Info: External power for the SR20 (long/technical)

Guest Discussion
1

I like to sit in the 'plane with the Battery Switch ON and play with the avionics - it’s a great way to learn - more real than the PC sims, and less stressed/hurried than in actual flight (especially IMC).

The problem is that all the electronics draws a respectable (> 10 Amp) current when everything is on; and since we have a 10 Amp-hour battery, I’d have no juice at all in short order.

I decided to buy an external power supply - something that could keep the battery “perked” so that I can play indefinitely and not feel rushed. The same device will actually charge the battery, although doing so is not officially recommended/sanctioned (we’re supposed to remove the battery for charging).

I bought the Schauer Four Seasons Fully Automatic 24 Volt 20 Ampere Battery Charger through http://www.aircraftspruce.com/main.html Aircraft Spruce & Specialty Company . It cost about $200 (there’s a 10 Amp version, certainly ample, for $124). It’s in the Electrical Section of my printed catalog, on page 350. I also bought a Lexan plug - AN2551 - from the same source. This is the plug that fits into the external 24 volt source on the side of the airplane cowling.

When the charger arrived, I decided to remove the crocodile clips that are standard (and designed to connect to the posts of a battery), and connect the AN2551 plug directly to the charger. [Some heavy duty soldering required - needs a blowtorch].

I connected the charger to the airplane, switched the Battery Switch to ON… and nothing happened.

The problem is that both devices (the charger and the airplane) are too smart. The airplane has an “External Power” relay that won’t connect the outside power source until it sees voltage is present; and the charger won’t provide power until it senses at least SOME battery voltage. In effect, both devices stand there saying “After you” - “No, After YOU”… etc.

An obvious solution is to use the charger the way it was intended - i.e. hook it up to a 24 volt battery (or 2x12 volt batteries in series), and connect those batteries in turn to the airplane. This arrangement has some advantages - for example, you could connect the battery to the airplane without the charger, provided it is charged; this would be very useful where there is no AC available.

However, I didn’t want the extra hardware (battery), so I modified the charger to add a pushbutton “trigger” to feed just enough voltage to the sense circuitry to convince it that it’s OK to start charging.

Now, after hooking the charger to the airplane, I switch the Battery Switch to ON, and press my Trigger pushbutton, and off it goes.

The actual modification is very simple. If you’re interested, send an email, and I’ll fill you in on the details.

Mike.

2

Mike: I don’t have my plane yet, but what I plan to do is use two 12 volt batteries in series with cables to the aircraft plug and then get a very small automatic 24 volt charger. There is probably a hand truck already designed for auto shop use that would work just fine. 12 volt batteries are pretty cheap and the charger could be bolted to the hand truck so that the whole rig could be stored near a.c. power and wheeled up to the aircraft as necessary. I haven’t priced this all out, but it should be comprable with the $200 for the 20 amp. 24 volt charger you have.

There are advantages to this system. (1) no modification of the charger is necessary (2) if the aircraft battery is really dead you have ample current available from your battery cart for engine starting and (3) if you are worried about drain on the aircraft batteries during ground use, you can power the small charger to make up most of the drain and (4) the battery cart can be left on the automatic charger so that you will have a fully charged back up battery should the aircraft battery fail to start the engine. The only disadvantage would be that you have the option of carrying the charger with you to another location. I’m not sure you would be doing this anyway.

I like to sit in the 'plane with the Battery Switch ON and play with the avionics - it’s a great way to learn - more real than the PC sims, and less stressed/hurried than in actual flight (especially IMC).

The problem is that all the electronics draws a respectable (> 10 Amp) current when everything is on; and since we have a 10 Amp-hour battery, I’d have no juice at all in short order.

I decided to buy an external power supply - something that could keep the battery “perked” so that I can play indefinitely and not feel rushed. The same device will actually charge the battery, although doing so is not officially recommended/sanctioned (we’re supposed to remove the battery for charging).

I bought the Schauer Four Seasons Fully Automatic 24 Volt 20 Ampere Battery Charger through http://www.aircraftspruce.com/main.html Aircraft Spruce & Specialty Company . It cost about $200 (there’s a 10 Amp version, certainly ample, for $124). It’s in the Electrical Section of my printed catalog, on page 350. I also bought a Lexan plug - AN2551 - from the same source. This is the plug that fits into the external 24 volt source on the side of the airplane cowling.

