How long will ONE Blue LED take to drain 6 X AA Bateries (9.2) Volts

[Mr 672A]

5Grubbish, you spent 55min typing your story but did not mention if you understood what I have been trying to suggest.
As you have successfully completed a professional looking off-grid solar power system, you are not excused

You have the display on the bench, just try this out, it should cost you no more than 5 minutes of your time:





You can just use your white wire for the bridges to the input terminals or thinner wires it required.
Because the polarity is unknown I didn't want to draw with back and red and used random colours.
If it doesn't work just swap the wires around on the input side.

I was going to do this when I got them as the lowest is 8V and that ok but I said the upper voltage for the LCD is 12V MAX but as you know the Batteries and the Controller changing them can go up to 14.20V DC before it Equalizers so that's 2.2V over the Max Limit and because of this I did not use this method.

[Mr 672A]

5Grubbish, you spent 55min typing your story but did not mention if you understood what I have been trying to suggest.
As you have successfully completed a professional looking off-grid solar power system, you are not excused

You have the display on the bench, just try this out, it should cost you no more than 5 minutes of your time:





You can just use your white wire for the bridges to the input terminals or thinner wires it required.
Because the polarity is unknown I didn't want to draw with back and red and used random colours.
If it doesn't work just swap the wires around on the input side.

This is the reason why I did not use this method as the BOX that the LCD Comes with in States that "ISOLATE POWER IS REQUIRED" So for me it means that to have a separate power supply for driving the LCD and measuring the Voltage that you want to measure and considering the LCD uses 8 to 12V AC or DC and that my controllers that charges the Batteries charge up to 14.20V and because 14.20V is higher than 12.0V I though you will damage the LCD by over driving it..
Now as you know I added the 12.2K Resistor to dull it, I made my VARIAC that red thing with a dial I made the Voltage to be 10.5V DC which is half rating of the LCD 8V to 12 V. Look at the sticker on the box for the LCD

[Uncle Fester]

This is the reason why I did not use this method as the BOX that the LCD Comes with in States that "ISOLATE POWER IS REQUIRED" So for me it means that to have a separate power supply for driving the LCD and measuring the Voltage that you want to measure and considering the LCD uses 8 to 12V AC or DC and that my controllers that charges the Batteries charge up to 14.20V and because 14.20V is higher than 12.0V I though you will damage the LCD by over driving it..
Now as you know I added the 12.2K Resistor to dull it, I made my VARIAC that red thing with a dial I made the Voltage to be 10.5V DC which is half rating of the LCD 8V to 12 V. Look at the sticker on the box for the LCD

It runs on 12V AC which is actually about 34Vpp !!!
The laws of Physics dictate that is about 17V DC after the internal bridge rectifier and the internal step down regulator must be able to handle that.
If you use 14V DC, that about 13V DC after the rectifier, so you still have 4V reserve.

The power is isolated with the bridge rectifier but you could try with 1kOhm resistors as bridges to the inputs instead of wire bridges if you want but it might show a few mV less but this is just to test it. If it works you can replace the resistors with wire bridges.

This is the same display as I have but yours has a bridge rectifier so you can use AC as a power source.
In my case I just bridged the +12V with the positive input so I can measure the battery that supplies it.

The bridge rectifier in yours always gets the polarity right no matter how you connect it.

Wotnot used the term "buck". It is US American for a step down voltage regulator. I agree it is confusing and makes no sense.

Using those step down regulators shown by wotnot in that Ebay listing, which you said you ordered does not isolate it any more from the battery than a direct connection as the negative(ground) is passed through.

[Mr 672A]

It runs on 12V AC which is actually about 34Vpp !!!
The laws of Physics dictate that is about 17V DC after the internal bridge rectifier and the internal step down regulator must be able to handle that.
If you use 14V DC, that about 13V DC after the rectifier, so you still have 4V reserve.

The power is isolated with the bridge rectifier but you could try with 1kOhm resistors as bridges to the inputs instead of wire bridges if you want but it might show a few mV less but this is just to test it. If it works you can replace the resistors with wire bridges.

This is the same display as I have but yours has a bridge rectifier so you can use AC as a power source.
In my case I just bridged the +12V with the positive input so I can measure the battery that supplies it.

The bridge rectifier in yours always gets the polarity right no matter how you connect it.

Wotnot used the term "buck". It is US American for a step down voltage regulator. I agree it is confusing and makes no sense.

Using those step down regulators shown by wotnot in that Ebay listing, which you said you ordered does not isolate it any more from the battery than a direct connection as the negative(ground) is passed through.

