Building a battery box, an iterative process.

[Jonathan in Hiram]

Of course it seems that practically everything I do on an ebike is an iterative process but usually not quite as fast as it happened this time.

I spent my spare time last week building this battery box for my Long Distance Long Wheelbase bent project, got it finished to the point I could install all the electronics and put it in the bike and go for a test ride before I fabricated the removable side cover on the right side. After I looked at it for about a day semi installed on the bike I decided I could do better both in terms of design aesthetics and fabrication technique, not trying to make fine furniture since I'm going to paint it all anyway but I didn't like the slightly sloppy and untidy way the batteries (12s12p 18650) had to mount in the box.

I built that box by measuring and cutting the pieces and then gluing it up in place in the bike so that everything would be exactly the right angles and so forth and it was a real pain to do it, took me a long time.

This last weekend I started over on the box, this time I used a technique I've seen granite countertop installers use, they don't measure so much as they make a pattern out of thin strips of wood laid exactly where the outside edges of the countertop need to be and glue them together, usually with a hot melt glue gun. Each piece of granite gets its own pattern, then they take the patterns back to the fabrication shop and lay them on the slab of granite and transfer the dimension directly by tracing around it onto the granite.

Here's a picture of my finished pattern, the vertical piece in the middle is just to add stiffness to the long spans at top and bottom, I used superglue instead of hot melt and just let it sit for five minutes undisturbed.

Marking a strip for the angle to cut on the end, the strip is laying on top of the bottom tube for most of its length and I'm marking with a carpenter's pencil against the rear tube.

Clamping the next strip with the angle also cut on its lower end, the superglue tube is at the ready. You go around the entire perimeter of space you wish to fill with the box the same way, cutting and fitting a piece and then clamping and gluing it in place, you can hold the strips to the tubes with masking tape or vinyl electrical tape, electrical tape is nice because you can put a bit of stretch on it and hold things fairly tightly, you can see the electrical tape I used on this strip at the far right of the picture.

I did run into one minor problem I hadn't anticipated when doing the layout, the cable clamp bolt for the front derailleur would interfere by about 1/8" with the very front pointy portion of my box, I bent the arm a bit and ground a bit more off the end of the bolt and also thinned the nut a bit too and managed to get enough clearance without doing anything drastic.

And here is the finished perimeter of the box jigged into place after I built it exactly to the pattern, it fit the hole perfectly with no adjustments required. This time the removable panel is going to be on the left side and I have the right panel already cut and in place, the glue is drying as I type this. Using this technique with the wood strips made it about 70% faster and 100% better fit job and aesthetic design than what I did the first time.

The best part about having heavy batteries down low and forward in the bike is that it actually handles better now than it did as a bare bike, feels more solid and stable on the road and I'm more confident of the grip on the front tire.

 

[jkbrigman]

Jonathan - great photos - this bike is going to be a long-distance, high-efficiency MONSTER.
I can't wait to see what kind of test results you achieve with it....
Great technique and idea on using the strips to fab-up the box. The box looks great nested into the frame the way you have it.

 

[John in CR]

My longtail cargo bike has a similar battery placement and I too used some plywood at the perimeter to help wedge it securely between the top and bottom main tubes. I used a belt sander to make a U shape in them for a very snug and easily secured fit. It's an ideal spot for batteries, and that bike has been down a number of times with different riders with 0 damage to the battery box, though I hope yours never proves itself in that manner.

I hate to add iterations to your process, but I do have significant concerns.
1. Rope or bungies are no way to secure batteries, because they can't fully secure a battery. Sure they can stop them from too much motion, but your goal should be that they can't move at all. Even a small amount of movement from road bumps bouncing around in there can stress the connections between cells, and those stresses especially on tab welds lead to early failure.
2. Controllers have aluminum shells for good reason...to dissipate heat, and they need air flow to do it. We've seen numerous members suffer controller failures putting them in pannier bags, and your wooden box provides far more insulation in that tight space. Simply mount it vertically at the back of your battery box with the wires entering from the bottom end of the controller. It's easy to make water resistant, and with wires entering from the bottom end water won't be able to follow them into your controller. Then just paint it black or a bike matching dark color to hide it. If you're only running moderate power then you could cover it with some dark mesh material to still allow some fresh air flow but make it invisible to even close inspection. That also will give you nice short primary cables from the battery to controller to motor. The low power wires for throttle, ebrakes, and monitoring/measuring devices can be as long as you want.
3. Judging by the wire thickness it appears that you have power mains going up to the handlebars. You want power mains to be as short as possible for less losses in the wiring, and bringing your main power wires up to the handlebars so they're constantly flexing and open to damage is begging for trouble.

