PMag issue

[N941WR]

Originally Posted by KRviator

...

What I've found through another VAF'er with this arrangement is that if you have ships power off but the engine is running above the self-sustaining speed for the P-mags is that the Dynon will then measure the PMag's internal alternator voltage.

This could give you early warning of a possible fault if you fly with ships power off to the PMag and ...

I am not sure this is correct.

During the development of the EICommander we built a test rig that allows us to spin two P-mags simultaneously with an electric motor.

After reading this post we spun up our test P-mags and measured the voltage across the power and ground leads. The measurement on one was in millivolts. The other one has a bad diode and put out over 24 volts. (We have known of this problem for some time and since we don't fly with these P-mags and because we may have been the cause of this failure, we haven't sent it in for repair.)

After checking with Emag, they confirmed that the P-mags have a diode to prevent them from back powering your electronics.

If you choose to connect the power leads to your EFIS, be careful because with no load, high RPM, and a bad diode the P-mag can put out well over 60 volts. (We have toasted some EICommander development units before we realized one of our P-mags had a bad diode.)

[revenson]

[quote=akarmy;930074]Yep Same ones Bill listed.

http://www.mouser.com/ProductDetail/...87yhfudQ%3d%3d


Does it matter that these are listed as 80v fuses, and not 12 or 14v?

I've been using ATC fuses without issue for 400+ hrs. hooked to an always hot battery bus (with switches of course). I have no idea what the voltage rating is. I assumed automotive fuses are always 12-14 v.

[akarmy]

Originally Posted by revenson

Does it matter that these are listed as 80v fuses, and not 12 or 14v?

Good question. I didn't know so I Googled it and found this on a ham radio site.

Fuses actually have TWO ratings. Voltage AND current.

1. You may use a higher voltage rated fuse anywhere a lower voltage fuse is used, as long as the current rating is the same. THUS, the Handbook statement that you can use a 1 Amp. 250 Volt fuse in a low voltage (e.g. 12 Volt) circuit in place of a 1 Amp. 32 volt fuse. You MAY NOT safely use a 1 Amp. 32 Volt fuse in place of a 1 Amp. 250 Volt fuse!

2. The voltage rating DOES matter. The fuses are designed to ensure that when a fuse blows, the result will not lead to an arc inside the fuse body. (600 Volt rated fuses are usually ceramic insulated to withstand the additional heat and stress from the possible higher voltage.

3. The current rating of a fuse is for AC OR DC. It does NOT matter. The "appearance" of a blown fuse tells you nothing about the type of current (AC or DC) going through the fuse, just the AMOUNT OF CURRENT flowing through the fuse when it failed. A large surge will "vaporize" the fuse element, whether it's AC or DC. A small amount of overload will often leave much of the element still visible, whether the current was AC or DC.

4. The fusible element width, etc. is NOT determined by the voltage rating, but by the current rating. 10 Amp fuses will appear similar, whether they are 32 Volt or 250 Volt units. Low voltage (e.g., 32 volt types used in Automotive applications) will often have thicker or wider, or physically "larger" fusible elements because they typically carry larger CURRENT than 250 volt rated fuses. Auto (cylindrical type) fuses often go up to 20 or 25 Amps, values not often seen in the 250 Volt variety. (Think about it: 20 Amperes from the AC line in the U.S. would be protecting 2400 Watts- a rating that meets or exceeds the main circuit breaker of many residential lines. (Usually 15 or 20 Ampere service.) Yet, 20 Ampere fuses are common in automotive lighting systems, Air conditioning systems, etc.)

[Noah]

Originally Posted by Bevan

Pmags have a built-in crowbar over-voltage protection system.

If you don't mind, where did you get this information?

[sblack]

this forum is awesome!

[GalinHdz]

Originally Posted by N941WR

I am not sure this is correct.

During the development of the EICommander we built a test rig that allows us to spin two P-mags simultaneously with an electric motor.

After reading this post we spun up our test P-mags and measured the voltage across the power and ground leads. The measurement on one was in millivolts. The other one has a bad diode and put out over 24 volts. (We have known of this problem for some time and since we don't fly with these P-mags and because we may have been the cause of this failure, we haven't sent it in for repair.)

After checking with Emag, they confirmed that the P-mags have a diode to prevent them from back powering your electronics.

If you choose to connect the power leads to your EFIS, be careful because with no load, high RPM, and a bad diode the P-mag can put out well over 60 volts. (We have toasted some EICommander development units before we realized one of our P-mags had a bad diode.)

THANKS for this good info. I may be reading the millivolts which gives me a GREEN indication on my EFIS when the engine is running and I cut the ship power to the P-Mags. I will have to re-think the installation since I sure don't want the P-mags to accidentally destroy my EMS if a diode goes bad.

[N941WR]

Originally Posted by GalinHdz

THANKS for this good info. I may be reading the millivolts which gives me a GREEN indication on my EFIS when the engine is running and I cut the ship power to the P-Mags. I will have to re-think the installation since I sure don't want the P-mags to accidentally destroy my EMS if a diode goes bad.

No problem, we are happy to help.

While we like what you are trying to do by connecting them to your EFIS, we have also tried to figure out a way for the EICommander to tell you if the P-mags are running off internal or ship's power. So far, no joy. The Pmag's serial stream does report the voltage its internal buss sees but it doesn't tell you where it is coming from. They may change that at some point in the future, and if they do, we will update the EICommander's software.

For now the only reliable test is to drop power to them.

[KRviator]

Originally Posted by N941WR

No problem, we are happy to help.

While we like what you are trying to do by connecting them to your EFIS, we have also tried to figure out a way for the EICommander to tell you if the P-mags are running off internal or ship's power. So far, no joy. The Pmag's serial stream does report the voltage its internal buss sees but it doesn't tell you where it is coming from. They may change that at some point in the future, and if they do, we will update the EICommander's software.

For now the only reliable test is to drop power to them.

There's no issue with that though is there? Once you're airborne, pull ships power and let the EICommander report the loss of voltage if it happens. Restore ships power, land and know you need to fix it before the next flight.

[Bevan]

Originally Posted by Noah

If you don't mind, where did you get this information?

I am positive I had received that tidbit during a phone discussion with Emagair but wasn't sure, so I just called them to confirm. Today, they said NO crowbar. Something has been misunderstood/remembered here so I oppologize for the apparent mis-information. Unsupported data from my post you're quoting has been deleted.

Bevan

[N941WR]

Originally Posted by KRviator

There's no issue with that though is there? Once you're airborne, pull ships power and let the EICommander report the loss of voltage if it happens. Restore ships power, land and know you need to fix it before the next flight.

As stated above, the EICommander cannot tell where the P-mag is getting power from, only that it is working.

Above around 800 RPM the 114 series P-mags automatically switch to internal power. So, turning off power in flight won't make any difference m grounding it is another story.

The older 113 series P-mags run off ship's power and only switch to internal power when they detect a loss of ship's power.

You can always do a quick, low power (1000 RPM), mag check before shutting down. (Or look at your EICommander, if installed.)