Thorn Cycles Forum
Technical => Lighting and Electronics => Battery Charging from a Dynamo => Topic started by: rossjeal on December 03, 2003, 10:29:26 PM
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Just fitted Shimano HB-NX30 hub dynamo and want to power my SMART halogen head lamps set up, or at least the 3 Watt lamp. The second lamp is 10 watt, I believe.
Wondered if I could connect dynamo in parallel with 6 volt sealed lead acid rechargeable battery which is part of the SMART headlamps kit.
This would allow the battery to be charged during daylight and ensure full battery power at night until battery capacity drops to only the dynamo output.
The Hub Dynamo is designed to provide 6 volt 3 watts.
The battery is rated at 6 volt 4.5 amps.
The mains operated battery charger is rated at 7.5 volts 500 MA
Does anyone have the electrical knowledge to advise on my proposal?
Regards, Ross Jeal
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I don't like the idea of discharging the 6V motorcycle battery through your generator. That sounds like an expensive experiment. I also have a Smart lead-acid set. A large diode would be needed to protect the generator but this would drop the charging voltage by 0.7V, so not enough volts to charge the battery. I believe these hub dynamos have a rectifier but they're not designed to be reverse biased. Your generator does not supply a constant 6V, it depends on how fast you pedal.
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To do this properly you need some electronics to rectify the ' dirty' volts from your generator ( assuming there's no rectifier in it) and also a voltage regulator to stop you producing more volts then needed.
This is because SLA ( sealed Lead Acid) batteries need a constant voltage charge, as against NiCads that need constant current
This needn't cost you much as the bits are cheap and the info is on the web if you put something suitable into Google.
You also need to look at the current ( Amps / MilliAmps ) needed to charge the battery and then add in the current needed to run the lights and then see if the generator will provide enough current , and under what conditions ( ie; light pedalling 60 rpm, or racing 120 rpm).
If you're serious about this let me know and I'll dig out some info for you ( my other pastime is Amateur Radio )
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As Ross stated, he wants to charge the battery during the day with the lights off. The Smart battery needs 7.5V 500mA to charge it.
A very similar simple 6V motorcycle system (where a 20W headlight runs off the alernator AC) consists of the alternator feeding a selenium rectifier straight onto the battery, no smoothing.
There are two problems. Most electronic stabilizers and dc-dc converters are low power, we need 3.5W, so diodes etc must be rated above this and possibly heat-sinked. Whereas the motorcycle circuit is designed for the job, the Shimano hub does not produce 7.5V unless you ride it over a cliff. Drawing too much current from the Shimano may melt it and they are very expensive: they are rated 6V 3W.
The advantages of a lead acid are that they can be recharged at any time, they can be constantly charged as in a car, they do not have to be discharged before recharging. So the mains charge unit is probably the best option. These little batteries can do an unbelievable amount of damage when shorted through something expensive. Get it wrong and you'll need a new hub and a wheel rebuild.
That said, I'm sure it is possible to charge the battery from the generator, at a low current trickle charge, provided that the Shimano hub is protected from over load. Please don't melt the dynamo. Good luck.
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You might like to look at the information here http://www.myra-simon.com/bike/dynotest.html#output. The dyno outputs all seem to level off over 20mph. I know the o/p is given in watts but if the load remains constant as in a bulb then it is the voltage that increases with speed (something to do with Ohm's law). The graph shows that the variation of output is quite wide over the normal speed range of a bike.
Also note that the 6V 4.5Ah (Amp-hour) battery can dump 27W for an hour through your dyno, and a lot more than 4.5A if shorted. I once dropped a socket wrench on the car battery and it melted a great lump out off the handle, it didn't bother the battery at all.
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A few comments:
Most bicycle dynamos are more or less constant current sorces. It is not possible to 'suck' more that some 0.6A out of them. So there is no way to overload them. The load's resistance defines the volatge and not the current (in a given range).
The battery cannot discharge through the dynamo for the very simple reason that there is a rectifier in between (as long as not part is faulty of course).
Even for medium speed (15mph) it is no problem to get 7.5V or more.
And you could both NiCd and SLA batteries charge with whatever you want (as long as you stay below the max current), the problem (or challenge) is just how to tell when it is full (overcharging is bad in any case).
Charging a 6V SLA with 7.5V does not bring a long life. It is better to start with 7.35V and when the charge current drops to some 100-200mA go down to 6.9V. As this is an outdoor application, you have to compensate for temperature, higher charging voltage at low temp and vice versa.
