Homebuilt charger for bicycle light battery packs and other equipment?

[Ian Wood]

Greetings:

I've got a project in mind for a self-supported cross-country cycling trip (on one of these, towing my gear and solar panels on one of these), but it's been quite awhile since I've picked up a soldering iron, and I haven't worked with solar panels before.  I was hoping that you might be able to steer me in the right direction, or tell me that I'm nuts and should stop bothering you.

I want to build a smart solar charger that will charge the batteries for:

Two front lights (probably two of these; they each use a 6 volt 4.5AH battery NiMH battery pack)

A set of cold cathode running lights that uses a battery pack made of 10 AA NiMH batteries

A rear light that uses two AA batteries

A Samsung i700 (a cell phone/PDA that uses a 3.7V Li-ion polymer battery)

A folding keyboard that uses two AAAs

The solar panels would be in a weatherproof enclosure attacked to my bike trailer.  The individual battery packs for all the lights would be in an enclosure on the bike's rear rack, connecting to the lights and also to the charging panels. I'd provide a place to charge the AAA batteries as needed and a plug for the i700.  I'd like to put a smart circuit in between each battery or device, so that charging begins at a predetermined battery voltage and ends at another voltage (still looking into various designs for building that).

I would only use the lights as necessary (I'd avoid trying to find a campsite after dark if possible) and probably not to the point of draining the batteries, so if they recharged over the course of 8-24 hours of sunlight exposure, that would probably be adequate.  I might need a bit faster charging times for the i700, but maybe not.

Anyway.  That's my Grand Plan.  But, as I said, I'm not sure where to start. So, my questions:

Given the batteries mentioned above, what sort of solar panels should I be considering?  

What are realistic charging times?  

Finally, do you have any suggestions about where to find info on similar homebuilt rigs, smart charging circuits, or working with solar panels in general?

Any help you could offer would be greatly appreciated.

Cheers,

--Ian Wood

[hiker]

add a rectifier to a bike generator--and charge your batt.s while riding...

you could even add some of those 3 pronged voltage regulators--for your diffrent

voltage needs.....

[Ian Wood]

Thanks for the input.

I considered and rejected the whole bicycle generator thing early on...I've got 30+ watts of lighting on the front end alone (I like to see the road ahead, not just the road surface in front of my wheel), plus all the other things I mentioned.  That means a hub generator (sidewall generators wouldn't cut it, even for charging...), which means a new wheel, and also means I have hub generator drag and drag from hauling batteries around.

So, I thought if I'm going to have batteries anyway, why not dig into the whole solar thing?

Hence: my showing up here.  

[srnoth]

Hey there Ian,

Some very cool ideas you have there. I have a couple questions and suggestions for you:

The various lights etc that you mentioned above all have different voltages, and therefore cannot be all charged directly from the same solar panel. So you have two options as I see it:

1. Get separate small panels for each item.

or

2. Build a small 12v battery bank with a couple medium sized panels charging this bank.

Getting separate solar panels for each item is complicated and has its problems. It means that you have to get a separate charge controller for each item, and I am not even sure if you can get charge controllers at such small voltages (2 AA batteries = 3v) or odd voltages such as 10 AA batteries = 15 volts.

So to simplify things, at least on the solar side, I would recommend getting some solar panels to make a 12 v solar array. (I am not an expert in solar, but I believe you can by several of those small 12v panels, and connect them together in strings of two (series) to get twelve volts, and then add as many of these strings together in parallel to get as many amps as you require). Then build a small 12v battery bank, and use a small charge controller to charge the batteries from some solar panels.  This way you have a reliable supply of power even when there is no sun. From this reliable 12v source, you can now go about charging the various items that you mentioned:

Two front lights (probably two of these; they each use a 6 volt 4.5AH battery NiMH battery pack):

I presume you mean that each light is 6v, and normally each would have its own 6v battery. I see two options for this. The simplest, in my opinion, would be to get some 12v headlights instead. It would make things a lot simpler. If you got 12v ones, you could connect the 12 batteries for the headlights directly to the 12v bank in the trailer, and they would become part of the bank and charge at the same time from the panels. If you have to go with 6v, you can connect the two 6v batteries in series, so that you can charge them with 12v, yet at the same time connect one headlight to one battery and the other to the other. This way each headlight will only see 6v. But make sure you always use both at the same time, or else you will end up with irregularities in the charge of each battery. Or you could get one of those new solar battery chargers, the ones that fold up, and are used to charge cell phones and laptops etc. I am not sure how many watts they are, but if you only use the lights for an hour a day, the might work.

