Construction pics of an xtracycle's LifePO4 pack

[oatnet]

Here are some pics of building the battery packs I built for the xtracycle. The "Freeloaders", as the xtra folks call the bags on the sides, have two sections. The bulk of cargo carrying capacity comes from the ballooney part of the back, but there is also a flat pocket that runs much of the length of the freeloader. I had these batteries in nicely configured bricks, but when I inserted them in this pocket they came in contact with the wheel. If I ifilled the pocket with a 1/4" plywood board it stopped the ballooning, but there wasn't enough room for the battery. Carrying the battery in the outer balloon pocket was too exposed, and not stealthy.

I realized that the 1" thick batteries would fit in the pocket if laid in a flat layer, the 1/4" plywood board could prevent bulge, protect the cells from road debris, and be a mounting platform.

I decided to connect the batteries with 1" copper strip I bought on ebay. Flat strip supplys maximum contact wtih flat screw terminals, and is also a structural element in my pack.

Phase 1: Making plates to connect the cells flat copper strip to get maximum conductivity to match the flat screw terminals.

I made a template of a connecting plate, traced it onto the copper strip, and drilled it out.


View attachment 02_IMG_3992 strip done.jpgOut of 50' of copper strip, this was all I needed.


The strips have been cut with metal shears, tapered at the ends to hold heatshrink, and pounded flat with a mallet while between two pieces of iron,

View attachment 3I cut leads for the charger to appropriately staggered length and then soldered them to the copper plate.

Shrinkrwap around copper plate. I cut out holes for the battery contacts and trim the ends to just fit. This provides strain relief for the charging lead and if the solder fails it will stay in place. I also like to minimize contact points so jacketing the plate makes it a little safer if someone jams a screwdriver in there.

A stack of plates ready to be installed.


Here is a completed wiring harness. I build it on the battery, and then heat shrink each charging lead in turn, ending up with a fairly rigid backbone. I built the harness on batteries but had to remove it and mount them the other way, hence this shot.

 

[oatnet]

The strip of wood up the center to act as a stiffener, protects the wiring harnesses, and it has a hole cut in it to thread a cable lock through. Also notice the holes drilled in the board for the wire ties. I later add large finger holes in each corner to make it easier to get in and out.


Here are the batteries laid out the way they are going to be mounted.


View attachment 3...and while using my heat gun on the final bit of shrinkwrap on charging harness, I melted the jacket on at least two of the wires, causing a short and a plasma ball that melted ALL of the charging wires and caused a bigger short until I clipped wires. One instant I was pushing the batteriens back against the wood, the next thing I knew there was an explosion of smoke. I thought one of the cells had gotten overheated and was ready to blow, LiCo style!


I originally intended to shrinkwrap these cells to the board. That probably would have worked well, although it is fairly permanent, not maintenance-friendly. Thanks to folks here, I found shrinkrwrap big enough, and I even mighta coughed up $35/foot for it... but not for a 25' roll of it, minimum order. Instead, zip ties are also non-conductive, light, strong, cheap, and easily replaceable for maintenance. I use one set of wire ties to wrap around the copper connector plates, holding each cell's terminals firmly against the center wood strip, preventing motion. I cut groove through the center strip so the wire ties are less exposed. The second string of zip ties holds the body of the battery to the boarrd, and also maintains some spacing between the cells to keep them cool. Also note the security hole cut in the center strip for running a tether.

Here is the back of the board, showing the wire tie pattern.

And finally, the two 36v packs assembled and ready to give my xtra 88.8v!

 

[oatnet]

One of the packs next to the xtracycle for scale.


The pack is halfway inserted here. The center strip is taught against the pocket, making a tent that shields the charging harness from contact.


The pack is fully inserted into the pocket. The flap sits above the pocket, giving me just enough clearance...

And finally, with the pocket closed. I need to take another picture with the velcro fully sealed and the charging harness concealed. As you can see, there is no way to tell there is a battery in the side pocket, even the hubmotor is concealed, making this the perfect stealth cycle. Plus it is flexibile enough to carry 6 bags of groceries and/or a human via the dedicated footpedals.

The packs ended up being just over 15lbs each, and the free radical keeps them stable and close to center of gravity. Although VERY convenient, I won't do another external charging harness, now that I have seen what can happen when you get a short in one...

I have found that with the weight of the batteries and the hubmotor, even standing still I can sway the mass back and forth - the bike is solid, but the hookworms are flexing! In addition, wiith all the weight in the rear my steering input on the front is more of a suggestion than an directive. Still, it tracks a true line and the long wheelbase helps at higher speeds.

 

[kyakdiver]

Oatnet,

Very nice job with the packs! I do have a soft spot for the Xtracycle and I think I'm going to try and do something like this with my Duct Tape packs.

Keep up the good work!!

Kyakdiver

 

[Roonster]

Hi Oatnet,

Really love your bike, looks like it came together in a great package.. Ever since seeing it I've been keeping my eye open for an Xtracycle I'd like to add one to my bike one of these days.

Where did you get the cells you are using? What are you using for a BMS and for charging?

Sincerely,

Roonster

 

[Dee Jay]

Wowee! Good stuff there oatnet... very neat design and thoughtful construction techniques.

So where do you park your bike again?? What's the location of your workplace? And do you have a anti theft device we should know about? RFID tracking device? Pager alarm? Just kidding! Keep it safe!

So many good builds on ES that I haven't commented on! Keep up the quality work everyone. 8)

J

 

[oatnet]

Really love your bike, looks like it came together in a great package.. Ever since seeing it I've been keeping my eye open for an Xtracycle I'd like to add one to my bike one of these days.
Where did you get the cells you are using? What are you using for a BMS and for charging?

Greetings Roonster,

Thanks!

I got the cells from Andy at FalconEV.com last October:
http://endless-sphere.com/forums/viewtopic.php?f=14&t=2503

Haven't looked at that link in a while - I documented "496 g (1 lb 1.5oz) on my kitchen scale", so 12 cells should weigh 13+lbs. Since the pack weighs in at 15+lbs, the entire packaging and mounting for pack, including the long (foolish) charging harness and wood panel, is only about 2lbs. Not bad!

I put many cycles through them in the old "brick" configuration - and hopefully many more cycles in the future. They came with the "Flintstone" chargers (do a search) which balance on charge, no discharge BMS but I rarely go below 70% DOD anyhow, to extend cell life.

-JD

 

[oatnet]

Wowee! Good stuff there oatnet... very neat design and thoughtful construction techniques.
So where do you park your bike again?? What's the location of your workplace? And do you have a anti theft device we should know about? RFID tracking device? Pager alarm? Just kidding! Keep it safe!
So many good builds on ES that I haven't commented on! Keep up the quality work everyone.
J

Thanks Dee Jay!