DIY bike lights / AA battery current

On 2006-04-22, Travis (aka Bruce) was almost, but not quite, entirely unlike tea:

1.7amps shouldn't be a problem. AAs seem to be rated about 2200mAH these days, so at 1A, with the internal resistance, I would expect it would last for almost precisely an hour.

Be noted though, that the initial voltage (maybe for 5/10 minutes?) will be somewhere around 14 or 15 volts. Hmmm, a bit high?

NiMH and NiCd are always going to be much more expensive than SLA, depends whether you want the weight saving or not. Oh, and the longevity, as long as you use a good charger.

--
TimC
Animals who are not penguins can only wish they were.

"Travis"

** That would be very bright and a point sized source.

Maybe dazzling to a motorist ?

** Good quality AA NiMH cells have a 1.7 hour run time at 1 amp.

Should be able to do 1.7 amps for 1 hour.

2.1 amp/hour capacity and more are available. ** A *long time* ago I had the same idea - used a 6 volt, 10 watt "sealed beam" GE lamp powered by 5 x WW2 vintage NiFe cells. Similar light output to an average motorbike headlamp using bulb and reflector.

Good for about a 45minute ride.

...... Phil

Technically it provides the right voltage. In practice the batteries can't provide that voltage at the desired current, and you get a dull light. This can be offset by increasing voltage - 12 AAs should give a bright light. However, you'll be doing well to get an hour out of a set.

You can get AAs to run 10W stuff OK, but 20 is just a tad too much.

Sub Cs can be got for I don't do night races or offroad stuff, its just to provide a nice wall

If you're doing home made commuter lights, get a 3W Luxeon ($20) and either a prebuilt regulator or get the el cheapo one from

which only involves a bit of soldering. A collimating lens and a heatsink and you should have something that runs nicely for a couple of hours off 5 AAs (use 6V, it's possible to use 4.8 (4cells ) but it's a bugger to get the regulator working well).

has some more info, though is wildly out of date.

--
Dave Hughes | dave@hired-goons.net
Striker, listen, and you listen close: flying a plane  is no different
than riding a bicycle just a lot harder to put  baseball cards in the
spokes.

As I said in my earlier post, but want to reinforce - you'll get serious voltage sag. I forgot to mention that cheap battery holders can't handle this type of current. I tried it and was losing around 0.5V per connection. I wondered why a lamp being run from 12 AAs was barely lighting up. Best option is to get tabbed cells and solder them up, but that makes charging trickier. If you know what you're doing you can gin up better contacts in the battery holder, but it's not that simple an exercise.

NiMH is actually pretty good value in AAs these days. Ebay and the huge demand for AAs in consumer devices means you can get ~2Ah cells for around $2.50-$3 each.

--
Dave Hughes | dave@hired-goons.net
"Did you know God had a plan for you?" 
"Does it involve a high-powered rifle and a belltower?"

The last two Silicon Chip magazines

have featured a circuit to drive up to 6W of Luxeon LED's. The circuit is based around a microcontroller chip and a switchmode power supply that keeps up the current to the LEDS as the batteries run down. It also controls the recharging so a laptop power supply or any approx 12v 700ma supply will be a suitable charger. They feature a 5W LED example on a bike and it looks really bright. They made the claim that it is bright enough to safely travel at 75kph, downhill of course.

It has a number of functions but the bicycle headlight version has a light sensor so that it flashes at 4 hertz when it isn't dark enough to need a full on headlight.

The preprogrammed microcontroller chip is available from Silicon Chip for $25 but you'd need to source the other parts like Circuit board.

Even if you d>

the 20w qh globe will exceed any led brightness and be a lot cheaper

12v 7AH SLH battery is cheaper and has less volt drop at heavy loads than the equiv 30x AA 2200 mAH cells and no heavier

you don't need a microcontroller or any other useless crap, just a battery wires and a switch

: >

: >> Another option would be a bank of 10 rechargeable NiMH AA batteries in : >> series. This would provide the right voltage, but I'm wondering if : >> they could provide sufficient current (I'm aware of issues of internal : >> resistance etc) and would they be able to keep up the current for at : >> least an hour (my commute time). : >

: > Technically it provides the right voltage. In practice the batteries can't : > provide that voltage at the desired current, and you get a dull light. : > This can be offset by increasing voltage - 12 AAs should give a bright : > light. However, you'll be doing well to get an hour out of a set. : >

: > You can get AAs to run 10W stuff OK, but 20 is just a tad too much. : >

: >> If not, what are some suggested alternative batteries and chargers that : >> would fit the bill? : >

