I am trying to build a battery full indicator, but the output of the opamp is erratic and unpredictable. I have added hysteresis and a decoupling Capacitor but the problem still persist…. Sometimes it exceeds the upper threshold significantly before coming ON while some times it doesn't even get close to it before coming ON.

How do I solve this problem?

 

hi PE,
Welcome to AAC.
Please post a circuit diagram.
E

 

An opamp is not a good choice to use as a comparator. Use a good comparator IC and be sure to use bypass capacitors on the power supply connections. That should help.

 

Use a Lm3914 to make a battery monitor, post your circuit please..

 

hi PE,
Welcome to AAC.
Please post a circuit diagram.
E

Alright, I have attached a draft

 

Not seeing any attachments?

Ron

 

Maybe you are seeing an attachment but I'm not. Do you see whatever it is you are attaching?

Ron

 

You can see it if you close your eyes and rub your belly.

 

You can see it if you close your eyes and rub your belly.

That covers it nicely.

Ron

 

I am trying to build a battery full indicator, but the output of the opamp is erratic and unpredictable. I have added hysteresis and a decoupling Capacitor but the problem still persist…. Sometimes it exceeds the upper threshold significantly before coming ON while some times it doesn't even get close to it before coming ON.

How do I solve this problem?

OK, but since the attachment is not visible to me, how about a verbal description of the circuit? I have done several of those and some of the folks have had the visualization skills to see it, and others the ability to draw it.
But really. There are several potential sources of grief, starting with that op amps make only "fair" quality comparators, since they tend to be used for linear applications while comparators are intended to output either hi or lo, and to do it accurately and quickly.
A comparison: I can drive a screw with a hammer and I can drive a nail with a screwdriver, but in neither case are the results as good as using the right tool.

 

He doesn't even say what battery chemistry. Lead-acid, Ni-Cad, Ni-MH, Lithium-ion or lemon juice.
A lithium-ion battery is no where near fully charged when its voltage reaches its maximum.
Also there was not one word about the battery voltage. 1.2V or 120V?

 

I can't see the schematic either.

I could add to the comments and suggestions above, but my crystal ball is foggy at the moment.

 

Looking at the attachment " This ", it appears that the V ref. is not stable. Might try something like
LM336Z, 2.5V, or LM385Z, 1.235 V.

 

Several companies make and sell IC devices made for that very purpose. Linear Technology and ST are the ones whose products I have seen, but others have them also. So worst case you can buy an IC made for exactly that application.

 

This is the attachment

 

Several companies make and sell IC devices made for that very purpose. Linear Technology and ST are the ones whose products I have seen, but others have them also. So worst case you can buy an IC made for exactly that application.

Yeah, like a 40 plus year old LM3914.

I have a hard time relating to a battery as full or empty. Just doesn't sound right. Hell I would just buy a battery level monitor for a few bucks and be done with it.

Ron

 

Are we supposed to guess what is that triangle thingy?

 

What is the battery voltage?

 

Professor.....Hmmm... scary to be his student

 

Professor.....Hmmm... scary to be his student

He didn't say professor of what.