Brand new - be gentle  

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Grepler
(@grepler)
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Joined: 2 months ago
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2020-02-04 5:57 pm  

Hello Everyone,

I am brand new to the group so please be gentle. ?

A little about myself. I have been a Network/Systems Engineer/Administrator for many years. I am fairly proficient in PHP, Javascript and SQL. I am learning Python and Arduino "sketch??" as well as Swift for iPhone. I am new to electronics so I am still learning how dc voltage flows and is managed. My goal is to build IoT devices for a living so get ready for some questions.....


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casey
(@casey)
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Posts: 363
2020-02-04 6:42 pm  
Posted by: @grepler

I am new to electronics so I am still learning how dc voltage flows and is managed.

dc voltage doesn't actually flow. Voltage (electric force) is more like the pressure you feel when you place a finger over the outlet of a tap (faucet) after turning it on. Electric current is like how much water comes out of the tap (faucet) per minute. Electric resistance is like the restriction in the pipes.  A battery is like a water pump.  A motor is like a water driven wheel.  And so on for electric power (watts) and induction (henrys) and capacitance (farads) ....

This post was modified 2 months ago 2 times by casey

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Grepler
(@grepler)
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2020-02-04 7:25 pm  

@casey

Thanks for the info Casey. Much appreciated. Are there equations for figuring out how much you need of each of these? For instance if I wanted to run a 3.3v Arduino and 4.6v servo on a battery, one would think that you would need 8v total. Which seems to work for a short time, maybe a few hours. But I see folks using less battery for months. How does that work?

This post was modified 2 months ago by Grepler

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ZeFerby
(@zeferby)
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2020-02-04 9:21 pm  

Hi @grepler, welcome !

Eric


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NewburyPi
(@dale)
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Posts: 88
2020-02-05 4:36 pm  

@grepler

@grepler Let me get to your direct questions first.

1. Are there equations for... - No. For a specific load (arduino or servo) the proper requited voltage is a characteristic of the load, and is usually stated in the datasheet. Note that if you attach an 8V power supply to any of the current arduino boards the board will be destroyed in a mater of seconds.

2. using less battery for months... - Less batteries is a confusing concept. A single type AA cell has a voltage of 1.5 volts (1.=5V). Connecting two of these AA’s in “series” you will create a battery with a voltage of 3 volts. If you connect two AA Cells in parallel, you will create a battery with a voltage of 1.5 volts and a current capacity of twice a single AA cell. Note that what we commonly call a “battery” is properly referred to as a “cell.” A battery is the term given to a collection of cells. This is somewhat confusing, because “batteries” are encapsulated (in metal or plastic) and we don’t get to see the inner construction.

However; it looks as though you need to get some of the basics of electricity under your belt, before we go any further. Below you will find some good Youtube videos, to get you started. I did a scan of what is available and while some videos are very low level, they are salted with inaccuracies and inconsistencies. The first two videos are succinct, and targeted on what you should be looking for. The third is by one of my favorite authors, ElectroBOOM. While the presentation is somewhat bizarre, the details are accurate and a good under-pinning of the previous two videos. The forth and fifth videos walk you into series and parallel circuits. These topics are important to understand in order to support an clear answer your question on 3.3v and 4.7V sources and loads. Please take some time to review these videos, and I’m sure the group here can fill in any blanks.

--
Dale


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Grepler
(@grepler)
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2020-02-05 4:38 pm  

@zeferby

Thank you . Glad to be here.


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Grepler
(@grepler)
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2020-02-05 4:43 pm  

@dale

Thank you for taking the time to put this together. I will give it all a good thorough view. Much appreciated.


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Grepler
(@grepler)
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2020-02-05 7:30 pm  
Posted by: @dale

Note that if you attach an 8V power supply to any of the current arduino boards the board will be destroyed in a mater of seconds.

Even if you connect it to the VIN pin?


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Pugwash
(@pugwash)
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2020-02-05 7:51 pm  

@grepler

The VIN pin is the exception, because between VIN pin and the Arduino ATmega328 microcontroller is a 5V voltage regulator.

SteveC - Topple Rudd Poltman


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NewburyPi
(@dale)
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2020-02-05 7:52 pm  

Oops! You're right. Vin runs to a voltage regulator, which will deliver 5 volts to the processor. However if you provide 3.3 volts on Vin, you will not likely not get enough voltage to run the arduino. The Vin pin needs to be powered at between 7 and 12 volts.

--
Dale


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casey
(@casey)
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2020-02-05 9:39 pm  

But I see folks using less battery for months. How does that work?

Imagine a battery is a tank full of water and a water pump. The pump can supply a certain amount of pressure (voltage). How much water flows out in a given time (current) depends on the resistance in the pipe and pump itself. The analogy isn't exactly right but sort of gave me a handle on visualising how electricity works providing you also begin to understand the differences.  So how long your battery lasts depends on how large the battery is (how full the tank) and the rate at which the water (electricity) flows out.  The amount of electricity (water) used by the Arduino depends on what it is doing and how often it does it just as how long your water tank stays full depends on how much water you take out of it over any given time.  However you are jumping ahead of yourself here,  first learn the basics then later you will be able to understand the explanations.  For example I have a little book "Programming Arduino Next Steps" that has a chapter on power consumption of Arduino Boards and when and how to reduce it.

