Cycling UK Forum

My plan to be on my bike and self-sufficient by way of re-charging my devices failed this long weekend round the Isle of Wight. In a way I'm glad it did before I set off on longer camping trips like the Netherlands this Summer.

I have a dynamo hub which powers my lights and a USB socket which charges my phone and GPS. All works well IF (and a big if) you aren't running the lights I found out. As some of you may know the weather on the IOW wasn't too clever this weekend and I was running my lights for safety reasons. I had my GPS plugged in and I'm 90% certain, the lights drained the battery from that before relying on the dynamo. If that's possible? I'm no electrician so I stand to be corrected. Normally I reckon on my GPS having enough battery power, without being plugged into the USB/Dynamo to last for 8-10 hours. It lasted 2 max!

So that was my issue which I need to resolve. I like the idea of having an external battery pack, and although the solar arrangement hasn't got the most efficient set-up according to reviews (18-22 hrs to recharge a battery pack), I like the idea of the Sun doing some of the graft for me.

The question is: Has anyone got a Powermonkey Extreme (solar) and what are your thoughts?

Many thanks in advance........b

I have a Powermonkey Extreme solar. Tried it on one tour but wasn't impressed. Despite plenty of strong summer sun in southern Germany I never managed to get it more than 50% charged in one day's ride.

What GPS have you got? My Etrex 20 lasts 2 tour days on one charge.

That sounds about right. I've got the edge touring which would last about 2 days riding or thereabouts, which is why I think the light drained it. I'd be interested to know if anyone has charged up their Powermonkey with a Dyno-hub...b

Does the GPS unit use more battery when it is plugged in? I think that mine does, thinking that it doesnt have to be frugal when being "fed" from the mains. So is it possible that it was consuming more yet not getting enough current from the USB to cover its needs.

From one person not too understanding of electronics to another.

I have just done a two weeks tour in France and I used a dynamohub to charge four AA batteries in my Ixon IQ headlight.

I found a rule of thumb that one hour's (lights off) charging would cover me for one day of GPS use!

I didnt have any trouble charging and using the lights simultaneously (though charging would be slower).
In my case the batteries would be powering the light when my dynamo wasnt turning and only charging when there was an excess from the dynamo.

I reckon a GPS unit will be consuming somewhere around 10% of your dynamohub's output. I would be more inclined to be suspicious of the phone's energy demands.

beardy wrote:Does the GPS unit use more battery when it is plugged in? I think that mine does, thinking that it doesnt have to be frugal when being "fed" from the mains. So is it possible that it was consuming more yet not getting enough current from the USB to cover its needs.

From one person not too understanding of electronics to another.

Nope it only seems to go haywire when I've got the lights on. If they are off the GPS maintains a 100% charge when plugged into the USB. I'm glad there's another non-electro-boff about [emoji95]

meic wrote:I have just done a two weeks tour in France and I used a dynamohub to charge four AA batteries in my Ixon IQ headlight.

I found a rule of thumb that one hour's (lights off) charging would cover me for one day of GPS use!

I didnt have any trouble charging and using the lights simultaneously (though charging would be slower).
In my case the batteries would be powering the light when my dynamo wasnt turning and only charging when there was an excess from the dynamo.

I reckon a GPS unit will be consuming somewhere around 10% of your dynamohub's output. I would be more inclined to be suspicious of the phone's energy demands.

Thanks. Useful obs for me. I'll try and do some more accurate timing of charging with/without lights and with my phone and GPS...b

Heltor Chasca wrote:I had my GPS plugged in and I'm 90% certain, the lights drained the battery from that before relying on the dynamo. If that's possible? I'm no electrician so I stand to be corrected. Normally I reckon on my GPS having enough battery power, without being plugged into the USB/Dynamo to last for 8-10 hours. It lasted 2 max!

I'm not an expert either, but I doubt that would happen. If each device (light and USB charger) goes straight to the hub, each device has it's own rectifier, which should prevent reverse flow. That's if the rectifiers use diodes.

Moreover, the GPS/phone's USB socket is almost certainly only set to allow power in (i.e. no host mode) anyway.

Otherwise you'd be able to turn the light on as bright as full with the wheel stopped. If you can do that, then that would prove the light is leeching the GPS/phone (unlikely).

