low ESR cap behind shunt resistor??

[powersupply]

I am enhancing my controller and noticed a weird thing:

There are 2 x 470/50V caps connected directly to the + and - of the incoming battery wires.

From there, in the - path, there is the shunt and behind that is another (same type) 470/50V capacitor, located at the FET power "bus".

Exactly the same arrangement like in the second picture (PA270018.JPG) in

http://www.endless-sphere.com/forums/viewtopic.php?f=2&t=3896

Now I understand that the incoming DC needs to be buffered, but the FET's need very much power for their rise times, so shouldn't the 2 x 470/50V caps berather positioned behind the shunt???

And just one 470/50V for buffering things like the two voltage regulators etc?

I see that the FET power "bus" is quite crowded, might that be the reason???

Here is my actual question:
I have a REAL low ESR 1500uF/75V cap which I would like to implement, where should I put it, directly at the incoming +/- from the battery or at the FET bus?

 

[bigmoose]

Fet bus and "centralized" not at one end or the other.

 

[powersupply]

Thanks for the reply, Bigmoose!

I left all the existing caps -which by their own admission are regular caps- in place and added my super low ESR cap.
Unfortunately it is mechanically impossible to mount it in the middle.
So I hooked it up behind the shunts.
Also added several 1uF/100V beneath the board along the FET power bus, mostly right to the pins of the FETs.

The controller would get really warm before the mod, I took a long ride earlier and now it is barely noticable, maybe a few C above ambient.

Here some pictures

Does the controller look familiar?
jdk411rz001 original
View attachment 3

jdk411rz001


and after the 1500uF 75V super low ESR cap


behind the shunts

 

[bigmoose]

Well done! and thanks for the pix. Getting those 1uf across the bridge from Upper Drain to Lower Source on each leg does a lot.

 

[powersupply]

Thanks for the kind words.

I had to undo a current mod with the shunts, the scooter would take off by itself, I nearly made a wheelie.

Unfortunately there is not much space for many caps beneath.
But they fit perfectly heightwise to support the PCB against the pressure the FETs exert through the clamps from above.

Those clamps are great BTW, I would read about the unscrewing individual FETs all the time, so this is definetly a huge timesaver.

The drawback, I am quite sure that the FETs would get so hot because of the mediocre heat transfer.

That was the main reason for the low ESR mod I did.

Also added some traces directly to the FETs.

Looking at the PCB, there are many unwired spots with names like XS2, S1, SM, 60/120 (I figured than one), DS, SM (unpopulated parts), L, ES, etc.
Do they sound familiar?

Maybe I should start a new thread for those. with a picture of the actual spots?

Thanks!