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No start on Pmags

erich weaver

Well Known Member
After many years of trouble free starting I recently began having problems. Initially thought perhaps it was a fuel problem but testing of AFP injection system showed it was delivering fuel at the proper rate at full throttle and idle positions. My PC680 battery was getting on in age, but the engine was still turning over when starting so I dismissed that as the problem. I was wrong, and Brad at emagair set me straight. While the engine was turning over at start, the voltage was being dragged down to the point that the Pmags were not functioning and of course at that low rpm they weren?t generating their own power either. Installed a new battery and all is well.

Feeling a little silly now, but maybe this will save someone else with pmags some head scratching when they suddenly have a startup problem.

Erich
 
Thanks for the post!

Your battery must have been really bad as you can hand prop our engines when one P-mag is powered by a 9 volt battery.

Good to know it was something as simple as replacing you battery. (BTW, some years back I attended a seminar by Concord and one thing the tech guy said that stuck in my head was that to extend the life of your battery, keep it on a battery tender.)
 
battery tender

... (BTW, some years back I attended a seminar by Concord and one thing the tech guy said that stuck in my head was that to extend the life of your battery, keep it on a battery tender.)
Is that a typo? I found this on their site:

http://www.concordebattery.com/main_air_tech.php
http://www.concordebattery.com/otherpdf/sa2.pdf

SERVICE ALERT ? BATTERY TENDER? BATTERY CHARGER
SERVICE ALERT - Number: 2 April 22, 2010
This service alert pertains to the Battery Tender? brand of battery chargers, made by Deltran Corporation, and to the SuperSmart? brand of battery chargers, also made by Deltran Corporation. The 12 Volt units come in various ratings up to 6 amperes. The 24 volt units come in various ratings up to 3 amperes. These chargers are intended for boost charging and to maintain batteries at a full state of charge.
It has come to Concorde?s attention that these chargers are not suitable for use with Concorde?s RG? Series aircraft batteries. The output voltage on these chargers is set too high, resulting in an overcharge condition which may shorten the battery service life. Furthermore, these chargers can fail internally such that the output voltage goes beyond a safe limit (i.e., over 34 volts on a 24 volt battery). This condition can damage the battery in a very short time period and, under certain conditions, lead to thermal runaway.
Concorde has reviewed product information on the Battery Tender website (www.batterytender.com) and discovered the following disclaimer:
THIS UNIT IS NOT APPROVED BY THE FAA. DO NOT USE WITH AVIATION OR TRUE GEL BATTERIES. For example, the maximum recommended recharge voltage for GILL AVIATION batteries is in the same range as true Gel batteries, even though some GILL AVIATION batteries are flooded cells.
Although the disclaimer specifically mentions GILL AVIATION batteries, it also applies to CONCORDE AVIATION batteries.
As a result of these findings, Concorde will not warrant batteries that have been charged using these brands of chargers. For a current list of approved battery chargers, contact our customer service department or one of our authorized distributors.
 
Wiring or battery, or both?

Bill noted that the Pmag will start/work with 9V (battery), yet the starter was turning over the engine. (Guessing it was more than a blade or two)

So, question for the gurus,... is a new battery the fix,...or should Pmag users look harder at wiring and voltage drops? (To avoid what would appear to be a non-start region,... when a mag might work)
 
System voltages can easily drop to 8v or less during starting with a weak battery or worn out starter, if you have the 'stock' PM starter those units require the heaviest current and hence will cause the voltage to drop more than the typical wire wound starter. Needless to say I'm not a fan of PM starters used with glass panels or electronic ignitions for this reason.
Old battery + PM starter = trouble
It should go without saying that good wiring, connections and contactors are also required.
 
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In my case, the battery was a PC680 and the starter a Skytec 149NL, not the lightweight starter that many have had issues with.

I note also that there have been numerous reports on this forum associating long term continuous use of the battery tender charger on the PC680 battery with significantly reduced battery life. I am hesitant to leave a charger on overnight anyway, so I don?t do this and have gotten good life from my batteries. In this case I just waited too long and mistakenly thought I was ok because I could still turn over the engine when starting, which was not the case.

Erich
 
You need to go to odessy battery site and buy one of these recommended battery charger/conditioners. I did about 2 years ago and have had zero issues. All battery minders/tenders/chargers are not the same. The type of charger depends on the type of battery!
 
You need to go to odessy battery site and buy one of these recommended battery charger/conditioners. I did about 2 years ago and have had zero issues. All battery minders/tenders/chargers are not the same. The type of charger depends on the type of battery!

Or do what I do, fly the plane more often. :rolleyes:
 
You need to go to odessy battery site and buy one of these recommended battery charger/conditioners. I did about 2 years ago and have had zero issues. All battery minders/tenders/chargers are not the same. The type of charger depends on the type of battery!

Can someone explain why we need to use a special charger when there is nothing special about the charging systems in our airplanes?
 
While we are getting explanations,....

Walt, et al,

Not arguing,... just trying to understand

Am I getting this correct? With a dead battery, (ok,.apparently just almost).... providing 8 volts to system,...while cranking the starter,... the starter is cranking the engine at a speed we should be getting a start? Wouldn?t the starter be operating on something like 7 volts or less, considering drops across solenoid and cable, and current at that voltage?

Guess I need to go look at the Odessy charge/output curve again,.... I thought it fell quickly,... so Such a scenario would be a hard to create.
 
Can someone explain why we need to use a special charger when there is nothing special about the charging systems in our airplanes?


For this discussion, I think folks are referring to the "trickle" style charger, usually left on the battery for days or weeks at a time-------vs an hour or two flight.

Also, in flight the charge output is regulated and basically keeping up with the airframe load.
 
Walt, et al,

Not arguing,... just trying to understand

Am I getting this correct? With a dead battery, (ok,.apparently just almost).... providing 8 volts to system,...while cranking the starter,... the starter is cranking the engine at a speed we should be getting a start? Wouldn’t the starter be operating on something like 7 volts or less, considering drops across solenoid and cable, and current at that voltage?

Guess I need to go look at the Odessy charge/output curve again,.... I thought it fell quickly,... so Such a scenario would be a hard to create.

As the battery cranks over the engine, it hits a compression stroke and slows down. When this happens, the starter draws more power from the battery. Apparently that was just enough to cause the voltage regulator on the P-mag's internal circuit board to shut down, protecting the electronics, in this instance.

A healthy battery will have enough energy to spin the prop and fire the ignition.

If he had magnetos, the engine might have started since they don't require energy from the battery to fire the plugs. Then again, it may not have started even then because mag's don't start as easy as electronic ignitions.
 
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