JohnJ80

Yes. If you’re using this to charge electronics, you really need to go through a battery to do so. Phones especially are sort of anticipating a steady power source to charge.

True. That’s part of the benefit to GaN. They have a much higher tolerance to temperature than traditional silicon. But I agree with you.

My experience touring and battery charging has been that you kind of have to hang around while it’s charging so your stuff doesn’t get stolen. At least that means it’s attended in the event of a problem.

adamrice 

1. There are a number of dyno to USB converters that all have different output curves. There are also different dyno hubs that are optimized for different wheel speeds.
2. I did use a solar panel on tour, unfolded across the tops of my panniers. Under optimal circumstances, it could recharge a couple of AA batteries (about 5000 mAh) over a full day of riding. It also stopped working after about 20 days. If my math is correct, dyno hubs will do a lot better than that.

JohnJ80

What solar panel and what dynamo? Not possible to figure out this comparison without the specs on each.

Most of the dynamo specs I’ve seen say 6V at 0.5A. So that’s going to be 500mAh best case (3Wh). An AA rechargable is around 2100mAh (some advertise 2400mAh, but my chargers never see that capacity on recharge) capacity so you’d have to ride - at full output - about 8.4 hours to charge two of them. Two AA batteries are just a little more than a cell phone battery (around 3250mAh or so). And that’s 8.4 hours moving at the best output speed for the dynamo. That’s not very much power. For example, a 13,000 mAh battery I have is about 34Wh so that would take ~32 hours to charge by the dynamo. That’s not a huge battery, it fits nicely in the palm of your hand. That same battery takes about an hour to charge plugged into a USB-C 30W charger that’s about the size of a cell phone charger.

If you had a dynamo that is, say, 10W output or higher, it’s going to start to be a pretty noticeable drag. So there’s a pretty low upper limit due to conservation of energy on what a dynamo can produce or at least what a rider of a dynamo equipped bike can tolerate.

The power curves, if I’m understanding them correctly, are the raw power output from the dynamo. That’s an AC output, I believe, so that has to be converted to something usable in DC and USB which will all have efficiency losses. So the raw output of the dynamo is not going directly at 100% efficiency into your battery.

Either way, unless you are in an area where there is no access to power, it’s probably a lot more efficient to have compact fast charger and a battery and get to an outlet. Off grid means think about ditching any substantial power items.

Tourist in MSN

When you factor in slower going up hills, stop lights, etc., I think I average 2 watts coming out of my Sinewave Revolution USB charger that is powered from a SP PV8 hub when touring. I put that power straight into a Voltaic V44 (now discontinued model) pass through cache battery that is also large enough to function as a powerbank to charge other devices while I am in the campsite. I usually charge my GPS and phone from the Voltaic while rolling (pass through). But camera batteries and AAA NiMH batteries for my taillight or headlamp (for my head) I usually charge from the V44 in the campsite from the V44.

adamrice 

I wasn't specifying any particular dyno hub, and it's been long enough since that tour that I don't recall the solar panel I was using. It wasn't this, but it was in the same ballpark.

Those are USB output numbers. I found it here, but that page was quoting a separate study. Looks like there is at least one dyno that will produce 5 W at 20 kph, which seems like a reasonable target speed and drag if you're dedicated to charging off the grid, and would generate power faster than a bike-sized solar panel could.

Tourist in MSN

I am not an electrical engineer, I just rely on graphs that look like they make sense to me. Such as the drag and output graphs here:
https://www.cyclinguk.org/sites/defa...ub-dynamos.pdf

I do not speak German, but the graphs in this one appear to make sense. I use the Sinewave revolution, bought it after I saw the graphs in this article.
https://fahrradzukunft.de/21/steckdose-unterwegs-4/

Both of those publications are somewhat dated, but the stuff they describe is still sold.

Touring, I consider myself lucky if I average 20 km/hour, unfortunately most of my tours have enough hills that I spend a lot of time on slower low wattage uphills and very little time in the higher wattage downhills.

JohnJ80

Yep. It’s a bit tricky to go back and forth between mAh and Wh for battery capacity. It’s probably easiest if we just look at this in Wh and use my 13,000mAh battery at 46Wh as a guide.

So presuming the dynamo produces 5W and there is no significant loss in power conversion from AC to DC or DC to USB, then running at those numbers and if all of it could be driven into the battery, it would take just under 10 hours to fully charge that 46Wh battery. That means 10 hours at speed (around 20km/h or about 12mph). Note that you can’t use an average speed of 20kmph to figure this out because below 20, the power drops super fast. Above that, you don’t gain much. So going 5mph faster to make up for being 5mph slower for the same time isn’t going to make up for the power loss. It’s going to be optimal to keep the speed pretty much right at that knee in the power curve. Fair to say, I think that 10 hours is pretty optimistic.

