General ESC Theory Discussion - Page 3 - RC-Monster Forums

10.27.2007, 06:40 PM

That's great. Are you able to see the direction of current flow in the graph? The DPR records in both directions, so that spike could be current drawn from the battery or current drawn by the battery...

Quote:

Originally Posted by lutach

I just did a little test just to see how it went. I ran my DPR in live mode and hooked it up to my MBX5T that is now equiped with a Schulze 18.97 and a 7XL motor. I gave it some throttle and let it go so it would freewheel and the graph stayed flat. I then gave it some throttle and hit the brakes and saw a little spike on the graph. Just to make sure I hooked the DPR to my BPP truck that has a Schulze 40.160 and Neu 1521/1Y. Gave it some throttle and let it freewheel and the graph stayed flat. Then I gave it some throttle and hit the brakes, same thing happened a little spike on the graph.

lutach · 10.27.2007, 07:03 PM

Quote:

Originally Posted by Aragon

That's great. Are you able to see the direction of current flow in the graph? The DPR records in both directions, so that spike could be current drawn from the battery or current drawn by the battery...

The spike was upwards so it actually went to the battery.

10.27.2007, 07:39 PM

Quote:

Originally Posted by lutach

The spike was upwards so it actually went to the battery.

Excellent! Do you plan to test it in driving? Braking at varying levels downhill would be interesting to see.

How much does the voltage spike?

suicideneil · 10.27.2007, 08:17 PM

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

lutach · 10.27.2007, 09:31 PM

Quote:

Originally Posted by Aragon

Excellent! Do you plan to test it in driving? Braking at varying levels downhill would be interesting to see.

How much does the voltage spike?

Today I actually got everything back together. The rear diff on the BPP let go and I had an issue with my Aveox in the MBX5T. So I will get some data on Monday if the weather is good. I didn't notice what + volts the spikes were. I just noticed they were there. I'm going to look in my previous data to see if it is there and I'll "prt sc" on a close up.

zeropointbug · 10.27.2007, 11:07 PM

So, you are seeing what I saw then, as far as a voltage spike to the battery? I saw, IIRC, about 0.25 - 0.5 volts spike, so even a little potential over the battery packs voltage will result in decent current levels going into the pack.

DrKnow65 · 10.27.2007, 11:16 PM

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

lutach · 10.27.2007, 11:45 PM

Quote:

Originally Posted by zeropointbug

So, you are seeing what I saw then, as far as a voltage spike to the battery? I saw, IIRC, about 0.25 - 0.5 volts spike, so even a little potential over the battery packs voltage will result in decent current levels going into the pack.

I will have to agree. The spikes seems like 0.25-0.5. I also noticed a sound coming from the ESC (Schulze 18.97). I listened closely to figure out where it was coming from and it was from the capacitors. It sounded almost like when you take a picture and the capacitor inside the camera recharges after the flash, but it was more like a blow-off valve. I have to see if the same spikes appers with the MM. If so, I think setting a little drag brake might throw some charge back into the pack.

GriffinRU · 11.03.2007, 01:24 AM

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

BrianG · 11.03.2007, 03:06 AM

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

12.12.2007, 12:03 PM

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. :)

12.12.2007, 12:24 PM

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

johnrobholmes · 12.12.2007, 01:35 PM

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 · 12.12.2007, 02:46 PM

Time for mechanical brakes?

BrianG · 05.15.2008, 02:34 PM

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?