Right. I will use a 1K Resistor as the bridge for the positive to not marked positive and use any small cable to bridge negitive to a not marked negitive and see what happens. The Only way you can find out if the supply is connected correctly is you have a - and for me you have the cables back to front. Its like a Multimeter. Will do it soon.

[Mr 672A]

FORGOT TO TELL YOU THIS!!!!

ATM my going dead (2 weeks today) 6 X AA Battery voltage is average 1.32V DC (that low) but what I HAVE NOTICED is when the Battery voltage is getting lower (remember the 6x1.5V Batteries) the screen shows the Voltage HIGHER so when I replace with NEW 6 Batteries the Voltage go back to normal and it within 0.5 V (From Lithium) but once again I replace the batteries with the dead one (1.32) and the LCD Shows a wrong voltage which is higher "eg" 14.60V and as you know it totally wrong.
For me the LCD to drive it to get it working you must use a constant Voltage and if you use the two wires from the 8 X 100 AH Lithium batteries they are not constant as in normal use of the whole system my OFF Grid will produce any thing 12.50 Volts (earl morning and if you drain more the night before I might have 12.30) to 14.25V (Absorbing) later in the afternoon. Now If I bridge it you are giving the LCD varying voltages, you can see it does not like it.
In simple the power that makes the LCD to work has to be constant regarding what you use your method or Wotnot Method otherwise it wont work. The first 2 days it was good with the 6 x dry cell Batteries but as you know the issue started when these batteries was going flat by the day.
Once again I need a Constant power supply and if I can't get this via your bridge method or Wotnot Method I will have to go back to the 230V 9V DC method that have a constant voltage. May my LCD are different to your ones.

[Mr 672A]

You can see this is wrong. Photo Taken at 1.00 PM Brisbane Time, the max should be 14.25 and I used the small trim pot to adjust it 3 times because the AA Batteries are going flat and when going flatter (No such word I think LOL.lol) it give a fake reading but if I change the 6 AA Batteries it becomes sort off correct as I have to adjust the Trim Pot the other way because the new batteries are 1.620 V .

[Uncle Fester]

FORGOT TO TELL YOU THIS!!!!


For me the LCD to drive it to get it working you must use a constant Voltage and if you use the two wires from the 8 X 100 AH Lithium batteries they are not constant

That assumption is incorrect.
The LCD must have a minimum of 8V to operate correctly.
The 6 empty AA batteries with 1.3V each would be 7.8V so the internal step down regulator of the LCD can not work properly anymore and you get false readouts.

Above 8V the regulator keeps the internal voltage stabile and it does not matter if it is running on 8V or 14V.

Nobody, not even the Chinese, would be selling an item like this if the readout varies within the specified supply voltage range.


I wish you good luck and may those cheap Chinese 240V power packs without registered C-tick cause you no grief.

I will not further waste my time responding to this thread.
Fester out.

[Mr 672A]

That assumption is incorrect.
The LCD must have a minimum of 8V to operate correctly.
The 6 empty AA batteries with 1.3V each would be 7.8V so the internal step down regulator of the LCD can not work properly anymore and you get false readouts.

Above 8V the regulator keeps the internal voltage stabile and it does not matter if it is running on 8V or 14V.

If you dont want to reply thanks your decision but I can only tell you all whats is really happening so far but the AA Batteries were 1.28V this morning that total 7.68V less than 8V Minimum that the LCD needs to drive it and yes the reading are erratic.
I got the DC DC Regulator this morning and will do a test and see how it behaves and if everything fails I will dump the Project.
Why should I lie, I'm tell you whats happening, I even give you the picture to see whats going on.

[Mr 672A]

What a test day I had today.
My daughter is typing because I am too tired and I have a full day of work to do tomorrow.

Now I tried uncle festers way of doing it by putting jumpers from one to the other side plus I tried the same using a 1K resistor and it failed. Theres no doubt that this LCD must be different from uncle festers LCD because it misbehaves sadly to the point that 50 minutes later the LCD blew up.

The next method I tried was WOTNOTs method which is DC to DC so I got my multimedia out, Dick smith and Fluke. So i connected the DC/DC device up but before this I used my variac to lower the voltage to 14.25 or 14.22 or 14.23 then after this I connected the Fluke on the other side and I found the voltage to be the same, 14.25. But I got a surgical flat screwdriver and wound the screw anti-clockwise (took a few turns) until i got to 10V. Now i select 10V because 10 is halfway between 12 and 8. So after this I wound the variac to 11.5V DC and measured the output and it was still 10V. Then i wound it back up to 12.5V and the output was still 10V (im getting very happy). Now after this I wound it to 9V on the variac and the output was still 10V (im getting very very happy). Then the last setting I did, I wound the variac to 15V and hell believe it the output was still 10V. I was happy as a pig in shi,t because I simulated the battery from fully charged 14.25V to the flattest where the inverter will shut down at 9.2V. In each case the output of this lovely device stayed at a constant 10V.

