Forums

mA-hour meter

Started by Unknown August 26, 2005
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.

>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 chec 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 ar sub 1Amp, I would reccomend that you measure the voltage across a curren shunt. Maxim has a part that will allow an external current shunt National has one with an internal one. I think TI (Burr Brown) & Linea 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 differenc amplifier that can handle input voltages beyond the supply rail. You ca make your own with resistive dividers at the input, or use a product lik the AD626, an Instrumentation amplifier from Analog Devices. Of cours this approach is not isolated. I am currently using the Allegro ACS704xx-005 current sensor and I hav developed I problem where the device "locks up". I am awaiting tec support to find out where the problem lies. -Aubrey This message was sent using the comp.arch.embedded web interface o www.EmbeddedRelated.com
<jswayze@gmail.com> wrote in message
news:1125081413.077909.242660@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..
On 26-Aug-2005, jswayze@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