Digital LED battery meter

Two 6 volts in parallel?

There are 12 volt analog meters for this, and there are some digital ones for trolling motors. I think I have even seen kits for this type of thing. I just can't point to it right now. Its not really a problem to design a ciruit.

greg

In series. I would like to have a meter for each battery; that way if one starts to fail I hope to catch it before it takes the other one with it.

I've looked at the analog ones; the good ones are about $50 US, and the cheap ones aren't worth it. So 2 meters = $100; I figure I can buy the parts for < $15 and learn something about PIC or similar uprocessors.

I have a computer in the van which communicates with my home server (long story) and one reason for going digital with this is to have long-range monitoring of the batteries. I figure I can set it up so that a particular LED on the maxim chip will trigger a GPIO pin which in turn will trigger a message to the home server to pay attention to the batteries.

--Yan

snipped-for-privacy@pitt.edu (GregS) wrote in news:e6c5rq$crf$ snipped-for-privacy@usenet01.srv.cis.pitt.edu:

LM3914 bar-graph IC app notes had some circuits for battery level meters. You can daisy-chain them for more resolution.

To drive the SPI input you would normally use a small micro with ADC. That would allow better accuracy, linearization and you could take temperature into account to get even closer.

If that's more than you want to get into, and you're only looking for rough indication of charge, you can use something like an LM3914 which won't be too bad.

Actual Reading with charge linear approxmation

Best regards, Spehro Pefhany

For lead-acid cells voltage is not a good indicator of charge, though you can get close if your measurement setup has a TC that tracks the cell.

Simplest: Just buy cells with the (hydrometer) float ball indicators on the side ;-)

...Jim Thompson

That's exactly what I am looking to get into. I normally work with embedded systems, but even that would be overkill for this (200 MHz, 32 MB RAM, etc...) I'm looking for a very, very basic uprocessor with a few channels of ADC that I can pick up for a few $$.

This is mostly a learning thing, rather than a money saving thing....

--Yan

Do you *want* to design a circuit ?

It's easy enought to get apair of this kind of thing

Graham

Some items currently available.

I put an analog one in my boat. I orginally had two batteries isolated, but I use them in parallel now. The older analog guage is very effective when trolling out on the lake. Different batteries as well as good-poor batteries will show slightly different voltages.I also installed dual digital battery voltage indicators. I could monitor watch each battery when they were isolated. Had to use a battery for the meters i bought which needed an isolated supply.

greg

They have fixed intervals though.

Graham

If two 6 volt batteries are always used in series they should be treated as a single battery - both same make/type/size, and bought at the same time. When one fails, replace both, 'cuz the second one probably won't be far behind.

I have four 6 volt batteries in series-parallel on my boat - when one fails, I'll replace all four.

It seems like a perfect application for a Microchip 16F676, which is a 14 pin flash device used in their $30 demo/development kit, which includes their MPLAB IDE. It connects via USB and a programmer is built in. The board already has 8 LEDs, and a Pot connected to one of the A/D inputs.

I think a battery charge indicator would be a valuable tool. It could be made to flash the LEDs at a low repetition rate to reduce power consumption. It could also sense and track charge/discharge cycles and possibly provide an indication of actual ampere-hour capacity by adding a small shunt.

Good luck. I can help if you run into any problems. Some of the assembly code is tricky.

Paul

What's powering the charge monitoring circuit? And you can't have two separate monitoring circuits each measuring up to 7V relative to separate references but ultimately tied together to message an external server without isolation.

Are you sure about this data?

What manufacturer - and for what type of cell? The voltages would suggest a 3 cell Pb-acid battery. Although for a given fixed set of discharge conditions (temp, rate, cell ageing) the cell voltage is higher for a greater remaining % capacity it is generally such a poor indicator that it is not (commercially) useable. This is why 'gas guage' devices came into being

I can't parse this. First, your run-on sentence suggests (I think) that a gas-gauge-type indicator isn't reliable, then you say that that's why they're there.

??? Rich

Gas-gauges devices (or at least the properly spelt ones) do not measure battery voltage to determine available capacity.

Do you have a link for this? I googled, and found what I think is the webiste, but no $30 dev kit...

Yes, my thoughts exactly. And it would be fun to build....

Thanks! It may be a while - summer is coming, so I plan to be doing lots of outdoor stuff. This is a good winter/cold weather project... :-)

--Yan

Never mind... I don't know how I missed this before....