The following is a review of the RC Models Distribution Lipo Voltage Guard, Manufactured by CSM Design Consultancy Ltd. The unit is a piezo sounder style voltage alarm that is fully programmable for different cell configurations and voltage settings. The unit consists of the piezo sounder and a small servo style lead for programming the lipo voltage guard. Initially some pictures of the unit .....
	The voltage guard is easily installed. The red and black wires should be directly soldered to the battery (lipo) connector leads on your ESC, effectively wiring the voltage guard in parallel to the lipo. This effectively puts the voltage guard right on the source cables for the lipo when installed in the T-Rex, enabling accurate measuring of the lipo voltage level during flight. The lipo guard is accurate to within 1% of the set voltage. Here are some manufacturer specifications : Operating Voltage 5V - 45V Minimum Threshold 5V (2 cells, 2.5V/cell) Maximum Threshold 34V (10 cells, 3.4V/cell) Precision 1% or better Current draw 35mz max. during alarm, <10ma otherwise Weight 4g Size 28mm x 20mm x 10mm The lipo guard is secured to the model using servo tape. Manufacturer defaults are for 3 cells and 3.0V per cell alarm threshold. The timed minimum hold feature is also set as default. At startup the lipo guard beeps four times to show it is active, it will not beep again unless your lipo hits the set threshold voltage. When this happens the voltage guard beeps at approx. 1 second intervals with single beeps. If you ignore this then when the voltage goes more than 0.1V below your voltage threshold then the alarm will beep twice every second. Ignore this and you go to three beeps per second at more than 0.2V below the set threshold. In the T-Rex I found my packs were starting to sag on or around when the factory default sounds the alarm. Ideally I wanted to avoid pack sag and land before this happens. I reprogrammed the device for 3.2V per cell as the threshold, I now get ample warning before the pack sags. The voltage guard can be programmed for anything from 1 to 10 cells and within a voltage range of 2.5V/cell to 3.4V/cell for the alarm setting. Programming is via the supplied cable which plugs from the Lipo Voltage Guard to your receiver (throttle channel). Programming is done by listening to beep codes and putting the throttle stick in the appropriate place to change that setting. Below are pictures of the final mounting of the sounder, well away from other electrical radio equipment.
	In flight the Lipo Voltage Guard works perfectly, sounding tones at around exactly the point I would expect, I've taken to not timing my flights now as the sounder lets me know before I hit pack sag or ESC power reduction mode. Lastly the Lipo Voltage Guard has two settings, timed minimum hold and indefinite minimum hold. Timed minimum hold sounds the alarm for twenty seconds on hitting the pre-programmed voltage, after which it changes to the present voltage. Indefinite Minimum hold sounds the alarm when the pack reaches it's lowest voltage since startup. Overall Conclusion A very cheap and worthwhile addition to my T-Rex. It removes the guesswork from pack flight times and allows careful monitoring of pack voltage levels. Hopefully this will also increase the longevity of my packs as I am never likely to over discharge by mistake, not that I do this but it's good to have the Lipo Voltage Guard there as a safety net. This is particularly useful for flights that are very stop start (difficult to time) rather than continual flying where a stop watch can work just as well.