Hobbymate Low Voltage Monitor LED/Alarm Review - RC Groups

Hobbymate Low Voltage Monitor LED/Alarm Review

Don't have a sixth sense that your battery is getting low on voltage? Hobbymate's newest lineup of alarms warns you before you get into a situtation that may damage your aircraft.



Weight:5.6 grams
Dimension:12.5 x 16.8 x 32 mm
Lead length:12”
Available From:Hobbycool.com

Editor's Note: This is Dr. Dave's 100th review with RCGroups.com! Dr. Dave is a guy who knows his RC stuff, and in fact, I have yet to find something that he can't (or at least won't attempt to) fly. On top of that he has a super cool wife, appreciates a good steak, and knows how to have a good time. Thanks so much, Dr. Dave! And congrats!

Hobbymate RC has released ta complete lineup of onboard battery monitors to better alert flyers of battery voltage conditions that may lead to a loss of power, loss of reception or in the worst scenario, a lost aircraft.

Alarm Contents

The battery monitor comes ready to install with instructions. Each monitor is individually packaged. The circuit board is wrapped in plastic for protection.

Monitor/Alarm Type

The monitors are designed for battery-specific installations - 2-cell through 4-cell and 6, 8, 10 and 12-cell LiPos. I swear I cannot tell the difference when I look at each of them, so make sure you mark them if you have more than one type. Each type provides both an LED and audio alarm.

The LED will shine bright blue if the battery is above the designated voltage for the cell number. It will flash if the battery is below a designated voltage. A red LED will light if the voltage is below the blue LED threshold and finally a red LED will flash and the audio alarm will sound if the voltage drops even lower.

Model: Blue LED Glows Blue LED Flashes Red LED Glows LED Flashes w/ Audio Beep
2S > 7.4v 7.4V – 6.8V 6.8V – 6.6V < 6.6V
3S > 11.1V 11.1V – 10.2V 10.2V – 9.9V < 9.9V
4S > 14.8V 14.8V – 13.6V 13.6V – 13.2V < 13.2V
6S> 22.2V 22.2V – 20.4V 20.4V – 19.8V < 198.V
8S > 29.6V 29.6V – 27.2V 27.2V – 36.4V < 26.4V
10S > 37.0V 37.0V – 34.0V 34.0V – 33.0V < 33.0V
12S > 44.4V 44.4V – 40.8V 40.8V – 39.6V < 39.9V


The battery monitor can be mounted either permanently or temporarily. At just under 6 grams the monitor can easily be installed with either some Velcro or even rubber bands. To make it functional to the ground pilot it must be installed on the exterior of the aircraft. It also is somewhat directional with the sound, so I would install it so that your dominant flight pattern direction has the alarm pointed towards you on final approach. It can also be installed on the top or bottom of the airplane.

Twelve inch leads are provided for two types of installation. If you want to solder it to the ESC leads this is fine, but most will use the pre-installed pin connectors and simply slip them into the positive and negative female receptacles of the balance leads. They fit securely.


In the air the alarm is fairly easy to hear on an electric. It reports with an audible beep at a steady slow sequence. My test plane and ESC continued to fly because the cell cutoff is 3.0V which is below the 3.3V alarm beep provided by the monitor. I could in fact, fly several more times around the pattern and at times with a reduced throttle completely stop the alarm. Once you hit the 3.3V threshold the alarm and red LED will go into action.

As you continue to fly to the ESC cutoff of 3.0V the beeping will continue, and on some passes, I was able to see the red LED flashing. The alarm remains active, and I could easily find the plane in the tall grass after I ran out of power, so it does operate as a lost plane alarm very well.


This is a nice product that can easily be added to plane. It is inexpensive and provides the sound alarm needed. On a fuel plane it would not be easy to hear the alarm at full throttle. But, one could easily “test” the battery condition by simply reducing the throttle to idle and idling or gliding by the pilot’s position. Of course this would have to be a routine one would use often after the normal amount of time and it has no reference to the fuel remaining in the tank.

