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Old 04-11-2006, 07:03 AM   #1
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Default GTB Capacitor network

I had the bright idea of checking how much my diffs were slipping by holding the car down on the ground and applying some throttle. When I did this the 5600mf cap, blew a lead going to the little board. I couldn't just leave well enough alone and tried to solder the lead back on. For some reason my solder would not stick the 2 leads together. I figured, 'fawk it' I'll run it like this and see what happens.... Noticed a definate power loss off line, no big deal. Now, let's just run this puppy down the road and check out the top end. As I drove it back to me to check it out one of the transient votlage suppressors went POOF and caught the shrink wrap on fire. Took it into work this morning and repaired the 5600 cap, soldered back on one of the capacitors, removed the rest of the blown TVS and am wondering:

#1 if I can run it with one less TVS until I get a new one.

#2 How much current runs though this capacitor network? It appears that the lead size on the cap is to small to handle large amounts of current. The failure may not have been due to current. The way the cap is soldered to the board leaves something to be desired. It was not glued to the board, but only shrink wrapped to it. Maybe the jarring of the cap during running caused stress on the leads, making them weak. Then when the cap discharged at a high rate it blew open the lead. If this were to happen to someone else it could be more detrimental. Once the main cap blows the current passes though the 2 TVS's and the 3 other small caps. Then... what happens if one of the caps short out?!? Then it would short out the supply voltage until either the board frys or the batterys blow up.

#3 If holding the car down so that the wheels don't turn, then applying power, will this always cause a problem? What if you are racing and the driveline becomes locked up. You naturally apply more power to make it move and POOF. Shouldn't this capacitor network be fused to avoid such disasters?

Does anyone have any part numbers for this CB?

Would increasing the cap capacity help in more torque down low. I can see what it's doing to the brushless system to increase 'punch'. More capacitance should make the punch last longer, no?
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Old 04-11-2006, 04:43 PM   #2
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The GTB has a locked rotor sensor so the GTB should have shut down rather than have blown something.
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Old 04-12-2006, 05:45 AM   #3
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Interesting. I had done this more than once and it worked just as you described. I just thought the motor was stalling due to the force put on the tires. Makes sense. I think I had to let up on the chassis slightly then push down. I have contacted Charlie at Novak and he basically told me the cap was the weak link in the system used to blow, saving the ESC. What doesn't jive with me is the fact that blame is being put on a oversized pinion. I don't think this is the case as I have ran this car full out with no thermal issues. Besides that, I don't race it. I just play in the yard and street. I don't feel that these types of problems should be evident. I repaired the capacitor network yesterday and the esc is working fine. The cap was flopping around as I had it velcroed to the rear bulkhead. It comes loose once in awile and bounces around. Maybe it shocked the leads enough to make them weak... OR.... me tricking the motor into running with slight movement made an overcurrent situation... this makes more sense than anything. If the protection is there to stop the motor from output in a locked rotor situation then I sort of bypassed it momentairally and put the unit into a overcurrent situation.

In any event, be carefull when doing something that I did!
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