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    I discovered a problem with the way we install the solenoids for our guns. During the 92 Nats Paul (Doc) Broring's ship developed what, at first, appeared to be "Radio Death". He bought another radio to replace the "dead" one only to have it also "fry". He though that he had something really shorted or crossed in his wiring. After looking at the ship we determined that the radios were OK but that all the servos had bitten the dust.

    While diagnosing the problem I discovered that every time the gun solenoids fired a fairly large spike was sent into the main power lines. As his radio was run off of the motor batteries this was bad news for the electronics.

    I have been running my radio and solenoids together for two years with no problems, but I have my radio more isolated than Doc's was, and have also been lucky, I guess. There is a simple solution to this problem.

    First a description of the problem. When any electo-magnetic device is powered on it generates a magnetic field. When the power is cut the field collapse (dies). This collapse generates a voltage spike, of the opposite polarity to the power input, that can get back into the wiring or blow out the electronic switch if one is used. This spike in the lines is what probably blew out Doc's servos.

    There are two simple ways to solve this problem.

    The first is to run the radio off of a receiver battery. This will work only if the radio is otherwise totally isolated from motor power. The rest of the ship would have to be "controlled" through mechanical switches run by the servo arms. Any other electronics would have to also be isolated from motor power. This will work but is not the best or even the easiest solution.

    The second and standard method is to hook a diode directly across the solenoid leads. The diode is installed "backwards" (the diode negative lead on the solenoid positive lead, the diode positive on the solenoid negative lead), thus it looks like an open connection to the power wires (see Figure 1). When the power is cut the diode shorts out the negative spike, preventing it from getting into the wiring.

    The diode should have a current rating of 10 times that of the electro-magnetic source. For our 6 volt solenoids (about .5 to .6 amp draw) this comes out to a 5 amp diode. The highest rating that RADIO SHACK carries is 3 amp. This is low but may work for those who can not get their parts anywhere else.

    The hook up of servo driven switches is shown in Figure 1. The main power transistor (Q1) is a RADIO SHACK TIP120 catalog #276-2068 $1.29. I connect the transistor to the solenoid leads close to the solenoid and dip it in DIP IT (the stuff they coat tool handles with). The signal wire of the transistor is then run to the "switch" in the radio box.

    I recommend this method for several reasons. The first is that this means less heavy power wiring has to be run in and out of the radio box. Also along with this goes the advantage that the noise from turning the solenoid on and off is that much further isolated by distance from your receiver. Another reason is that if something should short or burn the most of the time the damage will be outside the radio box. The last reason is that smaller mechanical switches can be used. I mount the transistor (and now the diode also) on a small piece of circuit board, connect the solenoid and signal wire, and dip the electronics several times until well coated. Be sure to separate the wires so that the DIP IT seals around them. You do not have to run a ground back to the switch if the radio shares the ground with the rest of the ship.

    For mechanical switches one 47K resistor is needed for all the switches. One switch can fire several solenoids for multiple gun setups

    I run my radio off of the motor batteries and have always used the following circuit (Figure 2) to isolate it from the motor noise. The electrolytic capacitor (the one with the + & -) is a RADIO SHACK 470 uf 35 volt cat# 272-1030. The other capacitor is the same type as we use on our motors (.047uf). The diode is a RADIO SHACK 3 amp cat# 276-1141. The larger capacitor smoothes out any dips in the voltage when the motors are first started and the smaller (motor type) capacitor filters out the higher frequency noise. The diode protects the radio from reversed battery hookup. The diode also drops the voltage from the battery (6.5 volt) a little closer to the regular operating range of the radio (6 to 4.8v).

    In addition I use ACE NOISE TRAPS on any servos outside the main radio box (generally the rudder servo) on smaller ships. On larger ships (more room) I put them on all the servos. This does not protect from voltage spikes but does help isolate the receiver from outside noise and radio interference.

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