Questions Regarding Alt. FW & GUI setup

[jsmith2307]

Greetings,

Crs2012 -

Find out what your amp draw from motors are.

Using a multimeter, unfused @ 20 amps I ran tests on a total of 4 motors, 2 off the simulator(I had extras) and 2 on the simultaor. The results were 2.5 amps, 2.6 amps, 2.75 amps, 2.6 amps under no-load. On initial startup I saw spikes (read off of the chart = #01) on my multimeter, #01 off the chart - 16.60 amps - 19.25 amps on all four motors.

I have not tested under a heavy load, yet.... Hard to figure out how do this!
jsmith2307

[crs2012]

Well from those readings you know that with zero load, the motors are within safe specs for your boards.
You can probably guess that your inrush current spike is approaching high levels.

https://en.wikipedia.org/wiki/Inrush_current_limiter
I'm guessing you should probably begin to research a solution for your inrush current spikes.

It's obvious that increasing load (torque) will increase your amp draw from motor( maybe 2x or 3x as a guess until you find out the true full load values) so

2.75 was your highest reading for normal use x 3 (assuming a 3 times value for load ) = 8.25A (under load) which is perfectly in spec of boards. x2 (double the value for direction change spike) puts you about 16.5A, which is still within operation limits. So this is still theory math because you need to solve what the true value is when applying load(torque). But if these values are remotely close, you can determine that operation of the motors are within spec of your boards. I will assume that it has worked in the past with your boards at some point in time without blowing the 25A fuses you were using. So these values are probably within reason.

The problem is that your in rush current starts at nearly 20A with no load.(19.25A/2.75A = 7) So we see that your inrush current spike is about 7 times your normal use. IF, the theory of load is 3x your no load reading this could make your inrush current spike more like 21 times your no load value. 2.75A x 21 = 57.75A! <---- fry your board before your 25A fuse knows what happened.

Keep in mind I'm pulling theory math based on several examples I've researched around the web to get a very general formula base to get some basic values. In no way am I assuming these values to be the true values you will experience. That can only be proven by you with your amp meter.

My best guess at this time is to find some inrush current limiter solution if you wish to keep your system as it is.

[jsmith2307]

Greetings,
Crs2012 ,

The problem is that your in rush current starts at nearly 20A with no load.(19.25A/2.75A = 7) So we see that your inrush current spike is about 7 times your normal use. IF, the theory of load is 3x your no load reading this could make your inrush current spike more like 21 times your no load value. 2.75A x 21 = 57.75A! <---- fry your board before your 25A fuse knows what happened.

.... I was using a 15 amp instead of the 25 amp.

Analyze what I’m seeing, please, I think this is what you are talking about!
I went down to my local electronic store yesterday and purchased 0-50 amps panel meter. And, I got quite the awakening! (See pics) The current draw on startup jumped to 0 to 40 amps in a fraction of a second, then immediately dove to below the scale, then went to 18 amps, then below 0 and finally it settled on 3 amps. Everything cycled in a fraction of a second! FRYSVILLE .....would you like FRIES with that BOARD?....

What would you suggest?


jsmith2307

[crs2012]

Without the true values under load I can only continue to theorize as to what the root cause can be.
These values so far are still suspicious of other possible causes to the burn out problem.

After reviewing the 24v23 motor driver information more thoroughly http://www.pololu.com/catalog/product/1456

Real-World Power Dissipation Considerations

The motor driver can tolerate peak currents in excess of 200 A. The peak current ratings are for quick transients (e.g. when a motor is first turned on), and the continuous rating of 23 A is dependent on various conditions, such as the ambient temperature. The main limitation comes from heating and power dissipation; therefore, at high currents, the motor driver will be extremely hot, and performance can be improved by adding heat sinks or otherwise cooling the board. The driver’s printed circuit board is designed to draw heat out of the MOSFETs, but performance can be improved by adding a heat sink. The MOSFETs have a theoretical maximum continuous current of 90A at 25°C, but dissipating enough heat to keep the MOSFET at this temperature is impractical for most applications; close to 40 A of continuous current should be achievable without too extravagant of a heat sink. For more information on power dissipation see the data sheet for the MOSFETs on the Resources tab.

Because there is no internal temperature limiting on the motor driver, the entire system should be designed to keep the load current below the 23 A limit. An easy way to achieve this is to select a motor with a stall current below that limit. However, because a good motor can have stall currents dozens of times higher than the typical operating current, motors with stall currents that are hundreds of amps can be used with this driver as long as the running current is kept low. For example, a motor with a 100 A stall current might run well at 10 A, leaving a safe margin for the current to double for several minutes at a time or to triple for several seconds. If the motor does stall completely for a prolonged period, however, the motor or driver are likely to burn out.

This is concerning, because it basically implies that your board would theoretically need +200A inrush current to fry it. The zero load inrush current readings you gave so far don't substantiate the theory yet.

So 2 possible scenarios at this point. Either your LOAD inrush current (or stall current) is over 200A, OR you have a wiring problem.

[jsmith2307]

Greetings,
Thru my endeavors, I finally found what I was looking for! This is a dyno test of test of the motor I'm using!
jsmith2307

[crs2012]

Wow, those are powerful motors.

I think this chart shows the potential of how your boards can get fried not only on inrush current, but during operation as well.

You mentioned earlier that 40A registered on inrush current with no load, that's 13.3333 x the no load normal operation of about 3A.
You see with just 25in/lb torque (load) that doubles to 6A. The threshold is around 103 in/lb torque (load) @ 12A because changing directions would double that up with 206 in/lb torque (load) nearly 20A. Which is just under the recommended 23A safe zone for the boards with no heat sinks or cooling fans.

IF the 200A is the threshold for inrush current limitation for a fraction of a second during start of motor,

we are guessing that 13 is the ratio of inrush current spike based on your zero load readings.

6A (25in/lb torque)x 13 = 78A <---- Much safer
12A (103in/lb torque) x 13 = 156A <--- dangerously high
20A (202in/lb torque) x 13 = 266A <--- fry board

So the last riddle to solve is how much torque is added to the motors when attached to your simulator to effectively spike your inrush current high enough to fry your boards. This theory shows just over 105in/lb torque could potentially do it.

It's a safe bet that you are probably 50in/lb - 75in/lb (torque) under normal operation, since you mentioned using a 15A fuse when you were able to operate the system. Changing directions would put you in the 100in/lb-150in/lb (torque) range which is brushing up against the 15A fuse limit. Which is also showing you could theoretically be crossing the threshold for 200A+ on inrush current.

In ANY case, these motors will not stall before your boards fry. They are VERY powerful, and can pull nearly 100A with up to 1,000 in/lb torque.
You MUST have some sort of limiter in your circuit if you choose to continue using these motors and those boards.

One last note... The fuse you are using may not be sufficient as a safety device either... If the fuse blew and the board still fried, that could be an indication that the current is arcing through the fuse and frying the board as well... Since I don't know the schematic to how you have your battery and boards wired, I can't really comment on this topic too much. But certainly another issue that needs some attention as well.

This site is for amplifiers and stereos but still good information about fuses there...
http://www.bcae1.com/fuses.htm

[jsmith2307]

Greetings,

This site is for amplifiers and stereos but still good information about fuses there...
http://www.bcae1.com/fuses.htm

crs2012,
I’m astounded by your knowledge of the subject matter! That is some good info!! An excellent article, by the way. I'm currently choosing from the NPC motor co. (wheelchair motors) list of acceptable motor drivers,... which are not cheap!
jsmith2307