This page (revision-18) was last changed on 2019-12-23 11:17 by Murray Altheim

This page was created on 2019-12-23 04:14 by Murray Altheim

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Power Supplies...nobody
PowerSupplies

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%%alias Aliased from [USB Power Supplies], [Power Supply|PowerSupply], [Power Supply Unit|PowerSupplyUnit] and [PSU] %%
%%alias Aliased from [USB Power Supplies], [WallSupplies], [Power Supply|PowerSupply], [Power Supply Unit|PowerSupplyUnit] and [PSU] %%
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When you're working on your robot you'll likely want to plug it into a wall socket rather than run it from batteries. You'd call that a [Bench Power Supply].
When you're working on your robot you'll likely want to plug it into a wall socket rather than run it from batteries. You'd call that a ''Bench Power Supply''.
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We'll focus on the [Raspberry Pi] since it generally requires more power than other [microcomputers/microcontrollers|microcontrollers]. The Raspberry Pi requires a 5 volt power supply and generates an onboard regulated 3.3 volt supply for its peripherals. Most processors suitable for small robots require either 5 volts or 3.3 volts, but if they have a USB connector on them it's likely so you can use a USB charger as a power supply. Obviously, ''read the user manual''.
We'll focus on the [Raspberry Pi] since it generally requires more power than other [microcomputers/microcontrollers|microcontrollers]. Most processors suitable for small robots require either 5 volts or 3.3 volts, but if they have a USB connector on them it's likely so you can use a USB charger as a power supply. Obviously, ''read the user manual''.
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For a Raspberry Pi you'll need a reliable __USB Power Supply__ (5 volts) with enough current capacity to run your processor (e.g., [Raspberry Pi]), your [sensors], [motors] and any other accessories (such as displays).
The Raspberry Pi requires a 5 volt power supply and generates an onboard regulated 3.3 volt supply for its peripherals. You can use a reliable __USB Power Supply__ (5 volts) with enough current capacity to run your processor (e.g., [Raspberry Pi]), your [sensors], [motors] and any other accessories (such as displays).
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Note: we'll cover [battery packs|BatteryPacks] elsewhere.
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!! How Much Power?
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[{Image src='USBPowerSupplies/nuclear.jpg' caption='Serious Power' alt='serious power' align='right' class='imgFloatRight'}]
There are a number of companies providing USB Power Supplies specifically for the Raspberry Pi. Each of the
different Pi models has differing power requirements (see below), with recommended PSU (Power Supply Unit) current capacities ranging from 700mA for the Model A to 3 amps for the Pi 4, but these numbers don't include sensors or motors.
!! So How Much Power?
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[{Image src='PowerSupplies/nuclear.jpg' caption='Serious Power' alt='serious power' align='right' class='imgFloatRight'}] There are a number of companies providing USB Power Supplies specifically for the Raspberry Pi. Each of the Raspberry Pi models has different power requirements (see below), with recommended PSU (Power Supply Unit) current capacities ranging from 700mA for the Model A to 3 amps for the Pi 4, but these numbers don't include sensors or motors.
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[Jaycar|Vendors] sell a ''[Mean Well 70W 5V 14A Power Supply|https://www.jaycar.co.nz/mean-well-70w-5v-14a-power-supply/p/MP3289]'' that actually __delivers__ 70 watts: 5 volts at 14 amps for NZ$54.90. It's not as pretty as the Apple unit but as a bench power supply it looks pretty good. Here's the specs:
! Some Pi Power Requirements
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Shown below is a portion of the table from the [Raspberry Pi FAQ|https://www.raspberrypi.org/documentation/faqs/#pi-power]. There's also a table showing typical power usage "during standard processes" (which doesn't include driving your robot up a steep incline). They define a "stressed" Raspberry Pi 3B as using 1.34 amps. Stall current on a robot motor can be 5 amps. Most robots have at least two motors.
Hmm. Clearly we need to think about this a bit more.
%%small
|| Product || Recommended PSU Current || Maximum USB peripheral draw || Typical bare-board consumption
| Raspberry Pi Model A+ | 700mA | 500mA | 180mA
| Raspberry Pi Zero W | 1.2mA | Limited by components | 150mA
| Raspberry Pi 3 Model B+ | 2.5A | 1.2A | 500mA
| Raspberry Pi 4 Model B | 3.0mA | 1.2mA | 600mA
%%
! A Potential Bench Power Supply
[Jaycar|Vendors] sell a ''[Mean Well 70W 5V 14A Power Supply|https://www.jaycar.co.nz/mean-well-70w-5v-14a-power-supply/p/MP3289]'' that actually delivers 70 watts (5 volts at 14 amps, do the math) for NZ$54.90. It's not as pretty as the Apple unit but as a bench power supply it looks pretty good. Here's the specs: [{Image src='PowerSupplies/bench-supply.png' caption='The Mean Well Power Supply: not so pretty' alt='mean well bench supply' align='right' class='imgFloatRight' style='margin-right:15%'}]
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\\
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%%small
|| Product || Recommended PSU Current || Maximum USB peripheral draw || Typical bare-board consumption
| Raspberry Pi Model A+ | 700mA | 500mA | 180mA
| Raspberry Pi Zero W | 1.2mA | Limited by components | 150mA
| Raspberry Pi 3 Model B+ | 2.5A | 1.2A | 500mA
| Raspberry Pi 4 Model B | 3.0mA | 1.2mA | 600mA
!! What is a Switching Power Supply?
%%aside
My dad used to really like trying to guess what was in his Christmas gifts. I remember one Christmas where as a joke I gave him an extremely heavy transformer from a [Bell UH-1 Iroquois helicopter|https://en.wikipedia.org/wiki/Bell_UH-1_Iroquois] that I'd bought at a local surplus store (I wanted the chassis it was in, or some such reason).
