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From: Joerg on 7 Aug 2006 19:42
Hello Michael,

>>
>>Well, for one thing, don't power it from a "car" battery, unless the
>>battery is on a continuous float charge. And _especially_ don't use a
>>jump-starting battery. They're designed to provide hundreds of amps,
>>for a minute or so. Use a golf-cart battery, wheelchair battery, boat
>>battery, whatever - the operative term would be "deep-cycle" or "deep
>>discharge".
>>

Correct.


> So a jump-start battery isn't a deep-cycle, eh? Thanks for the info...
>

At Walmart I saw a deep-cycle 12V last week for around $65, about the
size and capacity of a car battery.

--
Regards, Joerg

http://www.analogconsultants.com
From: pschoen@etiinc.com on 7 Aug 2006 19:47

mrdarrett(a)gmail.com wrote:
> mrdarrett(a)gmail.com wrote:
> > I have an old laptop (366MHz) which takes in 18.5V @ 3A by external
> > (switching?) power supply. (It didn't have a battery with it when I
> > bought it - got it 2 years ago for about $200.)
> >
> > I recently built an external battery pack, powered by 16 Energizer 1.2V
> > 2500mAh NiMH AA cells, to power my laptop in lieu of the external power
> > supply, and it does work. So far I have been able to run the laptop
> > for about an hour and a half, and still going strong. (Decided to stop
> > stress-testing at 1:15am, since I had work the next morning.) A far
> > cry from paying $150 for a "new" laptop battery, when the laptop only
> > cost me $200. Although, my 16 NiMH AA battery pack screams "GEEK!" at
> > anyone who glances at it... ;-)
> >
> > For my next project, a DC-DC converter.
> >
> > So... I'd like to convert 12VDC from a jump-start car battery to
> > 18.5VDC, at 3A.
> >
> > After reading a recent thread about avoiding Maxim like the plague, I
> > went over to TI's website, entered my parameters (Input V: 12VDC;
> > output V: 18.5 VDC; current: 3A.)
> >
> > I found this from the search result:
> >
> > http://focus.ti.com/lit/ds/symlink/tps5430.pdf
> >
> > but I was a bit confused why this would have been suggested, since it
> > seems to be a step-DOWN regulator.
> >
> > Any suggestions...?
> >
> > Thanks,
> >
> > Michael
>
>
> Eh, no response from sci.electronics.basics; belatedly cross-posting to
> SED. Better than multiposting... ;-)
>
> Michael

You could use an isolated 12 V to 6 V DC-DC converter and add the
output to your 12 volts from the battery. You could probably run it
with a full square wave without regulation to simplify feedback. Just a
high frequency transformer driven by something like a UC3526 and a
couple MOSFETs, and a simple rectifier and filter on the isolated
output in series with the battery voltage to get what you need. You
could use the PWM to make it regulated if you want.

Paul

From: mrdarrett on 7 Aug 2006 19:48

Joerg wrote:
> Hello Michael,
>
>
> >>I have an old laptop (366MHz) which takes in 18.5V @ 3A by external
> >>(switching?) power supply. (It didn't have a battery with it when I
> >>bought it - got it 2 years ago for about $200.)
> >>
> >>I recently built an external battery pack, powered by 16 Energizer 1.2V
> >>2500mAh NiMH AA cells, to power my laptop in lieu of the external power
> >>supply, and it does work. So far I have been able to run the laptop
> >>for about an hour and a half, and still going strong. (Decided to stop
> >>stress-testing at 1:15am, since I had work the next morning.) A far
> >>cry from paying $150 for a "new" laptop battery, when the laptop only
> >>cost me $200. Although, my 16 NiMH AA battery pack screams "GEEK!" at
> >>anyone who glances at it... ;-)
> >>
>
> Now don't show up at airport security with that concoction :-)
>

Oh, man! It's a pretty straightforward concoction - two 8-AA battery
holders, each with a 9V clip on top. I could disassemble it, but I
wouldn't want the clip on top to get shorted by any bare metal - could
cause a fire. The two 9V clips are soldered to a "C"-style Adaptaplug
from Radioshack.

http://www.radioshack.com/product/index.jsp?productId=2062425&cp=&origkw=adaptaplug+c&kw=adaptaplug+c&parentPage=search

I guess I could take apart the 16 AA's... I'd feel like a guerilla
soldier, though.

Then again, while I would be happy as a clam for maybe an hour or so on
the plane, once the batteries died, recharging would be problematic...


