Aluminum battery connectors. Headway cells.

[Patriot]

I just got 32 38120S cells in the mail. I spent the better part of two weeks now, figuring out what I wanted to use to connect the cells. My options ranged from copper flat stock, to making lots of little jumper wires with soldered eyelets.

It finally dawned on me that this is a bicycle, and that I should do my best to minimize weight. Even though the motor weighs 25lbs.

So, I decided to try some inexpensive aluminum flat stock from Lowes. It is 1/16" x 3/4". I bought three 3' pieces for about $10.

I spoke with the electrican, and he said that for aluminum, a 4ga wire is best. So, I figured the 3/4" wide stock would be as equivalent. He conquered.

Anyway, I'm going to try the aluminum stock to keep the weight down, and still keep my conductivity level as high as possible to pull up to a continuous 50amp draw at 48v.

pics will follow.

 

[gogo]

I had an older mobile home that had aluminum wiring. Several people warned me to go through, scrape the aluminum, and treat each electrical junction with grease that protects against corrosion. Apparently aluminum oxidizes easily and can become electrically resistive. It may be worth inquiring about with your electrician.

 

[Drunkskunk]

Aluminum is resistive. As metals go, its a poor conductor, even without the corosion and fire dangers Gogo refered to. Under the right conditions, you might turn the aluminum jumpers into heating elements.

But the real issue is the inneficancy of aluminum. 77% compared to 98% for copper.
Considering that your weight plus the bike, battery, and motor will likely fall between 200 to 300 pounds, how much efficancy are you willing to lose to shave an ounce or two off the total weight?

 

[Patriot]

I would prefer copper, but I really don't have access to the size of bars I want for connectors.

Is aluminum more resistive than copper? Yes.

However, when using the equivelant of 4ga wire for my connectors, it will offer similar resistivity to a 6ga copper connector. It will also be lighter. I just have to make sure I score the outside layer to get good contact. I spoke with an electrician about this, and he agrees it would work just fine, if not better because it's easier to work with for drilling holes, and lighter than copper. As far as performance goes, the the 4ga equivelant will make any resistive questions a non-issue.

However, I could end up being totally wrong, and the dang thing could practically explode in my face.

 

[boostjuice]

An Aluminium surface exposed to air forms a thin layer of resistive oxidisation only milliseconds after scoring. In order to get reliable conductivity at a compression joint, the use of lock washers which penetrates into the Aluminium surface is essential. As the teeth of the lock washers cut into the surface, they form an air-tight seal held under the torque of the bolt compression which will maintain conductivity long term, even when submerged under water. All Alluminium/steel chassis mains voltage appliances use lock washers at earth connection points. It is mandatory to comply with safety standards.

I think your weight saving aluminium idea is sound. You could even double the cubic volume of the Aluminium cell connecting strips and they would weigh less than copper strips weighing half its volume and provide minimal resistance.

 

[rguy56]

The dangers of aluminum wiring were wildly overstated. If the connection is proper, exactly as boostjuice states, you won't have any kind of problem.

 

[oofnik]

This is how I'm building my pack, using copper strips I cut and rounded from a flat scrap sheet. Still needs heat shrink and structural support. There are bits of double sided sticky foam between every cell for padding and airflow.
Tests at 30A look good so far. No heating. I don't exactly have an ebike to test with quite yet.

IMO, using aluminum conductors between cells instead of copper to save weight on an ebike is analogous to fitting a carbon fiber hood to an F350 super duty. :?

 

[mn_aerorider1]

If you don't want to construct your own straps, this site sells pre-drilled copper straps as well as other battery pack building hardware to match the 40138 cells:

http://www.rechargeablelithiumpower.com/oscommerce2/catalog/pack-accessories-c-24.html?osCsid=nugq3dkjibhbdqk7ehdelnlph4

Unfortunately, since I bought mine a month ago, they have upped the price from $.25 to $.81 apiece. Still not a terrible price for pure copper.