You've got a slick rig that looks to have great comfort for long range cruising, and especially with a DD hubmotor you've gotta build the electric drive system as failure proof as possible. If you get 20 or 50 or more miles from home, there's no pedaling back home, though at least the feet forward cranks will make it easier to walk the bike without banging your ankles on the pedals. Take it from someone who has tested a lot of stuff, and suffered plenty of failures exploring the limits.

 

[Jonathan in Hiram]

I don't have tab welds, I soldered every cell with a .008" diameter copper wire that fuses at 6 amps and let all the wires be longer than strictly necessary with a curve in them precisely for purposes of vibration resistance, it was a comment Luke made about parallel cells all dumping through one of the group that develops a short that got me thinking about it and then I saw Jehu Garcia do it on his Electric VW Samba bus project. For my parallel connections bars I hammered 14 ga copper wire fairly flat and the ends of the series strings are 10 ga also hammered flat. I think of it as a shade tree Tesla style pack.

You have to look closely at the picture but you can see the small wires, that's why I'm assembling the thing under a magnifying lens. You can only tell on a few of them from this picture but each one has a loop at the end where it solders to the cell, that's what the round tip pliers at upper left were there for, forming the loop at the end of the small wires.

I'm aware of the controller heat issue, I've been considering something like a P51 radiator intake, the P51 actually gained net thrust from the way the cooling system worked although I don't expect my controller to get hot enough for that to be a worthwhile exploit. Consider that 80% of the energy in that aviation gas turned into waste heat and you can see how there was quite a bit of energy to exploit in the cooling system.

No, no mains going to the handlebar, the kit came with some of that spiral wrap wiring neatener and I put all the leads that went to the controller in one, two brake leads, throttle lead and control box display lead. The wiring is nowhere near finalized, I have access to a warehouse full of junk electrical and electronic type stuff and will strip some appropriately heavy wiring out of something next time I get over there, it's not like I need all that much.

Thanks for your comments, I do appreciate your input, I read here on ES a lot more than I post and I've learned a lot from your many posts. Among other things I agree with your attitude that wearing protective gear leads you to take chances you otherwise wouldn't.

 

[trav]

I built a wooden box for mine as well, and it is indeed an iterative process. I have been thinking about rebuilding it one more time so that I can recess the side panels inside the frame. If I do it again, I am going to try your process; it looks like a good way to get a snug box.

One tip: try wrapping the box in some sort of waterproof material before mounting it. I rode home in a torrential rain storm the other day and was forced to wrap the box in a garbage bag.

 

[John in CR]

I don't have tab welds, I soldered every cell with a .008" diameter copper wire that fuses at 6 amps and let all the wires be longer than strictly necessary with a curve in them precisely for purposes of vibration resistance, it was a comment Luke made about parallel cells all dumping through one of the group that develops a short that got me thinking about it and then I saw Jehu Garcia do it on his Electric VW Samba bus project. For my parallel connections bars I hammered 14 ga copper wire fairly flat and the ends of the series strings are 10 ga also hammered flat. I think of it as a shade tree Tesla style pack.

You have to look closely at the picture but you can see the small wires, that's why I'm assembling the thing under a magnifying lens. You can only tell on a few of them from this picture but each one has a loop at the end where it solders to the cell, that's what the round tip pliers at upper left were there for, forming the loop at the end of the small wires.

I'm aware of the controller heat issue, I've been considering something like a P51 radiator intake, the P51 actually gained net thrust from the way the cooling system worked although I don't expect my controller to get hot enough for that to be a worthwhile exploit. Consider that 80% of the energy in that aviation gas turned into waste heat and you can see how there was quite a bit of energy to exploit in the cooling system.

