Overvoltage Protection Help

[Flyyak]

Need help with a basic overvoltage protection module or system. I have an RV7 with about 300 hours, a two screen G3X non touch and a G5, wiring harness prepared by Stein Air. Basic circuit breakers together with a 24 place fuse panel with 12 places assigned for avionics buss and 12 for sub fuse block buss. I have a alternator field CB and an Alternator field switch. The switch will cut/turn off the alternator to the main buss. I have installed an emergency battery LiFePO4 which is connected via a switch to back feed the avionics buss. I will attempt to attach a copy of my wiring diagram, photo of emergency battery and fuse panel for your review. I have replaced the Narco and indicator with a Garmin SL30 which is wired by RS232 direct to G5 rather than going through the can buss.

I have had very poor luck with PC680 odyssey batteries and have just replaced my last one with a Shorai LFX18A1-BS12. I have monitored the charging system closely since this replacement and have noted that after starting, the voltage may read on the G3X up to 14.6 or 7 and amps +3 or 4 for a very short period. I leave it at engine idle for several minutes before moving and the voltage drops to 14.4 and amps to +1 or 2. After a very short period the voltage will read 14.4 and amps will be at 0. Is that normal?

I have never had voltage above 14.8 with a dying odyssey or amps over +4. After reading many post when researching the Shorai battery there were concerns about a malfunctioning alternator, I have thought that it would be prudent to install an over voltage system to protect my avionics and the Shorai LiFePO4 battery and an under voltage protection for the battery. My emergency battery is not connected to be recharged by the alternator and I use it strictly as an emergency power source for my avionics. I charge it outside of my aircraft with a special charger (CTEK) and it will power up to 10 amps for over an hour (at least that what my bench test confirmed).

I have reviewed the Perhelion Design OV module and it may be sufficient wired per his diagram in between my alt fld switch. I have also purchased a relay module from Amazon VR1000 Single Phase Protection Relay Over-Voltage 9V-18V Under-Voltage 0.1V-6V AC/DC(D12)
by YWBL-WH but I do not think it will work.

If you have a simple wiring diagram or modules that I can plug and play, please post. I have attached a couple of pdf photos and a woiring diagram but I am not sure that I did it right. Thanks

[ColoradoSolar]

Don't know about over voltage protection but 14.8v while the battery is charging is fine.

[Pat Hatch]

You don't mention what alternator you have or whether it is internally or externally regulated. Also, does your Shorai battery have a BMS?

[Flyyak]

It's a standard Van's alternator, internally regulated and has operated flawlessly. Here is another attempt to add my wiring diagram. It's a pdf file so if it does not upload and someone can tell me a better way to attach it I would appreciate it.

[Flyyak]

Try again as jpeg

[Flyyak]

No BMS on Shorai. They have a special charger that is suppose to balance cells but I understand that you may only need to use it maybe every 6 months. Shorai customer support indicated that my CTEK which is specifically made to charge LIfEpo4 batteries should do fine. I also spoke to a couple of guys on this forum who said that they hardly ever attach a charger to their Shorai.

[Pat Hatch]

Originally Posted by Flyyak

Try again as jpegAttachment 887

Right, I note that Shorai batteries don't have a BMS. But even those Lithium batteries that do, over-voltage protection is still required or recommended. So your plan to install the Perihelion unit would be a good move with the internally regulated alternator.

You could wire your back-up battery with a diode and resistor to have your alternator trickle charge it in flight if you wanted to. It certainly would be more convenient.

[FireMedic_2009]

As stated above, 14.7V is fine. The initial jump of +4A is fine. It's showing the amount of amps charging the battery. You will always see 0 to +2A to keep the battery topped off.

If you have an alternator with an internal regulator that doesn't have OV protection like a regular automotive alternator (regardless if it's a 1-wire or 3-wire) then you would want to add a contactor between the alternator and battery contactor so you can disconnect the B-lead from the main bus. The reason is because it's possible for the alternator to fail in such a way that you will not be able to turn Off the alternator with the field wire so by using a contactor you can manually disconnect the B-lead. The field wire is connected to the contactor which connects/disconnects the B-lead with a breaker switch (field breaker switch). The OV Protection module (whether it be Perhelion, B&C, or some other brand) is connected to in series between the field breaker switch and the contactor. When the OV module detects a voltage a little above 16V the OV module automatically trips the field switch which causes the contactor to open. OV module detects the over voltage in milliseconds. I don't know how true it is but it's said voltage runaway on an alternator (although rare) can happen quickly, 2-5 secs, I don't know. It's cheap insurance in protecting your electronics.

Find out what alternator you have and check if it has OV protection. If it's a B&C then it has OV protection

[Pat Hatch]

Originally Posted by Flyyak

I have monitored the charging system closely since this replacement and have noted that after starting, the voltage may read on the G3X up to 14.6 or 7 and amps +3 or 4 for a very short period. I leave it at engine idle for several minutes before moving and the voltage drops to 14.4 and amps to +1 or 2. After a very short period the voltage will read 14.4 and amps will be at 0. Is that normal?

I think what you're seeing is normal and just your regulator adjusting the voltage between 14.4 and 14.7 volts. Some of that could be indication error, I suppose. Initially after engine start, it is normal to have an inrush of amperage to your battery to replace the energy that you just used to start, and once it's topped off, the amps should settle near zero. Looks like your shunt is set up to measure amps going to and from the battery and not the output of the alternator, so what you're seeing is normal.

[Danny King]

I would never be comfortable with an internally regulated alternator and a Lithium iron battery. I know it's rare, but it has already happened to an RV-8A. The alternator failed, and the internal voltage regulator dumped the alternator's output directly back into the field causing a huge over voltage. There was no way to turn the alternator off! The lithium iron battery torched off, and the pilot had to land on a road with a toxic smoke filled cockpit and a battery fire by his right foot! That was a close one!

I say just don't do it! I don't think you will find an internally regulated alternator on a certified aircraft. Add a lithium battery, and you are courting a possible inflight fire disaster.

Note: I have a Shorai lithium iron battery in my Kawasaki jetski, and my Yamaha motorcycle. I love the way they hold their charge for months. If I ever have one torch off, I'll stop the bike and get off or go swimming.