Monitoring percentage of charge (Solar - alternator) on Trimetric

[iowahiker]

Jim, You may have a difference in definition concerning the meaning of "full charge". 12.5 divided by 12.9 is 97% absolute but 12.5 volts is not 97 percent of the "working" battery capacity. 10 volts would permanently damage the battery at an absolute percentage of 77.5 (10 divided by 12.9 volts). A meter reading of 73% at 12.5 volts indicates a "working" range of (12.9-12.5)/(1.0-0.73) or 1.5 volts. 100% charge at 12.9 and full "working" discharge at 11.4 volts. Batteries should not be discharged below 50% of the working range (not 50% absolute) or 0.75 volts below maximum or 12.15 volts (12.9-0.75). I am not saying these numbers are correct only the meter is measuring "working" range percentage and the numbers you posted produce this working range. Full disclosure: I am not an expert in anything said here but I am very good with numbers, please feel free to correct me.

Edit: If you get very good with these numbers, you will find some shifting of the "working" range calculated from the voltages because the "working" range varies with temperature which "smart" meters measure.

2nd Edit: I have always thought the batteries "natural" self discharge rate was reported in terms of absolute percentage (not "working") while the maximum battery usage of 50% is in "working" so there is some mixing of apples and oranges.

3rd Edit: (obviously I have too much free time) AGM battery self-discharge rates can be between 1 and 3 absolute percent per month depending on battery temperature. Warmer batteries self-discharge faster. Worst case: 0.03 x 12.9 full volts / 1.5 working volt range = 26% decline per month in the "working" range or a "working" charge remaining of 74% after one month. (full disclosure, I am still not an expert but I can toss out a lot of numbers)

 

[DrJ]

Jim,

Thanks for keeping us updated on your trimetric readings. I have noticed that the voltage does not always relate to the percentage of charge left in the batteries. Lots of us have volt meters that give you a general sense of battery capacity, but noting is as helpful to know how much "juice" you have left as a shunt with a correctly adjusted meter. This measures exactly how many amps are passing through the battery and therefore an accurate accounting of the status of the battery.

Voltage can be accurate if it "load tested". This means that a certain amount of load (draw or power use) is placed on a battery for a certain amount of time. They sell load testers that you can do this exact thing. In our campers the trimetric battery monitor is more useful because it provides so much more information. I learned a ton about how batteries operate just watching that monitor.

As a side note, I have a second monitor on my camper right now - BM PRO Battery Check. It is a bluetooth monitor that hooks up very simply and then sends data to your cell phone. I am testing it along side the Trimetric and will give you an idea on my data as I am finishing up. It looks like a neat idea that may be the trimetric alternative for some people who don't want to run wires.

 

[RC Pilot Jim]

PV - just the screen display was turned off. I did not disconnect Trimetric from the battery.
Thanks for the comment about having to re-program the meter after disconnecting the battery. It makes sense, though.

Iowa - Thanks for your input. As a non-engineer I always struggle with understanding what I'm looking at. That is reason the WTW forum is so helpful to all of us.

Dr. J - Thanks for your comments also. BM-Pro sounds interesting especially since the wife and I broke down and joined the 21st century by upgrading our dumb phones to iPhones just recently. Wonder if they will work with the BM Pro?

 

[RC Pilot Jim]

Moved this update from "Measured FWC amp usage" to this one - subject "monitoring amp usage with Trimetric"

For those of you that don't have a battery monitor wanted to share the following test.

As most of you know our 100 watt Flex panel died and is now off the roof. Its replacement a Renogy 150 watt Rigid is in testing mode while I await the delivery of "3M 4950 VHB tape".

I turned on the Engle fridge Friday afternoon about 3pm, This morning the voltage reads 12.2. The Trimetric battery reading is 63%.
."Engle" fridge pretty efficient after 60 hours no charging.

The point though is if I don't have a solar panel on the roof and just run the engine for an hour without the Trimetric I will know the voltage reading NOT the percentage of full the battery reached.

When the sun gets a little higher I will connect the panel (after first turning off the fridge). After connecting I will turn it back on,

And report the time it took to charge battery back to 100%

 

[Happyjax]

I read all of the solar, charging.... threads with great interest as I plan to do my own when the time comes. I am curious about the statement that 12.9V is a full charge. Am I misunderstanding something as I thought full charge on a 12V batt was 13.6V... I'm sure it's my confusion but would appreciate clarification. I feel a bit lost

 

[DesertDave]

If you disconnect a battery from draw and charging and let it settle for say, 24 hours, to eliminate any 'surface charge', then measure the voltage, that voltage may well tell you something about the state of charge. That's where a 12.9V reading could indicate a fully-charged battery.

Many chargers use a charging voltage of 13.6 as a 'float charge', as a means to keep a fully-charged battery at full charge.

In my personal example, my battery bank shows either 12.9 V or 13.0 v after sitting for several days without charging or discharge.

Most of the times when people quote a voltage reading on this forum, they have taken the reading while there is some form of charge or discharge occurring.

 

[RC Pilot Jim]

Yesterday I started my test. Panel flat on ground plugged into 50 feet ( resistance?) of 12-2 cable plugged into back wall of camper. Camper in carport. When mounted on roof I estimate the run at 18 feet of 12-2 cable soldered at the connector.

