by Gary Thompson
After nursing a couple of questionable Ni-starters along, I wanted a way to keep my ni-starter ready to go. I talked the idea over with Lloyd Standley a couple of years ago, and we came up with the theory to use the 12vdc battery, in your flight box as a source for maintaining the capacity in your Ni-starter battery using an extremely simple circuit. The idea is to be able to use the time that you are not using your ni-starter to replace the capacity that you just used. This project can be completed in an afternoon.
There are many ways to do this: the best
probably would be to design
a fast charger that peak charges your ni-starter battery at all times,
maintaining it in peak condition. But for my purposes this is over-kill.
There are a number of variables e.g. ni-starter battery capacity, daily
usage, time at the flying field, 12vdc battery capacity. Compromising on
all of these, I came up with a 1 watt device that would fully charge a
flat ni-starter battery in 14 - 16 hours, or would approximately replace
the capacity that I normally use in a flying session -- about 5 or 6 starts.
The design below charges at the rate of 83 ma and works well with a standard
1200 mah ni-starter battery. It should have little effect on a 6 amp or
larger capacity 12vdc gel cell type starter battery during any flying session.
Here's what the HotSpot looks like:
Some pine wood (1x2 works well)
1/8" ply wood (1" x 1 5/16")
1 6/32 nut
1" nyrod and threaded rod
5/16" length of 1/4" dowel
2 male spade lugs (Radio Shack PN 64-3038)
2 female spade connectors (Radio Shack PN 64-3039)
2 330 ohm resistors, 1/2 watt (Radio Shack PN 271-1113)
1 12V red LED (Radio Shack PN 276-209)
Most people will only need to purchase the last two parts at a cost of $1.48 total.
The HotSpot uses two 330 ohm 1/2 watt resistors in parallel to limit the current used to re-charge the ni-starter. Along with an LED in parallel to show when current is flowing, gives a charge current of 83 ma -- about what you would use to charge overnight. Here's the circuit:
Make the ni-starter connector first. A 6-32 nut just fits. The stem is a 2-56 threaded rod threaded into a nyrod inner piece. The nyrod and threaded rod just fit perfectly into the 6-32 nut. Cut a piece of 1/4" dowel to 5/16 inch and center drill it for the nyrod/threaded rod. Allow 5/16 of the threaded rod to extend above the 6-32 nut and 3/8 below to extend into the dowel piece. Solder wires to the nut and the dowel end of the threaded rod Trim the dowel to act as a base for the ni-starter connector and epoxy together. Make sure the nut is epoxied to the dowel. (Note: Boyd Hjalmarson made his connector out of an old glow plug. Pull out the center post in a vice. Drill out to accept a tight fit 12 AWG wire - house wiring. Screw fit the plug into the lower body).
The body takes three pieces of wood. 1" x 1 5/16" backing piece can be made from 1/8" ply. The upper support is 1" square x 11/16" thick. Drill the center to 1/2" diameter to support the ni-starter barrel. The lower support will house the ni-starter connector assembly and is 1" square by 1/2" thick. Drill the center to 1/4" to accept the dowel base of the ni-starter connector.
The 1/4" hole will have to be enlarged along one side to take the negative wire connected to the 6/32 nut. Epoxy the two supports to the backing piece. After the epoxy has set, drill the corner of the upper support to accept the LED. Drill through with a drill that fits the lens, then counter drill about 1/8" deep to accept the lens base, which is slightly larger in diameter. This allows the LED base to sit down about 1/8" below the surface. Fit the ni-starter connector into the 1/4" hole and allow the 6/32 nut to sit 1/16" above the lower support. This allows clearance for ni-starters to grip under the nut. Epoxy the dowel in place. Drill two small holes for wood screws to secure the spade connectors at the bottom of the lower support. (see drawing).
Attach a 3 inch lead to each side of the LED and shrink wrap each leg. Keep track of the anode (+) leg, since this will eventually be connected to to the positive terminal from the battery. Flatten the spade lug connectors so you can screw them to the bottom of the lower support. Strip this anode leg of the LED and screw this to the positive terminal on the spade lug. Strip the lead from the 6/32 nut and screw under the negative terminal spade lug. Twist the two resistors together, solder and leave one leg on each. Place the resistors to the bottom of the lower support and solder one leg to the positive terminal spade lug and the other lead to the remaining LED wire. Secure the whole mess with a dab of goop to the bottom of the lower support.
Use wood screws to mount through the upper and lower supports to your flight box. I mounted mine on the inside of the box, so just came through the side of the box with 1 screw in each of the opposite corners of the upper and lower support blocks. Now wire a harness from your 12VDC supply (power panel) to the positive and negative lugs on the HotSpot and then set your ni-starter in the holder - the LED lights up telling you that it's being charged!
You may have to charge your 12VDC battery slightly more often, but it's worth it.