Battery monitor: useful tool or toy?

[Ductape]

Hello all. As we prepare for FT (mostly boondocking) I am working through the 12v upgrades. Got the 600 AH of Lifelines in place. Two banks of 6v pairs; 4 batts in all. Upgraded the converter to 80, probably change out the inverter later to an invert/charge unit as well. Will top it off with solar in the end.

Question I have is an AH monitor e.g. Trimetric seriously useful, or is a voltage check just as accurate (more accurate?) an indicator of SOC? Mainly interested in what will I really need to measure to make decisions on when to fire up the gen vs let the solar fill the bank.

Thanks again. I've spent a lot of my career working with tech but I am learning a lot from you guys.

[MEXICOWANDERER]

Hi westend, I am located 400 meters from the seething tropical Pacific Ocean. Usually around 26C with daytime air temps around 30C.

The salt air eats anything electronic. I've given up on microwave oven magnetrons. After a year, they start to hiss and pop and resemble the sound effects in a 1930's science fiction movie. That's just before they play possum.

I seal the edges of solar panels with hot tar, an unlovely process. But that's the only thing I've ever found that offers more than a temporary solution. The wire junction boxes can be labeled stuffing boxes, full of silicone grease. I smear on Varathane on bare aluminum and painted surfaces - around four coats, I lost track.

Individual cells would be goners in a week or two. It is common to ride in a local car and look between your feet and see a blur of asphalt. Look straight up and see if it's cloudy today.

[CA_Traveler]

All loads and chargers need to draw/charge through the shunt. For most of us the 500A shunt handles all of the loads. But some rigs can use a smaller shunt.

[BFL13]

Trimetric shunt can only go on one battery bank. Doesn't work with a split bank. You can use voltage connection B to read the voltage on another bank but no AH etc. Very frustrating if you want to run split banks so you can fill one while using the other and then switch around.

[Ductape]

OK, you guys convinced me. So should I go Trimetric or...

And should the generator starter run through the shunt? I prefer to install it that way: all the loads off 1 buss and the 2 battery banks connected to the bus with isolation switches. Planning on separate switching for solar so I can run on bank A while solar tops off B.

Should the shunt be sized for starter current or are transient OC alright?

[Snowman9000]

Well, they said the meter won't go to 200A, so I'd need the whole assembly. He did say he'd give me a price break if I want to go that way. I'll measure the genset cranking and decide if A) I can include it in the measured circuit, and B) do I care. The bigger the shunt, the bigger the measuring error on smaller readings.

An edit to an earlier post:
The meter can save all configuration settings. What it won't save is battery state of charge. Which sort of makes sense anyway. I think it is going to work just fine; I'll write a review on it at some point once it is installed.

[CA_Traveler]

Shunts have a voltage drop and any attached equipment has to be configured for the voltage. The Trimetric 2025 supports shunts 500/50mv with a 0.1V display and 100/100mv with a 0.01V display. Other shunts with the same voltage drop would work OK.

[Snowman9000]

jrnymn7 wrote:
Snowman, the shunt was my concern with that ebay meter you bought. I forget what the determining factor is, but I know I needed the 500 amper, with my 430Ah bank and 1000w inverter.

http://www.bestconverter.com/500-amp50mv-Shunt_p_96.html#.VFRODmewX1k

I don't know why I didn't buy the 5-40V, 200A version. Well, yes I do, originally I was just planning to monitor solar charging, and I wanted a shunt big enough to accept good sized ring terminals. So that is why I bought the one I did. Then I realized that other than (maybe) genset starting, which does not have to go through the shunt anyway, I could monitor everything with this one. Mission creep. 🙂

It appears I could buy their $10, 200A shunt and use it with my meter. I will write them and see.

[westend]

I have a solar controller with software that monitors more than I need to know. I also have a Victron monitor and an analog gauge. If I put a mark on the gauge or bought one with an adjustable range bar, I'd bet I would get pretty close knowing SOC/DOD just with voltage.
The Victron makes it too easy, just press a button and all of the info is there. I have the single bank monitor but Victron also sells one that will monitor voltage on a second bank. It is easier to install this device than installing a lamp fixture. The shunt, wire, and different mounting accessories are included. It is smallish and is backlit blue.

The Morningstar controller software can act as a monitor, too. You can create graphs and observe all current electrical, compare to find seasonal differences, yada. The downside is that a laptop/notebook/panel has to remain in use and powered if a user wishes to "stare and compare". If panel prices keep dropping, that might be a nice alternative for some systems. I could see having the panel communicate over wireless with the charging/battery system and be able to grab the panel for other use, as well.

