12amp vs 20amp generator

[C170U2]

Currently I have a 12amp generator installed, and it has proven pretty inadequate in keeping up with the meager load I put on it (nav lights, strobe, and transponder). When I install a radio I fear I wont get much of a charge at all on the battery. Is it worth the effort to swap out to the 20amp model or should I bite the bullet and go to the 35? If the 20amp would be enough I would rather just stick with that. Thoughts from anyone with a 20amp generator would be appreciated!

Thanks, Mike

[bagarre]

You can't go with a 35amp unless you have a dampened crankshaft.
Some of the C-145s have them. Your serial number will end with a D I believe.
From what I recall, all O-300s have them but you may want to verify that.

You could reduce your load with LED nav lights. Not sure it it will get you enough and the price might make it a wash either way.
Swapping to a20amp generator will require a new regulator as well.
Lots a conversations on the forum about this if you search around.

[canav8]

Mike, changing the generator size will not meet the demands. You must use a bigger battery or convert it to an alternator it order to meet your happiness requirements. The generator will come online around 1500-1700 RPM. An Alternator will come online around 1100 -1200 RPM. If you do a lot of night flying or stay in the pattern you will run a battery down quickly when using a generator. I fixed my problem with getting the Plane Power Alternator STC and haven't regretted it yet. Doug

[Bruce Fenstermacher]

Mike, your nav lights pull at least 5 amps. They are probably the single biggest draw unless you turn on your landing light.

Any generator over your 12 amp will improve what you currently have. The undamped cranked engines were made in '48. Doesn't mean you couldn't have one in you '49, I had one in my '50 hybrid because the engine was a '48. You can install up to a 25 amp generator with an undampened crank engine doubling your current capacity.

True as Doug says a generator won't come on line till the RPM rises and during this time your load is being carried by the battery.

I might have a 20 amp generator (pretty sure I still have it) I'll give you for shipping.

BTW you also have to change out your voltage regulator otherwise your 12 amp regulator will never ask more then 12 amps from the generator. Of course assuming your regulator is a 12 amp regulator. If you need a regulator I would buy a Zeftronics electronic unit which will lower the charge on RPM. (OK I'll be honest, I'd use a regulator from my partners stash after I could be reasonably sure it was an aircraft unit. And that is the true story I'm sticking to. )

[GAHorn]

Mike, changing the generator size will not meet the demands. You must use a bigger battery or convert it to an alternator it order to meet your happiness requirements. The generator will come online around 1500-1700 RPM. An Alternator will come online around 1100 -1200 RPM. If you do a lot of night flying or stay in the pattern you will run a battery down quickly when using a generator. I fixed my problem with getting the Plane Power Alternator STC and haven't regretted it yet. Doug

Mike, I'm not picking on Doug....but he's wrong on the important aspects of this.

Firstly, we cannot know if the 20A gen will resolve your issue until we know your electrical load. CONSTANT load should not exceed 80% of gen capacity. (Intermittent loads like landing lights are not important because they'll only be used for short periods of a few minutes and your battery will take care of that, with your gen replenishing the battery at other times. That's what batteries are in part FOR.

Alternators are not cure-alls. They also have drawbacks (such as loss of capability with dead batteries due to no self-excitement, and sensitivity to reverse-polarity possibly resulting in expensive/total failures, and avionics noise-generation, etc..) Additionally they are not cheap and some require expensive and temperamental regulators.

The use of modern solid state/miniaturized avionics has drastically lessened the need for high-output charging systems....a 20A gen might be all you need, and that would likely be the cheapest solution for you. (An exchange for a 20A gen can be done very cheap and your present regulator can be re-adjusted or an inexpensive mechanical one can be had in the 20A version.... or for about the same money you can go for 35A in both.)

If you're willing to cough up about $900 you can buy a new alternator conversion...or for about $350 you can buy a fresh-overhauled/new 35A gen/reg.

[C170U2]

Thanks for the replies. I'm thinking I will probably swap to the 20amp generator. I really don't feel like upgrading to a 35amp generator and having to rewire everything again. Went through all the electrical a few months back and don't feel like doing it again. Really wish I had thought this through more before I went through the trouble of testing and installing the 12amp generator. Oh well....live and learn.

Additionally, I might try swapping out to LED's in the Nav lights as well. That combined with getting around to putting the solar panel on top of the hangar to keep the battery on a slow trickle charge will probably keep me charged up and ready to go.

[GAHorn]

The only rewiring needed is to a 8 ga wire from the armature, to the regulator, to the aircraft buss (and replace the existing with the appropriate sized 35A fuse or cb.)

[Bruce Fenstermacher]

George hit it about right. And I'm not saying depending on what your trying to accomplish, that Doug doesn't have the answer. If I had a 60 amp alternator system sitting in my hanger I'd probably have to install it. But I'm not buying one cause I don't need it for what I want to accomplish.

