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solderless power tubes

Old 07-31-2007, 07:08 PM
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dcnpaulk
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Default solderless power tubes

I have been looking at the "solderless power tubes" developed and sold by MEC, http://www.modelelectronicscorp.com/index.php . It uses a "silver power paste" to enhance electrical contact between cells placed end-to-end. The cells are placed in a tube which uses compression from threaded rods and nipples to keep the cells in close contact. They claim these work great for A123 cells and have the obvious advantage in that no soldering is required (no heat, cell replacement easy, etc.) Has anyone used these, any experience with them? Does this idea sound feasible? Is it too good tobe true? [] I worry about the "silver paste" migrating from the contact point toward the shell and shorting out. TIA for any thoughts on this.

Paul K
Old 07-31-2007, 07:14 PM
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Red Scholefield
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Default RE: solderless power tubes

I made up a couple of 4S packs with the Powertubes. I did not use the silver power paste however. The packs seem to perform just as good as my other ones with welded interconnecting straps.
Old 07-31-2007, 08:26 PM
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dcnpaulk
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Default RE: solderless power tubes

Thanks, Red. I bought one of those DeWalt 36 Volt packs and am going to make up a few smaller packs. It occurred to me that with these "solderless power tubes", there is no practical way to bring out nodes for balancing, is there? I was planning on using the Cell Pro 4s or the Balance Pro 6s, so I would need these. My understanding is that the a123 cells will not destruct catastrophically like LiPos, but it is still best to balance them, correct?

Paul K
Old 11-06-2007, 08:50 PM
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Brad604
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Default RE: solderless power tubes

"there is no practical way to bring out nodes for balancing, is there?"

It can be done.
I used some silver plated copper strips 0.01 x 1/2 inch, cut so the full width contacts the button top, and cut with a 1/8 wide x 1/4 inch solder tab bent at a 90 degree angle. I used a dremel cutoff wheel and #11 xacto and made narrow slits just wide enough to let the tab through. I inserted the tab, then a battery with silver paste, the next battery, etc., soldered the wires to the tabs (quickly). I dremeled a hole/channel in the end caps for the wires (so the wires wouldn't dangle outside), and also soldered to the end pieces. I used two layers of kapton tape to insulate the exposed solder joints on the the tabs. If you try this, make sure to remove all burrs from cutting the strips. I also cleaned the strips with steelwool and alcohol/paper towel before assembling.

I've also seen it done just by drilling some holes, and squeezing the balance wires in between the cells. But that method has less contact area than using 1/2 wide strips. A bit higher losses I'd think, but at 30 amps probably ok. My motor pulls 70 amps though, so I wanted to do it right.

Note about A123. The button part you normally think of as the top of a battery and the positive terminal is actually the negative terminal. The case is positive. Learned that the hard way and had to take it all apart to fix...

Anyone know of a source for good quality silver paste, that's less expensive than the stuff MEC sells?
Old 11-07-2007, 09:38 PM
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dcnpaulk
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Default RE: solderless power tubes

That is a very clever solution! Not being so creative (and also cheap!), I decided to do it on the cheap. I used the side-by-side cell configuration as in the DeWalt batteries, keeping the tabs in place whenever possible (good for 4 and 5 cell packs). When necessary, I used commercial bars to link cells (solder to the tabs, not thecell). I found that for my purpose the side-by-side configuration fit the bulkhead spaces in my planes just right! I would have had problems with long sticks. Not being able to find the right size shrink tubing for these packs, I used glass fiber strapping tape, the kind used for heavy duty pqckage sealing. This tape I found is extremely light and tough. It also has good dielectric insulating properties. Soldering balancing nodes to the tabs was no problem.
Old 06-28-2009, 03:05 PM
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jcjr7
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Default RE: solderless power tubes

anytips on making two 5 cell packs from a 10 cell dewalt pack?

I am a beginner, better yet would you or anyone prepare a two 5 cell packs for me for me for a fee?

have broken the dewalt pack down but seem to get confused on putting the pack together with balancing wires.

I can order the balancing connectors and already have one set of deans plugs pigtails and one hyperion balance connector, it has one red wire and 6black wires, which is what they told me would work for a 5 cell pack.

plan to use one 5 cell pack for the electristar and have a spare 5 cell pack for a quick second flight.

3.4V times 5 cells equals 17V for the motor which seems to be close to the stock setup of two 7cell nimh 7.4V 3000mAh, equals 14.8V for the motor.

The lipo stock set up is two 7.4V 3200mAh 20C discharge batteries with balance, lipos which equals 14.8 volts for the motor.

How would I figure the mAh for the A123's?

How would I figure the mA
Old 06-28-2009, 04:07 PM
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everydayflyer
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Default RE: solderless power tubes

http://www.slkelectronics.com/DeWalt/hints.htm

A123S comes in 2300 and 1100s MAh sizes only.

Charles
Old 06-28-2009, 04:11 PM
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Zeta30
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Default RE: solderless power tubes

jcjr7

Here is a great site to help you with your balance connector confusion. I use this site a lot and is very useful.

[link]http://www.scriptasylum.com/rc_speed/_lipo.html[/link]
Old 06-30-2009, 10:20 PM
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dirtybird
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Default RE: solderless power tubes

If you want the tubes from MEC you are too late. They quit last fall.

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