General ESC Theory Discussion

[Serum]

it was matthias schulze who told me they used the battery trick for braking.

[suicideneil]

I think my brain just exploded..... please, continue- this is extremely interesting stuff.

[DrKnow65]

I love being corrected, that means I'm a little bit smarter now :)

[GriffinRU]

Brian great thread!
I suggest to check this pdf before we start with Q on smoke, brakes, fets, caps, regeneration etc.

[BrianG]

Nice PDF there! I just skimmed over it a little and it seems to have some REALLY good info! Thanks for that link!

I have something interesting to report!

I finally got my DPR back and put it on my BL X1CR to check what kind of numbers it pushes. I downloaded the data off it now and have been scratching my head trying to figure out why its current readings are so whacked.

The current graph starts at 0 when everything is powered up. But after that the graph shoots abnormally high! I'm getting readings of over 90A on a 10S buggy! Then I noticed where the graph settled when the car was stationary (had a few flips). Even though very little current was flowing at that moment, the graph reflects about 26A. Here's the most interesting bit!

I also noticed short spikes below 26A. The largest of those spikes that reached 0A reflects the battery pack being at 42V at the same time. Here's my take on it:

The DPR resets its zero point if the direction of current flow reverses. So when I connected everything up it's 0A point was true zero (ignoring radio load). The moment I braked for the first time, current flowed in the opposite direction back to the battery! The magnitude of the reverse current set a new zero point, and the old zero point effectively becomes a positive value on the graph.

I'll post the graphs shortly. But I feel pretty confident to say that a Kontronik Jazz ESC does recharge the pack under a braking condition! What's more is it seems like it caps the max voltage according to the lipo cell count (it is programmed in lipo mode). What's scary is that this means that my packs had to endure 26A spikes of charge current! Well, I'm not sure what the implications of that are, but they're not overheating or puffing, so I guess time will tell. :)

I would post the graphs here, but unfortunately this forum is graphically challenged. Check them out on my RCG Blog. ;)

[johnrobholmes]

I have had a lot of troubles with my dpr logger that the tech guys had no clue how to solve. Transient amperage spikes, voltage abnormalities, and data loss are really common. I am going to get an eagle tree for my next logger. They have a version with 40hz sampling.

[MetalMan]

Time for mechanical brakes?

[BrianG]

With the discussion of high ESC ripple current and the effect of using lipos that aren't quite up to the task, I was thinking of ways to help with this. What about using an inductor in series with the + battery line?

Yes, the wires would have to be quite large (probably litz wound), would weigh a few ounces, and there may be slight v-drop. But, an inductor is essentially a current storage device (via the magnetic flux), much like a capacitor is a voltage storage device. And an inductor opposes a change in current flow. So, the inductor will ramp-up/down current flow during high/low changes in current. Wouldn't thins help to reduce ripple current and voltage spikes getting to the battery? And since the ESC is constantly providing somewhat of a load (even when not driving a motor), inductor kickback should be minimal. Thoughts?

[GriffinRU]

Originally Posted by BrianG

With the discussion of high ESC ripple current and the effect of using lipos that aren't quite up to the task, I was thinking of ways to help with this. What about using an inductor in series with the + battery line?

Yes, the wires would have to be quite large (probably litz wound), would weigh a few ounces, and there may be slight v-drop. But, an inductor is essentially a current storage device (via the magnetic flux), much like a capacitor is a voltage storage device. And an inductor opposes a change in current flow. So, the inductor will ramp-up/down current flow during high/low changes in current. Wouldn't thins help to reduce ripple current and voltage spikes getting to the battery? And since the ESC is constantly providing somewhat of a load (even when not driving a motor), inductor kickback should be minimal. Thoughts?

No, No, No...

Only capacitors, and just a good bank of ultarcaps will convert low current LiPo into short-term (need to define voltage drop and timeframe, formulas available) high current killer power pack.

Inductor can be in motor leads, but not in power. Ripple current covered by capacitors, voltage drop can be covered by ultracaps and zeners (in one half).

[tom255]

Is it possible to buy Ultracaps somewhere? How expensive they are?

[zeropointbug]

Originally Posted by tom255

Is it possible to buy Ultracaps somewhere? How expensive they are?

Maxwell Technologies has some RC size ultra caps that would work wonderful for high powered BL setups. They are C size cells, 2.5v/120Farads IIRC.

I will get link in next post...

[lutach]

Yes, www.maxwell.com, www.enerland.com and www.maxfarad.com. The ones I'll be gatting are he size of a button cell just a bit bigger then the ones found in digital watches.

[lutach]

Originally Posted by GriffinRU

No, No, No...

Only capacitors, and just a good bank of ultarcaps will convert low current LiPo into short-term (need to define voltage drop and timeframe, formulas available) high current killer power pack.

Inductor can be in motor leads, but not in power. Ripple current covered by capacitors, voltage drop can be covered by ultracaps and zeners (in one half).

Artur,

I'm going to get the caps I told you about. I have to try it out and see where they stand.