> Look at the LM3478 from National. Nice chip, have used it myself but
> AFAIR it only comes in the teeny MSOP package. Besides some mundane
> parts around it you'd need a stiff N-channel FET, a beefy inductor and a
> fast diode that can handle the amps. Since it is usually operated at
> several hundred kHz your inductor won't have to be huge.

Hmm... would operating at that frequency cause bad things to happen to
the pilot's collision avoidance system, etc.? Encase it in aluminum
foil...?

>
> --
> Regards, Joerg
>
> http://www.analogconsultants.com

Thanks,

Michael

From: mrdarrett on 7 Aug 2006 19:52

pschoen(a)etiinc.com wrote:
> mrdarrett(a)gmail.com wrote:
> > mrdarrett(a)gmail.com wrote:
> > > I have an old laptop (366MHz) which takes in 18.5V @ 3A by external
> > > (switching?) power supply. (It didn't have a battery with it when I
> > > bought it - got it 2 years ago for about $200.)
> > >
> > > I recently built an external battery pack, powered by 16 Energizer 1.2V
> > > 2500mAh NiMH AA cells, to power my laptop in lieu of the external power
> > > supply, and it does work. So far I have been able to run the laptop
> > > for about an hour and a half, and still going strong. (Decided to stop
> > > stress-testing at 1:15am, since I had work the next morning.) A far
> > > cry from paying $150 for a "new" laptop battery, when the laptop only
> > > cost me $200. Although, my 16 NiMH AA battery pack screams "GEEK!" at
> > > anyone who glances at it... ;-)
> > >
> > > For my next project, a DC-DC converter.
> > >
> > > So... I'd like to convert 12VDC from a jump-start car battery to
> > > 18.5VDC, at 3A.
> > >
> > > After reading a recent thread about avoiding Maxim like the plague, I
> > > went over to TI's website, entered my parameters (Input V: 12VDC;
> > > output V: 18.5 VDC; current: 3A.)
> > >
> > > I found this from the search result:
> > >
> > > http://focus.ti.com/lit/ds/symlink/tps5430.pdf
> > >
> > > but I was a bit confused why this would have been suggested, since it
> > > seems to be a step-DOWN regulator.
> > >
> > > Any suggestions...?
> > >
> > > Thanks,
> > >
> > > Michael
> >
> >
> > Eh, no response from sci.electronics.basics; belatedly cross-posting to
> > SED. Better than multiposting... ;-)
> >
> > Michael
>
> You could use an isolated 12 V to 6 V DC-DC converter and add the
> output to your 12 volts from the battery. You could probably run it
> with a full square wave without regulation to simplify feedback. Just a
> high frequency transformer driven by something like a UC3526 and a
> couple MOSFETs, and a simple rectifier and filter on the isolated
> output in series with the battery voltage to get what you need. You
> could use the PWM to make it regulated if you want.
>
> Paul


Oh, that's elegant! Thanks!

Michael

From: Joerg on 7 Aug 2006 20:00
Hello Michael,

>>
>>Now don't show up at airport security with that concoction :-)
>
> Oh, man! It's a pretty straightforward concoction - two 8-AA battery
> holders, each with a 9V clip on top. I could disassemble it, but I
> wouldn't want the clip on top to get shorted by any bare metal - could
> cause a fire. The two 9V clips are soldered to a "C"-style Adaptaplug
> from Radioshack.
>
> http://www.radioshack.com/product/index.jsp?productId=2062425&cp=&origkw=adaptaplug+c&kw=adaptaplug+c&parentPage=search
>
> I guess I could take apart the 16 AA's... I'd feel like a guerilla
> soldier, though.
>

.... and then carry them in a leather ammo belt with an NRA sticker :-)

>
>>Look at the LM3478 from National. Nice chip, have used it myself but
>>AFAIR it only comes in the teeny MSOP package. Besides some mundane
>>parts around it you'd need a stiff N-channel FET, a beefy inductor and a
>>fast diode that can handle the amps. Since it is usually operated at
>>several hundred kHz your inductor won't have to be huge.
>
> Hmm... would operating at that frequency cause bad things to happen to
> the pilot's collision avoidance system, etc.? Encase it in aluminum
> foil...?
>

You aren't supposed to let any more leak out than the FCC alloweth.

But the same goes for use elsewhere. If you build something and then it
interferes more than permitted it could lead to problems.

--
Regards, Joerg

http://www.analogconsultants.com
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