Time % Full Volts Amps Load/No Load Panel Location Estmated Sun Angle

8:45 am 62 12.2 2.7 NO Flat 40* winter

9:45 am 67 13.0 4.0 No " 50*
9:50 am 68 13.0 4.9 net YES " 50* Fridge cycle on


10:35 am 71 13.1 5.8 net Yes " 60* Fridge cycle on
10:35 am 71 13.1 5.1 NO " 60*

11:30 am 75 13.4 5.5 No " 70*

At this point I tilted the panel into the sun for a couple of minutes .....WOW...Then back to Flat.

11:30 am 75 13.7 9.1 NO Load 70*

12:30 am 80 13.5 5.6 NO panel Flat 90*

By 1:00 pm 82 13.6 5.3 NO " 90*

Sun was over the high point and panel was in the shade so stopped the test

 

[DavidO]

Jim it looks like you have found one of the best reasons many of us carry portable panels. Placing a panel to point directly towards the sun GREATLY increases it's charging ability. This not only helps in the winter when the sun is lower but whenever we deploy our portable panels. I find I get great charging early in the morning and also late in the afternoon. These are the times that I'm set up and in camp. Coffee in the morning with the Trimetric showing that I am charging at 9 Amps is always a great way to start the morning.

Having a meter that let me KNOW what is going on with my electric system has added greatly to my enjoyment of camping in my hawk. I don't wonder or worry. It did make me upgrade my roof from a factory 95 watt panel to a 160 watt panel.

Enjoy your new 150 panel I can see that you have been enjoying your Trimetric as much as I do.

As you noted earlier your readings sometimes will jump from 95% to 100% in a minute, this happens with mine also. Any charging above around 92% is a blessing. An already full battery is hard to add more amps to. I think of it like packing a suitcase and having to sit on it to close it. If take your battery to 92% then turn everything off and let it rest for 24 hours your voltage will show you are fully charged (12.9V or 13V depending on your battery type and age.)

 

[RC Pilot Jim]

Thanks David. Hopefully more folks will add a battery monitor to their rigs. We still carry a 60 watt rigid portable for shade camping. Tilted into the sun it produces 3.6 amps enough for my system.

I mounted the new panel Wednesday, Feb 3rd. Pics and charging test on page 12 of the "Eagle amateur Build Post"
Click on the link under my signature.

Happy camping to you.

 

[RC Pilot Jim]

We just returned from a 10 day trip to Saline Valley, covering 730 miles - 116 bad off road driving.

Click on my link below my signature. Go to page 12 "((Eagle) shell amateur build" to review the information.

 

[RC Pilot Jim]

Been running the Engle fridge last several days to check the new 150 watt rigid panel output.

Today at 12 noon the battery was down to 84% (truck under carport last day and one-half). Moved truck out front into sun (yes we have sun and 79* today -yesterday it was 85*) then checked the Trimetric after about 5 minutes.

Amperage in " 7 amps " fridge off. Waited a few minutes - fridge cycled on (draws 2.5 amps running). charging amperage dropped to 4.6.- Wow.

Second check 12:45 pm - Volts: 13.7, Amps in 5.2 (fridge not cycling) Percent of full 90%. When fridge cycled (2,5 amp draw) amps in dropped to 4.0 .

Hmm re-read that third paragraph. I meant " WOW ". ..fridge running and panel is delivering 4.6 amps to the battery

 

[craig333]

Ummm, not so sure I want my phone knowing whats going on. I can see myself getting carried away checking my charge condition at every opportunity

One of these days I'll upgrade to a trimetric. I was surprised to see myself getting a 13v reading under my carport. I didn't check the amperage, I assume it wasn't much but to get anything under the carport was a surprise.

 

[Casa Escarlata Robles Too]

Question?
My 105W system,now battery 14+v,full.
Watt meter 9.22ah solar output 10.0+/-w.
No load on battery.As normal solar gain going to truck battery.
Is this OK?
Frank

 

[RC Pilot Jim]

Craig, that is the fun of spending $250.00 plus. One can now monitor (and worry about) whether the system is working properly

Frank, not clear on what you are saying. Did you say solar amps are going to your truck battery not your camper battery?

If you are going to the factory rally in April look me up. I will be in site # 8 where the party is located. I would love to see your set up.

OOOOOPS sorry Frank...I re-read your signature and realized you have an ATC "Bobcat" ...You guys need to have your own rallies...Lots of fun for all owners.

 

[Casa Escarlata Robles Too]

When there is enough sun shining on the panels my battery "isolator"will charge both camper and truck battery.
Frank

 

[RC Pilot Jim]

That because you have the magical "isolator " from ATC.
Heard its better than "Sure Power" because it will charge both batteries.

 

[Casa Escarlata Robles Too]

That because you have the magical "isolator " from ATC.
Heard its better than "Sure Power" because it will charge both batteries.

And it doesn't get hot.Works great for a rig that sits a lot of the time.
I don't need to start the truck every week or so.
Two fully charged batteries,can't beat that.
Frank