mA-hour meter
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From: jswayze on 26 Aug 2005 14:36 I'm working on an amp-hour meter (actually milliamp-hour) and am planning on using an Allegro current sensor to measure current from a discharging battery under load. I plan on displaying the accumulated amp-hours on an LED display, and a PIC will be running the show. Is the Allegro the best method for doing this, or is there another way? I haven't gotten into it yet, but it looks like the Allegro takes some calibration to make it accurate. Any suggestions? Thanks.
From: antedeluvian on 28 Aug 2005 16:44 >I'm working on an amp-hour meter (actually milliamp-hour) and am >planning on using an Allegro current sensor to measure current from a >discharging battery under load. I plan on displaying the accumulated >amp-hours on an LED display, and a PIC will be running the show. > >Is the Allegro the best method for doing this, or is there another way? >I haven't gotten into it yet, but it looks like the Allegro takes some >calibration to make it accurate. > >Any suggestions? Thanks. > > Since you are measuring mA (you don't mention how many) you should check out the FAQ on the allegro part http://www.allegromicro.com/faq/acs704faq/index.htm#Q6 Given the low resolution and accuracy issues, and assuming that you are sub 1Amp, I would reccomend that you measure the voltage across a current shunt. Maxim has a part that will allow an external current shunt, National has one with an internal one. I think TI (Burr Brown) & Linear Tech also have products. Here's a start at Maxim. http://para.maxim-ic.com/compare.asp?Fam=CS_Amp&Tree=PowerSupplies&HP=PowerSupplies.cfm&ln= But you don't need a dedicated part- you simply need a difference amplifier that can handle input voltages beyond the supply rail. You can make your own with resistive dividers at the input, or use a product like the AD626, an Instrumentation amplifier from Analog Devices. Of course this approach is not isolated. I am currently using the Allegro ACS704xx-005 current sensor and I have developed I problem where the device "locks up". I am awaiting tech support to find out where the problem lies. -Aubrey This message was sent using the comp.arch.embedded web interface on www.EmbeddedRelated.com
From: TheDoc on 28 Aug 2005 19:56 <jswayze(a)gmail.com> wrote in message news:1125081413.077909.242660(a)g47g2000cwa.googlegroups.com... > I'm working on an amp-hour meter (actually milliamp-hour) and am > planning on using an Allegro current sensor to measure current from a > discharging battery under load. I plan on displaying the accumulated > amp-hours on an LED display, and a PIC will be running the show. > > Is the Allegro the best method for doing this, or is there another way? > I haven't gotten into it yet, but it looks like the Allegro takes some > calibration to make it accurate. > > Any suggestions? Thanks. > Maxim has a few battery "fuel gauge" devices.. real low power..
From: Hershel Roberson on 29 Aug 2005 09:19 On 26-Aug-2005, jswayze(a)gmail.com wrote: > I'm working on an amp-hour meter (actually milliamp-hour) and am > planning on using an Allegro current sensor to measure current from a > discharging battery under load. I plan on displaying the accumulated > amp-hours on an LED display, and a PIC will be running the show. About a million years ago, I built a mA hour (actually a uA hour) meter using a voltage to frequency converter. There was an app note on a Analog Devices part that we used in a configuration for measuring current (I don't remember the part number). The neat thing is that it will integrate any peaks or spikes between output pulses, and has a very wide dynamic range (especially if you trim any ofset errors). We wanted to know the long time power consumption of a device that drew uAs in sleep-mode, and mAs when it had something to do. If it's for lab use, just connect a frequency counter and a few passive parts and you're done. -Hershel
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