The International Cessna^® 170 Association

1. Just because you have the original engine and it has a dampened crank that your airplane came with a 35 amp generator. And it does not mean that your airplane is currently wired with wire large enough to handle 35 amps.

The fact you have a dampened crank just means you are not restricted by Continental to 25 amps or less. That is it.

Yes a 35 amp generator is fine for your airplane so long as the system, wires, cb and regulator are correct and adequate.

2. CBs protect wire. That is it. The fact you have a 20 amp CB for the generator tells me the wire from the regulator to the bus bar may not be large enough to handle more than 20 amps. Your airplane likely had a 12 or 20 amp generator when it left the factory. You should not just replace this with a 35 amp CB. You must check all the wiring to the CB to insure it can care 35 amps.

But why is the 20 CB tripping. You do have Circuit Breakers right, not fuses as it left the factory? One reason is a load could be being applied that exceeds 20 amps. One such load could be a dead short or it could be a an accumulative load. Another reason is that CBs do just go bad.

Trouble shooting- Pull all other CBs. In this state the only thing the system is doing is feeding power to the main bus and no further and it is also charging the battery from the start. Your 20 amp CB should not blow. just charging the battery. If it does, figure out why. Is there a short between the regulator and the CB? If the CB does not blow, add one circuit at a time until they are all on or the CB blows. Try to isolate if you have another system after the CB that is bad or maybe the CB is bad.

3. Like I said, don't buy a regulator. Your regulator may not, is likely not the problem. You have a 35 amp gen. Almost any reg will regulate the power the gen makes. A reg smaller than the gen won't hurt anything. A larger reg will just burn out the gen over time if a load larger than the gen is capable of is asked of it. None of this explains why the 20 amp CB is blowing.

4. If you determine that in fact this is a regulator problem or you have an unairworthy regulator (one made for a car) I'd invest in a Zefftronics electronic regulator before I bought an expensive old style regulator..

Thanks again.

I think you mentioned earlier that Cessna to the best of your recollection, did not change the wire sizes in the various 170s. So you would think the wire would be OK. But it is old, and I should have it redone. but it is a huge job and expensive to rewire all those CBs and fuses.

The generator does have a circuit breaker, the fuse having been replaced some time ago. I have a mixture of fuses and CBs.

I don't really need anything close to 35 amps of power, but I would like to be able to turn my landing lights on at night or day without the breaker popping. It powers the other equipment in the aircraft fine...for a generator. I remember several years ago when a cessna maintenance facility was installing the seat stop modification, that when I picked up the airplane that late afternoon I discovered they left the battery on. Don't know why it was on to begin with. So the battery was very low. On the short flight to my home field, the generator breaker popped. No landing lights were in use. I guess it was trying hard to recharge the battery. After several minutes inflight, I attempted a reset. It popped again. I landed at my home field and charged the battery for a couple days. Since then it has been fine unless you turn on the landing lights. That puts it over the edge. I will try turning everything I can off and pulling the CBs and fuses. Then try one at a time. If the landing light had a problem, when the engine wasn't running on the ground and with just the master and landing light on, wouldn't I see the problem there with the battery draining like crazy and unusual amperage on the ammeter?

What size wire should I have to the bus for 25-35 amps?

I also looked at the 170 Assn Electrical Service Manual and it says for 35 amps needs a #4 or #6 wire. We are talking about the wire that comes through the firewall and goes to one side of the ammeter, correct? If so mine is nowhere near that big. I will check that tomorrow.

Ok let me try to keep this all straight. The gen CB is not the rating of the generator system. It is the CB that protects the battery wire from the bus bar to the regulator. It must be sized to protect that wire. That wire must be big enough to carry the highest output the generator is capable of. If the breaker is smaller it becomes the generator output limit.

In the 170A IPC electrical schematic this is wire #10. The A model IPC does not have wire sizes listed however it does have terminal sizes which can give a clue. Unfortunately other than AN659-1 which is for 18 awg max, I can't find a listing of the various sizes of AN659 and their capacity however it might reason the listing goes -1, 18 awg, -2 16 awg, -3 14 awg, -4 12 awg and -5 10 awg.

