When 12 volts is not 9.6 volts - Page 2 - Cycling Mob: Road Cycling, Mountain Biking and More

12-31-2006, 05:42 PM

On Sat, 30 Dec 2006 15:36:27 -0500, dgk wrote:

> I like to use rechargable batteries in my lights, and for the most part
> using a rechargable AA in place of a regular battery works fine. But
> with cold cathode bulbs on my bike, the little transformer thing needs
> 12 volts. So I replaced the normal 8 AAs with 8 rechargables. And it
> sort of works. But one bulb starts dimming after a half hour or so.
> Checking with normal batteries, this doesn't happen.
>
> I looked a bit closer at my rechargables, which are, it turns out, 1.2
> volts, not 1.5 like regular batteries. All rechargables that I looked at
> are 1.2. So, 8 * 1.2 = 9.6, not 12. Other stuff, like CD players, work
> fine on the rechargeables, but the cold cathodes have a bit of a
> problem. Obviously, 10 batteries instead of 8 should do the trick, but I
> don't have, and can't find, a case that holds 10 batteries.
>
> So, why do some things work fine with 1.2, and others not? And why
> aren't rechargeables 1.5?

Alkaline batteries can't deliver their rated voltage (1.5V) when connected
to a high current device like a bike light. With a bike light,
rechargeables (nicad or NiMH) may actually deliver more voltage, though
nominally rated for less (1.2V).

The "1.5V" of alkaline batteries drops quickly and steadily with use
anyway. Note how bike lights powered by alkalines start out very bright,
but dim steadily as the batteries wear down. With rechargeables, they
stay relatively bright for quite awhile before dimming significantly.

Matt O.

01-01-2007, 12:35 AM

Matt O'Toole wrote:
> On Sat, 30 Dec 2006 15:36:27 -0500, dgk wrote:
>
>> I like to use rechargable batteries in my lights, and for the most part
>> using a rechargable AA in place of a regular battery works fine. But
>> with cold cathode bulbs on my bike, the little transformer thing needs
>> 12 volts. So I replaced the normal 8 AAs with 8 rechargables. And it
>> sort of works. But one bulb starts dimming after a half hour or so.
>> Checking with normal batteries, this doesn't happen.
>>
>> I looked a bit closer at my rechargables, which are, it turns out, 1.2
>> volts, not 1.5 like regular batteries. All rechargables that I looked at
>> are 1.2. So, 8 * 1.2 = 9.6, not 12. Other stuff, like CD players, work
>> fine on the rechargeables, but the cold cathodes have a bit of a
>> problem. Obviously, 10 batteries instead of 8 should do the trick, but I
>> don't have, and can't find, a case that holds 10 batteries.
>>
>> So, why do some things work fine with 1.2, and others not? And why
>> aren't rechargeables 1.5?
>
> Alkaline batteries can't deliver their rated voltage (1.5V) when connected
> to a high current device like a bike light. With a bike light,
> rechargeables (nicad or NiMH) may actually deliver more voltage, though
> nominally rated for less (1.2V).
>
> The "1.5V" of alkaline batteries drops quickly and steadily with use
> anyway. Note how bike lights powered by alkalines start out very bright,
> but dim steadily as the batteries wear down. With rechargeables, they
> stay relatively bright for quite awhile before dimming significantly.
>
> Matt O.

I have to agree. My CatEye light is rated for 4 alkalines (6V) and I use
4 NiMH rechargeables at 1.2V for a total of 4.8V. The alkalines do start
out a little brighter but soon run dimmer than the rechargeable. I think
this is because the alkalines sink more under load than the NiMH. So an
alkaline can go from 1.5V no load to <1.2V full load, while a NiMH
pretty much stays at 1.2V, same as a NiCd, at least until you blow one
up from too much current. Just what I heard, except for the observed
results on my CatEye. The LEDs run at 3.4V (driven by 6V) down to 3.2V
(driven by some fried (1.0V) alkalines. The light is not linear with the
voltage since the LEDs are only current limited by some big resistors.
No fancy electronics to start/stop.
Bill Baka

