60 Amp Parallel System

I understand there is a way to convert the 337 30 amp system to a 60 amp parallel system. Does anyone have details on how to perform the conversion? Cost?

[kevin]

I imagine someone else who visits this site will have the data, but I know Tom Carr (tcarr@cessna.org), the Cessna Pilot's Association specialist for the 337, has a field approval for this that he provides copies of. (I suspect you need to be a CPA member, which I am.) He has installed the parallel regulators and the larger alternators on several 337s. I looked into it, but haven't really had much problem with my electrical system, so I have not gone ahead with it. I actually got a copy of the field approval from him, but I can't for the life of me remember in what highly secure location I filed it.

Kevin

[Ernie Martin]

Further to Kevin's reply, I seem to remember that GMAS strongly advises AGAINST this mod. If memory serves, his principal argument is that the mechanical load of the 60 amp alternator on the gear driven by the engine is a weak point which can lead to gear failure and then engine failure. He also wonders why, with today's relatively low-amp electronics, anyone would want so much current. Hope GMAS comes out of hybernation here and sets me straight.

Ernie

Well I seem to recall from the MYAT meeting that GMAS thought the Mod was a GREAT idea. Probably the best Mod for the Bird so far to date. . . .

Or, was it the other way around like Ernie said? Well, the only way we can find out is to defer to GMAS.

Huhummm. GMAS? Oh GMAS?

Keven
________
Masturbating

Ernie, I'm talking about converting the 30amp system (only one 30amp circuit on-line at any time) to a parallel system where both circuits are on-line. I'm not as concerned about upgrading the 30amp to 60amp alternators as I agree that with today's electronics this is unnecessary (unless you have full de-ice).

Kevin, I am also a CPA/Cessna.org member and will contact them. thx.

[Mark Hislop]

Jazzpilot:

I am familiar with the conversion you are talking about. I got the paperwork from CPA, and had it done to my 73 P337.

There are actually two parts of the converson. The first part consists of replacing the original voltage regulators with regulators from the 400 series Cessnas. These regulators are truly paralleling...they have a sensing lead that connects one to the other, and they always split the load between them. This is the main reason I went with this conversion. You can do this without putting on the 60 amp alternators.

The second part of the conversion consists of replacing the 35 amp alternators with 60 amp alternators. The only change necessary to do this (other than the larger alternator) is a larger gage wire to take the extra current from the alternator to the main bus. I didn't install the larger alternators, since I was a little leery of the extra wear and tear on the engine accessory drive gears. However, I did have a larger gage wire installed in case I ever change my mind.

I have had this conversion done for 4 years now. I've never had to adjust the regulators, and I've never had one of the alternator low voltage lights come on, regardless of my power settings. I used to have continual problems with one or the other alternator going "offline" during flight, as evidenced by the low voltage light coming on.

Mark

[Bob Cook]

1) the old system works great if properly set up.

2) the CPA system with the 400 regulators and a 337 work fine as well. Takes the hassle out of "tweeking" the existing system.

3) With a loaded king stack I draw 37 amps normal load which includes the pitot heat and all radios.

4) recommend a current shunt and meter so you know what the system is doing, otherwise you are just guessing! EI makes the best one for the buck.

5) If you have bad connections, contactors etc. you still will need to spend time bringing the system up to spec. after you spend 500 to 600 dollars on the 400 series regulators.

6) make sure the shear-drive or coupling is not slipping on either alternator. These were never designed to handle more than the stock alternators.....

Suggest you fix the problem before investing in a gold plated bandaid (mind you it does work as Mark says).

bob

[GMAs]

to answer your question.. no we don't like the upgrade... because the mechanical part is too week as it is...

You take a 25 amp system and then spin 38 amp alternators... it is just about at the max point... no you doubble it to 60 and.... you will have problems like you have never had before.... with your single engine operation practice... smile... yes they do break off the shafts and they do take the teeth off the small gear and mess up the cam gear and oil pump... see other articles...

As far as changing them... you don't need the CPAs' approval... cont engine has the 60 amp alternators listed in the TC's... and in their parts manuals.. so its just a direct change... but, if I were going to drive one...why stop at 60 amp... why not go to the new 108 amp alternator... that can be put on the accessory drive off the vacuum pump side... and it is belt driven.. getting rid of the gear drive alternator and making more room down below... smile... they put a cover over the existing alternator hole and hang the new alternator off to one side... yes you need new regulators.. if you change..

The old system is fine... and while the newer 400 alt regulators are better...the old ones are just as good... and will give you isolation... that the new ones won't... their are better regulators out than the 400 also... but, no one has seemed to look them up... bob is correct.. I would rather have a voltmeter and current measuring device off each alternator like the early cessna 337s had... but, then again who looks... if its working... good if its not... well...

[Bob Cook]

GMAS et al

Nice to hear from you.

the meter is GREAT. you know what load you have and you can verify each alternator is putting out required amount. Also good for load sheading when you drop one alternator off line. Saves troubleshooting the system. I honestly would not be without it next to the jpi and shadin. Idiot lights are for idiots!

Bob

[Kevin McDole]

Originally posted by GMAs
You take a 25 amp system and then spin 38 amp alternators...

Can you elaborate? What do you mean "You take a 25 amp system?"

why not go to the new 108 amp alternator...

Do you know if anyone gotten a field approval on this?

the old ones are just as good... and will give you isolation... that the new ones won't...

What do you mean by "isolation?" Are you referring to them not being independent, and therefore a single failure could knock out both?

their are better regulators out than the 400 also... but, no one has seemed to look them up...

Can you make any recommendation? Are you aware of any that have been done on a field approval?

Thanks - Kevin McD

[kevin]

Yes GMAs, I too would like to know what you mean by a "25 amp system". My avionics shop is slated to install a 20 amp power plug on my airplane (appropriate gauge wire, pullable circuit breaker, etc.) to run some equipment in the back seat for research work. As my airplane normally draws 15 amps total, our plan is to shut down the test equipment if I lose an alternator, but the two 38 amp alternators should provide plenty of power I would think, as long as they are both operating.

Is there a problem you see with this? Anyone else have a comment?

Thanks,

Kevin

[Bob Cook]

Kevin

The existing system is fine. You can get 38X2 amps without a problem. The 400 regulators work and there is a 337 out from CPA if you are a member.

There is nothing wrong adding 20 amp circuit. the DC compressors (air conditioning) used to draw in the order of 50 amps.

What GMAS was saying is the couplers were never designed for much beyond the standard alternators. You are loading the couplings down by adding larger alternors.

Again, you can get alternators that work off the accessory drive and not thru the couplings but it is not really worth the additional expense plus you need the engine adapters.

Make sure all connections are good. Get a good DC ammeter and shunt on both alternators and set the system up properly. I havent touched mine in two years once I replaced all diodes, caps and carefully set things up

fyi

bob

[kevin]

Mine is working fine too, after some of the same process. My alternators are not perfectly balanced, but they both contribute, and my EI gauge with switch for each alternator allows me to see that both are working.

Thanks,

Kevin