Solar chargers

rodgers73

I currently have a hub dynamo but I'm planning a trip where I want my bike to be as mechanically simple as possible so I'd prefer to use a solar charger for things like phones etc and strap this to my rack bag.

Weight isn't likely to be a huge issue so I could afford to have one slightly bigger than the pocket sized ones that are common on Ebay/Amazon.

I'm having a bit of a problem understanding the voltage/amp figures given for some of them so I have no idea what is a "powerful" charger and what is a low quality one masquerading as powerful!

Any tips on particular products you'd recommend or guidance on the sort of rating I should be looking for would be much appreciated.

whoof

Hi rodgers73
This has been discuss on the CTC touring forum some of this may be of use.
http://forum.ctc.org.uk/viewtopic.php?f ... r+chargers

andymiller

I suspect that solar chargers are the triumph of hope over experience, and hub dynamos are about as mechanically simple as it gets.

For short tours why not consider a power pack? For small devices like a basic phone these will recharge the device several times over with power to spare, and they should be enough to keep a smartphone going if you use it sensibly (eg turn off wifi and gps, dim the display, or even just turn it off when you don't need it).

Alternatively, when you stop for a meal or a coffee, find a place near a socket and charge up.

Campsite receptions will happily charge up devices for you. Or you could get a cable/adapter to use with campsite hookups.

mikpem

What capacity would be suitable with those power packs? I'm looking at similar things to the OP but the ratings on them don't really help with an electrical dunce like me.

For example, what are you going to get out of a 2600mAh portable charger? I'm thinking about using one on a multi day ride with the plan to use it to top up my phone when I stop for lunch. Is 2600mAh going to be enough if I charge the unit every night or would I be better off with 5600mAh or more??

rodgers73

The trip would be for several months and I may not be near an electricity supply in that time. Solar chargers it is I think!

Thanks Whoof - will take a look at that discussion

andymiller

rodgers73 wrote:

The trip would be for several months and I may not be near an electricity supply in that time. Solar chargers it is I think!

If you need a reliable source of power off-grid, your dynamo hub is as reliable as it gets. And as mechanically simple as it gets.



Leaving it at home doesn't make sense.

mikpem wrote:

What capacity would be suitable with those power packs? I'm looking at similar things to the OP but the ratings on them don't really help with an electrical dunce like me.

For example, what are you going to get out of a 2600mAh portable charger? I'm thinking about using one on a multi day ride with the plan to use it to top up my phone when I stop for lunch. Is 2600mAh going to be enough if I charge the unit every night or would I be better off with 5600mAh or more??

It depends on you phone - I bought Nokia 107 and it stays charged for days on end. But a smartphone would be a different matter.

The battery capacity of your device should also be specified in mAh eg an iPhone has a capacity (according to Google) of 1,440mAh. Now I think it may not be quite as simple as this, because you can't use 100 per cent of the power pack's battery capacity, but 2600mAh should give you one and a bit recharges.

rodgers73

andymiller wrote:

Leaving it at home doesn't make sense.

I know, on the face of it at least but I want to keep the mechanicals as simple as possible so anything other than an ordinary front hub is something I'd prefer to avoid.

andrew_s

The specification of a solar panel will give the maximum figure, so a panel that says 10W will only give that at mid-day in the tropics, with not a cloud in sight, and with the panel square on to the sun.
By the time you allow for not being in the tropics, it not being mid-day all day, cloudiness, and the fact that a panel strapped on the back of the bike will spend most of the time pointing anywhere but straight at the sun, you want to have a panel that's well over-specified for your actual needs.
I'd regard a 14W panel similar to this as the minimum.

Having a combined battery pack with it is an advantage as the battery will tide you over cloudy day, provided that there aren't too many on the trot.
Specifying battery packs in mAh is open to much misrepresentation. What you are really interested in is how much power the battery pack contains, as it's this that defines how many times you can recharge your iPhone. If a battery pack says 10 Ah on it, does that mean that it contains 4x2500 mAh li-ion cells at 3.7V each (37 Wh), or does it mean that it will supply 1 amp for 10 hours out of its 5V USB port (50 Wh)? If you are really being ripped off, you could even find that a "10,000 mAh" battery pack has 4x2500mAh NiMh AA cells in it, which is only 12 Wh.

andymiller

rodgers73 wrote:

I want to keep the mechanicals as simple as possible so anything other than an ordinary front hub is something I'd prefer to avoid.

See the exploded view in the previous post. The only real difference between the dynamo hub and a normal hub is that there's a coil and a magnet in the middle. The number of moving parts is the same, it's just that as the axle is turning round it's also turning a magnet inside a coil.

Here's an explanation of how a dynamo works:

Inside the dynamo a permanent magnet is rotated in the middle of some coils of wire. The rotating magnet produces a changing magnetic field and this generates electricity in the coils of wire.

http://www.gcsescience.com/pme21.htm

OK having a hub dynamo makes life a bit more complicated if you need to replace a spoke - but you can manage that by making sure the wheel is properly tensioned before you go, and carrying an extra couple of spare spokes. (Spokes on the front wheel are less likely to fail than the spokes on the back wheel).

There's really not much to go wrong with a bike hub. the most likely cause of failure is the hub flange breaking. I don't think that the chances of the flange failing are significantly greater than with a non-dynamo hub. If it does fail then you would to need to scrap the hub and replace it with whatever you can find locally. So if you really want belt and braces then maybe a hub dynamo and a solar charger.

marcusjb

I'd rate a hub dynamo over solar any day for touring or any other form of distance cycling.

I charge stuff via a Luxos U on one of my distance bikes and the tandem for touring. No issues whatsoever. I use them to charge up a back-up battery pack and then use those to charge the devices (for various reasons - partly to avoid connecting however many hundred quid a GPS or iPhone costs to it and partly to ensure I never need to charge off the dynamo at night as light and charging isn't possible, but I still want to keep my GPS running all night).

A battery pack will charge up my GPS many times and/or phone a couple of times - phones are the key issue and keeping them in flight mode or off is important to maximise battery life. With a £20 battery pack, I can go for quite a few days without any issue even without recharging the battery pack from the hub and/or finding power in hostels, campsites etc.

I'd rate a SON dynohub as far more reliable than the majority of front hubs with it's fancy pressure compensation seals etc.

I don't track individual wheel usage - but I've 3 SONs in total and I'd guess at the most used will have circa 25000km on it - i.e. half it's service interval.

Utterly bombproof.

But really, depending on how off grid your touring is, a battery pack will keep you going for a few days between civilisation without issue.

rodgers73

I have a hub dynamo on my current road bike so I'm very sold on them. But a lot of this about avoiding problems with my front wheel/wheels generally - I fear running out of spare spokes in countries or areas where obtaining unusual length spokes could be hard.

Am I right in thinking you need a different length of spoke to standard/common length ones, where hub dynamos are used? i.e. slightly shorter ones due to the hub having a larger diameter? If so, battery pack maybe a good compromise if solar chargers arent up to much