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MRC Super Brain 959

Super Brain Surgery

I recently purchased a pair of Super Brain 959 chargers. For the most part, I've been impressed with the chargers' performance, features and price. But, like most people, I'm baffled by the design's lack of effective cooling. After several consecutive charges, the charger case becomes too hot to touch and the display screen begins to malfunction. Many people simply setup a portable fan to cool the chargers. I decided to install a permanent cooling fan. For each charger I used one Micro Fan (Radio Shack 273-240, $11.99) and one 100 ohm, 1 watt resistor.

WARNING, the following modifications will void your warranty. I quote from the Super Brain manual, "MRC will not accept any charger for repair that has been modified in any way". Proceed at your own risk.

First I had to make a modified screwdriver because the chargers are assembled with "tamper proof" screws. I simply used a cutoff disk in a Dremel to cut a slot in the blade of the screwdriver.

I dissembled the charger into three pieces: 1) the top of the enclosure including the display circuit board, 2) the power transformer and power supply circuit board, and 3) the bottom of the enclosure.

The first modification was to cut the 12dc power cord from the circuit board and remove the cord. This, of course, has nothing to do with cooling, but I don't intend to use the dc input so it's more convenient to have one less cord dangling from the charger. If I change my mind, the cord will be easy enough to solder back on later.

There's no room for a fan on the inside of the charger, so I mounted it to the top of the top half of the enclosure. The directional arrow on the side of the fan should point up. That is, the fan will be drawing warm air from inside the charger and blowing it upward. Strangely, the fan blades are flush with the bottom of the fan frame. Accordingly, if I simply attached the fan to the enclosure, the fan blades would contact the surface of the enclosure and the fan would be unable to turn. Mounting the fan turned out to be the most difficult aspect of the project. Using a compass, I traced a circle onto the top of the enclosure equal to the diameter of the fan. Then I used my Dremel to carefully cut and grind away the top layer of vent louvers. I took my time with the Dremel and then cleaned up my cuts with a sharp hobby knife. Removing the top layer of louvers allowed the fan to spin freely and also opened up the vent for better airflow. I left the bottom layer of louvers intact for structural integrity.

Next I routed the fan wire into the enclosure and secured the fan to the enclosure with four zip-ties. I didn't use screws and nuts here because of the tight clearance between the enclosure and the power transformer. The zip-ties work just fine.

I connected the fan to the output of the bridge rectifier as shown. The voltage here is a filtered dc voltage of about 20 volts. That's a bit high for the fan so I inserted a series 100 ohm, 1 watt resistor. With the resistor, the fan voltage is about 12 volts. I simply soldered my connections to the diode leads as shown then I covered the resistor with a blue piece of shrink tube. Specifically, viewing the circuit board with the heat sink to the left and the power transformer to the right, the black fan wire is soldered to the left lead of the closest diode, the resistor is soldered to the left lead of the second closest diode and the red fan wire is soldered to the other end of the resistor. Be sure to observe proper polarity here. If you follow the circuit board traces, you'll see that the fan is connected in parallel with the big capacitor and that the polarity of the fan matches the polarity of the capacitor.

Next I set to work on the bottom half of the enclosure. I wanted to improve airflow around the bottom of the power transformer. I drilled two holes through the bottom of the power transformer tray and I used the Dremel again to grind four slots into the sides of the power transformer tray. Now the transformer has free air circulation around all four sides.

I also removed two pieces of foam tape from the top of the power transformer. The power transformer will be held firmly in place by the thickness of the zip-ties and will have better airflow.

Finally, I reassembled the charger and tested everything.

Before my modifications the chargers got too hot to touch and the display would begin to malfunction after two or three charges. With the fan modification the chargers get warm, but never hot and the display always works well. I've used these chargers for hours at a time with no problems. My torture test was to consecutively charge ten packs at 4.5 amps. Again, no problem. Note that the fan will run so long as the charger is plugged in. However, the charger should not be left plugged in while not in use. The fans will also work if you decide to use the dc power input. Notice that the two fans I ended up with are of different designs even though they have the same stock number. The fan with the smaller center would not require the louver modifications I described above. However, I would still recommend removing the top layer of louvers to promote better airflow. If you have the choice, I'd also recommend buying the fan with the smaller center because it has more blade area and seems to move more air. I've already purchased an additional "small center" fan that I may use to replace the "large center" one.

