Low Cost Battery Monitor

[GrowleyMonster]

My biggest issue with inexpensive digital panel meters is accuracy. Every meter I have tried, required finding and applying a correction to the reading. For state of charge estimation or calculation, an accuracy of 0.1% is called for. A half volt can represent 10% or more of State Of Charge for a 48v bank.

The unit described by the OP can be readily calibrated, making it quite useful I think. I may be looking into one on my next control upgrade for my propulsion system.

[sparrowhawk1]

Too simple of an answer to a complicated question(on my part) I too use the voltage to estamate the approximate charge of my battery. at 9 in the morning my solar starts kicking in and if I'm at 13 volts I know I'm not too deeply discharged. And my greatest indicator of state of charge is when I go into float mode. But if I had an hour meter for amps out and a hour meter for amps in it would take the guesswork out.

[conachair]

Originally Posted by GrowleyMonster

My biggest issue with inexpensive digital panel meters is accuracy. Every meter I have tried, required finding and applying a correction to the reading. For state of charge estimation or calculation, an accuracy of 0.1% is called for. A half volt can represent 10% or more of State Of Charge for a 48v bank.

The unit described by the OP can be readily calibrated, making it quite useful I think. I may be looking into one on my next control upgrade for my propulsion system.

This one is within +/-10mV of an expensive fluke meter. A worthwhile addition to any battery bank, wired straight to the terminals so you can see what's really going on a the battery rather than at the end of some wires. IMHO.

http://www.ebay.co.uk/itm/Digital-Vo...-/320701838199

[GrowleyMonster]

Originally Posted by conachair

This one is within +/-10mV of an expensive fluke meter. A worthwhile addition to any battery bank, wired straight to the terminals so you can see what's really going on a the battery rather than at the end of some wires. IMHO.

Digital Voltmeter, 12V D.C. Battery Monitor Panel Meter - UK seller | eBay

No good for 48v bank. Only 12v. For a 48v bank it needs to read up to 62v.

[Maine Sail]

Originally Posted by sparrowhawk1

Too simple of an answer to a complicated question(on my part) I too use the voltage to estamate the approximate charge of my battery. at 9 in the morning my solar starts kicking in and if I'm at 13 volts I know I'm not too deeply discharged. And my greatest indicator of state of charge is when I go into float mode. But if I had an hour meter for amps out and a hour meter for amps in it would take the guesswork out.

This may not be good way of determining battery SOC for many because there are just too many system variables.

Many controllers are not very "smart" and simply work as egg-timers. Once the batteries hit absorption they start a one hour or two hour timer etc... The egg-timer hours may not be sufficient for full absorption on the bank and flooded batteries really do need a good gassing voltage for battery health. Some el-cheapo Chinese controllers actually go straight from bulk to float if the daily egg-timer is exceeded. Many good quality controllers won't actually leave float, even over night, unless the battery voltage has dipped to a pre-set low such as 12.2V etc... Lots of potential variables..

That said with most small arrays by the time your bank has hit absorption you are damn near full anyway due to the low current source and the large Ah capacity bank disparity..

On of the ones I hear routinely is; "By mid morning my bank is back to full"..

I have heard this approx 40 times from various customers and only once was it actually true. This means 1 in 40 boaters with solar, in my market, were wrong about their battery SOC.....

The reality for most in the; "By mid morning my bank is back to full" camp is the banks are still in bulk and the voltage is still climbing towards absorption. Unfortunately they see 13.3V and incorrectly assume they are in float not still in bulk...

Also solar can trick Ah counters into false resets so that one needs to be watched too.

[sparrowhawk1]

Maine Sail. I have approximately 20 amps of solar( max, very rarely do I see more than 15-18amps) a 400 amp hour battery bank 14.8v bulk and a two-hour absorption. Is it safe to assume that I'm near full capacity when it switches to float? Also if I get a meter so I can measure amperage in as well as out I plan on putting 20 percent more back in the batteries than I take out, does this sound too high or too low to you? Thanks

[Maine Sail]

Originally Posted by sparrowhawk1

Maine Sail. I have approximately 20 amps of solar( max, very rarely do I see more than 15-18amps) a 400 amp hour battery bank 14.8v bulk and a two-hour absorption. Is it safe to assume that I'm near full capacity when it switches to float? Also if I get a meter so I can measure amperage in as well as out I plan on putting 20 percent more back in the batteries than I take out, does this sound too high or too low to you? Thanks

At approx .0375C charge rate you will not be hitting 14.8V until very high in the SOC range, perhaps 95% plus so when you go to float you will be at a fairly high SOC just may not be "chock full"....