The lead acid batteries main advantage here is, that they can be charged with constant voltage.
All known secondary cells can be charged at any time without any bad results. The only exception is that some chemistries do not like high charge currents at low temperatures.
A 6V 4.5Ah lead acid battery cannot give 27W for an hour. Not by far. SLA high current capacity is not one of their strong points. Be happy if you get 30 minutes on constant 27W output.
But short current is very high, so it is still a good advice to be careful.
Another good point: a 6V/4.5Ah SLA battery is pretty cheap, so you do not loose much when you damage it.
Best thing to do: join the bikecurrent list.
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My main concern is protecting the generator whilst charging the battery.
This generator is an alternator with a rectifier, not a dynamo. Its output voltage is dependent upon speed. Its output current is dependent upon the load, up to the point where it reaches saturation. The graph in the link shows this. The generators are not constant current over their normal operating range.
Here is a simplified summary :- A 2.5W 6V lamp represents a load of about 15 ohm. With 6V supply this will pass 0.4A. If you were to pedal slowly so that you only generate 3V then it would pass 3/15 = 0.2A, consuming 3V x 0.2A = 0.6W (a dim glow). If you were to pedal so fast so that 9V were generated then the bulb would pass 9V / 15ohm = 0.6A, i.e. 5.4W. However let us assume that the generator cannot provide more than 4W because it has saturated, this will cause the output voltage to drop to 7.7V. So it's self-regulating, you cannot overload the alternator by pedalling too fast but you can blow the bulb, or a badly built charging circuit.
The SLA is a 6V 4.5Ah (Amp-hour) battery, it does what it says on the tin: it can deliver 4.5A for an hour at 6V, that's 27W, for an hour. Alright, it won't like much it but it is designed to deliver half that power (12.5W) for two hours. A lead acid battery can deliver a huge amount of current through a low resistance load (such as your generator). A 75Ah car battery can shove a >200A surge through the starter motor. If your charging circuit & your alternator's rectifier are not man for the job & a fault occurs then you may see smoke coming out of the hub. Do not be inclined to experiment by shorting a SLA, it will overheat & buckle its plates.
For most cycling you probably won't be generating enough voltage (7.5V) to effectively charge the battery. A diode pump (a diode-capacitor ladder) can increase the dc voltage from the un-smoothed rectifier, voltage stabilization & protection can also be incorporated in this circuit. The instrumentation dc-dc integrated converters available are low power, they cannot generally handle the 0.5A, 3W produced by the generator. You do not need anything terribly sophisticated for this, you do need agriculturally reliable though.
I am investigating a suitable circuit to provide constant charging of the battery from the generator whilst simultaneously allowing the lights to be run from the battery. Problem is running the lights at 6V (they're already over-rated) whilst charging at 7.5V, doh.
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Hello all, new here.
I have recently been working on this idea myself and was surprised to see this topic posted.
I was given a very simple design to trickle charge a NiMH battery.
By running the positive and negative wires of your generator to a 1 amp full wave bridge rectifier, then through a 22 microferit capacitor to the battery, you should be able to trickle charge it.
I have not tried it yet but I noticed there are some talented people in here and was wondering what you think about it.
Any thoughts?
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Sorry for delay, had to ask some chaps at work about generators etc.
Ok, a bit of history: SA made a rechargeable lead acid Dynohub lighting system way back in '60s. This used a 4.8V battery & a full bridge rectifier. Problem was that if a bulb blew you could receive a very nasty shock from the handlebars. This is because an alternator is a more-or-less constant power device, so you can get over 200V with no-load (my colleague has measured this off a bottle dynamo).
Now you should be able to simply charge a lead acid from the alternator straight off the rectifier. Problem is that if the load changes then the voltage changes too. This can cause all the bulbs to blow. Our experience was from a 6V Vespa scooter that would happily blow 24V bulbs until discovered that the zener voltage clamp diode had gone u/s.
I cannot find a full spec for the HB-NX30 but from the diagram the wiring is non-reversible, so I am fairly confident that it has a rectifier. But it is designed to have a 3Watt load. If you do not give it a 3Watt load then its characteristics will alter. We do not know the load when charging the battery, it may be more or less than 3Watt equivalent.
