Micro CoGen.

I've been thinking about installing a BCLI and the two I've looked at seem to be nothing more that voltage meters.  Isn't there some way I can make it more complicated and more prone to failure?

36 Volts (3 - 12 volt marine deep cycle batteries) and I want to know how much ride they have left in them.

Casey

These systems are quite common place in marine applications. There are a number of highly regarded systems such as the "Link" battery charge level monitor. The systems do most of their monitoring via a shunt and the data entered by the user .... such as battery capacity. All charge or discharge current is monitored and you can get indication of voltage, current, total current withdrawn from the bank and estimated time before battery is depleted at the current draw level.

Like this one?

http://www.xantrex.com/documents/Discontinued-Products/Link20%28445-0196-01-01%29.pdf (http://www.xantrex.com/documents/Discontinued-Products/Link20%28445-0196-01-01%29.pdf)

I'd set it up on the two end batteries to serve the 12 volt design and switch between 1 and 2 to see what's going on?

I think if I hooked it to the 36 to 12 VDC step down convertor it might get tricked by the convertor trying to keep it at 12 volts regardless of input variation.

Casey

how about this?

http://www.ebay.com/itm/Golf-Cart-Battery-State-of-Charge-Meter-Analog-36V-Easy-to-Install-FREE-Shipping-/360478388410?pt=LH_DefaultDomain_0&hash=item53ee2fb0ba

ebay has analog ones like the one above and digital as well

ebay, "golf cart state of charge"

?  am i missing what you are wanting?

bob g

So just about anything will work as alls we're really doing is measuring the voltage and interpreting that value to be a percentage of full charge?  So one of these fancy smancy meters from days of old would be just as good?

http://www.ebay.com/itm/120999988429?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2648 (http://www.ebay.com/itm/120999988429?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2648)

or

http://www.ebay.com/itm/Vintage-WESTERN-ELECTRIC-DC-VOLT-METER-0-50-DC-VOLTS-SCALE-PANEL-MOUNT-nice-/140868966037?pt=LH_DefaultDomain_0&hash=item20cc71d695 (http://www.ebay.com/itm/Vintage-WESTERN-ELECTRIC-DC-VOLT-METER-0-50-DC-VOLTS-SCALE-PANEL-MOUNT-nice-/140868966037?pt=LH_DefaultDomain_0&hash=item20cc71d695)

Casey

Voltage can be used as an indicator of state of charge after a period of rest (useable but not accurate)  but in use, it's just not a very good indicator of SOC.  If you need a decent indication of SOC on the go, then you need something like the Link units Jen's suggested.

I found these:

http://www.goodboatgear.com/detail/3473/%20Link%2010%20and%20Link%2020%20Battery%20Monitors (http://www.goodboatgear.com/detail/3473/%20Link%2010%20and%20Link%2020%20Battery%20Monitors)

I guess I could check on the first and last 12 volt battery and then just assume the one in the middle is at about the same condition?

Casey

Casey,

The trimetric meter actually records the amp hours used from the battery and from that calculates your SOC (state of charge). When you set it up you put in the size of the battery bank so it knows what it's connected to. You will also need a shunt of the correct size to run your power through. I use a Trimetric to manage our off-grid battery bank.

I remember the Trimetric Tom uses from looking at commercial SOC meters years ago.  Good reviews, decent price.  I had to roll my own as no SOC meter I could find at the time had a serial data port I could use to get the data to my battery bank monitor/controller.

To answer your question, Casey, yes, you could manage nicely with a 12V SOC meter, if you find a bargain. All the batteries in series will be at the same SOC.

There is one SOC meter out there with no current shunt.  I think it's a British product.  Avoid that one. Without using current in and out, you'd need fairy dust or a crystal ball to compute an accurate SOC.

Only 2 ways to "estimate" the battery SOC.

A Voltmeter, gives a good guess, and the Totalizators are much more accurate.  Lead-Acid batteries give a nice linear curve as they charge/discharge, but Li-on and other chemistrys are much harder to estimate.

Great information as usual.  I even learned a new acronym - SOC.  Much nicer than BCLI.

Thanks again,

Casey

I was cruising Ebay and saw the hundreds of Clamp Multimeters.  And immediately wondered if any were smart enough out of the box to work as a reliable SOC meter?

Epoxy the device to the fuel tank shell, run the feed wire to the power distribution module up through it and presto - a really cool looking science project meter that would give current voltage and current readings at the flip of a rotary switch.  Maybe even find an LED displayed one.  Hold on, there's already a hole in the shell for where the fuel filler cap used to be located.