The key is what do you want. If you want to fly around with your landing light on all the time for recognition, you'll need more than 35 amps and that means an alternator. If you just want a bit more cushion to run your nav lights when you do turn on that radio you haven't installed yet, a 20 amp gen might work just fine. I somehow managed to fly to several conventions with only a 20 amp gen with two nav coms and only upgraded to a 25 amp gen when I installed two nav coms, glide slope, marker beacon and IFR GPS.

So it really all depends again on what you want to accomplish.

[bagarre]

If i were to fly around with my taxi and landing light on all the time, I'd opt for LED landing lights long before a 60amp alternator.
Even with the amperage, that circuit wasn't intended for continuous loads like that.

I rewired mine to two circuits so I could have an LED taxi light for continuous duty and a halogen landing light for short use.

[GAHorn]

The landing lamp circuits certainly ARE designed to carry the load. (10ga wire is more than adequate and is what was factory installed.)

[bagarre]

The landing lamp circuits certainly ARE designed to carry the load. (10ga wire is more than adequate and is what was factory installed.)

I always thought the landing light wasn't made for continuous load like that.

[Bruce Fenstermacher]

I always thought the landing light wasn't made for continuous load like that.

I believe in most cases the generator is the weak link in the system that dictates the light system not be operated continuously. Because the generator can not keep up with the load eventually the battery would be dead. However the wire circuit must be able to carry the load of the lights.

[n2582d]

The landing lamp circuits certainly ARE designed to carry the load. (10ga wire is more than adequate and is what was factory installed.)

Del's "factory" but not Cessna's. Cessna used 14 gauge which in my opinion is good enough for an intermittent load but not a continuous load for both lights. This has been discussed before:

... Keep in-mind that landing/taxi lights are not continuous loads. They are intermittent, and for the short time that all FOUR lamps are powered ...roughly just the time on final approach and landing, ...any excessive load is supplied by the battery.
(Your generated electrical power only needs to exceed total continuous demands. Continuous loads should not exceed 80% of generated capacity.)

George, I have some question about what is considered a continuous load and what is considered an intermittent load. In the Cessna Service Letters that I've seen landing lights are always listed as an intermittent load. However, in AC43.13-1B, Paragraph 11-68, Step 3, (d.) intermittent operation is defined as a maximum of two minutes. Who uses their landing/taxi ,lights for only two minutes? It's interesting that the 170B prior to s/n 25372 uses a 14 ga. wire to power both the landing and the taxi light. If this were to be considered a continuous load it should have a 10 ga. wire. With a separate wire to each 100W bulb, as in the post s/n 25372 170's, 14 ga. wire is adequate for continuous load.

[GAHorn]

The Cessna 170-B IPC clearly indicates that the landing/taxi light circuit is 10 ga wire. ... more than sufficient for the load.

Bruce, you've got the correct answer, but sort of a cart-before-the-horse way of viewing it, IMO. The generator is not limiting the intended useage of the landing lamps. The generator is/was sized for the original aircraft "continuous load" ...which never includes the landing/taxi lights. Landing/taxi lights are intermittent loads by definition, so the mfr'r only installed the generator to provide 80% of the continuous load (of the original equipment list.)

It's us pilots who have chosen to use landing/taxi lights for prolonged periods in busy airspace. (Remember, unless operating commercially, a landing light is not even required equipment.)

One of the reasons I installed dual landing/taxi lights was entirely due to this issue. (The main reason was to get rid of leading edge hangar rash which fortunately was at the exact mirror-location as the left-wing lights.)

I have a 35 A generator and prefer a generator system. In asking Del to make the dual mod for me I had the privilege of reducing the continuous electrical load by converting my original 200-watt land/taxi lamp circuit... by splitting it into seperate landing / taxi light circuits....and ending up with more visibility by having dual lamps lit up ...one on each wing leading edge. But instead of running a 200 watt system, I used dual 60-watt (GE 4451) lamps. These are a fresnel type lens which "scatter" the beam rather than the small "pinpoint" beam of the original dual 100-watt GE 4509 lamps. Not only do these provide a better/wider illuminated area while taxying... they also provide a wider illumination while airborne for anti-collision purposes. But since together, the taxi lamps only require a total of 120-watts instead of the 200 watts the original two lamps required, (and since I replaced my nav lamps with L.E.D. lamps further reducing the total electrical load)... I can run them continuously, which I often do in metropolitan areas.

And when I turn onto final approach out here in the boonies...or in town at the big airports.... I turn on ALL four lights (dual land and dual taxi) and my battery supports the total load just fine for the few minutes I'm on final approach. The generator recharges the battery during taxi in, and again during taxi out for the next trip. (I take off with all lamps on, but again switch to taxi lights only during climb out.) With the lamps spaced far out on the wings the airplane really shows up to others (who often think it's a much larger airplane..... but likely that's only an illusion due to my SPEED!)

[n2582d]

The Cessna 170-B IPC clearly indicates that the landing/taxi light circuit is 10 ga wire. ... more than sufficient for the load.

Could you show me a picture of where you find that? In every iteration of the wiring diagrams I have it shows #14 gauge. Probably alright for the the later ones which have one 14 ga. to each light but too small for a continuous load with one wire going to two lights like in the earlier 170 serial numbers.

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