[lmantuano]

Originally Posted by Vladis

Hello,

At first I could not either set the current reading. The monitor can work with different external shunts and it is not docummented how to set the type of shunt. With the support of the seller I was able to get it right.

I got some ceramic resistors and I created a load of 1.98A measured with my multimeter. The monitor showed 1.96A and I was happy. I can read a consistent advance in the amps being asked to the battery when I switch ON, one by one, the 20 LEDs that I have.

If your model is as the same as mine (even with a different shunt) I am available to exchange (by private mail) the steps taken to correct the current readings.

Regards, Vladis

Hi Vladis,

I have just ordered the same model as yours and I wonder whether you could PM me your experience so that I can hit the road running... thanx in advance,

Luigi M

[Vladis]

Originally Posted by lmantuano

Hi Vladis,

I have just ordered the same model as yours and I wonder whether you could PM me your experience so that I can hit the road running... thanx in advance,

Luigi M

Hello,

I will describe the problem I had and the solution that cured it. I hope it will help others, in the case they encounter the same situation.

My problem was about the current setting. Firstly, with no load, I long press the A/AH button until the display shows 00.00. This is the zero point setting. The 4 page leaflet tells me that I should then set the high current point. It suggests to use a 30A load (in the case of my 100A shunt). I only have a multimeter capable of measuring 10A. Also, when on anchor, I expect a consumption of between 3A to 8A and a litle more when navigating. So I assembled 3x 18 ohm (17W) ceramic resistors in parallel. I wired my multimeter in series with this resistor load and connected the set across the battery. The multimeter showed me 1,98A and the monitor showed about 1.2A. Also the display was a bit erratic. I expected that, by adjusting the high current point, I would correct this. So I enter into debug mode (long press SET button) and then short press SET until the lower display shows current. Then I press the V/W button to increase the reading from 1.2A up to 2.0A (or 1.98A). Then I save the setting as described in the leaflet (I skip this step). It looked right but, as soon as I switch off the load, instead of zero, I get 0.8A! This value is precisely what was added to 1.2A to get 2.0A.

So, I think that the high point setting is no good as it disturbs the previous zero point setting. I contacted the seller asking for help. He said that a 100A shunt should not be calibrated with a 2A load. I discussed the possibility of buying a 50A shunt (which should be my first choice). He said that the display unit could be the same if I get a different shunt. I asked how I could change the shunt setting. He said that there is a -FL- setting with different values. -FL-01, -FL-02, -FL-03, ..., up to -FL-09. He said that my display was sent to me with the -FL-02 setting which corresponds to a shunt of 100A. He said that to use the display with a 50A shunt I should change this setting to -FL-01. I do not know what shunts should be used with -FL-03 and so one. So before ordering a new shunt I tried to change this setting using the information he sent to me.

To enter in the "shunt changing mode" I should disconnect the power (I am using the power from the battery being measured). Then I should press and hold the SET button and connect the power again. If the monitor wakes up with SET button pressed, it enters this special mode and -FL-02 should appear in the bottom line of the display. To change the -FL- value I should short press SET several times until I get the desired value. To save the new value I need to short press A/AH.

So I tried this and changed -FL- to 01 and to 03 and got different but still uncorrected current readings. The INTERESTING thing is that by returning to -FL-02 everything started to work. This is strange since the unit was, in the beginning, in the -FL-02 state. So I repeated the current settings. As before, I set the 00.00 reading with no load. Then I tested the monitor with my 1.98A load. It showed me 1.96A! That was great! I decided not to correct this small difference as I do not know the accuracy of my multimeter and I did not want to disturb the zero setting, as it is important to distinguish between charging/discharging.

So that was my experience. I kept my 100A shunt as readings are now very precise and stable (not erratic as before).

Regards, Vladis

[lmantuano]

Thanx heaps Vladis,

I will use your info & experience once I get the device and set up a test bed for it.. I'll post my results and impressions after that time.

