7.2v Regulator v.s. Resistor

**Shadar Al'Niende** · 08-15-2010, 08:22 AM

I have recently run into a design issue and came up with a question that I am not sure I know the answer to. Originally I was going to go with a 4AAA NiMH setup for 4.8v and about 1a current capacity. There just is not space for this however, so I am looking at using 2AA Li-Ion instead. I considered a 6v regulator, but realized that a resistor might be a simple option since it is only turning about 1.2 v into heat. We do this all the time acceptably with LED's. Is there a reason why either a resistor or a regulator would be more efficient, and more so that the size comparison would be worth it?

Thanks for the help guys!

*edit: changed my voltage, 4xAAA NiMH is 4.8 not 6v...*

**Rhyen Skytracker** · 08-15-2010, 09:16 AM

4 NiMH is 4.8Volts not 6 volts and since the NiMH have more mAh than a Li-Ion of the same size you could use 4 AAA NiMH in a 2 x 2 config and have a mAh of 1000. You can mount the sound board on top of the batteries to sabe space.

I am working on a saber not that only has an ID of 1" in the section where the batteries will be and the 4 AAA NiMH batt pack fits with room to spare.

**Skottsaber** · 08-15-2010, 09:18 AM

I'm pretty sure that the only issue is the same as that of the buckpuck vs resistor, in that the regulator would be more efficient. Personally I'd go with the regulator, due to the fact that Li-Ions are notably more volatile than NiMH.

EDIT: Dang, Ryhen! You got there first lol

**Shadar Al'Niende** · 08-15-2010, 10:00 AM

Originally Posted by Rhyen Skytracker

4 NiMH is 4.8Volts not 6 volts and since the NiMH have more mAh than a Li-Ion of the same size you could use 4 AAA NiMH in a 2 x 2 config and have a mAh of 1000. You can mount the sound board on top of the batteries to sabe space.

I am working on a saber not that only has an ID of 1" in the section where the batteries will be and the 4 AAA NiMH batt pack fits with room to spare.

You are correct of course Rhyen, i meant 4.8, unfortunately the 2x2 configuration was what i was planning on, and it took up too much space

Thus the desire for the Li-Ions.

Without giving too much away, the problem i run into is i only have about 5" of space lengthwise and about .75" of space height and width wise to try to mount my batteries. (the board will have the 1" clearance needed for the width but the batteries will not) Even with a 2x2 configuration that is still .413" of space taken up by my batteries and my .5" board will not fit in the space provided (about .3" left) with roughly 3.5" of space taken up by the batteries (if not more due to solder) i only have 1.5" left to mount a sound card that is 2" long.

Two Li-ions would take up more space width-wise of the batteries, but would save me roughly 1.75" of space length wise. I could use this space to mount my board and another component.

Once again, thanks for the help guys as this will be an interesting challenge to overcome.

**Rhyen Skytracker** · 08-15-2010, 11:15 AM

Just make a bigger saber. LOL

**ARKM** · 08-15-2010, 11:16 AM

Shad, I ran into this very same issue and asked Do-Clo about it. He stated that using a couple of 1 amp or 2 amp diodes to drop the voltage down would be better than using a resistor or voltage regulator in regards to heat. Apparantly a resistor or voltage regulator gets quite hot when dropping from 7.2v/7.4v to 4.5v/4.8v but not the diodes. I will be using this setup in my Impractical Tactical build so that I can have my US 2.5 on top of a 2AA 7.4v battery pack (to save on space for other things) but still use Lux III/P4 LEDs without too much heat.

**Shadar Al'Niende** · 08-15-2010, 11:47 AM

ARKM, do you have a link to the type of product you are talking about? I am not familiar with them but would like to be

Rhyen...there is more than one reason why this saber will be called Agony... the length is already one of them

**ARKM** · 08-15-2010, 12:23 PM

Radio Shack has some 1 amp, 1.5 amp (3 pack) and 3 amp diodes. Here's a link...

http://www.radioshack.com/family/ind...2032269&s=null

Those are regular diodes however there is a diode known as a zener diode which is specifically designed to regulate voltage. When purchasing Zener diodes, it will state how much the voltage drop is. However when I mentioned this to Do-Clo, he stated to use the regular diodes, not the zener ones (not sure why). As such, I will be using regular diodes. Anywho, from what I could find on the net, the standard voltage drop for a normal silicon diode is about 0.7 volts (regardless of current flow). They are quite small so you should have plenty of room for several of them. I will be using either 1.5 amp or 2 amp diodes so that a can run a 1400ma LED if necessary.