schmidt SON 'pressure compensation device'

[Brucey]

The 'pressure compensation device' has been fitted to SON generators since 2002. For a long time I thought it was a diaphragm system connected to an axle-drilling, so that it would allow for pressure variations but still make a positive seal against water ingress. But actually it appears to simply be a length of tubing connected to such drilling, but open at the other end, such that its volume is enough to allow for possible temperature variations.

From the Schmidt website;


in red here fitted;


This page http://thelazyrandonneur.blogspot.co.uk/2007/04/son-dyno-hub-pressure-compensation.html describes the operation of the system in more detail, courtesy of a Peter White posting.

However this unit;



from here http://www.ibikempls.com/2013_05_01_archive.html

appears to have the 'pressure compensation device' (PCD) fitted and was described as having bearings in good condition, just rusty internals. So water got in there, either through the bearings or through the PCD. The guy is in Florida, so maybe it was salty water. I know you can get some water through the bearings without the bearings immediately failing. I also know that the breather hole can be blocked (eg with excess grease) and that this will cause the PCD to be ineffective.

But it does raise a few questions; is the open tube meant to allow the generator to dry out if it should ever get wet inside? Is there another failure mode? If the water is contaminated does the (now dirty) tube start to 'wick' water up it?

The internal state of used SON generators is not widely known; few people have seen inside a used one because Schmidt have variously made them difficult to get into, and/or won't sell you the tools to do the job. In fairness their factory overhaul costs are pretty reasonable, (20 euros for bearing replacement, 40 euros for PCD upgrade and bearings, both plus return postage) but from the UK the postage costs (about £10 each way to/from Germany) more than doubles the bearing replacement costs.

Some other Hub Generator snuff pics;



Union Wing 3 (basically similar to the first model SON 1996-1999, with no breather of any kind)



Shimano DH-3N30 after 'some use'

both above from here;http://translate.google.co.uk/translate?hl=en&sl=de&tl=en&u=http%3A%2F%2Fwww.mtb-news.de%2Fforum%2Ft%2Falternative-nabendynamo-zu-son-shimano-der-sp-dynamo.557756%2F

I've seen a few corroded shimano units too. Typically they go draggy and/or start making a scrawping sound which may lessen somewhat with use, but then be bad again after a period standing, or after the generator is given a smart tap with a wrench (which causes rust flakes to get into the magnet gaps again).

The more I see things like this the more I think Sturmey Archer's original (1930's!!!) design was in many respects a much better arrangement; it may have been born from a happy accident (they probably built the first one to fit a hub brake shell, I suspect) but in this design the airspace between the bearings is very small, and the generator parts are not inside it. Disassembly is very easy, and the generator and bearings can be overhauled and/or rustproofed quite independently of one another.

cheers

[mercalia]

Glad I use a £25 BM bottle dynamo - Some of those pictures are really dreadful, given the expense of the original units?

[[XAP]Bob]

My bottle dynamo failed after one season - and was never really that good (compared with a hub) in operation.

Given a wheel with a hub dynamo can be had for ~£40 I'm not convinced that the bottle is good value...

[Brucey]

I think it is only fair to point out that most such generators last five or ten years with no attention. Failures before then are unusual, and failures beyond then are not entirely unreasonable if neglected.

The objective of my original post was not to point out that all hub generators are rubbish, more that they can still fail under certain circumstances, and that maybe some preventative maintenance isn't an altogether bad idea.

cheers

[SA_SA_SA]

...
The more I see things like this the more I think Sturmey Archer's original (1930's!!!) design was in many respects a much better arrangement.... Disassembly is very easy, and the generator and bearings can be overhauled and/or rustproofed quite independently of one another.,,,

I wonder if the modern more "disposable" designs are just cheaper to make?

[Brucey]

I think they can be built a bit lighter, and that is probably why they are the way they are.

However it is quite clear that they were in many cases designed by people who either didn't know or didn't care about the practicalities of living with such things outside of the warranty period, or indeed understand some of the problems that will crop up in the real world, even inside the warranty period.

It would be quite easy to make a hub generator with cartridge bearings in it such that the bearings could be replaced easily from the outside of the hub, and where the airspace was vented properly too (i.e. such that water doesn't readily get in, but should it ever do so it doesn't get into the bearings and is able to escape easily).

The 'additional cost' of such design features could be pennies.

cheers

[SA_SA_SA]

I wonder why SA didn't use any of their later alloy brake shells for the dynohub?

[Brucey]

I've wondered the same thing. I think they did prototype it in about 1982.

But then I look at their current hub generators and what I see tells me that they have just bought (or reverse-engineered) the least expensive, least efficient hub generator on the market, and stuffed it into a hub.

Really.

[mig]

in your esteemed opinion then mr brucey are SON hubs worth the extra sovereigns?

[NATURAL ANKLING]

Hi,
I am new to this design and don't own one.
The problem I see is that you have permanent magnets which need protecting from iron debris
Iron rusts so water protection / open environment.
Bearings need lube and shielding from water / condensation.

As a circular tube revolving will collect rubbish and spread it all over the inside.

Along the lines of a vent (permanent vented to environment) but shielded on the revolving hub, such that water / condensation will drip out / be flung in use and will not leak if left in rain / laid down on ground except total immersion
Mmmm but magnets still rust Better sealing..............................

