# Compact Low Volt warning lamp interest?

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#### skydawg

##### Well-Known Member
Because my V8 engine on our C172 requires electrical power to keep the prop turning, we designed multiple layers of redundancies, most are in the software that controls the engine. But we wanted a self-contained big red idiot light that would illuminate if voltage from either battery drops below a set minimum. We developed the light circuit a bit more to do a couple of other things like flash if norm battery limits were exceeded, eventually having a small circuit made about the size of a dime. You can wire it in pretty much anywhere. Depending on how many I order, cost would likely be $60-$75. We are adding a few other features to it but nowhere ready to say those functions are proven yet, so it will just work as described below.

The thing works great and has proven reliable over the past 1.5 years of flight testing, including sub zero temps overnight and induced over voltage spikes and intentional shorts. It cost a lot less to order in quantity, so wondering if other builders would find it useful. Right now only the 12V version is programmed, but I can do a 24V if there's enough interest. You can see the thing in action on the corsairV8.com website, and I am pasting a page from the Corsair POH supplement manual below that details its operations. Let me know if you might be interested. I am not in the business of selling this stuff so I won't be able to offer much of a warranty other than it will work on delivery, but will try my best. I will know more on cost once I get an idea of quantity.

light will flash below 11.8V and above 15.0V

#### rv7charlie

##### Well-Known Member
Looks like a really nice product, but most of us with expensive avionics or electrically dependent a/c already have low voltage monitoring in our engine monitors/EFISs and overvoltage protection added to our charging systems.

Would you mind a couple of thoughts/suggestions from the more or less conventional powerplant guys?

#### skydawg

##### Well-Known Member
Please, all suggestions welcomed. Always room for improvement. Our system also has a display and internal low volt warning, but the lamp is wired as to be available after all other redundancies failed.

#### Pops

##### Well-Known Member
Log Member
At one time back in the early 1990's , after having a vacuum failure in hard IFR, I designed and built a low vacuum alarm with a flashing LED for the instrument panel and an audio output alarm to the audio panel and capable of automatic switching over to a backup electric motor powered vacuum pump at the time of the failure.
Tried to market it, sold a few. Cessna's engineers liked it, but turned it down when starting to build C-172/182's again because of the bean counters.
Selling safety is a hard sell.

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#### skydawg

##### Well-Known Member
Many stories as yours. Late 1990's I designed a simple low fuel level float switch that was used in cars for decades. It was cheap and proven. Fabricated a method to allow it to be adjustable so you would use it on different size tanks by adjusting how low the float was above tank bottom.... usually about 4 gal mark, and it simply grounded a wire to a illuminate big red bulb and/or buzzer. It worked great, last long time. FAA wanted me to do a lot of things to prove it worthy which would cost a lot of money. No product liability insurance co wanted anything to do with it.... their view was every time someone ran out of gas they'd blame it on the light not working. So I didn't do it anything with it other than install it on my boat.

Back then about 30 planes crashed each year due to fuel starvation, not sure how many now. In big planes we have such simple warnings, which would be great for single pilot task saturated event. The FAA still seems damned determine to kill GA, that's why EXP is growing so quick.

#### rv7charlie

##### Well-Known Member
What caught my eye was
light will flash below 11.8V and above 15.0V
A healthy lead-acid 12V will have resting voltage up around 12.6-12.8V and the typical lithium-iron-phosphate will be slightly higher. Modern charging systems operate at 14V & above. Most electrically dependent guys want instant attention-getting notification if the alternator quits, so the setpoint is usually around 13.5V, well above the 'resting' voltage of a 12V battery. When alternator power is lost, it's rare to have more than 30-45 minutes of battery power in reserve, so any low voltage warning means to get to the ground Now. For me at least, I want the max attention getting notice to happen at alternator loss, and any later status updates are available from the voltmeter itself.

The 15V+ notice might be somewhat useful, but far more important is some manner of fully automated 'crowbar' type shutdown when an alternator goes overvoltage beyond about 15.3-15.5V for more than a half second or so. Reaction time and certainty of action is more critical for the OV condition, since it can quickly destroy electronics.

FWIW,

Charlie

#### Derswede

##### Well-Known Member
I use one of these, visible in my instrument scan range. I use one with my solar system in my camper to monitor batt voltage. Cheap and bright.

#### rv7charlie

##### Well-Known Member
If you're that consistent with your scan, you have my admiration. For the rest of me, I need active alerts.