Adding capacitors to a Quark 125B
 

So in light of my failure to get an MGM controller to work, I'm going to try my luck with a Quark 125B (paired to a Neu 1515/1Y in my E-Revo). I've been reading about the thermalling issues with Quarks and will be getting Mike's heatsink, and perhaps a fan (although I'd like to avoid the fan if at all possible). Would prefer not to take it apart to do the internal mod that I've read about in these forums. I've been reading about adding capacitors, but cannot anywhere find instructions as to how to do this. Which capacitors exactly should I get, how many of them should I get, and to what exactly do I connect them?

Thanks in advance,
JPP

First of all, the internal mod NEEDS to be done no matter how big of a heatsink you get. The problem is that there are two thermal sticky pads that hold the ESC guts to the case. Those pads are fairly thick, do not conduct heat very well, and come unstuck after a while of running. For an external heatsink to work, you need to pull the heat from the FETs in the first place. Yeah, I know the mod is something that shouldn't need to be done, but we don't live in an ideal world so...

That said, adding caps is also a good idea. Since there isn't any extra room inside the case, you can add them on the power wires as close to the case as possible.

The easiest and most compact way to do this would be to:

• Determine the number of caps you want. 2 or 3 is good - any more won't help noticeably, but more won't hurt anything.
  
  
• Tie all the (-) lead of the caps together (denoted by the whitish stripe on one side of the cap) to make one thick lead. Do the same for the (+) lead.
  
  http://scriptasylum.com/forumpics/quark_cap_1.jpg
  
  
• Strip about 1/8" thick of bare wire on both red and black wires as close to the case as possible.
  
  http://scriptasylum.com/forumpics/quark_cap_2.jpg
  
  
• Wrap these leads around the stripped wires and solder. Make sure the black lead goes to the right capacitor lead!
  
  http://scriptasylum.com/forumpics/quark_cap_3.jpg
  
  
• Ideally, using heatshrink on the soldered connections is preferred, but may be difficult. I used a piece of thick double-sided electrical tape.
  
  http://scriptasylum.com/forumpics/quark_cap_4.jpg
  
  
• Insulate (heatshrink) the whole cap bank to totally cover the connections. It's best to leave 3/4 of the caps themselves uncovered to help them stay cool.
  
  http://scriptasylum.com/forumpics/quark_cap_5.jpg
  
  

Just be aware that there will be a slightly larger spark when you hook up your batteries since the total capacitance is higher. This is normal.

What a terrific tutorial; thanks! One question: I noticed that the capacitors you're using are 330uf 35v, and I think somewhere else I saw that you definitely need 35v. Don't know if you chose those because you happened to have them or if you bought them specially for this purpose. If I'm buying them specially for this purpose, what are the ideal specs? (My poor knowledge of how electricity works, and for that matter, what a capacitor even is, is hurting me here...) Do you have a recommended source?

i have 1500's@35volts they are the good ones niechicrons or something i cant remember exactly off top of head but if your interested they are 1.00 each

A member here (AAngel IIRC) got a bunch of these caps a while back and sold some in small amounts. Whatever you get, make sure they are low ESR types otherwise they will heat up badly and blow. Look for ones specifically spec'd as low-ESR (Equivalent Series Resistance) and 105*C or higher temp value.

35v is a good value to get for 5s. Generally, you pick a voltage that is ~35-50% higher than the max ESC voltage for longevity and reliability. 5s is 18.5v. 50% higher is 27v. So 35v is perfect. You can use higher voltage caps but they get physically bigger.

For the capacitance value, using multiple lower value caps is better than one large one. The current and heat is distributed more evenly among them and multiple ones have a better transient repsonse. So, if you want 1000uF total, it's better to use three 330uF instead.

As to where to find them, Mouser electronics or similar large parts suppliers will have them. RadioShack does NOT have them. If you use lesser-quality caps, they will overheat from the AC ripple and blow/pop.

