EEVblog 1485 - PedalCell CadenceX Bike Generator LOL FAIL!

[EEVblog]

The failed PedalCell CadenceX Bike Generator from the previous mailbag video is tested, torn down, analysed, hilrariously laughed at, and dodgily repaired.

00:00 - Failed Pedalcell generator - getting the pinout
02:00 - The PCB
02:40 - Oscilloscope rotation test
03:45 - Dremel speed-up!
04:22 - Generator teardown
05:32 - Hmm, what's going on with these stator coils
06:00 - Hall effect sensors
06:58 - A-HA Gotcha. These magnets make no sense at all!
08:47 - Someone skimped at the glue factory
11:27 - It's just a BLDC Brusshless DC motor being used as a generator
12:48 - Nothing that can't be fixed with some epoxy
14:00 - Vrooooom!

[Bud]

That is so funny, LoL 

[FrankieTheDog]

Wow, I can't believe this thing is $300!!! I wouldn't pay more than $20 for a hunk of junk like this.

[EEVblog]

FYI, one of the co-founders and the PCB designer is a viewers and responded in the comments.
He did delete comment offering me a unit to review though 

[Kleinstein]

A bruchless motor makes a decent generator. There is nothing really wrong with this. The main point is the quality of the motor/generator with the glue failing. Not sure about the construction of the motor and how large the stress on the glue is - it definitely is a construction that needs really good glue - not just at the inside, but also between the individual magnets. The glue between the magnets could be the tricky part, as the tend to stick together and squeeze out the glue.  It could be as little as a failure in mixing epoxy glue or proper cleaning of the magnets and than failing quality control.

I would normally expect quality control to run the motor to a decent speed (like 1.5 times the rated speed) and check for vibrations. So they should detect weak glue.

The laminated core may be just the cheapest way to get the iron core to provide the closure for the magentic field on the inside. There is nothing wrong with this.

[Ian.M]

I would suspect the laminated core is for assembly reasons.  There is a long history of press fitting laminations onto a shaft to assemble electric motor rotors without welding or the use of bonding adhesives,  and using a solid rotor would either require a shrink fit or adhesive bonding of the shaft or machining the shaft and rotor as one integral piece from bar stock, at considerable extra expense.

While its *possible* to glue magnets on the outside of the rotor, I question its use in this case.  Nickel plated magnets are known to be more difficult to glue reliably, and differential thermal expansion + most epoxy's tendency to soften at elevated temperatures, (in some cases loosing much of its strength well below the boiling point of water) make this sort of failure of a segmented magnet inrunner rotor, with no banding to provide tensile strength, far too likely.  Outrunner construction would have kept the glue lines under compression, and pancake construction would have allowed the use of a substantial outer band to provide the tensile strength to retain the magnets.

[janoc]

That looks like a low speed motor (given that it has those Hall sensors) that got massively oversped - and the (non-existing) glue gave way.

[Sonny_Jim]

Very enjoyable video and I'm ashamed to admit that I didn't notice the magnets not going round until Dave pointed it out.

[free_electron]

When used as a motor the stator portion is magnetized so it repels the magnets : they won't fly off.
when used as generator there is no magnetization in the stator. (well there is but much less , and depends on the current draw. current in the winding creates a field)

[nctnico]

Wow, I can't believe this thing is $300!!! I wouldn't pay more than $20 for a hunk of junk like this.

That is rather overprized. Over here you can buy AC alternators for a few euro to power the lights on a bycicle.  Nowadays the alternator is integrated into the hub of the front wheel on most bycicles because it gives less friction.

[thm_w]

Wow, I can't believe this thing is $300!!! I wouldn't pay more than $20 for a hunk of junk like this.

That is rather overprized. Over here you can buy AC alternators for a few euro to power the lights on a bycicle.  Nowadays the alternator is integrated into the hub of the front wheel on most bycicles because it gives less friction.

Yeah, as Dave says battery bank is often better but in some cases a hub dyno might make sense. eg on rental bikes where you want ultra high reliability, or for people biking for days at a time, etc.

They seem to have standardized on 3W output:
https://bike.shimano.com/en-EU/product/component/deorelx-t670/DH-3N72.html
https://www.halowheels.com/shop/wheels/dynamo/vapour-gxc-29-dyno-front-wheel/

So in that way the Pedalcell is "better" (7W claimed output). You can see on their page they are not targeting casual riders at all: https://pedalcell.com/
Design could probably be improved though, appears overbuilt for 7W?

[Kleinstein]

The 3 W probably comes from the required power in the old days with incandecent bulbs, AFAIR 2.4 W in the front and 0.6 W for the back as the required power in Germany and possibly other countries too.

[EEVblog]

When used as a motor the stator portion is magnetized so it repels the magnets : they won't fly off.
when used as generator there is no magnetization in the stator. (well there is but much less , and depends on the current draw. current in the winding creates a field)

Yep, good point.

[EEVblog]

Very enjoyable video and I'm ashamed to admit that I didn't notice the magnets not going round until Dave pointed it out.

Had me scratching my head for a while, thinking it's some new thing I haven't seen before.

[f4eru]

A bit overhyped stuff.
Take a cheap motor from China, make a generator.
Why not, but in this case the motor was not up for the task it seems.
Using laminations for the rotor is common, but with surface magnets it has no big performance advantage other than re-using the punched out bits in the center hole of the stator laminations (which would have to be scrapped for recycling). -> so cost reduction and environment advantage.