A set of cold cathode running lights that uses a battery pack made of 10 AA NiMH batteries

A rear light that uses two AA batteries:

This can be really simple or really complicated. The simple way is to buy a bunch of rechargeable AA batteries, and use a normal battery charger to charge them. Possible buy a really small cheap chinese inverter, and just use a normal 120VAC (household) charger to charge them. Maybe if it's that many batteries, get two or three of the chargers. Then, when you need to charge some batteries, fire up the inverter and charge the lot. When they're done, put them in the trailer ready for when they're needed again. Get extra rechargeable AA batteries, so you only need to charge when there are several waiting to charge. More convenient.

So, that is, 12V solar/batteries ---> Inverter ---> Normal Battery charger ---> Lots of charged up batteries!! ;-)

You can probably find some battery chargers that run of 12v, and this will probably be more efficient, but probably also more expensive.

A folding keyboard that uses two AAAs:

Same thing. Buy a couple rechargeable AAAs, recharge when necessary using normal charger.

A Samsung i700 (a cell phone/PDA that uses a 3.7V Li-ion polymer battery):

Simplest of all. Most cellphones/pdas have an adapter to charge them from a car cigarette lighter. They have a charge controller built in, so all you have to do is connect the adapter to the 12 solar/battery source, and plug the adapter into the cellphone and leave it there.

So that is one way of doing things. If you would prefer not to have to change batteries all the time, I suppose you could make some smart circuits to charge the various different voltages automatically, but it would be very complicated and liable to catastrophic failure (don't want to be stuck out in the middle of nowhere with no lights or cellphone now do you? :-(

If you really would like to install everything so that you don't have to worry about charging at all, then the simplest thing to do is make everything run off of a 12v battery bank. That is by far the simplest.

About the battery bank, it sounds as if your energy consumption will be very small, so a could sealed lead acid/wet cell batteries should suffice.

Oh, and of course, as was mentioned, you could charge the 6v batteries by peddling, using a dynamo, but that will be more work for your legs, so why to that when you can go solar?

Cheers,

All the best,

Stephen.

[Ian Wood]

Fantastic!  I had just started thinking "You know, it would be alot simpler if I could just build a big battery pack, run everything off that, and charge it."

So I was leaning towards option 2. But the Big Idea is to have everything charged via solar, so I either need to figure out how to run everything off a big battery pack and charge it, or at least keep it down to a minimum of two packs and two panels.

If I understand you correctly--the simplest thing is to match the battery voltage to the panel voltage.  Due to weight considerations (SLAs are heavy), I was leaning towards NiMH or NiCads; I don't know how well those co-operate with solar panels.  Do you know (or does anyone passing through the conversation)?

The trouble with the cold cathodes is they use a pre-made battery back with 10 NiMH AAs in it...and while they're great for riding in the country dark around my home, I don't really need them for a long tour, and should probably leave them at home.  I should probably also replace the rear AA-powered light with a 6- or 12-volt light that's intended to run off a generator.

That means I could pare the system down to 18 total volts for lighting.

So would something like Connecticut Solar's 10 Watt Grade/Backcounty Epoxy Folding Solar Panel (output: 18V at 750 mA) be enough to charge the lighting system's batteries? Or would I need more milliamps to get a reasonable charging time?  It'd be great if I could use something that, because they come with a cigarette plug receptacle...which would solve the cellphone problem.

I'm just not sure what the relationship between panel output for charging batteries is to the actual battery output required to run the whole thing...

[srnoth]

Exactly.

About the NiMHs. I am pretty sure that they can be charged from solar panels, but I believe you need a charge controller designed to charge them. Anybody please correct me if i'm wrong. Remember that you must have a charge controller, or you might over charge your batteries and wreck them. SLA's and all that heavey compared. You can get a coulple small ones like the ones they use in UPSs, which don't weigh all that much.

