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I would like to be able to disconnect the battery from the generator, in case of high voltage due to a voltage regulator failure. A handy way to do so is to install a relay on one of the two wires linking the generator and the voltage regulator or the charging wire connecting the voltage regulator to the battery positive post. The drawback of such a solution is that the relay consumes about 2 amperes of much needed electricity.
I read some (long) time ago a post of one builder who successfully installed a mechanical switch to isolate the battery from the generator (a switch coming from a tractor if I remember well). Could somebody give me the brand (and if possible the part number) of this mechanical switch and tell me how it is connected (on the charging wire between the voltage regulator central post and the battery or on one of the two wires between the generator and the voltage regulator), the location of the switch (in the cockpit or firewall forward) and what kind of link they used to operate it. Thank you for your help.
Renaud
Waiex 0161 TD AeroVeeTurbo 90% done and still a lot to be done.

Perhaps this is the post or thread you are thinking about?
viewtopic.php?f=6&t=2009&start=10#p27565

If you keep reading, Bob Meyers mentions the Tyco EV200 as a low current alternative to the traditional contactors.

The above solutions seem like they can handle a lot more current than you need. What about a simple automotive relay? I use one on my airplane instead of a traditional master contactor.

In case you haven't already, you should probably consider installing a suppression diode to protect against a voltage spike when you disconnect the generator.

I went through the same line of thought as you but ended up not installing any switch here.

waiex161 wrote:A handy way to do so is to install a relay on one of the two wires linking the generator and the voltage regulator or the charging wire connecting the voltage regulator to the battery positive post. The drawback of such a solution is that the relay consumes about 2 amperes of much needed electricity.

A 30/40A relay for the 20A Aerovee alternator shouldn't be drawing nearly 2A of continuous current, if even 1/10th of that.

I am planning to use an Earthx battery and they must have overvoltage protection. I am going with a Gigavac GX 11 contactor on the alt. output wire that uses 0.08A holding current on the coil. I have a Perihelion Design overvoltage module that will open the coil feed and drop out the alternator output wire when it senses 16V.

Rick Caldwell
Xenos 0057 fuselage riveting

I still like my dumb switch idea. I haven't finished it yet but it looks promising.

Thank you guys for your answers. I found the battery switch described by Brian Cotton, and I am pondering a way to install it.
Regards. Renaud
Waiex 0161 TD AeroVeeTurbo

For the record: B&C has a nice overvoltage protection kit that does what you're looking for. Designed by Bob Nuckolls of the Aeroelectric Connection, it comes with a wiring diagram and all the bits you need. They come in a couple of different flavors, depending on your system voltage and alternator amperage. See: http://www.bandc.aero/alternator-system ... ories.aspx

Enjoy,

--Noel

I installed the full overvoltage/relay kit that Noel linked above, and the amp draw is indeed very low when engaged.

Actually, I'm a little confused by the OP and some responses... are you looking for a mechanical Master Contactor, or a mechanical alternator switch/disconnect? The amp draw/capacity is much different for each, since the master contactor (presumably) needs to be rated for starter-level amp loads. Even so, a master contractor shouldn't be drawing more than ~1A when closed.

Rynoth wrote:Even so, a master contractor shouldn't be drawing more than ~1A when closed.

I also used the over voltage disconnect referenced above. It will work much faster than you can to disconnect in a high voltage situation.

To back up Ryan, I have sampled several typical continuous duty master contactors and they all average around .75 amps. I did take steps to save just over a half of an amp but in the end, the biggest savings in amperage was switching to LED strobes and nav lights. They were just starting to come out when I built so I used conventional strobes and nav lights originally.

NWade wrote:For the record: B&C has a nice overvoltage protection kit that does what you're looking for.

This is an excellent system that I can confirm, from experience with a bad connector, works very well. Highly recommended!

Dale Williams
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