01-01-2007, 05:01 PM

On Sun, 31 Dec 2006 19:30:14 -0000, Richard B
<[Only registered and activated users can see links. ]> wrote:

>[Only registered and activated users can see links. ] wrote in news:1167582164.367803.326110
>@n51g2000cwc.googlegroups.com:
>
>>
>> dgk wrote:
>>> I like to use rechargable batteries in my lights, and for the most
>>> part using a rechargable AA in place of a regular battery works fine.
>>> But with cold cathode bulbs on my bike, the little transformer thing
>>> needs 12 volts....
>
>SNIP
>>
>> But I'm curious about your "cold cathode lights." What are they,
>> exactly? Sounds like a flourescent or neon-type bulb?
>>
>> - Frank Krygowski
>>
>
>Perhaps he is talking about this...
>[Only registered and activated users can see links. ]
>
> Richard B.

Yes, that is it exactly. In fact, I bought them from that outfit. But
I think they are out of business and instead they come from Vibelights
now.

They are a bit (bit?) ostentatious. On the other hand, they really
make it hard to get hit accidently at night. Deliberately, well,
that's another story.

01-01-2007, 05:09 PM

On 30 Dec 2006 20:40:46 -0800, "peter" <[Only registered and activated users can see links. ]> wrote:

>dgk wrote:
>> I looked a bit closer at my rechargables, which are, it turns out, 1.2
>> volts, not 1.5 like regular batteries. All rechargables that I looked
>> at are 1.2. So, 8 * 1.2 = 9.6, not 12. Other stuff, like CD players,
>> work fine on the rechargeables, but the cold cathodes have a bit of a
>> problem. Obviously, 10 batteries instead of 8 should do the trick, but
>> I don't have, and can't find, a case that holds 10 batteries.
>
>You already have a case that holds 8, so buy a holder for two
>additional cells and connect the two battery holders in series so they
>deliver a full 12 VDC. However, you should note that rechargeable
>cells can be damaged if you discharge them to the point where they're
>getting reverse-charged. With 10 cells in series you might have a
>situation where one of the cells may have a little less capacity than
>the others and therefore it goes dead first. Even if the voltage of
>that cells drops to 0, you could still be getting 9 x 1.2 = 10.8 V from
>the other cells which may be enough to keep your device operating. But
>driving that current through the discharged cell will probably damage
>it.
>
>So when using that many cells in series you need to be careful that all
>the cells are well-balanced so they discharge at close to the same
>time. Keep cells purchased together as a set and always fully charge
>them at the same time. Also try to avoid running them to the point
>where they're close to fully discharged.
>>

I did exactly that. I went to RadioShack and got a 2 battery holder
and a few of those 9-volt battery connector things, which is what the
current holder uses. Then I just wired them together and velcored them
physically together. The lights look great.

I bought twelve rechargable AA batteries at the start of the cold(er)
weather and have been using eight for the lights and two for a CD
player. So I took the two from the player and am using them with the
eight, so all ten are around the same wear. The two formerly unused
ones are in the CD player.

They never get drained that much during the ride home, and now the
days are supposedly getting longer again so all should be fine. Once
in a while I discharge them all the way just to keep them honest. The
charger does that.

Thanks for the advice.