Now to do some maths:

18watts x 1 hour = 18watt hours per day.

(assuming using lights for about an hour each day)

0.75amps x 8hours daylight x 12 v = 72 watt hours a day.

So in theory one panel should do for the lighting.

Don't forget batteries are only about 50% efficient, so that is only 36 watt hours per day. Also the sun may not shine everyday.

So you might get away with one panel, but since they're so small, why not get about 4 to be safe. On a road trip, if one breaks, and you don't have a spair, that's it. Also, don't forget you have to run your cellphone and possibly charge other batteries too. SO better be safe than sorry.

For your battery bank size, Lets say you end up using 50 watt hours a day, then your bank needs to be 50/12 = 4.2 amp hours. To be safe, in order to have enough juice for those cloudy days, your bank should be atleast 10amp hours. Two small 12v SLAs should take care of that.

I forgot to mention, I assume that you will be mounting the panels in some sort of clear, weather/water proof container/bag on the top of the trailer thing you will be towing, this way it will charge the batteries once there is sun. And if your but the batteries in some corner of the trailer, the wieght of two small SLA's shouldn't matter.

Anyway,

It's late and I'm sleepy. I hope all my math is correct.

Cheers,

Stephen.

[RedLance]

To clarify a few things here:

Usually, it's best to have a battery voltage that is equal to or higher then your highest needed voltage.  Which in your case, is probably 12 volts for your cell phone charger.  The 18 volt solar panel that you mentioned, will work fine voltage wise, as the batteries will pull it down to 12 volts.  You might still want a charge controller, but you might not need one, I'll let someone else chime in on that.  

So, the headlights need 6 volts each, the cell phone/PDA needs 12 volts, through its car charger, and the tail light and keyboard need 3 volts.

I would probably eliminate all the "little" batteries, make a 6 volt regulator for the headlights and a 3 volt regulator for the tail light and keyboard, and run the whole works off the large battery pack.  The cell phone, keeps it's own internal battery, but the headlights, tail light and keyboard all share the big pack.  Can't use them away from the bike, but the keyboard is the only item that you might want to use, and for that you could keep a set of Alkaline AAA's if needed.

Even the cold cathode lights use 12 volts.  NiMH batteries are 1.2 volts nominal, so 10 of them is 12 volts, not 15.

An easy to make voltage regulator is here: http://ourworld.compuserve.com/homepages/Bill_Bowden/page12.htm

Here's a 39Ah battery: http://www.surpluscenter.com/item.asp?UID=2004120221573644&item=11-2538&catname=electric

It weights 40lbs, but you'd be able to go for a few days with no sun.

Or these: http://www.surpluscenter.com/item.asp?UID=2004120221573644&item=29-M-046&catname=electric

Are only 4lbs each, you could hook 3 or 4 in parrallel, and have up to 20Ah for only 16Lbs

RedLance

[Ian Wood]

Ahhh.

Let me see if I have this right (theoretically).

If I have a 12 volt front light set, a 12 volt side light set, and a six volt rear light, I can run the whole show at the same time from a 12 volt battery pack (with appropriate wiring and a regulator)?

So (I'm guessing), this means that what will determine how long I can run the whole show is the number of amp hours in my battery pack...and the number of watts drawn by each element in the system? (Argh...forget about it being late; even if I were wide awake I probably wouldn't have the math for that...the sad part is, I used to know this stuff.)

Finally, what about charge time?  One of my current light systems uses a 6V 5.5AH SLA and charges with a wall wart, which puts out 6VDC @ 500mA.  Takes 10-15 hours, steady, to charge the cell. How does that work out with a solar panel putting out 18VDC @ 750mA with a 12-volt pack?  

Ideally, I'd like to get the pack charged in two eight-hour days of riding, at most...and because I (hopefully) wouldn't be using the lights for more than an hour or so, they'd always be fully charged or nearly-so when I needed them.

Hmmm...I think I might need something in place to prevent overcharging, no?

