Resistance of Elektrolumens 3-to-D Battery Holders

Today I tested the 3-to-D holders (which I tend to call "adaptors") for their resistance.

Adaptor Description

A word about the adaptor. It's a clever and space-efficient design that hold 3 AAs in series in a cylinder which is the size of a D cell. How to put the AAs in is clearly marked. The top twists off, and a detent in the case prevents putting it back incorrectly. There is a contact on the outside of each end. They are connected to the inside contacts and springs with four little gold-colored rivets. Although two of the AAs go in negative end first and one AA goes in positive end first, all three springs are in the bottom of the cylinder.

The Test Setup

I used a breadboard of wires, battery holders, a variable resistor and meters that I had put together. I ran a current (in the range of a little over an amp up to almost 3 amps) through the various components I was testing. I then read the voltage. Using ohms law I calculated the resistance as voltage divided by current. I did this a handful of times for each test and averaged the readings.

To calibrate the test set up I measured the resistance of a "short circuit." That is, I just connected the alligator clip leads that I use together. The resistance measured was 0.017 ohms. This properly should then be subtracted from any of the following test results. I don't do that because it is relatively small.

Testing procedures

The first test was the spring-to-spring test. I connected the clip leads to the two springs in the base of the adaptor which were connected to each other with a stainless bus bar. This test was done to measure resistance in two of the rivets and in the springs combined.

The second test measured the resistance of the overall adaptor with dummy cells in it.. I wrapped aluminum foil and then tape around three spent AAs I had. (Why do we save our old used batteries? For occasions like this, I guess.)

I questioned whether the resistance could be reduced by applying Deoxit contact cleaner to specific locations. First, I used it on the two visible outside contacts. The resistance seemed to fall a little. Then I applied it to all springs and contacts and rivets and battery tips. The resistance was not decreased much at all. (I used the Deoxit on only one adaptor, because it's difficult to apply to the inside and it's messy.)

For Test 3, I wanted to test only the rivets. The cap of the adaptor has a contact on both the inside and the outside that is connected with only a rivet. The resistance I found for that test was very low – just about equal to the bread board resistance.

Finally, my use of aluminum foil to make the dummy batteries is suspect. One would be justified in questioning the contact resistance of the foil itself. So, I went back downstairs for Test 4. The resistance when gently touching the leads to the foil is very low.

Test Results

Procedure__________________Adaptor 1________Adaptor 2

Test 1. Spring to spring
. . Resistance____________0.74 ohms
. . Readjust test leads
. . Resistance____________0.58 ohms

Test 2. Overall resistance
. . Resistance____________1.44 ohms_________1.15 ohms
. . Deoxit 2 outside contacts
. . Resistance______________________________1.04 ohms
. . Deoxit all contacts
. . Resistance______________________________1.03 ohms

Test 3. Rivet connection
. . Resistance______________________________0.026 ohms

Test 4. Aluminum foil
. . Resistance______________________________0.042 ohms

Conclusions
<ul type="square">[*]The resistance that one of these 3-to-D holders adds in a circuit is about an ohm, perhaps more.
[*]The connections that the rivets make to the stainless conductors seem to be good. The stainless connectors themselves I think are good – they have a large cross section.
[*]The connection to springs is poor, even using alligator leads. After removing the leads and reclipping them, the resistance changed. The amount of resistance depends on the geometry of the connection. To me this suggests some surface corrosion on the spring. Visual inspection supports this idea. The springs are not shiny, but dull. I suspect that most of the resistance is the result of the connection between the batteries and the springs.[/list]
Paul

Re: Resistance of Elektrolumens 3-to-D Battery Hol

Paul,

Thanks for the very specific analysis. Since I have no instrumentation, I simly listed the sequence of contact points in the adapter, in this thread.

Sounds like you might have gotten to the bottom of the story. What would you suggest as a remedy?

Wilkey

Re: Resistance of Elektrolumens 3-to-D Battery Hol

Wow Paul, seems your finding different than mine. Actually, the spring connection is number two in resistancecompared to the rivets, in mine. However, If you look in the end of the spring, you can see rivets also. I am not saying your conclusion is wrong, but is it possible that you actually measure the resistance of rivets to spring to steel than the spring to the battery?

