November 2012
Q: Hi Steve,
Are all airplane batteries bad, or am I the only one that’s getting bad batteries? I don’t fly often, but lately it seems like every time I head out to fly to the next town for my biweekly dose of airport restaurant food, I find the battery is flat.
I don’t quite get what’s happening. It seems like I used to never have flat battery problems. I have been flying this same Piper Archer II for 12 years now and aside from spending a ton of cash on new avionics last year, I haven’t had to do a thing to my Archer.
What could be causing the battery to discharge so quickly?
—Flat Battery
A: Dear Flat,
You either have a bad battery, or you’re a victim of excessive parasitic load. But don’t dunk yourself in a bathtub full of sheep dip; parasitic load is a continuous small flow of DC current that is required to keep modern equipment such as computers, radios, clocks, radios and relays alive. This electrical load flows at all times, even when the master electrical switch is off. Parasitic circuits are also called “keep-alive” circuits.
Keep-alive circuits usually tap into the aircraft battery by attaching a separate 20 gauge wire to the battery side of the master contactor. Piper installed keep-alive circuits (labeled M1A in wiring diagrams) in later model single engine airplanes such as the PA-28RT-201.
Parasitic loads are usually quite small (less than 50 milliamperes, or mA) but they are continuous—and will always deplete the battery if the aircraft is not regularly flown.
Of course, if the parasitic load is large (over 1 amp), the battery won’t last a week. Large parasitic loads need to be investigated to determine the cause. It may be that a well-meaning but not-too-electrically-savvy technician has spliced into the keep-alive wiring instead of installing a dedicated circuit to power an added piece of equipment.
It’s easy to measure parasitic load if you have access to a digital ammeter. With the master switch off, remove the negative battery terminal from the battery post. Begin by setting the ammeter range to the 10 amp range to protect the meter in case there’s a serious current leak.
Place one meter lead on the negative battery post and one on the negative battery terminal and read the display. Keep selecting lower and lower scales (200 mA, etc.) until you determine the parasitic load value.
I copied the following formula for determining how parasitic drain affects battery capacity from the Concorde Battery Corp. website.
Time (hours) = 0.25 x C1/lp where C1 is the battery’s rated capacity in Amp Hours and lp is the parasitic drain in amperes.
For example:
If C1 = 28 Ah and lp = 0.05 amperes (50 milliamperes), then Time (hours) = 0.25 x 28/.05 = 140 hours or 5.8 days
The rated capacity of GA batteries can be found at Concorde Battery’s website as well as at the website for Teledyne Battery Products/Gill Battery.
For those members that have an aircraft with quick disconnects, Concorde Battery recently introduced a tool it calls the Parasitic Load Test Adapter (PLTA). This adapter makes it easier to perform parasitic load testing on business style aircraft equipped with the MS3509 style quick disconnect receptacle. PLTAs are not needed for aircraft that aren’t equipped with quick disconnect batteries.
A deeply discharged battery is subject to accelerated sulfidation of the plates that prematurely lessens cranking capacity.
If testing doesn’t reveal any problems with the existing keep-alive circuit on your Lance and the battery has shown to be healthy, there are a couple of ways to stop parasitic loads from depleting your battery between starts. You can pull the circuit breaker or remove the fuse of the keep-alive circuit. If these aren’t acceptable options, then you simply must go flying more often.
Happy Flying.
Q: Hi Steve,
I need to replace the door hold-open slider on my Piper Lance.
It never has been very reliable—sometimes it’s strong enough to hold the door open, but if the wind is blowing at all, the lock doesn’t work.
I’ve done a little research on the web and it seems like my best bet is to take off the Piper lock and put on a hold-open device called a Door Steward. Do you know anything about this product?
—Flopping in the Breeze
A: Dear Flopping,
I know what you mean; the Piper “Holder Assembly-Door” on my Comanche is totally worn out. This assembly is the same one that’s used on many single engine Pipers. The Piper part number is 65727-00.
An Internet search showed Piper holders for sale at price ranging from $99 for a reconditioned one (exchange) to $450 for a new one. I’m a big fan of Webco Aircraft since the company specializes in Comanches. Webco sells kit DK1 that includes a new spring, rollers, and rivets for repairing the original Piper holders.
I tried the DK1 repair kit, but my Comanche’s holder was already damaged to the point that the repair didn’t last very long. If your Piper holder is still in good shape, the Webco kit is the first choice economically, but it can’t do what the Door Steward does.
If you’re looking for a long-term solution I think the Door Steward door positioning device is the way to go. Unlike the mechanical Piper kit, the Door Steward utilizes a sturdy cylinder filled with inert gas that slowly extends to push the door to the full open position after the door lock is released. From what I’ve read, the gas charge is sufficient to hold the door open when taxiing yet is easy to overcome when it’s time to pull the door closed.
The FAA-approved (by STC) kit for my Comanche and for most Piper singles is the B40C10; list price is $210. Installation takes about an hour.
Happy Flying.
Know your FAR/AIM and check with your mechanic before starting any work.
Steve Ells has been an A&P/IA for 39 years and is a commercial pilot with Instrument and Multi-Engine ratings. Ells also loves utility and bush-style airplanes and operations. He’s a former tech rep and editor for Cessna Pilots Association and served as Associate Editor for AOPA Pilot until 2008. Ells is the owner of Ells Aviation (EllsAviation.com) and the proud owner of a 1960 Piper Comanche. He lives in Paso Robles, Calif. with his wife Audrey. Send questions and comments to editor@www.piperflyer.com.
RESOURCES >>>>>
Door Steward by Mtn View Aviation
mtnviewaviation.com
Webco Aircraft Co.
webcoaircraft.com
Concorde Battery Corp.
concordebatteries.com
Teledyne Battery Products
gillbatteries.com
