How to use Charge 3B

Thank you for buying a Tektite Charge 3B! It’s packed with features, and this blog post guides you through how to use all of them.

If you have any questions, thoughts, problems, or just want to share your experience, feel free to reach out in the #charge-3b channel in the Tektite discord: https://discord.gg/6uq7kxy6FZ

Plugging it in

To use Charge 3B, you need at least a 65W USB-C brick, but ideally you should use a 100W brick for full battery charging speed. Charge 3B automatically detects the wattage of the charger, and if it is exceeding the maximum it will reduce the charging speed. For example, when using a 65W brick and trying to charge 3 batteries on Turbo Mode (2A), the current indicator becomes red to indicate the power is limited to 1.6A:

Power is limited when using bricks under 65W

If the brick is not a 100W or higher brick, this is indicated when Charge 3B is first turned on. For example, many MacBook bricks only output 94W (even when they are advertised as 96W, since they output 20.5V):

Another issue you may have is with the iPhone braided USB-C cables. Those cables (and some other ones) have chips inside that limit the current available, so even if you are using a 100W brick, Charge 3B will still only have 60W available:

The Charge 3B can only use 60W, even with a 100W brick, due to the cable limiting the power

Once you have a suitable brick and cable combo, you are ready to use Charge 3B!

Charge 3B’s user interface

Here is how Charge 3B looks when turned on:

There are 3 sections, one for each charging port. The left section of the screen corresponds to the left charging port, the right corresponds to the right charging port, and so on. Each section of the screen / port is controlled independently, so you can use multiple different features at the same time.

Each port has a list of menus that you can scroll through. To scroll to the next menu, press the bottom part of the screen. For example, to go to the next menu (Fast charging mode) for the middle port, you would press here:

You can press on the top section to go back a menu. For example, to go to the previous menu (Slow charging mode) you would press here:

Once you select a menu, you can plug in a battery. Once the battery is plugged in, you can not switch menus! If you are in normal mode and you want to go to fast mode, you would have to un-plug the battery, switch to fast mode, and plug the battery back in.

The charging modes

4 of the menus are charging modes:

• Slow (0.8A)
• Normal (1.2A)
• Fast (1.6A)
• Turbo (2.0A)

The number is the amount of current being used to charge the battery. Using more current means the battery will charge faster, but it also means the battery will heat up more while charging which over the long term is bad for battery health. Because of this, I recommend using Normal or Fast mode to charge batteries during practice and Turbo for competitions, where you need your batteries charged quickly. When you plug in a battery while in one of the charging modes, the battery will automatically begin charging:

There are 5 numbers shown:

1. Voltage — The current voltage of the battery. Although every battery charges to a different level (and batteries in worse health charge to lower voltages generally), a voltage around 14 is usually approaching being full while 10–12 is low. This is the same voltage shown in the driver station.
2. Current — The amount of current going into charging the battery. This should correspond to which charging mode you’re using, but can vary if the battery connector is loose or you just plugged in the battery.
3. Power — The number of watts going into charging the battery. This is just voltage * current.
4. Charge time (hours:minutes:seconds) — The amount of time the battery has been charging for.
5. Charger temperature — This is not the temperature of the battery! This is the temperature of the charging circuit inside of Charge 3B. This shouldn’t go over 100 C.

The main one to look at is voltage, which sort of acts as a progress indicator for how charged the battery is. If you have 3 batteries in charge and you need to get the most charged one, you can generally just grab the one with the highest voltage.

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When done charging, the menu turns green and Charge 3B enters TOP-UP mode (shown below), where a small charging current is applied to keep the battery voltage high. This shuts off after an hour, at which point Charge 3B fully disconnects the battery and the screen simply says DONE.

Internal resistance (IR)

When you start driving or stall a motor on your robot, you will notice that the voltage of the battery goes down, but goes back up when you stop stalling the motor / driving. This is because the battery voltage drops when drawing current. For every amp of current drawn, the amount of voltage drop is equal to the internal resistance of the battery. For example, if the internal resistance is 0.100 ohms (100 milli-ohms), if a motor is stalling and drawing 9 amps, the battery voltage will drop 0.100 * 9 = 0.9V. Since voltage drop negatively impacts the performance of your robot, you want to use batteries with low internal resistance.

Charge 3B allows you to measure the internal resistance of your battery, which is often a good sign of the health of the battery. A lot of high-temperature charging, age, and use can all contribute to internal resistance becoming higher. To measure the internal resistance (IR), switch to the IR mode and plug in the battery. Charge 3B will cycle through various currents and average out the voltage changes to calculate IR.

⚠️ FOR MOST ACCURATE MEASUREMENT, MEASURE IR WHILE THE BATTERY IS DISCHARGED A LITTLE (~12–13V)

IR measurement of a pretty new battery

The number ending with “m” is the number of milli-ohms of resistance. Here is what to look for:

• 90–110m: Very good — New batteries should be in this range, and these are great for competition
• 110–130m: Good — Probably not new, but still good and usable in practice and competition
• 130–160m: Fine — Definitely usable for practice, and you can choose whether to use this in competition depending on the number of motors, power draw, and power requirements of your robot.
• 160m+: Bad — Probably still usable in practice but it will drain quickly and sag a lot. At this point you may want to consider cycling your battery (explained below)

IMPORTANT NOTE: TAMIYA CONNECTORS (shown below) INTRODUCE 30–80m OF RESISTANCE! I highly recommend removing them and replacing them with XT30 or PowerPole connectors, which are usually in the single digits.

This is what a Tamiya connector looks like, I highly recommend removing it!

Charging Statistics

Charge 3B keeps track of how much power and time you have spent charging. You can see this in the Stats mode:

There are two numbers displayed in the bottom: total energy (in watt-hours) and total charging time (in days, hours, and minutes). To put the energy in perspective, as of writing this, 1000 watt-hours of electricity (1kWh) costs around 19 cents in the US. I’m excited to see the

This menu will also display the voltage of the battery plugged in but not charge it, so it can be useful if you just want to measure the voltage of a battery.

Using the external resistor

The right-most side of Charge 3B has a white port, which you can plug in an external resistor into:

This allows Charge 3B to discharge the battery plugged into the right port, which means the right-side has extra menus and features. When cycling through the menus on this port, you will see CYCLE and STORE. Both of these menus require the external resistor to be plugged in to function.

Battery storage

The storage mode of Charge 3B

If you aren’t going to use your battery for a while (1mo+), leaving it fully charged (14V+) or heavily discharged (<11V) can stress the internal chemistry. You can switch your Charge 3B to STORE mode on the right-most port and plug in a battery and it will get charged/discharged to 12V at which point you can unplug it and store it somewhere.

Battery cycling

The cycle mode of Charge 3B

High internal resistance can be caused by crystals that form around the electrodes of the battery in heavy use. If your battery has high internal resistance, this may be the cause. To solve this you can use the CYCLE menu on the right-most port, which fully discharges and charges your battery several times at low current. This can break up those crystalline formations and reduce the internal resistance of a heavily used battery, making it useful again for competition or practice use.

However, note that batteries can only do a finite number of cycles before they go bad, so use the cycle mode sparingly!