This is essential for the care of your battery - if you let your battery fall to low in voltage, the battery will become permanently damaged and unusable. This wire will be the one farthest away from the red wire. The red wire should match up to the 3s pin. It will then cycle through various measurements. You can push the button on the battery monitor to change the voltage that the alarm will sound or even turn it off. You can change the monitor to values between 2.
We recommend the default setting of 3. The harness also has a switch to easily shut power off to the ArbotiX Robocontroller. This allows us to compare the properties of a battery and help us determine which battery pack is suitable for the need at hand. There are three main ratings that you need to be aware of on a LiPo battery. So what does it all mean? Let's break it down and explain each one. A LiPo cell has a nominal voltage of 3.
For the 7. This is sometimes why you will hear people talk about a "2S" battery pack - it means that there are 2 cells in S eries. So a two-cell 2S pack is 7. I thought mistakenly that this was common knowledge, but after a handful of emails on the topic, it was clear I needed to clarify what nominal voltage is.
Nominal voltage is the default, resting voltage of a battery pack. This is how the battery industry has decided to discuss and compare batteries. It is not, however, the full charge voltage of the cell.
LiPo batteries are fully charged when they reach 4. In the early days of LiPo batteries, you might have seen a battery pack described as "2S2P". This meant that there were actually four cells in the battery; two cells wired in series, and two more wired into the first two batteries in parallel parallel meaning the capacities get added together.
This terminology is not used much nowadays; modern technology allows us to have the individual cells hold much more energy than they could only a few years ago. Even so, it can be handy to know the older terms, just in case you run into something with a few years on it. The voltage of a battery pack is essentially going to determine how fast your vehicle is going to go.
So if you have a brushless motor with a rating of 3,kV, that motor will spin 3, RPM for every volt you apply to it. On a 3S, it will spin a whopping 38, RPM. So the more voltage you have, the faster you're going to go. The capacity of a battery is basically a measure of how much power the battery can hold.
Think of it as the size of your fuel tank. The unit of measure here is milliamp hours mAh. This is saying how much drain can be put on the battery to discharge it in one hour. Since we usually discuss the drain of a motor system in amps A , here is the conversion:. I said that the capacity of the battery is like the fuel tank - which means the capacity determines how long you can run before you have to recharge. The higher the number, the longer the run time. But there are companies that make batteries with larger capacities.
Traxxas even has one that is over mAh! That's huge, but there is a downside to large capacities as well. The bigger the capacity, the bigger the physical size and weight of the battery. Another consideration is heat build up in the motor and speed control over such a long run. Unless periodically checked, you can easily burn up a motor if it isn't given enough time to cool down, and most people don't stop during a run to check their motor temps. Keep that in mind when picking up a battery with a large capacity.
Q: Why do we use voltage, and not capacity, to determine how charged a battery is? A: The reason we use voltage to determine the charge level of a battery stems from our difficulty in measuring capacity.
Voltage is simple to measure — if you've ever used a voltmeter to measure a AA battery, you understand how trivial it is to measure voltage. Capacity, however, is nearly impossible to measure accurately. We can measure how much energy is going into a battery at least somewhat accurately , but we can't measure how much is actually in the battery. Think of it like beakers of water. For voltage, the beaker is transparent, and we can easily see the amount of water in the beaker in the same way we can measure voltage whenever we like.
On the other hand, we have the beaker representing capacity, and it's opaque — we can't see through it, and so the only way to know how much is inside is to empty it and measure the water energy as it's leaving the beaker battery. Because amperage and voltage are intertwined, as we will discuss later in detail, the voltage of a battery does correlate, approximately, to the capacity left in the battery, and while there are times when the voltage can deceive you, in general, it's okay to rely on voltage as our primary measure of how full a battery is.
This question was asked by Donald via email, and made complete sense to include my answer to him on the guide. Thanks, Donald!
Voltage and Capacity had a direct impact on certain aspects of the vehicle, whether it's speed or run time. This makes them easy to understand. The Discharge Rating I'll be referring to it as the C Rating from now on is a bit harder to understand, and this has lead to it being the most over-hyped and misunderstood aspects of LiPo batteries.
The C Rating is simply a measure of how fast the battery can be discharged safely and without harming the battery. One of the things that makes it complicated is that it's not a stand-alone number; it requires you to also know the capacity of the battery to ultimately figure out the safe amp draw the "C" in C Rating actually stands for C apacity.