Beardy is probably correct, but the light is the final straw - it causes the available spare power to be too low (possibly the dynamo voltage is dragged too low for the USB charger to work properly anyway). So the GPS/phone behave as if they have USB power (possibly longer screen timeouts/higher brightness/more active processes) but actually isn't being effectively recharged.

edocaster wrote:

Heltor Chasca wrote:I had my GPS plugged in and I'm 90% certain, the lights drained the battery from that before relying on the dynamo. If that's possible? I'm no electrician so I stand to be corrected. Normally I reckon on my GPS having enough battery power, without being plugged into the USB/Dynamo to last for 8-10 hours. It lasted 2 max!

I'm not an expert either, but I doubt that would happen. If each device (light and USB charger) goes straight to the hub, each device has it's own rectifier, which should prevent reverse flow. That's if the rectifiers use diodes.

Moreover, the GPS/phone's USB socket is almost certainly only set to allow power in (i.e. no host mode) anyway.

Otherwise you'd be able to turn the light on as bright as full with the wheel stopped. If you can do that, then that would prove the light is leeching the GPS/phone (unlikely).

Beardy is probably correct, but the light is the final straw - it causes the available spare power to be too low (possibly the dynamo voltage is dragged too low for the USB charger to work properly anyway). So the GPS/phone behave as if they have USB power (possibly longer screen timeouts/higher brightness/more active processes) but actually isn't being effectively recharged.

Thanks edocaster. I'm sure I need to check the settings on the GPS as it was powering down (although set not to) at about 75%! Confucius reigns...b

In other news on the battery back-up scene:

I rung Powertraveller who do the powermonkey kit (in Hampshire) to check on dynamo/charging stuff and a couple of other inane questions you would expect from a twit like me and I ended up talking to a lady in the tech department who recommended a battery with 3 times the power as a further option:

https://www.powertraveller.com/en/shop/ ... xplorer-2/

You don't get all the bells and whistles and you don't get a DC in port, just USB. But I don't need them as my devices have all the relevant bits and my bike/home/car set up is USB friendly. BUT if you punch in the code PANBLK you get a FREE Powermonkey Extreme Solar Panel worth £35.00. https://www.powertraveller.com/en/shop/ ... nly-black/ And although it doesn't have great reviews yet, it works well enough for me in the Summer. There is another more efficient, large panel for £110.00 for lower light levels if you wanted https://www.powertraveller.com/en/shop/ ... xpedition/

Ring Pete or Matt on 01420 542 980 with your PANBLK code https://www.powertraveller.com/ I did ask for a free shower-cap or pencil for recommending them but I didn't have the right tone of voice so got turned down No affiliation to seller etc etc blah blah..........b

So have you used the solar charger yet? it sounds like you have "it works well enough for me in the Summer", but you've only just ordered it.

when i looked into solar chargers a few years ago, the reviews were bad for on bike charging, unless you can guarantee bright sunshine perpendicular to the panel, all day.

The best way to ensure most efficient use of the panel is never to have it in your shadow, which would mean only ever riding in a northerly direction, north west -ish in the morning, north mid day, north east-isn evening.

so i bought a power gorilla. ( https://www.powertraveller.com/en/shop/portable-chargers/professional/powergorilla/ ). This tops up two garmins every night, the phones every few days (depending on phone use, we don't turn them on until the evening, check in with kids, check weather, turn off). lasts about 7-10 days on full charge from the start.

I can't use a dynohub as i have my disk brakes on the right fork leg.

andrewjoseph wrote:So have you used the solar charger yet? it sounds like you have "it works well enough for me in the Summer", but you've only just ordered it....I can't use a dynohub as i have my disk brakes on the right fork leg.

I haven't used one yet. No. Forgive my poor education and poor linguistic skills guv. From the reviews the little one should "do for now" and as it is being thrown in for "free" I'm not expecting the Earth and Moon. With the Explorer 2, reviews suggest 12-15 hours full charge with optimum conditions. And as I'm a gardener in the UK I'm educated enough to realise there is no such thing as optimum sunlight here. I'm expecting to charge the battery pack via my dyno-hub mainly, if I'm not lit up.

As far as dyno-hub/disc brakes go: Have a look around. I've got a Surly DT with a Shimano XT dynamo-hub so it is definitely doable....b

I've spoken (emailed) with several makers, because i have my disk brake rotor on the right of the hub, it would mean the chances of the hub unscrewing enough to compromise the wheel strength during use, are too high.

andrewjoseph wrote:I've spoken (emailed) with several makers, because i have my disk brake rotor on the right of the hub, it would mean the chances of the hub unscrewing enough to compromise the wheel strength during use, are too high.

Interesting. What did Shimano say to you?

The general concession from the people i contacted (can't remember exactly who), was: "there is a danger of the hub unscrewing due to precession if spun in the opposite direction while loaded."

I believe this is true of all hubs that are screwed together.