Poor Man's Trimetric?

[BFL13]

I want a cheap sort of 12v battery monitor that can measure at least 100a and keep track of AH. Need some advice here on whether these possibles are any good in the first place, and then about the actual AH counting. I see some of these have a limit on how high they count AH before resetting. I need say 300AH range to show on the minus side as battery bank gets drawn down. Some have AH reset buttons like the Tri.

This one does KWH it seems? Is there a math conversion to AH I can apply?


http://www.ebay.ca/itm/DC-100A-LCD-Voltage-Current-KWh-Watt-Car-Battery-Panel-Power-Monitor-Combo-Me...

Or for more money, this one says it does AH.

http://www.ebay.ca/itm/DC-120V-100A-Volt-Current-Ah-Power-Combo-Meter-Charge-Discharge-Battery-Monit...

I have looked at swapping my Tri back and forth between 5er and TC as needed, but is a total PITA. I could ease that by getting just another Tri shunt and some wire and just swap the display unit, but that costs as much as the ebay gizmos. (But at least I would know the Tri does what I want for sure)

Has anyone tried out these sort of monitors or can suggest a better one something like the above two for under $50? (I don't want to build one like Mex would out of a bunch of $1.49 bits and pieces!)

Thanks for any help on this. I don't know how to tell for sure if these or similar are any good or do what I want.

[Harvey51]

I have the one in the first post, second link, only mine is the 25 amp version.
It has served well for a whole year now. I don't know how accurate the amp readings are but I'm pleasantly surprised that the amp hour tracking is so good I have never needed to reset it - it reads the 188 amp hours I set as the battery capacity when I start a trip fully charged - and comes right back to 188 after we get home and the solar panel tops up for a day or two.

Come to think about it, charge is not lost as easily as energy. I wouldn't buy the one that measures KWH's because you would have to put more KWHs into a battery than you took out to recharge it because you take out energy at a lower voltage than you must charge with. If it really measures energy (volts x amps x seconds) rather than charge it would be a poor indicator of state of charge.

My complaint was that the wire terminals on the device are too small - I could use only 14 gauge wires. Hopefully the higher amperage model has heavier connectors.

[MrWizard]

MrWizard wrote:
i use a Turnigy RC power meter to measure watts , watt hrs, amp hrs, peak watt, peak amps

its in between the solar charge controller and the batteries

its rated for a peak of 130amps, but that is short time RC motor load
not microwave baking a potato or 200amp charger

its good as long as continuous load/charge is less than 65 amps

and it only measures one way

so you need two if you want to read power use and power charge
it does not do add & subtract "tally" tracking

oops !!!

[MrWizard]

i use a Turnigy RC power meter to measure watts , watt hrs, amp hrs, peak watt, peak amps

its in between the solar charge controller and the batteries

its rated for a peak of 130amps, but that is short time RC motor load
not microwave baking a potato or 200amp charger

its good as long as continuous load is less than 65 amps

[MEXICOWANDERER]

Thissun'll take you right down to the natzass...


http://www.aayushienterprises.com/images/Products/Rishabh/digital-panel-meter/pdf/13.pdf


Flavored with Curry not Soy Sauce

[BFL13]

landyacht318 wrote:
That ammeter your linked only reads Loads or sources, not both at once. It will read Zero amps on a 100 amp load when it is wired to read charging amperage.

Actually twisting the voltage and Amperage calibration pots was quite difficult as any pressure on the mini pots skewed the readings for a couple seconds after one removed all pressure from it, and while they appear to be phillips head, I had to use a very small flat heat in one of the 4 crosses to turn them.

Sorry to be a negative Nancy.

Shirley you aren't a Nancy.

So I will have to choose or get two! My priority by far is the battery charging amps. Thanks for the warning on that.

We'll see how it works out. Lives don't depend on the results, but it would be nice if it actually does what I want.

[landyacht318]

That ammeter your linked only reads Loads or sources, not both at once. It will read Zero amps on a 100 amp load when it is wired to read charging amperage.