And while we're on the subject of batteries--anybody know anything about Hawker Cyclon batteries in this kind of application?

Many thanks for all the fine input, folks; I truly appreciate it.

[RedLance]

"If I have a 12 volt front light set, a 12 volt side light set, and a six volt rear light, I can run the whole show at the same time from a 12 volt battery pack (with appropriate wiring and a regulator)?"

Correct

"So (I'm guessing), this means that what will determine how long I can run the whole show is the number of amp hours in my battery pack...and the number of watts drawn by each element in the system?"

Also correct

I haven't quite gotten a grasp of the whole charge time verses amp hour capacity yet...

I THINK, if you had 1000mAh out of your solar panels, (Iknow you only said 750mAh) that it would take 1 hour to put 1000mAh or 1Ah into your battery.  I think that's how it works, so with 750mAh of solar, and say, 10 hours of sun, you have put 7.5Ah into your battery pack.

Assuming of course, that you can get the full 750mAh for the full 10 hours.

Then you need to know the wattage or amp draw of all your lights and other equipment, and if that figure is under 7.5 Ah, then you should be ok.

RedLance

[kell]

One comment about the cell phone.  You can do it without having 12 volts to run your cigarette-plug-in charger.  A cell phone charger puts out 5 volts or a bit more, typically.  So if you only have 8 volts for example, you can still make your own charger out of a linear regulator that puts out the correct voltage.  Look at the label on your wall wart charger to see what voltage you need.  Like mine says 5.3 volts at 500 mA.  I made a car charger out of a three-pin 5 volt regulator, the kind every Radio Shack has on the shelf (I figured 5 volts would be close enough, and it worked).  I had to screw the regulator chip onto a heatsink because I was running off 12 volts (actually 14 with the car running), and burning up that extra voltage, the heat has to go somewhere.  A 5 watt 7 ohm power resistor on the input of the voltage regulator helped too.

If you run a six volt system you might be able to charge the cell phone directly, perhaps with a power resistor in series.  If your phone takes half an amp to charge (500 mA), 2 ohm resistor will drop a volt.

I'm just trying to think of ideas that will save you from having to use a complicated system with two or three different voltages.

[troy]

Dear Ian,

You'll never get ten hours of good output from your solar panel.  Even with a fixed intallation that is optimized for aiming at the sun, you'll generally get 4-6 hours of good output.  In a mobile situation, aiming at the sun will be a hit or miss kind of thing, so don't count on full output for the 4-6 hour peak sun.  

Despite that, your plan still has excellent merit.  Just buy a bigger panel, like a "30 watt", which would hopefully produce about 20 watts for say 4 hours, to make:

watts x hours = watthours

20watts x 4 hours = 80 watthours.  

volts x amps = watts, so you can calculate the watts used by each device.  Then multiply watts x time used for each device to calculate watthours needed.  Tack on 33% more for inefficiency and you should be pretty close to what you need.

Good luck and have fun!

troy

[wiredwrong]

Jacket Charged by the Sun

[Ian Wood]

Good point. And the math I need.

This is why I adore the Internet. Thanks!

[Ian Wood]

I ride a recumbent. ;-)

[Ungrounded Lightning Rod]

Have you looked at the stuff Steve Roberts did for his bike oddesy?  (There's a book out.)

(I believe he invented or comissioned the first LED blinky bike taillight in order to be safe at night on a limited power budget.)

If I recall correctly his bike didn't START out with a trailer.  But over the 15 years on the road he kept adding stuff and eventually added the trailer.  (Came up with a cheap, light, and strong construction method:  Epoxy over cardboard.)

[Peppyy]

Hi Ian.

I too was going to suggest LEDs for safety lighting. Lightweight, efficient and easy to work with. For that matter the LED flashlights they have now might be just the ticket for headlights too. Voltage regulators, (three pin type) as mentioned above and resistors are all you would need to convert them to your 12v battery. I have run some of the superbright LEDs on 2 AA dollar store batterys for up to 10 days continuosly before they start dimming.

I would think along the lines of trimming down the weight and increasing the efficiency. I still wouldn't skimp on the reserve power if I only had solar to charge with.

