The International Cessna^® 170 Association

Where can I find info on upgrading my 20amp gen system to a 35amp system.

I think the appropriate IPC would show the part numbers of the 35 amp generator and matching regulator. Then you would need to change them out,change the fuse or circuit breaker in the generator circuit,and make sure the wiring is heavy enough for the higher ampacity.Then do the paperwork. The only "kits" I know of for upgrading charging systems are for an alternator.
Why do you want to upgrade to the 35 amp generator? The reason I ask,my airplane was upgraded to a 60 amp alternator by a previous owner. I kinda wish he'd just left the 35 amp generator which was in it alone--just overhauled it if that was needed. Reason: lighter weight,also the generator will charge even if the battery is stone dead once you get it started. Since my airplane has minimal radio gear & is rarely flown at night,I don't need all that electrical capacity.
I admit,20 amps is kinda on the low side,so it probably is a good idea to go to the 35 amp generator. I was just curious if you have trouble with the lights browning out on you or something like that.

Eric

You might be able to get a real deal on a 35 amp generator and regulator from someone upgrading to an alternator. You could post here about it,and also put an ad in the Flypaper. You can get a generator from Spruce or someone but you'd have to forfeit the core charge if you didn't have an old one to turn in.

Eric

First, you should confirm you have a dampened crankshaft. Then trade your gen with a 35A (Delco-Remy PN 1101898) from one of the overhaulers. (I like Aerotech in Louisville, Ky., but El Reno in El Reno, Ok. is also good.) You'll also need a 35A regulator (PN 118385, or 1118704, or VR300-14-35), and upgrade the wiring from the Arm terminal of the gen to the regulator, and from the reg to the Bat buss to 10 ga wiring as a minimum. (8 ga is even better). Change the fuse/CB to 40A. (I know, that sounds wrong, but 40A CB is correct and OK by FAR 43. A 35 A CB or fuse may "pop" when the gen is operating at it's approved max output. A 40 A device will "pop" when an overcharge condition occurs, still protecting the wiring against fire.)

Thanks for the information. Yes, I do have the dampened crank and three reasons I want to upgrade. First, my 20amp gen has unknown hours on it, and previous owner had installed a Zeftronics 35amp generator controller, so I want to match it up. Also, want to add a heated pitot so I need a boost in amps. Going this route is a lot less money than the alternator upgrade. Since the 35amp gen is on the Type Certificate is a 337 reguired for the change?

No 337 is required if you use the correct part numbered generator and it is installed as Cessna would have. I'd check to make sure your electronic regulator will work with the 35 amp alternator both electrically and paper work wise.

I've wondered besides the legality, why would it make any difference if you had a dampened crank or not for the 35 amp gen. I don't have a dampened crank and would love to go to the 35 amp gen myself.

It's fortunate that the 35A regulator didn't burn your 20A generator up. You must not be using so much electrical power to demand more than 20A or the regulator would request it, and the gen would overheat after a period. (In theory, it's OK to use a lower-rated reg on a gen, but not the reverse.)
In your case, simply swap the gen for a larger capacity unit (1101898) and check your wiring to be adequate between the gen/reg/bat and upgrade the fuse/CB and you're good to go after a logbook entry, as this is specified in the TCDS.
The reason a dampened crankshaft is required for a 35A gen, is that the heavier electrical load passes increased torque demands back through the crankshaft gearing, and imparts increased vibration to the crank. (Each time an armature coil passes a field pole within the gen, a slight pulse of vibration is passed back through the system to the crank. This is a stronger impulse on the 35A gen than on the 12 or 20A gens.) Over time, undampened cranks can exceed their vibratory limits and may fail.

N9149A wrote:No 337 is required if you use the correct part numbered generator and it is installed as Cessna would have...........

The general consensus seems to be that a 337 is not required if the part being installed is listed on the TCDS. This makes sense. However,EDO 2000 floats are listed on the TCDS for the A&B models,but I'm pretty sure you should file a 337 if you install a set. Granted,most of us would agree this is an "alteration" and changing from a 20A to 35A generator is an "upgrade",but exactly where do you draw the line between a modification that requires a 337 and one that doesn't? Note that I say modification--the 337 form sez "major repair or alteration" across the top.
For example,the Scott 3200 tailwheel is approved per the TCDS--item 204(b). The standard tailwheel was the Scott 3-24B--item 204(a),I believe this is the equivalent of today's Scott 2000. Anyway,if you change from a 3-24B to a 3200,is a 337 required? Or just a logbook entry? A W&B recalculation would be required for sure,there's a 3 pound difference in weight plus a 3 inch difference in arm,according to the TCDS.

Eric

Read the title of the Form 337----"Major Alteration or Repair". If it's a change in configuration (to skis, or floats, for example) yes, a 337 would be appropriate. If it's a repair to sheet metal that's more than 6" long (see FAR 43) yes, ...it's a major repair.
But does it need to be submitted for field approval? No. It merely needs to be filed,...along with the comments "....as per the TCDS." and a logbook entry and W&B, if necessary.

The modern-day 337's I have say "Major Repair And Alteration" across the top. Does that mean major repair and major alteration,or major repair and ANY alteration?
Also,from my non-A&P standpoint, I understand that a "field approval" is for unapproved mods (such as installing a Pratt R-985 on the front of my ragwing ). This is what section "3. For FAA Use Only" of the 337 is for.
A previously approved mod,such as an STC'd STOL kit or something like that.does not require a "field approval". But it does require a signoff in section "7. Approval For Return To Service" by an IA,FAA Flt. Standards Inspector,or other entity as listed in that section.
As far as I can tell,a field approval always requires a 337,but a 337 doesn't always require a field approval.
Like the title sez,a 337 is also required for a major repair,even one conforming with the TC and all regs. In my opinion.

Eric

Eric

I just sent eight 337s in on my airplane, none of which required a field approval. Most were STCs, one was the Javelin (type Certificate), and one was tso'd avionics, and one was for the soundproofing on which I attached the burn test. I only got one back.....I missed signing it

If one contemplates a mod that will require a field approval of the kind that are still available the 337 form can be used to initiate discussion with the FAA, just have your mechanic fill it out and send it in with a note that that is what you would like to do and that work has not been started. They love that. They hate someone going off and doing a bunch of work without an STC or prior discussions.

Not flying again. Cowl is off and being repaired and painted. Tired of a red nose on a tan airplane.

When my 20 amp generator started giving me problems, I went through the same thoughts. Rebuild the 20, upgrade to a 35, or get an alt. I eventually asked for the the 35 amp upgrade, and my generator and regulator were sent to the rebuilder. To my surprise, the same generator came back, newly rebuilt, but with a '-35' newly stamped at the end of the existing part number. Cables were changed to #8 by my a/p. I guess thats the rebuilders way of upgrading without a 35 amp generator core charge.

I do know that Airtech will give you credit for your 20 amp when you purchase a 35 amp from them. It just isnt as much as the 35 amp core charge, so it costs a few more dollars.

Bob