# Lithium Battery Monitor Question

#### DC_Kid

Joined Feb 25, 2008
796
i am not a guru with lithium batts, but i am working with LiFePO 24v 24Ah batt and i need a simple led/lcd "full empty" monitor, displays a scale and/or %, etc.
i see some inexpensive items on e bay, but i am not sure if they are of proper scale. as example, a 24v LiFePO might be full at ~29v and on empty near 21v, so a monitor must be scaled in that range. a programmable scale would be excellent. looking for that sub $10 item, etc. any suggestions on items that work properly. #### Dodgydave Joined Jun 22, 2012 9,066 Any voltmeter can be scaled, show the item you're thinking of. #### ronv Joined Nov 12, 2008 3,770 i am not a guru with lithium batts, but i am working with LiFePO 24v 24Ah batt and i need a simple led/lcd "full empty" monitor, displays a scale and/or %, etc. i see some inexpensive items on e bay, but i am not sure if they are of proper scale. as example, a 24v LiFePO might be full at ~29v and on empty near 21v, so a monitor must be scaled in that range. a programmable scale would be excellent. looking for that sub$10 item, etc.

any suggestions on items that work properly.
All depends on how fancy you want to get. Here is a nice write-up with some chips:
https://www.digikey.com/en/articles/techzone/2014/jan/fuel-gauge-ics-simplify-li-ion-cell-charge-monitoring

#### ian field

Joined Oct 27, 2012
6,539
i am not a guru with lithium batts, but i am working with LiFePO 24v 24Ah batt and i need a simple led/lcd "full empty" monitor, displays a scale and/or %, etc.
i see some inexpensive items on e bay, but i am not sure if they are of proper scale. as example, a 24v LiFePO might be full at ~29v and on empty near 21v, so a monitor must be scaled in that range. a programmable scale would be excellent. looking for that sub \$10 item, etc.

any suggestions on items that work properly.
Specification is pretty tight if you want to avoid a fire.

Monitoring the total battery voltage won't do - you need to monitor each individual cell, and implement some form of balancing while charging.

Everyday Practical Electronics magazine published a balancer project - but it probably won't handle as many cells as you're talking about.

#### DC_Kid

Joined Feb 25, 2008
796
Last edited:

#### ronv

Joined Nov 12, 2008
3,770

#### gramps

Joined Dec 8, 2014
81
That one specifically says that it is " not for Lithium iron phosphate battery".

#### ian field

Joined Oct 27, 2012
6,539
That one specifically says that it is " not for Lithium iron phosphate battery".
It all serves to highlight that messing with lithium cells can be dangerous of you don't watch what you're doing and above all; read the small print.

#### ronv

Joined Nov 12, 2008
3,770
That one specifically says that it is " not for Lithium iron phosphate battery".
Good eye.