It was recommended to me that a 7.5V zener be fitted to clamp the voltage. That way you can charge the battery whilst running the lights, or with them off. The zener needs to be a big one, capable of 3Watts or more, these are normally fitted with a heat-sink (which is handy because you can bolt it to something).
Incidently discharging a 22muF from 200V through your flesh can be an envigorating if rather painful experience. The SLA does not need current smoothing.
There is a diagram given in Rob Van der Plas "The Penguin Bicycle Handbook" for a SA Dynohub charging a 4.8V or 6V NiCd through a 12V 1A full bridge recitifier. The battery is permanently connected to the rectifier, the lights are connected to the battery via a switch.
Happy Christmas.
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Dear Snapper,
(did not look in here for a while).
1. Unless the new Shimano Inter L is completly different that all the others (and I know only about one bicycle dynamo which is completly different), you have a basic misunderstanding: Most bicycle generators are constant current sources. As things are not perfect (and there is no real need to be), they just behave much more as a current source than as a voltage source.
It's output voltage depends on the load resistance, as soon as the minimum speed is reached. That means twice the resistance is twice the voltage and twice the power. Of course, if you need more output voltage, the minimum speed is higher.
Our dynamos here are completly different to batteries, they do not deliver (more or less constant) a voltage like 9V.
2. Saturation does NOT depend on the power delivered. Let's assume the insulation is good for more than we need, you could get easily 30W (and probably much more)out of a SON without any saturation. People have run 220V lightbulbs from a SON for demonstration (at horrible RPM of course). Saturation comes when the current is too high. As constant current devices do not deliver much more than their rated current, this is nothing to worry about. But not all devices are equal. Where have you measured saturation on a bicycle dynamo? I'm very interested in the model and the circumstances? Was it on an Inter L?
3. I have never seen a bicycle dynamo molten down due to overload, although I experimented with them quite a lot (and used them even more). Which brand was it under which load?
4. Alternators are no constant power devices, the are (as stated several times before) constant current sources. The high voltages you mention, came from a resonating circuit, funny enough I was never able to experience them by myself. I know about nobody ever hurt (electrically) by a bicycle dynamo. On powerlines, this is called Ferranti-effect.
5. What you seen in Myra's diagrams ist the voltage behaviour when you load a dynamo with the usual bicycle light. That means, when your load is different, these curves look different. When you put two 6V/3W bulbs in series, the lines will look similar, but the scale will be different. Myra is very knowledgeable and will tell you nothing different than I, probably in a better language .-)
6. When you use a good full way rectifier (either a low drop or a synchronous one with almost no drop) you will get charging voltage for a 6V SLA pretty easy. As the peak voltage is 1.4 times higher, starting starts at pretty low speed (shloud be easy to check). As long as the rectifier is OK, there is nothing to worry about the battery discharging through the dynamo. Beeing cautious is alway good and the use of a fuse is not bad at all (I never use them, BTW).
7. SA dynohub: They were only rated at 300mA, for &V that meant 1.8W, so just in case somebody finds one somewhere, do not be disappointed. And do not disassemble them (a long story). And 4.8V lead acid?
8. A 7.5 is a simple and good solution, but will start to waste energy at pretty low speed.
9. DC/DC converters are available in all sizes and tastes.
10. Again: A 4.5Ah SLA will NOT deliver 4.5 A for an hour, maybe for 40 minutes or less.
After all: I will check the Inter L as soon as I have time if it is really that different as Snapper writes.
In the menawhile: Happy Chrismas
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Have a look at this:
http://www.mark-ju.net/bike_ride/equipment/charger.htm
Very complicated system, but seems to be doing the lot!
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Dear PetLu,
I do hope we are talking at cross-purposes because we seem to be saying the same thing. Please re-read my message of 23/12. In the earlier message I gave a very simplified rendition of ohm's law, which as you are aware does not apply very well to ac.
1. Bicycle generators are by-and-large alternators, their output is ac current. Some of these generators, especially those designed to operate a standlight appear to have a rectifier built into them. None of them deliver a constant voltage. The output votage will be dependent upon the load. My professional collegue described them as more-or-less constant power devices but noted that it is the internal & external load that will regulate the current.
2. The saturation I refer to is the magnetic flux, once saturated no more power will be obtained. The insulation can be as good as you like, you cannot get more power out that you can induce. You can probably light a 240V bulb with the cheapest bottle dyno you can find, it depends on its load resistance. As the voltage is dependent upon the load, so you can obtain a voltage in excess of 200V for a no-load bike dyno:- disconnect your dyno & put your DVM across it.
