SMC Precision Lipo Alarm

We are proud to introduce our Precision Lipo Alarm designed to get a more precise cutoff then an ESC.  When running the Traxxas or Arrma ESC which are known to have the cutoff set to low and not adjustable this is a must have item if you are interested in getting maximum cycle life out of your packs.

With standard Lipo alarms the alarm is set at the desired cutoff but the alarm doesn’t account for voltage drop which occurs under heavy acceleration.  This means the normal alarms will go off when the pack/cells haven’t reached the desired cutoff voltage.   The SMC Precision Alarm has been designed to have a delay before the alarm goes off so this prevents voltage drop from heavy acceleration to trigger the alarm.   The Precision Alarm will go off once the desired cutoff is reached.  You can see the difference between a normal alarm and the precision alarm by clicking on the video link below.

https://youtu.be/jZH8ZE8xYXE

As you can see in the video with the normal alarm set at 3.70V per cell the alarm goes off after a few heavy accelerations.  The voltage of the cells is at 3.82V so there is still a good amount of play time left in the packs before the 3.70V cutoff is reached.   We then switched to the precision alarm set at 3.70V per cell and we didn’t film the entire session but we got around 7 minutes of play time before the alarm finally went off.   As you can see the cells were at 3.72V.   This precision alarm is more precise then the ESCs cutoff as the voltage is measured at the cells by connecting the alarm through the balance connector.   This by passes the voltage drop encountered in the power connectors and power wires.

We recommend you start with a 3.70V cutoff and see where the cells end up when the alarm goes off as the internal resistance of the cells will impact the amount of voltage drop.  So packs with higher internal resistance cells may require the voltage to be lowered to 3.60V per cell. 

The Precision Alarm is good for 2S to 8S packs.  We sell it as a kit which has a 6S extension cable so you can mount it permanently in your vehicle where there is room.  We also include 2 pieces of Velcro so you can mount the alarm either on the pack like the picture below or in the vehicle using the extension cable.  We recommend to use the fuzzy side of the Velcro on the back of the alarm.

To set the cutoff on the alarm you must connect it using the proper polarity so the outside black wire on the balance connector must be connected towards the left when the alarm is facing you.  You can see this in the picture below.   To adjust the cutoff press the button on the end of the alarm until you reach the desired cutoff which we recommend to start at 3.70V.  Please note the precision of the cell voltage readings on this alarm can be off by a few hundredths of a volt so it’s not recommended to use this alarm to check the precision of how well your charger charged the cells or if the cells are perfectly in balance once charged.

Below is a picture of the precision alarm installed in an E-Revo with the included extension.  We recommend you always put the alarm on the pack that is connected to the negative side of the ESC.  We also recommend you label your packs and switch sides every use.