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# Need help, regarding LED circuit

#### YEN

Dec 13, 2017
3
I need help in the configuration of a Circuit.

My circuit Consists of 9 5mm LED's

Each LED is rated at 20ma at 12V

what battery do recommend for powering all 9 LEDS at at least 9 Volts

I know that the LEDS need to be connected in parallel otherwise the LEDS will be drawing too much voltage.

so a run down of components
• 9V LED X 5
• 9 volt battery
• Push switch
I need a resistor before the LEDS but am stuck.

This circuit is for a Bike light Project if that helps at all.

I know what in series the Voltage is simply added together

at 9 volts and 9 LEDS, wouldn't it be 81 Volts ?

#### kellys_eye

Jun 25, 2010
6,514
If the LEDs are rated for 12V operation then you ideally need a 12V supply.

This presumes the LEDs are pre-wired with series resistors to ensure 20mA current flow when 12V is applied.

At 9V they will draw 15mA and there will be a reduction in brilliance (not much) but they will still work.

You will need to wire them all in parallel and the total consumption will be 5 x 15mA - 75mA (assuming you use the aforementioned 9V supply)

#### YEN

Dec 13, 2017
3
If the LEDs are rated for 12V operation then you ideally need a 12V supply.

This presumes the LEDs are pre-wired with series resistors to ensure 20mA current flow when 12V is applied.

At 9V they will draw 15mA and there will be a reduction in brilliance (not much) but they will still work.

You will need to wire them all in parallel and the total consumption will be 5 x 15mA - 75mA (assuming you use the aforementioned 9V supply)

Thank you for the reply, i am not sure what the Forward voltage is on the LED's

They ARE pre wired, I just picked any old 5mm LEDS.

I need to have a total of 9 LEDS each rated at 20ma and 12v in a circuit with a Push switch.. Not much more to it then that.

https://gyazo.com/7ca17d66a1a1c137e0d2211de2d20df4

What i am using

https://www.ebay.co.uk/itm/3mm-5mm-...hash=item58d8f9f909:m:mxpyY_UXvItZOM5lclKqaug

#### kellys_eye

Jun 25, 2010
6,514
Pre-wired LEDs already have the series resistor fitted so no external resistors are required.

Your eBay link shows the LEDs to be fully capable of working at 9V or 12V, running at 9V just means slightly lower light output.

If you want to get the full brightness from them at 9V then you will need to change the resistors soldered to the leads. Don't bother - it will be hardly noticeable.

#### YEN

Dec 13, 2017
3
Pre-wired LEDs already have the series resistor fitted so no external resistors are required.

Your eBay link shows the LEDs to be fully capable of working at 9V or 12V, running at 9V just means slightly lower light output.

If you want to get the full brightness from them at 9V then you will need to change the resistors soldered to the leads. Don't bother - it will be hardly noticeable.
Thank you very much for your Replies.

#### Audioguru

Sep 24, 2016
3,656
The ad for the cheap Chinese no-name-brand LEDs is missing the important spec's of brightness and viewing angle. They might be too dim and might produce such a narrow beam that you cannot see them unless they shine directly at you. They might be fine in a flashlight but poor for a bicycle.

From 9V their current will be about 14mA so 9 of them will be 126mA. A little rectangular 9V alkaline battery will last for about 3 hours and will slowly dim during this time.

#### BobK

Jan 5, 2010
7,682
They are not cheap. £1.99 for 1 LED and resistor! You could get 100 for that price.

Bob

#### Audioguru

Sep 24, 2016
3,656
The ebay photo shows about 15 of them for 0.99 of a British pound. Shipping is 3 pounds.

#### BobK

Jan 5, 2010
7,682
The ebay photo shows about 15 of them for 0.99 of a British pound. Shipping is 3 pounds.
If you look below, it lets you pick the size, color, and quatity. If you pick 10mm, white, and one, then press “buy it now”, the price is £1.99

Bob

Sep 24, 2016
3,656
It is a rip off.

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