Battery Charge Level Indicator (BCLI)

[Jens]

maybe i am missing something, but i don't see a complicated and expensive solution being any better?

Of course you are missing something here Bob ..... why work with a simple volt meter if you could have much cooler looking combo gauge. After all, he who has the most toys wins !
Personally I would also have a readout of the specific gravity on each cell to better monitor my charge levels !

[mobile_bob]

"Personally I would also have a readout of the specific gravity on each cell to better monitor my charge levels !"

well now, that puts a whole nother color on the subject!



bob g

[BruceM]

Most of the better SOC meters do adjust for Peukert effect, charge efficiency at the present SOC, temperature effect on actual capacity, etc.  Mine does.    Nobody does just simple AH integration anymore (aka totalizers), I just used that as a simple explanation.  I didn't want to worry Casey with a Peukert compensation chart.

I'm sure that with practice and maybe a few specific gravity readings along the way, you could learn to correlate a certain voltage under your typical driving load with capacity remaining.

[LowGear]

Don't you worry no bit about no stinking pukit level.  I'm sticking with KISS.

Simple is as Simple does is our motto here in Paradise.

Casey

[LowGear]

why work with a simple volt meter if you could have much cooler looking combo gauge. After all, he who has the most toys wins !

Right after KISS comes TRUTH!  It's hard to define but you know it when you see it.

Casey

I just ordered my first "gauge":

http://www.ebay.com/itm/New-MASTECH-MS2108A-ac-dc-current-clamp-ampere-meter-to-the-real-thing-/251176056525?pt=US_Ham_Radio_Transceivers&hash=item3a7b4276cd  I didn't have any choice once I noticed the back-lit LCD readout.  Can't you just see that heavy cable coming up through the gas filler - through the clamp for current and back down by the front of the tank to "who knows where?".

OK, this isn't my machine but it's pretty darn close.

[scottpeterd]

I've spent years playing with battery monitors. 

My favorite (esp. if you want a serial interface to pull data off with) is the Outback Mate (old style) combined with the FlexNet monitor.  However, those are some big bucks.

If you want something affordable, check out the Tunigy 130A meters.  The a multi parameter reporting device, made for model airplance use.  But they read up to 130 ampsDC.  They report instant, peak and cumulative volts/amps/wattts on the readout.  No data interface though.

http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=10080

They are unidirectional, so i use one for the load side and one for the charge side. Simple math to figure out your real battery level. A 3 pin header allows you to reset the counters.

I've been using them for about two years on solar installs and my sailboat (one for each charge source: alternator, solar, wind)

Best part: $23.

Pete

[BruceM]

Awesome post, Pete.  Integrating AH used for anything up to 60V, for $23 is amazing.  Screw Peukert, that would get you in the ballpark for SOC much better than looking at battery voltage.  You can just adjust your effective AH capacity to match your typical current draw pattern.

Thanks very much Pete, this is quite marvelous.

[mobile_bob]

does the turnigy use an external shunt to measure 130amps?
it seems inconceivable to me that it could handle 130amps with those small
wires on a continuous basis?

does anyone know what it can handle safely on a continuous basis?

bob g

[LowGear]

My Ebay seller counter offered.  How do you wire the Tunigy 130A meter into the battery pack?

Casey

[mobile_bob]

unless it has an external shunt, i fear  you would smoke the little bugger driving a
golf cart motor.

bob g

[Jens]

In all my years of fiddling, one thing (maybe two) remains constant:

Buy good quality tools - crappy tools will fail breaking your project and require buying the good tool as well as all the bits of the project you broke.

There is a huge difference between stingy and frugal - Stingy makes a pile of garbage out of your project, frugal will produce something that you will be proud of for the rest of your life.

Having said all that, I must admit that I have not learned that lesson well yet and I end up spending significant amounts of time and money to re-do the crap into a frugal project.

.... and as it applies to this thread - buy the meter that is meant for the job and quit waisting time wallowing in indecision!

[BruceM]

I did some checking.  It's common for 36V golf cart motors to draw 275 (!) amps.   Bob was right, the Turnigy going to smoke.  Bummer. 

Plan B- Put the Turnigy in parallel with another shunt or wire loop, so that the turnigy sees  1/10 of the current.   Then the turnigy stays cool, and reads 1/10th the actual AH used.  (Or some other handy fraction.)

[scottpeterd]

I don't belive the 130A rating is anywhere near sanity.   But I use it regularly at 30A, and no troubles.

If you want higher ratings, crack the case and bypass the internal shunt with one more appropriate to your needs.  Google some of the EV forums and you'll find photos and instructions

For that price, getting the logging features alone is an incredible bargain.  It costs well over $100 to do the same with an Arduino fitted with current measurement, data logging (SD card), and display shields.

These are essentially Chinese clones of the Watts-Up meters, at one-half the price.

As to their quality: I have over 100 of them in use metering pico-grid projects in Africa, and only one failure in more than a year.  Try to find a way to meter 24v DC to a rural African home where the average monthly bill is $3.

Pete

[scottpeterd]

As to hooking it up:

The diagrams show inserting it in series with both positive and negative leads.  One side of the meter is for connection to the source; the other side is for connection to the load(as in PV:Battery or Battery: Motor0

What I've found is that only the negative lead needs to be in series.  Either of the positive leads can be connected to the B+

[uber39]

this is the gauge that I now use on my EV, it takes all its measures off an external shunt.
http://www.ebikes.ca/drainbrain.shtml
You know how many Amps you start with, and this tells you how many Amps you've taken out
Also tells Volts and speed and distance and Watts per mile the list goes on.
   


      Ian