DC Battery amps vs. Motor Amps

General topics and discussions about the VESC and its development.
maxkinz
Posts: 29
Joined: 30 Jun 2017, 14:41

Re: DC Battery amps vs. Motor Amps

Postby maxkinz » 06 Jul 2017, 11:46

Just to clarify - the FLUKE is inline with the Motor not the input. Before messing up it would read a value very close to the set current.

rew
Posts: 905
Joined: 25 Mar 2016, 12:29
Location: Delft, Netherlands.

Re: DC Battery amps vs. Motor Amps

Postby rew » 06 Jul 2017, 12:28

maxkinz wrote:Also the FLUKE was definately not damaged as it was also not involved - worked before switched polarity - does not work anymore ...
I don't understand FLUKE wasn not damaged ... does not work anymore.

maxkinz
Posts: 29
Joined: 30 Jun 2017, 14:41

Re: DC Battery amps vs. Motor Amps

Postby maxkinz » 06 Jul 2017, 13:11

Sorry for the confusing description. What I meant to say is that the FLUKE is definately not damaged and working as it is supposed to. Before my accident when i told the VESC to push 3.5A with the FLUKE inline with the Motor it would read something like 3.534A - in the range of what one would expect so almost perfect. Now if i do the same after my inverse polarity mishap but otherwise same setup the fluke would read different values between 2 and 5 A so I think the VESC is not supplying a stable current output anymore. Nothing else about the setup has changed.
I hope it is understandable like that.

rew
Posts: 905
Joined: 25 Mar 2016, 12:29
Location: Delft, Netherlands.

Re: DC Battery amps vs. Motor Amps

Postby rew » 06 Jul 2017, 13:19

OK. So something in the "measure currents" is now broken. Yeah, that could happen when you apply reverse voltage.

Have you checked the 5V and 3.3V rails? Are they stable?

IMHO the DRV chip is one of the most difficult chips on the board. It certainly has contact with the applied "battery" voltage. You may think that it's one chip, but in fact it's two (in one plastic enclosure). So, the one that is connected to the reverse voltage is the 5V stepdown converter. Possibly if that's the part that's misbehaving, then you can still use the VESC with an external 5V DCDC converter. I expect most of the rest of the ssytem to be remain "powered down" because it's the DCDC converter chip that is handling the big reverse voltage.

Hmm. You used a battery? Then also the mosfets were subjected to more current/power than allowed. Check for shorts between the motor wires and the power wires. 6 combinations, each checking one FET. Measure both ways (i.e. 12 measurements). Use the diode measurement position of your multimeter and you should see 6x "infinite" (more than 2V) and 6x about 450mV.

maxkinz
Posts: 29
Joined: 30 Jun 2017, 14:41

Re: DC Battery amps vs. Motor Amps

Postby maxkinz » 06 Jul 2017, 14:49

Thanks for the suggestion,
I was able to measure the FETs and somehow the meter said 0.3V on all of them no matter wich way - I don't know but I think the meter is "smart" in that it checks both directions every time as it seems to display the direction on the monitor ... - maybe I need to repeat that with different settings...

So my first guess is there is no damage to the MOSFETs - would be confusing anyway as I was easily able to drive a small brushless motor for tests as my first thought was I might have fried a MOSFET or its body diode for that matter with the battery (the brushless I tested with is an older model EC32 series maxon motor). I did not connect its hall sensors. It ran completely fine in BLDC mode using the detection and threw out plenty torque considering how small a motor it is. The Values in BLDC tool did not make a lot of sense (appearently it "generated" electricity while running at 30% duty cycle so I guess I'll be making a lot of these and sell electricity for a living from now on.... :mrgreen: ) but it ran nicely. From my understanding all 6 FETs are needed for that.

Except for the current output in constant current mode, and I can only externally measure that for DC operation with the drill setup, I have so far not found a fault with the controller. I am going to recheck the rail voltages later today. I actually have a spare DRV around as I heared they tend to be a problem but since its a fine pitch i'd rather wait to know its the cause of all this fun before risking breaking a somewhat working controller. I ordered another VESC this morning so I will hopefully be able to resume my measurements soon.

