help with an LM3914 voltage gauge

[tacticalemu]

I am trying to make a voltage gauge with the LM3914 that will measure over the range of 12-24V. It will be used to indicate the voltage in two 12V batteries connected in parallel. I only want to use one chip to just measure the range in 1.2V steps in the bar mode. I am a little confused though about how I should set up the reference voltage across the divisor to do this?

 

[Mikebits]

You might want to try the LM3914 calc made by Eric Gibbs
https://www.electro-tech-online.com/blogs/ericgibbs/136-single-dual-lm3914-v3-0-calculator.html

 

[tacticalemu]

hmmm... well i tried to use that, at your suggestion, however, it appears that i cannot get it to run on windows seven... even after attemping to install the visual basic library, it seems that windows 7 is incompatible with them... any suggestions?

 

[tacticalemu]

never mind... some creative .dll installing got it working

 

[JimB]

...measure over the range of 12-24V.
It will be used to indicate the voltage in two 12V batteries connected in parallel.

Two 12v batteries in parallel give 12volts.
You would do better with a range of 10 to 15 volts for the voltmeter.

Similarly, two 12v batteries in series give 24volts.
You would do better with a range of 20 to 30 volts for the voltmeter.

Your requirements as stated will just use the bottom segment of the bargraph display.
Seems a bit pointless to me.

JimB

 

[tacticalemu]

Did I say parrallel? I meant series. And for this application, I will do better with a range of 12-24V. The batteries are deep cycles feeding a 12V regulator that puts out a constant 12 as long as it input it greater. We need a simple meter to see how far from our starting 24 we have dropped so we know when to change the batteries, basically so we arn't at 13V and then send it out unknowing of the low battery.

 

[JimB]

If your batteries are lead-acid types, the normal fully charged voltage will be about 12.6v, and at 10v the battery is well and truely discharged.
If you discharge the batteries to 13v with two in series you are killing the batteries and they will not last very long.

This is why I suggest 20 to 30 volts for a 24v battery.

Note that when charging, the voltage will rise to 28v(ish) when the battery is fully charged.

Look here for more information:
https://batteryuniversity.com/


JimB

 

[tacticalemu]

Hi Jim. As I stated they are deep cycle and discharge to much lower voltages. We have already run them down regularly to 6V a piece, which although not a problem for the batteries, is a problem for us, which is why we are trying to make the gauge to monitor them. Its not pleasant to see the whole thing shut off for no reason to find it was something as simple as low batteries...

edit: also, I would rather just have help with the circuitry for what I asked than debate what kind of batteries I have. I don't mean to seem rude but its kinda off topic.

edit number 2: also, if you notice, i keep saying we... this is on a team, and i am not one of the powers to be... although i agree that they shouldnt be run down that far and have voiced my concerns to them, im not in a decision making position... that being said, they asked for a 12-24V gauge and thats all, so that all i am making...

 

[ghostman11]

never mind... some creative .dll installing got it working

care to share your creativeity? alot of people like myself running windows 7 and it would be realy helpful to know how you got round it
cheers jason

 

[tacticalemu]

i googled the missing dll, wit was something like msvbvm50.dll or whatever it was that it was missing, downloaded just the dll, and copypasta'd to both system32 and system folders


edit: i got it off this site https://www.dll-files.com

 

[ghostman11]

thanks for the info i am sure it will help others

 

[ghostman11]

had a bit of a play with it and i think its a great program!!! well done Eric realy nice job