01-01-2007, 05:18 PM

On Sun, 31 Dec 2006 19:19:23 -0000, Richard B
<[Only registered and activated users can see links. ]> wrote:

>Mike Ellis <[Only registered and activated users can see links. ].uk> wrote in
>news:4596dcc2$0$2754$[Only registered and activated users can see links. ]:
>
>> dgk wrote:
>>> I like to use rechargable batteries in my lights, and for the most
>>> part using a rechargable AA in place of a regular battery works fine.
>>> But with cold cathode bulbs on my bike, the little transformer thing
>>> needs 12 volts. So I replaced the normal 8 AAs with 8 rechargables.
>>> And it sort of works. But one bulb starts dimming after a half hour
>>> or so. Checking with normal batteries, this doesn't happen.
>>>
>>> I looked a bit closer at my rechargables, which are, it turns out,
>>> 1.2 volts, not 1.5 like regular batteries. All rechargables that I
>>> looked at are 1.2. So, 8 * 1.2 = 9.6, not 12. Other stuff, like CD
>>> players, work fine on the rechargeables, but the cold cathodes have a
>>> bit of a problem. Obviously, 10 batteries instead of 8 should do the
>>> trick, but I don't have, and can't find, a case that holds 10
>>> batteries.
>>>
>>> So, why do some things work fine with 1.2, and others not? And why
>>> aren't rechargeables 1.5?
>> Some things work fine whilst others don't because the application
>> isn't so voltage critical. It could also be that the internal
>> circuitry reduces the input voltage to a lower value so that lower
>> voltage cells will work. The reason that rechargeables are only 1.2
>> volts is because the chemical reaction only produces 1.2V whereas the
>> chemical reaction of regular batteries produces 1.5V. I'm afraid its
>> all down to the chemistry.
>>
>> Mike
>>
>
>Why not susbtitute a small sealed lead acid battery, AKA a Gel Cell...
>
>Look at this site:
>[Only registered and activated users can see links. ]
>
>Or if you really want to get ceative see:
>[Only registered and activated users can see links. ]
>
> Richard B.

Thanks. I do have a spare SLA battery from an old Nite Hawk bike light
that I don't use much anymore and I considered using that. I thought
it was 12 volt but I just looked and apparently it's only 6 volts.
Anyway, it weighs a lot. It's the type that fits the water bottle
cage.Nah, I think I'll stick to the NiMHs.

01-03-2007, 08:28 PM

On Mon, 01 Jan 2007 20:01:24 -0500, dgk <[Only registered and activated users can see links. ]>
may have said:

>On Sun, 31 Dec 2006 19:30:14 -0000, Richard B
><[Only registered and activated users can see links. ]> wrote:
>
>>Perhaps he is talking about this...
>>[Only registered and activated users can see links. ]
>>
>> Richard B.
>
>Yes, that is it exactly. In fact, I bought them from that outfit. But
>I think they are out of business and instead they come from Vibelights
>now.
>
>They are a bit (bit?) ostentatious. On the other hand, they really
>make it hard to get hit accidently at night. Deliberately, well,
>that's another story.

Never underestimate the power of human stupidity.

--
My email address is antispammed; pull WEEDS if replying via e-mail.
Typoes are not a bug, they're a feature.
Words processed in a facility that contains nuts.

01-04-2007, 06:58 AM

On Wed, 03 Jan 2007 22:28:19 -0600, Werehatrack
<[Only registered and activated users can see links. ]> wrote:

>On Mon, 01 Jan 2007 20:01:24 -0500, dgk <[Only registered and activated users can see links. ]>
>may have said:
>
>>On Sun, 31 Dec 2006 19:30:14 -0000, Richard B
>><[Only registered and activated users can see links. ]> wrote:
>>
>>>Perhaps he is talking about this...
>>>[Only registered and activated users can see links. ]
>>>
>>> Richard B.
>>
>>Yes, that is it exactly. In fact, I bought them from that outfit. But
>>I think they are out of business and instead they come from Vibelights
>>now.
>>
>>They are a bit (bit?) ostentatious. On the other hand, they really
>>make it hard to get hit accidently at night. Deliberately, well,
>>that's another story.
>
>Never underestimate the power of human stupidity.

I was just thinking that some folks might be offended by the lights
and aim for me - kidding I think. I have had people stop me to ask
where they can get them; mostly kids who think that they're way cool.
I just think that they're one more element in avoiding getting
clobbered at night.