3. Melt down is not caused by over running the alternator but if you should manage to pass the battery current through the alternator coils, which generally has rather thin wire, they melt. The current capacity of a wire is measured in mho (reciprocal ohm) and is proportional to its diameter.
Meltdown of alternator coils occurred several times with a BSA Bantam motorcycle which enjoyed blowing its Selenium recifier. The Triumph Tiger Cub m/c also displayed this tendency.
4. I know of two people hurt (but not diectly injured) by bottle dynos which are earthed through the frame developing a fault when a bulb blew. One rider was slightly injured when they fell off.
5. Myra's diagrams explain what I mean. The voltage behaviour of a bike dyno loaded with a standard bicycle lamp set. That's what we are dealing with here as the constant load.
6. A good full wave bridge rectifier i.e. the one with four diodes... Schottky diodes were recommended for the job because they have a lower voltage drop, normal diodes drop about 0.7V. However if the Shimano Hub has a suitable recifier then there is no point adding another, it would just drop the voltage. The rectified o/p is not smoothed, there is no need. You are not getting a steady voltage, it will peak over the necessary 7.5V (rms~1.4x actual). You could use a Cockroft Walton circuit to double the ripple voltage but this was thought unecessary. A 7.5V Zener will clamp the maximum to that voltage by clipping the ripple so we do not over charge the SLA. So whilst we get 7.5V we are effectively charging the battery & when we get less we will still be assisting the lighting. Please note the the Inter-L/Nexus is not actually designed capable of powering the full 12.5W of the Smart lamp set on its own.
7. SA Dynohubs came in various flavours. Mine had a Miller lighting set with a 4.5V backup battery. Nothing fancy, you had to risk the front spokes to reach under the lamp to switch over. The dynohub may have been rated as 6V (but see earlier) but the bulbs were rated much lower.
The rechargeable system had the battery in a cylinder clamped to the d/t like some a large diameter pump. This was a wet lead acid of some lower voltage that the generator. The NiCd mentioned elsewhere is the 4.8V job. oops.
8. 7.5V is what the SLA should be charged at. The Zener should not waste too much energy since the more time the circuit spends at 7.5V the more the SLA will charge.
9. A dc/dc converter was considered but thought to be an unecessary complication (kiss).
10. What does 4.5Ah mean then?
40 minutes at 4.5A is 3Ah. Smart state 2 hours on both lamps, they use 12.5W at 6V dc i.e. 2.05A. My slide rule makes that 2.05 x 2 = 4.1Ah. The battery itself says 4.5Ah. BTW it has an unmarked fuse to prevent any disasterous short circuit.
On a half our run I use the 2.5W on the first leg until out of the street lights then I switch to the 10W until I get to the farm where the road narrows, then use both (12.5W) so I can see the ditch & the potholes. The return journey is the reverse. I have used the battery for about 8 hours without recharging it. Go figure.
Happy New Year.
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Having attempted to read the above posts, I will be contacting whoever runs the forum to insist that English should be the only language used in messages. God knows in what tongue you lot are speaking. ;-)
Bruce
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Sorry Bruce, this so called English is the best I can do, but it may be even harder for me: There are words used I could not find in my dictionary. 'envigorating' for example.
To make it worse: There are so wonderful and more than complete documents from people who made lots of measurements. But all these data is either German or Dutch. Just in case somebody knows a working translation service (I have no idea if babelfish works for these):
Two very good ones how to charge a 12V battery with a dynamo (German!):
http://www.enhydralutris.de/Fahrrad/12V-Standlicht8.pdf
Even better with the mentioned Shimano hub dynamo and a 12V sealed lead acid battery (but in Dutch):
http://www.welmers.net/hurricane/electric_.html
And the almost 400 page bicycle light 'bible' (German!):
http://www.enhydralutris.de/Fahrrad/Beleuchtung.pdf.gz
greetings PeLu
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A related topic under discussion now
http://www.cyclingplus.co.uk/forum/topic.asp?TOPIC_ID=18578
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You need about 8 volts from the dynamo.
1n4001 Vin ____ vout 1n4001
d-----anode/cathode-|-------|7805|-------anode/cathode
y + |gnd +
n 4700uf 1k variable 6v
a 25v resistor sla
m - | -
o------------------|-----------------------------------
Should cost about £3 to make adjust the 1k variable until you get around 6.7 volts output . You need about 8 to 24v from the dynamo.
