jkurkjian

I am doing a glow to electric conversion of an airplane I've had for 20 years. The motor is a Hacker C50, ESC is a Hacker Opto77, and power is from 3 3s2p LiPo packs wired in series. I've made my own series harness and it includes a high voltage UBEC to power my receiver and servos. With the batteries connected to the harness, my Whattmeter measures 38VDC. So far, so good. My next step is to program up the Opto 77 with the Hacker Master Programming Box. I have a separate receiver pack hooked into the Programming box as well as the ESC signal cable. When I try to plug in the ESC to the battery harness, I get sparks (enough to startle me). There are no stray wires, solder splashes, or any other type of visible short sources.

I removed the ESC from the system and simply plugging in the final battery also caused sparks (again, enough to startle me).

I now have one of the UBEC input leads cut, so it's out of the system. I still get sparks when plugging in the ESC.

The only common denominator is my harness, but I measure the proper voltage at the output end. The harness uses Deans connectors and it is pretty easy to see that there are no shorts anywhere.

Has anyone had a similar experience with high-voltage systems and know this to be "normal"? Personally, I don't think so, but I am not omniscient. Note that the Whattmeter plugs in without any issue (but there's nothing on the load end either).

Thanks,
JK

normgoyer

Hi, I will research your problem with my electrical engineer friend and get back to you. I will also digest your problem overnight and get back to you in the am. I have seen sparks when plugging various components iny AXI systems including my toaster so at higher voltages it may be normal but these components cost big bucks and it is better to sure. Norm

normgoyer

Hi I just reread your letter again and I spotted something that happened to a friend of mine. He had an BEC ( battery eliminator circuit) plus he used a separate receiver battery, instant spark and smoke and good bye one ESC and BEC. You cannot connect a receiver battery and BEC connection to the receiver at same time. If you only used the extra receiver battery to program the ESC but did not have your receiver plugged in that is a different situation. I have stopped using BECs in my larger airplanes and only use an ESC and a separate receiver battery. Much safer that way. After I lost a good airplane due to bad cut off voltage I gave up on using a BEC. What plane are you working on and how much does it weight and what is the wing span and area? Those facts will tell me a lot as well. Norm

jkurkjian

Hi Norm,

Thanks for the quick response. As a clarification, the "receiver battery" I mentioned was used to power the Hacker Programming Box; it was not plugged into the receiver (nor was the ESC plugged into the receiver). Only the UBEC was plugged into the receiver. There was no electrical path between the UBEC output and the receiver battery. BTW, "sparks" occurred both when the UBEC was and was not plugged into the receiver.

WIth regard to the aircraft, it's a Goldberg Eagle 63. The estimated AUW is 6 to 6.5lbs. I'm not worried about any of the system specs; I have already ran it through MotoCalc. The predicted current draw is only around 17A and power output is 70W/lb. If anything, the Hacker motor is being underutilized. The Eagle is intended as a trainer for my kids. When they "graduate", I plan on moving the system into a much sportier airplane.

John

algutkin

My Feedback: (1)

I have 15 aircraft that have been converted from nitro to electric, and on each and every aircraft there is a spark when connecting the Dean connector. If you plug the connector in all the way nothing gets hot and there are no more sparks. The spark only happens when they touch on plug in. Want to know why?

Even when the switch is off, electrictiy is still flowing and there is a completed circuit. The current that is flowing is not strong, but there is a demand and therefor a spark when the connection is made. If you fail to disconnect the lipos from the BEC when you are finished flying, this small demand will deplete and ruin the lipos. While I am typing this post I have several packs of lipos in the garage charging. I left them connected and the voltage dropped from 11 volts down to 7. The charger thought they were 2S packs instead of 3S and wouldn't charge. I am trying to restore them back to the correct charge, but, previously I failed at this.

I guess what I am trying to say is simply this. The switch does not shut off all electric power, it just shuts it off to the receiver. The motor doesn't run when the switch is off because the receiver is not sending to the controller, however power is still going to the controller via the BEC.There is still a slight demand, thus, a spark when re-connecting after a disconnect.

Think about this, the lipos are connected to the controller, the controller is connected to the motor. That is a compelte circuit. The BEC is tapped off of the controller, runs to the switch, then to the receiver. So turning the switch off does not disconnect the power to the controller or motor. There still is a completed circuit between the batteries to the controller to the motor. The only thing missing is the imput from the receiver to tell the controller to start the motor, but the current is still there, and when you connect the dean connector, the current want to jump and complete the circuit.

Hope this helped.

Al G

normgoyer

Hi John, you are going to have a screamer there. You surely have plenty of power but you can always throttle back but you can't throttle up if the power isn't there. If all of your wiring is correct and all components are working the unit should work. I also get sparks when I plug in my 22.2 batteries in the sytem. I suggest that if you don't already have one put in a heavy duty switch between the motor leads and the ESC to isolate the system. this could prevent an accident while carrying the bird out to the flight line. Your system with 38 volts will almost run my Ghia. Do you really need that much juice? You never stated whether the system worked in spite of the fireworks. Norm

That is one of the reasons that I am flying all electric. I carry my plane to the flight line ready to go and when it is my turn I simply place both the receiver and motor switches in "ON" and take off.

tahustvedt

A spark is normal, especially on high voltage systems. The reason for the spark is that the input capacitors on the UBEC and ESC are (empty) and cause a short burst of current as they charge up. This current isn't very high but the higher the voltage the bigger the spark.

There are ways to eliminate the spark but it's not cause for concern. I once made a jumper system where the current first went through a resistor when the battery was connected and this caused the capacitors to charge more slowly because the resistor lowered the voltage. There would be no spark. After a few seconds I would install a high current jumper in parallell to the resistor for flying.

jkurkjian

It looks like "nerves" was the answer. Because of the sparks, caution (ok, nerves) caused me to not find out if the system worked (i.e. I never completed the electrical connection).

The spark being caused by the input capacitor makes sense since caps initially act as "shorts" when fully discharged and "opens" when fully charged. Thanks tahustvedt!

System works fine now.

Thanks all,
John

normgoyer

John, hope you have many years of flying fun with your electrics. Son Robert, Senior Editor of Flying Magazine, lives in Austin and loves the area. He previously lived in Greenwich, CT when the magazine was located there. He has a Cherokee Six and Cirrus SR-22 at your airport. Norm

algutkin

My Feedback: (1)

John:

Remeber to disconnect the lipos when not in use. Lipos will continue to discharge if left connected. Like I said in a previous post, the circuit is complete when the Deans connection is made and there will alway be a slight current drain. That is what generates the spark. Spark is always generated when there is a bad connection and the electricity attemps to complete the circuit by jumping over the bad connection. When you attempt to plug in a Deans connector, you have a bad connection until it is plugged in all the way. It should be noted that the current drain is still there even if the capictor is fully charged or discharged. If the lipos are allowed to discharge below a certain level, they are ruined.

Experience teaches us many lessons, if you have a bad connection with any household appliance, the plug will get hot, melt the plastic and eventually short out and blow the fuse, that is if it doesn't burn down the house first. With RC, if you hold the Deans connectors apart, and the current attempts to jump the connection, your Deans connector will get hot, and the copper terminals inside will turn black. Deans connectora are all about making a good connection to avoid the sparking and burning of wires when there is a bad connection.

I had to respond, because the capacitor explanation does not apply to all connetions, and all connections will spark if the connection is not solid.

Al G.