Breakers as Switches - Good Idea?

I often see GA and gliders that use breakers as switches. Is this such a good idea? Are breakers rated to be used as switches? These aircraft usually, but not always, have at least a master switch.

Our tow plane uses Tyco W31 series breakers which incorporate bat handles and are designed to be used as a combination of a breaker and a switch. http://www.aircraftspruce.com/catalo...?clickkey=5950

What say you?

John (http://aviation.derosaweb.net)

Years ago, my glider's panel was rewired by an owner of a FAA certified repair station / avionics shop. He used two circuit breakers as the main (and only) switches on my panel. I have two batteries and he installed two breakers. They look like the breaker you have linked to at Aircraft Spruce.

The breakers are wired so I can turn on one, or the other, or both at the same time (switching from one battery to another and not losing power to the panel.)

I must say, the extremely neat bundle of white wires, expertly run behind the panel, sure looks good compared to the rat's nest of Radio Shack stuff that was there before!

Ray

On Tuesday, February 16, 2016 at 11:59:49 AM UTC-5, Six-Seven Romeo wrote:
I often see GA and gliders that use breakers as switches. Is this such a good idea? Are breakers rated to be used as switches? These aircraft usually, but not always, have at least a master switch.

Our tow plane uses Tyco W31 series breakers which incorporate bat handles and are designed to be used as a combination of a breaker and a switch. http://www.aircraftspruce.com/catalo...?clickkey=5950

What say you?

John (http://aviation.derosaweb.net)

Unless a breaker is designed for "switch duty", I would not use a breaker as a switch that gets's lots of use.
Mostly because the wear during each operation slightly reduces the amp rating of the breaker. What this means is that it will (gradually, over time) trip at lower and lower values.
A hot ambient temp add's to this (since most are thermally tripped). The result is that on a warm/hot day after multiple cycles, the "normally fine" breaker may trip on you, causing you to at least wonder, "What's happening?", or losing a flight computer/radio/logger/etc. when most inopportune.....

Granted, you could argue that it will take 20 years of recreational use to create this issue (I'm just picking a number here), but breakers are breakers, switches are switches.
Personally, I prefer fuses over a lot of breakers although you do need to keep correctly sized spares around.

Hi John,

I used similar, though a different brand, when I rebuilt my panel. All aviation grade and to FAA & EAA specs and guidelines. The examples you quoted have a cycle rating of 6,000 operations at 100% load and 10,000 mechanical operations. In other words, no problem in using them as a switch. The compensation graph in the specs will allow you to correct for peak-summer (high temp correction) operation.

I won't have the pleasure of flying with the CC armada at Ridge this spring.. I trust you'll have fun nonetheless!

CJ

Adding 1 amp switch/breaker for 200mA instrument draws 10% more power from battery because breakers have internal resistance. That may or may not be significant. If you have 10 hrs battery capacity, you will loose on hour.

At 07:49 17 February 2016, krasw wrote:
Adding 1 amp switch/breaker for 200mA instrument draws 10% more power
from
battery because breakers have internal resistance. That may or may not be
significant. If you have 10 hrs battery capacity, you will loose on hour.

I doubt that.

10% of 200mA is 20mA, or 0,02A.
It would then take 50 Hours to reduce the charge by 1AH.

Is that a problem?

At 09:16 17 February 2016, Tim Newport-Peace wrote:
At 07:49 17 February 2016, krasw wrote:
Adding 1 amp switch/breaker for 200mA instrument draws 10% more powe
from
battery because breakers have internal resistance. That may or may not
be
significant. If you have 10 hrs battery capacity, you will loose on
hour.

I doubt that.

10% of 200mA is 20mA, or 0,02A.
It would then take 50 Hours to reduce the charge by 1AH.

Is that a problem?



I replaced all the circuit breakers with fuses in my ship. I reason that
circuit breakers cause a voltage drop and use unnecessary power.
I did not see any benefit in being able to reset a breaker in flight as I
wouldn't do it. If a breaker trips it is usually for good reason and
should, therefore, stay that way until you are safely on the ground.

