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From: Jasen Betts on 6 Dec 2009 04:58
On 2009-12-05, John Doe <jdoe(a)usenetlove.invalid> wrote:
> I need to power three Cree XLamp XRE LEDs. The standard sealed lead
> acid battery is 12 V, but it is heavier than I would like to carry. I
> have some spare rechargeable 14.4 V DeWalt tool batteries.
>
> The L7812 regulator says it needs at least 14.5 V. will a 14.4 V
> NiCad tool battery be acceptable for that?

what exactly are you doing with with the 12V. - what circuit are you
planning to use for the LEDs ?

In most cases 14.4 from a rechargable battery pack is a good
replacement for 12-14V from from a "12V" lead-acid battery.

From: John Doe on 7 Dec 2009 10:01
Jasen Betts <jasen(a)xnet.co.nz> wrote:

> John Doe <jdoe(a)usenetlove.invalid> wrote:

>> I need to power three Cree XLamp XRE LEDs. The standard sealed
>> lead acid battery is 12 V, but it is heavier than I would like
>> to carry. I have some spare rechargeable 14.4 V DeWalt tool
>> batteries.
>>
>> The L7812 regulator says it needs at least 14.5 V. will a 14.4
>> V NiCad tool battery be acceptable for that?
>
> what exactly are you doing with with the 12V. - what circuit are
> you planning to use for the LEDs ?
>
> In most cases 14.4 from a rechargable battery pack is a good
> replacement for 12-14V from from a "12V" lead-acid battery.

I just weighed eight 2ah AA NiMH batteries. They weigh less than
one third of the next alternative, so they are looking very good.




--
thanks to the replies
From: Tim Wescott on 7 Dec 2009 14:02
On Sun, 06 Dec 2009 18:53:59 -0500, Tom Biasi wrote:

> "Tim Wescott" <tim(a)seemywebsite.com> wrote in message
> news:uL6dneaZrNjegYHWnZ2dnUVZ_vZi4p2d(a)web-ster.com...
>> On Sat, 05 Dec 2009 18:59:49 +0000, John Doe wrote:
>>
>>> I need to power three Cree XLamp XRE LEDs. The standard sealed lead
>>> acid battery is 12 V, but it is heavier than I would like to carry. I
>>> have some spare rechargeable 14.4 V DeWalt tool batteries.
>>>
>>> The L7812 regulator says it needs at least 14.5 V. will a 14.4 V NiCad
>>> tool battery be acceptable for that?
>>>
>>> Thanks.
>>
>> In case you haven't figured it out, DO NOT connect a plain-old LED to a
>> stiff voltage source like a NiCd or lead-acid battery. At least,
>> unless you want a burnt out LED and an unhappy battery. You can kinda
>> sorta get away with it if you have an LED that drops 1.5V and a dry
>> cell battery, but it's still not good practice.
>>
>> LEDs want constant current sources -- which is what the other posters
>> are offering up to you.
>>
>> --
>> www.wescottdesign.com
>
> I was assuming he was using the Cree XLamp used as a replacement bulb
> operating at a nominal 12 VDC. They are used routinely in RVs and
> routinely operate at 14+ volts while the vehicle is running.
>
> Tom

I wasn't sure, which was why I qualified my statement with the "plain
old".

And I couldn't remember the nominal DC bus voltage during charge -- I
thought it was more like 13.8?

But, that thing should have some sort of current limiting, if not
outright current regulation.

--
www.wescottdesign.com
From: Tom Biasi on 7 Dec 2009 15:49

"Tim Wescott" <tim(a)seemywebsite.com> wrote in message
news:LJednduH4qLDzIDWnZ2dnUVZ_gli4p2d(a)web-ster.com...
> On Sun, 06 Dec 2009 18:53:59 -0500, Tom Biasi wrote:
>
>> "Tim Wescott" <tim(a)seemywebsite.com> wrote in message
>> news:uL6dneaZrNjegYHWnZ2dnUVZ_vZi4p2d(a)web-ster.com...
>>> On Sat, 05 Dec 2009 18:59:49 +0000, John Doe wrote:
>>>
>>>> I need to power three Cree XLamp XRE LEDs. The standard sealed lead
>>>> acid battery is 12 V, but it is heavier than I would like to carry. I
>>>> have some spare rechargeable 14.4 V DeWalt tool batteries.
>>>>
>>>> The L7812 regulator says it needs at least 14.5 V. will a 14.4 V NiCad
>>>> tool battery be acceptable for that?
>>>>
>>>> Thanks.
>>>
>>> In case you haven't figured it out, DO NOT connect a plain-old LED to a
>>> stiff voltage source like a NiCd or lead-acid battery. At least,
>>> unless you want a burnt out LED and an unhappy battery. You can kinda
>>> sorta get away with it if you have an LED that drops 1.5V and a dry
>>> cell battery, but it's still not good practice.
>>>
>>> LEDs want constant current sources -- which is what the other posters
>>> are offering up to you.
>>>
>>> --
>>> www.wescottdesign.com
>>
>> I was assuming he was using the Cree XLamp used as a replacement bulb
>> operating at a nominal 12 VDC. They are used routinely in RVs and
>> routinely operate at 14+ volts while the vehicle is running.
>>
>> Tom
>
> I wasn't sure, which was why I qualified my statement with the "plain
> old".
>
> And I couldn't remember the nominal DC bus voltage during charge -- I
> thought it was more like 13.8?
>
> But, that thing should have some sort of current limiting, if not
> outright current regulation.
>
> --
> www.wescottdesign.com

Yes, those devices are made for such use. The OP shouldn't need to do
anything to use the NiCads.
Vehicle nominal charge voltage is about 13.8 V but trips above 14 are not
uncommon.
Regards,
Tom


From: Robert Roland on 8 Dec 2009 09:51
On 07 Dec 2009 15:01:09 GMT, John Doe <jdoe(a)usenetlove.invalid> wrote:

>I just weighed eight 2ah AA NiMH batteries. They weigh less than
>one third of the next alternative, so they are looking very good.

If weight is very important, you may want to take a look at LiPo
batteries. They give you specific charge density at least double of
what you get from even the best NiMH stuff.

They're more expensive, and you need a new charger, so cost might
become an issue. Radio control plane and helicopter modelers don't
even consider anything else these days. They are, of course, very
picky when it comes to weight.
--
RoRo
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