VERY nice work Paul.

Looks like you really did a nice job, and did this right.
This confirms what I was thinking about these holders.

The design is great, but the connections need alot of work.

Thanks for takeing the time to do this. /ubbthreads/images/graemlins/thumbsup.gif

Sounds like the spring contact to the rivit that the spring sits is poor?

Bill

Re: Resistance of Elektrolumens 3-to-D Battery Hol

Wilkey,

I had not seen your post or I would have added the description of these tests to it. I'm glad to hear you got your holders safely. It appears that Wayne mounted a Herculean effort to get them all sent out.

For not having a DMM, you certainly squeezed a lot of information out of the holders. Listing the sequence of contact points is a good idea. It helps us discuss what's going on, and at first glance the connections are quite baffling. I agree with all six of your observations with the exception of number 3. I have found it not possible to put the cap on incorrectly.

You ask, "What would you suggest as a remedy?" Aye there's the rub. I can't think of anything that would allow us to use these adaptors for super bright incandescents unless we bypass the springs. Using your convention in your referenced link, one could put a small strip of aluminum foil on top of springs 1 and 2, connecting battery 1 cathode to battery 2 anode. Spring 3 could be bypassed by soldering a wire to a new electrode, placing the electrode between battery 3 cathode and the spring, passing the wire through the rivet hole, and soldering the other end of the wire to a larger electrode outside of the adaptor which would make contact with the Mag spring. This is a rather clumsy fix and is probably not practical. (I tried to get straight the battery and spring numbers. If I screwed up and it reads screwey, please let me know.)

If we're going to insist on passing currents like 3.5 amps, we need a new setup. Let me outline one I am thinking of, modelled after the way I put a double string of 123s in a Mag D host. I use a front bulkhead, in principle, like the cap on Wayne's holder . . . and a rear bulkhead like the bottom of Wayne's holder. I add a wooden dowel secured to the bulkhead or bulkheads in some way to prevent the batteries from rolling around and making an improper connection. The same setup could be extended to hold three stacks of AAs. Each stack would hold 2 or 3 AAs, whatever is needed. Instead of running the stacks of 123s in parallel, we would run stacks of AAs in series to get 6xAA or 9xAA or even 12xAA.

Maybe someone will have a neat idea for modifying Wayne's holders for high current applications. If not, I'll start working on the above idea.

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Shiftd and Bullzeyebill,

Measuring spring to spring in Test 1 does involve a circuit path that goes through two rivets. Using that test alone does not mean for sure that the springs are the problem. But the fact that the resistance changed when I re-attached the alligator leads in a different position on the springs implies that the problem is indeed at the interface between the leads and the springs. This is confirmed by Test 3 in which the resistance of the rivet connection in the cap is measured to be very small.

After reading your post I questioned the validity of the Test 3 measurement because the rivet had been treated with Deoxit contact cleaner. So, I pulled out a new adaptor (call it number 3) and ran the test over again. I measured 0.012 ohms. This confirmed my conclusion that the resistance is in the springs. It could be at the junction with the battery or the junction with the rivet.

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Jtice,

Yup. I think that the connections do need work. Note, however, that we (the high current guys) are trying to use this adaptor in a way that was not intended for it. It was designed, as I understand it, to provide a compact power source for LED lights. I have read that it works very nicely for that. But you can only push a good thing so far.

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ShiftD,

I took a peek at your post in the other thread on how to repair the 3 to D. It appears that you are able to bypass some significant portion of the resistance. You may have something here. It certainly looks more promising than my aluminum foil fix. /ubbthreads/images/graemlins/smile.gif

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Everyone,

I wish I had checked the latest threads before starting this one. There's so much valuable stuff in the other one, Troubleshooting the 3-D Holders. I wish there were a way that they could be shuffled together.

Paul

Re: Resistance of Elektrolumens 3-to-D Battery Hol

Maybe a Moderator could put all of these 3 to D threads together in one thread, except Waynes original thread re 3 to D's. Right, Wayne IS the Moderator. Go for it Wayne.

