My Ebike

[wurly]

Hi Everyone.
Well after a little delay, i now have my bike running with electric power. It isn't finished, as i intend to move things around a little or possibly transfer the whole setup to another bike.
I merely wanted to build an ebike for my own interest, just to see what exactly is involved. I have to say, i have the 'bug' and i'm already thinking about building another.
My commute isn't actually that far and i can quite easily manage the journey after a year of continued cycling. However, when i need to pop into town i usually take the car because it's all uphill on the way back, and to be honest it's quite a chore. I think my Ebike will change that.

Here is my old slightly scruffy MTB
(I am having trouble posting photo’s so I shall link you to my photobucket pages)

http://www.pedelecs.co.uk/forum/electric-bicycles/3429-my-ebike.htmlhttp://s219.photobucket.com/albums/cc224/gearhead188/ebike/

First job was to lace in the 36Volt Tongxin motor. I picked up an unused ‘shop soiled’26 inch dual layer rim from a local cycle shop for a tenner (bargain).I have never laced a wheel before, but luckily my brother has, so with his guidance and a book called 'The Bicycle Wheel' by Jobst Brandt and several internet spoke length calculators i went to SJS cycles in Bridgewater to buy my selected length spokes. A few days later after a couple aborted attempts my new wheel was trued, pre-stressed and finished. It runs nice and true and the all spokes make the same sound when plucked. (I did go around and recheck them after a few miles).

Fitting the wheel into my front forks was a dream. They were wide enough without having to stretch and bend them for clearance. Even the slots were they correct size. The only modification need was to lower the slot to enable the brake blocks to line up with the wheel. This was easily achieved with a new(ish) file and also gave me the opportunity to 'level' the slots so the wheel rim sits with equal distance to the brake blocks. I flattened the swages at the far end of the slots so the spindle l/nuts sit level. At this point i decided not to fit torque arms as i don't think the tongxin motor is going to be powerful enough to twist it's way out of the slots(i might rethink this later).

You may of read my previous post about my battery choice. I did intially want to try 3 12Volt SLA but decided on using 30 10000mAH rechargable NiMH D Cells. Using battery holders from Maplins i wired up 5 batches of 6 and a 20amp fuse all in series not really knowing whether this set up would give me the depth of discharge required, but you have to start somewhere!!

This nicely fitted into my daughters old school sports bag (she's 25 now and doesn't need it anymore)

You may see from the next picture my liberal use of reusable cable ties and automotive connectors. There is a good reason for this. I really didn't know how it was going to perform and i could change things fairly quickly as needed.

The battery packs were slowly charged at work as i still do not have a NiMH charger yet.

Eventually 'E' day arrived.

Last Saturday morning. I strapped (cable tied) my multimeter to the handlebars to monitoring current drain. My first electric bike ride was disappointing as i watched the current reach 5A the leds switching off all but the last red one and the controller cutting out at 30Volts. My choice of batteries were a mistake i thought to myself.

However i perseversed with my ride (it was a nice day ) switched monitoring current to monitoring voltage and finding a 'sweet point' on the throttle. OK i have some assistance not much, but at least something.
Some modification to the battery pack was required. Saturday afternoon was spent soldering up all 30 batteries (still in batches of 6) and refitting them to the Maplin’s holders. I cycled to work on Monday using the power noticing a slight improvement. I recharged the batteries once more not knowing if it was volt sag through battery connections or batteries not fully charged causing the lack of power.

Cycled home Monday afternoon (uphill)and what a difference! I didn’t have my meter with me, so I couldn’t tell how much currant drain was happening, but I was very pleased with the battery performance. Another recharge today, and I think the batteries are at maximum charge. At one point I noticed currant drain @ 16A, this was at slow speed but also showed what the power was available from the batteries.
[FONT=&quot]This is more like it.
At this point in time I think I need to get to know my Ebike better and this weekend I will see exactly how far the range might extend to. I might be even more pleased…..
Cheers
Mel
[/FONT]

 

[flecc]

Thanks for the report Mel. Those Maplin battery holders can be a bit dodgy if I know the ones you mean, and soldered connections are better.

At least the cells are proving to be ok in series, always a possible source of problems.
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[frank9755]

Interesting report, but all I get on the photo site is a big red no-entry sign with lots of Russian writing! Would be interested in seeing the pictures.
I too laced a Tongxin into a wheel the other week as my first wheelbuild; not as hard as I'd feared!

 

[wurly]

I have edited the link Frank. Try it now. It maybe your browser/blocking software.