After this I connected it to my system and I became depressed because this DC/DC device does not like my LCD screen. You wonder why the box says "Isolated Power is required" because whatever I tried, it failed. It spat the dummy out. It was actually worst than uncle festers method. There is no doubt that theres a connection between the input DC to the output adjustment DC that the LCD screen does not like. It spat the dummy and it was not long after this that my second LCD was dead. Yes I still have the blue LED on but everything else was off.

Now after pulling my hair out of my head I got my 3rd LCD out and I removed the 1.2 resistor (brightness) and replaced it this time with a 9.99oHm, better still a 10K one which is slightly brighter than the 12.2 i said about before. So I wired this new 3rd LCD screen in using the battery 6X AA pack and everything worked okay. 2 seconds later I unplugged the headphone jack socket and I plugged in a 240V 9V power pack and it was spot on. The first thing I noticed was that the power pack was showing the correct voltage minus 0.02 but when I put the battery pack (6X AA) back in it was alot higher by up to 0.5V or higher as I stated this before. When the batteries get flat it gives a higher reading on the LCD but as you guessed I replaced the 6 AA batteries with new ones and it measured the same voltage or pretty close to the same as the power 240V 9V pack. So work that out. No doubt by this you can see this LCD screen requires a separate unattached power source otherwise it spits the dummy out and eventually will shi,t the screen. Theres something in there that is affecting this to a point that it died. Also you can see it likes the power pack and tomorrow I will chase up an Australian approved power pack for 24 hour 7 days a week work.

Anyhow I would like to thank all for contributing in this thread. It has been an interesting challenge. I say uncle fester, his LCD screen must be different from mine. Another thing i'd like to say is that my LCD screens were not marked positive and negative in any way. Maybe the DC/DC device picked this and this is a possibility of why it died because it was the other way connected (Bad luck). It would have been good for the manufacture to mark positive and negative not leave an open. Because i suspect the reason why it died was because of this, conflicting powers.

[Uncle Fester]

Forget the expensive power packs.
How about you just order 2 of these for $5 each and be done with it:


You just want to see if your batteries are getting too low, you don't need 10mV resolution for that.

[wotnot]

Forget the expensive power packs.
How about you just order 2 of these for $5 each and be done with it:


You just want to see if your batteries are getting too low, you don't need 10mV resolution for that.

True .... all I can think of wrt both your & my approaches at powering this type of meter seemingly failing, is the meters OP has are somehow different (under the epoxy blob =) ; that wouldn't surprise me ~ so much of this chinese made stuff gets knocked off .. or ... a good batch comes out which gets positive feedback, lulling ppl into buying, when every subsequent batch is total crap.

[Uncle Fester]

True .... all I can think of wrt both your & my approaches at powering this type of meter seemingly failing, is the meters OP has are somehow different (under the epoxy blob =) ; that wouldn't surprise me ~ so much of this chinese made stuff gets knocked off .. or ... a good batch comes out which gets positive feedback, lulling ppl into buying, when every subsequent batch is total crap.

Looking at the link Mr 672A supplied:

it says LCD Battery Indicator Monitor Voltage Meter Volt Tester
Where in the world would one be forced to use a mains operated power supply(or waste 6 AA batteries every 3 weeks) to monitor the battery of a car/boat/caravan which would be the most common applications for this?
Well apparently in China, although it doesn't look like a very popular item when the listing says only 2 have been sold and one left.
I also can not find any seller in Australia for this item, obviously for a good reason.
The listing also says

• Input connection-reverse protection.

The bridge rectifier(assuming it is functional) also provides reverse protection from the supply side.
This must be as you say some dodgy batch of flawed design, where they added a sticker to cover their asses after too many complained.

[wotnot]

The listing also says

• Input connection-reverse protection.

The bridge rectifier(assuming it is functional) also provides reverse protection from the supply side.
This must be as you say some dodgy batch of flawed design, where they added a sticker to cover their asses after too many complained.

I think that's where the telltale signs of BS start ~ clearly the PCB footprint shows there\s room for a transformer, and the rectifier bridge was there for that purpose...