No, no mains going to the handlebar, the kit came with some of that spiral wrap wiring neatener and I put all the leads that went to the controller in one, two brake leads, throttle lead and control box display lead. The wiring is nowhere near finalized, I have access to a warehouse full of junk electrical and electronic type stuff and will strip some appropriately heavy wiring out of something next time I get over there, it's not like I need all that much.

Thanks for your comments, I do appreciate your input, I read here on ES a lot more than I post and I've learned a lot from your many posts. Among other things I agree with your attitude that wearing protective gear leads you to take chances you otherwise wouldn't.

.008" = 0.2mm = 32awg wire which X 12 strands for the 12p is nowhere near enough wire to pass your battery current through even if it is controller limited to 20A. That 32awg x 12 is only the sum total equivalent of between 21 and 22 gauge wire. Even the cheapest Chinese pack wouldn't use wire that thin to pass battery main current. It's the parallel connections that can have a smaller gauge, because they shouldn't see main current.

 

[John in CR]

I built a wooden box for mine as well, and it is indeed an iterative process. I have been thinking about rebuilding it one more time so that I can recess the side panels inside the frame. If I do it again, I am going to try your process; it looks like a good way to get a snug box.

One tip: try wrapping the box in some sort of waterproof material before mounting it. I rode home in a torrential rain storm the other day and was forced to wrap the box in a garbage bag.

I only used wood for the perimeter frame. I glued each series string to the next before making my parallel connections. Then wrapped that in an overlapping layer of duct tape. The cell ends, the 2 large rectangular sides got cardboard and closed cell foam held in place by another layer of duct tape. Then the wooden frame around the perimeter. I next used 1mm aluminum sheet like wrapping paper as the outer shell, and after getting 2 good creases to fit the top piece of wood, I wrapped it like a Christmas present with the front, back, and bottom ends having the terminating edges of the aluminum, but in a double layer sealed with silicone. I used short flat head screws to attach the hidden layer to the wood before bending over the final edge and gluing it down. The wires and balance taps came out of the lowest point of the pack, which is the bottom rear corner.

I've used the same sheet aluminum on several battery builds, and it works like a charm. I just go to significant lengths to make sure the cells can't short on the aluminum, and that all corners have an overlapping layer of aluminum to prevent an open edge for water to enter.

Though I avoid the rain, it's not because of my battery, and it's been rained on a number of times. It even got hit by a rogue Pacific Ocean wave at the turning of the tide when LFP had it on the beach 4 years ago. A single drop of water got in the hall connector, which I neglected to protect with duct tape, but once we blew that out, the bike was back on the road.

John

 

[Jonathan in Hiram]

.008" = 0.2mm = 32awg wire which X 12 strands for the 12p is nowhere near enough wire to pass your battery current through even if it is controller limited to 20A. That 32awg x 12 is only the sum total equivalent of between 21 and 22 gauge wire. Even the cheapest Chinese pack wouldn't use wire that thin to pass battery main current. It's the parallel connections that can have a smaller gauge, because they shouldn't see main current.

It's not the first time I've done this, I have about a thousand miles on this type of pack fusing already.. You have to realize that a .008" wire bare in the open air sheds heat far more readily than a dozen of the same wires bundled together and wrapped in insulation, the longest path the heat has to get to the surface of the copper is .004" and I'm sure you know how fast heat propagates in copper, only silver is a better conductor of both heat and electricity. I've shorted out a pack with 16 ga wire as a test and the 16 ga burns up nearly instantly while my little fuses remain unperturbed. I've also deliberately shorted a cell fused this way by puncturing it while paralleled with eleven other cells and the fuse on the shorted cell takes it out of the circuit in moments.

http://endless-sphere.com/forums/viewtopic.php?f=14&t=58363

I'm retired on a limited fixed income more of which than I would like goes to medical expenses even though for my age I'm pretty healthy so I have to figure ways to do what I want to do by using smarts and scrounging rather than money. I got all the batteries from a friend who does electronics recycling, I got old laptop packs and stripped out the cells and tested them for leakdown, capacity and internal resistance then built capacity matched banks for my pack(s). If you look carefully at my picture you'll see more cells in the upper right corner that were soldered together in a more normal fashion, I've ridden both and can't tell the difference in performance at the rather lowish level I'm looking for. Given the fact I'm using cells of questionable provenance I'm prepared to take a slight performance hit for the added safety factor, I really, really don't want my bike burning up because one faulty cell shorts out at an inopportune moment and takes the rest of the pack with it because the other eleven cells in the parallel group take a dump through it.

