Benefits of parallel batteries?

[Phaserburn]

I am wondering how one would calculate the benefits of having a duplicate set of batteries in parallel? For example, 2 sets of 3x123 powering a SNII, Blaster VI or MR-X? Are there increases in current provided or voltage under heavy load, up over 1A?

 

[LEDSmith]

The obvious benefit will be that your run time will double.

 

[PaulW]

Phaserburn,

Yes, both voltage and current, and hence power, are increased a little. Because there are two strings of batteries, each battery supplies only about 1/2 of the current it would otherwise deliver. Because the current is less the voltage drop is less. I have measured the voltage of a 123 cell to follow a relationship which is closely approximated by:

V = 3.0 - 0.3 * I

This relationship is good for currents between 1.0 and 2.5 amps through the cell. Let us assume a SN II on 3x123 draws 2.0 amps. The voltage output is:

V = 3 - 0.3 * 2 = 3 - 0.6 = 2.4 volts per cell

If we add another string of 123s, then each string will supply only about 1.0 amps, and the voltage is now:

V = 3 - 0.3 * 1 = 3 - 0.3 = 2.7 volts per cell

The added voltage will actually increase the current a bit to perhaps 1.1 amps such that the entire current draw is about 2.2 amps.

The run time will be approximately doubled.

It's a good question you ask because 2 strings of 123s can be fit in a Mag D. /ubbthreads/images/graemlins/grin.gif

Paul

 

[Phaserburn]

Yes, they could. That is exactly what I am after. I was actually thinking of 4xPila 150's in my MR-X. At 1.5A, the MR-X would stay in regulation longer I think than simply double the time it does on only 2 cells, due to the heavy load. Know anyone who is capable of making this adapter that I could talk to? Anyone out there who can help me make the Tandem-D adapter? /ubbthreads/images/graemlins/buttrock.gif

 

[PaulW]

Phaserburn,

You may get some useful ideas from reading about how to make a two stack.

Paul

 

[milkyspit]

PaulW, that's amazing! I started designing a tandem battery adapter for the MR-X light back in August (roughly) before I destroyed the rear endcap of the adapter due to my own incompetence in metalworking. /ubbthreads/images/graemlins/frown.gif

Funny thing is, I independently settled on EXACTLY THE SAME DESIGN with respect to the support rods attached to the rear endcap and "floating" above the front endcap. The only difference is that my support rods are made of lengths of PVC pipe of appropriate diameter.

Strange but true! /ubbthreads/images/graemlins/icon15.gif

One question for you about those wooden dowels: were you ever concerned that in a particularly bad scenario, the wood might become toasty enough to ignite? /ubbthreads/images/graemlins/mad.gif

Yes, when I'm engineering stuff I expect the worst...
/ubbthreads/images/graemlins/icon3.gif

 

[jayflash]

If a suitable bulb is available you may have better results by running the cells in series. The higher voltage better overcomes the resistance between all the contact points. The exception to this is that batteries with high internal resistance may benefit form a parallel arrangement. Paralleling cells has some other drawbacks which are avoided by a series set-up.

The practical problem may be obtaining the proper bulb. If none is available then parallel will be better than a single set of batteries.

 

[PaulW]

[ QUOTE ]
milkyspit said:

One question for you about those wooden dowels: were you ever concerned that in a particularly bad scenario, the wood might become toasty enough to ignite? /ubbthreads/images/graemlins/mad.gif


[/ QUOTE ]

Oh boy! No, I never gave it a thought. Under a high enough current condition, it could perhaps become a real torch! /ubbthreads/images/graemlins/grin.gif

Paul

 

[Cougar_Allen]

LOL! /ubbthreads/images/graemlins/eek.gif

Seriously, it can't get hot enough to char wood while you're holding it unless you have a lot more pain tolerance than I do, and it can't do more than char it a little because there isn't much oxygen in there. Worry about the insulation burning and melting -- the wood dowels are the least of your worries.

-Cougar :{)

 

[Steelwolf]

Remember that because you have two strings of cells supplying the current, they each only need to supply half the required current, which in turn means that you should have less losses to internal resistance. So under really heavy load, 1A and up for AA cells, you may find that runtime increases by more than double.

With twin strings of CR123, you may not see that benefit unless drawing maybe 2A or 3A of current. Lithiums do have lower internal resistance and better ability to deliver higher currents without their voltage dropping too much.

 

[RussH]

[ QUOTE ]
PaulW said:
[ QUOTE ]
milkyspit said:

One question for you about those wooden dowels: were you ever concerned that in a particularly bad scenario, the wood might become toasty enough to ignite? /ubbthreads/images/graemlins/mad.gif


[/ QUOTE ]

Oh boy! No, I never gave it a thought. Under a high enough current condition, it could perhaps become a real torch! /ubbthreads/images/graemlins/grin.gif

Paul

[/ QUOTE ]

Remember Fareinheit 451? That was supposed to be the average temperature for paper to start burning. You are looking at something similar for wood to char, depending on type. I'd be more concerned about it absorbing moisture & maybe becoming conductive. It's already going to have a 10-20% moisture content, IIRC. I don't see that as a problem in most applications however, provided you use it at the proper end of the stack (negative, in most cases).

 

[JSWrightOC]

You could also treat the wood with a lacquer or varnish. That would at least slow down the absorption.

[ QUOTE ]
RussH said:
*snip* Remember Fareinheit 451? That was supposed to be the average temperature for paper to start burning. *snip*

[/ QUOTE ]

That was a weird book. I had to do a report on that one in high school...

 

[Cougar_Allen]

Am I the only one who remembers when a breadboard rig was made on a breadboard? /ubbthreads/images/graemlins/eek.gif

 

[JSWrightOC]

I've never done it before, but my dad has. I am familiar with breadboarding, and "spaghetti" wire, however. /ubbthreads/images/graemlins/smile.gif

 

[PaulW]

I have a breadboard for testing flashlight components. Well, actually it's a piece of 11" x 12" pine. It was all I could find. It works well for holding stand-offs so that I could solder all wires. It's large enough to hold both voltmeter and ammeter, as well as a lot of battery holders and clip leads for bulbs. I find it useful for measuring volt-amp characteristics of bulbs and batteries.

Before I had it I couldn't get the resistance of my connections low enough to mimic what's going on inside a good flashlight. Now, by taking the ratio of voltage to current for a particular component, I can even find resistance even in the milli-ohms.

Paul

 

[milkyspit]

PaulW, you can't just say something like this without photos, man! /ubbthreads/images/graemlins/icon15.gif

Pretty please? /ubbthreads/images/graemlins/bowdown.gif

 

[PaulW]

Milky,

He he. Everything I say is without photos. I don't have a camera. I've stayed away from getting one because prices are falling. And I haven't taken the time to research what would be best for me. It's a matter of time and money going into flashlights, rather than a camera. Maybe I'll have to revisit my thinking on this. /ubbthreads/images/graemlins/blush.gif

But I can tell you the board itself is beautiful. It's a left-over scrap from an expensive piece of lumber. What's mounted on it is ugly though -- the wires are all different colors and sizes; the solder job is sloppy; and the battery holders are just nailed in. But it does the job.

Paul