I just want to say thanks for doing all these tests You seem to be consitently a step ahead of me, which means I get to sit back and wait for your results
Yes I am also seeing this problem with an unmodified 206 controller at 50v when running my Astro.
It only happens in the delta mode where the motor draws significantly more current than when it is in wye.
The cutting out problem can not be cured by adjusting the timing, but I can make it worse!
I have no problems with an EB218 (18 FET) controller on the same setup.
I have tried programming various combinations of phase and battery current limits, seems to make no difference.
Jeremy Harris wrote:gwhy,
The test for this would be to deliberately programme a low phase current ratio and then see whether or not the problem is worse (apologies if you've already tried this). If changing the phase current doesn't make a difference then it's likely to be something else, like a momentary voltage drop under high peak current demand conditions causing the controller to glitch, as has already been mentioned. It might be worth lowering the LVC to as low a voltage as possible, in case voltage drops are the problem (again, apologies if you've already tried this).
matt_in_mtl wrote:OK, well that was fast...
I just went ahead with my shunt mod.. and the results aren't good.
I started by measuring the voltage drop across the stock shunt at a constant measured current. I repeated this for a few currents from 1A to 3.7A (I couldn't go higher without figuring some way to load the motor on the bench). I measured between 5mV and 16.2mV across the shunt which comes out to approx 4.5mohm. I think I saw the value on the forum before, but don't remember if this is what it was. I then soldered in some about a 1-inch long piece of solid copper wire in parallel. I did another test, and arrived at 0.6mV at 2A which gives me 0.3 mohm! It is possible that this is too low, but the controller worked OK. Unfortunately it did not work as well as it had before my mod. I can reach full throttle if I am gentle. Once revved up it is generally OK, however if I crack the throttle open the motor will blip and die. This suggests to me that we may not be looking at a firmware issue I am finding my results a little bit strange considering that it seemed like others have been able to get much higher power from these 6-fet controllers.
ZapPat wrote: After soldering up the shunt, did you reduce the programmed current limits in the controller by the same factor as the shunt was changed - so about 10X lower?
Have the controller's caps been upgraded to handle the extra current ripple?
matt_in_mtl wrote:My thought was to try to see if I could 'trick' the controller into allowing higher current. If I had lowered the current by 10X then I would have been the same ~30A true phase current as pre-mod.
gwhy! wrote:I dont know how good this diagram is, But there seems to be some difference between the R45 value ( with a meter )on the 12fet board and the 6fet board , its all in the right ball park ( I need to sort out better light and get something to magnify everything up as my eyes are getting very old and are not what they used to be before I try anything with power going thought it ).
ZapPat wrote:OK, maybe don't cut it down by 13X as your shunt did changed, but at least reduce the previous limits by at least 4X or 5X or else your shunt mod won't help you from hiting the same overcurrent cutoff as before. You want the controller's programmed limits to be hit *before* the brutal overcurrent cutoff current is hit, so if you leave the limits programmed the same as before the shunt mod it wouldn't help.
Jeremy Harris wrote:Of more interest is the transistor, QF1. This is a switch, that will take pin 27 of the 116 low if the voltage across the shunt exceeds about 0.6 - 0.7V. This limit can't be programmed, as it's wholly dependent on the shunt value. I'm guessing that this is a backstop "emergency" current limit, that kicks in to kill the controller in the event of a current overload. It seems likely that this "might" be the cause of the cutting out problem, but the way to prove it would be to put a 'scope on pin 27 and see what happens.
matt_in_mtl wrote: If the cutoff is firmware based, then my 10X reduction in shunt resistance would raise the cutoff to over 300A. I don't see any way that my motor could be pulling over 300A at 50V sitting unloaded on the bench?
Not if your software is letting it go 10X+ higher than before...matt_in_mtl wrote:So, wouldn't this mean that the cutting out would quit also if we decreased the voltage across the shunt by lowering the resistance?
Jeremy Harris wrote:I think we might be getting somewhere with this observation. I'd not bothered to look at the current limit circuits (plural!) before, but can now see some areas to look at closer.
Firstly, there is a current measurement capability there, as the voltage across the shunt is being fed to an analogue to digital converter in the controller, that will give the controller the average current being drawn from the supply.
Of more interest is the transistor, QF1. This is a switch, that will take pin 27 of the 116 low if the voltage across the shunt exceeds about 0.6 - 0.7V. This limit can't be programmed, as it's wholly dependent on the shunt value. I'm guessing that this is a backstop "emergency" current limit, that kicks in to kill the controller in the event of a current overload. It seems likely that this "might" be the cause of the cutting out problem, but the way to prove it would be to put a 'scope on pin 27 and see what happens.
*edited to add:*
I can see a fix, if what I think is happening can be proven. The capacitor and resistor, C20/R43, control the rise time of the voltage to QF1 base. This means that increasing either will slow down the rate of rise of voltage, which would then smooth out rapid high current peaks. This may well get rid of the cutting out problem.
ZapPat wrote:gwhy! wrote:I dont know how good this diagram is, But there seems to be some difference between the R45 value ( with a meter )on the 12fet board and the 6fet board , its all in the right ball park ( I need to sort out better light and get something to magnify everything up as my eyes are getting very old and are not what they used to be before I try anything with power going thought it ).
R45 on both my 212 and 206 is the same, as well as all the other parts around that current-sense conditioning area of the controllers.
Does anyone know what function the transistor QF1 (close to the 5V regulator) do? It looks to be hooked up to the resistors and caps used for the current sense circuitry... although even this looks the same on both boards.
gwhy! wrote:Hi Jeremy,
They may well be the same value but there seems to be a difference in how quick the cap c21 charges up between the 6fet and 12 fet with the meter. I know there are a lot of things can effect this, and the only real way to see what this part of the circuit is doing is with a scope.
Jeremy Harris wrote:Matt,
Looking at the circuit I'm near-certain that the brutal cut off is the QF1 switch, not anything in the programming.
The fix may be something as simple as increasing the value of C20 by enough to slug down the big spikes, or adding a resistor across it to divide down the voltage.
Here's an experiment to test this idea. Fit a 1k resistor in parallel with C20. This should double the "emergency current limit" point. Should be easy enough to test.