Need a diagram for 24v Battery Monitor using LM3914 chip

[sprat]

Hi
I have 2-12v batteries connected in series (24v). Can someone help me with a circuit diagram using lm3914 chip to monitor the voltage state. I have looked around but all I can find is a 12v diagram. I would like to lowest to be 21v and the highest to be 29v
Any help will be greatly appreciated

 

[Roff]

Do you want to power the entire monitoring circuit off the battery you are monitoring? Dot mode or bar mode?

 

[sprat]

Yes I would like to power it from the batteries. I would prefer bar mode

Thanks

 

[Roff]

Yes I would like to power it from the batteries. I would prefer bar mode

Thanks

I'll try to design it for you. Bear in mind that bar mode will draw more current than dot mode. It's easy to change, though. You can install a switch if you wish.

 

[sprat]

Thanks a lot. Can you please include the switch in design

 

[Roff]

I haven't tested this, but I don't think I screwed anything up. :roll:

 

[Roff]

Sprat, what is attached your battery? I just realized that, if the load (or an alternator/generator) generates noise spikes on the battery, we may need to add filtering in front of the LM317.

 

[sprat]

The batteries are running my UPS.

 

[Roff]

The batteries are running my UPS.

I edited the schematic, adding 10ms of filtering in front of the LM317. I hope that's enough. The max power dissipation of the LM317 will be more like 1.5 watts with the change, instead of 2 as indicated on the schematic.

 

[eblc1388]

Hi Ron,

I suggest an alternative, for discussion purposes only.

I have not used the L3914 before so this might not work.

The power supply LM317 is similar to yours and outputting 15V. I would then setup the LM3914 to gives a 10V reference voltage, with RLO grounded. So the scale for SIG input becomes 0-10V for 10 LEDs.

I'll then use a TL431 to drop a constant 20V from the input signal before feeding this to the LM3914 SIG input.

The first LED will light at 21V and the last at 30V, giving a one volt step per LED.

Do you think this will work?

 

[audioguru]

Lots of ways to skin the same cat (rat?). :lol:

 

[Roff]

Something like that should work, although I don't see how you can use a TL431 to level shift down to 1.0V. I gave some thought to a level shifter that would do that, but concluded the attenuator would be simpler.

 

[eblc1388]

Something like that should work, although I don't see how you can use a TL431 to level shift down to 1.0V. I gave some thought to a level shifter that would do that, but concluded the attenuator would be simpler.

The TL431 is a shunt regulator or adjustable voltage zener which need just 0.5mA or higher to maintain regulation. Using external resistors, the terminal voltage can be trimmed to any value from 2.5V to over 30V.

My suggestion works like this. If the battery voltage is 24V, the voltage across the TL431 is always 20V(Constant), then the voltage scross the bottom resistor must be at 4V.

 

[Roff]

OK, I get it. That's pretty simple.

 

[bryan1]

Hiya Ron,
Eh mate thanks very much for designing that battery circuit I've been looking on the web for ages trying to find a circuit so I can monitor my 24 volt battery bank in my shed. One query as I'm inputting pure DC from a solar array I should be able to simplify the input side thru the lm317 as spikes won't be a problem. Oh if if I may dare I've got a bank of Nife batteries which float around 16.5 volts so how would I modify the circuit to suit. Silly me used my 12 volt lm3914 circuit and ended up seeing the magic smoke :cry:

Cheers Bryan

 

[sprat]

So guys what would I use to get that 10v reference on RHI?

 

[Roff]

So guys what would I use to get that 10v reference on RHI?

Do you want to change the design to eblc1388's scheme?

 

[sprat]

I am going to do yours

 

[sprat]

I did your design AND IT WORKS PERFECTLY

THANKS !!!!!!!!!!!!!!!!

 

[Roff]

I did your design AND IT WORKS PERFECTLY

THANKS !!!!!!!!!!!!!!!!

WOW! That was fast!