the day before you want to run, and a last-minute unplanned bash session is out of the question.

Also, I would be remiss if I did not add – don’t fast charge (greater than 1C) unless you KNOW your battery is rated for the higher charge rates. Battery damage, battery overheating, fires, and other bad things are a real possibility if you charge a battery at a higher than it’s rating. Know your batteries and stay within their limits.

So now let's look at how all of this rolls in together. Charger power is based on both amps and watts. If you want to charge a 2s battery at 5amps, you need a charger that is rated for both 5 amps and more than 37watts (we did this math already) – so a basic 5amp, 50w charger is fine.  Similarly, if you want to chare a 4s pack at the same 5amps, you need a charger that is rated both for 5amps and more than 74watts.

Now, with the 4s battery, that basic 5a 50w charger can’t cut it. It will be watt limited to 50w, which at 14.4v is about 3.4amps.  Now to add another layer on to the math – you don’t really want to run any electrical device at 100% output for long periods of time. Plus, there are other factors, like high summer air temperatures, can mean that a 50w charger can’t really put out the full 50w without overheating.

With all this in mind, I recommend adding “Safety Factor” to your charging needs. This means, buy more wattage than you need, by about 20%. With this safety factor in mind, 50w chargers are only good for 2s lipo or 7c Nimh. A 3S needs about 75w, 4s 100w, and 6s, 150w (assuming a 5a charge rate in all cases).

Ok, that was a lot of info. Let’s put it together into some real-world examples and find some chargers that would fit the needs.

Scenario 1: You currently running nickel metal 6 or 7 cell packs and have a capacity of around 2000 to 3000 milliamp hours. You would really like to get some of those big capacity 5000 milliamp hour packs though. In this scenario you can get by with a basic 50-watt single Channel charger.

Most basic Chargers will not have a problem charging nickel metal packs up to 5000 milliamp hour, and they most even have the ability to charge LiPos later if you decide to go that route. Chargers like the Hitec X1, or SkyRC B6AC are good, full featured, inexpensive ($50) choices. If you are on a very tight budget, $25 will get you a Prophet Sport Mini 50W Multi-chemistry Charger (or similar) that can still charge several different battery types, but lacks some features like Discharge, and lipo features like Storage Charge.

If you start looking into off-brand chargers, re-brand chargers, and clone chargers there is a huge selection of 30-80w chargers, many with a full set of features priced between $20 to $50.

Scenario 2: you currently have only the one RTR, with one or two nickel-metal batteries, but after seeing the enthusiastic reception from your kids, or friends, you could see yourself buying another RC car or two soon down the road. Also, you know you'll want lipos very soon, maybe even 3s packs. In a case like this, you'll want to look at Chargers that can charge more than one battery at a time, and that have a bit more than the basic 50 Watts. A 2-channel, or 4-channel charger with 80 to 100 watts per Channel will be more along the lines of what you will need down the road. This will allow you to charge the higher capacity 3s facts quickly and charge several packs at once so that you can have several Vehicles ready to run all at the same time. If you fall into this group, you should be looking at 2 or 4 channel chargers, with wattage between 50w to 100w per channel.

Some chargers to look at:

There are lots of other good choices in this charger size, from Dynamite, Ultra Power, SkyRC and others.

Scenario 3: Maybe you jump right into 1/8 scale, or you find yourself dreaming of a big truck like the Traxxas X-Maxx. Running these big scale cars, you know you'll be needing 4S or 6s batteries, with large mAh capacity. These larger batteries need a much more powerful charger. Plan on looking at a charger that can push a minimum of 200 watts per Channel, with 300 or more being a better goal.

Some cars will use parallel packs instead of single large brick-style batteries. That is to say they will run 2-2s, 2-3s, or even 2-4s packs. If you plan on going this route, you may be able get by with a charger that only needs 100 watts per Channel (for 2s or 3s parallel), but you will be charging twice as many batteries for every run of the car. This makes getting a 2-channel or 4 channel charger even more important.

For larger scale cars, Chargers to look at:

The brand Junsi also has several very nice Big Watt charger, like the iCharger 308Duo (2 x 800w, $270, DC only) but most are DC only.

Speaking of DC power

As you shop for chargers, you will see most of the Big Wattage chargers are DC input only – as are a lot of attractive mid-power chargers.  This means you can’t plug them into a wall receptacle. You will need to either hook them to a 12v car battery or get a dedicated AC to DC power supply – sometimes called Power Supply Units, or PSU for short.  When buying a PSU, you must make sure the PSU is rated for the wattage you will need for your charger – including another safety factor. So if your charger is rated for 2 channels of 300w, you need (300 * 2) + 20% safety factor worth of PSU wattage – about 700w.

There are many hobby branded PSU’s sold by most of the same brands that make chargers. Also, there are several brands, both small home based vendors and big national brands, that convert used / salvaged / reconditioned PSU’s from computers and servers for hobby use.

The advantage of these converted PSU is cost – per watt, they typically cost about half of the hobby branded PSU’s. A Team Trinity (converted) 12vdc 900w PSU runs about $85. A 1500w 24v from an Ebay seller like “lipoconnectionsolutions” can be had for about $80. Compare this to a hobby-designed PSU from Junsi, you get 1200w PSU for $270.  Are the hobby power supplies worth the extra money? Well, that is a personal choice, but I chose a converted PSU for my personal use.

Proper Care of LiPo RC Batteries

The last thing I want to touch on is proper care and feeding of LiPos.  This subject really should be an article of its own, as there is a fair amount of information that is important to understand regarding LiPos. However, I would be remiss if I did not go over at least a few basic LiPo safety tips.

  1. Always use some sort of fire proof container while charging your batteries. Lipos can catch fire, and this most often happens either while charging or while running.
  2. Use a fireproof lipo container when storing a LiPo. Because yes, they can catch fire just sitting there. This is a rarer case, but it does happen sometimes.
  3. Don’t over charge your LiPo. Make sure your charger is in a Lipo mode that will stop when the cells reach 4.2v per cell.
  4. Don’t charge at a higher C-rate than your battery is rated. (we already covered this one).
  5. Don’t discharge a LiPo below 3.0v per cell – this can physically internally damage a lipo cell.
  6. If you have a LiPo that swells up like a balloon – THIS IS A DANGER SIGN!  Take this battery out of service, and store it safely outside, and plan on discharging it and disposing of it as soon as practical. DO NOT try to puncture the plastic cell wrapper, that WILL cause a fire. Yes, there are lots of Youtube videos of people doing this, but it is a “don’t try this at home” kind of thing.

6 Steps to proper LiPo battery care – 1. Always use some sort of fireproof container while charging. 2. Use a fireproof container to store your LiPo battery. 3. Don't over charge your LiPo…

In closing

The RC hobby is about having fun, first, foremost, and always. Charging batteries is a necessary part of the hobby. If you chose a charger that does not fit your needs, you will find yourself spending more time with your charger and batteries than you do driving your car.  If choose the right charger, it will be a seamless part of your kit, something you won’t have to spend a lot of time thinking and stressing over – which will translate into more fun time with your favorite RC’s!

What are your favorite RC chargers? Be sure to tell us in the comments below or in the forums.