Would a broken DCDC converter in the DRV result in any communication issues with the STM32 ? I get no fault codes and other than the measurements all seems to be fine... I will have a look at the VESC's schematic later.

Thanks for all the help !

devin
Posts: 225
Joined: 08 May 2017, 01:55
Location: San Francisco, California, US

Re: DC Battery amps vs. Motor Amps

Postby devin » 06 Jul 2017, 16:12

@maxkinz are you saying you increased the 3A amp limit on your 10v lab supply? and after doing this, the motor amps measured between vesc and stalled motor is inconsistent between test runs?

can we see a picture of the inconsistent motor amp measurement after the vesc is connected to a DC supply which is able to provide at least the "motor amp" value # of dc amps at constant voltage?
Last edited by devin on 06 Jul 2017, 16:24, edited 1 time in total.

devin
Posts: 225
Joined: 08 May 2017, 01:55
Location: San Francisco, California, US

Re: DC Battery amps vs. Motor Amps

Postby devin » 06 Jul 2017, 16:18

also, I'm not sure what it means but "KB control" is checked in the bottom right corner of your screen shot with a setting of 3 amps current:

Image

^Also I notice that the average negative values of the green and red amp lines on the chart add up to roughly the average positive value of the pink amp line...

So I'm assuming the PWM combination of the "negative amps" of phase 2 & 3 adds up to and results in the positive "amp draw" of phase 1 (pink line).

Also can we see a screenshot of your "motor configuration" tab?

devin
Posts: 225
Joined: 08 May 2017, 01:55
Location: San Francisco, California, US

Re: DC Battery amps vs. Motor Amps

Postby devin » 06 Jul 2017, 18:05

To illustrate, i vertically flipped the green line and placed it directly underneath the unchanged pink line...

Image

Image

Image

Image

^They aren't exactly the same waveform, but pretty darn close.

maxkinz
Posts: 29
Joined: 30 Jun 2017, 14:41

Re: DC Battery amps vs. Motor Amps

Postby maxkinz » 06 Jul 2017, 19:22

hey devin! Thanks for the effort ! - I think that it should be exactly the case as only 2 leads are connected in DC mode so correct me if I'm wrong but I think that the currents should be exactly the same except opposite directions. The difference would thus be inaccuracies in the measurement. If that is the case the shunt resistors are fine I guess because they measure the same value - so maybe rew is right and the reference voltage is off. KB control as far as I know stands for keyboard control so you're able to drive the motor by the arrow keys on your keyboard but it didn't ever affect anything when using the current control option.
@maxkinz are you saying you increased the 3A amp limit on your 10v lab supply? and after doing this, the motor amps measured between vesc and stalled motor is inconsistent between test runs?
Nope I did not Increase anything - the setup was exactly the same before and after the accident. I wanted to connect a battery to verify my results were independent of the power source when I screwed up. So I reverted the change to assess the damage. That's when I got results inconsistent with before the accident. I am fairly certain I destroyed something. I will go check the power rails tomorrow.

Thank you guys for helping !

devin
Posts: 225
Joined: 08 May 2017, 01:55
Location: San Francisco, California, US

Re: DC Battery amps vs. Motor Amps

Postby devin » 06 Jul 2017, 19:50

Maybe keyboard control refers to battery amps...

and current control refers to motor amps?

when you are in keybord control, if it is referencing battery amps, then what the vesc wants to draw is 3 battery amps at 10v -- 30w...

but to achieve this stalled, it actually requires 8.88 battery amps, 34.09% of the time -- which averages to 3 battery amps---

--but your lab supply sees the vesc trying to draw 8.88a, then lowers the 10v to a lower voltage to keep it below 3a supply at all times... never allowing the vesc to draw its planned 8.88amps...

like 2 computers having a war over how many amps to draw... the lab supply wins since it's "upstream" of the vesc... perhaps.


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