Brian

 

[Patriot]

An Aluminium surface exposed to air forms a thin layer of resistive oxidisation only milliseconds after scoring. In order to get reliable conductivity at a compression joint, the use of lock washers which penetrates into the Aluminium surface is essential. As the teeth of the lock washers cut into the surface, they form an air-tight seal held under the torque of the bolt compression which will maintain conductivity long term, even when submerged under water. All Alluminium/steel chassis mains voltage appliances use lock washers at earth connection points. It is mandatory to comply with safety standards.

I think your weight saving aluminium idea is sound. You could even double the cubic volume of the Aluminium cell connecting strips and they would weigh less than copper strips weighing half its volume and provide minimal resistance.

So, what you're saying is I can't use the regular SS split lock washers that came with the cells?

Oh man.

 

[swbluto]

IMO, using aluminum conductors between cells instead of copper to save weight on an ebike is analogous to fitting a carbon fiber hood to an F350 super duty. :?

I like the analogy. The "weight saved"/"total weight" ratio is pretty minuscule.

 

[AndyH]

If you don't want to construct your own straps, this site sells pre-drilled copper straps as well as other battery pack building hardware to match the 40138 cells:

http://www.rechargeablelithiumpower.com/oscommerce2/catalog/pack-accessories-c-24.html?osCsid=nugq3dkjibhbdqk7ehdelnlph4

Unfortunately, since I bought mine a month ago, they have upped the price from $.25 to $.81 apiece. Still not a terrible price for pure copper.

Brian

Thanks Brian. The prices are still getting dialed-in and vary with the supplier. They're down a bit now. Don't forget to ask for the E-S discount. Andy

 

[pgt400]

ACE hardware sells copper strapping in plumbing section, every 4th hole lines up perfect. You can double it up for lower resistance. Bendable, easy to solder to and cheap.

 

[Patriot]

I looked for the copper strap at my local hardware store, and couldn't find any. No matter, I just got done building the battery, and I still need to wrap it. Overall it looks good. Hopefully I won't have any problems with the aluminum connectors.

My electrician said I could easily get away with using the SS split washers instead needing to buy a bunch of the washers with teeth. He said, just sand it good to a shiny finish to get the best connection possible, and it will be fine. Also, making sure I give it really good torque when I finally get the BMS leads attached is vital, because that really is when it gets the best continuity between cells. Right now, it's just assembled with the screws being snug to hold it together. I'll take some pics and post them on here.

My new battery!!!

 

[Doctorbass]

That's nice battery packs you built guys!

A simple way to get flar cooper bar is to go to your home hardware local shop or similar and to take cooper tubing and then to flaten them.

simple..

cheap..

efficient!

doc

 

[Patriot]

As I checked the voltage, I got a good 51v with my cheap little meter. I don't have a digital meter, so I can't get an exact measurement. It's good enough to tell me the cells are good, which is all I care about now. I may have to invest in a good Fluke though, especially when my motor testing phase for the build will be coming soon.

 

[pgt400]

Pack looks great, which bms will you be using?

 

[Patriot]

^^^ I just ordered all the parts I need to to build GGoodrum's open source BMS.

I got the board in the mail a few weeks ago, and have been waiting for an excuse to buy the $60 in parts needed for the 16 channel version.

I will probably get myself a cheap SLA charger off ebay, since I won't need a very high current setup, and his BMS will apparently work well with cheap SLA chargers. This is a benny for me, because my budget is getting tight, and I don't want to spend $200 on a nice LiFePO4 charger.

All I need to do now, is beef up my soldering skills.

 

[pgt400]

Heres a pic of the strapping I got from ACE hardware. Who did you get your cells from? Maybe the guy who buys then for audio amps? (John I think). My plan is to use the same BMS, (2) 12 channels units and (2) 36 volt 6 amp chargers for my 72v 40 ah pack.
View attachment DSCN1514.JPG

 

[MitchJi]

Hi,

Also, making sure I give it really good torque when I finally get the BMS leads attached is vital, because that really is when it gets the best continuity between cells.

