Is there a way improve the LVC shutdown

[suicideneil]

Oh, that looks rather nasty, what happended there exactly?

[Gee]

I'm not sure. It was recommeded that I add another capacitor to it and bam there goes my esc. If I could only remember who it was.....


JK it was running fine with the extra capacitor. I had 3 or 4 packs with the extra capacitor installed. Would water shorting out the board cause a melt down like that? I had it out for a run and it was wet out. Didn't wrap it in the usual plastic bag though. Came in and turned it and the controller off. I didn't uplug the batteries though I had to help the nieighbor. Later on I smelled the smoke. So it was quite a while after I had shut it off that this happended. I thought lipo fire at first. Threw those batteries in the barbie outside. The batteries are fine. I had another HV esc do this to me while I was running it. It was bone dry out no chance of water doing it to that one.

Maybe it was me when I added the extra capacitor. If I got the wire too hot adding the other cap. Maybe it worked itself loose from the tabs on the esc. I don't know it sat there for a long time before I noticed any smoke smell.

[suicideneil]

Water would certainly cause a dead short on the exposed PCB, if it joined any of the solder joints together and such. Could be condensation also, going from cold/wet outside to warm inside. I would have thought though that if the capacitor or soldering was bad, it would have gone up in smoke as soon as you turned it on.... nasty either way.

[Gee]

Yeah, turning into one of the month like I had last fall. Power supply for my charger died today. There another 50 to replace. Got a supply that will get me by. Unlike last fall when I replaced the esc with the same ones this time were upgrading. That what you suppose to do when something breaks right? Otherwise why break it.

[BrianG]

OK, I did a little playing around with the Novak 4s LVC. The internal resistance of the unit is 200k ohms. So, depending on how much of a delay you want, you pick a capacitor that will discharge to ~12v using 200k ohms as the discharge resistance.

Since the internal resistance is constant (and it is because I checked), you don't need the additional discharge resistor shown in my original diagram. So, the new diagram looks like this:



I created a little Excel spreadsheet which helps to pick out the proper capacitor for the delay you want. Just fill in only the green boxed areas.

• Resistance (ohms): Enter the LVC internal resistance, 200,000 in this case.
• Capacitance (farads): I used 22uF. Other common values for ~25v are 10uF and 47uF, but don't provide the right delay IMO, but that's up to you.
• Battery Voltage: Self-explanatory. Use the nominal battery voltage. For a 4s pack, use 14.8v.
• Time Constants to show: Caps are accepted to be charged/discharged in 5 time constants, but if you want to see more detail in the lower time ranges, use a lower number.
• Euler's number: This is a constant for natural logarithm base. Leave as-is unless you really want to mess with it.

The table will show the time, discharge capacitor voltage, and charge capacitor voltage. And the graph will reflect this.

I figured a delay of ~1 second before the cap reaches LVC threshold of 12v should suffice, while still retaining full LVC functionality. So, for a 22uF cap, the discharge voltage is at 12.033 at 0.91 seconds (use 0.3 for the "time constants to show" to view this). If you use a 10uF capacitor, the cap will discharge to 12.033v after 0.41 seconds if you wish.

That's about it. Don't forget the diode or this will not work. Germanium works better because of the lower voltage drop (0.3v compared to the 0.7v of a normal silicon diode). Also, don't forget that the LVC will trip a little earlier because of this voltage drop. Any diode with a PIV value >= 100v will work fine, so 1N4002, 1N4002, etc.

[BrianG]

Incidentally, the formulas for finding capacitor voltage at any time (not just during the 1,2,3,4, or 5 time constants) are:

Charge:
capacitor_v = v_battery X (1 - 2.7182^(-t / (R X C)))

Discharge:
capacitor_v = v_battery X 2.7182^(-t / (R X C))

capacitor_v = capacitor voltage at "t" seconds
v_battery = battery voltage
2.7182 = Euler's constant
t = time in seconds
C = capacitance in farads
R = Resistance in ohms