Also that solar panel you linked to is 7W per hour at full sun. Presuming it works at that rate which is optimistic but probably as much as above with it’s discounted losses probably puts them in the same order of magnitude at least. That also seems to be born out by your experience. Either way, that’s a tiny panel in terms of output. You can now get a 20W panel that weighs the same. Even presuming that this panel won’t run anywhere close to it’s max, it’s still going to probably beat out the dynamo for charging time by a fair bit.

I am an electrical engineer but I’m just looking into dynamos now. If you can’t spend significant time at 20km/hr, it’s just not worth it. Look at how fast the power drops off. Using 3W as the power output of one of these, you’d spend nearly four hours of pedaling at 20km/hr to charge a cell phone from 0 to full charge. Using the 0.5A output and converting that to mAh would mean nearly 6 hours. That’s a lot of work for not a lot of charging. And that’s presuming 100% of those 3W get into the battery every hour and that there are no losses.

I’m thinking pretty hard about buying a 20W solar panel and seeing how well it actually does - seems you can get a decent one for about $75 and it weighs a bit over 500g. But, on the other hand, time spent getting outlet time is probably a more productive strategy unless you’re completely off grid.

I guess I’m seeing that the primary application for a dynamo is for bike lighting without a battery. There, the losses are not bad because the output of the dynamo can go straight into an incandescent light bulb without any lossy conversions. But after that, it looks like solar is coming on pretty hard and with LED bulbs which are less lossy than incandescent - well I’d have to say that dynamos are going to get squeezed out. They seem to be so near the margins for power produced against watts of cyclist leg power consumed vs battery needs.

As for wheel drag - I’ve put my road bikes away for the winter (I’m in Minnesota) so I can’t easily go out and see how much power it takes me on the flat to move at 20 km/hr but I’d guess it as 50-70W. That would be for an unloaded road bike so somewhat more for a loaded touring bike. Either way, putting out roughly an additional 10% over that many hours doesn’t seem to me like a good tradeoff to charge up a cell phone. A cyclist generates suprisingly little power which thanks to the efficiency of a bike can be turned into decent forward motion.

So, looking like the outlet strategy is probably still the most efficient.

J.

Tourist in MSN

It depends on how much you plan to have your phone on, etc. If you are careful to avoid wasting power, not a problem. I went for a couple weeks on my last tour without plugging into an outlet anywhere. Needed good quality low resistance cables, left the phone off or in airplane mode with no apps running most of the time, when i used the phone (screen on) on wifi to check weather forecasts the battery had to be warm to avoid losing too much battery reserve, etc. Minimize screen time and it is not a problem. I did not get around to buying a sim card for the country I was in, so my phone was a wifi device only, thus when it was on it was in airplane mode.

I ran a GPS when rolling, but only about a quarter or maybe a third of the time that I was rolling was used to charge the GPS. I charged up my AAA batteries in the taillights once a week to keep the taillights bright. Charged camera batteries as needed, etc.

I am not saying skip the solar, do whatever you want. I am just saying that if you are careful about power usage you do not need a lot of power.

Regarding drag, that first of two links that I posted in post number 31 on the second page of the link it said that generator drag was only 5 or 6 feet of elevation per mile, that is about one tenth of one percent grade. Often around home when I am not charging up batteries I leave my dyno powered lights on because it does not hinder me at all, I can't feel any drag. I am sure there is drag, but it is so little I can't tell it is there.

But if you are a power user, phone screen on much of the time, then a dynohub will not do it for you. If you are an electrical engineer, you know how to calculate how much power you need.

Someone on this forum used a Forumsladder (spell?) because it got more power out of the USB than the other chargers, but he could feel the extra drag on the dynohub wheel when riding.

Wiggle

Tourist in MSN, your post really illustrates that the more important side of the equation is power management.

Whether it be a dyno or solar, there simply isn't a large amount of energy available for harvest relative to how quickly it can be depleted if you're not careful. Solar is interesting but is at the mercy of weather conditions and it seems like a cumbersome solution to have them setup on a bike. It's another matter entirely if you want to leave them setup in a campground or other location while you travel.

Big battery banks and access to outlets can allow for a generous amount of energy use but in a situation where you are away from the outlet long enough it really becomes a matter of "energy in" vs "energy out".

