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Re: Another EV bike :)

Posted: Sat Feb 08, 2014 11:55 am
by mattcarr
Wow Chris, that is great work and amazing to see. You really have been putting in some effort there.

Good to not that when you connected one pack to your motor that the coltage drop wasn;t too much - lets hope it is the same when it come to some real testing.


Re: Another EV bike :)

Posted: Sat Feb 08, 2014 12:17 pm
by ChrisBarron
Thanks Matt, yes the small voltage drop does look promising. I'm looking around in the garage for a suitable load, and I have an old milklfloat motor, rated for 72V, at about 15HP. Hopefully it will draw 20-30 Amps continuously at 37V, or something in that ballpark, to give me something to check the pack's performance against.

I've just soldered tabs to another ten modules this morning so they're ready for the interconnects. That gives me another 37V pack of ten modules and it took less than two hours, the interconnects will take about 20 mins to add.

I've underestimated how many tabs I would need and have run out, so I'll be cutting anothe 800 tabs tonight while I watch tv.

At this rate I should probably start thinking about the design of the motor mount, before sending plans to the machine shop who will CNC it for me.


Re: Another EV bike :)

Posted: Sun Feb 09, 2014 8:25 pm
by ChrisBarron
The second pack has come together nicely, and I'll soon be starting the assembly of the two remaining packs. I'm starting to think that unless I'm careful I'll have an accident, because the packs are quite flexible as a result of me not locking each of the packs ten modules together (to enable easy disassembly if needed). I'll figure out a way to add some rigidity to them , but for now I'll be very careful, I've already had 2 tabs accidentally touch one another and even with discharged cells the plasma ball was pretty impressive !

I've started working on the design of the electronics required to monitor the voltage/temperature of each battery, and possibly also add a takeoff point to allow external charging/discharging of each internal module to be carried out to aid with balancing , should it be required.

Here's how I assembled the second pack...

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Look at those bonded strips at the bottom right, seven -ve at the bottom and seven +ve above them, and only a small gap in between them keeping the amps at bay. Hence why I'm being very careful !

Re: Another EV bike :)

Posted: Wed Feb 12, 2014 9:53 pm
by ChrisBarron
I wasn't sure this time would actually come a few weeks ago, but happy to have finished assembling all 4 packs.

The three laying down are being charged by the open frame variable supply on top (below the Fluke meter), I'm slowly bringing them up to 41V. After 41V has been reached I'll stop and check individual submodule (21 cells) voltages to determine if balancing is needed.

After assembly the voltages of each of the three latest packs were 36.47V, 36.63V and 36.55V , which is pleasingly consistent considering that all of the submodules were made from roughly equal mixes of cells of similar measured capacities, all at slightly different voltages and before any charging had taken place.

The pack stood up on it's side is being charged module by module at a painfully slow 2.5Amps. Each module is absorbing roughly the same amount, between 36Ah and 38Ah (some differences might be as a result of using a hobby charger which needs to be reset after 10Ah has been delivered). If it is possible to extract 25Ah from each pack then then the whole battery is a 100Ah 37V unit !

The metal straps coming from the end of the packs will all eventually be bonded together with a copper strap/bussbar, to which I can bolt through and bond regular ring/eye terminals to them.

I've been looking into adding some sort of external support structure and I happen to have some rigid plastic panels (you can see them slid between each of the three horizontal packs) which I could clad both sides of each pack with. Then all I would need is a large enough metal enclosure for each pack.

Electronics wise, I'm still looking into it !

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Re: Another EV bike :)

Posted: Fri Feb 14, 2014 10:31 am
by mattcarr
That is some great work there. So, the pack is 100ah at 37 volts - 3.7 kwh. Do you know what the weight of it is so far?

I am thinking that I may well start to build a small pack for myself. I want a 24 volt pack that I can use to run my travel fridge from on a day out, so I am looking for around 14ah in capacity. I may do a 12volt pack as I have a nice rugged 6 watt portable solar panel I could hook up with it.

Re: Another EV bike :)

Posted: Sat Feb 15, 2014 9:25 am
by ChrisBarron
An attempt to weigh one of the four packs on the bathroom scales says they're 10kg on their own. Then , weighing myself first holding the pack in my arms and then subtracting my weight, the scales read just under 10kg. (bathroom scales aren't too accurate at the bottom end of the range usually, but this doesn't seem too far off....I suppose it depends if yoiu worry about half-pounds or not !)

The weight of a single cell is about 45g to 47g.

I have 210 cells, so 10000g / 210 cells = about 47.5g per cell inclusive of solder, tabbing strip and plastic spacers.

My 18650 pack weight should finish up at about 43kg, including enclosures, mounting hardware and electronics.