When the charger arrived, I decided to remove the crocodile clips that are standard (and designed to connect to the posts of a battery), and connect the AN2551 plug directly to the charger. [Some heavy duty soldering required - needs a blowtorch].

I connected the charger to the airplane, switched the Battery Switch to ON… and nothing happened.

The problem is that both devices (the charger and the airplane) are too smart. The airplane has an “External Power” relay that won’t connect the outside power source until it sees voltage is present; and the charger won’t provide power until it senses at least SOME battery voltage. In effect, both devices stand there saying “After you” - “No, After YOU”… etc.

An obvious solution is to use the charger the way it was intended - i.e. hook it up to a 24 volt battery (or 2x12 volt batteries in series), and connect those batteries in turn to the airplane. This arrangement has some advantages - for example, you could connect the battery to the airplane without the charger, provided it is charged; this would be very useful where there is no AC available.

However, I didn’t want the extra hardware (battery), so I modified the charger to add a pushbutton “trigger” to feed just enough voltage to the sense circuitry to convince it that it’s OK to start charging.

Now, after hooking the charger to the airplane, I switch the Battery Switch to ON, and press my Trigger pushbutton, and off it goes.

The actual modification is very simple. If you’re interested, send an email, and I’ll fill you in on the details.

Mike.

3

Mike: I don’t have my plane yet, but what I plan to do is use two 12 volt batteries in series with cables to the aircraft plug and then get a very small automatic 24 volt charger.

Stephen,

Your idea is perfectly sound, and probably makes the most sense for most people. In my case, I don’t have anywhere to keep a “cart” - my airplane is kept in a communal hangar. So the advantage of the charger (for me) is that I can carry it in the trunk of my car, and never worry about acid spills, etc. It’s also lighter than car batteries.

If/when my circumstances change (i.e. when I get my own hangar), I will certainly do exactly what you’ve suggested.

By the way, I have a perfectly wonderful, brand new, purpose-modified electric charger to swap for a T-Hanger in Central NJ…

  • Mike.
4

Modern sealed maintenance free batteries do not leak regardless of attitude and are available in sizes for equipment like mowers, motorcycles, automobiles, and trucks which allows you to select the power you want which you can carry safely.

For six tenths of a pound more weight than a spare G-243 (stock battery for SR20) and a bit more than twice the space (17.7x9.4x14.9)you could carry the 900W 120V (1000W max) Honda EU1000 generator.

You could use it to preheat the engine and cabin with a small hair dryer set on low.

If you could change it’s 12V output to 24V it would be near ideal.

I’m hoping a 1400W or so unit will come out soon at only a few pounds more.

With the weight and efficiency of these new small OHV engines maybe the SR22 would be better off with an APU instead of the second battery.

It could have built-in engine and cabin preheat and charging.

You could use it to preheat the engine and cabin with a small hair dryer set on low.

Mike: I don’t have my plane yet, but what I plan to do is use two 12 volt batteries in series with cables to the aircraft plug and then get a very small automatic 24 volt charger.

Stephen,

Your idea is perfectly sound, and probably makes the most sense for most people. In my case, I don’t have anywhere to keep a “cart” - my airplane is kept in a communal hangar. So the advantage of the charger (for me) is that I can carry it in the trunk of my car, and never worry about acid spills, etc. It’s also lighter than car batteries.

If/when my circumstances change (i.e. when I get my own hangar), I will certainly do exactly what you’ve suggested.

By the way, I have a perfectly wonderful, brand new, purpose-modified electric charger to swap for a T-Hanger in Central NJ…

  • Mike.
5

Modern sealed maintenance free batteries do not leak regardless of attitude and are available in sizes for equipment like mowers, motorcycles, automobiles…

For six tenths of a pound more weight …and a bit more than twice the space …you could carry the 900W 120V (1000W max) Honda EU1000 generator.

Doug,

Also great ideas. For me, the charger will suffice for now; but I may well add batteries and/or the generator later, especially if I acquire a place to keep them.

  • Mike.