From a pre-flight test perspective though, you can get a quick feedback on the condition of the battery voltage very quickly. One could also use the monitor to check the battery condition by applying a load to the servos and noting the LED on the monitor. My eyes are just not good enough to see the LED while the plane is in flight.

Is This For a Beginner?

For anyone that has not learned to know when a battery if getting low, or if they fly on an ESC without the cutoff, which I know 3D pilot do all the time, this is a good product to add to the onboard systems.

Flight Video

I have provided a video that shows several of the features of the alarm/LED/monitor. First, is the in-flight video in which you can indeed hear the alarm sounding. As the plane turns away and the alarm is opposite the pilot position, the beep seems only slightly weaker. I could not see the LED very well, and possible this was due to the rubber band slipping over a portion of the LED. Right at the end of the fight clip you can hear the ESC cut-off of the motor. Nonetheless, it is audible. Second up is the lost plane alarm where you can hear the alarm with the plane on the ground very well. I believe in just about any situation if one was within 200 feet they would hear the alarm. You can also see the red LED flashing. The last portion of the video is the ESC cutting off while the alarm is still armed. I lower the throttle and start the motor again until the cut-off occurs a final time. Still enough warning and power left to the get plane home.



I think in essence what you have here is an early warning system for in-flight battery conditions. Otherwise, you would fly to the point of the ESC cutoff and then have to chop the throttle and get the plane home. I do realize many fly 3D planes without the cut-off parameter set because nothing could be worse than a full motor cut-off in a close to the ground hover. But this monitor can preempt the possibility of both a full ESC cut-off or a total loss of power if the cut-off is not set. It does work well. It also has the ability to let you know instantly the condition of your battery before flight and during servo loading in pre-flight.

I believe at the price of $5.00 you have a great backup system for protecting your investment. I understand some of you, and me included might possibly know when our batteries are getting low, or we program our transmitters to alert us of the normal time in flight. But this is just too simple to pass up.

The Good

  • Lightweight
  • Audio and LED alarm
  • Lost plane Alarm

The Not-So-Good

  • Could have a louder alarm especially for fuel motor use
  • A larger LED
Last edited by Angela H; Jun 04, 2012 at 12:33 PM..
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Jun 05, 2012, 06:48 AM
Dr. Dave
I continue to use this product and recently grabbed my trusty Apprentice and three batteries and headed to my flying field. Got there and routed the alarm wires along the fuselage and mounted the alarm under the rubber bands on the wing. What I quickly realized was the sensitivity of the alarm to the condition of my first battery. After plugging everything in I ran up the motor and moved the servos and immediately noticed the LED flashing to tell me the battery was low. I now use these alarms by switching them between all the planes I fly to first check the battery (just forget which ones I charge at times) and to monitor in flight battery conditions. Simple, easy to use and cheap.
Last edited by 78dave; Jun 07, 2012 at 06:05 AM.
Jun 15, 2012, 11:14 AM
Surface, Air & Water Rc Toys..
freechip's Avatar
I used similar products and up until telemetry I found that they work great, mine were very loud and bright.
Jul 19, 2012, 08:54 PM
jackerbes's Avatar
I'm not using any of these at this time but noticed and read the review.

It would seem that you can greatly simplify the complications of owning and keeping track of a number of different models for the different packs of various sizes by simply buying a 2S version and use it with any size pack by plugging it into the balance connector so that it is only monitoring either the first two or last two cells in the pack.

The cell to cell variation in voltages is normally quite small on healthy packs so acting on the voltage in a pair of cells should be just as useful as acting on the pack voltage.

For those that are unclear on the concept, this will show how the widely used JST-XH balance connectors are wired:


They don't mention if these are reverse polarity protected or not. It may be that if you connect it to too many cells it will damage it of course. And they may not be reverse polarity protected either.

Maybe the reviewer can take some of the test samples and determine if these are reverse polarity or over voltage protected? The makers could include that info on their web page too to be more helpful.

Jack (who lives and flies in a heavily wooded area and really should have some of these...)

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