Sounds like a fun project, Best of luck to you.

[ghurd]

My take on it is a little different, so here's my 2 cents.

I seem to believe it will do quite nice with conciderably less battery and panel than most people are suggesting.

A 20 watt panel and a 7.2ah battery (5.5 lbs) should do the trick.

For a little more reserve, maybe a 9ah battery (7 lbs, but much more $$$)

You'll need a controller. Maybe a tiny little Morningstar SG-4?

Try to get a headlight light head that uses a seperate battery pack, but just buy the extra heads. Replace the 6v bulbs with 12 volt bulbs of half the current, same watts, same brightness. Or a little less than half the current (don't go over half the 6v current with the 12v bulbs or the lenses etc can melt)

The tail light could be a 12v LED in a suitable housing.

Same for the running lights, or LED marker lights for semi trucks (try the truck stops for a selection).

A 12v 'car charger' for the phone/PDA. Most of them are 1 hour chargers.

Carry a few spare AAAs for the keyboard, they don't use much power.  For the actual hours it will be used it will probably be cheaper and lighter than rechargables and chargers. AAAs are easy to find along the way.

Panels put out some even in the crappiest weather.

Charging the phone/PDA between 11:30 and 12:30 will increase the efficiency some.

Red or Amber LEDs will save you a lot of power, and the ones for semi trucks are mass produced and quite cheap.

The 7.2ah battery will give 84 watt hours per day.

a 20w panel will full charge it most days, most places. Unless you are riding in the winter.

A 32w panel (uni-solar US-32) is cheap, light (3 lbs?) and common. They can take some flexing too. Around a foot X 3' (?). Peak current 1.96 amps

Possibly cheaper than most 20w panels. I don't care for this series of panel, but it should be very nice for this application.

A pair of the 7ah batteries may be cheaper than a single 9ah. That would give 14ah, or 170 watt hours per charge. The 32w panel would charge them in a day and a half. A 20w panel, a little more than 2 days.

Call me lazy, but I wouldn't want to drag all the extra stuff around on pedal power.

G-

[Ian Wood]

Trouble with LEDs is they're good for being seen, but not so good for seeing.  My bike tops out around 40 mph or so downhill (less with the trailer), and it's easy to "get ahead" of my headlights, especially out in the country dark where there aren't any streetlamps. LEDs are fine for rear and side lighting, though.  I'm planning to adapt a NiteRider LED tail light, which uses 1 watt and is (according to the manufacturer and user reviews) insanely bright.

Lupine used to make a 26-LED array for biking--sort of like a Lexus headlight for your bike. But it cost $675, so that's right out.

Halogen bulb-based lights meet at the intersection of cost and long-throw lighting, especially if I can get just the lights without the manufacturer's batteries.

[Ian Wood]

Now, I"m a novice here.  I figured I would need something to prevent overcharging, and maybe smooth out the ups and downs of panel output.  Is that what the controller does?  If so, the Morningstar would be great, because it's so small...

[TLSea]

A small wind generator added to your solar setup would cut down on the weigh of your battery bank.

A bike doing 15 to 40 mph is plenty of energy to turn a muffin fan at charging rate.  It would work at night and add to redundancy.

[ghurd]

Yes. The controller takes care of everything.

[troy]

But a wind gennie that operates while riding adds drag and increases peddling effort, which he wants to avoid.

best regards,

troy

[hvirtane]

You might try making

a sail wing wind rotor,

which you can carry

with you as parts.

A draft picture

in my diary.

You might also

charge your battery

with the bicycle

itself. Most of the

electric bicycle engines

are charging batteries,

when going downhill.

You might install

such set. While

camping you can lift

the bike backwheel

on a stand and cycle the

the batteries full...

- Hannu

[hiker]

just buy one of those weedeater size gas engine chargers---and forget about all the other bulky stuff--and charge your batts in a fraction of time it would take solar!

plus there good on fuel--so you only need a 1/2 gallon or so..

[srnoth]

Too nosy. Stress on the noisy. And personally, I can't stand the whine that those things make at full power. Sounds more like an extremely loud mosquito. And I think he really wanted to use this as an opportunity to start out in solar.