Regards & Merry Christmas

Luigi

[goboatingnow]

Im amused at people talking about 0.1%/1% accuracy on a battery monitor.

The fact is amp hour counting is a very crude measure of battery capacity, even when you apply a ( inevitably static peukerts exponent) correction factor. If you get a state of charge indication thats within 10% you are doing very well indeed and few monitors manage this.

people are confusing precision with accuracy

[Vladis]

Hello,

I admit that I used the term precision in the wrong context. My native language is not English but that does not excuse my inaccuracy. My main problem was accuracy and was able to fix it. I was also pleased with the final reading precision .

I do not bother with the SOC that the monitor shows. I only would like to have accurate readings of voltage and amperage of my batteries as I was not happy with the readings from the system that came with the boat (VDO panel).

I was informed that this monitor was designed to lead acid batteries only. After my purchase, I discovered one company who claimed to be the designers of the unit that I got. They referred to my unit as model MTX-105 and they say that their new model is MTX-105P. These models have the same size (box) and have similar functions except that, in the case of the new model, the user is capable of setting the KS parameter for different types of batteries. When I was ready to buy this new unit, I was able to fix the problem I had (as described above) and so I did not go ahead with the new purchase.

For those interested the company I refer to is www.cqbluejay.com and they sell their units through alibaba (or aliexpress? I do not remember).

Regards, Vladis

[Thriftyprepper]

Hi Vladis, i bought the same meter but with 200A 75mv. It has been a week now but i still cant make it work.

I calibrated it by measuring the shunt value with a multimeter after i turned on all devices my inverter can handle.

The value i got is 2.6mv and i divide that with .375ohms (2.6mv / .375ohms = 6.93A)

With the value i got i entered this to the meter and worked fine but the problem is the amps going in to the battery from my solar charge vontroller. The value is way off and inaccurate.

Do you have sny suggestions? Many thanks.

[Vladis]

Originally Posted by Thriftyprepper

Hi Vladis, i bought the same meter but with 200A 75mv. It has been a week now but i still cant make it work.

I calibrated it by measuring the shunt value with a multimeter after i turned on all devices my inverter can handle.

The value i got is 2.6mv and i divide that with .375ohms (2.6mv / .375ohms = 6.93A)

With the value i got i entered this to the meter and worked fine but the problem is the amps going in to the battery from my solar charge vontroller. The value is way off and inaccurate.

Do you have sny suggestions? Many thanks.

Hello,

It looks like you adjusted the reading for 6,93A. Now you need to make sure that, with no load, the meter reads zero! If that is case it will read both curre! nts in and currents out! If you read my post here you will see that my initial problem was precisely this! May be, if you try what I have done, you can solve yours as well! However my unit is 2 years old and new ones may have different firmware (just guessing).

I am extremely happy with the monitor! It counts (5 sampling readings per second) AH going out from the batteries or going in into the batteries. At the middle of a sunny afternoon it shows 100% (=280 AH in my case). Then, when the sun goes down it stars to decrease and at 8 am it shows about 75% (which agrees with the consumption of the freezer). Then the sun and the solar panels increase the energy in the batteries again. In days of no sun (very rare here :-) ) I switch on the engine to charge the batteries!

I hope you get yours working as mine!

Regards, Vladis

[Thriftyprepper]

Originally Posted by Vladis

Hello,

It looks like you adjusted the reading for 6,93A. Now you need to make sure that, with no load, the meter reads zero! If that is case it will read both curre! nts in and currents out! If you read my post here you will see that my initial problem was precisely this! May be, if you try what I have done, you can solve yours as well! However my unit is 2 years old and new ones may have different firmware (just guessing).

I am extremely happy with the monitor! It counts (5 sampling readings per second) AH going out from the batteries or going in into the batteries. At the middle of a sunny afternoon it shows 100% (=280 AH in my case). Then, when the sun goes down it stars to decrease and at 8 am it shows about 75% (which agrees with the consumption of the freezer). Then the sun and the solar panels increase the energy in the batteries again. In days of no sun (very rare here :-) ) I switch on the engine to charge the batteries!

I hope you get yours working as mine!

Regards, Vladis

Thank you vladis for your immediate reply. It seems that mine should be configured at fl - 03 now it's reading 0.00 when the inverter is OFF. I'll monitor if there are any changes. I hope i finally solved my problem. Many thanks vladis!