Actually twisting the voltage and Amperage calibration pots was quite difficult as any pressure on the mini pots skewed the readings for a couple seconds after one removed all pressure from it, and while they appear to be phillips head, I had to use a very small flat heat in one of the 4 crosses to turn them.

Sorry to be a negative Nancy.

[BFL13]

landyacht318 wrote:
we posted only 3 minutes apart so I do not know if you saw my post.

But what you decided on is the 200 amp version of the 100 amp version I employed and found to be inaccurate at low currents. I'd have to assume the 200 amp version is even more so at low currents.

I was never able to get it calibrated so it would read both 38 and 1.5 amps accurately, in fact anything under 1.5 amps could not be calibrated correctly. It would read 0.0 amps when 0.78 amps were still flowing.

That 9 dollar meter might cause 100$ worth of headaches.

Real amps accuracy doesn't matter for my purpose and the amps will not be making up an AH count so they don't matter for an accurate count there. I will check the accuracy against the usual amps I have seen on the Tri for various things to make sure it is in the ball park though. The voltage is cross-checked with other voltmeters so I will know if it reads high or low and by how much.

I just want the ammeter for when battery charging at 100a or so to make sure the charger(s) are running properly at start up, and to see when amps are tapering to my target for turning off the generator. Eg 5 amps per battery is approx. 90% SOC, so at 20 amps with the four 6s.

Also I look at the amps to see that the inverter is behaving right when I turn on the microwave or something.

[landyacht318]

we posted only 3 minutes apart so I do not know if you saw my post.

But what you decided on is the 200 amp version of the 100 amp version I employed and found to be inaccurate at low currents. I'd have to assume the 200 amp version is even more so at low currents.

I was never able to get it calibrated so it would read both 38 and 1.5 amps accurately, in fact anything under 1.5 amps could not be calibrated correctly. It would read 0.0 amps when 0.78 amps were still flowing.

That 9 dollar meter might cause 100$ worth of headaches.

[BFL13]

I decided to save my brain from all that watts stuff, and get this for the 5er ( I don't need an AH counter there, but I do want the V and the A to 200a) and put the Trimetric in the TC for its AH counter, which I am used to.

Thanks for the good input everyone.


http://www.ebay.ca/itm/DC-0-300V-200A-Shunt-Voltage-Current-Panel-Meter-Digital-LED-Voltmeter-Ammete...

[landyacht318]

I thought I saw something on Amazon, but it was the same as your first link.

Check out this' monitor' if you want a laugh, but maybe the voltage enjoying types will like it for the warm and fuzzies having no basis in reality:

http://www.amazon.com/SMAKN%C2%AE-Battery-Indicator-Capacity-Meter-Blue/dp/B00UY9PY44/ref=pd_sim_469...

Could you install another correct Shunt and some twisted pair leads for the trimetric and swap it to the TC any easier?

I assume new leads would require a rezeroing of the trimetric with zero loads on each swapping to achieve any accuracy in amp readings.


It appears this problem has no inexpensive solution.

I had one ammeter with the same shunt shown in your links, and its resolution on 1.5 amp loads or less was quite poor.

I think for the accuracy you seek, something requiring the Deltec 500 amp shunt or similar might be required.

On a side note I often see on other forums how people with portable 12v compressor chest style fridges recommend turning the fridge off overnight and then claim they only lose 1 or 2 internal degrees in 8 hours. If this was the actually accurate, and not just an internet claim, then it is likely cold enough outside to barely require refrigeration at all.

My 1.8 cubic foot 12v compressor fridge's consumption really declines to about 7.5 AH in 24 hours when average temps are mid to high 50's, but climbs upto the 24Ah range at close to 80f and will be closer to 34AH at 90f.

I put this 64 AH maximum wattmeter on the input leads to know this:

http://www.amazon.com/GT-Power-Analyzer-Consumption-Performance/dp/B00C1BZSYO/ref=pd_sim_422_31?ie=UTF8&refRID=0CDNR1CH8CRFT3PYZFXX

When it exceeds 64AH, it flips back to zero and starts recounting.

Wish I could help, but other than having another shunt and the ability to swap the trimetric easily from rig to rig, I think you are in the two trimetric camp.

