My wife has a set of LED lights that eat battery's (3) 1.5 AA and I wanted to convert the string to a USB adapter and plug them instead.

This USB port (https://www.amazon.com/SECKATECH-Re...939&sr=8-45&keywords=white+ac+to+dc+converter) outputs 5v 4.2A can I simply add a few resistors to reduce the voltage or do I also need to worry about the amperage?

In series AA battery's would produces 2400 mAh, I think, so is that difference negligible?

Thanks.

vbtalent?

 

Nothing to worry about, just plug it into the leds, 0.5v won't make much difference, done it myself several times with a phone charger.

 

Not needed but if it made you more comfortable, you can add in series a forward conducting shottky diode of proper current rating.

 

no need to worry use it directly , some USB ports even give you only 4.8 V not 5V

 

OK cool!

With additional mAh being produced by the outlet is that negligible?

When would you be concerned about too much amperage?

Thanks,

 

Can you post pictures of this "LED light"? (specifically the internals)
It "could" be relying on the internal resistance of the batteries to "feed" the LEDs with the proper current..
But I suspect it probably has a resistor or similar to set the current that the LEDs will receive..

A resistive load will only "draw" what it needs from the power supply.. The supply won't force all its power into it..

 

Not needed but if it made you more comfortable, you can add in series a forward conducting shottky diode of proper current rating.

It almost certainly has some internal resistance, if you can't get at it to measure it - and are better at maths than me; you can measure the current at 2 different stable voltages and calculate the series resistance, but you have to stay close to the specified nominal voltage. It might be as simple as measuring the current at the correct voltage and calculating the resistance to drop 0.5V.

For the "atom bomb to kill an ant hill" brigade - the ideal solution is a buck/boost converter. The only advantage is no dimming as the battery runs down - which isn't going to happen anyway running from USB.

Another alternative is a rechargeable lithium cell - the steady state terminal voltage is close to that of 3 series nickel chemistry cells. A lot of stuff designed for alkaline cells is less than satisfactory on nickel cells - a LED lamp should just be a little less bright.

 

My wife has a set of LED lights that eat battery's (3) 1.5 AA and I wanted to convert the string to a USB adapter and plug them instead.

This USB port (https://www.amazon.com/SECKATECH-Re...939&sr=8-45&keywords=white+ac+to+dc+converter) outputs 5v 4.2A can I simply add a few resistors to reduce the voltage or do I also need to worry about the amperage?

In series AA battery's would produces 2400 mAh, I think, so is that difference negligible?

Thanks.

vbtalent?

Hi,

How fast does it kill the batteries?

If the batteries are rated at 2400mAhr and the batteries run down in one hour, then they probably draw something like 2 amps which the USB port will not be able to put out unless you have a hub with a wall adapter that puts out 5v at 2 amps.
If the batteries run down in two hours, then maybe it is more like 1 amp which probably still wont work without the hub.
If the batteries run down in four hours you might have a chance at using the USB port with or without a hub.

Many people just use a 5v wall wart for this and so the computer does not have to be turned on just to run the LEDs.

 

Still no problem, " outputs 5 V @ 4.2A ". No specification on time to eat batteries given.

 

Thanks for all the reply's!!

"Eat batteries" was more of a metaphore in terms of time. I would say a few days of long light times and the batteries are done an overnight usage where she forgets to turn them off and the batteries are pretty much done.

So here's my plan of action... install an AC outlet with at least a single USB port (USB 2.0 I think) for continuous power, include a manual on/off switch and remove the battery box and wire up a USB plug in its place and plug it in... seems simple enough which is why there's probably some issue lurking.

I assume the resistor would be contained in the battery box?

 

Thanks for all the reply's!!

"Eat batteries" was more of a metaphore in terms of time. I would say a few days of long light times and the batteries are done an overnight usage where she forgets to turn them off and the batteries are pretty much done.

So here's my plan of action... install an AC outlet with at least a single USB port (USB 2.0 I think) for continuous power, include a manual on/off switch and remove the battery box and wire up a USB plug in its place and plug it in... seems simple enough which is why there's probably some issue lurking.

I assume the resistor would be contained in the battery box?

Is it intended to run off 3x alkaline cells?

Fresh alkaline cell can put out a smidge over 1.6V, no doubt the device takes into account the cell dropping just under 1V - or as much as you'll put up with.

The voltage isn't *THAT* critical.

If you want to run it from 5V - just measure the current and calculate the resistance to drop 0.5V at that current.

 

I've got several of those lying around. There seems to be a microprocessor circuit inside that flashes the LEDs.
They work fine with a 1N400x diode i series with the 5V wall-wart: would probably work without it, but I have tons of diodes

 

OP, the MAX current those outlets will output is 4.2A, and that's probably 2.1A per USB port. Don't worry about extra, unused amps. If your string of lights draws 1amp or 2 amps, you're still fine.

Even if the LEDs are driven with 5vdc and not 4.5vdc, you are over driving them, but the extra voltage is spread over all the LED lamps. Again, no need to worry. The supporting electronics in your light string are far more likely to break on their own, rather than an LED popping early from the voltage being a tiny bit too high.

Like the others said or implied, just wire in a male USB connector and you're good. No resistors needed. That's the nice thing about the string of lights you chose.

NOTE: I make LED lights for fun. I'm also familiar with power packs. If they say one port outputs 2.1amps, that's the max they will output.

 

Many thanks for the input.

I'm now free of alkaline battery's...

VB,