Battery advice for LED project

[nunny]

Hi guys,

I have a new project im undertaking whereas i need to drive a string of RGB LED flex on a battery pack.

ideally I would like the battery pack to be a custom made long cylindrical one, circa the same size a a "d" size cell but can be up to 1m long if needed.

I need the LED flex to run worst case scenario onto full white for approx 6-8 hrs. my supplier has x 2 different types of LED flex that can either run at 36w/m or 72w/m.

ideally I need to run x4m of flex at once. all the control side im happy with its just batteries are a new area that i have yet to explore and there seems to be so many options.

so questions are as follow.

• what minimum AH will i require
  
• what type of battery will best suit my needs.
  
• can this be mad from off the shelf cells joined together or does anybody have any ideas as what would be the best option..
  
• would i gain any advantage by running the 24v LED flex as opposed to 12v

.


many thanks in advance

Mike

 

[KJ6EAD]

Are you sure those are W/m ratings and not mW/m?

The higher voltage will be more efficient assuming you're using one of those segmented strips with the built-in limiting resistors. The higher voltage will also reduce your controller/driver current to half what it would be at 12V.

 

[nunny]

Sorry I just re checked, its actually

72w / roll for the 300 led which is 5m in length

or

36w/roll for the 150 which is 5 metres in length

regards

Mike

 

[nunny]

If I was to use the 24v strip, what issues would I have if I used say 4 x 6v 4000mah cells as per the link

http://www.thebatteryshop.co.uk/5dh4-0lap3-785-p.asp

and ran them in a series configuration.

Mike

 

[CocaCola]

If I was to use the 24v strip, what issues would I have if I used say 4 x 6v 4000mah cells as per the link

http://www.thebatteryshop.co.uk/5dh4-0lap3-785-p.asp

and ran them in a series configuration.

4 x 6v 4000mah cells 'might' power one 36W strip for 1½ - 2 hours or it 'might' power one 72W strip for about ½ - 1 hour... It potentially could fail trying to source the drain required for the 72W strip, and would struggle to supply the 36W strip, or at least be working hard...

 

[nunny]

Hi CocaCola,

this is where my inexperience shows im afraid.

What AH would i need assuming i was to run the lower wattage strip to achieve 6-8 hours.

I would also like to make it a simple charging system as i will be making multiples of this item.

is maybe Lead acid the way to go and to redesign my battery compartment?

Mike

 

[nunny]

Hi KJ6ead.

what is the best way of measuring actual usage?

Mike

 

[CocaCola]

At minimum in a perfect world, about 12,000mAh, in reality probably closer to 18,000mAh or better...

Each 24 Volt strip @ 36 Watts draws 1.5 Amps (1500mA)
Each 24 Volt strip @ 72 Watts draws 3.0 Amps (3000mA)

In theory, perfect math and in a perfect no loss world with no other variables you would take the batteries mAh and divide it by the drain (Amps) of the circuit as I listed above... But that is not the real world, lots of variables come to play based on my experience you can skim off about 25% of the run time right off the bat for a more practical number... Also at high drains like you are requiring the run time skim off percentage grows vs a very low drain circuit that will actually get closer to the 'perfect' theoretical run numbers ...

So in theory if the circuit draws 1000mA and you use a 4000mAh battery, you could in theory get 4 hours run time (4000/1000) in reality you will likely get closer to 3 hours (-25%)

 

[CocaCola]

Are you sure those are W/m ratings and not mW/m?

Those Wattage ratings are consistent to what I have seen for RGB strips, they are full Watts...

 

[KJ6EAD]

Hi KJ6ead.

what is the best way of measuring actual usage?

Mike

It's not so much about measuring, although that may be part of the process, as deciding. If you look at the specifications for your LEDs you'll see that there's a wide range of current draw rates depending on which colors are being used. Are you running all 3 colors at all times or what?

By the way, running all 3 at their maximum will not yield white light. If you want white, you have to reduce the power to 2 of the colors by some dimming method. You haven't said anything yet about what controls you're intending to use.

 

[nunny]

Thanks Cocacola

So to err on the side of caution, if i was to look at using x2 12v sealed lead acid 18AH packs wired in series?.

is that the best way to go for cost efficiency and ease?

Mike

 

[KJ6EAD]

Those Wattage ratings are consistent to what I have seen for RGB strips, they are full Watts...

Yes, he later said those were figures for a 5m length so the actual numbers are 7.2W/m and 14.4W/m.

 

[nunny]

KJ6EAD

i intend on using a dimmer that is controllable via a RF remote control, and the answer to the question if they are to run full white is i dont know.

the boxes are to be used to illuminate some set pieces and the event organiser may choose to have on static R,G, or B or a mixture of the 3.

i want to be able to work on worst case scenario, and plan to have them on full white for the 6-8 hours stated.

Next question will be coming up with a charging method to charge a quantity of these say 20 in a reasonably easy manner.

Mike

 

[KJ6EAD]

You can buy the chargers and even the controllers easily enough. Were you intending to build your own?

 

[nunny]

I intend on doing as much off the shelf as possible, ideally would like a charger bank so I can in essence plug all the battery boxes into 1 or 2 chargers, do these even exist?

Mike

 

[KJ6EAD]

Yes but they're very industrial. You can get separate small chargers much easier. You don't need to charge faster than 10 hours do you?

 

[nunny]

so a charger for each 12v battery?

i am going to case them into a box so would it be possible to get a 24 volt charger and keep the batteries in series or make a switching method to set the batteries back to parallel and charge x 2 from a 12v charger.

i see there is a hour rating against these batteries, i.e 18ah at a 20hr rate, is this relevant to my situation?

Mike

 

[KJ6EAD]

so a charger for each 12v battery?

i am going to case them into a box so would it be possible to get a 24 volt charger and keep the batteries in series or make a switching method to set the batteries back to parallel and charge x 2 from a 12v charger.

i see there is a hour rating against these batteries, i.e 18ah at a 20hr rate, is this relevant to my situation?

Mike

Yes, you can get 24V chargers. The 2A versions for wheelchairs are about $40.

Look at the datasheet for the battery. It will show a derating curve to give you an idea of your capacity at an 8 hour rate. This is what Coca was referring to when he said you'd lose 25% off the top.