The International Cessna^® 170 Association

A Christmas gift was an aircraft quartz clock from Instrument Services Inc. in Roscoe Illinois that i want to put in my 52 170b. The instructions say use in a 12 volt system only.It is the clock they recommended for the 170. I noticed aircraft spruce also calls it a 12v clock. So are these airplanes 12v or 14v? And will this clock work? It claims to be a direct replacement for the Borg made electric clock in Cessna,Piper,Beechcraft and others.

jeff

Jeff

They are 12v though you are correct that when the generator or alternator is turning and producing power it would be appropriate to the voltage to rise to over 14 volts. 24 volt aircraft actually make nearly 28 volts.

I'm sure you have the right clock voltage.

Yes, Bruce is absolutely correct, of course.
12 volt systems are also commonly called 14 volt systems because the battery in them is nominally a 12 v battery, yet the charging system is nominally 14 v (even tho' it may operate normally as high as 15 volts...the ideal is 13.8 volts. As corrosion builds over time, many connections no longer have perfect connections. Don't be distracted by such trivia. The charging device (alternator or generator usually) will ordinarily produce 1-3 volts more than the battery.

Another example is a 24 volt system...which is actually a 28 volt system, but will operate nominally correct anywhere between 24 and 29.5 volts before it is considered out-of-spec.

Having this site sure makes working on our 170's a lot more enjoyable! I am amazed when i read the posts and see how much useful (most of the time) knowledge you guys seem to carry around in your heads.
The membership in the 170 association is the best value out there.
Jeff

Did manufacturers go to the 24 V system in order to use smaller (lighter) wiring (higher voltage, less amperage)? That is something that someone somewhere told me. It makes since, is that correct?
David

That's the primary reason....i.e., less weight. (Also, more avionics selections are available.)

Other things get lighter too, such as motors, relays & solenoids. Anything with contacts can use smaller contacts, as the size is more dependent on amperage, which is lower with higher voltage at the same power requirement.

Did manufacturers go to the 24 V system in order to use smaller (lighter) wiring (higher voltage, less amperage)? That is something that someone somewhere told me. It makes since, is that correct?
David

They went to 24v batteries (28 volt system) for power requirements. As the equipment list grew the power requirements also grew. It got to the point that 60, 80 amps were not enough. Same deal with cars at 6 volts could not cut it so they went to 12v. I do not see why cars aren’t at 24 volt systems now, but i am sure it will be shortly. Also the 12 to 24 change reduces the heat and line loses considerably

dave

Many of the avionics offerings now have power supplies that accept anything from 11-33 volts.

Miles

I do not see why cars aren’t at 24 volt systems now, but i am sure it will be shortly

Actually, some of the newer vehicles are 42 volt - more on your high end vehicles though. We have not seen any roll through our shop as of yet but it will be coming.

Paul
N3458D

Another factor to keep in mind when consideribg aircraft storage batteries and their nominal voltage is cost. As the voltage goes up, so goes the price.

I sure hope that garden tractors maintain their current 12v. systems!

Paul-WI wrote:

I do not see why cars aren’t at 24 volt systems now, but i am sure it will be shortly

Actually, some of the newer vehicles are 42 volt - more on your high end vehicles though. We have not seen any roll through our shop as of yet but it will be coming.

Paul
N3458D

Our engineers have been working on 48 volt automotive equipment. They say the reason for going to the higher voltage is that they've reached limits in the power they can get out of the alternators and keep them reasonable. The way out of that issue and provide enough juice for the newer cars is a higher voltage electrical system. At least that's their story, sounded good to me.

tye