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“A powerful energy source” – an interview about the “Forumslader”

forumslader Long ago, on Rad-Forum.de someone had the idea to build a charging device which uses the energy from the hub dynamo to charge electronic gadgets. While meanwhile similar devices are available from commercial producers, was developed there as a community project. Jens During from Cottbus, Germany, documented the development on Forumslader.de and he was responsible for moderating and fostering the development. Now, the „Forumslader“ (German for „charger from the forum“) is also further developed on the Liegeradforum.de, where mainly Patrick Hagemann, who is studying electronics and engineering in Jena is driving the development further. BentBlog talked to them now.

BentBlog: Jens, you are the driving force behind the „Forumslader“. What was your intention for its development and what can be done with it?

Jens: I was looking for a powerful energy source for my strong self-built lights – but this one should be self-rechargeable to avoid ending up without light on my commute to work due to forgotten recharge (27km single way, 15km through forests with lots of wild boar). So my first built was the public standlight-circuit 12V by Wolfgang Bergter. It worked pretty well but soon I was looking for possibilities to enhance the performance.
At the same time Markus (cyclist) in the rad-forum.de developed a dynamo-charging-device for 4 NiMh cells – I added some of my ideas there and the original Forumslader was born (now called the 6V-Lader because it is working with 6V internally).
To broaden the application range and to receive more enhance the amount of harvested energy, I developed the first 12V-Charger which was technically a simplified charger based on the one my Wolfgang Bergter with first performance enhancements. Later, JohannW suggested a slow ride step – thus the current 2-step Forumslader with further improved performance evolved. Now it also had a possibility to directly attach USB-devices and to make use of very different storage batteries.
From my point of view, this charger was very universally applicable, enormously effective and easy to build. However, It seems as if it was rather unrealistic to assume everybody could braze or knows someone who could help him braze…
At this time, Andreas Oehler asked for a test device for his big charger comparison – in the course of the years, several commercial dynamo charger were brought to market but no comparison of these devices was available. Due to its sensational result in this test, the Forumslader became very popular also outside the Radforum.
I had been working on an automatic switch of the two steps for a while but until getting in touch with Patrick and Malte, this did not work correctly.

BentBlog: So, by this, did you archieve all of the aims you had prior to the development? Is anything left to be done?

Jens: Well, the effort for building it currently seems to be too intense for a lot of people. Additionally, I do see potential for further performance improvements
Patrick is working on a more convenient way of building the Forumslader and also an internal low-voltage-switch-off was implemented by him.

BentBlog: Reading in the rad-forum.de you get the impression as if each self-builder builds the device differently. Is this flexibility the big advantage of your solution over commercially offered devices?

Jens: The biggest advantage is the by far highest charging performance of the Forumslader compared with all other chargers and the biggest universality e.g. by the possibility to apply all 12V charging adaptors from the automobile-devices sector. Additionally, don’t forget that at the beginning of its development, there was for a long time no commercial dynamo charger available. In the rad-forum.de you can therefore find all kinds of device generations of the Forumslader and, of course, also all kinds of individual adaptations of the base circuit.

BentBlog: Where do the commercial devices perform worse or better?

Jens: Well, the commercial devices are often nicer and smaller, sometimes cheaper. But there are no chargers for users with high energy demands – for electricity-autarkic bike travellers with high energy consumption, there is currently no alternative than the Forumslader (currently, there are a couple of world travellers who who update their blog or webite during their journey using electricity from their Forumslader).

BentBlog: Can only electric enginers build the Forumslader? What is essentially needed to build it?

Jens: Not an engineer, but currently you still have to be able to frickle. At a maximum, I prepare readily set platines – more is impossible due to timely constraints (a situation, Patrick intends to improve significantly).

BentBlog: Are there any prerequisites regarding the dynamo to make use of the Forumslader?

Jens: Every hub-dynamo without voltage limitation works perfect (practically all the usual ones), side-runners need an internal modification, it may generally not be a regulated dynamo such that the high internal voltage of the Forumslader can be reached.

BentBlog: Patrick, how did you notice the Forumslader?

Patrick: I was asked by a forum-user if I could build a Forumslader for him. He sent me a link to Jens’ website and I became curious.
After having built a charger, I got in contact with Jens whether the charger could be improved.

BentBlog: You then took the initiative in the Liegeradforum.de to modify the charger. What did you not like about the original device?

Patrick: The “problems” of the original device were on the one hand the extremely timely manufacturing method, on the other hand the missing protection for the batteries. Further there was only a manual solution for switching the speed levels. The casing usually was a big problem as it was too complicated to position the LEDs and the switches in an intelligent way without resulting in a huge casing.

BentBlog: Now you finalised a ready development stage. Did it satisfy your expectations?

Patrick: Currently, 5 prototypes are produced and sent to 5 test users. One of them e.g. is riding the ROAM. The other test users cover different parts of the intended use. On the one hand there are hobby-riders with 1000km/year and on the other hand touring riders with 30000km/year. The chargers will be tested for a month now. Afterwards there will be a progress report. If there are no new problems, the charger and the circuit diagram will be published (on Jens’ site).
The “Urprototype” was already pretty promising. The charging output was over a wide range above 10W, the automatic speed level switch and the battery monitoring system worked without any problems. Now there will be the every-day-use-test.

BentBlog: How easy is it to build this version of the charger?

Patrick: The charger is mainly made of SMD parts. These are comparably big, hence it is a little bit easier to position them compared with the old charger. But usually we would deliver the platine readily equipped.

BentBlog: What are SMD-parts? And why is it easier to build the charger with them?

Patrick: SMD-parts are “surface mounted devices” without a wire to be put through holes in the platine. Hence, you do not have to drill holes. You save roughly 40% in time due to not drilling and pre-bending of the parts. An additional advantage is the extreme vibration-resistance as the parts sit right on the board.

BentBlog: Will there be a commercial offer of the Forumslader?

Jens: I would like to keep the Foumslader as s public project – if skilled home-builders re-build this device for friends, this follows exactly the intention of publishing it. iAlso the Forumslader would not exist today if people such as Wolfgang Bergter, Olaf Schultz or Andreas Oehler kept their knowledge for themselves. With a commercial offer of the Forumslader I see a high interest from the industry to keep the building details secret (why should a firm such as BUMM publish the circuits of their E-Werk?).

BentBlog: Thank you very much for the interview!

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