Below 12V: USB, Powerpack and Battery Lighting

Making portable lamps has become a much more viable proposition, with modern battery technology storing a lot more power for a given size and weight, and LED lamps being a lot more energy efficient than filament bulbs.

The two things we need to look at initially are the supply power, and the bulb specifications. Then we can specify the wiring requirements, and anything else that may be needed in between the two, such as for voltage regulation.

Supply Power


The USB specification (1 to 3) states that the voltage can be anywhere between 4.75 and 5.50V DC, and that the voltage drop must be less than 0.17V. So the effective voltage may be between 4.58 and 5.50V.

The wires in a USB cable have standard colours, and for power red is +ve and black is ground.

USB versions 1 and 2 provide a maximum current of 100mA (0.5W), or 150mA (0.75W) for USB 3. This is called the low power mode; high power modes with significantly higher power outputs are available, but these require signaling from the lamp to the USB power supply to switch them on, so electronics is required to enquire of the charger what protocols it supports, and/or tell it which protocols you support. Also, the cable used must be capable of transmitting the power without going into meltdown, so the charger must be able to identify the cable's capabilities. After this data exchange, they can negotiate which protocol to use.

For our purposes, we need to differentiate between charging of a battery / power pack, where the voltage and current don't need to be constant (and often intentionally are not, e.g. when a charged battery switches to trickle charge), and powering a lamp directly, which needs a constant voltage and a minimum current. Also, we need to be able to ignore some mobile phone charging protocols which are tightly tied in to the processor used in the phone, as this manages the charging.

USB (2) in a Nutshell

USB Charging Standards

Unless stated otherwise, the voltage is fixed (within tolerances) and the current is the maximum available.
Type may be: General for direct powering of devices and/or charging of batteries; Charging for battery charging; or Phone where the protocol is tied in with the phone's processor, so cannot be used on other devices.
Apart from USB, I have generally just given data on the latest version of the protocol

USB 1.0 General
USB 3.1/ Also may offer PD
USB Battery Charging (BC)
USB-C Current mode5315GeneralThis is USB-C without PD. Requires a USB-C cable
USB-C Power Delivery (PD) 2.0/3.02 max5100GeneralRequires a USB-C 2.1 cable for max power, standard USB-C cables support 20V, 3A, 60W. Devices negotiate voltage and current. Used by Apple and Google.
USB-C Power Delivery (PD) 3.0 PPS205100GeneralRequires a USB-C 2.1 cable for max power, standard USB-C cables support 20V, 3A, 60W. Devices negotiate voltage and current. Used by Apple and Google.
USB-C Power Delivery (PD) 3.15 - 480.5 - 5240GeneralRequires a USB-C 2.1 cable for max power, standard USB-C cables support 20V, 3A, 60W. Devices negotiate voltage and current. Used by Apple, Google, Samsung.
Apple Fast Charging21 max?5?Max 20??Uses USB-C PD but needs an Apple cable, and an Apple or compatible charger
Huawei SuperCharge 2.05525PhoneBased on Qualcomm QC
Motorola Turbo Power??68??Uses Qualcomm QC, or version 30 and later can also use USB-C PD
MediaTek Pump Express 4.06530PhoneMediaTek protocol, compatible with Qualcomm QC
OnePlus Warp Charge 60T106.565?Based on Oppo Super VOOC. Proprietary phone and cable
OnePlus Dash Charge5420Based on Oppo VOOC
Oppo Super VOOC 2106.565?Oppo protocol, proprietary charger and cable
Oppo VOOC5525?Oppo protocol
Qualcomm Quick Charge (QC) 5> 20> 5> 100PhoneTied in to Qualcomm chipsets. 100W requires USB-C cable, lower power can use other cable types
Samsung Super Fast Charging104.545?Samsung protocol
Samsung Adaptive Fast Charging9218PhoneBased on, and compatible with, Qualcomm QC 2.0

The confusing world of USB-C charging, explained

Electronics Level USB-C Information

Evaluation Boards for USB Type-C USB Power Delivery
How standalone power delivery controllers simplify USB-C PD design
Simplify Your USB-C PD Design Using a Standalone PD Controller
USB Type-C Power Delivery (PD) Controller Interface / Communications Development Kits
Designing with USB-C - Lessons Learned, Dubious Creations blog
Sparkfun USB-C Power Delivery Board
DollaTek USB-C Voltage selector
Merourrii USB-C voltage selector board

USB-C Cables for Charging

How we Test USB-C Cables at PC World
Best USB-C cables 2024: Get quality charging and data transfers

USB-C to fixed DC Voltage Cables

These are generally for USB-C PD power supplies. The cable is set to a fixed DC output voltage, and includes the necessary electronics to get the power supply to output this voltage.
I'm not sure what happens if you use it with a power supply that cannot supply the desired voltage.

Mission Engineering 529 M USB-PD Converter - not a cable but a converter


A powerpack is just a marketing term for a rechargeable battery which may be charged from a fixed DC voltage, mains power or USB. There may be 1 or multiple outputs, again in a variety of formats and levels.
There are many out there! These are a fairly random selection of ones that look useful.


There are a number of battery sizes and technologies available, the most common of which are given below.
Note that the voltage given is the maximum, when the battery is fully charged and not under any load. As the load increases, and the charge in the battery reduces, the voltage will reduce, e.g. a 1.5V battery may drop down to 1.0V.

SizeIEC nameANSI nameTechnologyNominal voltageTypical capacity (Wh)Rechargeable
AAALR0324AAlkaline1.51.3 - 1.8Some
AAAKR0324KNiCd1.250.38 - 0.63Yes
AAAHR0324HNiMH1.250.75 - 1.6Yes
AAZR6?NiZn1.60 - 1.652.97Yes
PP36KR6111604Ni-Cd7.2 / 8.40.864 / 1.008Yes
PP36HR617.2H5Ni-MH7.2 / 8.4 / 9.61.26-2.16 / 1.47-2.52 / 1.68-2.88Yes
PP3Varies-Lithium polymer7.43.848Yes
PP3Varies-Lithium ion7.44.588Yes
PP3--Lithium iron phosphate9.61.92 - 3.072Yes


USB Component Suppliers

SupplierWall ChargersCablesPower packsOther
Eaton / Trippliteyy