1
\$\begingroup\$

Installing a USB-C Port on a Longboard for Charging

I'm exploring options to install a USB-C port on my longboard to utilize its enormous ~400 Wh battery for charging my phone/laptop/anything.

Initial Idea: Buck Converter

The simplest approach I've considered is using a buck converter. For example:

DROK DC-DC Buck Voltage Regulator on Amazon

Challenges

  1. Voltage Limitations: A basic buck converter wouldn't support the higher voltages my laptop might require.

  2. Source vs. Sink: The further I look into it, the more I find that most online DIY USB-C guides have to do with building a sink port rather than a source, and I'm pretty sure I want to make a source/host port.

Questions

  1. How can I support a range of voltages to accommodate both small and large devices?
  2. Does there exist some premade breakout-board-like product that can do the bucking down from 54.6 V to 5 V / 9 V / 12 V / 15 V / 20, and the handshaking to select the highest supported voltage from the sink/device?
  3. If not, what should the circuit look like on a high level?

Thank you, Zach

New contributor
Zach is a new contributor to this site. Take care in asking for clarification, commenting, and answering. Check out our Code of Conduct.
\$\endgroup\$

3 Answers 3

2
\$\begingroup\$

What you are after is a charging port, not a host port.

  1. With a buck converter that has controllable output voltage. Controllable may mean any method you can think of, like switching voltage setting resistors externally, or commanding the converter through I2C bus if it has one.

  2. Maybe, but it might not have the input range you need. Also if you are asking what to buy and from where then it is off topic.

  3. By making a circuit that is a PD charger. It maybe needs a MCU with a PD controller which is programmed to act like a PD source, which negotiates with the PD device and based on the PD negotiation controls the output voltage control circuit to provide the negotiated voltage. And, does it in a way that is compliant with USB Type-C and USB PD 2.0 or PD 3.0 standards and does not fry your laptop, so you need to be familiar with these.

So it requires a lot of effort. It might not be a beginner project. Even some experts I know that have designed these have fried a few laptops while testing. If you value your phone or laptop, do not attempt to DIY this.

You might be better off by bucking the battery volage down to say 12 to 13 volts and buy a standard car charger that suits your needs.

\$\endgroup\$
1
\$\begingroup\$

I agree with user justme that it's not easy project to build a USB-PD charger output from ICs, and there are many off-the-shelf USB-PD charger solutions available with 12/24Vdc input for the automotive and marine accessories market. So, best path is try to find a step-down (Buck) switch-mode power converter for your battery output range down to fixed 24 Vdc (or 12V) output, then connect its 24V output to an off-the-shelf USB-PD charger.

I built a DYI portable battery power station, and found many USB charger options for 12/24Vdc input to high-power 60W USB-PD type-c (sufficient for most laptops), often with additional 18W QC3 USB type-A output, which seems to fit your desires. Some good examples are the Powerwerx Quick Charge 75W USB Device Charger and the Ouffun 83W Car Charger with Power Switch, Waterproof DIY USB Port 12V Socket.

I suggested a 24V intermediate voltage instead of 12V because some of the USB-PD dc-input charger devices will only provide their highest range 20V PD output mode when their input voltage is above about 21V (i.e. some don't output full power at 12V input, so read specs carefully). Most automotive accessories already support 24V input. Yet a 12V intermediate voltage would be an valid option too for a DC-input USB charger.

One additional thing to consider, your proposed source 54.6V battery is likely 15-series Li-Ion cells, which typically has an output range of 40.5V to 63.0V. Some appropriate DC-DC converters will only have input range 30-60V, which may not be adequate when the battery is full and connected to its charger. You might measure the maximum voltage observed at battery output for your usage scenarios, and see if it ever exceeds 60V, which could open up much larger selection for the DC-DC converter. Alternatively, just look for 36V to 72V input range DC-DC converters.

\$\endgroup\$
-1
\$\begingroup\$

You have two main challenges to solve

  1. generate the required voltage
  2. transmit the power over USB-C

1 - Generating the required voltage

There are buck converters that are able to convert 50V down to 5V. I am personally most familiar with TI components because of which I used the TI Power Designer with the following parameters

  • VIN_min = 40V, VIN_max = 60V, Justification: your battery voltage is not constant and you want to have some margins.
  • Vout = 5V, Justification: The most simple USB power supply is 5V (more about that below)
  • I_out = 3A, Justification: This results in a 15W output which is decent and, if you want more than 3A, your buck converter most likely needs external fets which is undesirable.

The Power Designer returned multiple designs, for example one using the LM76005 buck converter. I highly encourage you to not blindly trust the tool but to ensure the proposed circuits work as expected.

Transmit the power over USB C

As a user, one often thinks that charging your phone over USB-C is as simple as plugging a device into a power plug. It is not. Among the different USB standards, USB-C is interesting for power applications because it allows higher power throughput (up to 15W according to the USB-C standard). In contrast, USB 3.0 allows for up to 4.5W. Laptop chargers often implement the USB-PD standard which allows up to 240W of power throughput.

USB-C and USB-PD are difficult to implement because you need communication between the device and host in order to negotiate the voltage and current. I therefore recommend you to get started by implementing normal USB 3.0 charging. This doesn't stop you from using an USB-C connector (side note: you would not be able to get certification to sell this as an usb-c product, but I highly doubt you care about that).

Summary

In order to implement this, you need to

  1. Use a buck converter to convert your battery voltage down to 5V.
  2. Connect the 5V output and GND to a USB connectors power and GND pins.
\$\endgroup\$
6
  • 1
    \$\begingroup\$ What you suggest is a 5V only supply, most laptops would not even start charging and phones would complain about slow charger. The 5V cannot signal more than 3A without using PD. And you would have to implement this as a Type-C plug, as only plugs are allowed to always output 5V even with no detection about plugging it in to anything. Type-C receptacles are especially forbidden to provide supply without detecting a device that needs power. And Type-A receptacle without BC protocol the devices may limit to 12W, unless you signal DCP or QC. Type-A to Type-C cables limit to 900mA without QC/BC. \$\endgroup\$
    – Justme
    Commented Jul 10 at 23:03
  • \$\begingroup\$ USB-C supports negotiation of up to 100W of power (5A at 20V) using the PD protocol. \$\endgroup\$
    – Finbarr
    Commented Jul 10 at 23:47
  • \$\begingroup\$ @Finbarr There are just two small issues with that comment. First of all, that was true some years ago, but not any more. Currently PD can support up to 240W, at 48V and 5A. And this answer suggests to just use 5V without PD or any other protocol to negotiate other voltages, so 5V 3A is max you can signal then. \$\endgroup\$
    – Justme
    Commented Jul 11 at 5:12
  • \$\begingroup\$ USB-C supports 15W (without the PD) and up to 240W when using the PD protocol (which is not part of the original USB-C standard. \$\endgroup\$
    – mlx11
    Commented Jul 11 at 8:41
  • \$\begingroup\$ @Justme I completely agree with that. The problem is that the person asking this question most likely isn't able to implement a USB PD circuit -> I proposed 5V because it is significantly easier to do. \$\endgroup\$
    – mlx11
    Commented Jul 11 at 8:46

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.