Comments by Cindy D.

  • Understanding battery capacity: Ah is not A

    Understanding battery capacity: Ah is not A

    - 15 December 2017

    Thinking 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

    Understanding battery capacity: Ah is not A

    - 15 December 2017

    I 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!

New Products

JST SH-Style Cable, 4-Pin, Female-Female, 63cm
JST SH-Style Cable, 2-Pin, Female-Female, 25cm
ACS37030LLZATR-065B3 Current Sensor Large Carrier -65A to +65A, 3.3V
JST SH-Style Cable, 4-Pin, Single-Ended Female, 75cm
CT433-HSWF50DR TMR Current Sensor Compact Carrier 0A to 50A, 3.3V
CT433-HSWF20DR TMR Current Sensor Compact Carrier 0A to 20A, 3.3V
CT432-HSWF50MR TMR Current Sensor Large Carrier -50A to +50A, 5V
CT432-HSWF30DR TMR Current Sensor Compact Carrier 0A to 30A, 5V
CT433-HSWF30MR TMR Current Sensor Compact Carrier -30A to +30A, 3.3V
JST SH-Style Connector Board for Micro Metal Gearmotors, 2-Pin, Side-Entry (10-Pack)
Log In
Pololu Robotics & Electronics
Shopping cart
(702) 262-6648
Same-day shipping, worldwide
Menu
Shop Blog Forum Support
My account Comments or questions? About Pololu Contact Ordering information Distributors