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Basic Electronics » Need to replace Wall Watt

April 24, 2015
by Ralphxyz
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I need to replace a 110v x 3.3 volt 600ma Wall Wart.

This is for a LED light.

Should I just stack some coin cells?

Or use a resistor with a 9 volt battery?

I haven't the slightest idea of battery ampacity.

April 24, 2015
by JimFrederickson
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I think you best bet would be to get a Switching DC-DC Converter.

They will provide the 3.3v, if you get the proper one, that the device is designed for
and expecting. They will also utilitize the power in the battery more effectively.

The cost is between $3-7 generally.

Using a resistor will be simple, but it is going to waste alot of your power potential
comming down from 9v and it is not going to produce a regulated 3.3v only something
approximate that will diminish over time.

April 24, 2015
by Noter
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Maybe a lithium-ion battery would work best, 3.60V is probably close enough.

April 24, 2015
by Ralphxyz
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Wow, reading the specs for lithium coin cell batteries really makes my head spin.

I'll look at other batteries for more capacity.

I have a rechargeable 3.7v 730mAh battery that I might try but I do not know if I want to use a rechargeable.

I have a bunch of lithium 3.6v AA batteries I'll give one a try. I had forgotten I had them.

I suppose I could always put two or more in series if I needed more ampacity also.

April 24, 2015
by BobaMosfet
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Ralphxyz-

Can you explain more about your project please? The load, running duration, and critical-nature will determine what you use for power.

Thanks

BM

April 25, 2015
by Ralphxyz
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Hi BM, the project is to replace a wall wart with a battery for a LED flexible shaft work light.

The wall wart outputs 3.3v 600ma.

The light will probable be on for a 1/2 hour every couple of days.

I do not want to have another cord to deal with.

I hope there will not be a problem with using the 3.6v lithium batteries I actually have 12 of them so they would last a long time.

April 25, 2015
by BobaMosfet
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Ralphxyz-

Thanks for the links. I looked up a compatible bulb to see exactly what it's power requirements were, and it was right at 2W, which pretty much matches the 3.3v @ 600mA output of the wall adapter.

The batteries you're looking at aren't sufficient, per their datasheet. The rating on the outside (2.4Ah) is an ideal rating, and only nominally guaranteed at 2mA at 68F, at 2.0VDC load. If you ignore the posted rating, and simply work with volts and current, the maximum recommended continuous current output is 60mA. So you'd need 10 in parallel to light the bulb for any length of time.

In this case, I think the 3.6V is probably okay. The capacity .v. current chart on the datasheet doesn't extend beyond 10mA output, so you can't really see how long it will sustain given current at higher levels. The highest they go is 2.1Ah and that only is only at 1mA.

Since they don't go beyond 10mA; hook 10 batteries in parallel, connect it to your bulb, and time it. Be aware of any expansion, ventilation, or thermal characteristics the batteries might have during discharge for safety.

BM

April 25, 2015
by Ralphxyz
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Thanks BM, I suppose I could make a battery case with my 3D printer.

Here is a 170 lumen LED flashlight that operates off 2 AA batteries

Looks like one battery would last about 10 hours. For the Energizer E91.

That would be ok.

Ralph

April 25, 2015
by BobaMosfet
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Ralph-

What exactly are you trying to light? Are you supplementing with solar or anything?

BM

April 26, 2015
by Ralphxyz
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It's a work light that mounts (magnetically) on a lath or band saw or other machinery.

Or it could be used for a work space light.

April 26, 2015
by Ralphxyz
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Well I replaced the wall wart with a rechargeable Lithium 3.7v 730mAh battery I had just to see it work!!

ta da works great, I probable will not do a duration test I just wanted to see it work!

I'l try some other batters once I get the holders for the batteries and find the male connectors.

I have the female connectors, they are similar to JST but not the same and are not interchangeable.

A real pain I could always switch the batteries to "standard" JST which I might have to do, it would make life simpler.

April 26, 2015
by Ralphxyz
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I found the male connector they are JST-PH connectors. The freight from this company is expensive they do not use USPS but they are the only ones I have found.

May 01, 2015
by BobaMosfet
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What is the type/number and manufacturer for your 3.7v 730mAh battery, please?

BM

May 01, 2015
by Ralphxyz
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Not sure it just says 3.7v 730mAH it is ~1"x 1.25"

May 02, 2015
by BobaMosfet
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Ralph,

Ah, OK. I wanted to look up a datasheet for it, but if it's unmarked, you wouldn't be able to tell. Sounds like a cell-phone type of battery.... is it?

BM

May 02, 2015
by Ralphxyz
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No not a phone battery. I got it from Rayshobby.net.

I got it to power the ESPToy.

It's a cool WiFi module.

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