JohnJ80

I don't disagree at all. In fact, I think we are saying the same thing but coming at it from opposite sides.

What I think I'm seeing as I look into this is that the cost/benefit of the dynamo is pretty limited since if you're an electronics user (even a cell phone) you really need to have a battery to store the output from the dynamo. Cell phones and other advanced consumer electronics depend on a more consistent charging source in order to charge efficiently. Neither a dynamo or a solar panel provide that so a battery is a given. And for getting the charge into the device, the personal effort either goes into finding an outlet and using it or in manually managing your battery and device charging. So, a horse a piece for effort but with the addition that the dynamo adds the cost of the dynamo wheel and that's where the diminishing returns come in. It's an expensive way to charge but may be appropriate if you want to be or have to be completely independent of the grid.

I also think that the day is rapidly coming where dynamos are going to be replaced by more efficient solar panels. I'll have to test more, but I think we are pretty close to being there and certainly will within the next 5 years or so if not there now. Feels to me like we're close to parity already. If I get this 20W panel for testing, it would be a good test since solar up here in the high northern latitudes is not the most efficient. If panel power ratings continue to increase as they have and the weight decreases at the same time, it may come soon to the point where you don't have to charge while you're riding. There may be adequate time in sun to do it while camped.

Also, the very best use case would be power generation that required zero watts from the cyclist. I agree that current dynamos are a low power drain from the cyclists legs but the power produced is also commensurately low. Getting to where it might be a lot more useful would be in the 10-15W range and that's going to be too much from the legs of most cyclists. So there's the upper limit. You can't get more because of conservation of energy and the limitation of the strength and endurance of a touring cyclists legs.

I agree - except to say that the solar efficiencies are not static and are improving. That is not the case with dynamos. If anything, the need to charge via USB is detrimental because it adds one or two more lossy stages that reduce efficiencies. On the other hand, the development money behind solar is going to keep improving performance for the foreseeable future.

I do want to add the comment here that with the advent of USB-C PD charging and with some of the new GaN based chargers coming out, you get both fast and high power charging out of small and light chargers. I just got a 45W charger that I backed on Kickstarter that is marginally the larger than most 5W cell phone chargers that come with the phone. Many of the new batteries coming out accept a 30 to 40W USB-C input for charging. On that 46WH battery that I have (12,800mAh), that will charge from zero to full in about 90 minutes. If you don't deplete it, then it's obviously that much faster. That's pretty amazing for a fast and compact charging system. So the exposure to leaving a battery on a charger for hour and hours is pretty much mitigated at that point. This is worth keeping in view for the next couple of years because there will be a lot of advances here.

Exactly and that is becoming a narrower use case than in the past because of the improving power performance of electronics.

There is also the tradeoff that adding some battery capacity can also mean a substantial reduction in weight and volume of touring gear. Paper maps and reading materials, which are heavy and typically bulky, can be replaced electronically. Those things are single purpose, whereas the same cell phone/charging material can be more multipurpose.

adamrice 

Interesting. Obviously one's setup would need to provide a surface for laying out a solar panel, which isn't always the case, but I hadn't run all the numbers, and assumed that solar couldn't compete with a dynamo.

Tourist in MSN

I usually build up my bikes from parts. I have only bought one complete bike in the past several decades. My first two touring bikes, no dynohub because I built those before USB charging became a thing. Built up my third touring bike in 2013 and by then was charging stuff with USB, I added the dynohub because the cost was only adding the hub cost and subtracting the cost of a plain non-dyno hub. Thus, the dynohub wheel was quite cheap. The fourth touring bike I built up in 2017, same thing, bought the dynohub and built up the wheel with it. Unfortunately (in my opinion, others may disagree), bike builders are trying to sell to the mass market and if most buyers do not see the advantage of a dynohub, the bike manufacturers are not going to put new dynohubs on new bikes. And, a dynohub means more labor cost to add wiring and light(s) when they build up a new bike. Thus, for most people that have to add a wheel, a dynohub is quite expensive because they already own a perfectly good wheel that would become redundant.

I bought the dynohub solely for battery charging, not for lighting. My most recent bike tour, five weeks in the Canadian Maritimes, I used two AAA powered taillights, used NiMH batteries in the taillights and for the headlamp for my head for campsite use, charged them from the pass through power bank. I brought a bike headlight just in case I wanted to go somewhere at night or through a tunnel, but never used it. The bike headlight was a $5 one I bought on Ebay, shipped from asia, powered by USB cable with no batteries. Thus, would plug it into the power bank if I needed light.

