Battery life meter=viable or junk idea?

[MrDEB]

Been designing a battery operated device that consists of two separate units both of which run on battery power. Found lots of online calculators etc. for determining battery life expectancy but have yet to find any that agree with each other.
My idea is to use a PIC, a current sensor, the UART or LCD for display.
You connect the meter to your project, run the project through its paces and the meter measure and calculates amount of current drawn, calculates battery Ahr/MAhr rating needed depending on battery chemistry etc.
For example - you have an LED game you designed and built. The current demands change constantly but the meter averages out vers time to give a viable battery requirement.

 

[MrAl]

Hello there,


Yes you can do that. What you do is monitor the current and add it all up over time.
For example, say you draw 100ma for 1 hour, then that's 100maHr so far, but then you draw another 200ma for 2 hours, then that's another 400maHr so the total now is 500maHr. Another 100ma for 4 hours would be another 400maHr, so that added to the previous total is 900maHr.
You can use this to estimate remaining run time too knowing the batteries AHr rating and sometimes the 'p' factor for that battery.

 

[MrDEB]

BUT is it worth pursuing or just an idea?
Sounds unique but ??

 

[kubeek]

The question is, do you want to sell it? Do you want to do it as an open hardware project? Do you need it for yourself?

It is not a bad idea, even though I think it could be made into a litlle more than what it is now, by adding some more functionality like for example long-term logging of current and voltage.

 

[MikeMl]

Duplicate post

 

[MikeMl]

BUT is it worth pursuing or just an idea?
Sounds unique but ??

There are ready-made chips that do this...

Search for "battery management".

To do it yourself, you will have to implement an ∫ (integral) in software.

 

[JonSea]

Dallas-Maxim battery fuel gages.

Use of these will lead to new adventures (and many forum topics) of trying to understand 1-wire or I2C protocols. Plus, you pretty much have to decide on battery arrangements before you start.

 

[dr pepper]

I was once approached to do this for boat battery systems so you knew how much battery time you had left, or how long to run the engine and recharge, but I never bothered with it, I've been in business once doing that kind of thing, not too keen to do that again.

You'll need as mentioned to sample the current/voltage and produce an average, the sample rate will need to be fast enough not to miss any sudden demands, or you could put together an analogue circuit to do the job.
I've just built a bench supply (also on this site) which calculates the wattage of the o/p, the software isnt difficult, multiplying current by time would give you amp hours.

 

[MrDEB]

Holly cow I never realized any real need but I guess I was wrong.
All I had was just an idea that at this time I am just contemplating but that's it.
Just an idea.
Will, just out of curiosity, look over Jons link
Thanks

 

[dr pepper]

An idea is only a start, making a business out of anything is a whole business in itself, often leaving the developer behind.

 

[MrDEB]

You got that one right.
I have been working on a fairly simple project and find many roadblocks that differentiate the developer from the idea itself.
But trying to combine the two is really difficult.

 

[dr pepper]

I didnt mean that, but you are right.
Producing anything involves a lot more than just producing, all the ancilliary management to me seems far more work.

 

[k7elp60]

Been designing a battery operated device that consists of two separate units both of which run on battery power. Found lots of online calculators etc. for determining battery life expectancy but have yet to find any that agree with each other.
My idea is to use a PIC, a current sensor, the UART or LCD for display.
You connect the meter to your project, run the project through its paces and the meter measure and calculates amount of current drawn, calculates battery Ahr/MAhr rating needed depending on battery chemistry etc.
For example - you have an LED game you designed and built. The current demands change constantly but the meter averages out vers time to give a viable battery requirement.

I think it is a good idea. In fact I have copy of an article written by A.J. Caristi in the November 1994 Popular Electronics magazine. It is pretty straight forward. It uses a voltage to frequency converter to convert a 0.1Ah to a pulse. It then counts the pulses on a two digit counter, which monitors the Ah use from the battery. If you would like I can scan the article and post it.
Ned

 

[Electroenthusiast]

Do you actually want to find the remaining life of the battery? if yes, then you can do it as simple as possible. the voltage of the battery gradiently decreases as you use. So you can simply know the percentage of it remaining with it.

 

[MrDEB]

I just got curious but now intrigued to calculate how much battery amp hour rating is needed for a project determined by actual current measurement. Found several battery life calculators on the web but none seem to agree on end result.
Lets say you built a battery powered project then run the project through its paces with a meter to measure actual current draw then calculate amount of battery capacity required for said project to run x number of hours.
Wouldn't doubt everyone on this forum has been there and the battery goes dead prematurely due to the battery not having enough capacity.

 

[dr pepper]

Laptops and other devices have an intelligent chip inside the battery pack, the chip calculates from various measurements including volts, charge and discharge current, temp, age of the battery etc and gives you a good indication of the remaining capacity and the remaining overall life of the battery.
The drawback is you have to fit the chip to a new battery pack, and it has to stay with it.
I cant remember any chip numbers, someone might be along in a minute that does.

 

[k7elp60]

here is the article

 

[tcmtech]

Personally I have never trusted battery life monitors of any sort. I have a number of devices with them and I have found that not one is the least bit accurate.

 

[MrDEB]

THANKS looks like interesting reading.

 

[k7elp60]

Personally I have never trusted battery life monitors of any sort. I have a number of devices with them and I have found that not one is the least bit accurate.

I have never used a battery life monitor. I have a lot of experience with SLA (sealed lead-acid) batteries of the 10AH and less and I find even thou they are produced by different manufactures the charasteristics vary by manufacturer. I have configured them in series, parallel and such. I have used them in mostly in stanby status...that is using float charging at about 2.3 to 2.35 volts per cell. Sometime I get great life out of them and sometimes I don't.