Be careful. I'm not sure if its an issue with the Headway Cells but Ypedal snapped a PSI Stud. He had been warned about the possibility and was proceeding very cautiously. It might also be possible for the stud to turn inside the cell (I did that once with a 12v automotive battery).

 

[Patriot]

^^^ I know. That's why I like the headway cell design better than PSI. The PSI/BMI cells of this type have a protruding stud that you attach a connector to with a small nut. This is the only design flaw (which is not really a flaw), but not preferable in design, imo.

These Headway cells have a large steel end cap that has a threaded hole which a small screw is screwed into. The threads are pretty beefy , and the screws are basically an M6/8? 6mm SS that screws inside it. Much better design than PSI/BMI imo. This helps minimize extra stud from sticking out which could potentially get caught or snagged on something. Also, if you want, you can attach much thicker bar connectors. Just get some longer screws to make them work, which is what I did with mine.

If you'll notice in my pics, the spots where the connectors double over to connect to the next row of cells above them, add up to 1/8" thick. The bars are already 1/16" x 3/4" wide. They are quite stout, and are equivalent to more than a 4ga wire, which gives me even more continuity than the rolls of copper straps with holes in them shown in the other pics. I got about 14 extra SS screws that are 10mm long to accomedate for the extra thickness. They have a much lower chance of getting snapped or stripped from assembly than a single fine 6mm stud.

Anyway, I'm just waiting for my BMS parts now, so I can get to work on my soldering.

 

[Ypedal]

Looking good !

I mostly agree with the psi vs headway difference in mounting options.. only thing im curious to know is how much of a difference in conductivity you get via Aluminum studs ( PSI ) and the plated or SS material the Headway cells use.. ( are the ends magnetic ? )

Next time you have the camera out, i'd love to see a closeup of the ends of the cells without the screws in them..

edit to add: The PSI threaded studs are Hollow !! so extra care is needed not to snap them off.

 

[Patriot]

I believe the ends of the Headway cells are nickel plated. A couple of them actually had a few specs of rust, which I easily brushed off. So, they obviously have some Fe in the steel caps, and are not stainless steel. The threads in the caps are plenty robust for a snuggly torqued and airtight connection to prevent further corrosion. If one keeps these away from the elements, I can't see them rusting to any significant level, even years down the road. Unlike the aluminum in PSI, the Headway threads or screws won't be nearly as easily stripped or broken off from mild torque.

The easiest way to describe the way they are built, is to take a "D" cell and picture a threaded hole in each end.

 

[Doctorbass]

I confirm... the headway cell have both end that are attracted with rare earth magnet .. and the cylinder case too... brieff.. all magnetically attracted...


for exemple, on the A123 cell it's only the nickel strip that are spot welded that are attracted witgh magnet.. none of the A123 M1 cell parts are magnetically attracted..... but the 18650 (1100mAh) A123 cell does.

Doc

 

[Patriot]

I'm not sure if these would be better if they were encased in aluminum or not. It certainly would make them a smidgeon lighter for Ebikes.

As it is, my 48v/20ah pack of 32 cells, with all of the aluminum connecting bars, comes in it at almost exactly 24lbs.

One benefit I can think of. The steel casing does make them much more capable of withstanding physical abuse. This may be beneficial for anyone building a motorcycle, or even an electric car. These batteries could withstand an impact better with less chance of rupture from impact, etc. I'm not sure how much of a factor it would be, but a little better in the durability department, none the less.

 

[AndyH]

... Unlike the aluminum in PSI, the Headway threads or screws won't be nearly as easily stripped or broken off from mild torque...
The easiest way to describe the way they are built, is to take a "D" cell and picture a threaded hole in each end.

http://www.endless-sphere.com/forums/viewtopic.php?f=14&t=8109