# Ideas for powering micro-diode strands for six hours

#### Ellie Dee

I am about to order 5000 2M strands of micro-diodes - 20 diodes per M - 40 total - and want them to last for the duration of a party - 6 hours - with the capability of on/off/slow twinkle. I have been told that the two coin batteries cartridge - CR2032 - won't last that long - that I will have to go to a 3AA battery cartridge. Seems like overkill to me. I've also considered some of the smaller battery banks (I've purchased 3500mA battery banks at Walmart for less than $5) and wonder if I specify a USB connector to the strands - if this might be a better solution - and it's rechargeable. Any suggestions? #### Pommie ##### Well-Known Member Most Helpful Member Do you have a link to the diodes? Mike. #### gophert ##### Active Member 40 diodes per strip x 5000 strips is 200,000 LEDs. Let's make sure assumptions. OPTION 1 (Dim light) White LEDs, 3.1v forward voltage drop 5mA 15.5 mW per LED 200,000 LEDs 3100 watts of power required for lighting LEDs Plus 20% energy lost (600W) Total 3700 watts. OPTION 2 (normal) White LEDs 3.3 forward 20 mA 200,000 LEDs 12400 W of power required for lighting LEDs Plus 20% energy lost (2500 W) Total 15100 watts For reference, you can get about 3 Watts from a D-Cell battery for 6 hours. For Option 1, you would need about 1200 D-cell batteries or For Option 2, you would need 6000 D-Cells If you want to use button cells, you'd need at least 10x as many but those are not intended for rapid discharge so you'd need even more (likely one battery per LED for the dim option. #### Ellie Dee ##### New Member Gophert - thank you so much for working on a solution to my challenge. My need is for a power supply for each of the 2M -40 diodes, 5M - 100 diodes, and 10M - 200 diodes strands. So I know that I can get one of the "lipstick case" battery banks with 2500 mA - and I need to know if this is large enough for either of the sizes to last for 8 hours with 80% brightness at the end of 8 hours. The size and shape are important as the fairy lights will be used for decorating tables around tailgating parties and the battery pack needs to be unobtrusive and easy to hide on table. #### Ellie Dee ##### New Member Pommie - I do not have a link to tell me what power is required to drive a strand of 40 micro-diodes. I'm hoping that someone will know what those are and how much energy they require - what V and A - to run the various number of diodes for 8 hours. #### gophert ##### Active Member Pommie - I do not have a link to tell me what power is required to drive a strand of 40 micro-diodes. I'm hoping that someone will know what those are and how much energy they require - what V and A - to run the various number of diodes for 8 hours. You know where to place the order but you cannot tell us where the link to the item you are ordering can be found? Something is wrong here... #### alec_t ##### Well-Known Member Most Helpful Member the battery pack needs to be unobtrusive and easy to hide on table. Unfortunately that's unlikely . Assuming a 20mA LED current, even a 2m LED string would consume at least ~2.4W of power, i.e ~20Whr over an 8 hr period, so its power supply would be quite chunky. #### Pommie ##### Well-Known Member Most Helpful Member My daughter bought some solar powered led lights similar to these. They lasted 4 hours after it went dark. She wanted them to last 6-8 hours so I opened one and found a (just one) rechargeable AAA battery. Replacing this with an alkali battery made them last for about 12 hours. So it may be possible. Mike. #### dknguyen ##### Well-Known Member Gophert - thank you so much for working on a solution to my challenge. My need is for a power supply for each of the 2M -40 diodes, 5M - 100 diodes, and 10M - 200 diodes strands. So I know that I can get one of the "lipstick case" battery banks with 2500 mA - and I need to know if this is large enough for either of the sizes to last for 8 hours with 80% brightness at the end of 8 hours. The size and shape are important as the fairy lights will be used for decorating tables around tailgating parties and the battery pack needs to be unobtrusive and easy to hide on table. What kind of high-class tailgating party is this where there are decorated tables? I've never been to one so I don't know but I always thought it was like a big informal spontaneous barbeque thing. Why does it have to be on the table? You can't hide it under the table and conceal it behind table cloth? Or hung off the underside of the table via the table leg support. 40 LEDs x 20mA x 8 hours = 6400mAh. Plus some headroom since in actuality you can't get that much out of it. So more like 8000mAh for a single LED string. If your strings take around 6V then a battery pack that size is probably going to be the size of a beer can...that's with a good battery chemistry like lithium, the pack will be around the size of a beer can. But I don't recommend you go with lithium since you have a lot of batteries to manage, they are fussy, fail dangerously, and are expensive (expect$80 for a single pack).

So with another cheaper battery chemistry, your packs would be even larger. You never said if you needed rechargeable or not. But recharging 5000 batteries doesn't sound like fun, but neither does using 5000 disposable batteries. Does the table arrangement let you get away with a single (or a few) large central batteries?

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#### Pommie

##### Well-Known Member
Why are people stuck with this 20mA figure? Modern LEDs are bright with just a couple of mA. If you just want them to flicker then a few hundred micro amps will suffice. This is for table decoration, not to light up the whole place. As i said above, one AAA battery lit a 6 meter string for 12 hours - not very brights but suitable for purpose.

Mike

#### dknguyen

##### Well-Known Member
Why are people stuck with this 20mA figure? Modern LEDs are bright with just a couple of mA. If you just want them to flicker then a few hundred micro amps will suffice. This is for table decoration, not to light up the whole place. As i said above, one AAA battery lit a 6 meter string for 12 hours - not very brights but suitable for purpose.

Mike
Well, it is a tail gate party...those are at night right? So might as well light up the place.

Unless it's during the day...but then you might need it to be bright to see it anyways? I dunno. I just use conservative numbers since we know nothing about his LEDs.

#### tomizett

##### Active Member
I think the first stop here should be to order one of the LED strings and do some subjective testing - find out exactly how much current you need for the brightness you want, and what the forward voltage is at that current. Then we can do some meaningful calculations on batteries.
Jumping in and building 5000 of something without a prototype sounds like trouble to me.

#### audioguru

##### Well-Known Member
Cheap bright LEDs have a very narrow viewing angle and will not work to light up a place.
My string of fairy LEDs are just a bunch of dots of light that do not light up anything.

#### gophert

##### Active Member
Why are people stuck with this 20mA figure?
Because the OP said...

last for 8 hours with 80% brightness at the end of 8 hours.
A few milliamperes to start will not yield 80% brightness unless you want to pretend this means something other than 80% brightness.

#### Pommie

##### Well-Known Member
80% of very dim is still very dim. The OP also stated that they had been told 3 AA batteries would do the job so we're not talking huge amounts of power.

Mike.

#### gophert

##### Active Member
80% of very dim is still very dim. The OP also stated that they had been told 3 AA batteries would do the job so we're not talking huge amounts of power.

Mike.
I have 2 meter strands that have LEDs That take 20 mA each (nom).
How do you know the OP's are dim?