I make lots of sla chargers all the time.
m3gsi.
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I've been wondering about doing exactly the same thing - charging Smart 10W/2.4W with 6V 4.5Ah from a dynamo of some kind. I have the lights and they have served me well for the last couple of years, but depending on weather conditions the capacity can be marginal for my return commute. I have tried using along with a small smart halogen front on rechargable AA's which I use to be seen or if the Smart set dies, but it's a lot of fiddling around recharging batteries. This year I have with been toying with either keeping a second charger at work to recharge the battery during the day or using a dynamo (bottle or spindle fitting)to keep the charge up or as a back-up if the batteries die. So my question is - has anybody made any progress in getting this to work since the last post in July? If so, I'd be very interested to find out how and any pitfalls! Thanks
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I didn’t realize this thread had been going on. I’ve looked into the “on bike power” question before, but couldn’t find a satisfying answer at the time. In the past I went for a more minimalist approach with a high capacity set of Ni-MH AA’s and a 110/220AC power socket charger and all my appliances being energy efficient, so I could get away with weeks without power socket.
I soldered up a Luxeon LED front light about a year ago, which is plenty for me to cycle by at night. Now these are becoming commercially available. Cateye makes one and Exposure Lights, makes an awesome light which uses 2x 5Watt Luxeon’s.
However, a laptop was out of my league. It is now starting to make more sense to me, to use solar panels as supposed to a dynamo, since flexible panels have become much more affordable. The Coleman Exponent Flex 5 (5watt) looks ideal for about £70, works even if your standing still, and zero drag. But less good when its cloudy. L
Mark McLean’s multi charger looks the business. Unfortunately I haven’t got the skill to put one together though. So who’s going to produce these for the cycling community?
I’ll be following this development with interest.
Cheers,
Stijn
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The Dec 2004 issue of What Mountain Bike? magazine features two gadgets that do this... there's the Coleman Folding Solar Panel (see http://www.ipcsolar.com) and a special friction dynamo (see http://www.cat.org.uk - go to the shop and search for "pedal").
The solar panel seems a little less practical and is a bit expensive at £90... The latter is only £20! Both send power to a cigarette lighter socket, so any mobile should be able to be charged with them. The dynamo seems an essential accessory for Thorn owners who have dynamo braze-ons but use battery-powered lights!
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Hi, I don't know what's the actual status on this thread but I've come up with a solution to the question posed here. I'm using a Shimano Nexus Inter L and a 6V 4 Ah SLA battery. I'm not sure that the alternator has a built in rectifier, this can be checked by measuring the output voltage with a DC voltage meter and you'll see the needle going left and right, or is using an LCD meter, you'll see the minus sign appearing and dissapearing as you spin the weel. So I did my own rectifier with a 1A bridge and a 4700 uF capacitor. The device has a switch which allows two functions 1) The alternator charges up the battery at a max current of 300/350 mA (limited only by alternator and circuit voltage drops), at a speed of 18km/h the charging current is around 250 mA and at 25km/h the charging current is around 300 mA. 2) The switch can me moved to this position to put the battery in paralell with the load, which in my case it's a Luxeon LED that draws around 250/300 mA (it's electronically limited). The alternator is capable of feeding the load up to 300 mA and the rest of the job is done by the battery. When you stop the battery does the whole job.
It would be a little bit difficult to explain the circuit design using just words here, but one thing I can definitely say is that putting a rectified signal in paralell with the battery is a inefficient way of charging it because the battery's internal resistance to charge would require a higher voltage to get a decent charging current than the one the alternator can provide. This was the model I used at the beginning anyway. You could easily get between 200/300 mA the the rpm had to be much higher than those needed to get the same current with the newer design. The solution I've come up with is using a NPN transistor whose collector is plugged to the negative pole of the battery, and the battery is plugged to Vcc in turn. then the emmiter is connected to a resistor that mirrors a reference voltage (eg 0.3 / 0.6 V for schottky or regular diode). This circuit tends to "force" a current into the battery in order to charge it regardless of the input voltage, obviously within certain limits like alternator max current and output voltage. It's a rather constant current design than a contant voltage design. SLA' should be charged with constant voltage, but taking into account that the riding time is not too much, this should not be a problem. However a comparator can be added to shut down the charge in case it goes above 7.0 or 6.9 volts.