Once you know the capacity, it's pretty much a plug-and-play math problem. Using the above battery, here's the way you find out the maximum safe continuous amp draw:. The resulting number is the maximum sustained load you can safely put on the battery. Going higher than that will result in, at best, the degradation of the battery at a faster than normal pace. At worst, it could burst into flames. So our example battery can handle a maximum continuous load of A.
The Burst rating works the same way, except it is only applicable in second bursts, not continuously. For example, the Burst Rating would come into play when accelerating a vehicle, but not when at a steady speed on a straight-away. The Burst Rating is almost always higher than the Continuous Rating. Batteries are usually compared using the Continuous Rating, not the Burst Rating.
There is a lot of vitriolic comments on the Internet about what C Rating is best. Is it best to get the highest you can? Or should you get a C Rating that's just enough to cover your need?
There isn't a simple answer. All I can give you is my take on the issue. When I set up a customer with a LiPo battery, I first find out what the maximum current his or her application will draw.
Let's look at how that works. However, the ratings on the motor aren't the whole picture. The way the truck is geared, the terrain the truck is driving on, the size of the tires, the weight of the truck It's very possible that the final draw on the battery is higher than the maximum motor draw.
So having that little bit of overhead is crucial, because you can't easily figure out a hard number that the truck will never go over. For most applications, a 20C or 25C battery should be fine. But if you're driving a heavy truck, or you're geared up for racing, or you have a large motor for 3D flying applications, you should probably start around a 40C battery pack. But since there is no easy way to figure this out, I encourage you to talk to your local hobby shop to have them help determine which battery pack is right for your application.
There is one very important rating we haven't talked about yet: Internal Resistance or IR. Problem is, you won't find the IR rating anywhere on the battery. That's because the internal resistance of a battery changes over time, and sometimes because of the temperature. However, just because you can't read the rating on the battery doesn't mean it isn't important.
In a way, the internal resistance is one of the most important ratings for a battery. To understand why the IR is important, we have to understand what it is. In simple terms, Internal Resistance is a measure of the difficulty a battery has delivering its energy to your motor and speed control or whatever else you have a battery hooked up to.
The higher the number, the harder it is for the energy to reach its preferred destination. The energy that doesn't "go all the way" is lost as heat. So the internal resistance is kind of a measure of the efficiency of the battery. Measuring the IR of your battery requires a special toolset. You either need a charger that will measure it for you or a tool that specifically measures internal resistance.
Given that the only tool I have found for this at least in the hobby world is almost as expensive as a charger that does this for you, I'd go with a charger for this process. Some chargers measure each cell's IR separately, and some measure the entire battery pack as a whole. Since internal resistance is a cumulative effect, and the cells are wired in series, if you have a charger that does each cell independently, you need to add up the IR values of each cell, like this:.
Suppose we have a 3S 3-cell LiPo battery, and the measuring the cells independently yields these results. To find the total internal resistance for the battery pack, we would add up the values for the three cells.
Either way, the goal is to have the IR for the entire pack. The first reason internal resistance is important has to do with your battery's health. As a LiPo battery is used, a build up of Li2O forms on the inside terminals of the battery we'll go more in depth on this later in the Discharging section. As that build up occurs, the IR goes up, making the battery less efficient. After many, many uses, the battery will simply wear out and be unable to hold on to any energy you put in during charging - most of it will be lost as heat.
If you've ever seen a supposed fully charged battery discharge almost instantly, a high IR is probably to blame. It says that the current Amps through a conductor between two points is directly proportional to the difference in voltage across those two points.
In the formula, the resistance is measured in Ohms, not milliohms, so we'd have to convert our measurements. If we use our previous 3S LiPo, and plug it into the equation along with a 1A draw, we can find out how much our battery pack's voltage will drop as a result of the load. First, we have to change the equation to solve for volts, which would look like this:. So our battery would experience a tiny drop in voltage when a 1A load is applied.
Considering our 3S LiPo is around Well, let's see what happens when we increase the load to 10A. Now we see that when we increased the load 10X, we also increased the voltage drop 10X. But neither of these examples are very "real world". Let's use the Slash VXL from the previous section and plug those numbers in. If you recall, our Velineon motor has a maximum continuous current rating of 65A. Let's assume we manage to hit that mark when driving and use that.