The dry weight of the engine which I removed is accepted to be 140-150lbs (min 65kg) , (there was also a 1000cc engined version weighing in at 180lbs !) Add to that 65kg the engine fluids (3L oil + 3L water) , the very heavy exhaust (11kg) and a tank full of fuel (21.5L at 0.737 kg/L) the total weight of the original engine and support system was about 97kg. Considering the starter battery and frame mounted electronics (ignition coils, rectifier, ignition controller) and I reckon that I have about 100kg to play with in order to stay within the limits of a standard bike

The electric motor I'll be using, (unweighed so far....or perhaps I already did that but forgot !) must be in the region of about 20kg, so that's about 40kg less than stock so far. I need to add in 24 headway cells, the motor controllerand possibly an onboard charger too....I think even then I still have plenty of headroom to install the supercapcitor and still run lighter than stock :)

The Headways would add another 740Wh, so 4.5kWh total, and if I replace the volume and weight of the supercapacitor with more Headway's, or even more 18650's I could potentially get to over 6kWh which I think would give me a very nice range.

Matt, for a 12V 14Ah system I guess you would need to go with 4 series cells, for 12V - 16.8V. Just plucking figures out the air here for convenience, if you used 1400mAh cells you would need 40 (4 series, 10 parallel, '4s10p'), at 47.5g/cell to get a pack at the high end of your requirements weighing just under 2 kg. with cells of 2100mAh capacity it would weigh 33% less.

All I would say for your application is that some sort of low voltage cutoff device would definitely be required for unattended operation !

Re: Another EV bike :)

Posted: Sat Feb 15, 2014 10:14 am
by ChrisBarron
Some more info.....

Each 210-cell pack measures (before enclosing) 310mm x 285mm x 70mm. For 925Wh at 37V.

I've weighed the motor and controller (and some short interconnecting cable)at 29kg combined

Total weight so far, for the 3.7kWh 18650 pack + motor + controller = 72kg.

I've designed the layout for shortest cable runs, so will allow 2kg for power cable and another 1kg for Anderson SB120 connectors to hook them into a power bus.

I guess I'm 25kg under stock weight, so adding more cells of either 18650 or Headways doesn't look like it will cause a weight problem. I prefer Headways just for the sustained currents they can produce. The 24 Headways which I have weigh around 8kg, for 740Wh at 37V. (adding a further 24 would be really nice)...thats about 90Wh per kg - which is pretty amazing because my 210-cell 18650 packs also yield 92.5Wh per kg !

I were to use new 18650's I'ld be happy relying on them alone to produce the currents I need. If the cells were new I suppose a modular battery pack ncould be produced so if I were mostly running about locally I could do so in lightweight mode, adding a support pack for more range/current when required.

Re: Another EV bike :)

Posted: Sun Feb 16, 2014 3:24 pm
by ChrisBarron
The first pack has been clad now, and reliable terminations have been added.

The cladding is a high temp thermoplastic sheet which I had lying around. It's fixed to the cell holders by screws which screw into a carefully drilled pilot hole into a gusset between cells in the holders.

I'm glad the pack is modular because when I was screwing into one holder yesterday, with a 12mm long (dia 2.5mm) screw it drove in at a slight angle and punctured a cell. Nothing seemed to be wrong at first but a few minutes later there was a pop and the cell convcerned emptied it's electrolyte, inside the cladding.

Replacing that cell took less than 15 minutes, including removing the cladding, and I've reduced my screw length to 10mm to make sure it won't happen again. As a safety test i measure for continuity between each screw and battery terminals now.

The termination of the strips has been made by folding a piece of copped sheet over the stack of strips and soldering them together with the copper. A hole is then drilled through the copper and the strips and a bolt installed. Some offcut plastic strips provide a shield for the terminals and produces a nice amount of spare room at the top of each pack for fitting some monitoring electronics.

In the side of each pack there are cutouts, placed over one of each submodule's interconnector, to which I'm going to attach balancing/monitoring leads, via 11A polyfuses at the submodule end(resetable fuses).

The cladding and terminating takes about an hour, and is well worth it because of the additional safety and in particular rigidity which it imparts to the submodule assemblies.
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Re: Another EV bike :)

Posted: Mon Feb 17, 2014 4:14 pm
by ChrisBarron
A bit more detail about the termination/terminal method I'm using.
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Re: Another EV bike :)

Posted: Mon Feb 17, 2014 4:23 pm
by ChrisBarron
3 full packs completed now :D

The one on the left in these pictures is still being charged module by module with a hobby RC charger at 2.5A. The modules take about 32Ah before they come up to 4.2V and then another 4 to 6Ah as the current falls from 2.5A to 0.02A

This last pack will be clad in the same way as the others once it's charged.

I need to make a small 10-cell pack now to test some ideas for pack voltage/temperature monitoring devices.
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