If anyone is interested in this circuit, please email me at scott1981ar@yahoo.com.ar
Thanks and I hope to get in contact with someone here.
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Hi, I don't know what's the actual status on this thread but I've come up with a solution to the question posed here. I'm using a Shimano Nexus Inter L and a 6V 4 Ah SLA battery. I'm not sure that the alternator has a built in rectifier, this can be checked by measuring the output voltage with a DC voltage meter and you'll see the needle going left and right, or is using an LCD meter, you'll see the minus sign appearing and dissapearing as you spin the weel. So I did my own rectifier with a 1A bridge and a 4700 uF capacitor. The device has a switch which allows two functions 1) The alternator charges up the battery at a max current of 300/350 mA (limited only by alternator and circuit voltage drops), at a speed of 18km/h the charging current is around 250 mA and at 25km/h the charging current is around 300 mA. 2) The switch can me moved to this position to put the battery in paralell with the load, which in my case it's a Luxeon LED that draws around 250/300 mA (it's electronically limited). The alternator is capable of feeding the load up to 300 mA and the rest of the job is done by the battery. When you stop the battery does the whole job.
It would be a little bit difficult to explain the circuit design using just words here, but one thing I can definitely say is that putting a rectified signal in paralell with the battery is a inefficient way of charging it because the battery's internal resistance to charge would require a higher voltage to get a decent charging current than the one the alternator can provide. This was the model I used at the beginning anyway. You could easily get between 200/300 mA the the rpm had to be much higher than those needed to get the same current with the newer design. The solution I've come up with is using a NPN transistor whose collector is plugged to the negative pole of the battery, and the battery is plugged to Vcc in turn. then the emmiter is connected to a resistor that mirrors a reference voltage (eg 0.3 / 0.6 V for schottky or regular diode). This circuit tends to "force" a current into the battery in order to charge it regardless of the input voltage, obviously within certain limits like alternator max current and output voltage. It's a rather constant current design than a contant voltage design. SLA' should be charged with constant voltage, but taking into account that the riding time is not too much, this should not be a problem. However a comparator can be added to shut down the charge in case it goes above 7.0 or 6.9 volts.
If anyone is interested in this circuit, please email me at scott1981ar@yahoo.com.ar
Thanks and I hope to get in contact with someone here.
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quote:
Originally posted by ahconway
The Dec 2004 issue of What Mountain Bike? magazine features two gadgets that do this... there's the Coleman Folding Solar Panel (see http://www.ipcsolar.com) and a special friction dynamo (see http://www.cat.org.uk - go to the shop and search for "pedal").
The solar panel seems a little less practical and is a bit expensive at £90... The latter is only £20! Both send power to a cigarette lighter socket, so any mobile should be able to be charged with them. The dynamo seems an essential accessory for Thorn owners who have dynamo braze-ons but use battery-powered lights!
Has anyone tried this gizmo yet?
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I would also like to get sorted a 12v system, not just to run lights but to charge my lights mobile and GPS as I'm planning a sposored ride from southern Spain to London. Weight is going to be a crucial thing as it is as Im going to be carrying all my food with me as well as tent and sleeping bag towed behind on a trailer (This is going to be fun over the pyrenees mountains I can tell!)
I was thinking about a trickle charge system. I do know my old teacher at school was a whizz at electronics - He was also a pervert and took naked pictures of a load of kids including me. Maybe it's time to forgive and forget and bribe him into building me a system for free before I try to get the police to prosecute again?
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http://seoulp4bikelightshombrewed.blogspot.com/2007/05/my-requirements-re-touring-bicycle.html
My experience yes Shimano dynohub is great! click link for my doings re. independent power system on touring bike.
cheers bryfos[:D]
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It should be the 75Ah car battery can shove a >200A surge through the starter motor. If your charging circuit & your alternator's rectifier are not man for the job & a fault occurs then you may see smoke coming out of the hub.
_________________
LED Flashlight (http://www.flashlightz.com/)
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My B&M IXON IQ front light takes 4 x AA batteries.
The manual says there is a recharger adapater that utilises a dynamo.
1 - It's a superb front light
2 - It sounds like a simple solution if you need AA batteries topped up
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Since this is a dated but frequently-viewed topic by guests, I suggest also searching using the terms "Battery-charging" and "Tout Terrain The Plug 2" (no quotes) under the "Lighting" category. Much of the later discussion about dynamo battery charging has taken place in those threads.
Best,
Dan.