On Wednesday, February 17, 2016 at 5:15:06 AM UTC-7, Jim White wrote:
At 09:16 17 February 2016, Tim Newport-Peace wrote:
At 07:49 17 February 2016, krasw wrote:
Adding 1 amp switch/breaker for 200mA instrument draws 10% more powe
from
battery because breakers have internal resistance. That may or may not
be
significant. If you have 10 hrs battery capacity, you will loose on
hour.

I doubt that.

10% of 200mA is 20mA, or 0,02A.
It would then take 50 Hours to reduce the charge by 1AH.

Is that a problem?



I replaced all the circuit breakers with fuses in my ship. I reason that
circuit breakers cause a voltage drop and use unnecessary power.
I did not see any benefit in being able to reset a breaker in flight as I
wouldn't do it. If a breaker trips it is usually for good reason and
should, therefore, stay that way until you are safely on the ground.

I think the right way to look at this is to take a gander at the spec sheet of the referenced part. At the top of the sheet is a table showing the resistance that the breaker introduces for varying current ratings. It shows for example that a 5A breaker introduces 0.03 ohms. Next, consider the peak load of the device that you're powering. If it's a radio, for example, look at its transmit current. Let's say the peak current is 1 amp. Then the voltage drop across the breaker is: V = iR = (1)(.03) = 30 mV. That's insignificant. The actual effect on battery life is that it will more likely be extended by the introduction of the additional load; it's just that the drop out point for the connected instrument will be 30mV lower. For a lithium battery with a fairly sharp fall off, I think you'll normally end up net positive to battery life by the introduction of the small series load (as long as the connected instrument works down to the steep part of the battery discharge curve).

And, BTW, fuses have resistance too -- it's the same game with a fuse.

At 17:17 17 February 2016, Steve Koerner wrote:
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And, BTW, fuses have resistance too -- it's the same game with a fuse.

I was using ETA 106-P30 trips that have internal resistance of 0.9ohm for
the 1a and 0.05 for the 5 amp. The problem was my Becker radio which only
likes to work at 12V+. The 5amp breaker dropped the voltage by over 1V on
transmit which for SLA batteries made it unworkable. A standard blade fuse
had much less impact.

I now use LifePo4 so this is now a mute point. However one point to note
with trips is the trip time. Mine were 10 seconds at 2x rated load.
Standard fuse trips much faster.

Jim

keskiviikko 17. helmikuuta 2016 19.17.54 UTC+2 Steve Koerner kirjoitti:
On Wednesday, February 17, 2016 at 5:15:06 AM UTC-7, Jim White wrote:
At 09:16 17 February 2016, Tim Newport-Peace wrote:
At 07:49 17 February 2016, krasw wrote:
Adding 1 amp switch/breaker for 200mA instrument draws 10% more powe
from
battery because breakers have internal resistance. That may or may not
be
significant. If you have 10 hrs battery capacity, you will loose on
hour.

I doubt that.

10% of 200mA is 20mA, or 0,02A.
It would then take 50 Hours to reduce the charge by 1AH.

Is that a problem?



I replaced all the circuit breakers with fuses in my ship. I reason that
circuit breakers cause a voltage drop and use unnecessary power.
I did not see any benefit in being able to reset a breaker in flight as I
wouldn't do it. If a breaker trips it is usually for good reason and
should, therefore, stay that way until you are safely on the ground.

I think the right way to look at this is to take a gander at the spec sheet of the referenced part. At the top of the sheet is a table showing the resistance that the breaker introduces for varying current ratings. It shows for example that a 5A breaker introduces 0.03 ohms. Next, consider the peak load of the device that you're powering. If it's a radio, for example, look at its transmit current. Let's say the peak current is 1 amp. Then the voltage drop across the breaker is: V = iR = (1)(.03) = 30 mV. That's insignificant. The actual effect on battery life is that it will more likely be extended by the introduction of the additional load; it's just that the drop out point for the connected instrument will be 30mV lower. For a lithium battery with a fairly sharp fall off, I think you'll normally end up net positive to battery life by the introduction of the small series load (as long as the connected instrument works down to the steep part of the battery discharge curve).

And, BTW, fuses have resistance too -- it's the same game with a fuse.

I was looking at 1 amp breaker specs, there the resistance is 0,61 ohms. Trip time for 10 times nominal trip current is 0,4-2,5 secs, which is quite slow. Of course for radio or xpdr you would probably use 5 amp switch with lower voltage drop.