12VDC to 18.5VDC
in [Basics]
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From: mrdarrett on 9 Aug 2006 01:19 mrdarr...(a)gmail.com wrote: > Paul E. Schoen wrote: > > ... > > > You will probably need to "roll your own", but it should really be nothing > > much more than a small toroid about 1" diameter, wound with a couple dozen > > turns of wire, if you use about 50 kHz PWM. #22 to #26 AWG wire should be > > OK for 3 amps or so. Otherwise, you could probably use parts of an old > > computer power supply. Of course, you can just buy a DC-DC converter, but > > 18 watts will probably cost at least $50. > > > > Paul > > > My PWM controller is basically this: > silly, forgot the link: http://www.cpemma.co.uk/555pwm.html (sleep deprived - woke up 4:30am this morning to fly out to LA for a meeting.) > Probably a silly question to ask, but just making sure: should I make > C1 equal to 200 (or the more commonly available 220) pF to get 50 kHz? > Any special type of cap, or would a simple ceramic do? > > Thanks, > > Michael
From: Paul E. Schoen on 9 Aug 2006 15:07 <mrdarrett(a)gmail.com> wrote in message news:1155100783.237344.201930(a)i42g2000cwa.googlegroups.com... > > mrdarr...(a)gmail.com wrote: >> Paul E. Schoen wrote: >> >> ... >> >> > You will probably need to "roll your own", but it should really be >> > nothing >> > much more than a small toroid about 1" diameter, wound with a couple >> > dozen >> > turns of wire, if you use about 50 kHz PWM. #22 to #26 AWG wire should >> > be >> > OK for 3 amps or so. Otherwise, you could probably use parts of an old >> > computer power supply. Of course, you can just buy a DC-DC converter, >> > but >> > 18 watts will probably cost at least $50. >> > >> > Paul >> >> >> My PWM controller is basically this: >> > > silly, forgot the link: > http://www.cpemma.co.uk/555pwm.html > > (sleep deprived - woke up 4:30am this morning to fly out to LA for a > meeting.) > >> Probably a silly question to ask, but just making sure: should I make >> C1 equal to 200 (or the more commonly available 220) pF to get 50 kHz? >> Any special type of cap, or would a simple ceramic do? >> >> Thanks, >> >> Michael > The 555 will handle 50 kHz, but 200 pF is marginal. It would probably be best to change the pot to 10k, and then use a 2 nF capacitor for C1. Ceramic or film types are OK. You cannot just put a transformer in place of the motor, because you will have DC which will saturate it. The easiest method is a push-pull design with a center tapped primary, and the best IC is a regulating PWM controller such as SG3526, UC3526, or TL494, which is designed to drive two MOSFETs or bipolar transistors. It has provisions for soft start, overcurrent shutdown, dead time, and voltage regulation. They are used in many switching power supplies. For wire size, you can use my spreadsheet at: http://www.smart.net/~pstech/WireSize.xls It shows that #22 AWG should handle 3.8 amps. #20 allows 5.3 and #18 will handle 7.6 amps. These values are for a conductor in free air with something like 30 C temperature rise. Use the heaviest wire that will easily fit the core, for best efficiency. Good luck, Paul
From: joseph2k on 12 Aug 2006 12:46 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 might want to try this part: http://www.linear.com/pc/productDetail.do?navId=H0,C1,C1003,C1042,C1031,C1061,P24012 -- JosephKK Gegen dummheit kampfen die Gotter Selbst, vergebens. --Schiller
From: mrdarrett on 12 Aug 2006 13:04
joseph2k 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 might want to try this part: > > http://www.linear.com/pc/productDetail.do?navId=H0,C1,C1003,C1042,C1031,C1061,P24012 > > -- > JosephKK > Gegen dummheit kampfen die Gotter Selbst, vergebens. > --Schiller Thanks for the link! Michael |