scootergrisen said:
I have been thinking about the same with such a powercord reel from a vacuumcleaner.
But the problem i see is that part of it is not protected.
The spinning part and static part most have som metal sliders and unprotected connectors.
I don't think that will be good to use outside.
Even if it is protected against rain it will get moisture inside it.
There's this type, if you can afford them and you don't mind the relatively gigantic size
https://www.amazon.com/Weatherproof-Outdoor-Extension-Stamping-5320T-SW/dp/B07MBVF1Y1
It's very dry here most of the time except during the infrequent rains (which can be flash floods!) so for my purposes it is unlikely to be an issue with the salvaged vacuumcleaner reel. However, for anywhere that does have significant humidity, rain, etc., you might need to oil the metal parts of the reel inside to prevent moisture attacking it.
There should be no electrical connectors inside it--on mine all the connections are done outside it either at the AC plug to the wall when plugged in, or at the charger itself in my case, or the charger cord in yours if you're not directly wiring the reel to the charger, but just using the reel as an extension cord. In the latter case, you'd simply do whatever waterproofing you can to that connection, which you would have to do with any other kind of extension cord, anyway. If your reel did for some reason have internal electrical connections, you could waterproof those similarly, unless they are the type that are sliding electrical contacts along a ring. For those, the best you could do is coat (or pack) the area with dielectric grease and periodically check it.
EDIT: I am wrong about the one I have--it does also use the sliding contacts on a ring...but it already has dielectric grease in the area, and it is covered with a dust-jacket so it could be kept re-packed with grease as needed.
But in my case it would be inside the cargo-seatbox with the battery, not outside the trike, so it wouldn't be exposed to water at any time anyway, unless the trike was flooded to the point it got on the battery anyway, in which case I'd have worse things to worry about.
The ones on this page
https://picclick.com/Sears-Kenmore-Canister-vacuum-Magicord-reel-from-1973-182467069347.html
are very similar to what I have; the reel is black on mine, and the red wire shown there is black on mine, but the rest appears the same. I can't see the back of theirs; mine is a metal plate covering the spring assembly.
In either case, the reel I have has been quite durable; the vacuum it came from was at least 40 years old and served us well (the hose disintegrated and was repaired, the motor brushes replaced once, eventually something happened that took out the motor but I no longer remember what it was; I saved the reel and the heavy-duty footswitches when recycling the rest of it).
I have tried something like this for a computer mouse where you pull the connector and the box stays in the middle of the cable.
I think that way you can put it on any cable without modifiing the cable.
But then if i have 10 meter cable and only need to pull out 2 meter the box with most of the cable needs to go on the ground which i dont like.
0036947_nexhi-retractable-ac-power-extension-cord-5-feet-black.jpeg
The problem with all of those types that I've ever opened up is that in the center of the reel, there is a very sharp fold of the cable. Most wires are not designed for that kind of stress on their insulation, and over time the plastic may "retreat" from the high-stress area, thinning the insulation and potentially even parting entirely, if the environmental temperatures ever get high enough to soften the plastic that much (or if the temperature swings are enough to eventually cause thermal cracking of the stressed plastic insulation). It's not *as bad* with a flat cable like that shown, but if using a round cable there will be a lot of tension stress on the part that is on the outside of the bend, and compression stress on the inside--more the larger the overall diameter, and the tighter the total bend is.