When 12 volts is not 9.6 volts

12-30-2006, 11:36 AM

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?

12-30-2006, 12:40 PM

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

12-30-2006, 07:40 PM

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.
>
> So, why do some things work fine with 1.2, and others not? And why
> aren't rechargeables 1.5?

As already mentioned this boils down to the basic chemistry involved in
each type of cell. The lead-sulfuric acid cells used in car batteries
produce a bit over 2 V/cell and therefore you get 12 V from 6 cells in
series. Rechargeable lithium ion cells produce about 3.7 V/cell while
NiCd and NiMH cells are about 1.25 V/cell. The latter is close enough
for many devices designed to run on the nominal 1.5 V/cell produced by
alkaline cells.

12-30-2006, 10:09 PM

On Sat, 30 Dec 2006 15:36:27 -0500, dgk <[Only registered and activated users can see links. ]>
may have said:

>So, why do some things work fine with 1.2, and others not?

An alkaline that delivers 1.5V unloaded may only be supplying 1.3V or
so under load due to internal resistance. The internal resistance of
the typical rechargeable is lower; its output maintains close to rated
voltage farther into the discharge cycle. If the device has a fairly
high drain level, the rechargeable may actually deliver a higher
voltage than the alkaline, but a device which loads alkalines to the
point that their output drops to that of a NiCd will also drain them
in a frustratingly short period of time. As a result, manufacturers
of battery-powered items tend to choose batteries that will maintain
the desired operational characteristics for an acceptable period...and
this means that the load is low enough that the delivered voltage of a
rechargeable typically still will not be as high as that of the
alkaline unit with the same physical form factor. Where the device is
voltage-sensitive, rechargeables may not work in place of alkalines.

>And why
>aren't rechargeables 1.5?

Chemistry.

--
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.

12-31-2006, 04:33 AM

On Sat, 30 Dec 2006 21:40:25 +0000, Mike Ellis <[Only registered and activated users can see links. ].uk>
wrote:

>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

I was afraid that it was going to be something elemental.

12-31-2006, 07:22 AM

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....
> I looked a bit closer at my rechargables, which are, it turns out, 1.2
> volts, not 1.5 like regular batteries. ...
> So, why do some things work fine with 1.2, and others not? And why
> aren't rechargeables 1.5?

Werehatrack's answer was exactly right.

To put it another way, the voltage measurements that give you 1.5 volts
and 1.2 volts are taken when there's no current flowing. If you took
an ordinary incandescent flashlight and measured the voltage actually
delivered to the bulb while it's shining, you'd find the two types of
batteries delivered pretty similar voltages at the bulb. If, instead,
you were feeding voltage to something that required little current, the
voltage delivered by the two battery types would be different.

But I'm curious about your "cold cathode lights." What are they,
exactly? Sounds like a flourescent or neon-type bulb?

- Frank Krygowski

12-31-2006, 08:43 AM

"peter" <[Only registered and activated users can see links. ]> wrote in message
news:1167540046.542659.294810@v33g2000cwv.googlegr oups.com...
> The latter is close enough
> for many devices designed to run on the nominal 1.5 V/cell produced by
> alkaline cells.

Um, wasn't it Carbon/Zinc that produced the original 1.5 volts that is also
approximated by Alkaline cells.

- Skip (an old fogey)

12-31-2006, 10:19 AM

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.

12-31-2006, 10:30 AM

[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.

12-31-2006, 02:59 PM

Richard B <[Only registered and activated users can see links. ]> wrote in
news:Xns98AA750566CE1bluerandoneegmailcom@216.168. 3.50:

>> But I'm curious about your "cold cathode lights." What are they,
>> exactly? Sounds like a flourescent or neon-type bulb?

Cold cathode lighting is a very encompassing term. I guess marketing uses
it because it sounds, uh, cooler. It's basically any type of lighting that
uses excited gas from emitted electrons, without a heater to emit light.

So it includes your average neon lights, but it could also be any other gas
- xenon or argon for different colors, for example. It could even be
vacuum, and then you've got it striking some other glowing material
(phosphor-screen) to make light.

Nodey