Using this scale the #10 wire was 12 awg. Comparing to the B model IPC which does list wire size and then for a '52 which is the closest we can get to the earlier models we see this #10 was 14 awg. I said I do not believe Cessna changed wire sizes over the years but I don't know. I have just discovered however that at least one wire size for this wire was changed from 14 awg to 10 awg in '56. So it seems this wire was 12, then 14 and finally 10 awg.

The wire that carries the load and must be large enough to carry the max the generator can produce is the wire from the starter to the amp gauge and then to the bus. Throughout the series of B model this wire was 10 awg. I don't know what size this wire is in an A model however the AN659-5 might indicate it was 10 awg.

The wire guage size chart in the ESM is for NON-intermittent circuits. Cessna probably considered the possibility of pulling 35 amps continuously pretty remote and used the next smaller gauge. 6 guage wire would carry 35 amps continiously no question, 8 guage would probably be sufficiant as well.

So now I'm confused. Seems you have a breaker that pops but only when you have your landing lights on. Which breaker is this, the gen breaker or the land lights? BTW with both landing lights on, if you have the 100 watt 4509 bulbs, that circuit is pulling about 15 amps by itself. This is why most 170 owners don't fly around with both stock landing lights on all the time.

Bruce Fenstermacher wrote:Ok let me try to keep this all straight. The gen CB is not the rating of the generator system. It is the CB that protects the field wire from the bus bar to the regulator. It must be sized to protect that wire.
...

Not quite, Bruce. In a generator system, the wire from the bus bar to the regulator IS the output of the generator. That wire should be sized and protected for the output of the generator, at a minimum. Looking at the schematic in the owners manual, the field circuit is the one through the second pole of the master switch, and has no circuit protection.

Made sense with my eyes crossed. I'm going to rewrite it.

There, I think I have it correct with changes and additions in red.

What do you think Miles?

Should have referenced this earlier and it makes more sense than the table show in our ESM

43.13-1b
11-49. DC CIRCUIT PROTECTOR
CHART. Table 11-3 may be used as a guide
for the selection of circuit breaker and fuse
rating to protect copper conductor wire. This
chart was prepared for the conditions specified.
If actual conditions deviate materially
from those stated, ratings above or below the
values recommended may be justified. For example,
a wire run individually in the open air
may possibly be protected by the circuit
breaker of the next higher rating to that shown
on the chart. In general, the chart is conservative
for all ordinary aircraft electrical
installations. Looking at this table the wire #10 which I think is a 12 awg wire found in the 170A could be protected by a 30 amp CB or a 20 amp fuse. The B models serial 20257 to 26995 the #10 wire is 14 awg and could be protected with a 20 amp CB or a 15 amp fuse. 26996 and on the #10 wire becomes the #129 wire and is now 10 awg and can be protected by a 40 amp CB or a 30 amp fuse.

So if you have a B model , your going to want to upgrade the size of the #10 wire to 10 awg and protect it appropriately to use a 35 amp generator. If you have an A confirm the 12 gauge wire (or larger) protect it with a 30 amp CB (20 amp fuse) and you will be good to go to the limit of the protecting device you choose. A model and you want to get all 35 amps change the #10 wire to 10 awg and protect it with a 35 amp CB.

Boy, that is good stuff guys. I know I have asked a lot of questions and I appreciate the patience and the passing along of your knowledge to me so I may better understand my airplane and keep it safely flying!

To clarify, it is the generator breaker that pops, not the landing light CB. That is because the landing lights are usually the last thing to be switched on. If I had everything else off then started with the landing lights on it would be fine by themselves I think, but will confirm. In building the system load up backwards, ie landing lights first, then the other loads one at a time, eventually, the CB will pop because I have exceeded the rating of the generator breaker. I will confirm this when I can. I will also just turn on the master switch (no engine running) and note the discharge on the ammeter. Then I will turn on the landing lights and note that discharge rate. Subtraction will show me if my landing light draw is about the 15 amps you mention.