Cheers,

Stephen.

[Ian Wood]

Yeah, the ideas was to be totally independent of as much fixed infrastructure as possible--including electrical sockets and gas pumps.

Of course, I will be carrying fuel for my stove...but that's different. ;-)

All of the comments I've gotten here have been very helpful--I'll have a project diary up soon, so those who are interested can see how it all turns out...

[skravlinge]

With a lot of stuff to make electric on the bike, you may think of it not is more heavy to pedal around whith it than connect a generator to the wheel?

A minor battery backup may be used  so you don't have to use the generator then you travel uphill. Can you easy swith, you load downhill most of the time.

[richhagen]

If it were me, I'd want two ways to charge the battery.  On cloudy or rainy days, the solar panel will put out almost no power.  Even my thin film panels, which do better than the mono and multicrystaline panels in low light, put out almost no charging current in crappy weather.  I would opt for a plastic type thin film panel, like the unisolar line, and a small morning star type potted controller as both are lightweight and somewhat harder to destoy. I would oversize the panel and battery slightly for those crappy days.  Then I would want some sort of bike generator that I could adjust so that on sunny days it could be disconnected or removed to limit drag.  If the voltages fell in the right range for the generator, the rectified output could be connected to the same charge controller.  I'd probably put a couple or more zener diodes, each connected with a 1 ohm resistor or so (to balance the load between them) across the rectified output to limit the voltage to what the charge controller can handle.  I might also add a relatively small capacitor to make the output more of a level dc that the charge controller is used to seeing.  Only thing is that I've yet to see a bike generator for trickle charging 12 volt batteries. I suppose you could rewind the stator of a 6 volt bike generator, but I'm not sure how many milliamps of charging you would get. Lastly, I would definitly choose lights, chargers, ect that could be all powered or charged from the 12 volt pack.  I would obtain switching type chargers (for cell phone, keyboard, ect) over shunt type if they are available as they are far more efficient.  Shunt regulators waste the extra power as heat, switching type function as a dc-dc converter and are more efficient.  if you are converting 12 volts to 5 volts for your phone, with a shunt regulator you are wasting 7/12 of the power, whereas with a dc-dc converter, you could easily exceed 80% efficiency.  Incidentally, dc-dc converters of reasonably high efficiency and a variety of voltages can usually be found on E-bay for not a lot of money. Many have slightly adjustable output voltages.  I would also make sure that it is easy to turn off electric items independently and conveniently that you do not need, such as the running lights.  That way, if power was getting scarce, you could minimize the amount you are using.  You should have a fun project.  Keep having fun, Rich Hagen

[ghurd]

Some of those cheap surplus 'car adaptors' are switchers. Often the catalog will tell.

I bought a ton of them 5/$1 to get the output plug and wire assembly.  Tore the big plug apart to find switching regulators!  Not bad for 20 cents.

G-

[daltxguy]

Hi Ian,

I don't really want to discourage you but as someone who has crossed the US on a bicycle, I can offer this advice. It is really not that hard to find power outlets every few days. We charged things up at campsites (borrowed the power sites for a while), gas stations, school libraries, city parks and the odd time when we stayed in the basement of a church, or a fire station etc. An outlet was never too far away. I carried a PDA and a cell phone the whole way and never ran out of juice.

The other thing, is that you might find that you will not use your lights much, especially if riding in the summer months. The days are plenty long enough to get to your next camp site before it gets dark. I carried only a battery powered headlight and taillight on the trip and can't recall an occasion where I actually had to use it. I mostly used it to search for things in the tent at night.

I think the idea is cool but you may be sending the whole thing back home after a few weeks when you realize that the extra weight being carried around is not worth the effort and wish you had an extra spare tube or tires instead.

best of luck with your project and your trip.

Steve

[commanda]

Headlights.

There is at least one project on the web. Use 12 volt 50 watt downlights and a pwm controller. Buttons for up & down pwm (more & less light). Almost certainly available commercially. There was much discussion about this quite a few years ago now on the Sydney Mountain Bikers mailling list (yes, I used to ride mountain bikes).

Amanda