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Schmidt Son dyno hub, e week and cpap battery

Old 04-26-13, 06:39 AM
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Schmidt Son dyno hub, e week and cpap battery

Hello all.

I am hoping to be able to tour with my small travel cpap and battery. I am wondering if the dyno hub and ewerks can recharge my cpap battery.

The battery is speced at:

Li-ion 14.4 v
5200 mah 75 wh

Last edited by chefisaac; 04-26-13 at 07:13 AM.
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Old 04-26-13, 10:07 AM
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Originally Posted by chefisaac
Hello all.

I am hoping to be able to tour with my small travel cpap and battery. I am wondering if the dyno hub and ewerks can recharge my cpap battery.

The battery is speced at:

Li-ion 14.4 v
5200 mah 75 wh

Dynohubs put out 6V AC at around 3 watts. Batteries need charging voltages higher than their output voltage, and since you're referring to an LiOn battery, you'd need an appropriate smart charger as well. That's also a relatively large capacity battery.

In short - not especially practical. You'd be better off working on finding someplace to charge it periodically.
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Old 04-26-13, 11:08 AM
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need more added to the circuit.. what is the charge voltage, google fu can find the E Werks output

I suspect the company was thinking Travel = motels and hotels with mains power for recharge..

Step down from 110/220vAC, not step Up from 6V/3W.. AC [alternators in hubs now..


might have to do more on the CC to have recharge power in the overnight lodging..

Generically thinking:

Math: that 14,4 v battery is likely composed of 12 1.2v battery cells .

and as such a battery pack can be made up of 5 units of 2.88v each
[yea 5/12ths is not a whole number] for charging purposes or 4 of 3,6V each
3 cells in series .. 4 of them in parallel, or charged in sequence individually..

then once all are charged , then switched back in series again to total 14.4v

given voltage drops off as the battery discharges I suspect the thing actually operates at 12v.

might be able to runoff a 12V Motor Bike Gel lead-acid battery ..


If, at first, you don't succeed, then, you read the Manual

Last edited by fietsbob; 04-29-13 at 09:39 AM.
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Old 04-26-13, 11:41 AM
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Originally Posted by chefisaac
Li-ion 14.4 v 5200 mah 75 wh
Your CPAP battery likely consists of 8x2600mah 18650 Li cells, arranged 4s2p.

A 4s2p 18650 cell holder would allow you to use 18650 cells (3.7v nominal, 4.2v max hot off the charger) that could be recharged from a 6v dynohub. However, no 4s2p cell holders exist AFAIK. However 4s1p 18650 cell holders do exist and are inexpensive. You could use 2 of these cell holders in parallel to attain 14.4v / 3-6mah.

https://www.batteryspace.com/battery-...ong-20awg.aspx

A simpler and far less expensive solution (than Son hub+rim+spokes+ewerk=$500) would be to buy one or more spare batteries and recharge from AC whenever possible at diners, etc. Also, EWERK is rated to 2.8-13.3v, so it is inadequate to charge a 14.4v battery.

https://www.peterwhitecycles.com/ewerk.asp
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Old 04-26-13, 02:59 PM
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Let's say you had a custom charger adapter made to run from a 12V (6W) dynamo (double the output of most dynamos, including the Schmidt unit). If everything were perfectly efficient, then the 6W would charge the 75 WH battery in 12-13 hours of riding. But it isn't- charging batteries is only about 50% efficient. So charging the battery would take 24-26 hours of riding. So to charge the battery in 12 hours of riding (a very long day, BTW), you would need 2 of these generators and a very clever engineer friend to build the circuit. And then you'd need to pedal the bike afterwards.

And 12W electrical is a pretty big drag to put on your pedaling- it's really about 24W mechanical drag with the inefficiency of converting mechanical energy at the wheel to electrical at the terminals. Most people put out about 100W at a good cruise speed, and the extra 24W of mechanical effort would feel like riding through mud. I'd feel like hare-Kari after just an hour of that, let alone 12 hours.

The 3W Schmidt unit would take about 48-52 hours of riding to fully charge a flat 75 WH battery. It just doesn't have the oomph to do it. But it is more efficient mechanically than the 12V bottle dynamo.

Best to just take extra batteries and chargers and stop and charge them whenever you can (restaurants, gas stations, staying in motels).

Last edited by cycle_maven; 04-26-13 at 03:12 PM.
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Old 04-27-13, 03:01 AM
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Crap, I think I am screwed. I want to be able to tour and not worry about recharging the cpap battery at stops and stuff. Maybe I am making a big deal out of nothing.

I don't think getting another battery is the best choice. The multi nigh battery I did get was pricey and is heavy. So I am not sure. Thought about a roll up solar panel they sell with the cpap.
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Old 04-27-13, 03:12 AM
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Originally Posted by chefisaac
Crap, I think I am screwed. I want to be able to tour and not worry about recharging the cpap battery at stops and stuff. Maybe I am making a big deal out of nothing.

I don't think getting another battery is the best choice. The multi nigh battery I did get was pricey and is heavy. So I am not sure. Thought about a roll up solar panel they sell with the cpap.

