What is my Trimetric telling me?

[DonC]

Now that I have one of these cool little tools I need to figure out what it is telling me.

On my trip to Death Valley last week, with my new 300w of solar, I was at a full 4 of the dummy lights at all times. Checking my Trimetric I was never below 12.4v in the am, and usually 12.8v or higher by 10 am.

A few times I would also check the "% battery full" and this is my question - I jotted a few combinations down:

13.0v and 95% full
13.0v and 76% full
12.8 and 90% full
13.2 and 80% full

So, same voltage but less % full. Or a lower voltage but higher % full than a higher voltage.

What does it all mean?

 

[RC Pilot Jim]

Hmmm did you call Bogart Engineering and ask them about the descrpancy?

 

[Platano]

Now that I have one of these cool little tools I need to figure out what it is telling me.

On my trip to Death Valley last week, with my new 300w of solar, I was at a full 4 of the dummy lights at all times. Checking my Trimetric I was never below 12.4v in the am, and usually 12.8v or higher by 10 am.

A few times I would also check the "% battery full" and this is my question - I jotted a few combinations down:

13.0v and 95% full
13.0v and 76% full
12.8 and 90% full
13.2 and 80% full

So, same voltage but less % full. Or a lower voltage but higher % full than a higher voltage.

What does it all mean?

Your voltage is going to be highly variable depending upon the level of power you are drawing from the battery or putting into it. The percentage full is really an indication of the amp-hour capacity. That is, how much energy is in the battery. Battery capacity is measured in amp-hours while voltage is simply a measure of electrical potential. The Trimetric monitors how many amp-hours are put into the battery and how many are removed and should be programmed to know what the capacity of the battery is. Important points to remember:
1. Voltage is a measure of electrical potential (how readily the electrons want to flow if given a chance)
2. Amps is a measure of the rate of electrical current. (How many electrons past a given point per second)
3. Amp-hours is a measure of quantity or amount of charge in the battery. (Thus if you have 1 amp for 5 hours you have 5 amp-hours stored. Likewise, 5 amps for 1 hour will also give you the same amount or 5 amp-hours).

In your example, you may have drawn 20% of your amp-hours from the battery (i.e. 80% Full), but the solar may be actively charging which would raise the system voltage. Likewise, you may be 90% full, but actively discharging through various loads so the voltage would read somewhat lower.
Hope this makes some sense. Overall, those numbers look awesome and I can't imagine that 300w (watts too are a rate of power) can't keep up with the needs of an FWC. As long as you are getting back to 90%+ by day's end your golden.

 

[DrJ]

Don,
Platano is making some great points.

Here is something simple to do next time to help you out.
Measure the voltage, amps and percentage of charge on your next trip. Check and record them 3-4 times a day if you want. All 3 of them help you understand what's going on. They all tell you something slightly different.

I've noted similar readings many times with mine. It has to do with all of the energy coming in and coming out of your batteries. Solar in, fridge and heater and lights draw power out of your batteries.

If you are charging up to 90% or more everyday than your system is working great and you should keep plenty of ice cream in the freezer!

If you post your results here again, I'm sure it will be helpful to others and we can interpret them for you.

 

[DonC]

Platano - that was helpful. On all but one cloudy day I was back to 95 - 100% full by the end of the day.

Without something like a Trimetric I now see that there are situations where you can have 4 lights but be at 75% full, and not know it, and think you are in better condition than you are.

With my new 300W I'm not too worried about it anymore, but I will continue to watch it my next few trips so I learn what cloudy/sunny days and sitting/driving days do to my system.

 

[Hobart78]

I have the trimetric and Bogarts SC-2030 solar charger to manage the two 100 watt solar panels on my Hawk. I spoke with a Bogart rep yesterday about programming of the trimetric, I used the values in table 4 of the users manual for the SC-2030 and wanted to discuss that. He recommended one change to the P2 setting from 0.5% to 1.0%. I still need to connect the negative wires from other loads refrigerator, furnace etc. to the shunt. Finding it difficult to access those wires at the buss bar located in back of the cabinet. In Portland/Vancouver area for the next couple of weeks. I get excited when we get sun here so I can check on the solar.

 

[esimmers]

Platano discusses the key lesson here: Voltage is not usually an accurate measure of battery "fullness".

"Resting voltage" is about the only time a voltage reading can give you an accurate assessment of state-of-charge.. That means the battery disconnected from charge or load for several hours (some would say at least overnight, but the longer, the better). To use voltage as an accurate indicator of state-of-charge you can't have had a charge or load on it for several hours. That's why a voltage reading is usually only a very rough estimate of battery state-of-charge; who wants to leave their battery disconnected from load or charge for hours on end?

Here's an experiment. Some night when there's no solar or shore power charging going on, and no load on the battery, note the battery voltage on the TriMetric. Then turn on several loads (lights, pump, whatever you have). Note how the voltage drops more and more immediately on each device being turned on. Then turn all the loads off. Note how the voltage jumps back up to what it was originally before you turned the loads on (or jumps up back close to the original voltage, depending on how long you ran those loads).

The same thing happens with charging. The charger may put out 13+ volts which would be shown on the TriMetric. But as soon as the charger is disconnected, the voltage reading will drop down to reflect battery-only voltage.

That's the beauty of the TriMetric and its battery-percentage display when set up properly. The device doesn't rely solely on voltage to determine state-of-charge but also keeps track of amp-hours in and out, essential measurements if you want to know accurate state-of-charge while the battery's in use.

This is also why the "dummy lights" are only a rough measure of state of charge; they measure voltage only and are subject to the errors discussed here in this thread.

Good questions, though. The TriMetric takes careful initial calibration and interpretation, but its accuracy is worth the cost and effort to learn how to use it.

 

[ntsqd]

Hobart,
As long as the shunt is between the battery and every ground wire (no matter how they branch or are connected to each other) then you're golden.
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The way that I think of electricity is like plumbing. Voltage is your "water pressure", Current (Amps) is how much water is flowing out of the faucet or what-ever. 5 amp-hours is roughly analogous to 5 gals per minute.
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An issue that will eventually come to the surface is battery aging vs. the programmed settings in the TriMetric. As they age batteries don't hold as much as they did when new. So when you notice that it doesn't matter what you do, you can't get the system above XX% SoC, it's probably the battery(ies) and not what you're doing or not doing.