## Integrate ampere measurement over time?

## Integrate ampere measurement over time?

(OP)

Hello,

I am looking for an I2C device that can help with accurate measurement of amps (+/- 50A @30VDC) flowing in 2 directions (in and out of batteries). I am currently using an Arduino to do this but accuracy is low in terms of available bits at the ADC but especially with the sampling rate I am able to do the measurements (10Hz) with. Is there a chip that is able to integrate the amps over time until I read it?

Thanks

Markus

I am looking for an I2C device that can help with accurate measurement of amps (+/- 50A @30VDC) flowing in 2 directions (in and out of batteries). I am currently using an Arduino to do this but accuracy is low in terms of available bits at the ADC but especially with the sampling rate I am able to do the measurements (10Hz) with. Is there a chip that is able to integrate the amps over time until I read it?

Thanks

Markus

## RE: Integrate ampere measurement over time?

TTFN

I can do absolutely anything. I'm an expert!

FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers

## RE: Integrate ampere measurement over time?

## RE: Integrate ampere measurement over time?

It'll be tricky to even find a current sensor much better than that. Certainly doable, but not a trivial step.

You should break this up into three parts.

1) Current measurement sensor (tricky)

2) ADC with as many bits as you like

3) uC to do the management and integration

If it's for solar power, you should obviously design for minimal power consumption. No point having a solar control system that needs hundreds of watts .

## RE: Integrate ampere measurement over time?

What do you mean by "uC to do the management and integration"?

## RE: Integrate ampere measurement over time?

TTFN

I can do absolutely anything. I'm an expert!

FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers

## RE: Integrate ampere measurement over time?

## RE: Integrate ampere measurement over time?

The Temperature Coefficient of Copper (near room temperature) is +0.393 percent per degree C." (Resistance,to be clear) So if the temperature of the copper shunt drifts by 10°C (very possible, could be more), then you've got a 4% error in the assumed resistance, and thus 4% error in everything that follows.If you're worried about 10-bit resolution, there are perhaps other issues to address. Unless you've already addressed them. Like using different material for the shunt, or measuring its temperature and compensating, or actively controlling its temperature.

Yes, the uC would interface to the ADC, and can do the integration of the current over your selected time intervals. It's almost certainly the simplest approach to integrating the current as you'd mentioned. In theory, you can integrate with analog hardware, but it's likely a lot more effort to design and debug.

## RE: Integrate ampere measurement over time?

TTFN

I can do absolutely anything. I'm an expert!

FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers

## RE: Integrate ampere measurement over time?

I goggled "uC" but did not find anything useful.

## RE: Integrate ampere measurement over time?

Use a microController to do the management and integration.

There are a truckloads of pre-made units that could do this for you. You'd need to do some programming. Some would have a lot of it done already, none would have it all done though.

Keith Cress

kcress - http://www.flaminsystems.com

## RE: Integrate ampere measurement over time?

Gunnar Englund

www.gke.org

--------------------------------------

Half full - Half empty? I don't mind. It's what in it that counts.

## RE: Integrate ampere measurement over time?

I am already using a micro controller to do all of it - my problem is I can only sample the ampere with a rate of 10 measurements per second and in a very dynamic load pattern I might miss a few peaks.

VE1BLL is talking about an analog method of integrating measurements - how is this done?

## RE: Integrate ampere measurement over time?

The INA226 appears to have at least 10x that bandwidth

TTFN

I can do absolutely anything. I'm an expert!

FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers

## RE: Integrate ampere measurement over time?

It's likely a lot more effort to design and debug allthe associated analog circuitry, than repeatedly sampling and integrating in a uC (micro

).controller## RE: Integrate ampere measurement over time?

I can do absolutely anything. I'm an expert!

FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers

## RE: Integrate ampere measurement over time?

Thanks for your suggestions. I will start a new thread about a more important problem in a minute.

Markus

uC = micro-computer was interesting news ;)

## RE: Integrate ampere measurement over time?

Controllerwhich is generally considered a fully-supported-on-a-single-die processor. Like an Atmel or PIC.Keith Cress

kcress - http://www.flaminsystems.com

## RE: Integrate ampere measurement over time?

http://www.linear.com/product/LTC4150

Generates a level to tell the direction of the current and a pulse with the frequency proportional to magnitude, it does the integration for you.

Designed as a coulomb counter for battery management, has pretty good accuracy (0.3% of full scale error). Range set by a shunt resistor.

## RE: Integrate ampere measurement over time?

## RE: Integrate ampere measurement over time?

Z

## RE: Integrate ampere measurement over time?

[gnd]--[2 or 3 cells]-+-[Rshunt]-+-[cell]--[cell]-- ... --[Batt+]

The current range is set by the shunt resistor. +/-50 amps full scale would be 1 milliOhm. Plenty of options there:

http://www.digikey.com/product-search/en/resistors...

I did something similar for a 15 Amp-Hour 48 volt battery pack.

## RE: Integrate ampere measurement over time?

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

## RE: Integrate ampere measurement over time?

Z

## RE: Integrate ampere measurement over time?

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]