So I'm looking for a low voltage alarm for my Li-Polymer batteries since they can get damaged if they go below 3 volts per cell. This crazy guy called WolfDragon tells me he can build one, and here we are a mere couple weeks later and he's already sent me a beta board to test.
I introduce to you the WolfDragon LiPO PCB Lite Alarm. The version I received has an audible Piezo buzzer alarm which retails for $17.50, and it can also come with a LED visible alarm for $15.
The product comes to you in two small packages:
The left package has the board, buzzer alarm, shrink wrap to cover everything, and a sticker with the version information. The right package has the plug that goes on the balance port of your LiPo battery complete with wires, along with an extra female port if your battery is missing it, and some shrink wrap.
Close-up of the alarm board front and back. It's approximately 23 x 16 x 6mm in size
Size comparison to some 6mm BB's and a penny.
Installing the buzzer alarm is simple. The wires are color coded, and the board is marked with A+ and A- (alarm positive and alarm negative wire). Since I wanted this as compact as possible I removed the wire and soldered the alarm directly onto the board.
Installing the balance plug wires is similarly simple. Black wire goes on the "G" (Ground/Negative), and for a three cell pack (11.1v) I installed the other wires in sequence on B1, B2, and B3. A 2-cell/7.4 pack would go on G B1 & B2, and a 4-cell/14.8v pack on G B1 B2 B3 B4.
This is the board installed on an Intellect 11.1v 20C 1400mah battery (if you're wondering the tan colored part is a 30 amp resettable fuse courtesy of Gandolf; and yes Gandolf, I'm still working on that other review for you, I didn't forget
When the board is first plugged in the buzzer goes off twice with an intermittent LED flash, then flashes three times and you know the board is working properly.
I requested this board to fit in incredibly small spaces since I only use Lipo's when I'm really cramped for space. This shows how an 11.1v 1400mah LiPo, with 30 amp automatically resettable fuse, and a low voltage alarm all fit in the buffer tube of a standard M4 rifle.
My other gun which is tight on space is a VFC AIMS AK47; which holds the battery in the same space as any other folding stock AK does, and this alarm still fits perfectly.
My first test was to use a fully charged battery. My gun is shooting 400 FPS with .2's at 30 RPS and I dumped an entire 300 round hi-cap in one trigger pull and the alarm did not go off. I proceeded to shoot another 300 round hi-cap with 100+ shots in semi-auto in very quick succession, then mixed it up with semi-auto and bursts and the alarm did not go off.
I then discharged the 11.1v battery to 9.1 volts (when I snapped the picture it dropped to 9.04 volts. On the first shot the alarm went off just as it should. I charged it up a little more to 9.2 volts and for a little bit (before it dropped below 9.1 volts) the alarm wouldn't go off. It seems to be very precise in it's voltage sensing as advertised.
I will be doing real world torture tests when I attend Battle For Tolland and Op Pine Plains in May, and will be trying this out in my 540 FPS with .25's semi-auto DM rifle as well.
This board seems perfect and extremely reasonable in price considering if you drop the voltage of your pack the first time you will damage it and can loose mah capacity (these 1400mah batteries cost $50 each for example and I would hate to damage one of my $80+ LiPo packs because of something stupid like a few extra shots which drop the battery below 3 volts per cell).
My only advice is to use a very fine soldering tip; the connections on the board are very small and if you use a larger tip, or have the soldering iron at too high of a voltage you may run into problems.
If you're wondering why to purchase this alarm where there are other non-Airsoft-specific alarms for $5-10, then the answer is simple; those commonly give annoying false voltage readings because our batteries can drop to below 3 volts per cell for a split second since our guns pull a lot more amps on the first shot (read this post for more first hand experience with that problem:
http://forums.airsoftmechanics.com/index.php?topic=1801.0). This alarm doesn't have that problem since it's programmed to read the true voltage of the battery pack when it's not under strain.