Wait, this might be helpful:
http://www.cruisersforum.com/forums/f14/low-cost-battery-monitor-137003.html

[MEXICOWANDERER]

I must smile at BFLs advance to appreciate why kWh has a place in battery management.

The best way is to establish your own personal, precise, CEF for your own personal battery bank. This is why I SCREAM about chargers not having the ability to be absorbsion voltage adjustable with at least 150% time allowance at absorbsion voltage limit to allow amperage to slump to 2-3% of total bank amp hour capacity. A few trials using a hydrometer will tell a person how long the battery must remain at this minimum amperage to have the batteries fill to capacity. Use the weak-sister cell of the bank and make life easier.

The CEF calibration should be performed every six-months with heavily cycled batteries. It isCRUCIAL to insure all cells are at maximum gravity before doing a CEF calibration.

Once a CEF calibration has been established voltage is used to insure both amperes and amp hours are stable for the C rate and return amperage minimum indication which tells you the batteries are full, INDEPENDENTLY of the amp hour or kWh meter reading. If the readings all agree which includes hours totalization of amperage or wattage then batteries are cgarged, performance is verified, and battery management reaches a new dimension with a 10-second glance at the meter.

A vital operation is the ability to reset or zero the meter. Everytime a non automatic zero rrsetmeter cycles to a new day the previous day's readings will bias current readings. When CEF is manually adjusted by past-zero-positive amp hours, it is vital to compensate for this as the meter has no idea which day is involved so CEF has to be manually calculated. Meters that have manually settable CEF are only useful if CEF compensation (not available on all meters) can be adjusted percentage point by percentage point to YOUR exact CEF definition.

This is a lot of information that should be discussed segment by segment to make it more comprehensable for the average Joe.

[BFL13]

smkettner wrote:
Voltmeter is all you need.
Start charging at 12.4 to 12.1 volts under light load. Be aware of the time if you have limited generator hours.
Stop charging 60 minutes after battery hits absorption voltage.
Repeat next day as needed.

Extended 48 hour charge upon return.

Yes same as before I got the Tri in the 5er, but what I want is to follow the action in the TC with its 120v fridge over maybe six days off grid with the solar getting some AH in and the loads taking some out with the bank declining in SOC over all.

The decision point is turning out to be in the evening after a few days whether to shut off the fridge and ride it out till it is time to go home, or whether there is enough reserve to get by with the fridge still on, with a look at the weather forecast for solar prospects. (also how long will the milk last, can we get a bag of ice to put in there, etc)

Can't wait till next morning's "morning voltage" when there is no solar input to screw up the voltage reading or any big draws either. Don't want to leave the fridge on all night with no solar input if it is getting close. The AH counter is the way to tell how close you are getting when voltage is going up and down.

Turning the fridge off and restarting later turned out to be futile. Once things warm up in the fridge it takes too long to get back to proper temperature if it ever does. So turning it off is a serious decision. Lesson: have a propane fridge!!!!

I can live without the Tri in the 5er, but do want an AH counter in the TC. I could just swap it over, but am looking at these low cost monitors. I don't know enough about them, which is why I am looking for some clues here. 🙂

[time2roll]

Voltmeter is all you need.
Start charging at 12.4 to 12.1 volts under light load. Be aware of the time if you have limited generator hours.
Stop charging 60 minutes after battery hits absorption voltage.
Repeat next day as needed.

Extended 48 hour charge upon return.

[BFL13]

brulaz wrote:
2 Oldman assumes the 13V and uses Wh = V x Ah

So 1000Wh / 13V = 77Ah

But your V will not always be 13V and any conversion will be slightly off.

The 13V assumption is the problem.

Might be easier to start with an idea of battery bank Wh when full and when half full, but that is with two voltages 12.7 and 12.1

ISTR Mr Wiz uses Wh. Maybe he can say how he does that.

So at least there might be a way to get " close enough" to an AH count, since there will also be a "low load-camping type resting" voltage same as now to use as a cross-check.

If both the OP monitors would actually work, then the price difference is the cost of having AH vs WH and whether that is worth it to not have to do the conversion.