I am confused about one thing though. OK, a lot of things. Bruce, early on in the discussion of this topic you said I would have to change the regulator to one of the appropriate amperage because if the currently installed regulator was a 15 amp rating then it would never ask for more. So since I do have a 35 amp generator, don't I need a regulator with a 30 or 35 amp rating? And then an appropriate sized CB? And a #12 awg or #10 awg wire?

My plan: I will see if I can get an idea about the wire size used to go from the regulator to the ammeter and then from the ammeter to the bus. Once that is taken care of I will switch to a 30amp CB if the wire size is 12awg, or perhaps a 35 amp CB if the wire is changed out to a #10awg. Probably go with the 30amp breaker. Have I got this right?

Of course the easiest thing is to change my lights to FAA/PMA approved LEDs. Then I will have plenty of power as it is I bet. But to change the landing lights is about $550. If I change all 3 position lights and strobes, the rotating beacon and the landing lights, the bill would be about $2,000.00 for approved parts. Plus install observation and approval from my IA. Ouch! Most bang for the buck is probably just the landing lights since my system as it is does fine unless the extra load of the currently installed landing lights is turned on.

Also, in reviewing the ESM, it says for the 35 amp generator, a cooling air duct should be used. Mine only has the shroud with the cooling snout or tube attached. There is no air duct attached to that shroud. Does anyone else out there have a cooling air duct attached to their generator?

Thanks again for all the guidance guys!

Steve

sreeves wrote: To clarify, it is the generator breaker that pops, not the landing light CB. That is because the landing lights are usually the last thing to be switched on. If I had everything else off then started with the landing lights on it would be fine by themselves I think, but will confirm. In building the system load up backwards, ie landing lights first, then the other loads one at a time, eventually, the CB will pop because I have exceeded the rating of the generator breaker. I will confirm this when I can. I will also just turn on the master switch (no engine running) and note the discharge on the ammeter. Then I will turn on the landing lights and note that discharge rate. Subtraction will show me if my landing light draw is about the 15 amps you mention.

Your theory that that landing lights load exceeds the 20 amp gen breaker so it pops doesn't add up if your regulator is one rated for and asking the generator for 20 amps or less. So I would suspect your regulator is one rated at greater than 20 amps.

What should happen at that point the generator is maxed out at say 20 amps because that is the size of the generator or the regulator, the generator should give all the regulator is asking but the amp meeter showing a discharge to make up the difference of what the generator can't produce and the load. The difference is being drawn off the battery. Many 170s do not have a generator system that can sustain a full instrument panel, nav lights AND landing lights without discharging the battery.

I am confused about one thing though. OK, a lot of things. Bruce, early on in the discussion of this topic you said I would have to change the regulator to one of the appropriate amperage because if the currently installed regulator was a 15 amp rating then it would never ask for more. So since I do have a 35 amp generator, don't I need a regulator with a 30 or 35 amp rating? And then an appropriate sized CB? And a #12 awg or #10 awg wire?

Don't be confused. You should have a regulator rated at the same size at your regulator. This is the only correct way. What I was conveying is that if your regulator is less than the generator you won't hurt anything, you just won't get what the generator is rated for cause the regulator can not ask the generator to produce it. However if your regulator is rated larger than the generator it will ask the generator to do something it can not and the generator will fail.

My plan: I will see if I can get an idea about the wire size used to go from the regulator to the ammeter and then from the ammeter to the bus. Once that is taken care of I will switch to a 30amp CB if the wire size is 12awg, or perhaps a 35 amp CB if the wire is changed out to a #10awg. Probably go with the 30amp breaker. Have I got this right?

Here is what I'd do. Confirm the #10 wire is large enough to handle the 35 amp load. Replace it if not and then install a 35 amp CB. If after doing this you find your regulator will not drive the generator to 35 amps when required, you can pretty much figure you need a correct/regulator.

Of course the easiest thing is to change my lights to FAA/PMA approved LEDs. Then I will have plenty of power as it is I bet. But to change the landing lights is about $550. If I change all 3 position lights and strobes, the rotating beacon and the landing lights, the bill would be about $2,000.00 for approved parts. Plus install observation and approval from my IA. Ouch! Most bang for the buck is probably just the landing lights since my system as it is does fine unless the extra load of the currently installed landing lights is turned on.