That's around 6. Pretty respectable, but it's still a reasonable drop in voltage. But so what? What does that actually mean? That means it spins 3, RPM per volt.
On a fully charged 3S LiPo we'll see this assuming no voltage drop :. Now, assuming we can hit that 65A draw on our unloaded motor which we can't in real life, but for the purposes of demonstration we can , here's the RPM on the same motor with our voltage drop from before:.
See the drop in performance? That's the effect Ohm's Law has on our hobby. A lower internal resistance means your car or truck or airplane or boat or helicopter goes faster and has more power. This is the stage of constant voltage. While the charging voltage is maintained at the maximum pack voltage, the flow of current continues owing to the difference between the pack resting voltage and the charge.
With the rise in resting voltage, the difference narrows down until it comes quite close. The charge current drops more during this phase. Finally, when both the voltage and charge current reach their specified values, the charging cycle completes. Nearly all new LiPo chargers are equipped with cell balancers. Older chargers might need an external balancer so that balance charging can be ensured. The balancer makes use of the LiPo balance connector for accessing each individual cell.
When it is connected, it can monitor the voltage of these cells and discharge high cells if the need arises so that all the cells can be at the same voltage.
If you are not sure that your charger is provided with a balancer, there is a simple way to find out. If you have to plug in balance leads to your charger from the battery, it indicates that your charger has a balance function. On the other hand, if you merely use the main connector with your charger, your charger lacks the function of balancing.
Using the main lead for your charger implies that the voltage of the whole battery is read and not individual cells. Therefore, you will need to use a battery monitor to make sure that you do not encounter any problems with the battery. You also have the option of getting separate battery balancers for your LiPo cells so that the voltages of each cell are equal.
However, if you get a new LiPo charger, it is quite unlikely that you will have to worry about balancers. How do you balance a LiPo battery? As the cells get close to the maximum charge of 4. Fast Charge Some chargers have a fast charge feature which in my opinion is more of a gimmick than a useful feature.
Fast charge allows you to save abit of time when charging your battery as it will skip the balancing step. In fast charge mode the charger will only look at the overall voltage of your battery and will stop slightly below the maximum charge for safety reasons as the battery might not of been perfectly balanced at the start of the charge. This is only usefull if you want to get flying int he air, but in reality this does not save much time over a proper balance charge so to get the most life out of your batteries its best to always use the balance charge.
Another useful feature that some chargers have is the Lipo storage mode. What I normally do is after a flight, if I know I am not going to fly for a few days I will use the storage mode on my charger to half charge the batteries. Then when I know I am going to fly again I will fully charge the batteries before heading out to go flying. They are set to beep when the voltage of your battery gets low so you know to come and land.
But some like the battery alarm pictured below include a display that will show you the voltages of each individual cell, as well as the overall voltage of your battery which makes it a very quick and convenient way to check your battery voltage before going out to fly. Digital Multimeter Since most drones are electronic devices, having a multimeter is a great resource to help debug problems etc… They are actually not that confusing to work and its a great resource is check your battery cell voltages, and testing for cold solder joints.
If you are not sure how to use one, check out the video in our how to use a multimeter guide. These are fireproof bags that you can use to safely store and transport your batteries. Always better to keep things safe. I hope that you found this guide of some value, but if you have any questions just ask them below and I will be happy to try and help To be honest I cant remember the last time I looked at the screen as I always just unplug the battery after I hear the music tone.
Hey Thanx for the info above. No that will not work if your lipo charger does not support 6 cells. The charger needs to monitor the voltage of each cell in your lopo, otherwise over time the you could end up over charging a single cell and damaging your battery, or worse, causing it to explode. How about LiFePO4 battery packs? I am quite confused, please shed some light on this Thanks! A lot of people who go out and buy a drone me included discover the battery issues and mysteries and all the wires and baby-sitting needed for the LiPo batteries are akin to looking for the Seven Cities of Cibola.
Years ago I actually built a real airplane took 2 years and installed the fuel system and valves, the avionics, electronic ignition, installed the engine, transponder and when it was all done, hauled it to an airport and made an appointment for an FAA inspector to come and inspect it.
After he approved it, I then had to fly it! And you gotta hook up a USB cable from the charger to your computer? And you gotta balance the batteries?
People buy cars with automatic transmissions these days to simplify driving. Thanks for sharing your perspective and also very impressive that you built your own plane!
0コメント