With your 3.3v arduino and 4.6v servo and a 9v power source you can reduce the voltage (pressure) to each part where required.  How this is done depends on the requirements and can be a simple voltage divider to a much more complex circuit with feedback.

 

 

This post was modified 2 months ago by casey

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Grepler
(@grepler)
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2020-02-06 5:05 pm  

@casey

I think I am getting it. Volts are the potential energy while current is the amount of energy flowing through the circuit. Can you recommend any videos that talk about how devices use the current and deplete the battery and why batteries have different ratings like a 1.5v AA battery has more mAh than a 9v battery.


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NewburyPi
(@dale)
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2020-02-06 6:26 pm  

@grepler Yep, you're getting there. 

I haven't come across any suitable videos pertaining to your question. However, the two links below will give you a starting point. Basically the current capacity (mAh) of a battery or cell will be dependent on the size of its electrodes. The larger the electrodes making contact with the electrolyte of the cell, the larger the surface area for the electron producing chemical reaction, and therefore the number of instantaneous electrons available to flow.

In the case of your AA vs 9V comparison, the single AA Cell has a much larger electrode surface area than the 9V battery. If you were to disassemble a 9V battery(Not recommended, It's messy and there are plenty of sharp pieces to cut yourself on) you would find six smaller 1.5 volt cells inside. It is the small electrode surface area of the smaller parts of the 9V battery that reduces the current capacity. From the first link below you find that the AA has a current capacity of 1000 mAh and the 9V battery has a current capacity of 500 mAh. This shows the AA cell has electrodes approximately twice the size of the individual electrodes in the 9V battery. 

There is another capacity that is important to consider when selecting a battery, That is the Power Capacity. If you take the rated Current Capacity of a cell/battery and multiply it by the output voltage, you will have an approximation of the power capacity in milliwatt hours (mWh). In this case the AA cell has a power capacity of 1,500 mWh while the 9V has a power capacity of 4,500 mWh. If you only needed 1.5 volts (at 10mA say) for your circuit, the 9V battery would last longer. 

Note my calculated numbers are approximate because the output voltage of the cell/battery will drop while it is being used. Also there are losses doe to efficiencies in a regulator (required to drop 9V to 1.5V)  that would impact on total available power capacity of the 9V battery. 

Basic cell/battery data for comparison purposes:  http://www.techlib.com/reference/batteries.html

More detailed cell/battery data:  https://en.wikipedia.org/wiki/List_of_battery_sizes

Hope this helps.

--
Dale


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casey
(@casey)
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2020-02-06 7:14 pm  

If a particular 1.5v AA battery has more mAh then a 9v battery it just means the 1.5v battery is storing more electricty than the 9v battery. Voltage is just the pressure provided by the battery not how much electricity it has stored.  Again think of a tank of water. It is not just the pressure (volts) that determine how long the tank can deliver water it depends on how much water is in the tank to start with and how much water is taken out per unit of time. So the mAh is just a measure of how much electricity the battery can provide before it runs out.  A large 1.5v battery might "store" more electricity than a small 9v battery.  The voltage is just the pressure at the outlet.

How much electricity actually flows out at any given time depends on the voltage AND the resistance in the circuit.

Electrical Pressure (voltage) = Intensity of Current (amps) x Resistance (ohms)
E = I x R
where voltage, ampere and ohms are the units of measure like inches are to Distance.

Battery by the way refers to a collection of electric cells. A 1.5v battery has one cell. A 9v battery will have six cells. It is the size of a cell and the chemicals they use which determines the amount of electricity they have stored. If you pull a little 9v battery apart you will find it is made up of six tiny 1.5v cells connected in series. 

The voltage of a battery is the pressure the battery will try and maintain between it's  + and  -  terminals.  Batteries also have an internal resistance which limits the current (gallons per minute) they can deliver.

As you can see here the Arduino is being powered by 9volts made up of six 1.5 cells connected in series.

testRig

This post was modified 2 months ago 7 times by casey

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casey
(@casey)
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2020-02-06 8:44 pm  

@Grepler

To sum it up with regards to your post.

Volts are a measure of Electric Force (pressure) between two points, the same as air pressure in your car tyre is a measure of the pressure difference inside the tyre compared with air pressure outside the tyre.  An electric current, measured in amperes (amps), is the amount of electricity flowing past a give point at any time like the rate at which air exits a car tyre when you remove the valve. You can vary the rate at which the air exits the tyre by placing a finger over the outlet thus increasing the Resistance.

The mAh capacity rating refers to the storage capacity available for a particular battery.

How much electricity the battery actually delivers at any time depends on the resistance of the electric load  in the circuit.  An electric load can be a motor, an Arduino board, a light bulb, a heater and so on.

Current (amps) = Pressure(volts)  /  Resistance(ohms)

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