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Comments by Cindy D.
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Understanding battery capacity: Ah is not A
- 15 December 2017Thinking about it some more, my instinct tells me that the 0.667 A figure is probably the correct amp draw. When it runs, it inflates the cuff with an air pump. It makes a loud RRrrrrr sound, which tells me it's using a motor to do this, and motors usually have a pretty good-sized current draw, right? My hunch is that the 5V 1A power supply is the right choice (well 5V 750 mA would be closer).
Understanding battery capacity: Ah is not A
- 15 December 2017I have a blood pressure monitor, and I'm trying to figure out how much current it could possibly draw (to see whether I have an existing wall wart I could use). It takes 4 AA cells in series, so with each cell ranging from 1.2 to 1.5 volts, we have 4.8 to 6 volts for the four cells. A 5-volt power source would be okay.
It's the current draw that's confusing, due to the information printed in the manual. AA cells are maybe about 2800 milliamp hours, I've read. So you could draw 2.8 Amps for one hour, or something less for a lot longer. The booklet says in the back that you'll get "approx. 1500 uses when used once a day for 2 minutes with 4 new alkaline batteries." So, 1500 uses x 2 min/use x 1 hr/60 min = 50 hours of use. I then divided 2800 mAh by 50 hrs, so that the hours cancel out, leaving 56 mA per use. Does that seem right?
The problem is that the bottom of the machine says "RATING: DC 6V 4W" Watts is Volts x Amps, so 4W = 6V x Current; Current = 4W/6V = 0.667 A (rounded). This is 667 milliamps, not 56, which is quite a difference! Is the rating something different than actual value during use? Or is the 56 mA an amount of storage, and not actual current while in use?
Do I need a 5V 100mA power supply? Or a 5V 1A power supply? Thanks!