Help with issues for LED strip

Shane1985

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Hi Folks,

I recently received a sample of a product that I had ordered (a custom item) from China. The product was a display case with LED lighting. The company produces Acrylic items and didn't have much in the way of LED products. Here's a picture of the underneath of the top of the case with the LED's:

Lid.jpg


1) The output of the light - when I placed batteries in the case the light was very intense, almost blinding. After a period of about 2 hours the light had faded signifyingly. After 4 hours it was very dim, and after about 5 and a half hours dimmer again. Reading on previous forum posts I think the issue is to do with a driver to control the output? The batteries had overheated and if you look closely you can see the battery wrapper was peeling off.

2) Battery life - I'm trying to work out what the battery life should be if the output of the LED's were regulated. I don't have any experience in this but was trying to google how to work out. My calculations thus far:

Batteries of 2.5 Ah
12 Volt LED strip

So to get the Amp Hours:
30 (Watt Hours) = 2.5 (Amp Hour of battery) x 12 Volts (LED strip)

So then to get the hours the batteries to last is dividing the watt hours by the battery power:
30 (Watt hours) / 9.6w/m strip = 3.125

Is that correct? Do I need to multiply the time above by 8 for the 8 batteries.

Any help would be greatly appreciated. Thanks.
 

DIWdiver

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Your calculation looks correct if there's a meter of strip in there. It looks like a little less to me.

You already multiplied by 8 to get 12V, so don't do it again.

Based on your description of the performance, I would guess there's no driver in there, just resistors. Did it seem like the output was steady for a while before starting to drop?

Drawing 9.6W from 8 cells shouldn't make them melt the wrappers (by the way, I noticed that before reading anything). You probably started out well above 9.6W. Or... The melting seems to be mostly on the outside. Was there a cover over them, that might have been drawing heat from the LEDs, and melted the batteries?
 

znomit

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Are those no name alkaline AA batteries? Looks like that needs a bit of power, alkaline batteries don't do particularly well in high drain devices.
Try some NiMH (I'm a fan of eneloops), you'll likely double the runtime and have more consistent light output.
 

Shane1985

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Thanks for the replies guys, much appreciated.

DIWDiver, there is about 85cm of strip so just under a meter. The output was steady for about 1.5 to 2 hours before I noticed a drop off in light. I'm surprised by the battery life being so low. I think I might need a redesign and just use a USB cable for power. The melting of the batteries could be from the led lights, I noticed that where the strips were glued on the other side of the lid had a slight ridge formed from the heat. I'll have to look into placing something underneath the strips to stop heat absorption in the lid.

Here's a picture of the case, at the top is a light diffuser above that the lid.

LED%20Case%2012.jpg


LED%20Case%208.jpg
 

Shane1985

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Thanks for the tip on the batteries NiMH batteries, will look into getting some. Although most I see seem to be 1.2 Volts, can't seem to find 1.5V in NiMH.
 

znomit

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Thanks for the tip on the batteries NiMH batteries, will look into getting some. Although most I see seem to be 1.2 Volts, can't seem to find 1.5V in NiMH.

Yep. NiMH are rated at 1.2V and give a fairly consistent voltage (1.3V-1.1V) over their discharge curve. Alkalines start at 1.5 and quickly drop to lower than the NiMH under significant load.
Perhaps not as bad as the eneloop marketing but you get the idea:
pp-eneloop-discharge.png

https://www.panasonicbatteryproduct...-batteries-aa-4-pack-with-individual-charger/
 

Dave_H

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It strikes me that these strips are probably designed for automotive (12-14vdc) power or for regulated 12vdc supply. The useful range for alkalines, taking 1.0v per cell as end of service, causes supply variation from 12.8v down to 8v. This assumes no other drops though there might be a series diode, probably nothing else from how it bahaves. Most likely strip uses groups of three series LEDs each with dropping resistor; easy to visually confirm with power off. Value of the resistor is usually a 3-digit value code. Dave
 

Dave_H

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Sorry I have to send this as multiple posts but something is screwing up my paragraph formatting, running everything together. Dave ------------------------------------------------------------------------------------------------------------------------------------ As for eneloops (as good as they are) doubling the runtime I am doubtful of. They are typically 2000mAh and would supply lower output voltage than fresh alkalines and therefore a bit lower brightness and current initially, but more constant brightness; so some advantage. Instinctively I would think a display case lamp should hold up more than a few hours between battery changes; even double that seems short to me.
 

Dave_H

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Problem with rechargeables is however good the initial cell matching (should start with same brand, type, capacity, and age) sooner or later one of the weaker cells will run down before the others. With eight series cells and probably no low-voltage cutoff, the dead cell may get reverse-charged, which will ruin it. Replacing with a new one will work for a while. On the other hand, using alkalines at the rate they are burned through would cost a small fortune, especially premium brands. Dave
 

Dave_H

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Thanks for the replies guys, much appreciated. DIWDiver, there is about 85cm of strip so just under a meter. The output was steady for about 1.5 to 2 hours before I noticed a drop off in light. I'm surprised by the battery life being so low. I think I might need a redesign and just use a USB cable for power. The melting of the batteries could be from the led lights, I noticed that where the strips were glued on the other side of the lid had a slight ridge formed from the heat. I'll have to look into placing something underneath the strips to stop heat absorption in the lid. Here's a picture of the case, at the top is a light diffuser above that the lid.
If strips were designed for 12v use, you will not be able to power them directly from 5v USB, without adding some type of boost converter. Visually check for the strip LED configuration I mentioned earlier (3 LED + resistor per group) which is for 12v. Looks like product is just not designed for long run-time.You might be able to obtain and wire in a constant-current LED driver which would help. Need to determine how much current required for acceptable brightness, work back to run time and decide if it's good enough. Dave
 

DIWdiver

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If you are willing to use a cable for power, why not use a 12V wall wart? They are cheaper than a few sets of alkalines, cheaper than any rechargables+charger, and will run till the cows come home, for pennies a day.
 

Dave_H

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If you are willing to use a cable for power, why not use a 12V wall wart? They are cheaper than a few sets of alkalines, cheaper than any rechargables+charger, and will run till the cows come home, for pennies a day.

I was assuming the OP wanted a non-wired power setup but if not, you are correct,
a wall-plug adapter would work well at low cost.

There are unregulated and regulated ones. I would skip unregulated (or poorly
regulated) usually a bulky transformer type. Switching-type of 12v 1.5A to 2A would
suffice. I see these regularly at thrift shops for $2-$3; always test first but have
never got a bad one.

Brightness and current drain could be reduced somewhat by inserting one
or two power diodes, or an additional series resistor, though not very efficient.

Dave
 
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