I mostly charge things while rolling, power from hub goes to Sinewave Revolution charger, that USB power goes to the Voltaic V44 pass through cache battery, and while rolling I suspect (but do not know for certain) that I have less power loss if I am charging the pass through battery while simultaneously discharging the pass through battery to add power to my GPS batteries or my phone battery. But camera batteries and taillight batteries, I charge up in the campsite at night.

There were not many places to plug in for charging up the batteries where I took the photo. The photo was not my Maritimes trip, photo below is from my Iceland trip when I went into the interior.



In 2017 I carried a small solar panel on a kayaking trip where I had no power source for 16 days. At the end of the trip I decided that the weight of the panel and AA/AAA charger was the same weight as the batteries I could have carried if I brought more batteries instead. Panel would only charge two AA batteries at a time, not big enough to put four AA batteries into the charger. I do not know if I will ever bother with a solar panel again, likely to just carry more batteries.



I am using the low discharge Ikea Ladda (white) AA and AAA Ni MH batteries in the charger above. At less than $2 per battery, they are a bargain and perform as good as some of my older Eneloops.
https://www.ikea.com/us/en/p/ladda-r...tery-90303880/
https://www.ikea.com/us/en/p/ladda-r...tery-70303876/

Photo below was from my last bike tour without a dynohub in 2014, there was an empty electric campsite near the hiker biker site where I was camped, thus I was charging up stuff in the empty site, which was a major hassle. I was charging AA batteries, a camera battery and a cord to my tablet that was outside of the photo area. Fortunately I had brought one of those three into one outlet adapters. That trip I was kicking myself for bringing my 700c touring bike that did not have a dynohub when I had a dynohub on the 26 inch touring bike that I left at home.

Tourist in MSN

Everything electrical that I brought on my last trip, except my watch was not shown and the dynohub is not shown.

Wiggle

Welcome to my homebase, hope it was a good trip

I'm new to bike touring but not electronics/batteries/lights and still trying to decide my strategy for next summer when we do some tours probably only about a week long or two at most.

I've got a triple solar panel that folds up to about the footprint of a standard sheet of paper but thicker of course. Maximum rating is 3 x 1.1A @5V. But getting full output is fairly optimistic so I typically run them through a parallel combiner and plan to pump that all into a 25000 mAh USB battery bank. That depends on the trip itinerary though.

If we aren't hanging out around a certain camp site more than a day or two the case for solar is less appealing. Honestly too I doubt we'd have much trouble accessing an outlet and with all that capacity in the power bank there is a quite a buffer before we need power.

Electrical loads will be:
Headlamps - Armytek Tiara A1 Pro Warm (runs on AA or 14500 Li-Ion) and Zebralight H53 FW (AA) (hers).
Additional Flashlight - Armytek C2 Prime Pro (18650 Li-ion).
Bike Light - Fenix BC21R V2 (18650 /w integrated USB-C charger) and PB Super-flash Turbo (2 x AAA).
Smartphone: BB Key2LE and iPhone 6s plus (hers). We keep the Blackberry loaded up with off-line maps but don't use it for "live" navigation. More of a check-in and then go type approach.
Bike computers are just Sigma 16.12 STS models on both bikes. They take CR2032s and if they die out there it's not the end of the world, guess I could carry a couple spare coin cells.

We keep the phones off much of the time or in Airplane mode. I have a small 700 mA mini Li-ion charger for the 18650 and 14500 cells as well. I have a USB based charger for the AAs and AAAs but I'm inclined to just pre-charge a couple Eneloops or bring some L91s/L92s there instead.

I'd love if there was a AA version of the Super-flash as it would allow me to consolidate down to only two battery types. I don't want a USB version I really value being able to hot swap cells.

Tourist in MSN

I would prefer AA over AAA, but my taillights use AAA. The photo in the post above yours, I had my two taillights along with a lot of other stuff. One taillight was the Planet Bike Superflash and the other is Planet Bike Superflash 65. Both operate great on my NiMH AAA batteries.
https://www.planetbike.com/store/sup...ight-1067.html
https://www.planetbike.com/store/sup...ail-light.html

You can buy adapters that allow you to use AAA batteries in a case the size of an AA battery if you would not mind instead standardizing on AAA instead of AA, but I suspect you would not since an AAA has only about 40 percent of the capacity of an AA battery.