Casey

No, current and voltage won't directly tell you the state of charge.  You need to integrate the current used over time. Not very practical to do with a stop watch, calculator, and a note pad every 10 seconds or so while while you're driving.

Maybe you should just monitor voltage for a while and see if that's sufficient for your needs.

there is also another fly in the ointment to consider

the peukert effect

a battery that is used for traction will likely have a much higher current draw than
what the 5, 20 or 100hour rating would be

this means that the voltage will drop to the point the battery is near dead, but if you let is sit for several minutes it will recover some of its capacity and you can drive a while longer.

for the purpose of knowing where you are at with state of charge  in a golf cart, a simple volt gauge is likely going to be most useful in my opinion.
the reason being you can only drive until the gauge says you are dead and thats it, wait a while and you might get to go a bit further, but basically that's it.

i don't see any reason to have some fancy and expensive meter system that calculated amps out vs voltage  etc to illustrate how much battery is left?  not when
the simple volt gauge is going to tell you all you need to know.

one of those golf cart meter, showing full-----half-----empty, is going to tell you when you will be walking or looking for a receptical to plug into.

all one would have to do is put in the gauge, drive it down the road to about half empty, and return back to the starting point, if the gauge then said empty and you got home, all is good

if on the other hand you were a little short of getting home, maybe you mark the gauge with a little nail polish line showing at what point you ought to be thinking of getting home?

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

bob g

Keep It Simple Smarty shall be the reining (in) factor.  Isn't it interesting that I can get one of these clamp multimeters for half the money that many many venders want for just a voltage meter?

Thanks again for your adult supervision.

Casey

Quote from: mobile_bob on October 26, 2012, 04:30:47 PM

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 !

"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

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.

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

Quotewhy 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 (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.

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 (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

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.

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

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

Casey

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

bob g

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!

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.)

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

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+

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

Ian

that is a cool unit!
thanks for the link

bob g

This is a neat unit especially the high current version and water resistant as well.  Amazon has it for $175.

Thanks,

Casey

Nifty.   I wonder if the MPH can be translated to flywheel RPM easily ?

Quotehttp://www.ebikes.ca/drainbrain.shtml

The units can be purchased from their web site $130 USD
speed is calced from wheel diameter so you should be able to work it to tell RPM. I'll have a think about the maths and see how I go ??
I must admit its much more fun then the golf cart gauge I had before.
     

        Ian

I've got this thread bookmarded.  $130 is doable for a operating machine.  "operating"  Yup, four syllables - it's an important word. 

I've already ordered the $28 back-lit multimeter but if my Polaris is going up and down the driveway at Christmas I know what Santa will be bringing me.

Casey

A great thread, thanks Casey.

I'm really happy that Pete posted about the Turnigy bargain unit, it's just what I need to build an inexpensive 12V battery discharge capacity (AH) tester.

I did find some info online about changing the Turnigy meter to an external shunt, though I won't need it for this application.  I want to test the remaining capacity of my 5 year old 110AH AGM battery that supplies my home and shop 12V needs, including running the 10 watt circ pump for my in floor heat. 

Now if I can find a cheapo 12V PV charge controller on ebay to use for a  low voltage load disconnect, I'll be all set and won't have build anything custom. 

Thanks Pete!

i read on the website, iirc that the rpm can be set up to read out
by inputing the wheel diameter to 1666 and setting something else
and then the readout will show a result that is in km/hr, but actually is rpm
if you multiply the screen number by 10.  or something like that.

i breezed through the writeup and i am pretty sure there is a way to set it up
to read out rpm, it just won't say rpm.

or somesuch

pretty neat unit though.

they talk about being able to alter the firmware for a price, maybe if we told them about our forums, and put together a preorder, they would alter the screen info to readout what we need, for a reasonable surcharge per unit?

just a thought

bob g

Bruce,

I've tried many custome circuits and devices for a LVD.

The two best ones I've found are:
1- Battery saver for 12v coolers.
2- Stecca 5 or 10A charge controllers

My biggest beef with them is that they set the LVD at 10.5 volts (under load), which I think is too low.  But they are reliable.  They both let the battery come back to about 11v before reconnecting.  The cooler saver is about $25 in the states (I think I got the last one from Amazon).   The Stecca's are about $25 to $40 here in Uganda; should be about the same in the US.

Thanks Pete.
I've found a 10 amp PV charge controller from China on ebay with an 11 volt LV cutoff. $10 incl. shipping.  I'll be testing with a 50 watt 12V bulb for a load, so that will work fine.