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Old 22nd July 2010, 11:50 AM   #11
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Originally Posted by ThyDntWntMusic View Post
35volt capacitors, 220uF, 4 in parallel, Rubycon brand, 105 degree rating.

esc is rated for 2-4s lipo, its intended for lipo use
Funny. Not much to do but replace them all... or ask the manufacturer, or send it to them for servicing, giving the details you've posted here, which is probably the preferred option.

If it's intended for LiPos, then it'll have a cutoff circuit that is intended to prevent you over-discharging them. It recognises the number of cells, then sets a lower limit for the incoming voltage and cuts off when it reaches that. This may be what's kicking in, but the diagnosis is complicated by the overheating caps. They're almost certainly not being caused by the battery, but could be responsible for a low voltage being seen by the cutoff circuit. You might get some insight by putting a DMM across the input voltage and monitoring that from start to cutoff.

w
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Old 22nd July 2010, 07:37 PM   #12
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not sure the manufacturer speaks very good english.

it has a lipo cutoff, but, the esc is indicating overtemp, and its not actually shutting down, just running slow.

cut off can be set for 2.6/2.8/3.0/3.2/3.4 volts per cell and it auto detects the number of cells.

I believe the default is 3.0, most of them are too low anyway!

these runs were all done on a fully charged battery, so I dont think the lipo cut off is the issue.
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Old 22nd July 2010, 08:27 PM   #13
Magura is offline Magura  Denmark
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The simple solution is a bigger heatsink.
That or a small fan, like the 25mm fans used in computers.
I have seen this issue before, and the caps are most likely still ok, it's just that the manufacturers has a bad tendency to claim more than the real world can offer.

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Old 22nd July 2010, 09:15 PM   #14
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That or a small fan, like the 25mm fans used in computers.
I was going to suggest this, but it looks from the picture like there are already 2 fans in there, or is it just one for the motor? Is it possible something is obstructing the airflow, or that the ESC fan is intermittent?

It's difficult to know what to suggest otherwise, other than replacing the caps on a speculative basis, unless you feel up to drawing a schematic of the circuit. I don't really understand why an ESC would need that much capacitance in there even if it has a BEC.

w

If that is a fan on the ESC, is it possible to turn it round so that the airflow is reversed?

Last edited by wakibaki; 22nd July 2010 at 09:19 PM.
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Old 23rd July 2010, 07:58 AM   #15
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there is a fan in the speed controller.

the capacitors are actually mounted externally, I believe there is a thermistor on the PCB between the mosfets, so when the capacitors get hot, they heat up the thermistor too, without the heatsink warming up.

The fan is currently sucking air in through the top, blowing it out through the heatsink, and out the sides of the speed controller, and through the capacitors.

I'll try swap it to make better use of convection, and also so the capacitors get the air before its warmed by the heatsink
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Old 23rd July 2010, 08:06 AM   #16
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Old 24th July 2010, 12:04 PM   #17
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ok, I used this again today.

the heatsink got to 50 degrees, while the capacitors were at 90...

I do not understand this!

however, I have another similar speed controller, and it runs three 1000uf 25volt capacitors.

so..

120amp speed controller - 880uf/35v capacitors
150amp speed controller - 3000uf/25v capacitors

I think I need more capacitance! maybe this 120amp was meant to have like four 470uF 25volt, but they ran out
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Old 24th July 2010, 12:37 PM   #18
djQUAN is offline djQUAN  Philippines
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try panasonic FM caps. I had good luck with them in high current switching use.
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Old 24th July 2010, 06:14 PM   #19
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Quote:
Originally Posted by ThyDntWntMusic View Post
120amp speed controller - 880uf/35v capacitors
150amp speed controller - 3000uf/25v capacitors

I think I need more capacitance! maybe this 120amp was meant to have like four 470uF 25volt, but they ran out
I think part of the answer lies in the 35 volt rating. AFAIK, ESR (electrical series resistance) of a capacitor increases with voltage rating (someone correct me if i'm wrong here), so it's more likely to get hot. Also less capacitance means more ripple current which at this level is bad bad bad for caps, so yeah you need more capacitance, but try to get 25 volt low ESR caps.
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Old 24th July 2010, 11:07 PM   #20
godfrey is offline godfrey  South Africa
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I agree ultra-low ESR is needed. It's probably more important than the amount of capacitance.

Thinks: Heat is proportional to power dissipation which is I squared times R.

I'm not sure about ESR increasing with voltage rating. I've heard the opposite suggested as well.

It's best to look at the specs though, and aim for low ESR, high ripple current and high temperature. Caps intended for SMPS could be good, or maybe solid caps?
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