How to monitor battery state of charge

[rfloyd99]

Based on advice I recently got here I upgraded my TT battery setup to two golf cart batteries. I won't be upgrading my converter or any other parts of this system (or adding solar) at this time, although I got lots of good advice on that for later.

My goal is to increase our ability to boondock for a few days here and there on our upcoming six month trip.

One piece of advice I would like to follow is to install a monitor so I can know when to put a charge in the batteries before running them down farther that is prudent.

I've looked on Amazon but don't know enough to decide on a product. (I prefer Amazon, walmart or an auto parts store since we're leaving next week).

Can someone please tell me what I should be looking for as a monitor, and also what readings will indicate that I need to charge up soon?

As always, thanks for the great input available here.

[westend]

I have some larger analog gauges and also, a Victron monitor. The large gauges let me see at a glance what is happening with the electrical systems. The Victron can count amp hours.

[MrWizard]

mount the shunt at BUSS bars ?

make a lexan or plexiglass or circuit board, support under the shunt ?

or flat mount the shunt on top of the battery
but the sensor on the side or on the wall ?

several ways to do this with out cable weight hanging on shunt

[tenbear]

I hard wired a voltmeter and ammeter and mounted them in a convenient location. They tell me all I need to know about the battery state of charge. Cost me under $20 at eBay, and a little time.

[MrWizard]

You need to run wire
You have to run wire to the batteries for voltage sense and amperage
You can't get amperage from the idiot light wiring it has to come from the shunt at the battery, or the shunt built into the meter, which all power in and out has to go thru the shunt to measure amps

[aguablanco]

Harvey51 wrote:
When using the voltmeter remember it just shows the charging voltage when charging and only gradually decreases over a few hours after charging ceases so you cannot find the per cent of full charge for a few hours after any charging. Also, drawing current from the battery decreases its voltage adding another complication to the voltage method. I wasted my first set of batteries relying on the idiot lights which use the voltage method.

This $29 battery monitor always shows the percent of full charge accurately and has positive reviews on this forum. The 25 amp version has worked very well for me for several years. Ebay.com battery monitor

The question I have is, can I hook this meter up using the wiring from the idiot light? That would be simpler for me if it is possible since I wouldn't have to run new wiring to the idiot light panel.
Thanks,
RichH

[MEXICOWANDERER]

ktmfrs

Right On!

Only one single cable per post. Here's why. If a cable to post connection (vulnerable to acid with a flooded battery) goes bad ALL the power is lost and diagnostic work is instantaneous. Go to the battery. With multiple post connections, partial system loss means having to trace out the malfunction.

Locate a cutoff switch and buss bar AWAY from flooded battery fumes. Here's where even MORE 5mm LEDs were used on Quicksilver. Soldered bridges between lugs and the buss bar. Bad connection? The LED lights. I have the L-16 (similar size) Rolls & Surrette batteries and I suspect they are 7% antimony critters. Even with exquisite volt/temp float, they need makeup water every 8-10 weeks (less than 1/2 cup per cell.

That means they gas and from the color darkening of the battery posts and pure lead dipped lugs having anything else near the posts would be a big detriment.

Battery posts are NOT solid lead busses leading down to the grid header on ANY TYPE of battery. The posts are pressure-squashed pin-and-hole assemblies. On Mil-Spec batteries I had to meld molten lead to enjoin post to grid header. Drill, melt antimony bar, with an acetylene plumbers torch. These were military L-Pad post units

[ktmrfs]

MrWizard wrote:
Wireless multimeter dot com

Two videos at bottom of page

Use any external shunt you want 100 amp 500 amp doesn't matter

App has calibration in settings for calibrating the shunt

Has voyage alarm and other settings

my bad, didn't look at the webpage, since the link didn't mention any other shunt options. with the external shunt it I think it would be a very good competitor to a trimetric. easier to install, less expensive, and for many or most applications give all the data one really needs.

If I was installing it, i wouldn't add the external shunt to the battery terminal, rather not have something hanging off the battery terminal, but install it hard mounted.

[MrWizard]

Wireless multimeter dot com

Two videos at bottom of page

Use any external shunt you want 100 amp 500 amp doesn't matter

App has calibration in settings for calibrating the shunt

Has voyage alarm and other settings

[MrWizard]

ktmrfs wrote:

MrWizard wrote:
The shunt goes in the main positive line
So it works just the same as those with a shunt in the main negative line

Small cheap Android tablet
Or your old smart phone
Equal dedicated display
Plug into USB charger adapter, mount it any where you want it

I'm going to keep my 200 amp wired shunt monitor

But I do like this thing

It is a neat idea with IMHO one FATAL flaw. the 30A max on the shunt. How many of us have chargers with a max output current of 30A or less? or solar panels with a max output current exceeding 30A.

The shunt should be 50A minimum.

Did you go to the webpage for full detail

That is the internal shunt
Not the external add on shunt

[doughere]

DiskDoctr wrote:

MrWizard wrote:
https://www.amazon.com/Wireless-Multimeter-Bluetooth-Battery-Monitor/dp/B0184XHL1K

wireless Bluetooth battery monitor, mounts at battery monitor with your smart phone or tablet

How would that work with multiple batteries? One per battery?

2 6 volt in series is one battery. 2 12 volt wired in parallel is one battery.

Multiple batteries isolated from each other would require separate monitors.

Doug

[pianotuna]

I thought most shunts were either 100 or 500 amps?

Just like T2R, I would spend my (limited) dollars on a bigger battery bank, but I would monitor voltage, which can be done for a tiny outlay of cash.

[time2roll]

$130 + shunt.... I would just add two more batteries first.

[ktmrfs]

MrWizard wrote:
The shunt goes in the main positive line
So it works just the same as those with a shunt in the main negative line

Small cheap Android tablet
Or your old smart phone
Equal dedicated display
Plug into USB charger adapter, mount it any where you want it

I'm going to keep my 200 amp wired shunt monitor

But I do like this thing

It is a neat idea with IMHO one FATAL flaw. the 30A max on the shunt. How many of us have chargers with a max output current of 30A or less? or solar panels with a max output current exceeding 30A.

The shunt should be 50A minimum.

[MrWizard]

The shunt goes in the main positive line
So it works just the same as those with a shunt in the main negative line

Small cheap Android tablet
Or your old smart phone
Equal dedicated display
Plug into USB charger adapter, mount it any where you want it

I'm going to keep my 200 amp wired shunt monitor

But I do like this thing