Wiggle

Yeah I'd really prefer to go all AA instead (or AA + 18650). With the AAAs I also doubt I could still use my headlamps on high-mode, suspect they'd wither under high-current. Heck those lights can't even run well on high with an Alkaline AA, they really need NiMH or L91 to hold steady current.

Tourist in MSN

Oops, in previous post forgot to say it was a great trip. Flew to Halifax, rode up to Cabot Trail. Then back to mainland and then the ferry to PEI. Then through Charlottetown for Canada Day weekend, Then the bridge to New Brunswick. Then down to Bay of Fundy where I watched the tides for a few days from Five Islands Provincial Park campground, then back to Halifax. Not a lot of miles each day, it was a relaxing trip in that regard. Total about a thousand miles.

I think it was North Mountain that was 13 percent grade, it would have been nice if it was about half that steep.

Wiggle

Very nice, sounds like a good tour, you definitely hit alot of good spots. We are lucky to have these options available locally to us

JohnJ80

A couple of comments -

1. We can’t make the comparison about the effectivity of a solar panel vs a dynamo when all we have is “small solar panel.” Specs please. I’m guessing that solar panel you show is a 5W or so panel. I agree - that’s going to take an unacceptably long time to charge. Now, what if that were a 20W panel that would charge your batteries in several hours and it weighed the same?

2. When I talk about charging at an outlet, I’m not talking about 15 year old charging technology and battery chemistry. I specifically mentioned a battery that was 50% more capacity than what you show in that picture that would charge the capacity you show there in about 30 minutes compared to several (to be generous) hours with that charger.

So in both cases, I’m talking about commercially available state of the art products compared to a dynamo, not state of the art from several years to decades past.

So we need to talk apples to apples here and this doesn’t do it. But I would love to compare once the specs are known. Then we can make a decent informed decision and have a good understanding of what this looks like.

I totally get it. When you go off grid, away from power, then you need to be stingy with power, reduce your power needs dramatically from what we typically expect in 2019, and find a suitably stingy way to charge them. No disagreement on that point unless we can get a high power solar panel that is light weight. That’s what I’m wondering about with some of the 20W panels (claimed) that are around 500g.

JohnJ80

Here’s the 20W panel at 500g that I want to test.

https://www.omnicharge.co/products/20w-solar-panel/

Wiggle

500g for 20W is pretty good. My 3 x 1.1A panel would be about 16.5W output at full capacity and it looks thicker and probably heavier than that one you linked. Similar footprint though.

I double-checked too and the power bank I'm using is actually 26000 mAh. That's alot of capacity, the size is reasonable but it is fairly dense and heavy.

Tourist in MSN

I do not want to get into an argument, what works for me you have made clear that it would not work for you. i am just pointing out that you can get by quite nicely without a lot of power usage.

1 - Panel was probably about 1.5 watts, if my memory is correct I think it had somewhere in the 350 milliamps on the USB port when aimed well. I have two of them.

2 - If I am a couple days of travel from the nearest outlet, does not matter if it is 15 yr old tech or current. Many bike tourists never want to venture more than a day from an outlet or grocery store, but I often carry a couple weeks of food on my bike or in my kayak or in my canoe and go to some far off place.

I have better things to do than sit around next to an outlet or next to a solar panel, would rather get my charging done while I am riding. And usually when I am in the campsite, the sun is low enough that you don't get a lot of power out of a panel of any size.

Or, in the case of water travel, bring the batteries with me. And when you are far from cell coverage, no need to have a cell turned on. In this case maybe 20 minutes a day of weather band radio is all I need along with my GPS and lighting for night.



But the GPS batteries are a must so you know where you are and where you are going. Especially when the fog arrives.

noglider 

I love your pictures and stories, Tourist in MSN .

Tourist in MSN

Thank you.

JohnJ80

I agree - a 1.5W solar panel is the next thing to worthless. I wouldn’t be happy with it either. I’m talking about a 20W panel (13x more power at about the same weight) - that’s a giant difference; more than an order of magnitude. They are not comparable.

And I agree, if you’re away from the grid, then you have to manage your power. I also don’t want to sit around an outlet for a long time either but 30-45 minutes seems like a nice compromise for charging from an outlet with a current tech charger for considerably more battery capacity compared to hours with an old tech AA battery charger for less capacity. My point is that if we’re comparing 15yo tech to current tech, we’re not even close to what we can do today with state of the art batteries and chargers, especially that which is being enabled with the new USB-C PD standards.

So thanks for your input on this. I got what I needed. Dynamos are not workable for what I’m trying to do.

J.