 

[Jonathan in Hiram]

I built a wooden box for mine as well, and it is indeed an iterative process. I have been thinking about rebuilding it one more time so that I can recess the side panels inside the frame. If I do it again, I am going to try your process; it looks like a good way to get a snug box.

One tip: try wrapping the box in some sort of waterproof material before mounting it. I rode home in a torrential rain storm the other day and was forced to wrap the box in a garbage bag.

I'm either going with automotive paint which should seal the surfaces against normal levels of rainfall or some of this carbon fiber vinyl I found out about just a couple of days ago.

http://www.amazon.com/gp/product/B0059XEM9I/ref=ox_sc_act_title_1?ie=UTF8&psc=1&smid=AUDSH3EXZRVQ

Using pigmented shellac as a base coat seals things pretty well, it's designed as a sealer to keep stains and the like from bleeding through underneath your paint coating, say if your kindergartner scrawls on the wall with markers, you put this stuff down and it will keep that marker from bleeding through the paint you put over it, which it will without the shellac undercoat.

http://www.amazon.com/Kilz-Primer-Sealer-Stain-Killer/dp/B0006I0OQ6/ref=sr_1_cc_3?s=aps&ie=UTF8&qid=1410346730&sr=1-3-catcorr&keywords=kilz

 

[skeetab5780]

It looks like on your first pack you did it properly on the parallel connections, but on the second it looks as if they are in the series. So they may turn into heating elements. Unless I'm looking at it wrong.

 

[Jonathan in Hiram]

It looks like on your first pack you did it properly on the parallel connections, but on the second it looks as if they are in the series. So they may turn into heating elements. Unless I'm looking at it wrong.

The physical layout is different but the schematic is the same, I used fuses on either end of my second pack build just because it was more convenient.

I just got back from my third ten mile plus ride with the system as shown and so far everything is go.

 

[windtrader]

Great DIY battery build. So old school resourceful yet functional.

On first glance the thin wires between cells seems too small but is the idea current passing between any two cells is limited to one cell's capacity, so heavier gauge wire is not necessary? An added advantage is any failed cell is easily identified and exchanged?

 

[Jonathan in Hiram]

Great DIY battery build. So old school resourceful yet functional.

On first glance the thin wires between cells seems too small but is the idea current passing between any two cells is limited to one cell's capacity, so heavier gauge wire is not necessary? An added advantage is any failed cell is easily identified and exchanged?

Mostly it's a safety measure, keep the parallel groups from discharging all through a single internally shorted cell in that group because the shorted cell will blow the fuse.

None of the individual cells will put out enough amps to pop the fuse wire (6 amps) even if they are shorted, this is really about a 25 amp battery, the laptop cells are happiest at about 1/2 C but I have selected cells that will do 2C for a few minutes without overheating drastically. I sorted through a lot more cells than what you see in the packs to get the ones I used.

Identifying bad cells is pretty easy in this setup but you'll still have to pull the whole pack apart to change one out, at least in the plastic holders. The bamboo skewer build it was possible to change individual cells out fairly easily without disassembling the whole thing, however it was really bulky and hard to package. The bulk didn't matter on my last build (see my sig) because I had a large bag to put the batteries in that held them with plenty of room to spare, for this build though I needed a more compact physical package because of the space limitations inside the frame.

 

[windtrader]

OK. This makes more sense as the batteries you use are such low C ratings. Most run at multiple C which would make those thin wires inadequate.

 

[Jonathan in Hiram]

OK. This makes more sense as the batteries you use are such low C ratings. Most run at multiple C which would make those thin wires inadequate.

Fusing current in copper wire goes up really quickly with wire diameter, for instance copper wire with a diameter of .020" (24 ga) fuses at 29 amps when in open air.

http://www.powerstream.com/wire-fusing-currents.htm