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Don’t do this

werxcv01

Well Known Member
As a new owner of an RV-8 with one P-Mag, I did not know that the company warns against turning the master switch (and thus the P-Mag) on while using a battery charger. I now know. Just received the overhauled P-Mag back from E-Mag and am planning to reinstall it next week.

I have to thank E-Mag for the great service. I shipped the unit right before the winter weather hit the sunny south, so UPS was a week late delivering it. However, the turnaround was less than 4 business days. In fact, I received it back within a week of it arriving at their shop.

I will be posting reminders near the master switch, on the charger, and under the oil filler door to NEVER SWITCH ON THE MASTER WHEN THE BATTERY CHARGER IS CONNECTED!
 
My E-mags (P-114) are on separate switches, which works well for me. The only time I flip the switches is for starting the engine. Otherwise, they're off while doing avionics stuff on the charger with the master on and the engine not running. I leave the plane on the Odyssey float charger all the time when it's not flying.
 

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As I’ve posted multiple times, never run the panel (or anything else) with a battery charger connected. Your expensive avionics will thank you for not sending them trash for power. And no, having a battery on line at the same time does not “filter” the trash. The trash is AC noise riding on top of the DC voltage.

End the problem. Run the panel, charge the batteries, or do both at the same time by connection a real, regulated power supply. This $100 unit is light and will do everything you need: https://mfjenterprises.com/collections/power-supply/products/mfj-4230mv

Carl
 
As I’ve posted multiple times, never run the panel (or anything else) with a battery charger connected. Your expensive avionics will thank you for not sending them trash for power. And no, having a battery on line at the same time does not “filter” the trash. The trash is AC noise riding on top of the DC voltage.

End the problem. Run the panel, charge the batteries, or do both at the same time by connection a real, regulated power supply. This $100 unit is light and will do everything you need: https://mfjenterprises.com/collections/power-supply/products/mfj-4230mv

Carl

I can testify to this power supply. Rigged a nice little connector to my battery that I can access under the panel and hook up to the power supply. Works very well.
 
As I’ve posted multiple times, never run the panel (or anything else) with a battery charger connected. Your expensive avionics will thank you for not sending them trash for power. And no, having a battery on line at the same time does not “filter” the trash. The trash is AC noise riding on top of the DC voltage.

End the problem. Run the panel, charge the batteries, or do both at the same time by connection a real, regulated power supply. This $100 unit is light and will do everything you need: https://mfjenterprises.com/collections/power-supply/products/mfj-4230mv

Carl

Thanks for putting this in layman’s terms. I will consider getting this power supply.
 
My E-mags (P-114) are on separate switches, which works well for me. The only time I flip the switches is for starting the engine. Otherwise, they're off while doing avionics stuff on the charger with the master on and the engine not running. I leave the plane on the Odyssey float charger all the time when it's not flying.

My -8 also has a power switch to the P-Mag to be used to test its internal alternator. I wasn’t sure if that switch completely removes the P-Mag from the airplane’s electric system or not.
 
i have my linear bench power wired to plug for a cigarette lighter power outlet. leave the master off, plug bench power into power receptacle and turn on bench power. i am comfortable accessing its power up to 7 amps. enough to drive anything in the panel. easy to pull fuses on the stuff you don't want power to.
 
As I’ve posted multiple times, never run the panel (or anything else) with a battery charger connected.

Carl

So it is the unclean power that is the sole cause of this P-Mag failure?

BTW. I have an older MJF 25 amp - -silent and durable.
 
Can you share what damage was done?

The circuit board was damaged and had to be replaced. Also the thermal sticker showed excessive heat and was replaced. This aircraft has been flying several years with this P-Mag with no noted issues. The last recorded maintenance was in 2017 when there was an issue with the tachometer reading the P-Mag. There is a blast tube blowing on the unit and there have been no modifications to the cowling or any other part of the engine compartment. Besides the issue with the charger being connected when the master was turned down, the only other thing I can think of is that this particular set up has two plates behind the oil cooler for cold-weather operation. One covers about 1/3 of the cooler and the other covers a little bit less than 2/3. Either one or both can be installed. I have not had either one installed but I can’t imagine that enough air would be flowing through the oil cooler to reduce the airflow through the blast tube on the P-mag.
 
Is the warning about not powering the panel while charging the battery particular to P-mags?

For six years, I have routinely connected a battery charger while updating my Dynon Skyview.
 
Is the warning about not powering the panel while charging the battery particular to P-mags?

For six years, I have routinely connected a battery charger while updating my Dynon Skyview.