Can I assume you want to fly around all the time with your nav and landing lights on. If so figure out how to reduce that load. It can be very expensive if you just buy the expensive options. There are lower cost LED alternatives for your nav light bulbs and landing lights. See these threads.
http://cessna170.org/forums/viewtopic.p ... 2&start=15
http://cessna170.org/forums/viewtopic.php?f=24&t=1008
http://cessna170.org/forums/viewtopic.php?f=24&t=7323

Besides that many 170s have been wired to operate one or both their landing lights rather than just both. Operating one light cuts the amperage in half.

Also, in reviewing the ESM, it says for the 35 amp generator, a cooling air duct should be used. Mine only has the shroud with the cooling snout or tube attached. There is no air duct attached to that shroud. Does anyone else out there have a cooling air duct attached to their generator?

Thanks again for all the guidance guys!

Steve

Steve I'd bet there are many 35 amp generators installed with no cooling tube. As nice as our EMS is it is not official and some of that info is best practices found from experience. I do not know what category the blast tube for 35 amp generators info falls under. I do not recall an official source that requires it. But knowing this forum if there is one, someone will chime in with the source in an hour or so. My own A model has been flying for probably 35 years with a uncooled 35 amp generator. Doesn't mean you should. A cool generator will be a happier generator.

Thanks once again for the clarifications.

Now I need another one. About the new LED lighting. Is it a legal requirement to have the replacement leds be the approved ones?

The part about being wired for either one or both landing lights is total news to me. I have only the one switch so I have to add an aux switch somewhere?

BTW, I really don't intend to fly around all the time with the landing lights on. It is just a nice anti-collision feature in and near airports. Sometimes the tower will ask for a landing light for recognition. Happens at Sun N Fun all the time during the arrival over the lake (Parker). I just would like to be able to use them whenever I need them without reservation.

And you should be able to use them any time you need Steve. But like many, we balance how much and how long against battery reserve/recharge time.

I can't recall if any of the landing lights where ever wired individually from Cessna, but it can and has been done. Assuming you still have piano keys, the switch already there for your lights is a double throw switch. From the factory you can only move the switch one way or half of the switch. I believe you remove a gromet and the switch can be moved up and down thus giving you the option to run another wire out to the landing lights so that one or both of the lights can be chosen. This has been done.

LED bulbs. First you must understand what a standard part is. Here is a explanation from the FAA: https://www.faa.gov/aircraft/safety/pro ... _parts.pdf

In short a bulb, for example our position light bulb which is Cessna part 0423006-6 is a Grimes 1512. But it is a standard part. You don't have to buy one Cessna stamped 0423006-6 on and it does not have to be made by Grimes. It can be made byGE, Phillips, Sylvania or likely a manufacture in China. What has happened is light bulb manufactures have started making 1512s with LEDs as the source of light rather than a tungsten filament. They are calling them the equivalent or equal as the 1512 and so, they are a 1512.

Do you have to buy the the expensive LED replacements? Read this thread from George if you haven't already and you decide. http://cessna170.org/forums/viewtopic.php?f=24&t=7323

I think PSA is probably selling standard parts and so long as they perform as well as the incandescent bulbs to the naked eye, few will question it.

Sounds good to me.

Did some tests today with just the battery powering the system. Put a charger on the battery, then turned on the master switch. Ammeter barely moves, very slight discharge. I then turned on the landing lights which showed about 15 amp discharge (just like Bruce said). Turned off the landing lights and turned on the nav lights/rotating beacon (they are on the same switch in my aircraft) which shows 7.5 amps discharge. Then turned off nav lights/beacon and turned on strobes which showed 5.0 amp discharge. Just the radios shows a 2.5 amp discharge and the electric turn and bank shows 1.0 amp discharge, lower than I thought it would be. Turning everything on together shows about 30 amps discharge. So no wonder the 20 amp generator breaker would pop.

If you had asked me, I would have given you those exact numbers. Not that I know your aircraft, it is that these numbers are pretty consistent throughout the fleet. Was worse when you had tube radios. LEDs as they replace the incandescent bulbs will reduce the load significantly.