12VDC to 18.5VDC
in [Basics]
|
From: mrdarrett on 7 Aug 2006 16:54 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
From: mrdarrett on 7 Aug 2006 18:39 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
From: Rich Grise on 7 Aug 2006 18:54 On Mon, 07 Aug 2006 15:39:35 -0700, mrdarrett 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...? > > Eh, no response from sci.electronics.basics; belatedly cross-posting to > SED. Better than multiposting... ;-) > 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". I can't adivse you on a boost regulator, but I do think it seems simpler to just use 24V of batteries, and regulate it down with a linear regulator on a mongo heat sink. Or did you want this thing to be portable? ;-) Good Luck! Rich
From: mrdarrett on 7 Aug 2006 19:24 Rich Grise wrote: > On Mon, 07 Aug 2006 15:39:35 -0700, mrdarrett 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...? > > > > Eh, no response from sci.electronics.basics; belatedly cross-posting to > > SED. Better than multiposting... ;-) > > > > 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". > > I can't adivse you on a boost regulator, but I do think it seems simpler > to just use 24V of batteries, and regulate it down with a linear regulator > on a mongo heat sink. > > Or did you want this thing to be portable? ;-) > > Good Luck! > Rich Well, portability was kind of the idea, since I already have the 110 AC-to-DC switching power supply... ;-) I was planning on using the jump start battery, without using my square-wave inverter (Vector 75W I think is what it is) to power the switching power supply, and exchange this extra bulk with a homebuilt DC-DC converter. So a jump-start battery isn't a deep-cycle, eh? Thanks for the info... Michael
From: Joerg on 7 Aug 2006 19:38
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 :-) >>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...? >> 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. -- Regards, Joerg http://www.analogconsultants.com |