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Posted By Topic: 18v cordless battery as a power sorce?

benben
Mar 26 2018 17:19

hey guys, was thinking of running some 24v led strip (left over from a job) from my 18v milwaukee battery.

it works but had a few queeries,

1) is the 24v load going to be an issue?

2)will the led strip over drain my Lion battery and harm it? i have been told the battery tells the tool to stop going when flat through additional pins and since the led strip wont have these it might fully drain the battery. ( battery might have internal cut off)

appreciate any help ( i know not quiet electrical related sort of.)
   

evanh
Mar 26 2018 22:15

Too many variables to answer simply. You\'ll probably need to provide schematic of LED strip to be sure.

LEDs themselves have the diodic conduction curve, albeit a poor one, so are current driven, not voltage. Directly applying a fixed voltage low impedance power source to a LED will either not turn on or cook it in short order.

That said, it is possible to find the sweet spot with effort but not a generally advised approach.

What is usually done on cheap setups is add a series power resister so as limit the current through the LED. The resister can be embedded in the LED strip. This has the down side of throwing away energy though.

Better designs use a DC-DC converter that combines output current regulation, for the LEDs, with a flexible input supply voltage. This of course is a little box of electronics.


   

evanh
Mar 26 2018 22:31

If the strip is built for 24 volts (with the above mentioned resister) then 18 volts (21 volts fully charged) won\'t really be enough.

You might get a low light level.


   

evanh
Mar 26 2018 22:34

Is it 5 LEDs in the strip? I think it\'s about 4 volts per LED. Which makes it 5x4= 20 volts + another 4 volts for limiting resister.

   

evanh
Mar 27 2018 17:29

Oops, typo, resistor rather.

   

benben
Mar 27 2018 20:56

thanks for the replys, the battery measures 20v at the terminals (18v under load?)

the led strip is the standard type from the whole =saler, 24v dc,

i hooked it up and works fine but was worried about the workings of the battery
   

evanh
Mar 27 2018 22:35

I have no idea what you have purchased. How many LEDs in the strip? Can you see any resistors beside one or more of the LEDs? Is there any branding/model or datasheet?


   

evanh
Mar 27 2018 22:37

To answer the question I\'d need to know if the LED strip could operate below the minimum of the battery. But that depends on how the strip functions.

   

evanh
Mar 27 2018 22:39

If you have an adjustable power supply you could run the LED strip off that and find out what voltage they stop glowing at.

   

BrianW
Mar 27 2018 22:46

Since no one else seems to have actually read your question, then the simple answer is if the LED\'s work fine for you, then great, but the battery is a different story.

Emailing Milwaukee is probably your best option here.

   

Satobsat
Mar 28 2018 08:57

You could get yourself one of the DC to DC converters in the below link. You can leave it connected to your strip and monitor the voltage visually to get an idea of run time remaining for a given input voltage.
Both output voltage and current are adjustable so you need to be careful you don\'t blow up the strip when setting your system up.
Best to get a spec sheet from the LED strip manufacturer. If you know what brand and type of cells are in the battery pack you can get a spec sheet that will tell you the minimum discharge voltage of each cell add say 5% to this to avoid damaging your battery.
You should also think about what would happen if you do stuff up your battery,are they still under warranty? Are you happy to lie to the supplier and claim a new battery under warranty even though you used it outside of their recommendations?
Why not just buy the Milwaukee led flash light skin that uses the same 18V battery?
https://www.trademe.co.nz/electronics-photography/other-electronics/electronic-components/other/auction-1579380091.htm?rsqid=4baff28374024e87b419790d6b48dc73
   

benben
Mar 29 2018 19:47

brian W on point.

led strip works fine, dont care about that really.

just dont want to damage my battery, i might try it and watch the battery and see if it cuts it self off

cheers tfor the help