Multiple power sources -one wall socket or battery... possible?

Thread Starter

TogetherInElectricDreams

Joined Jan 23, 2019
48
Hi everyone,

I really don't know what I need, what it's called or how I would do this? As I have said in other threads I am putting together a kitchen for my son, each component needs powering, there are 5 but I don't know how I will power them and how do I make it so it's safe? I have been told I need a "power bank" but I don't know if that's actually what I need. I'd like something rechargable that I can stick onto the kitchen and everything runs from it so there's no worries about having things plugged into the wall.

Items that are drawing power

Play microwave using a strip of LED lights and an Arduino Nano -volts/power unknown
Play dishwaser using an Arduino Nano -volts/power unknown
Water pump 12V
Led strip in Oven -voltage unknown.

What are my options here please? I can't even envisage what this would look like.

Your help and suggestions are appreciated, please feel free to use simple language -I'm still learning.
 

RPLaJeunesse

Joined Jul 29, 2018
64
Use a 12V "sealed lead-acid" or VRLA battery big enough to run the pump for a few hours. (If pump takes 1/4A then a 1AH battery is big enough for that.) I'll guess another 1AH of battery will handle the Nano and a few LED lamps (+1AH). Get a small (and safe!) charger, and use it carefully so as to not overcharge the battery. Power the Nano off the +12V. Get a 5V buck regulator good for 1A or so, use that to run the LED lamps. Or skip the buck regulator and use 12V LED strips. The Nano driving logic gate n-channel FETS should be fine for switching things, be sure to use a clamp diode across the pump or the FET will short out. Also use the Nano to sense the battery voltage, and implement a low-voltage all-off feature to protect the battery
 

Wendy

Joined Mar 24, 2008
21,906
OK, I am up to speed on this thread.

1. Decide what you want,+5V, +12VDC, or what? +12VDC is easy to convert to +5VDC. Just use a LM7805
3 terminal voltage regulator, They are cheap and relatively easy to get, Unless I am mistaken either power supply can be used to power your Arduino.If you want to connectorize these connections A USB port is great for +5VDC. If you are interested in my help ask your questions her as I'm now watching this thread.
 

RPLaJeunesse

Joined Jul 29, 2018
64
Using a 7805 to get 5V from 12V works, but at higher currents like 1A it can dissipate many watts, possibly 7+. At that dissipation the part needs a heatsink good enough to keep the chip temperature below its rated maximum in the hottest environment it will see. (I'll not bother with datasheets, and give a rough guide from experience.) I'd use 125C chip max for good life, and 50C for the hottest seen in the home. 75C chip rise is thus allowable, with 7 watts dissipation the chip requires a total heatsinking about 10C/W or better. If you allow 2C/W for the package and mounting then the heatsink should be rated for 8C/W or less. Bear in mind for 5V at 1A you now need a 12V 1A supply.

FYI even cheapo buck regulator modules can achieve 80% or better efficiency. With a buck regulator 12V to 5V at 1A would dissipate about 1.25W, and the 12V supply is more on the order of 500mA instead of 1A. But it's all tradeoffs - heat vs cost vs design effort. My rule of thumb is if the input voltage is twice or more of the output voltage then using a buck regulator module is worth the effort.

There are also buck regulator modules billed as "7805 equivalent", even using the same 3-pin footprint. You might want to look into these.
 

djsfantasi

Joined Apr 11, 2010
5,705
Unless I am mistaken either power supply can be used to power your Arduino.If you want to connectorize these connections A USB port is great for +5VDC. If you are interested in my help ask your questions her as I'm now watching this thread.
@Wendy ,

You’re not mistaken. But to clarify, each different voltage level supplied to the Arduino, requires different wiring...

Just sayin’:rolleyes:
 

Wendy

Joined Mar 24, 2008
21,906
Eventually sometime soon I will begin my trek learning the Arduino, but that has not happened yet. My training is w/ discrete components. I consider myself an expert in older tech.
 
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