Best amp-hour battery monitor?

[synovialbasher]

Hi,

I'm looking into getting a decent battery monitor for my 125 watt, 286 ah system. I've been looking at a few and I'd like to hear what the experts think.

Currently,  I'm looking at the Trimetric meters, the Xantrex LinkLite, and the Victron BMV 600. Has anyone used these? I've considered the pentametric too, but the price for a computer hookup seems a little out there.

I really appreciate all your opinions!

Joe

[Frank S]

You didn't mention what your charging energy source was Solar PV,  wind,  hydro or whatever

But the general concision around here would probably be the Doc Watson
Key Features of "Watt's Up" Mini Power Analyzer:
Measures energy (Wh), charge (Ah), power (W), current (A) and voltage (V) for any rechargeable battery pack from 4 - 60V, including NiCd, NiMH , and SLA, and Li-Ion battery packs
Connector to use a receiver battery for measurement down to 0 V
Captures current peaks and voltage minimums(droops)
Accurate & precise - 0.01 A current and 0.01 V voltage resolutions
Rugged - handles 50 A continuous and 100 A peak at 60 V
14 ga., 7 x 37 stranded, high temp silicone rubber insulated wire without connectors
Small & Light: 2.8" long x 1.7" wide x 0.83" thick (70 mm x 44 mm x 21 mm), 2.5 oz.
Acts like a wire so doesn't affect model's performance. Precision current sensing resistor, with only 0.001 Ohm resistance and circuitry only draws 0.007 Amps
Uses DSP to increase ADC resolution and differential measurement amplifiers to increase noise immunity
Factory calibration stores constants in EEPROM to compensate for component tolerances
One Year Warranty
Complete User Manual


Specifications:
Voltage 0-60 V, resolution 0.01 V. That's a 14 cell series li-poly pack!
Current 0-100 A peak, 50 A continuous, resolution 0.01 A
Charge 0-65 Ah, resolution 0.001 Ah. That's ~32 Amps for two hours!
Power 0-6500 W, resolution 0.1 W. That's ~8.7 Horsepower!
Energy 0-6500 Wh, resolution 0.1 Wh. That's lifting a 50 pound model into outer space (65 mi.)!
Operates from 4.0-60 V, 0 V with optional receiver battery pack
16 x 2 STN LCD display
Powerful, 8 MIPS micro-controlle
Color: Electric Blue


Applications - Specially designed for RC Battery Packs to help you:
Set speed control cutoff voltages and currents
Tune performance by comparing different setups of propeller, motor, gearing, speed control and battery
Measure a full battery charge and compare to spec when charger claims done
Check peak currents are safe for battery, speed control, motor, wiring and connectors
Predict airplane flight time based on ACTUAL conditions in your model
Check battery capacity and health and whether battery should be retired
Verify that the minimum voltage under load is within specifications
Check for wiring and connector power losses.
Fine-tuning your electric RC cars & planes for great performance doesn't have to be a guessing game
Measure power and energy consumption of ANY device with a rechargeable battery pack, such as:
Airsoft gun battery pack
Bike lighting battery pack
E-bike and Scooter battery pack
Combine the power analyzer together with our 2.4V - 7.2V, 7.2V - 12V, 24V NiMH universal smart chargers, and with 3.6V - 14.8V Li-Ion battery charger It is perfect tool to monitor battery pack's performance

[synovialbasher]

You didn't mention what your charging energy source was Solar PV,  wind,  hydro or whatever

Sorry, forgot to mention that. It's solar pv.

I've looked at the watt's up meter and the only complaint I have with it is that it doesn't tell you how full your batteries are. It's a great little tool and I might end up buying one for other stuff... But I was looking into a more programmable and complex analisys compared to the watts up.

Thanks, though!

[DamonHD]

Knowing how fill your batteries actually are seems to be much harder than you'd imagine.

For my very low current loads, battery voltage is a reasonable indication.

Rgds

Damon

[synovialbasher]

Currently, I'm using the voltage, but from what I understand this isn't a very accurate measurement at all. Batteries get surface charge phenomenom, where they appear more full because the voltage is driven up by the charging source.

I wanted a battery meter to really see how far down I discharge my batteries each night. Every morning I find them between 12.4 and 12.8 volts, but I wouldn't mind a little more data. If I can squeeze even more power out, that's even better.