Disclaimer… I am an electronics amateur. I designed this circuit by way of tinkering and trial and error. There is no CAD system. There is no laboratory. There are no research assistants. There is no UL approval. I'll not be responsible for you blowing up your charger, burning down your house, electrocuting yourself or any other havoc you may cause in your attempts to duplicate this project. Hope someone out there finds this useful.

Super Brain Surgery Update

It's been more than a year since I purchased my first pair of MRC Super Brain 959 chargers and added my cooling fan modification. I've been happy with their performance so I recently purchased a second pair of Super Brain 959 chargers and set about modifying them with cooling fans as I did with the first pair. I mostly followed the same procedure as before, but with a few differences. Note that the newer Super Brains appear to use standard phillips head screws, so you won't need to make a modified screwdriver as before.

The first difference is I decided to use a 1.5 inch hole saw to cut away the upper layer of louvers where the fan will be mounted. I found that the pilot bit in the center of the hole saw was too awkward to control around the delicate louvers. So I started out with many smaller drill bits and slowly worked my way up to the size of the pilot bit. There are seven rows of louvers. I found the center of the fourth louver and that's where I started drilling. Cut carefully and check your work often. Remember, you only want to cut through the top layer of louvers. After the cut has been made, use a small pair of wire cutters to cut away the top layer of louvers inside the circle. Finally, I cleaned up all my cuts with a sharp hobby knife. The pic below shows the charger after I used the hole saw, but before I took the wire cutters to it.

In retrospect, the Dremal/grinding procedure that I used on the first pair of chargers was more time consuming and far more messy. However, the hole saw method I used on the new pair of chargers was far less forgiving. It's very easy to break the louvers if the pilot bit or the saw gets hung up. If you have access to the precision of a drill press, I think the hole saw would be the superior method.

After the upper enclosure was prepared, I installed the fans and wired them as before.

Depending on the age of your Super Brain 959, the charger may or may not have a heat sensitive protection component on the lower circuit board. My previous two Super Brain's did not have this component. The new ones did. The first pic below shows the lower circuit board from one of my new chargers. The heat sensitive component is the thin orange component located between the big copper coil and the big capacitor. The second pic below shows the lower circuit board from one of my old chargers. The old chargers did not include the heat sensitive component. Others on the Internet have claimed that this component is too sensitive and that it should be removed. According to my own experiments, I agree.

Before I began modifying my chargers, I tested them right from the box. I plugged them into an AC power source, set their outputs at the maximum 4.5 amps and began charging a pair of 6-cell 2400 stick packs. Starting from room temperature, I was only able to get about six to eight minutes of charge time before the chargers overheated and shutdown. This shutdown manifests itself as an apparent false peak. Six to eight minutes, of course, is not enough time to charge even one stick pack. I dissembled one of the chargers and found that so long as I kept the heat sensing component cool, I could consecutively charge as many packs as I wanted without incident. So let's get rid of it. Using a soldering iron, I removed the heat sensing component and replaced it with a jumper wire. This jumper wire with carry the full current to the batteries, so don't skimp on the gauge of the jumper. I drilled out the PC board holes a bit so I could use a heavier jumper.

The pic below shows the circuit board again with the jumper in place of the heat sensing component. Of course there's now nothing to shut down the charger if it gets too hot, but that's what the fan mod will prevent from the get go. The pic shows the fan wiring connections to the diodes on the right as before. Before I closed up the enclosure, I bundled up the fan wires with a zip tie. Also notice that I drilled a hole in the upper right corner of the enclosure and rerouted the DC input cord out the back. Then I rerouted the battery output cord out the left side where the DC input cord was previously. More on this in a moment.

The final pic shows all four of my Super Brain chargers. The old chargers are at the bottom and the new chargers are at the top. The upper right charger is finished except for the actual installation of the fan. The chargers on the left have had their battery output cords rerouted to the left. I did this simply so the chargers could sit side-by-side more compactly. Recall that I simply eliminated the DC input cords on the old chargers. I decided to keep the DC input cords on the new chargers, but I rerouted the cords out the back of the charges, reduced their length to about three inches and replaced the alligator clips with male Deans plugs. My new DC input cord consists of a cigarette lighter plug on one end and a pair of parallel female Deans plugs on the other end. The cigarette lighter plug is Radio Shack stock number 270-1590. The plug has a built in ten amp fuse that appears to be sufficient. Be sure the plug in your car is also sufficient.

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Page Updated 8/5/03