Ways to protect MMM when used with subpar batts

[himalaya]

Originally Posted by Bondonutz

why do they use 12G with some of the Flightmax 4s 30C packs I bought and one of my buddys who has 3s Turnigy packs have 8G wire.
WTF is up with that ?

Wire gauge in LiPo packs usually reflex the current level. for Turnigy, say a 5Ah pack, I found they use 10AWG on 20C but 8AWG on 30C models, 'cause their supposed current handling capability differs, 100A vs 150A.

Back to the topic I agree with BrianG, ADD EXTRA CAPACITORS.

MMM 's power smoothing capacitor totals only 990uF, electrolytic type. Yes they are high quality Rubycon ZLH type for switching power supplies but still electrolytic. In such a 100A+ switching/pulse application, 990uF electrolytic is far from adequate.

According to Rubycon datasheet, the ZLH35V330uF handles ripple current of 1.33A, three on board totals 4A, only. And the reality is ESCs are all switching type, currents are all in pulse form. This may not be a huge problem in RC cars for its not fully loaded continously. A high quality battery with extremely low source resistance will help A LOT smoothing out the ripple current, making the voltage relatively constant.

When subpar packs are used, because they have higher IR, extra capacitors are highly recommended, 4700uF or greater. Make sure they are high quality type designed for switching power supplies. They will iron out most voltage ripples to help the on board caps survive as well as the whole ESC.

This thread has been very informative, and I'm glad it turned into a healthy discussion.

Update - I borrowed a 4s pack to try and found that the car was just too fast for the indoor track with it. So, I picked up a 3s Zippy (25C 5000) for <$50 and it seems to work quite well. I figure the lower voltage will reduce the amp draw, voltage stress, ripple, etc., and be safe to use. (?) I've kept the gearing and ESC settings the same so far, and I get about 25 mins. runtime until 3.5V/cell LVC kicks in. The motor and ESC come off just warm, and the pack a step above stone cold. I am slower on the straight than the 4s guys, but not by that much, and from the looks of it, I should even be able to go up some on the pinion for a bit more speed. Other than that, the tame setup and budget battery seem to be fine together. Do I still need to add more capacitors?