[DamonHD]

Yes, I agree, surface charge issues do reduce accuracy, but I don't think any method of determining SoC is completely reliable.  Eg, you can count Ah in and out and allow for losses and temperature and day-of-week, and still not be quite right.

I have been experimenting with noting the voltage at midnight to catch it near its lowest (since mine is solar-charged), but still the surface charge issue is there unless there is a large enough cumulative load.

Rgds

Damon

[bob g]

another problem with using voltage as an indicator of state of charge
relates to the loss of capacity due to sulfation

as the sulfation starts to harden and crystallize more and more active plate material is taken out of play, so as the effect gets worse, you have less and less capacity left, and even though the remaining active material will charge up and show nearly fully charged the battery is dieing a bit at a time.

what would be nice is some sort of electronic specific gravity sensor, something that could be fitted in the fill cap and down into the electrolyte.

i have often wondered if one could devise such a unit, such as the "green" eye thing used by delco and others on car batteries over the years. instead of a green float ball, maybe some reflective or magnetic
float that could set off either a phototransistor or hall effect sensor when the specific gravity reached a certain level.

in my mind the only true indication of state of charge is the specific gravity of the cell in question.

i think voltage could be used in a relative way, however over time there would be a shift that would need to be accounted for, so maybe an alternative method would be the use of a microcontroller and coding so that one could periodically adjust the code to compensate for shift in specific gravity, which would be checked periodically with a handheld hydrometer.

so maybe you test with a hydrometer to assure that the battery is fully recharged periodically, and then use voltage measurements for state of charge between those periodic specific gravity tests?

the need to remove the surface charge could be accomplished via the controller applying a specific load for a predetermined amount of time prior to a voltage test? that way the test could be the same every time, and at the same time of day or night every time?

other than that, i have considered the use of a kw/hr meter, one of the electronic versions as used for residential use.  they are programmable and be set to read out watt/hrs and calibrated to whatever one wants... for instance,  if we adjust the calibration to account for inverter efficiency, battery charge efficiency, and any other aspect, we can then have a reading that would indicate fairly closely how many watt/hrs of power we have removed from the batteries and therefore what needs to go back into them.  this of course would not be perfect either, but probably a better indicator than by simply using voltage as an indicator of state of charge?

bob g

[DamonHD]

Testing SG ain't viable for SLAs such as my gel batteries of course.

You might be able to be a bit smarter with a computer in the loop and the luxury of time, eg looking at my graph over 1-month plus you can see the lack of spikes and the trough depths in periods of poor sunshine:



When I see the voltage sagging too much overnight and on a downward trend I intervene manually (moving loads off the battery, connecting more panels, etc) as well as automatic regulation based on voltage (my loads stop doing non-essential things below certain thresholds).

Rgds

Damon

[hydrosun]

I've installed many trimetric meters for people. The trick is to not rely on one number to monitor the battery bank. The % full gives a broad indication of how full the battery is but doesn't tell you if sulfation is cutting into the capacity of the battery. Battery voltage and amperage going in or out  will give you more clues at what is going on in your battery. Using a hydrometer will tell you how well you have charged up the battery and if individual cells are failing. So you need to cross check with different tools to manage the battery bank for longest life.
Chris

[synovialbasher]

I've installed many trimetric meters for people. The trick is to not rely on one number to monitor the battery bank. The % full gives a broad indication of how full the battery is but doesn't tell you if sulfation is cutting into the capacity of the battery. Battery voltage and amperage going in or out  will give you more clues at what is going on in your battery. Using a hydrometer will tell you how well you have charged up the battery and if individual cells are failing. So you need to cross check with different tools to manage the battery bank for longest life.
Chris

Thank you! I'm really looking for what you described. I just want a relative number on how full the batteries are at any given time. I've heard a lot about the trimetrics and they seem pretty good. Has anyone tried the serial input on the 2025A units to try and connect these to your PC? I can't find much information about it, and if someone's been able to log this data I'd love to hear how its done!

Bob G., I think you're right on with an electronic hydrometer meter idea. It's by far the most accurate. Maybe a good entrepeneur idea??? I'd buy one in a heartbeat if they were available.