I bought a used Schmidt dynohub and I can't figure out if it works ok or something is wrong with it. The light part is great, but there seems to be a lot of resistance in the wheel. If I try to spin it when it's in the fork, it stops after a few rotations whereas if I do the same strength spin my regular front wheel basically spins a really long time. The light part works great. I think it's an older wheel, as I couldn't find the water drain hole or whatever it is that means it would be a newer one.

You confuse magnetic pulses with bearing problems , I expect.

I have a 28 and a 20 model Schmidt hub. excellent stuff..
I only note magnetic drag in the truing stand, never while riding the bike .

there are precision sealed bearings supporting the axle
all the solutions, should they fail, service is requiring sending hub out
so bearings will be replaced.
going thru Peter White cycles in NH. the sole US importer.
any technical questions , send them his way , or ask the German company directly.

electric power, for the lights, like so many other things is not a free lunch.

What you feel by spinning it by hand is entirely normal.

There is no hole for draining water, as far as I know. The hub has sealed bearings. I have had a Schmidt Dynohub since early 2003, and it has never been serviced. That's the equivalent of some 40,000km of riding in widely different conditions -- heat, snow, rain.

After a 1200km randonnee some years ago, a fellow participant picked up the wheel as I loaded the bike on to a car and spun it while holding the axles with his hands. It, naturally, felt a rough as guts, and he suggested I was in dire need of new bearings. That was after I had covered about 10,000km of the 40,000km mentioned above.

As fietsbob says, don't try to service the hub yourself. It requires specialist tools. Giving it to a bike mechanic will almost inevitably cause serious damage, mainly the snapping off of the terminal block. Unfortunately for Americans, it does mean sending it to that guy fietsbob mentioned.

Older hubs are differentiated, IIRC, by a black band. I don't think their age is indicated by any sort of drainage hold. IIRC again, the older, black-banded ones didn't have bearings that were as well sealed as the newer ones, but the issues were comparatively insignificant.

We now have three in the household, and a fourth was on one of Machka's bikes when it was stolen. I think they are fantastic, in terms of design, engineering and performance.

There is nothing wrong with your hub, this is how they are supposed to be. The resistance you feel when rotating by hand is matched by a small acceleration as the magnet finds a new resting position. These balance out at normal riding speed. The resistance due to power output is almost impossible to feel when riding.

Thanks everyone - good to know. The little hole I was referring to that I can't find was described on Peter White's website https://www.peterwhitecycles.com/schmidt.asp :

"Current production hubs (since early 2003) have an ingenious system to prevent water from getting far enough into the hub to cause corrosion. So this is an issue for older hubs, but not for any hubs you would be buying now, or might have bought since early 2003. For this system to work, there is a tiny hole in the middle of the axle. You can see it if you remove the skewer and look down the axle. And for the system to work, this little hole must be open, not clogged up with grease. So if you grease your skewers, just put a very thin layer of grease on them. Don't slather grease in a thick layer all over the skewer as it might clog up the little hole and then it's possible for water to get sucked in through the bearings, causing corrosion. So if you grease the skewer, wipe most of the grease off before putting it into the axle."