ESCs and extended power wires: Should we add capacitors?

[Pumpkinguy]

This thread is an oldie but a goodie. I'm thinking about moving my esc location further out for a number of reasons. I did this esc today just as a mock up.

Stock caps are 470uf and these are 1200. Probably way overkill.
1 x 1200uf would fit better and effectively double the stock capicitors. I may go that route.

 

[Motopreserve]

I thought that the suggestion was to use the same caps as the ones Currently installed. I could be wrong, that was read a while back, and miles into that initial thread on the subject

 

[Pumpkinguy]

The same type of caps but ultimately the only downside to going larger is weight and cost. They weigh nothing and cost nothing imo.

 

[Ccard]

This thread is an oldie but a goodie. I'm thinking about moving my esc location further out for a number of reasons. I did this esc today just as a mock up.

Stock caps are 470uf and these are 1200. Probably way overkill.
1 x 1200uf would fit better and effectively double the stock capicitors. I may go that route.

Adding [2 x 1200 uF] 2400 uF should compensate for an additional 10 inches of wire length for the power lead to the ESC.

I read an article that discussed these matters in technical detail, but that was a few years ago and I can't find it anymore.

I did find a thread on RCgroups that seems to be inline with what I recall from the 'other' article.
Here's a link => http://www.rcgroups.com/forums/showthread.php?t=952523

It boils down to: ~ 220 uF additional capacitance [Low ESR Caps] for each additional 10 cm/4 inches of length.
[ Post #572 in above link ]

Also a low motor/ESC PWM rate is better for long battery lead situations... and Japanese caps are preferable.

 

[Pumpkinguy]

Here is my process.

A drop of ca glue to hold them together.
Bend the wires. - to one side and + to the other.
Trim the first wire so it doesn't extend past the outside of the second cap.
Slip heat shrink over the wire then solder the 2 together.
Slip a tiny length of heat shrink over the soldered area.
Wrap the - around the negitive wire, the positive around the positive then solder.
I still need to put some heat shrink over the end with the caps. Just waiting on longer servo wires. I need about 4" longer. View attachment 27067View attachment 27068View attachment 27069View attachment 27070

 

[Ccard]

With all that capacitance there's going to be the potential for huge arcing/spark
on battery connect.
This could cause the connectors to sort-a spot weld at the initial contact points making the connectors feel 'sticky' ..or ruin the contact mating surfaces.
One way to mitigate this is to use some sort of a pre-charge connection with power resistor.
For instance, a 5 watt / 100 ohm power resistor for what appears to be a total of 20000 uF would take about 10 sec to fully charge the caps.

Chris

 

[Pumpkinguy]

I have thought of it all my friend.

I already use a sparkless/sacrificial harness to install battery #1. Then I install battery #2. Then I remove sparkless/sacrificial harness from battery #1 and reconnect #1 normally. Make sense?

 

[Ccard]

I have thought of it all my friend.

I already use a sparkless/sacrificial harness to install battery #1. Then I install battery #2. Then I remove sparkless/sacrificial harness from battery #1 and reconnect #1 normally. Make sense?

Yes it does. You've got it under control... I can say no more.

Cheers
Chris

 

[Pumpkinguy]

JuSt in case someone reading can't visualize it. View attachment 27089
The red connector is an as150 (anti spark)

 

[Pumpkinguy]

I just smoked a motor on the bench. Tmotor u7-490v2. 2 minutes at 90% throttle with 18" props. pulling 68 amps.
I don't use 18" props but these motors are rated for them. I was doing a esc temp test. I am not real deep with electronics. Could this have anything to do with the extra caps? Motor was up around 200F at time of failure. View attachment 27129

 

[Motopreserve]

Oh man! Sorry to hear that. I guess better on the bench than in the air - but now you've got more questions than answers?

What part of the motor was the 200f measurement taken at?

 

[fltundra]

Caps had nothing to do with it. Max amps for those motors I can see is 62 amps. You just overheated that one, carbon fiber mounting is not a good heat sink.

Max Continuous current(A)180S.............................................................44A
Max Continuous Power(W)180S.......................................................1300W

 

[Pumpkinguy]

Ya. Maybe I was a little hard on it. Lol. That motor pulls 80 amps at full throttle with 18's. I do like to push my bench tests.
Moto, thay temp reading was on the Bell. Probably hotter inside.