Can you select powered campsites when you tour, and plug in?
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Old 04-27-13, 03:25 AM
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Originally Posted by Machka
Can you select powered campsites when you tour, and plug in?
i think that's my last resort to be honest. That and perhaps solar power roll up panel but I am still on the fence about that. I guess it limits my "freedom" of where I can camp.
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Old 04-27-13, 03:35 AM
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Originally Posted by chefisaac
i think that's my last resort to be honest. That and perhaps solar power roll up panel but I am still on the fence about that. I guess it limits my "freedom" of where I can camp.
Most campgrounds have a power section. In fact, in many cases, there are a lot more powered sites than unpowered ... and they are often nicer than the unpowered, and closer to the toilet blocks. Rowan and I have started considering powered sites when we camp, and have gone that route on several occasions.
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Old 04-27-13, 11:14 AM
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I tried looking for a usb charger for CPAP batteries, but too many of them helpfully have a usb charger output so if one exists it's too hard to find.
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Old 04-27-13, 11:30 AM
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This sounds interesting... https://www.rei.com/product/846334/bi...73#video-inner
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Old 04-27-13, 01:33 PM
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Originally Posted by chefisaac
Crap, I think I am screwed. I want to be able to tour and not worry about recharging the cpap battery at stops and stuff. Maybe I am making a big deal out of nothing.

I don't think getting another battery is the best choice. The multi nigh battery I did get was pricey and is heavy. So I am not sure. Thought about a roll up solar panel they sell with the cpap.
I'd guess an average size solar panel would take a long time (more than a day's sunlight) to recharge the battery from flat, even longer than using the dynohub to recharge individual cells as I proposed in #4.

I still believe a spare battery would be most practical. I think you can find a spare for less than the CPAP maker is charging. I doubt it's a unique battery, it's likely one available from from generic cell/battery shops, for less.

Also, it seems you might want (need?) a spare battery in the event your primary (only) battery quits on you mid-tour.
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Old 04-29-13, 01:54 AM
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Can I suggest a rethink? Charging batteries at campgrounds is a joke. Hell my phone takes about an hour to charge and my GPS isnt much different from memory. What I do remember from my last big tour was swearing never to have to sit in campground bathrooms/laundries etc. again. It was having to do this that made me splash out on the E-werk and cache battery in the first place. I've never looked back. You cant leave your stuff for a second on charge as its likely to be knicked. Mine now charges whilst I ride in a brilliant fit and forget method that the clever boys and girls at B&M deserve a pat on the back for creating. There, nuff said
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Old 04-29-13, 05:00 AM
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Originally Posted by rifraf
Can I suggest a rethink? Charging batteries at campgrounds is a joke. Hell my phone takes about an hour to charge and my GPS isnt much different from memory. What I do remember from my last big tour was swearing never to have to sit in campground bathrooms/laundries etc. again. It was having to do this that made me splash out on the E-werk and cache battery in the first place. I've never looked back. You cant leave your stuff for a second on charge as its likely to be knicked. Mine now charges whilst I ride in a brilliant fit and forget method that the clever boys and girls at B&M deserve a pat on the back for creating. There, nuff said
It's not a matter of a re-think, it's a matter of physics. As has been noted, the E-Werk has neither the ability to achieve the voltage to charge a 14.4v battery, nor the current capacity to do so in a reasonable amount of time even if it had the additional 2 volts or so required to do so.
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Old 04-29-13, 06:00 AM
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Originally Posted by mulveyr
It's not a matter of a re-think, it's a matter of physics. As has been noted, the E-Werk has neither the ability to achieve the voltage to charge a 14.4v battery, nor the current capacity to do so in a reasonable amount of time even if it had the additional 2 volts or so required to do so.
I think the best bet is another battery, or for this trip, an extension cord might do the trick. We will see.
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Old 04-29-13, 08:30 AM
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A dyno hub will only supply a given amount of power based on hub design (almost all about the same) and hours of use each day, with some variation with speed. If you get 3 watts out of a hub for five hours of actual rolling time, that is 15 watt hours. If you rode your bike for only five hours, that means that in a day you better not need more than 15 watt hours of power. My point is that you might want to find lower wattage equipment. Since watts into the system is quite limited unless you have frequent convenient access to power outlets, it may be best to figure out if your electronics can be replaced with lower wattage electronics.

Over the short term (a few days) a battery can be a substitute for a power supply if you start the trip charged and end a short trip discharged.

But over the long term, a battery is only a storage device, not a substitute for power. And, every time you put energy into a battery and take that energy out later, you lost some of that energy because as a storage device they are not 100 percent efficient. Thus, if you can charge spare batteries that directly power your devices instead of power packs that you use later to recharge your device batteries, that will help. I usually assume that I only get half the power out of a NiMH battery compared to what I put into it, at best.

I used to tour with a netbook computer. Last summer I knew that I would have very limited access to power during a week and a half, thus the netbook stayed home and I bought a small android tablet for the trip in part to lessen the weight but mostly due to power requirements.

If you want to triple your generating capacity, chuck the panniers and use a kiddie trailer that has two wheels, then put a dynohub in each of those wheels. With your front wheel having a dynohub, you tripled your power supply compared to front wheel only. I say this in jest, but it really makes my point that your power input is quite limited.
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Old 04-29-13, 03:26 PM
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I dunno- if the 75WH battery is rated for multiple nights, a combination of a single 12V bottle generator and recharging the battery from the mains when the opportunity presents itself, may just take you through the tour. The 6W that the generator puts out will have noticeable drag, but it may be possible to arrange things so that charging the battery on the fly is a fairly rare occurrence (plugging it in whenever you stop for a sandwich, doing laundry, etc.). Do they have a quick-charger? How long does it take to charge? I doubt anyone would steal a CPAP battery from a campground bathroom- no market for them. Unlike a cell phone or a GPS...

Last edited by cycle_maven; 04-29-13 at 03:29 PM.
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