The International Cessna 170 Association

Once in a while I stumble across a non inflated-aviation-priced gadget that really works great. Having finally purchased a Stratus for use on a long trip, I immediately noted the need for TWO(2) 2.1 amp USB charging ports, if I wanted to keep it, and my iPad topped off during flight. After a brief search, I found a really nice, compact Cigar lighter USB charger that has a total of three(3) ports. They connect as follows: 2.1A for the iPad, 2.0A for the Stratus, 1.0A for my Android cell phone. Here's the cool part - it cost only $9.99 with free shipping. I just came back from a 20 hour trip, and it was able to stay ahead of the demand for all devices. They started less than fully charged, and after each leg, they finished fully charged. And, there was no interference with the radios as noted with some others Here's the link:http://www.ebay.com/itm/111549480654 and a picture of the item in action.

I have a hard time keeping my ipad charged with a 2.1 A (rated ) charger.

My concern here is what would this draw from the lighter socket? Is the wiring/fuse adequate?

AD 79-08-03 requires the cigar lighter to be disconnected from it's original connection straight to the hot bus and protect the circuit with a fuse suitable for the wire used in the circuit. A cigar lighter normally draws about 10 amps. Presumably the circuit is wired and protected for at least that and maybe more. And that is 10 amps at 12v.

The USB is using a voltage regulator to drop the 12v to 5v. The 2.1 amps output is at 5v. Though not exactly correct since we are not considering the current requirement of the voltage regulator, 5v at 2.1 amps is about the same as 12v at 1 amp.

All USB chargers are not created equal. Most will not deliver 2.1 amps to all the sockets. Sometimes it is only one if at all. But if we found one that could deliver 5v @ 2.1 amps to all three plugs, it would likely not be pulling more that 12v @ 5 amps from the cigar litter.

Shut off the GPS?? Arash, you Luddite!

That's a good-looking charger, but it's Apple-centric. Great for the iPad and iPhone, but not the Samsung devices, which use a different "keying" scheme to tell the charger how much charge to deliver. I gave up trying to figure it all out and now just use my AC inverter. I plug each device's charger into 120VAC and let the charger do the work.

Aryana wrote:It's worse that you know Dave...I'm actually proficient with using both my VORs!

At the same time??

A simple hand held GPS will give you the radial and distance from any VOR station, and the distance will not be "slant range" unlike a DME.
As a matter of fact, the hand held GPS will give you more accuracy than a VOR when considering the allowable varience of the VOR system.
The next time you are on an airport with a VOT, check your VOR bearings against your GPS (if you happen to have both available).

Back to the topic, Bruce's analysis was correct. If we talk about electrical power (watts) we can answer the question with some numbers. The 3 ports supply a total of 5.1 amps at 5 volts DC. The product of amps times volts is watts, so we are supplying a maximum of 25.5 watts from the 3 outputs. Now, to produce that power from the ships DC bus, we work the problem backwards and divide 25.5 by 12 to get 2.125 amps. (Actually we would divide by the alternator output voltage of 13.8, but we'll keep it simple.) No electrical circuit is 100% efficient, so we can assume the charger can draw more than 2.125 amps. But, inefficiency generally shows up as heat, and the charger certainly did not get hot during operation.

As Bruce mentioned, the cig lighter was required by AD to be protected by a fuse or circuit breaker. The two C170 schematics I've looked at show the lighter socket on the same 25 amp fuse as the landing lights, so assuming the socket was wired with #10 gauge wire, nothing would have needed to be done to comply with the AD. Now, since I've installed LED landing lights, I have no worries about total current flowing in this circuit. With normal incandescent bulbs, it could be possible to exceed 25 amps if the charger was operating, and both taxi and landing lights were turned on. I would hope that circuit was designed with at least 3 amps "head room" over rated load, but I have never actually measured it. (I certainly would not be as comfortable flying at night if I had not installed circuit breakers shortly after buying 33C.) If this 3A or so is a concern, measure what you are actually drawing, using a decent digital multi-meter. Then, if total current is an issue, either protect the lighter socket with its own breaker, or lessen the load by installing LED landing lights.

For those looking for 2 port solutions here is one made by Belkin; iPad/Phone cable with Lightning connector included:
http://www.ebay.com/itm/111713639876 Cost is a reasonable $8.99 with free shipping!

so assuming the socket was wired with #10 gauge wire

That was the problem and the reason for the AD. The wire was not 10 gauge. And so a separate breaker for the wire used was called for.


I use the Belken USB Karl linked to and am happy with it.

Will it work on a 24 v system? The ebay seller doesn't know!

There are no Apple-centric chargers, there "keying" system is in their cords and the device. Don't know how the Android stuff works.

DaveF wrote:Shut off the GPS?? Arash, you Luddite!

That's a good-looking charger, but it's Apple-centric. Great for the iPad and iPhone, but not the Samsung devices, which use a different "keying" scheme to tell the charger how much charge to deliver. I gave up trying to figure it all out and now just use my AC inverter. I plug each device's charger into 120VAC and let the charger do the work.

Avee8or wrote:Will it work on a 24 v system? The ebay seller doesn't know!

Sorry - the input voltage is specified as 12 - 18 VDC. That's 10 volts under the 28VDC a 24 volt system operates at. It's a rare consumer product that can handle a 28VDC input.

Thanks, Karl. I have found several usb power adapters that work at 28 v but they tend to be poor quality...best so far is from Wal Mart, but this one looks to be more robustly built.

I'll throw another solution out there for comment. If anyone needs a digital clock, as well as a way to charge USB devices, here's an interesting product: MD93 Series Digital Clock & USB Charger. It's here at $580:
http://www.chiefaircraft.com/aircraft/f ... -md93.html
I found it as low as $555 from another source, but this will be one of the more expensive options, although maybe a bit more elegant than an adapter always hanging out of a cigar lighter. Anyone have any first-hand reports on this one?

https://www.pacificcoastavionics.com/pr ... arger.aspx
Better price!

Wow! $500 + for a digital clock and a simple ubs charger It will be a cold day in Death Valley before I spend that kind of money on a rather simple digital clock and a charger that I can get at Wal Mart for $400+ less However, there are those with lots of extra bucks to spend, so go far it