The gluing process of magnets is not easy to do right, especially on an uneven surface.
Magnets can be magnetized before or after gluing.

Possible failure causes:
- overspeed outright (unlikely)
- overtemperature of the glue due to longer high speed/high load use
- excessive vibration (using a simple 6 diode rectifier induces vibrations magnetically)
- bad gluing process

[nctnico]

Wow, I can't believe this thing is $300!!! I wouldn't pay more than $20 for a hunk of junk like this.

That is rather overprized. Over here you can buy AC alternators for a few euro to power the lights on a bycicle.  Nowadays the alternator is integrated into the hub of the front wheel on most bycicles because it gives less friction.

Yeah, as Dave says battery bank is often better but in some cases a hub dyno might make sense. eg on rental bikes where you want ultra high reliability, or for people biking for days at a time, etc.

Recently I changed the rear light on my bike with one that can be powered from the dynamo in the front hub. I use my bycicle as a regular means of transport and having battery powered lights just sucks.

[EEVblog]

Recently I changed the rear light on my bike with one that can be powered from the dynamo in the front hub. I use my bycicle as a regular means of transport and having battery powered lights just sucks.

How much light do you need on the rear?
A red light flasher lasts for ages on a couple of AAA's.

[janoc]

Recently I changed the rear light on my bike with one that can be powered from the dynamo in the front hub. I use my bycicle as a regular means of transport and having battery powered lights just sucks.

How much light do you need on the rear?
A red light flasher lasts for ages on a couple of AAA's.

Until you forget about it exactly because it is so low maintenance  - and then it doesn't work/stops working (and you don't notice because you can't see it) when you need it. In the best case you only get a ticket. In the worst case you could be dead.

Dynamos (well, alternator but nobody calls it that) were used for ages and not having to care about the lights (that the battery is still good/charged, that you didn't forget it at home if removable, etc.) has advantages. Obviously, people who don't ride in the dark often and/or care about the extra resistance when riding don't like them but for the rugged city bikes that aren't used for riding long distances in complete darkness anyway it is a reasonably good solution.

Especially if you are using the bike every day for commuting to/from work (which I suspect is nctnico's case, given that he is from Netherlands where everyone is biking daily). Having to deal with a rechargeable front light and battery powered rear does suck - I had that on my old bike when I lived in Denmark (also a country where everyone bikes everywhere) and given how much night time biking one does there due to the latitude (4pm it is dark already from mid-fall to about mid-March, it is dark until 8-9am next day), that meant riding at least twice a day in complete darkness to and from work. You do want the lights to be reliable in such conditions and it is easy to forget things.

[free_electron]

if only someone made a small solar panel charged light ...
- you don't need to spend energy pedalling to generate power
- the sun comes up for free.

[thm_w]

if only someone made a small solar panel charged light ...
- you don't need to spend energy pedalling to generate power
- the sun comes up for free.

Yeah that can work well for some situations, especially if your bike is safe to be left outside all day. But other places thats not possible, and winter may be commuting in the dark both ways.
https://www.rydon.eu/product/rydon-front-light-color-housing-black/
https://www.aliexpress.com/item/1005001413273158.html

A flexible panel or backpack solar panel might get you 5-10W: https://www.electronicshub.org/best-solar-backpack/ could be good if you are doing a desert trek.

[CatalinaWOW]

A wrap with Kevlar thread would be a good way to avoid the adhesion problems.  The motor performance is highly dependent on making the gap as small as possible, but this motor didn't seem to care about that so there is room for this type of fix.

What seems odd is the weird mix of quality.  Board is top notch.  Motor isn't.  Perhaps the design staff is like Dave, highly interested and competent in electronics, not so much in the mechanical and electro-mechanical side of things.

[themadhippy]

.  Nowadays the alternator is integrated into the hub of the front wheel

Nothing new there,sturmey archer were doing way back in the last century with there dynohub..One of my first successful projects as a yoof was a battery back up that automatically switched over when you stopped pedaling,and charged the battery if the lights were off.

[oliv3r]

Hey Dave,

what's up with the squiggly PCB traces? They look like they where drawn by hand, by a child. Is there any sensible purpose for that? I get HF nicely rounded traces, but this definitely doesn't look like that.

[Per Hansson]

what's up with the squiggly PCB traces? They look like they where drawn by hand, by a child.

Occam's razor logic: the part is made in China, probably by children.
Just cuts out the middle man to have them design it too 

[nctnico]

Recently I changed the rear light on my bike with one that can be powered from the dynamo in the front hub. I use my bycicle as a regular means of transport and having battery powered lights just sucks.

How much light do you need on the rear?
A red light flasher lasts for ages on a couple of AAA's.

First of all: don't use a flasher. It makes it hard to see where you are actually going when it is dark. Not helping to be more visible; more the contrary.

Secondly: eventually it will run out of batteries (typically after a year at the worst moment; the batteries can not be changed without a screw driver) and in cold wheater batteries don't work that well. Nowadays I just flick a switch and the lights go on while driving. Driving without proper lights on a bycicle in the dark is asking for problems.

[thm_w]

Since Dave said red light, that would be on the back.
A flashing light is necessary during the day for visibility, its not realistic to have such a bright light on continuously.

Of course at night, solid light on front and back is preferred (with some pulsing pattern).

This is not quite Netherlands, where cars are aware they are being constantly surrounded by bikes.