Rereading, I think my guidance above was unclear. With the BAT rocker was ON and the 70A breaker OFF, you need a brief presence of 12-24V on the appropriate APU connectors to trip the internal relay that takes the APU plug live so that an accidental wrench drop won't spoil your day (and battery and wiring). Polarity-sensing chargers that "wait" to see at least some voltage of the correct polarity before switching on. They will not trip the short protection relay on their own. I have two 12V/7A gell cells taped together that I use to trip the relays for a fraction of a second. After the click, your charger will maintain the connection.
My read of the current limiting circuitry on your new charger is that it will still dump 20A into a substantially discharged battery. The reference to "current limiting" applies to the fact that it monitors battery voltage and reduces current in two stages as the battery approaches full charge. There are some issues here, too, but probably relevant only to certified battery fanatics.
Thanks Robert - that's my thinking as well. I completed the moving of the wire internally and that will leave the voltage output hot 100% of the time the unit is "ON", thus correctly supplying power to the plane. I don't plan on using this charger for anything other than floating a small charge on the battery when I'm not using the plane for a while, or powering the avionics for Garmin updates or just working with them.
I don't ever anticipate using this charger on a heavily discharged battery. For that I would likely remove the battery and use something far more appropriate to recondition the battery.
Paul Papa Sierra Shirley
N14PS 2010 DA40.1100 WAAS, TAWS-B, SVT, Jepp ChartView, SafeTaxi,
GFC700 w/VNAV, GTX33 Mode S, & Avidyne TAS600 Active Traffic
PapaSierra wrote:Thanks Robert - that's my thinking as well. I completed the moving of the wire internally and that will leave the voltage output hot 100% of the time the unit is "ON", thus correctly supplying power to the plane. I don't plan on using this charger for anything other than floating a small charge on the battery when I'm not using the plane for a while, or powering the avionics for Garmin updates or just working with them.
I don't ever anticipate using this charger on a heavily discharged battery. For that I would likely remove the battery and use something far more appropriate to recondition the battery.
Hi
I have bought the same charger/apu and am having problems. I contacted Scott at Schauer and have checked that the red lead is on the correct terminal. I am able to charge our spare battery OK and the green light turns amber until fully charged when the light turns green again but when connected to the aircraft DA42 the green light remains green and when the master switch is turned on the ammeter shows a small discharge.
As you have described I only want to keep the battery charged (should the Master switch be on?) and from time to time enter routes etc on the ground which takes a heavy toll on the onboard battery if engines are not running.
You mentioned pulling circuit breakers but this leaves me with dead screens (Garmin 1000) so I have no idea what is happening to the battery and anyway the light stays green.
Can you give me any advice as to what I am doing wrong?
It sounds like you don't want to pull the 70A breaker and set the BAT rocker to ON. If so, the only way to get your charger connected to the battery through the APU is to connect the charger normally, then momentarily connect a correctly polarized 24 volt source to the APU in parallel. This will activate the internal relay that normally isolates the APU pins from the battery. (If you put a voltmeter on the pins you will see zero volts when nothing is connected to them.) Once the relay activates, your charger will be connected to your battery and from there on the current it delivers will sustain the connection. I used this method for awhile before I changed to a direct connection to the battery. I rigged up two 12 volt 7A gel cells and left them in the hangar with the charger.
For those of us who like schematics and such, here is a diagram from the AMM that shows how the battery, the external power plug, and the associated switches and relays are connected.
It sounds like you don't want to pull the 70A breaker and set the BAT rocker to ON. If so, the only way to get your charger connected to the battery through the APU is to connect the charger normally, then momentarily connect a correctly polarized 24 volt source to the APU in parallel. This will activate the internal relay that normally isolates the APU pins from the battery. (If you put a voltmeter on the pins you will see zero volts when nothing is connected to them.) Once the relay activates, your charger will be connected to your battery and from there on the current it delivers will sustain the connection. I used this method for awhile before I changed to a direct connection to the battery. I rigged up two 12 volt 7A gel cells and left them in the hangar with the charger.
Thanks, much appreciated.
However as a total non tecchie I cannot see me connecting a 24 volt source (even if I had one) for fear of doing damage.
