Caps & FETs

[M 800STD]

I know little if not nothing of electrics so hope someone here can advise me.

Ok, firstly external caps.  How do I work out the correct amount of capacity and voltage required?

Could this have a detrimental effect if I go too big?

Is there a rule of thumb or any maths I can use to work out my requirements?

Next, I have an ESC which I want to upgrade the caps and FETs.

How do I work out the optimum components to use?

When selecting components what's the hierarchy?  For example max working temp, ripple current, ESR, etc.

 

Thanks in advance.

 

 

[WillyChang]

What exact ESC are we working on?  

Generally unless you've got some special supplier of components up your sleeve there's usually not much improvement ti be gotten by changing to better MOSFETs than what's already spec'd/installed by factory. 

FETs are usually wired up parallel in banks anyway; if you need more current just tack on more (of same model) to each bank

Re Caps... power caps on the battery input? (vs filter caps on motor)

Size there's no set rule... usually it'll be around 2000-8000uF for externally mounted caps. Polarised electrolytics, nothing too fancy. Minor point but "bigger" caps usually have a "slower" response... you can use multiple smaller caps in parallel to add to similar total capacitance but "faster" response (folks like Novak started selling little PCBs with multiple caps on it - just solder the whole module in)  

Voltage rating is "maximum operating voltage", general commonly available caps usually around 16V which is more than needed. Higher volts usually be a bigger/heavier unit. 

Don't lose any sleep over low ESRs, no point. Won't see much need for extended temp ratings eg 105degC as they won't be sealed inside closed boxes to bake.

Schottky, much? 

[M 800STD]

Well since posting this my choice in ESC has changed so the intention of modifying an ESC has changed, although I may take this up as a little side project.

I'll PM you with regards to manufacturer and details when I get a bit more time, I'm sure this can be improved.

My thinking was to increase the integrity of a high amp ESC with newer components that are now available.  Such attributes of these volt/current thresh holds as well as max working temp, ripple, ESR and so on.

I would use parts readily available from RS Components or Farnells.

This project was for a 4s speed challenge car, so all aspect very important.  Hopefully I'll have my car built for August to attend the speed challenge in Wales.  Record, IIRC, 163.9mph on 4s.

[WillyChang]

RS/Farn catalogues = nerd pron  don't go digging under me bed!! 

Meh didn't think there's been that much groundbreaking improvements in MOSFET in past 20yrs apart from manufacturing purity/quality & size/packaging; the tech was pretty matured back in the 1980s already. IMHO it's mostly been leaps (dives?) in price if anything. 

Dunno haven't tried mucking about with FETs on brushless yet. 

Would've thought some HV thing from a 1/8th would suit; we'd bolt in 14.4V dual batt ESCs to run long 550 can motors for velodrome running.

Lately you've got that new Traxxas Maxx thing doing 6s too, any use?

[M 800STD]

I can't stop looking! 

There were a few new items, with high current draws and high max working temps - Caps/FETs.

It did make me wonder as to the spec of ESC components used, hence why I asked the manufacturer the question.  Waiting for reply - they've been really good so far and would supply the ESC in whatever state I want it in.  There's 25 caps and 48 FETs on this ESC.

Something like the Mamba XLX would do but I have an MGM with custom firmware in the works.  Motors, I'm having a 85mm long 3 turn LMT motor being built.  Specced/custom car also being worked out.

 

Just had a quick look at Traxxas.  This body looks nice.  I think Protoform do one as well.  https://traxxas.com/products/landing/ford-gt

[M 800STD]

163.9mph...

 

[Kingfisher]

I can barely keep a car straight with the silver can. I can only imagine the skill required to keep that thing from going into orbit.

[M 800STD]

I know some of the guys run with gyros.

I've got a heading lock gyro to help, as I can't drive in a straight line.

Sounds epic!

 

Have a look in outside world section, wet stuff thread - you may like the vids.

[WillyChang]

I turn the steering dualrate all the way down for velodrome, like 20% of max throw if not less. 

[M 800STD]

Yeah steering rate will have to be reduced, to help.

Also ESC will have medium launch, power, so you just nail the throttle.