# Battery percentage display on analog meter

#### iharshtalwar

Joined Jul 19, 2023
2
Hello people,

I'm doing a small project where I am trying to display the battery percentage of a scooter on an analog meter. My battery output is 60v and 45amps. The lower and upper peak voltages of the battery is 56v and 65v respectively. Currently I'm trying to do it with a diode with reverse bias condition which conducts from 56v to 60v. I’ve directly connected the diode in reverse bias condition to one of the coil. I am able to crack it but not accurately. I need a diode which conducts in reverse bias condition from 58v to 65v. But I'm unable to find any such a diode. Any idea guys?

#### Ian0

Joined Aug 7, 2020
8,947
Hello people,

I'm doing a small project where I am trying to display the battery percentage of a scooter on an analog meter. My battery output is 60v and 45amps. The lower and upper peak voltages of the battery is 56v and 65v respectively. Currently I'm trying to do it with a diode with reverse bias condition which conducts from 56v to 60v. I’ve directly connected the diode in reverse bias condition to one of the coil. I am able to crack it but not accurately. I need a diode which conducts in reverse bias condition from 58v to 65v. But I'm unable to find any such a diode. Any idea guys?
A zener?

#### iharshtalwar

Joined Jul 19, 2023
2

#### Ian0

Joined Aug 7, 2020
8,947
Don’t forget that only the open circuit voltage is an indication of state of charge. When you put a load on the battery the voltage will drop.

Also, for your gauge to read zero the current through the zener must go down to zero. Zeners are only accurate at the rated current (generally 5mA). The accuracy is hopeless at very low currents.

You can improve things a bit by using several LM4040 in series. Then it will be accurate down to 60uA.

#### Dodgydave

Joined Jun 22, 2012
11,151
A zener diode will conduct at it's strike voltage, so if you use a 60V one the meter will read from 65 to probably 59V..

Or you could use a TL431 and set your own voltage with resistors.

#### Ian0

Joined Aug 7, 2020
8,947
A zener diode will conduct at it's strike voltage, so if you use a 60V one the meter will read from 65 to probably 59V..

Or you could use a TL431 and set your own voltage with resistors.
Unfortunately not. TL431 doesn’t work below 1mA, and the resistor current adds to the meter current.