ieee@ecf.toronto.edu (IEEE Student Branch) (02/13/91)
Help! I am building a device that needs a power hungry halogen bulb (5V, 0.8 amperes). With a standard 9V NiCad battery and 5V rectifier I only get 1.5 minutes of useable light. I could use 4 1.5 (actually 1.2 V) NiCads, but these would take up more space (space is important). There was talk of "VARTA" batteries packing more energy into the same 9V size. Where are these available (esp. in Canada?) Any other suggestions for power sources. I need to use Halogen bulbs because of its colour temperature: its much whiter than incandescent bulbs. Any suggestions on other sources for Halogens? Your suggestions would be most appretiated. Linas Dauksa dauksa@ecf.toronto.edu dauksa@ecf.utoronto.ca
jws@cica4.mlb.semi.harris.com (James W. Swonger) (02/13/91)
Try four AA NiCd batteries. Nominal voltage will be 4.8V; the package will end up about 1"x1"x2". AAs are usually about 450mAH; the "9V" cells are about 75maH as I recall. If you take apart the generic "9V" you will find 6 small cylindrical cells. Cutting the connection and using four removes the need for the dropping diode. You still end up with a lame battery. The newer 8.4V batteries use a stack of flat cells specially designed for the "9V" application rather than the cylinder sort which seem to be Q&D adaptations of the AA, cut off at the knees.
tomb@hplsla.HP.COM (Tom Bruhns) (02/15/91)
>Help! I am building a device that needs a power hungry halogen bulb >(5V, 0.8 amperes). With a standard 9V NiCad battery and >5V rectifier I only get 1.5 minutes of useable light. I could use >4 1.5 (actually 1.2 V) NiCads, but these would take up more space >(space is important). There was talk of "VARTA" batteries packing Might not help the space much, but National makes a little 5V switching regulator with very low external parts count. You could get a _regulated_ 5 volts. If the 9V (~8.5V) battery is about 80 mAH, you would get about 80mAH * 8.5V/5V * 75%, or about 100 equivalent mAH at 5 volts. That should run the bulb for about 1/8 hour, or 7-1/2 minutes. I would think the regulator would be a big gain in stabilizing the color temp, which you say is important! An alternative would be a step-up switching regulator operating from a single AA cell (or two); space about the same, maybe a bit more operating time?? ("left as an exercise for the reader")
george@wombat.UUCP (George Scolaro) (02/22/91)
In article <5170105@hplsla.HP.COM> tomb@hplsla.HP.COM (Tom Bruhns) writes: > >>Help! I am building a device that needs a power hungry halogen bulb >>(5V, 0.8 amperes). With a standard 9V NiCad battery and >>5V rectifier I only get 1.5 minutes of useable light. I could use >>4 1.5 (actually 1.2 V) NiCads, but these would take up more space >>(space is important). There was talk of "VARTA" batteries packing > >Might not help the space much, but National makes a little 5V switching >regulator with very low external parts count. You could get a >_regulated_ 5 volts. If the 9V (~8.5V) battery is about 80 mAH, you >would get about 80mAH * 8.5V/5V * 75%, or about 100 equivalent mAH at >5 volts. That should run the bulb for about 1/8 hour, or 7-1/2 minutes. I have recently purchased some of the 9V Varta brand nicads, because of their 7 cell construction. The data sheet that comes with them (bought via a distributor) shows discharge curves for 100mA and 200mA. Remember that this battery has a 100mAH capacity. Minutes Voltage@100mA Voltage@200mA 5 8.3V 7.2V 10 8.1V 6.2V 15 8.0V 20 7.7V 25 7.4V 30 7V My tests: Minutes Voltage@12mA 8hrs 10mins 8.56V 9hrs 14mins 8.43V 9hrs 19mins 8.40V 9hrs 34mins 8.26V 9hrs 40mins 8.00V Rapid decrease at this point, battery flat From this you can see that the capacity of the battery is grossly diminished at high current draw. The 100mAH capacity is rated at 0.1C, i.e. 10mA draw. If you are drawing 0.8A, I'm not surprised that you get mere seconds of use. In fact most nicads and gell cells quote their capacity at a specified currect draw, usually 1/10th of their capacity. The conclusion is that you have to derate the battery's capacity if you exceed the specified current draw/capacity. To select the battery that solves your problem you'll either need to perform more experiments, or get comprehensive discharge curves from the battery manufacturers. Lot's a luck. -- George Scolaro george@wombat.bungi.com [37 20 51 N / 122 03 07 W]