Battery-Solenoid-Earth Cabling

[pfjay52]

Ok guys this is my first real post so please be gentle with me! i have a new ( to me) PA-18-150. the battery is slow to spin the motor. i intend to move it forward under the pilot's seat and instal an Odyssey liteweight battery in the near future. as well as move the solenoid , etc. to the same location.
in the meantime i have been investigating the original battery box and wiring. IMHO the whole setup is pretty archaic, and obviously meant for good old lead-acid batteries ( i have a nice Concord sealed unit).
surely all those original connections thru the battery box are a source of voltage drop before the solenoid is even activated. my unit has bare braided flat copper cable which has been soldered at the ends and drilled for each connection.
why not just drill an oversize hole each end of the box , insert a rubber grommet and fit nice sized insulated cable direct from the battery post to the solenoid and ground??
would this mod require an STC or field approval?
also, just above the pilot's head on the right hand side and immediately aft of the Circuit Breaker board, is a plate about 4" square with a 2 pin screw in style plug in the middle and a solenoid ( similar to the starter) behind and connected to it. any ideas ?
thanks for your help , and i look forward to picking your respective brains some more in the future.
cheers,
Phil

 

[Icecub]

Phil,
Welcome to SC.ORG.

First, check for a voltage drop in the circuit with a voltmeter. Battery minus to ground; bat plus through solenoid; solenoid to starter. The checks have to be done while starting.

Secondly, check if the cable from the solenoid is made of aluminum or copper. There is a mandatory Piper Service Bulletin 836A, requiring replacement of aluminum cables.

Finally, check the type of starter. If you have the original heavy Prestolite
I would replace it with a new lightweight one. I have B&C myself and recommend it.

The solenoid in the right wing root is for the landing lights.

Good luck,
Vidir

 

[Steve Pierce]

I have seen the mod done you are talking about. Bogert Aviation has a nice STC'd fix also. http://www.bogert-av.com/battery_mod.php

 

[Fortysix12]

Performing the mod you referenced should be the difference between night and day. However, starter motors can drag if wore out not matter how much juice you put to it. If you jump it with another battery does it spin better. Its' something simple. Maybe a bad battery cell.

 

[Mikey]

Phil,
I know a lot of folks like having the battery moved forward, but be mindful of the CG shift. These things are nose heavy to start with. W/ decent sized wire and good connections, the voltage drop from the battery to frame for that short cable should be minimal.
Chris

 

[Josh]

http://www.skytecair.com/Troubleshooting.htm

click on the printable version, I had the same problem with a Citabria I have, the battery is all the way back behind the baggage, the battery cable must be 15 feet long! but this simple test will determine your prob.

 

[RMREBOB]

As far as the CG shift goes, I think it is better to combine the battery move with the replacement of the starter with a light weight, the generator with an alternator, and installing a light weight oil cooler on the rear baffling all of which move the CG aft and compensate for the battery. The net weight loss is significant and the CG shift is minimal. In addition the new light weight starters are made with rare earth magnets and produce much more cranking power with less weight and less current draw on the battery.

 

[jnorris]

why not just drill an oversize hole each end of the box , insert a rubber grommet and fit nice sized insulated cable direct from the battery post to the solenoid and ground??

Gee, that's the way mine is set up. Been that way since I got the plane. I thought that was the standard setup!!