I'd put his real gift under the transformer and when he opened it there were some laughs, ha ha. For a minute. He then picked up the transformer and dropped it into what he thought was an empty box full of wrapping paper, except it ''wasn't empty''. It contained the Royal Albert tea cup I'd just given my mom. Ugh. — [Murray]
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The above is a portion of the table from the [Raspberry Pi FAQ|https://www.raspberrypi.org/documentation/faqs/#pi-power].
Some power supplies (what we might call "old school") use a [transformer|https://en.wikipedia.org/wiki/Transformer] to convert the wall voltage (110 volts in the Canada, the US and Japan, 200-240 volts in most of the rest of the world) down to the low voltage (5-12 volts) used for our robot. The more power we needed, the larger the transformer. The amount of power that could be delivered was almost in direct relation to the size the transformer. Transformers can get big and heavy.
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A __[Switching Power Supply|https://en.wikipedia.org/wiki/Switched-mode_power_supply]__ (also called a "switched-mode power supply) doesn't use a big transformer. Most laptop power supplies are switching power supplies. If you're on one of the robot vendor web sites you'll see switching power supplies advertised. AdaFruit sells a 5 volt 10 amp for US$30, another one for $25. Most of these units have the benefit of being able to run from either 110 or 240 volts.
The only issue is that most of them don't end in a USB connector but rather a male DC plug; you'd have to convert that to a micro USB male, which is what's on most microcontrollers. Perhaps we need a [Recipe] on
[how to convert power from DC male plug to micro USB|HowToConvertPowerFromDCMalePlugToMicroUSB]...
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The problem is, the companies selling these units are not always very honest about the power ratings of their
products. Apple seems to be the worst: they sell two adapters (listed as the ''Apple 87W USB-C Power Adapter'' and the ''96W USB-C Power Adapter'') that are likely the most expensive on the market and are not showing their output ratings in watts but seemingly their power ''requirements'', i.e, not what they __deliver__ but what they __use__. Of course it says nothing about this on the box. It's 87 watts, right? [{Image src='USBPowerSupplies/5w-adapter-thumb.png' link='https://support.apple.com/library/content/dam/edam/applecare/images/en_US/accessories/Adapters/5w-adapter-tech-spec.png' caption='Apple 5 watt USB adapter' alt='Apple 5 watt USB adapter' align='right' class='imgFloatRight'}]
The problem is, the companies selling USB chargers are not always very clear about the power ratings of their
products. Apple seems to be the worst: they sell two adapters (listed as the ''Apple 87W USB-C Power Adapter'' and the ''96W USB-C Power Adapter'') that are likely the most expensive on the market and are not showing their output ratings in watts but seemingly their power ''requirements'', i.e, not what they __deliver__ but what they __use__. Of course it says nothing about this on the box. It's 87 watts, right?
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[{Image src='USBPowerSupplies/12w-adapter-thumb.png' link='https://support.apple.com/library/content/dam/edam/applecare/images/en_US/accessories/Adapters/12w-adapter-tech-spec.png' caption='Apple 12 watt USB adapter' alt='Apple 12 watt USB adapter' align='left' class='imgFloatLeft'}] To give you an idea of how far this is off from that advertised 87 watt promise, delivering 87 watts at 5 volts it should be delivering __17.4 amps__. Apple's unit is clearly using 87 watts to deliver 15 watts (3 amps at 5 volts) of power. You can check this yourself by using an online [Watts to Amps Calculator|https://www.rapidtables.com/calc/electric/Watt_to_Amp_Calculator.html] or [Amps to Watts Calculator|https://www.rapidtables.com/calc/electric/Amp_to_Watt_Calculator.html].
To give you an idea of how far this is off from that advertised 87 watt promise, delivering 87 watts at 5 volts it should be delivering __17.4 amps__. Apple's unit is clearly using 87 watts to deliver 15 watts (3 amps at 5 volts) of power. You can check this yourself by using an online [Watts to Amps Calculator|https://www.rapidtables.com/calc/electric/Watt_to_Amp_Calculator.html] or [Amps to Watts Calculator|https://www.rapidtables.com/calc/electric/Amp_to_Watt_Calculator.html].
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What's strange is that Apple has delivered honest reporting on its other units. Their tiny 5 watt unit delivers 5 volts at 1 amp. Their 12 watt unit delivers 5.2 volts at 2.4 amps. They provide technical specification for these smaller models, but the "Tech Specs" for the 96 watt model just says "USB C". What gives?
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[{Image src='PowerSupplies/5w-adapter-thumb.png' link='https://support.apple.com/library/content/dam/edam/applecare/images/en_US/accessories/Adapters/5w-adapter-tech-spec.png' caption='Apple 5 watt USB adapter' alt='Apple 5 watt USB adapter' align='left' class='imgFloatLeft' style='margin-right:2em'}] What's strange is that Apple has delivered honest reporting on its other units. Their tiny 5 watt unit delivers 5 volts at 1 amp. Their 12 watt unit delivers 5.2 volts at 2.4 amps. They provide technical specification for these smaller models, but the "Tech Specs" for the 96 watt model just says "USB C". What gives?
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[{Image src='PowerSupplies/12w-adapter-thumb.png' link='https://support.apple.com/library/content/dam/edam/applecare/images/en_US/accessories/Adapters/12w-adapter-tech-spec.png' caption='Apple 12 watt USB adapter' alt='Apple 12 watt USB adapter' align='right' class='imgFloatRight'}]
This page (revision-18) was last changed on 2019-12-23 11:17 by Murray AltheimTop