E-Mag warns about it specifically for their products but after reading some of the responses to my original post and after talking to a local RV builder, I think you risk harm to your avionics by doing this. If I find that I need to regularly power up my panel and I can’t trust my battery, I would get one of the power supplies mentioned in the earlier posts.
 
robust design

Decades age I did design engineering. Down the hall was David Sun who became a zillionaire as Kingston Memory. Good for David. But I had the better real estate in the building though, a glassed in cubicle overlooking the lab area. Lots of talent there. Maybe it was part company culture, or specs or instinct, but the products I did, I designed to be overloaded, over voltaged , over temp'd and maybe take a lightning zap or two. It is part of good design

The FAA is of like mind with their TSO's . Critical to flight electronic accessories must be able to survive several kinds of serious electrical insults without going toes up. A buzz box charger across a starter battery should not cause any serious transients. Starter batteries are excellent protection for anything on the line. So long as the battery is on line in parallel with, in this case, an Emag, transient damage should be unlikely.

One important exception is that using any unregulated charger on a very dead battery with little load will likely get you 18 volts or more as soon as it is connected. Maybe that is where the problem is. The Emag may not be able to handle a continuous overvoltage. Can it?.

An over volt event in the air is not unheard of. It shouldn't turn your airplane into a glider. I would think that a design goal for electronic ignition should be operation at a very minimum of 150% over voltage. The thought of a runaway alternator taking out your ignition systems - cascading failure is not good.

I judge from reports here that the E/Pmag is a pretty solid product. However, this thread is about how delicate the device is. I am concerned for a product that should be reliable and robust to the point of being nearly impregnable to damage from something like a charger

The good news is that everyone can replace their shabby HF charger with a regulated power supplies that can be used as bench power supply, battery charger or as stand-in for an alternator while building/testing. They are available for about $30 on Ebay, etc. I got one about 3 years ago and use it as a bench power source. It is rated at 15 volts 27 amps and ~100 to 250 VAC input. A tiny pot in the corner will adjust the voltage ~11 to 18 V. It has the good stuff like OV and foldback overload/short protection and puts out near pure DC. Recommended.

Several sources for similar. Here is what they look:
https://www.meanwell.com/webapp/product/search.aspx?prod=LRS-350&mws=731CEC2D6F

Ron
 
Thanks. What brand and model of battery charger did the damage?

It was the Odyssey battery charger charging an Odyssey battery, but as I understand it, any charger will create a “dirty” charge that can damage unprotected electronics. An electrical engineer could probably provide a technical explanation.
 
BatteryMinder

I have a BatteryMinder (Model 2012-AGM) charger and the documentation says "Patented full-time high frequency pulse desulfation (NOT high voltage) prevents battery..."

The p-mag documentation says, "Note 2: DO NOT power the ignition ON if/when you have a battery charger
connected to the bus. Some chargers are designed to pulse the battery with
high voltage that can damage electronics."

I accidentally had the battery charger on for a minute with the ignition ON and my p-mag does not appear to be damaged. When I do a full runup the p-mag checks out fine. That's why I was curious about the failure mode you experienced.

Note: If any of you are following my other thread about Low CHT/EGT on #4 at high power (https://vansairforce.net/community/showthread.php?t=198385) settings and thinking that the battery charger is the cause. It is not, the incident with the battery charger occurred after the temperature anomolies.
 
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I believe the damage to my P-Mag happened over a period of time, with my flipping the master switch on to check the charge. You should have a switch that supplies or removes ship power from the P-Mag, so you could keep that switch off whenever you use a battery charger.
 
I believe the damage to my P-Mag happened over a period of time, with my flipping the master switch on to check the charge. You should have a switch that supplies or removes ship power from the P-Mag, so you could keep that switch off whenever you use a battery charger.
Based on what you are writing, it might be that you don't have the pmags wired as recommended by the factory.

https://emagair.com/wp-content/uploads/2017/08/Manual-LC114v28.pdf

https://emagair.com/downloads/

pmag wiring diagram.png
 
SNIP Starter batteries are excellent protection for anything on the line. So long as the battery is on line in parallel with, in this case, an Emag, transient damage should be unlikely.
SNIP
An over volt event in the air is not unheard of. It shouldn't turn your airplane into a glider. I would think that a design goal for electronic ignition should be operation at a very minimum of 150% over voltage. The thought of a runaway alternator taking out your ignition systems - cascading failure is not good.

Ron

A couple of comments:
- A battery on line with a charger will absorb DC voltage spikes, but it will do little to nothing for AC or RF noise.
- If memory serves, the pMag is isolated from ship power once running.

Carl
 
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