...the reverse polarity protection... if they're referring to the power input (as opposed to the metered input) is just a consequence of leaving the bridge incircuit for DC power input...and removing transform & installing links..

....and if that were the case, why does the box only have DC checked off...AC would be fine as well...whatever they were designed for (if anything), at a minimum they're being repurposed here.... poorly...

[Mr 672A]

Forget the expensive power packs.
How about you just order 2 of these for $5 each and be done with it:


You just want to see if your batteries are getting too low, you don't need 10mV resolution for that.

Got the system working perfect for 4 days. If the Lithium batteries say 13.60V my LCD above the door will say 13.60V or 13.61 or 13.59V Its that close BUT, BUT I have to use a 240V 1AMP power pack to be this critical and this power pack has a approval number EESS 210342 and I check it on the EESS Site and its there. Out of curious I got my Decade box out and added resistance in the supply circuit simulated battery "eg" those 6 AA Batteries dying but a you know its a power pack feed by 240 or 230 volts and the voltage will stay constant maybe on very hot days the voltage will go down because the street voltage will go down and if this happens the output on the power pack possible will go from 9V DC (normal) to 8.5V DC and tried this and the LCD Lithium Batteries on the LCD screen came up with 13.75 and 6 INTERESTING!! so it prove that I found before the Batteries going dead on the Supply side possible the same if the street voltage goes down (to many AIR Con on the street going) will effect what the LCD is Showing. I believe what Uncle Fester is saying because the Voltage range is from 8 to 12Volts so the LCD should be the same but for me if I give it 10 Volts (not 12V) and let it run down to 8volts I get a different reading from the LCD which will be higher.
TWO LCD's Dead.
I say because there is no polarity on the 4 connections on the LCD it must not like to be connected the way I connected them so I say there was a internal short that fried them. Did not blow a 2amp fuse but the LCDs are dead as a door nail.
Funny thing is I bough 3 off them, two are dead and they are the new ones but the one that I'm using now the abused one its the original one that I have changed the resistance twice (blue LED) and played with the trimpot (at least 20 times) to balance the the reading on the LCD and it still good. I have order 2 more from China to replace the dead ones.
I might get the Cheap one's that Uncle Fester found just for playing, I checked Ebay Au and found nothing before.
Yesterday I turned off both strings and ran the Lithium batteries down to 12.45V and this morning I put both the Strings back on (F.ck its raining in Brissy today) and noted that the Batteries using two multimeters (disk Smith and my Original Fluke) read the same 12.45V and the LCD above the door was telling me it is 12.44V and 12.43V Hummmmm.
Anyhow what important to me is the 12.4 or 12.3 not the last number (forgot what it called) that moves regular so if the girls in the house see 10.5 Volts start panicking

[Mr 672A]

Check today two times. The Lithium Batteries in the battery cabinet was 13.35V, The LCD above the Door was 13.34V and on my wi Fi Phone the app from Victron told me my Batteries via the Inverter was 13.35V, can get better than that. The second test was similar The Lithium Batteries were 13.69V, The LCD above the door was was 13.68 then 30 seconds later after I tested the V on the Batteries that was 13.69V I found the LCD to be 13.69V. WOW.
I want to do a test when we have rainy days so I want to see the Lithium Batteries go down to 12.2V or 12.5V and see what do I get on the LCD Panel and take note what the inverters says.
The Blue LED in the LCD screen is perfect now, You can't see the Blue in the day time and at night you can see barely see a slight blue around the corner reflecting on the white kitchen cabinets and that it 1K was too bright, 12k was to dark and 10K is spot on.

[wotnot]

An error of 0.01 volts would be within the reading accuracy error rate of the measurement devices... even the temperature of the interconnecting wires matters down at this level =)

[Mr 672A]

An error of 0.01 volts would be within the reading accuracy error rate of the measurement devices... even the temperature of the interconnecting wires matters down at this level =)

Yes its good enough for me and considering I'm using my own Power supply to feed this power pack and the Victron inverter has the output set to 230V regarding when its on 13.90v DC or 10V DC I should have no problem with variable output from the power pack that will allow the LCD to Change. Yeah I say Busted!!!!. Tested Late last night testing this morning, all ok.

[Mr 672A]

Its been weeks since I added a power pack to my LCD Project and all is well. Because of continual raining in Brisbane and low sun shine I have go a lower expected solar gain to a point that I decide to take 90% of load off the Off Grid system and the LCD has done his job. The Batteries were 12.23 Volts DC using my multi-meter and the LCD said it was 12.23 or 4 Volts DC. That's accurate enough for me.