Electro magnet replacing permanent magnets...................

[Brucey]

in your esteemed opinion then mr brucey are SON hubs worth the extra sovereigns?

That is a very good question. I think they are the only hub to come with a five year warranty, they are also one of the lightest, lowest drag hubs. They also do special narrow hubs, hubs for small-wheelers, wide front hubs, and they do more different hub drillings than any other maker. So if you need a 'special' or you simply want the best available, that is your hub.

But they are not that much lighter or lower drag than some others out there, so it is down to price, warranty and servicing if you have a choice of other hubs.

If you don't intend to open up your own hubs ever, then you can almost regard shimano units as 'disposable' because although they can be repaired and serviced, finding someone to actually do it isn't that easy. In the respect that Schmidt offer any kind of service at all, then this is arguably a bonus.

Given that you can buy two or three good shimano hubs for the price of one SON, or six or seven cheap shimano hubs for the same money, there is the value option, for sure.

If you are prepared to do some preventative maintenance, then a shimano hub is a good choice; you can regrease/rebuild the LH bearings easily (just like any normal hub) and you can (using a syringe or fine-nozzle grease gun) re-lube the RH bearing too, all without disturbing the electrical connectors.

It isn't that difficult to re-do the electrical connections in fact, and nor is it that difficult to unscrew the innards from a shimano hub generator, provided you have the correct tool. I've concluded that any hub generator, if used in all weathers, will likely end up a bit damp inside, sooner or later. If this is not to eventually cause corrosion, I think you need to do something about it.

All generators will (if they are going to be used for -say- five years plus in all weathers) benefit from being treated internally with a corrosion proofing agent, like waxoyl. If you can get the hub apart, this isn't a difficult to job to do.

So as to 'is it worth it?' I think it depends on your expectations, your approach to maintenance, and one or two other things like that.

cheers

[NATURAL ANKLING]

Hi,
Oh, keep seeing old sturmey front hubs, some back ? with dynamo, are they worth saving
How much new ? I might even get one to build in a wheel, 3W is enough for auxilery lamps etc.

[Brucey]

SA hub generators are definitely worth saving; in combination with a 3s or 4s rear hub they are reasonably weight-efficient, even compared with new equipment.

The old front dynohubs have a 3/8" axle and run on 1/4" bearings; this is an immensely strong and durable arrangement too.

A couple of things to watch out for;

1) don't separate the magnet and the stator. They can come out of the hub as a pair, and can be cleaned/rustproofed as a pair if required.

2) These hubs make around 2W power; this is plenty for town use (and is enough for many people outside of town with good quality LEDs) but it isn't 3W.

cheers

[NATURAL ANKLING]

Hi,
Seen several this year but they turn up on old type bikes, so there is no other parts I can use.
I could have a museum by now If I had the space.
The local recycling centre have changed their staff and nothing sells as they want too much money
Now instead of cutting the prices they just have a clear out to make space, they don't even chuck the junk first either
I really need to justify buying a bike for one part, If I don't then it just goes to the metal man or landfill.......................

[mig]

in your esteemed opinion then mr brucey are SON hubs worth the extra sovereigns?

That is a very good question. I think they are the only hub to come with a five year warranty, they are also one of the lightest, lowest drag hubs. They also do special narrow hubs, hubs for small-wheelers, wide front hubs, and they do more different hub drillings than any other maker. So if you need a 'special' or you simply want the best available, that is your hub.

But they are not that much lighter or lower drag than some others out there, so it is down to price, warranty and servicing if you have a choice of other hubs.

If you don't intend to open up your own hubs ever, then you can almost regard shimano units as 'disposable' because although they can be repaired and serviced, finding someone to actually do it isn't that easy. In the respect that Schmidt offer any kind of service at all, then this is arguably a bonus.

Given that you can buy two or three good shimano hubs for the price of one SON, or six or seven cheap shimano hubs for the same money, there is the value option, for sure.

If you are prepared to do some preventative maintenance, then a shimano hub is a good choice; you can regrease/rebuild the LH bearings easily (just like any normal hub) and you can (using a syringe or fine-nozzle grease gun) re-lube the RH bearing too, all without disturbing the electrical connectors.

It isn't that difficult to re-do the electrical connections in fact, and nor is it that difficult to unscrew the innards from a shimano hub generator, provided you have the correct tool. I've concluded that any hub generator, if used in all weathers, will likely end up a bit damp inside, sooner or later. If this is not to eventually cause corrosion, I think you need to do something about it.

All generators will (if they are going to be used for -say- five years plus in all weathers) benefit from being treated internally with a corrosion proofing agent, like waxoyl. If you can get the hub apart, this isn't a difficult to job to do.

So as to 'is it worth it?' I think it depends on your expectations, your approach to maintenance, and one or two other things like that.

cheers

thank you.

i've long been interested in seeing / using a SON hub just to see how it operates, if it is better. my experience in generators is limited to one (a good one) only. i wonder how a company like SON would answer if the suggestion to use waxoyl or similar would be on new units? would they plug the fewer number of rebuilds into their spreadsheets and find the reduction in incoming euro from rebuilds wasn't to their liking? or maybe genuinely think it's a novel and useful idea?