Mex,
How is the available labor situation around your labratorio down there? Individual solar cells are still cheap. You can get all the other bits and pieces on E Bay. Maybe someone close by wants to learn to solder?

[MEXICOWANDERER]

Oh sheeze, at 4.17 eqvt/gallon for diesel I don't need a timer, my teeth chatter with nervousness when that thing is running. At 3,019 teeth clacks I run up the hill and switch it off.

Wish the solar fairy would come visit and leave me a stack of panels. Enough to plaster atop the generator battery shed. But enough panels to feed 3 Torrey 2 meter freezers + one Viking would be quite a load - the fairy would have to be a female Schwarzenegger model with turbo.

[NinerBikes]

MEXICOWANDERER wrote:
I wish I had that gift...

:h

Oh hush, now! You have a smart phone, why haven't you created a battery charging algorithm Application already for it, or found one on Google PlayStore yet? Believe me, it's out there, someone has thought of it. Set a timer on your phone, so you know when to shut the Kubota off.

[Bend]

jrnymn7 wrote:
Snowman, the shunt was my concern with that ebay meter you bought. I forget what the determining factor is, but I know I needed the 500 amper, with my 430Ah bank and 1000w inverter.

http://www.bestconverter.com/500-amp50mv-Shunt_p_96.html#.VFRODmewX1k

From Bogart:

- 500A/50 mV SH-500-50; Maximum recommended continuous current: 410 Amps. Meter current resolution is 0.1 amp. Size: 3-1/4 x 1-3/4 x 1-7/8 in.; 8.25 x 4.5 x 4.75 cm.

100A/100mV SH-100-100 Maximum recommended continuous current: 70 Amps. Meter current resolution is 0.01 amp. Size: 2 x 1-3/16 x 1-3/4 in.; 4.8 x 3 x 4.3 cm.

- 1000A/100mV SH-1000-100 Maximum recommended continuous current 650 Amps. Meter current resolution is 0.1 amp. Size: 7-3/4 x 2-1/2 x 1-1/8 in.; 19.7 x 6.3 x 2.8 cm.

More info:
http://bogartengineering.com/sites/default/files/docs/SHUNTInfo2.pdf

BFL13 wrote:
...
It is true you can get by without a monitor, but once you have one, you would not like to go back 🙂
...

+1

[jrnymn7]

Snowman, the shunt was my concern with that ebay meter you bought. I forget what the determining factor is, but I know I needed the 500 amper, with my 430Ah bank and 1000w inverter.

http://www.bestconverter.com/500-amp50mv-Shunt_p_96.html#.VFRODmewX1k

[Snowman9000]

I did a little playing tonight with that elite.element combo meter. It seems like it can be a poor man's Trimetric. From what I can tell, you can set the battery AH capacity, or any reference number you want as a substitute. Like say 50% of your AH capacity. And you can tell it how full you are now for AH in percentage terms. From that point on it will track net AH in and out, and tell you where you are in AH storage and percentage. No Peukert compensation though. At some point you'd have to guesstimate and reset your numbers.

Unfortunately it appears it loses those settings if you disconnect it from power. But, you can leave it connected and blank the display with one press of a button. I will install it on the battery side of the disconnect switch, and will have an on-off switch so I can turn it off if need be.
====
EDIT to add: The meter can save all configuration settings. What it won't save is battery state of charge. Which sort of makes sense anyway.
====

The shunt is only 100A, so no good for those with bigger inverters. Maybe not even enough for a genset starting? Not sure. I think they sell a 200A version too.

Anyway, it's another ebay-China hobby project type of thing. If it works half- decent it should be useful to me.

[BFL13]

I use the Trimetric as a voltmeter, ammeter, and AH counter that I can reset. (That reset is very important.) I especially like to compare voltage with AH count as a cross-check of "reasonableness" wrt each other.

Using the voltmeter in between the furnace being on (lights and fans off) is close enough to "resting" to get an estimate of SOC using the usual guides like Trojan's 50% is 12.1v. Ignore advice that this is not "correct"--it is "close enough" while camping.

If you have solar, take this "morning voltage" before the solar "wake-up" time. After that the solar charging increases the voltage.

Unfortunately the Trimetric is very expensive and it appears you can get the same info from gizmos on eBay costing a fraction of what the Tri costs.

It is true you can get by without a monitor, but once you have one, you would not like to go back 🙂

BTW the monitor that goes with a solar controller is a waste of money since you can't make any use of its info. It only shows the AH the solar did, not the AH your battery bank saw. (Solar can run loads besides charge the batteries, so the solar AH count is not the same as the "real" AH count.)