State of Charge LED indicator

[swu36]

Hello,

I am trying to build a SOC LED indicator for my 48V battery with 8 LEDs, which displays the following pattern when the battery has SOC of about 87.5%: (link: http://gph.is/1MiTU4k)
The battery comes with a SOC indicator and I am to replace it with the 8-LED system.
Any suggestions on how this could be done, preferably using what I already have?
Thanks in advance.

 

[Martaine2005]

Hi swu36,
I am probably out of my depth here, but what 'soc' has your battery got?
Is it working directly from 48v?
There are some dedicated 'state of charge' ic's.
I have never used one but the LM3914 is a 10 led or bargraph chip to do what you want. The caveat is, it's a 12v chip. Hence my original question!

Martin

 

[Martaine2005]

Any suggestions on how this could be done, preferably using what I already have?

What do you have?

Martin

 

[swu36]

Hi swu36,
I am probably out of my depth here, but what 'soc' has your battery got?
Is it working directly from 48v?
There are some dedicated 'state of charge' ic's.
I have never used one but the LM3914 is a 10 led or bargraph chip to do what you want. The caveat is, it's a 12v chip. Hence my original question!

Martin

Yes I think the 5-LED soc meter is directly working from 48V. I found this: http://www.instructables.com/id/12V-Battery-State-Of-Charge-Indicator/?ALLSTEPS which is also using LM3914. Can I simply scale down the voltage with resistors?

 

[swu36]

What do you have?

Martin

Sorry for the vague wording - I was just wondering if the original soc meter could still be of any use, but it doesn't look like it...

 

[Martaine2005]

Yes I think the 5-LED soc meter is directly working from 48V. I found this: http://www.instructables.com/id/12V-Battery-State-Of-Charge-Indicator/?ALLSTEPS which is also using LM3914. Can I simply scale down the voltage with resistors?

Prbably not! 48v to 12v is quite a jump.
Have you checked how your 'soc' works on your battery?
What circuit is there and what voltage it uses?
I doubt the battery is running a circuit at 48v! to run a led charge status.
Can you check this to confirm? And post what voltage the circuit requires?

Martin

 

[swu36]

Prbably not! 48v to 12v is quite a jump.
Have you checked how your 'soc' works on your battery?
What circuit is there and what voltage it uses?
I doubt the battery is running a circuit at 48v! to run a led charge status.
Can you check this to confirm? And post what voltage the circuit requires?

Martin

Will do. Would you suggest that I take it apart to look at the circuit?

 

[Martaine2005]

Yes, you need to know what voltage is going to your charge state circuit!
If it's 12v, then it makes it easier.
It could be a dedicated 5v circuit. Who knows!

Can you post a link to the battery you have?
And a pic of the circuit for the charge status?

Like I said, I am out of my depth here but can more than likely 'inspire' someone who has experience to chip in'
The more info you can provide, the more help you will get.

Martin

 

[swu36]

Yes, you need to know what voltage is going to your charge state circuit!
If it's 12v, then it makes it easier.
It could be a dedicated 5v circuit. Who knows!

Can you post a link to the battery you have?
And a pic of the circuit for the charge status?

Like I said, I am out of my depth here but can more than likely 'inspire' someone who has experience to chip in'
The more info you can provide, the more help you will get.

Martin

Thanks for the help!
The battery is ICR18650-26FM Samsung.
Sad news - the circuit is indeed running at 48V. Even 49.6V (the battery is over charged). I have taken the indicator apart and this is what I've got...

 

[Martaine2005]

Sad!!! Not exactly!
The points you are checking is the input to the circuit board.
The red and black are from the 48v battery.
I was refering to a point that feeds the leds.
I am useless with smd components, the names, codes can be anything.
It does look like you have several regulators on the board though.
I would wait til morning and get some real expert help!!
You have done the right thing by posting a pic.
Sorry I cannot help you further.

Martin

 

[cjdelphi]

to be honest, that side of the pcb shows mainly resistors and transistors...

it's as simple as voltage dividing and if it reaches 0.6v on the base of that particular divider, the transistor conducts turning on one led ...

 

[Arouse1973]

to be honest, that side of the pcb shows mainly resistors and transistors...

it's as simple as voltage dividing and if it reaches 0.6v on the base of that particular divider, the transistor conducts turning on one led ...

Yep five LEDs and 5 transistors, I would go along with that.
Adam

 

[Martaine2005]

Yep, totally makes sense now.
I know an IC is made of many components like transistors.
The ref designator U is for IC. I thought Q was for transistors.
So, I guess U can be used for transistors too.

Well, the best advice I gave was wait til morning for the experts.

Martin

 

[swu36]

to be honest, that side of the pcb shows mainly resistors and transistors...

it's as simple as voltage dividing and if it reaches 0.6v on the base of that particular divider, the transistor conducts turning on one led ...

I am still confused as of what to do...could you please elaborate on that? Will I be dividing the voltage from 48V straight down to ~0.6V for the LEDs?

 

[Martaine2005]

Probably something like
100% = 50.93, 90% = 50.47, 80% = 49.99, 70% = 49.49 etc.
But not sure though
Martin

 

[Arouse1973]

Yep, totally makes sense now.
I know an IC is made of many components like transistors.
The ref designator U is for IC. I thought Q was for transistors.
So, I guess U can be used for transistors too.

Well, the best advice I gave was wait til morning for the experts.

Martin

Yep it depends on what software package you use. I tend to use Q or TR for transistors and U or IC for integrated circuits. U is denoted for "inseparable assemblies" items that are, well just that. Q came from a German name for a property of the transistor I believe and not the shape of the first metal can version as most people think.
Adam

 

[cjdelphi]

measure the resistor that's in series with the led, at that voltage i'd expect it to be between 1 - 2k?

the voltage comes from a voltage divider say 10k and 100k that small amount of current providing it's > 0.6v on the base pin... it'll make the transistor begin conduct between the collector and emitter thus providing current to the led

circuit's easier to see how it works

 

[cjdelphi]

another option is an opamp (if you can find one for 40v) or comparator but the transistor version is probably cheaper to build....

 

[cjdelphi]

I just quickly made a rough circuit so please don't assume this will work in real life, but with potentiometers you could use this method....

 

[Martaine2005]

I just quickly made a rough circuit so please don't assume this will work in real life, but with potentiometers you could use this method....

That looks very neat. What software is that?
It actually shows the direction and switching etc.