Master switch

[KenSandyEggo]

My battery seems to run down a bit if it sits for a few days. Maybe I need a new one. (I removed my clock for a panel-mounted tach for the 2nd ignition system.) I was perusing my J.C. Whitney Aircraft Supply Catalogue and saw some master switches and installed one. I'll see if that helps......provided that I remember to turn it off.

[le-wardy]

Ken, is your battery a sealed item or one with removable caps ??

[StanFoster]

Ken: I had the same problem after wiring my RAF. It would take about three days and the battery would go down. I finally took off all the leads off the positve terminal and did an ohm check. I found one that showed a high resistance...but not infinity like it should have been. I traced the wire down and found I had wired one wire wrong. After that...infinity on my ohm scale and the battery stays charged. :D

Stan

[KenSandyEggo]

It's a sealed Odyssey dry-cell, Les.

Thanks, Stan. I'll have to check that out.

[Doug Riley]

Ken, those heavy cables make it look like the switch handles even the heavy current to the starter. Is that true?

[KenSandyEggo]

Yes, Doug. Is that O.K? The switch is designed as a master cut-off and is rated at 1,000 amps, if I recall. Should the starter be wired some other way?

[Doug Riley]

Ken, maybe some other folks will jump in on this. My impression (and the way I did it) is that one generally runs the heavy wire that powers the starter directly from the battery to the plus terminal of the solenoid. This eliminates a bit of voltage drop* that's bound to occur in (a) the 2 extra connections, (b) the (presumably longer than a direct shot) wires and (c) the switch itself. It also could save a tad of weight, given how heavy that #2 wire is... and, if you don't run the starter circuit through your master, you probably can get away with a lightweight little, lower-current switch.

All these are small issues, as long as you have a master that can handle the start current without heating up. Even with a Frankenstein's-lab master switch, I still wouldn't flick the master while holding the ignition in "start" position! Could get sparkish.

* voltage drop is probably a bigger issue here in East Icicle than it is in ever-balmy Sun-Diego.

[KenSandyEggo]

Doug, I just checked the catalogue, and it is rated at 1,000 amps. Seems to be working O.K., so maybe I'll leave it alone unless I note any problems.

[barnstorm2]

Ken,
Something else to check.

If the solenoid is going bad in your pre-rotator or starter for the engine this can cause an energy drain.

[KenSandyEggo]

Tim, how can the solenoid go bad in the prerotator and cause an electrical drain? It's cable-operated. Did you think I had en electric prerotator?

I haven't had the charger on in several days and I checked the battery today. It was holding 12.5 volts, whereas before the switch, it would have been down some.

[gyroman]

Hey KennyJ,

I read there was an earthquake out your way, everything OK out there? We wouldn't want anything to happen to your gyro, er um I mean we wouldn't want anything to happen to YOU or your gyro... I heard it happened offshore, just south of the border...

[barnstorm2]

Yes, Ken. I thought you might have an electric pre-rotator. Though your master switch is solving the drain problem, I would still be wondering what was eating the power?

[KenSandyEggo]

Toby, the quake was a non-event for me. I didn't even feel it. I was pulling my car into my hangar when it happened, so I didn't feel a thing. My neighbor behind me came running in and asked if I hit the wall with my car. He said a few photos fell off the wall. There was no damage around here, just a little shaking.

Tim, I don't know that much about wiring, but could the starter being constantly energized have been causing the drain? That's the way the manual called to wire it. I know it was live, because I accidentally got a spark when I touched it with a screwdriver or something, even though everything was off.

[barnstorm2]

Ken,

Though my Dad was an electrician, I did not pay enough attention when I was a kid. Now it is too late.

Though through experience, I do know that light power drains have often led me to find starters that were going bad.

If you take the big negative wire off of the starter and it stops draining your battery then you have it. A multi-meter (volt-ohm) would help here. That is really just an annoyance. It is just a matter of waiting for your starter to fail.

If that does not cure the problem then you have a ground leak somewhere and that would worry me.

[StanFoster]

Seriously Ken....take off your leads going to the positive post. Take you ohmeter and check each lead to ground. If there is anything but an infinity ohm reading...there is your problem. If you have infinity ohm readings..then the only way your battery will go down is if the battery itself is bad.

Again...I had the same problem...took the positive leads off....found one that measured less than infinity...and traced it to a point I had misread on the schematic. I corrected it....the ohm reading went to infinity...and the battery drain went to zero. End of problem. :D

Stan

[mceagle]

Ken,
All starter motors are "hot wired" to the solenoid. This is normal and should not cause any power drain. Some batteries are worse than others with "narural drain" over time (eg sealed types) and if you combine this with a small draw from a wiring problem, a capacitor or radio memory connection, then you have the potential for battery depletion over time.

[KenSandyEggo]

Stan, I'll check it soon.

Tim, I have a sealed type, so I'm guessing it's just a natural drain as you mention, but I'll check, as Stan suggested.

[Mike Hook]

One more thing to check on your power loss. I have 30 years experience as a electrician in the mines and on construction. Check to see that there is no corrosion around any terminals, It can track the dc voltage and cause a drain there too. I have found many times in the mines when dc equipment started to act funny there would be tracking on corroision some place justttttttt out of sight.

Mike

[Udi]

Ken - your Odyssey battery should not lose more than 0.1 volt per month on it’s own. These batteries have a much smaller internal losses than regular lead batteries. The switch you installed is a good idea, but I would also recommend that you look for the root cause of the drain. I would use a multi-meter and check how much current is being drawn from the battery with your battery switch in the "on" position. If you find a draw of more than 1-2 milliamps (mA) when everything is turned off than you have a problem.

In my gyro, the only permanent draw is from the rectifier. The rectifier is drawing about 0.5 mA all the time. This is normal, and it is a very small draw, considering the capacity of the battery.

If your Odyssey is model 680, than it has a capacity of 16 Ah (which means it can supply one ampere for 16 hours). With a constant draw of 0.5 mA (one half of a thousands of an amp), it would take three and a half years for the battery to drain completely.

If you don't have a multi-meter, buy one. They only cost $20-$30. Find what is the amp draw from your battery, and calculate how fast the battery will drain. If you find that the battery is draining faster than your calculation shows, than your battery may be getting old. To check for current, you connect your multi-meter in serial with the wires that you check. In other words, disconnect a wire from the battery, and place one probe on the battery, and the other on the wire. This will tell you how much current is going through this wire.

Good luck.

Udi

[mceagle]

Udi, what happened to the little gyro that used to taxi across the bottom of your posts?

[KenSandyEggo]

I do have a multimeter. Now if I can only find the directions.

[Udi]

Udi, what happened to the little gyro that used to taxi across the bottom of your posts?

Tim - it ran out of gas and crashed... :(

Udi ;)

[Ron Marlett]

Another thing to consider is the rate of charge. If your electrical system is not topping off the battery, a very small drain(EFI computer memory voltage?) could be fully depleting your battery in a very short time. What is the voltage measured at your battery with the engine running? Running over 2000 RPM?

There has to be a difference in potential for current to flow into the battery and charge it. If the voltage reaching the battery is not high enough above the fully charged voltage of the battery, the battery will NEVER reach full charge. You could have a 200 amp alternator on your ship but if it's voltage regulator is only getting 12.5 Volts to the battery, the battery will never fully charge. A 12.5 volt 200 amp alternator output would of course run all the electrics on the ship just fine if the depleted battery would crank it over hard enough to start:).