I have an old Cessna aircraft clock (CA-6254) that was powered off of a 12v aircraft system. The reverse of the clock has terminals labeled Ground and Battery. Is there any way to power this clock (to accurately tell time) without a 12v aircraft-size battery? Can it be adapted for a plug for household power? I’d like to get it running again, sans airplane.
If it runs on 12V, all you’d need is a wall wart rated at 12V and whatever current to clock requires. Is there a plate attached saying what the current draw is?
As GaryM notes, all you need is a 12v power source - not an aircraft battery. I wasn’t able to find the specs for this device, but it’s unlikely to draw more than about 250ma.
Here’s one on Amazon, 12V and 2A, more than enough.
LE DC 12V 2A Power Supply Adapter, AC 100-240V to DC 12V Transformers, Switching Power Supply for 12V 3528/5050 LED Strip Lights, 24W Max, 12 Volt 2 Amp Power Adaptor, 2.1mm X 5.5mm US Plug https://www.amazon.com/dp/B019Q3U72M/ref=cm_sw_r_cp_apa_HnnFzbG1XP3AV
Just cut off the plug and you’re good to go.
12 VDC is 12VDC … it doesn’t really matter where the 12 VDC comes from … any 12V battery, two 6V batteries in series, or even 8 “D” cells (1.5V) in series …
Getting 12 VDC from a 110 VAC outlet is a little trickier … you need a “power supply” that will convert household voltage into clock voltage … and these are readily available “off-the-shelf” …
The clock will draw the current it needs, so we do have to make sure the power supply can provide this level of current … but it shouldn’t be a problem unless we get some manner of micro-mini power supply … so do check the amps the clock needs and make sure the power supply is rated over than value …
Cessna clock … GREAT idea … I hope you get this done …
Thanks for the inputs. Unfortunately, there are no electrical specs on the clock I can see. There is a faint “Borg Clock Div” stamp, and the two screw/nut terminals marked “GND” and “BATT”. My google-fu only turned up the clock is 12v.
I may try the PSA GaryM suggested as it’s inexpensive and appears to provide a no-fuss way to connect wires from the clock terminals to the PSA.
Do you have, or can you borrow, a current meter to test the clock? An old clock like that might draw 2 or 3 amps instead of 250 or 100 milliamps. It might be worth it to measure once, before buying a dedicated power supply.
A current meter would only do any good if he already had a power supply capable of producing the current the clock draws, and if he had that, he’d be fine.
I just Googled 12 volt aviation batteries, in hopes that that might be a useful guide, but it looks like they’re typically rated for hundreds of amps. Now, I’m sure only a tiny fraction of that would go to the clock, but that’s still not very helpful.
I do not expect him to have a full electronics lab with attendant power supplies handy, but even a common 12V automotive or marine battery would be enough to do the one-time testing (maybe he owns a car), if he had the current meter. Even one of those little multimeters should be good enough.
Given the size (ebay link) and the fact it is just an electric clock and has no other functions the likelihood that it is drawing more than 2 AMPS is very small.
I suppose I could check to see if the clock works by testing it with my car battery. I live close to an auto parts store and a Batteries+ store that might be able to do an actual current-draw test on it. (I don’t own a current meter)
I found the clock in my dad’s garage after he died years ago, and it’s been sitting on my office shelf ever since. I thought it would be fun to see if I could get it going with a minimum expenditure of resources. You have been a big help, thank you.
ETA: Astro, your link shows a clock just like mine (mine has a “Jan 62” ink stamp on it)
Are you sure it’s 12V? Small aircraft systems were typically 14V or 28V; according to Wikipedia, the Cessna 172 switched from 14 to 28V in 1978. If it’s 14V, a 12V adapter might still power it but wouldn’t be ideal. I’m sure that an amperage of 2A like the one that GaryM suggested would be more than sufficient for a clock, though that particular adapter is a switching supply with the ability to handle up to 240V input so it’s probably more pricey than you really need. Besides voltage, also make sure you get the polarity right. I’m pretty sure that aircraft, like most modern cars, have been negative ground for a long time, but you need to verify.
Cessnas are actually 12V, not 14.
The distinction is that cars use a 12V battery and a ~14V generator or alternator and call that a 12V system. Meanwhile, light airplanes use a 12V battery and a ~14V generator or alternator and call that a 14V system. IOW, same electricity, different names.
A typical lightplane battery of the relevant era is almost identical to a small car battery of the same era. The sort & size of battery you’d find in a subcompact, not in a mongo pickup truck.
Since light airplanes tend to sit unused for a long time, the clock needs to be real low draw. Just as the mechanical clocks common in 1960s cars were real low draw.
GaryM’s Amazon suggestion will be fine.
This is a good point. As with automotive loads, “12 V” is really around 14 V. (The alternator usually generates a voltage somewhere between 13.5 and 14.2 V when the engine is running.) If it were me I would purchase or build a 14 V DC regulated power supply. Since it’s a clock the current draw will likely be small, so the max current capability of the power supply probably isn’t important.
So there’s no way for a hand-held digital multi meter (like the automatic Greenlee I have) to determine the current necessary to run a device unless it’s already running on the necessary current?
Yes, that’s true. You can’t measure what it will need later. You can only measure what it is needing now.
OK, pardon my ignorance here. Couldn’t you take your multimeter and measure the total resistance of the circuit, and then plug that and 12VDC into Ohm’s law to figure the current draw?
No. For anything more complex than a resistor, the effective resistance depends strongly on voltage (i.e. current is not proportional to voltage).
But I do think we are over-thinking this. There’s very little chance a clock will draw more than a few watts.
If I were in your position, I would reach in to one of my junk drawers, and I’m sure I’d find a 12V power adapter (power brick) for some piece of electronics I’ve long since thrown away. I’d just hook that up. Even if you don’t have something like this, maybe you know someone who does?
Note that the unit in GrayM’s link #4 is only eight bucks …
If that thing draws over 2 amps it would be burning hot to touch - equivalent to a 25W light bulb. If it draws more than a few tens of milliamps I’d be very surprised.