"Tung-Yep, Philip" wrote: > > Chris, > > I suspect this is down to the type of voltage regulation you're > using. If it's a linear regulator, you're lucky to be getting > 30 seconds - most linear regulators need ~7 volts input minimum > to be able to provide 5 v out. This covers voltage drops across > the regulators transistors. If it's a switching regulator, the > minimum input voltage depends upon the design but again the most > common types need 7 v or above. If you're not using a regulator, > then you're lucky not to have blown a component. > > The easiest solution is to get a battery pack with a higher > voltage output although with linear regulators you will "lose" > the power associated with any excess voltage above 7 v as > waste heat. A switching regulator should be much more > efficient at handling higher voltages and will run cooler as well. There is another possibility, it's Low Voltage Dropout Voltage Regulators. They have designed regulators that get down to as little as .3V difference between input and output voltages. Check the specs for the one you decide to use, .7V is much more common. They cost more, and I'm not sure how well they work in parallel. I know they aren't available in as high of amperage outputs as regular linear regulators. Now I recommend looking for a switching regulator that can handle the expected load plus another 50%. you really don't want to overload your power supply circuits. They need to have good working margins or they may fail. An example of a problem I helped debug. The circuit was supposed to draw about .75A max. So they specked a .8A power supply for it. Unfortunately there was a fault in one of chips that caused it to sporadically draw excessive power under some conditions. Generally what happened was the current load would spike for a ms or two, then settle back down. It didn't spike high enough to cause much of a drop in voltage. Even if it did the circuit designed to deal with lowered voltages for extended periods. What the problem was, was sometimes the power supply controller couldn't keep the voltage from spiking to high when the excessive load stopped. This caused one of the chips in the circuit to fail after about 2 months of operation. > Note that it's possible to put your batteries in series and so > get 12v nominal input but get knowledgeable advice before doing > this - I think there are some risks associated with putting > unmatched cells in series. Yes there are risks with putting unmatched cells in series. It's the possibility of cell reversal for NiCd and NiMH types, and more dire effects with Li-Ion batteries. Li-Ion cells are hurt very bad when they are pushed past their limits. Having said that, it is still possible to go in series. Just don't expect to be able to squeeze every last bit of power out of the battery packs. Because when one pack/cell reaches full discharge you have to stop discharging. The energy still available in the other cells is not useable without harming the fully discharged cell unless you take the fully discharged cell out of circuit. There are battery pack controllers designed to do this, but you won't find them in anything but the newest designs as they have only hit the chip market in the past year or so. > Regards, > > Philip > > > -----Original Message----- > > From: Pubnix Net Axess [SMTP:] > > Sent: Tuesday, July 04, 2000 6:01 AM > > To:
> > Subject: Typical battery size in terms of maH capacity > > > > > > Hello, I am building a fairly typical setup, > > Jumptec LCD6/166/128 ram > > 3.2 gig laptop drive > > Keyboard > > Twiddler > > M1 (right now, but I will be replacing it b/c frankly I think it is awful) > > Plan to add other things as well. > > > > Was wondering what type of batter capacity most of you have. I've wired > > two Rat Shack 6v 1800 maH NiMH camcorder batteries (in paralell) and find > > that it will power the rig on only for ~ 30 seconds then power off and > > cycle. (works fine w/ a PC PS, the batteries test out ok with a Multi > > Meter) -- | Bryan Andersen |
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