The battery choice was my biggest concerns Flecc. Had the exchange rate been favourable at the time i needed them i might have gone for LiPo BMS charger and all the 'gubbins' from Ping. As i said, it's just an experiment for me and if the NiMH prove to be a good choice then it all turned out well.
Incidently the 30 cells weighed in at 5.27kg. I think i'll build a battery compartment out of sheet aluminuim and mount it low down on the frame as the bike does feel top heavy.

 

[frank9755]

Looks good!
One question - where is your controller? I couldn't see it. I hope it's not in the black bag on your crossbar, as they need to be in the open air to stay cool, as they have been known to burn out!
Also, what motor speed are you using and how does that translate to hill climbing and assist speed on the flat?

 

[flecc]

Incidently the 30 cells weighed in at 5.27kg. I think i'll build a battery compartment out of sheet aluminuim and mount it low down on the frame as the bike does feel top heavy.

That compares to the eZee NiMh battery, 5.5 kilos with it's plastic case.
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[wurly]

Controller is under the rack held on by..........cables ties!!!!!
It's a 190 rpm as suggested by John. It feels about right, can't comment on hillclimbing abilities just yet, but certainly assists up to 16mph where current drain reduces to 1A-2A depending on my effort. It would be nice to test it in a strong headwind. I'm sure we will get them soon...

 

[Fecn]

Nice work mkc1. I recently completed building myself a battery pack for another bike using 66 cheap Aldi C-Cells. Soldering is definitely a better option than all those Maplin battery holders - In the past I have found that the wire springs on the battery holders are only good for about 5A of continuous current.. over that and they start to get hot and melty.

Here's the pack I just finished building... 26.4v, 12Ah.... I got 11292mAh out of it on my last discharge test which I figure is good for a battery which cost me less than £66 to make.

 

[wurly]

Looks interesting. Especially the housing you are making for it..can you give me some more info?
The Maplin holders were bought to be used as 'holders' i didn't think the spring and contacts would be up to much. I thought i'd try it before taking a big soldering iron to my batteries.
So you used 4000mAH cells for £1 each? Like you say £66 is very cheap for a battery pack, I would have to make a pack with a 100 of those cells to get 36V 12AH and 66 for 36V 8AH......still cheap as long as the longevity of the cells is good.
How heavy is your pack?
Never been to Aldi and if i knew they stocked rechargeable cells i might have made some effort to visit.
Tell me, how did you do a discharge test? Did you just hook it up to a big resistor or gradually load the pack somehow? it certainly sounds like you did a bench test.

 

[Fecn]

Looks interesting. Especially the housing you are making for it..can you give me some more info?
The Maplin holders were bought to be used as 'holders' i didn't think the spring and contacts would be up to much. I thought i'd try it before taking a big soldering iron to my batteries.
So you used 4000mAH cells for £1 each? Like you say £66 is very cheap for a battery pack, I would have to make a pack with a 100 of those cells to get 36V 12AH and 66 for 36V 8AH......still cheap as long as the longevity of the cells is good.
How heavy is your pack?
Never been to Aldi and if i knew they stocked rechargeable cells i might have made some effort to visit.
Tell me, how did you do a discharge test? Did you just hook it up to a big resistor or gradually load the pack somehow? it certainly sounds like you did a bench test.

The cells came from three different branches of Aldi - I cleared them all out. They're next to the checkouts in 2-cell blister packs with an apparent price of £2.99, but they come up as £1.99 on the receipt. It took me a few days to get hold of all the cells that I needed.

The first thing I did was to implement a passive safety feature. NiMH packs under high loads can get very hot.. sometimes hot enough to melt the plastic sleeves on the cells, which in turn causes short circuits within the pack. I wrapped each cell in a single layer of masking tape to act as a non-meltable barrier between the cells. That way, there'll be no short circuits until it actually catches fire (smiley removed to work around 4-image-per-post limit)

In order to solder the cells together in a consistent fashion, I knocked together a quick wooden jig which would hold the cells nicely lined up whilst I soldered. I cleaned up the surface of each of the battery contacts using some 800-grit wet & dry paper and then tinned a small area using a very hot soldering iron. The aim of the game when soldering to batteries is to heat the cell as little as possible, and the best way to do this is with a very hot iron, a small contact area and a short contact time. Heat on, solder on, heat off.

The case for the pack is made from 90-degree plastic angle from my local homebase and High Impact Polystyrene Sheet which I ordered from mutr.co.uk about 2 years ago. It's the stuff they we used to use with the vacuum forming machine back when I was at school. I cut the HIPS sheet and plastic angle section using a pair of scissors and glued it all together with Cyanoacrylate (Superglue). Because I didn't trust the CA on it's own, I drilled a bunch of holes and plugged them through with a hot-melt glue-gun as a sort-of poor man's screw.

