Battery Charge Level Indicator (BCLI)

[LowGear]

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

[Jens]

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 All charge or discharge current is monitored and you can get indication of voltage, current, total current withdrawn from the bank and estimated time before battery is depleted at the current draw level.

[LowGear]

Like this one?

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

[mobile_bob]

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

[LowGear]

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

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

Casey

[BruceM]

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.

[LowGear]

I found these:

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

[Tom Reed]

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.

[BruceM]

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.

[mike90045]

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.

[LowGear]

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

Thanks again,

Casey

[LowGear]

Incredible Brain Flash

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

[BruceM]

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.

[mobile_bob]

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

[LowGear]

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