I think that I could manage pulling a breaker and I did try this but I have noticed that there is one for each engine plus another marked battery for 90 amp. I have tried other things like turning alternators off but am really nervous at possibly damaging any components. It is not really practical to get the battery out as I want to update the avionics. I am sorry to bother you further but I would be grateful if you would give me a step by step on the procedure you use. Schauer have been helpful but say that this problem is restricted to Diamond aircraft and understandably don't really want to get involved. When I bought the unit I assumed it was just a case of plugging it into the Aux power socket the plugging the unit into the mains power and turning it on!
Actually Michael, the problem is not restricted to Diamond products. Many APU plugs have this protective relay and the problem, if you can call it that, arises from the fact that both the aircraft and the charger are waiting to see each other's voltage before they apply their voltage . Given all of the variables, my suggestion would be to install a direct charging connection to the battery, as I believe most of us have eventually come to as a permanent solution. It may sound difficult but a skilled mechanic should be able to do it in 30 minutes. I am on the road, dictating on my phone, so I cannot look up the link. If you search for "battery connector" or similar you will find the discussion and pictures of the hook up. I believe it is the best permanent solution. Apologies for the dictation errors.
rwtucker wrote:Actually Michael, the problem is not restricted to Diamond products. Many APU plugs have this protective relay and the problem, if you can call it that, arises from the fact that both the aircraft and the charger are waiting to see each other's voltage before they apply their voltage . Given all of the variables, my suggestion would be to install a direct charging connection to the battery, as I believe most of us have eventually come to as a permanent solution. It may sound difficult but a skilled mechanic should be able to do it in 30 minutes. I am on the road, dictating on my phone, so I cannot look up the link. If you search for "battery connector" or similar you will find the discussion and pictures of the hook up. I believe it is the best permanent solution. Apologies for the dictation errors.
Thanks Robert,
I did investigate getting a permanent charging connection installed in the front baggage hold but our technicians seemed to imply that this was dangerous and would not be approved (either by them or our insurers!) They pointed out that they already use an APU (very pricy unit) when working on the aircraft and that was what the " Cessna port" was there for. Hence I bought the Schauer which was advertised to carry our three requirements.
It seems that the unit literature was inaccurate and didn't mention that it was not "Plug and Play" Not sure what to do next but thanks very much for your help. I will certainly go back to Schauer and express my disappointment.
As for the hard wiring position of your mechanics, I'm not sure I agree but other DAN members may have more insight into that issue.
This said, it might be easier to remedy the problem on the side of the Schauer than the Diamond. All you need to make the APU connection "live" is for the charger to deliver 24 volts for a fraction of a second. If I had a schematic for your charger, I could likely suggest how you or your mechanic could add a simple push-button momentary switch that would do that. Your procedure would then be: (1) plug the Schauer APU plug into the Diamond APU, (2) set the switches correctly on the Schauer and then plug it into 117 VAC, (3) momentarily press a button you would have mounted in a convenient place on the Schauer. You would hear the Diamond relay click and you would remain connected so long as the Schauer remained powered up and the APU connection was not interrupted. For the price, Schauer should have provided that capability in its charger.
A long shot: Schauer's voltage sensing system (that's what is causing the problem) may require a few milliseconds to kick in. If so, that fraction of a second could be all you need to trip the Diamond relay. You can test this by repeating steps #1 and #2 above. The ideas is to have the Diamond's relay "ready and waiting" with everything configured when you plug the Schauer into the 117 VAC supply. You might unplug and plug it in a second time to see how it behaves with partial charge on its capacitors. I would give this solution a 10-15% chance . . . but, hey, it is worth a try.
The problem may be in the wiring of your charger plug. If you look at the plug, there are two larger pins, and one smaller pin. The power is delivered through the two larger pins, but it is the smaller pin that needs power to close the external power relay. I suspect that maybe the charger is not even connected to the small pin of the charger plug.
To solve this problem, Schauer would have to provide 24 volts to the small pin all the time to keep the relay closed, and then supply the charging voltage to the larger pins as it must do now. From the picture, it looks like the charger only has 2 wires on the connector to the Cessna plug.
On the other hand, if the plug is hot when the charger is powered on, then you could just connect the small pin to the positive larger pin inside of the red plug and it should work. Have you tried testing the charger output with a volt meter when it's not connected to anything to see what you get?