Bill

Re: Resistance of Elektrolumens 3-to-D Battery Hol

By all means. I would really like to see a concerted effort to fix this. After all, we are mod and gadget guys at heart.

PaulW, your bulkead idea seems to be the better solution for high current setups. For one, it drastically decreases the number of contact points. That in itself is a good thing. Unfortunately, it looks like one would have to build one for each three-grouping of batts. Unless you make the spacer rods themselves adjustable. I've been thinking about using telescoping radio antennas as the spacer rods. I believe you can buy these at RadioShack. In this design, you simply stretch the bulkeads out as far as you need them to be. It wouldn't be as sturdy as solid dowels, but would allow adjustability. Realistically though, I don't think the idea would have much applicability.

I agree with the original intent of these holders. But isn't 1 ohm of resistance the same 1 ohm whether you push a LS or a CA809?

Wilkey

Re: Resistance of Elektrolumens 3-to-D Battery Hol

Thanks for your input here guys. The problem of resistance being narrowed down to the springs is a help. I'll look into it.

Wayne

Re: Resistance of Elektrolumens 3-to-D Battery Hol

Wilkey,

Second question first. Well, an ohm is not an ohm. In a low current operation the resulting voltage drop (V = I * R) is not as large. Now the 809 requires 1.3 amps and requires 3 holders (3 ohms total) to give it the 11 volts it needs. The 5-watt LS is designed to operate at 0.7 amps and uses 2 holders for direct drive. In the first case (809) the voltage drop is V = I*R = 1.3*3 = 3.9 volts. In the second case (LS) the voltage drop is V = I*R = 0.7*2 = 1.4 volts. If you want to drive a WA01185 at 3.5 amps with 3 holders, the voltage drop would be V = I*R = 3.5*3 = 10.5 volts. This is an absurd voltage drop which means that the assumed 3.5 amps is not possible. In fact you would have to take the bulb out of the circuit, i.e. short circuit the holders and get about 3.5 amps.

On your first comment: In describing the adapter I'm proposing, I didn't want to get too detailed because it's a bit off-topic here. But let me add a little. The "spacer rods" do not function to keep the bulkheads apart. The batteries keep the bulkheads apart, and the single Mag spring keeps the whole thing in contact. It's possible to visualize this if you assume that the battery stacks won't twist around and buckle. What prevents the buckling is the rod (just one). It acts like a fourth battery stack and keeps all the cells lined up. But that doesn't prevent the front and rear bulkhead from rotating and getting misaligned. To do that, the rod is secured to both bulkheads so that the whole thing will always be aligned. But now the spring action won't work because the rod keeps the whole thing from being compressed adequately. The solution is to remove a lttle section of the rod (perhaps 1/4 inch) from just the right place close to the rear bulkhead. If it's done right, the spring will work and the configuration will be automatically aligned.

I haven't built one of these for the AAs yet, but I've built similar adaptors (for parallel stacks of 123s), and they work well. They use screws and sheet aluminum for the contacts and have negligible resistance. If and when I get a design working, I'll share the drawings with you. You might be able to post them for anyone else who chooses to try it. I'm not guaranteeing I can make this work, but if I do, I'll share it.

Paul

P.S. (Edit) for Wayne,

I just saw your post. I hope what we're doing here is helpful to you. It seems that while the holders work well for the Blaster VI and Blaster Jr., some of the folks who who are doing crazy things with incandescents would be really appreciative of your efforts to build a high-current model.

Re: Resistance of Elektrolumens 3-to-D Battery Hol

Thanks for the clarification Paul. I understand now. While 1 ohm is 1 ohm is 1 ohm (apologies to Ms. Stein), the effect of said ohm can vary dramatically depending on the specific power configuration.

Wilkey

Re: Resistance of Elektrolumens 3-to-D Battery Hol

Please see this thread. It contains further discussion on this subject, a mod for reducing the resistance, and a report of the resistance measured for the modified 3-to-D battery holders.

Paul