For the final touches, I added a few safety features. A 20A blade fuse inside the pack links the two halves. An LM35 3-wire Temperature Sensor is embedded in the pack and fed back to my charger via an old RJ45 connector. Two 72C 10A thermal fuses should hopefully provide an if-all-else-fails level of protection should it ever end up being charged incorrectly. I'm using a 250V 30A Neutrik Speakon connector to allow me to plug cables on/off the pack.

Each of the cells in the pack (including the solder blobs) weighs just-short of 71 grammes. The 66 cells in my pack weigh 4686g. I don't know what the plastic bits weight, but it's fairly insignificant. The whole pack probably weighs 4.8KG

I have a Bantan E-Station 902 RC charger which can charge any battery chemistry (NiCD,NiMh,LiIon,LiPoly,LiFePo4,Pb) from 1.2v to 50v. It can also do charge/discharge cycle test and hooks up to a PC to display graphs etc. I used it to discharge each cell to 0.9v before I connected them in a pack configuration. That way they should all require roughly the same amount of energy on the first charge cycle.

I haven't had the chance to thoroughly test this pack in the wild yet. I did a 10-mile test ride on Monday and it performed admirably, but I have a couple of 40-mile ideas to try out someday soon when the sun is shining.

 

[wotwozere]

Hi

I cannot believe you have made a batteryfrom the beginning, well done nice pics, you must be einstine.

thx

Bob

 

[wurly]

There is a lot of useful information there Fecn. Thanks.
I find it interesting to see how others go about their builds and you have obviously approached it with a fair amount of thought especially the temperature sensor. I tried to look up exactly what you are using, but all i found were voltage regulators..are you sure that is the device number and not a LM335?. It has me thinking about using a thermistor to control a voltage regulator during the charging process...but maybe i'll just go and buy a charger first and go from there.
I'm rather jealous of the battery charger you have there. I will have to sort out something soon. Using the the works Farnell PSU is fine while i'm at work, but no good to me for weekend use and it's not really suitable for NiMH i think.
The last charge up for my batteries was tuesday and they still have useful energy having used the bike everyday last week.I have been really thrashing the batteries to see how they perform. I gave them another charge this morning hoping to have a nice long ride this weekend and i'll report back.
Mel :0)

 

[Fecn]

I find it interesting to see how others go about their builds and you have obviously approached it with a fair amount of thought especially the temperature sensor. I tried to look up exactly what you are using, but all i found were voltage regulators..are you sure that is the device number and not a LM335?.

Yes.. A fair amount of thought went into this pack as I might just possibly have blown up a pack back in June and ever so slightly nearly set the house on fire a little bit (large burn hole in one office chair). The pack I exploded was a 12.5V, 6.9Ah pack made from 30xAAs. I used to use it for powering in-car gadgets when out of the car. I did a 2A fast-charge on it one evening using a current-limited variable PSU and forgot about it when I went to bed. As I've now experienced the joys of being woken up at 3AM by a smoke alarm and fumbling for my doorkeys in a dressing gown whilst AA cells exploded 4 feet away on my desk, I no longer charge packs straight from a variable PSU, and take all the safety features very seriously.

My bad on the temp sensor.. it is an LM35, not a 335. I don't have any special preference for that sensor.. It's just the one that my charger happens to use.

It has me thinking about using a thermistor to control a voltage regulator during the charging process...but maybe i'll just go and buy a charger first and go from there.

The quick and dirty trick to charging NiMH batteries is that when they're fully charged any excess energy comes out as heat. The general trick is to just dump some amps into the cells until they reach 45C and then trickle charge at 50-100mA thereafter. There is a more complicated way of charging which relies on detecting a minute voltage drop when the cells get full.

I'm rather jealous of the battery charger you have there. I will have to sort out something soon. Using the the works Farnell PSU is fine while i'm at work, but no good to me for weekend use and it's not really suitable for NiMH i think.

Funnily enough, I would recommend getting a dedicated charger with as many safety features as you can find ... after blowing up the pack in June, it was very easy to get my wife to approve the purchase of a swanky expensive charger.

The last charge up for my batteries was tuesday and they still have useful energy having used the bike everyday last week.I have been really thrashing the batteries to see how they perform. I gave them another charge this morning hoping to have a nice long ride this weekend and i'll report back.
Mel :0)

I still need to do a decent range test for my pack. Sadly it looks like this weekend's out now as I have to go up north for some work.

 

[flecc]

The quick and dirty trick to charging NiMH batteries is that when they're fully charged any excess energy comes out as heat. The general trick is to just dump some amps into the cells until they reach 45C and then trickle charge at 50-100mA thereafter. There is a more complicated way of charging which relies on detecting a minute voltage drop when the cells get full.