: > Sub Cs can be got for remember their name. That's for 3.5Ah, which will handle the current OK, : > and give you a solid 2 hours of light. To go more than that you'll need a : > bigarse SLA or a bigarse budget. : >

: >> I don't do night races or offroad stuff, its just to provide a nice wall : >> of light for my winter night commutes. : >

: > If you're doing home made commuter lights, get a 3W Luxeon ($20) and : > either a prebuilt regulator or get the el cheapo one from : >

which only involves a bit of soldering. A : > collimating lens and a heatsink and you should have something that runs : > nicely for a couple of hours off 5 AAs (use 6V, it's possible to use

4.8 : > (4cells ) but it's a bugger to get the regulator working well). : >

: >

has some more info, though is wildly out : > of date. : >

: > -- : > Dave Hughes | snipped-for-privacy@hired-goons.net : > Striker, listen, and you listen close: flying a plane is no different : > than riding a bicycle just a lot harder to put baseball cards in the : > spokes. : >

: :

A few years ago I did pretty much the same thing - mounted a standard 20W halogen dichroic lamp on my mountain bike, except in my case I used a 12v gel cell hung from the top tube. The battery was a common or garden 7Ah unit as used in alarm panels etc. and cost about $17. It would have weighed quite a bit more than the NiMH pack you are talking about, but my bike wasn't any kind of high-performance thing so it really didn't matter.

It was very simple to set up, worked very well only needing charging about once a week.

Aaargh! Poo, I saw that on the front and didn't actually grab the issue. Might have to buy the kit from Jaycar in a month's time. Thanks for the heads up.

During the day maybe. I reckon @ 75km/h you'd be outrunning an HID. Hmm, The rec.bikes FAQ seems to indicate 5ms^-2 is a reasonable maximum deceleration for a bike, and it'd be in the right ballpark. 75km/h is near as spit to 20ms^-1, so it'll take around 4 seconds to stop.

Basic physics says the stopping distance is (4*20)-(0.5*5*4^2) =

80-40=40m. So you'd need a light that's got good light out to 40m - add another 0.5s for reaction time, and that's 50m. Searching a few articles on dansdata indicates you'd be doing well to see 25m by a 5W Luxeon, which matches pretty closely to what I've observed using them.

--
Dave Hughes | dave@hired-goons.net
Strange things are afoot at the Circle-K.

Generally you tend to aim the light down onto the road. Its main purpose is to let you see where you are going {:-).

OTOH, I do run a 50 watt when I am on brightly lit streets with lots of neon signs etc.

** Only the biggest fools argue from the general to the particular - like f****it cyclists.

A given cyclists has to dazzle just ONE oncoming motorist to initiate a life changing experience.

Anyone for paraplegia ????

** Intended purpose and actual effect are independent variables - f****it. ** Silly things cyclers do when out crawling the red light districts .....

Explains why no one gives the *slightest shit* about a mangled cycler bleeding to death on the roadside.

...... Phil

Travis wrote:

