Alternator restart

[fredh]

We are looking for the Alternator rstart Battery pack, anyone know where it is hidden?
Thank you Fred

[Pete Somers]

Hi Fred
It is located under the top instrument panel hatch, look at the starboard side above the co-pilot control tube and they are installed in a battery holder. You can get this batteries from a local source.

Cheers
Pete

[Jerry De Santis]

What model and year is your Skymaster?

[hharney]

Originally posted by Jerry De Santis
What model and year is your Skymaster?

Jerry,

It is a 73 P337G, according to the list on the left of Fred's message. Fred, you are based at Z98?

[fredh]

Thank you for the replies. I looked briefly under the instrument panel, and through the top access panel. I didn't see it. I will have more time later this week to look closer. I was told that they are D cell batteries, either 2 or 4. That would be a large holder. Not to easy to hide. Also my airplane is a 1973 P337G.
Thank you
Fred

[fredh]

I am based at Z98.
Fred

[John Hoffman]

Fred - I have a 73G also and the battery pack is a pretty simple affair with 2 D cells attached to the bulkhead, easy to see by removing the pilots side avionics panel. As simple as it appears could also be pretty easy to relocate so you might have to search around a little.

[Dale Campbell]

I have the 337H model and my battery pack is located just above my right knee, close to center radio rack. Dale Campbell

[Dale Campbell]

I have the 337H model and my battery pack is located just above my right knee, close to center radio rack. Dale Campbell

[Dave Underwood]

I can't see the battery pack listed in the P Series Parts Manual anywhere. On my 1978 P it is above my right knees, behind the trim wheel, and if memory is correct, it was attached to one of the braces behind the trim wheel.

FYI - Dave

[stackj]

From Page 15A-23 of the service manual - Does this help?

[gkey]

Firstly, I am no expert on this, but here goes:

-- QUESTION--
This was my question to the CPA forum many moons ago:

I read the following in my POH (1976 337 G): "An alternator restart system, consisting of a momentary push-button type switch and four alkaline dry cell batteries...". Someone please explain this to me. I know about the push button, but batteries? Are there batteries somewhere that I have to change out for fresh ones? Where are these batteries? How do I know that this restart button will work at all? I cannot find out by reading the POH.

--ANSWER--
For those of you who do not know Tom Carr, he is in my eyes almost like the God of 337's - he is a walking encyclopedia on all technical matters regarding these planes. This was his answer:

"It has been my experience that the owner’s blind faith in the alternator restart system has lead many 337 owners down the primrose path of complete charging system failure and related expenses. I feel the placard on the instrument panel above that push button switch should be reworded to say, “If You Have To Push This Button, Something Is Seriously Wrong And You Had Better Be In VFR Conditions Or Preferably On The Ground”.

Here is my thought process on the restart system. If you look at the electrical system schematic in the owners manuals or POHs for the 337s that use that system you will see the alkaline battery pack will deliver 6 volts to the field terminals of both alternators once the button is pushed. This is assuming of course the small polarity diodes in the circuit just aft of the push button switch are NOT failed in the open position. That is a VERY common fault (reason #1 to REMOVE the battery pack).

I have seen where a new 337 owner listening to a CFI (with no 337 and more importantly no 337 electrical system experiences) gave the advice to just press that button whenever both alternator discharge lights were on. That operation took its toll on his bank account until better instructions were learned about that button.

During a taxi out to the run-up area with both engines pulled back to idle RPMs it is not uncommon for both of those "alt out" lights to come on, due to the low alternator output. The button is pushed and the alternators go into an UNCONTROLLED OUTPUT CONDITION since the regulators are being bypassed. If the button is held longer than it should be, the sound of alkaline batteries exploding can sometimes be heard if the polarity diodes have shorted, since the alternators are trying to charge those D cells. Usually the diodes burn open but not always (back to reason #1).

The uncontrolled output from the alternators can trip off the overvoltage sensor and that shuts down the regulators. Until the master is cycled off and back on, expect no output from the alternators unless you hold the button in again. This will be your second chance to explode the D cells if that has not already occurred.

Let’s say you run the battery down while waiting for a clearance, low engine RPMs, no output from the alternators, battery trying to carry avionics and lighting load and then everything gets quiet, the master contactor opens up. Pressing the button brings the alternators on line and you decide to increase the engine RPMs. The battery now may or may not come back on line depending on how low the charge still in the battery is. If it comes back on then the current surge from the alternators to a very low battery can over heat the cells and short out the battery internally. Short battery life results, forcing you into a very expensive hobby of buying a lot of batteries.

If the battery does not come back on line the alternators will not stay on line very long since the battery serves as an accumulator to the charging system helping to keep the bus voltage even when the regulators are in their off cycle with no output from the alternators. The surging bus voltage also causes the over voltage circuit to shut down the system.

This total electrical shutdown is GUARANTEED when launching off in IFR conditions just after the gear has been selected up, so I have been told. If it is VFR conditions then the total failure may take another ten minutes, again, so I have been told.

I feel that the alternator restart system is nothing but trouble and when it is used can cause some very expensive repairs when you have to buy charging system components.

I would DISCONNECT the battery pack and placard the system as INOP. Just my opinion."

--RESULT--
I have disconnected my system, and labelled it INOP. I only get the alt warning lights come on when taxiing or idling. I just added a little load (like switching on my landing lights), or increased my RPM's to 1200, and the alt warning lights went off.

Someone on the forum then added: "Replacing the regulator with a zeftronics one (which is STC'd) completely removes the need for the battery operated system anyway."

[Pete Somers]

Why disconnect something that might save your life one day. I am sure that the Cessna design engineers would not have put this system into the 337 without going through all the pros and cons.
The Alt restart system provides a voltage to the field of both alternators to excite the field and get them back on line. Once you have let go of that button the restart batteries are disconnected from the field and no longer suppling a field voltage as the alternators are now on line the battery contactor now come on and the battery will charge at a rate that the regulators will allow and the battery can take. Remember the battery is a lead acid battery and will take a lot of punishment to short out plates etc.

This CFI who said press the Alt Restart Button when the Inop lights come on at low RPM, should quite honestly either read the POH or go for retraining on the airplane he is allow to operate in.

If you run the battery down during taxi or holding at low RPM, does that not show you are not monitoring the systems and adjusting to maintain the serviceability of those system, common pilot practice!

You have got a lot of if's in this and when it comes down it, has anyone on this group had trouble with the ALT Restart? If the system is check out first flight of the day and the batteries are replaced IAW the service manual, wheres the problem?

BTW we always set the idle on the 337 to 900-1000 rpm. This solved a lot of problems, if you set them to 600 rpm the fuel flow settings and cooling are affected.

Would be interested to read your comments

[fredh]

They were located pilot side behind center quadrant. Mounted upside down with a little cheep plastic cover. Thank you all for your help.
Fred

[sgettings]

I have a 1973 337G that needs the relays for its alternator restart board (the one in the middle of the front/upper firewall). Can anyone determine the mfg/part numbers for these relays? They should be small (about 1"), possibly rectangular devices mounted in the lower/outer corners of the circuit board. There may also be a left and a right version, so the part numbers may be different.

Thanks!

Scott