Temperature controlled charge cut off (dT/dt) by using a thermistor is by far the most reliable and accurate with Nimh, hence that being the normal way with good dedicated chargers.

They often have a secondary safety cut off at a predetermined voltage level, but the voltage increase slope at the end of charge is so gradual that it's a poor method from an accuracy point of view.

The modern view for some while is that continuous trickle charging is not advisable with NiMh. The recommended safe trickle charge rate has been C.05, but when trickle charging is incorporated now a better method of intermittent pulsing is often used, usually one part in three with the sum of the input under C.05. It's still best to timer limit it though to prevent cell damage.
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[Fecn]

Temperature controlled charge cut off (dT/dt) by using a thermistor is by far the most reliable and accurate with Nimh, hence that being the normal way with good dedicated chargers..

Although it is unusual for Flecc to be right about anything in this particular instance, he is (of course). I exported the graph from last night's NiMH charge. I was intentionally charging at a very low rate (C/10) as I was hoping to be able to illustrate voltage versus temperature cutoff.

The lines on the graph are Voltage, Charging-Amps, Temperature and Capacity respectively. The blue line is all over the place because the charger pauses every 10 mins to see how the pack voltage behaves - If the voltage drops too suddenly when the current is removed then it indicates a failed cell within the pack and the charge is terminated.

For the first 7 hours of the charge, you will see that the pack temperature hardly changes. At around 450 mins, the temperature starts to rise as the cells begin to convert the excess charging energy into heat instead of absorbing the charge. At around the same time that the pack starts to heat up, the voltage curve flattens off.. again because the extra energy is being converted into heat instead of a voltage increase. This levelling off of the voltage curve eventually becomes a slight dip. Although you cannot really tell from the graph, the voltage has already started to dip from the peak of 32.31 down to 32.28 at the end of the graph. If it had gone down another 2mV (down to 32.26) then the charger would have terminated the charge using delta peak voltage detection instead.

In total the pack soaked up 11417mAh on this charge. I'd normally expect it to soak up a little bit more than that (more like 14000mAh), but because the cells are so densely packed, there's not really anywhere for excess heat to go. I'll give it a top-off charge before I'm ready to use it anyway.

 

[flecc]

Although it is unusual for Flecc to be right about anything in this particular instance, he is (of course).

One of my luckier guesses then.

Glad those cells are working out ok so far, always a potential for mismatch problems with cheap NiMh cells in series.
.

 

[Fecn]

Glad those cells are working out ok so far, always a potential for mismatch problems with cheap NiMh cells in series.
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Although I soldered the pack together with random cells, I did a couple of rounds of weeding-out-the-weaklings whilst I was building the case. I gave the pack a few charge/discharge cycles down to 24.2V whilst monitoring the individual cell voltages with a multimeter. I replaced the weakest 4 'triplets' (12 cells in total) with fresh ones.

The dozen cells which didn't make the grade ended up in my kid's Christmas presents (which was the original reason why I'd bought a few packs before I realised how good the price was). The weakest cell I got was a mere 3066mAh. Every cell that I used in the pack managed at least 3650mAh measured at a C/2 rate.

 

[flecc]

Coincidentally I had the same sort of duds ratio when building a 128 AA cell battery for my eZee bikes, and by a
similar ratio of low capacity:

.

 

[Fecn]

Coincidentally I had the same sort of duds ratio when building a 128 AA cell battery for my eZee bikes, and by a
similar ratio of low capacity:

.

I read your AA battery page before building my own pack. I was interested that you'd gone for 4p32s rather than 32s4p as the cells-in-parallel config is better at dealing with weak cells. Each series chain is only as strong as it's weakest cell, where as each parallel cluster is a handy average of the cells within it. 4 bad cells (one per chain) in your pack would have a seriously impact on performance, whereas in a 4p config, the bad cells would all have to be in the same cluster for the effect to be as bad.

All a moot point now I guess as you tested half of your pack to destruction now anyway.

I have found a source of dirt-cheap tabbed 18650 2400mAh lithium cells now ... at prices comparable per-watt-hour with the Aldi NiMH cells... As I already have a couple of lithium pack balancers waiting for me to use them, I think a £100 LiPoly pack might be one the cards soon. I figure the Tesla motor company might be onto something with their battery pack built from 6500 x 18650s.

Sorry mkc1... we seem to have rather hijacked your thread to talk about batteries. Hopefully you're finding it interesting anyway

 

[flecc]

I deliberately chose the worst configuration to give worst case testing with cheap very small cells, rather than trying to include compensations as it was really more a viability trial of using than a need for a battery.

As I'd suspected, the current delivery rate was inadequate for a full size battery anyway.

Multiple small cells do perform better when they are adequate though, hence Tesla using them. Expensive though!
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