Advise needed for running LED lights from a powerbank

DaveMK · Nov 23, 2020

audioguru said:
Why are you buying no-name-brand way over-priced junk from China? Did you see the shipping charge? They do not have 8.2 ohms anyway.
At my local electronic parts store they have the needed 8.2 ohms, are good quality and cost almost nothing.
You do not need 1% or metal film. Instead 5% and 1W carbon film are fine and cost less.

I'm in the UK, there is no shipping charge on the item I posted, and they're pennies each.
The reason I'm buying no-name brand is because I'm clueless and don't know what brands are worth buying.
The reason I'm buying on Ebay is that I don't have a local shop that will stock specialty items that I've linked to.
I've found these, and will order now.

1W Carbon Film Resistors Full range available (10 pack) 0.33R-2.2M Free P&P | eBay

Rated power: 1W. Resistor type: carbon film fixed value. Body length: 10mm. Overall length (with pins): 63mm.

www.ebay.co.uk

Is there a specific name for the type of wiring I should use, and where on the circuit I should solder the resistors, so that I can google a diagram?

Thanks

Pommie · Nov 23, 2020

Assuming you're going to use the 1W LEDs with an average forward voltage of 3.4V and the power pack outputs 5V then,
The current required is W/Vf = 1/3.4 = 0.294A = ~300mA.
The voltage dropped by the resistor needs to be 5-3.4 = 1.6
The resistor value needs to be V/I = 1.6/0.3 = 5.4Ω
The power requirement of the resistor is V*I = 1.6*0.3 = 0.48W.

So, a 1 Watt 5.6Ω (E24 series) in series with each LED should work fine.
Note, each LED and the resistor are wired in series and the bank of LEDs (and resistors) are wired in parallel.

Assuming the power pack can supply 2A then it can power 2/0.3 = 6 LEDs.

HTH.

Mike.
Edit, the link to the resistors you posted are E12 series so don't contain a 5.6Ω value. The 6.2Ω value should work fine.
Also, your LEDs will need a heatsink. If you've not already bought them consider buying ones with a heatsink.

audioguru · Nov 23, 2020

The powerbank max output is 2.4A and there are 12 LEDs so the current in each LED must not exceed 200mA.
The ad for the high current L:EDs did not spec the forward voltage and many white power LEDs have a minimum forward voltage of 3.2V. Then my 8.2 ohm resistor sets a current at (5V - 3.2V)/8.2 ohms= 220mA. OOPS! Use 10 ohms.
If the LEDs are actually 3.4V then the current with 10 ohm resistors will be (5V - 3.4V)/10 ohms= 160mA or 196mA with a 8.2 ohm resistor. If the LEDs are 3.6V then the current will be 140mA into 10 ohms or 171mA onto 8.2 ohms.

Pommie · Nov 23, 2020

The reason I put all the calculations was so the OP can calculate different configurations.

Mike.

DaveMK · Nov 24, 2020

Thank you to everyone who has offered advice and suggestions.

I've just placed an order for the bulbs, heat sinks, thermal grease, and resistors (10 ohms).
Do I still need the step up DC converter?

Pardon our interruption...

DaveMK · Nov 24, 2020

Pommie said:
The reason I put all the calculations was so the OP can calculate different configurations.

Mike.

Thanks for that Mike.

Diver300 · Nov 24, 2020

DaveMK said:
Thank you to everyone who has offered advice and suggestions.

I've just placed an order for the bulbs, heat sinks, thermal grease, and resistors (10 ohms).
Do I still need the step up DC converter?

Pardon our interruption...

No. That was only needed for the 12 V strips. You are working from 5 V which is the voltage that the power bank produces.

DaveMK · Nov 24, 2020

Diver300 said:
No. That was only needed for the 12 V strips. You are working from 5 V which is the voltage that the power bank produces.

Thank you.
So will I now split a USB cable and use 2 of the wires from that to go to positive/negative? on the final bulb?

Diver300 · Nov 24, 2020

DaveMK said:
Thank you.
So will I now split a USB cable and use 2 of the wires from that to go to positive/negative? on the final bulb?

Yes. Any USB cable will do. The biggest wires are normally + and -.

Put the resistor in series as well.

audioguru · Nov 24, 2020

DaveMK said:
Do I still need the step up DC converter?

Since ebay says it "Provides power and charges your 5V devices" not 12V devices then you should double-check with the manufacturer. But in Item Specifics it looks like the manufacturer also says "Output Voltage: 5V".

Even if their text is wrong and the output is really 12V then they do not know that a 12V battery is charged from a voltage that is higher than 12V.
Can you believe that its output is 2A or is its input 2A??
They do not know these important things.

EDIT: They also do not know the voltage of their LEDs.

DaveMK · Nov 24, 2020

Diver300 said:
Yes. Any USB cable will do. The biggest wires are normally + and -.

Put the resistor in series as well.

Thank you.

DaveMK · Nov 24, 2020

audioguru said:
Since ebay says it "Provides power and charges your 5V devices" not 12V devices then you should double-check with the manufacturer. But in Item Specifics it looks like the manufacturer also says "Output Voltage: 5V".

Even if their text is wrong and the output is really 12V then they do not know that a 12V battery is charged from a voltage that is higher than 12V.
Can you believe that its output is 2A or is its input 2A??
They do not know these important things.

EDIT: They also do not know the voltage of their LEDs.

Thank you.

DaveMK · Nov 24, 2020

I'll update this thread once all the bits and bobs arrive.
Thanks for all the help so far!

DaveMK · Dec 9, 2020

All of my components have arrived except for the aluminium channel.
I've already soldered the bulbs to the heat syncs.
Is the photo I've attached wired correctly?

Diver300 · Dec 9, 2020

DaveMK said:
All of my components have arrived except for the aluminium channel.
I've already soldered the bulbs to the heat syncs.
Is the photo I've attached wired correctly?

I'm sorry to say it's not.

The negative of all of the LEDs should be connected to the negative of the USB lead.

One end of all of the resistors should be connected to the positive of the USB lead.

The other end of each resistor should connect to the positive of just one LED, and to nothing else. There will be 12 of those connections, one for each LED, and they are all separate.

DaveMK · Dec 9, 2020

Diver300 said:
I'm sorry to say it's not.

The negative of all of the LEDs should be connected to the negative of the USB lead.

One end of all of the resistors should be connected to the positive of the USB lead.

The other end of each resistor should connect to the positive of just one LED, and to nothing else. There will be 12 of those connections, one for each LED, and they are all separate.

Thank you very much!
So like this?
Is speaker wire ok for the wiring?

audioguru · Dec 9, 2020

Speaker wire will work fine and it can carry 15 times the current used by your 12 LEDs so thinner wire can also be used.

gophert · Dec 9, 2020

I, personally, would add a switch. A switch is a lot easier than pulling/unplugging all the time.

DaveMK · Dec 9, 2020

audioguru said:
Speaker wire will work fine and it can carry 15 times the current used by your 12 LEDs so thinner wire can also be used.

Perfect. Thank you.

DaveMK · Dec 9, 2020

gophert said:
I, personally, would add a switch. A switch is a lot easier than pulling/unplugging all the time.

Thanks. I would prefer a switch. Do you know of anything small and simple to attach?

Advise needed for running LED lights from a powerbank

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