Here is what I did to my 'Quark', if you want to call it that anymore. I used some flattened copper tube as buss bar and soldered 6 extra caps directly to the board. After I did that, I got magic-Mike the make me a FET clamp to squeeze the FETs with thermal paste (AS-5), and mounted it to a large heatsink for great cooling.... a little overkill, yes.... do I regret it, never! :na:

Anyways, it runs even better now with these mods to it, smoother (if that's possible), I can't even try to make it cog, it seems like a sensored brushless system now. It stays super cool running 7s2p A123 (equal 6s lipo) on a Neu 1512 3D (1700Kv.), and it has got awesome power with power readings on Eagletree of 2100 watt spikes. The motor gets up to 160F at the end of a 30 min runtime.

EDIT: I also got my caps from AAngel. A group purchase sorta.

I still have a whole bunch of caps too if anyone is interested. They are: Nichicon 330uf 35v. Send me a PM.

Thanks Chris, I received the caps yesterday. Great deal, I'll be adding a pair just like Brian shows in his how-to above.

Thanks for the speedy shipping!

Harold

anyone got a direct link to the ones that are good from mouser electronics?

I'm trying to copy this mod. How the capacitors are attached to the copper tube, + and - cords?

Also, how are the FET clamp + heatsink and Quark put together to get correct pressure between copper and fets?

HERE is the link to more pics on the MOD.

"How the capacitors are attached to the copper tube, + and - cords?"

-What I did was lay the cap down, trim the leads on them, wrap tape around it once to make sure they don't move... then lay the +, or - leads onto one of the copper bars, then using a decently powered soldering iron, use alot of solder to bond them to the copper bars. I kinda slid the iron along while applying the solder behind it as the copper had alot of thermal capacity to do this.


"Also, how are the FET clamp + heatsink and Quark put together to get correct pressure between copper and fets?"

-The FET clamp is aluminum, Mike made it for me, so if you want one you could ask him if he still has the CAD file to machine it again? But, I just took the maximum thickness (can't remember exactly), something around 5mm from FET surface to FET surface, IIRC... then used that. The clamp was quite tight yes, I felt like it was going to crack something, but it was fine. It was perfect pressure on the FETs, it sucked every lat bit of heat from them and efficiently transfered it to the large heatsink (overkill) I got from a PC video card that died. How the FET clamp is attached is by thermal adhesive paste (arctic silver brand)... and that worked great!

In the end though, the Quark ended being killed... because it was mounted in a stupid spot, and when doing a wheelie, the truck flipped over and put alot of pressure on the body shell, and the Quark was right underneath, and pushed on the 'brains' board and shorted soemthing out, killing the brains board, the power board on it is fine however! I am going to redo this mod with the Quark I have now, as summer heat is on the way...

Hope this helps! Any other questions?

Thank you VERY much for your excellent pictures of the details and other information aswell. Now I understand the structure. Sorry to hear that your Quark died, are you going to make exactly the same kind of FET clamp and capacitor system for your new Quark too? Or is it a new evo model?

I just received Nichicon 35V 330uF low esr capacitors for this mod and I got a processor heatsink (copper+aluminum) which have to be cut a little smaller due to it's weight.

Otherwise Quark 125B is very good esc but it allows only 10 mins driving with 6s2p A123, then it needs couple of minutes to proceed.

Oh for sure! My pleasure!

Yes, I am going to use the same clamp, as it's just thermal paste (not adhesive) on the FET clamp between the FETs, so you can transfer any Quark onto the setup as you wish.

Just for information, my ESC temps when running 7s2p geared a hair under 50mph (and big battery...) were I think never more than 10 degrees F over ambient, IIRC. You couldn't tell it had been running even, VERY nice. I could push the truck as hard as I wanted... and plus it seemed to have ran smoother, especially on startup, never cogged, ever. With my new Quark, it's annoying when I cogs, always at the wrong moment. Which only happens to me on 7s2p though, which was the same problem ppl have on 6s lipo.

If you want it compact check this:
http://forum.rcdesign.ru/index.php?a...ntry&id=119589
http://forum.rcdesign.ru/index.php?a...ntry&id=119590
http://forum.rcdesign.ru/index.php?a...ntry&id=119591
http://forum.rcdesign.ru/index.php?a...ntry&id=119592
http://forum.rcdesign.ru/index.php?a...ntry&id=119593

Yeah, to be honest, yours should work just fine with even the most high end setups. What were the temps on that thing anyways? The only benefit my FET clamp has is the cap bank on the esc, which will make it that much more durable, although, overkill I might add, but none the less.