Travis it's easy to make up a good soldered battery pack. I have two NiMh packs that I've made myself. One is about 2.5 amp hour and the other is 4 amp hour, both rated at 12 volts using 10 cells in each. I made them from Sony batterys but most brands are quite good now. You have to get the ones with the tabs on the top, but be careful because some have stainless steel tabs which you need to spot weld and some have tinned tabs. The tinned tabs are the ones you want. Lay 5 cells side by side oriented so that the positive of one end is next to the negative of the other. To do the connections you have to bend one of the tabs backwards against its original bend, and you may have to trim off some of the tab but leave enough so they completely overlap for the width of the end of the battery. Now you get some fine sand paper or steel wool and give the tinned surfaces a bit of a rub or else the solder won't stick to it properly, they seem to leave some sort of coating on them at the factory. Next apply some solder to the surfaces but don't solder them together yet. Use good solder which has about 70% led and 30%tin which has the lowest melting temperature. The secret to good soldering is to always keep things clean. Clean the surfaces before you solder them, make sure the soldering iron tip is clean and free of crud, wipe it on a cloth and apply fresh solder to it before making each join. The active component of the flux evaporates out of the solder very quickly leaving accumulated crud which is why it's important to always wipe the tip and apply fresh solder. (The flux is inside the solder.) So now that you've tinned all the tabs, use electricians insulation tape to bind the 5 cells together so they don't move. Carefully solder all the tabs together. Because you've presoldered them you should only need to push them together with the soldering iron and the solder already on them should be adequate to make the joint. Wrap a heap more tape around it to make it firmer. Make a second pack of 5 the same way. Now solder some wire to the the main positive and negative of each pack, plus a short bit that joins the two packs in series. Allow longer length than you think you'll need. I use special flexible wire from Farnell or Radio Spares which is like the wire used in multimeter leads, it has a lot of fine strands and flexes without breaking. Don't use single strand wire, it won't last long at all. Secondly, use red for positive and black for negative, that way there is no mistakes. Use the wire to join the two packs instead of the tabs so as to allow for some flexibility of the pack if it gets jolted around on the bike. Now that you've got it all together wrap a heap more tape around the whole pack so every part of it has at least three layers of tape over it. By now it should be a nice solid pack. Now you need to put some connectors on it. The ones I use are from Dick Smiths, they are a whitish plastic and you can buy the pins separate from the plug. I use the two pin plug, it's designed so that it will only fit one way so you can't reverse the connections and blow things up, as an extra precaution I have one male pin and one female pin in each plug so there's no way I can get it wrong. My lights, chargers and battery packs are all set up with this arrangement. I use LED lights which are fed via a Luxeon current regulator which allows me to use between 8 and 14 volts and I have two NiMh batterys and two Lithium Ion batterys so I can swap between any of these batterys on my lights by simply unplugging one and plugging in the other. I wrap the battery in bubble wrap and push it into a cut off water bottle which goes into the cage on my down tube. An important thing is to remove the battery from the bubble wrap when you charge it as the bubble wrap is a very good heat insulator and you'll cook your battery if it goes into an overcharge state. Lithium Ion batterys are especially susceptible to this. (I know from experience!) I've been using my batteries for at least two years now without problems, my two old Gel Cell batteries are unused in the shed. (Lead acid batteries should always be stored in a charged condition, a flat lead acid battery dies very quickly.)

A good charger is the MW1768 from Master Instruments.

It needs a 12 volt supply which might be a problem but it has a meter in it and will charge 12 to 14 volt packs which most chargers won't do. Master Instruments also have some other good chargers that are worth looking at.

Good riding

Friday

My mountain bike and road bike both have twin 5 watt luxeons. The arrangment is excellent for the road, for mountain bike riding I sometimes wish I had a bit more when doing screamingly fast technical downhills, but for the other 95% of the time it's great and when I'm doing easy stuff or slow uphills I turn one light off. They're super reliable and my design is very light, I never remove them from the bike.

Friday

the old ones are best, putting a 20W lamp in a small plastic case is asking for problems.

1.7A seems like a heavy drain on them. they'll not meet thair 20-hour capacity at that rate.

try getting a datasheet from the makers of the cells you're looking at.

power tools seem to use sub-C size so that size may be cheeper and/or have better high current performance..

I'd look at lead-acid, as it's much cheaper for the same charge capacity but Christchurch is flat and I'd not be be lugging the thing up upteen hills going there and back.

--

Bye.
   Jasen

Hi Travis, check out the following link for a 12v 7.2Ah sealed lead acid battery and charger for AU$35, I haven't seen both any cheaper. Go down the page to you see the package of battery and charger.

Also, Jaycar is selling a 12v 7.2Ah sealed lead acid battery for under $20 at the moment.

"Jasen Betts"

** NiMH cells give very close to full rated capacity over a 1 hour discharge - only if discharged in less than half an hour will there be significant loss of capacity. See:

Ni-Cd cells are even better in this regard giving full capacity even over a

4 minute discharge.

SLA batteries are not so good, their capacity drops alarmingly when discharged in an hour or less.

** Cos that slack kiwi prick Jasen is too lazy too look up data and see how wrong the info he spews about is.

....... Phil

[effluent deleted]

Wow, aus.electronics has some people with ... issues ... heh!

Some do, some don't. It depends on the cell. I find the lower capacity ones seem to deal better with high loads than the higher capacity ones on occasion. Nonetheless, I've personally observed regular sub 40 minute run times on a 20W bulb with 11 AAs, and the light output was always a bit iffy. My 10W halogen on the same battery pack would push 2 hours.

For 20W I'd say go a reasonable bit above 2Ah capacity

--
Dave Hughes | dave@hired-goons.net
"Soon we will be able to harness the rotational energy from Orwell's
grave to solve all world energy problems" - GigsVT

** The majority of such cells currently on sale do.

Since the OP will be buying new cells, earlier generation ones are irrelevant.

....... Phil