Capacitor For MM 4S

[GriffinRU]

Originally Posted by Maciolus

Will Panasonic FC 3300uf 25V be also suitable? I am using 4S2P A123 cells.

Yes,
18X25/2750mA/0.020Ohms - looks alright for 4S A123

[Maciolus]

Originally Posted by GriffinRU

Yes,
18X25/2750mA/0.020Ohms - looks alright for 4S A123

Thanks!

[Arct1k]

When we say poor connections / resistance - is it measurable at no load with a multimeter?

PS lets buy castle pizza

[Bernie Wolfard]

Arct1k,

You cannot measure the amount of resistance with a standard multimeter it is too low. Even though it is low, it is significant because resistance goes up with the square of amperage.

To measure very low resistance values you put a set amount of amperage, say 10 amps, accost the part being measured with a lab quality power supply then measure the voltage accost the part with a voltmeter accurate to at least ten thousands of a volt. Then use Ohm law to calculate the resistance, ohms = volts / current. I don't know how to measure internal resistance or a battery but obviously this method will not work with them.

Artur, I think Patrick, Castle Creations owner and chief engineer explained why tantalums are not appropriate for these applications, one of these being they can explode from the amount of inrush current we get in these applications. Patrick is a systems engineer who has a long resume including being lead engineer at Garmin, Allied Signal and others.

Bernie

[GriffinRU]

Originally Posted by Bernie Wolfard

Arct1k,

You cannot measure the amount of resistance with a standard multimeter it is too low. Even though it is low, it is significant because resistance goes up with the square of amperage.

To measure very low resistance values you put a set amount of amperage, say 10 amps, accost the part being measured with a lab quality power supply then measure the voltage accost the part with a voltmeter accurate to at least ten thousands of a volt. Then use Ohm law to calculate the resistance, ohms = volts / current. I don't know how to measure internal resistance or a battery but obviously this method will not work with them.

Artur, I think Patrick, Castle Creations owner and chief engineer explained why tantalums are not appropriate for these applications, one of these being they can explode from the amount of inrush current we get in these applications. Patrick is a systems engineer who has a long resume including being lead engineer at Garmin, Allied Signal and others.

Bernie

:)

You can do the same measurements with batteries as with caps.

BrignG - You need to have something as precision reference.

P.S. Resistance also would be temp and current dependant not to mention vibration...

[BrianG]

Low resistances can also be measured with a conductance meter (reciprocal of resistance). However, measuring low resistances like that is hard because the meter leads and connections can affect the measurement appreciably. For this reason, measuring voltage drop is easier. Why would you need a lab quality PS though? As long as you have an accurate and calibrated voltmeter (with the proper resolution), you could measure the voltage output of any PS and the V drop on a small resistance (shunt maybe).

Also, IIRC, the internal resistance of batteries is not linear. Instead of supplying the resistance value of cells, manufacturers should supply the resistance curve.

[Arct1k]

I guess thats a no for me and my $20 multimeter then :)

[BrianG]

lol, probably not.

@Artur; As long as you measure the output voltage of the PS, know the value of the precision shunt/resistor, and measure the v drop of the shunt, why would you need a good PS? Wouldn't the various measurements account for any PS deficiencies?

[GriffinRU]

Originally Posted by BrianG

lol, probably not.

@Artur; As long as you measure the output voltage of the PS, know the value of the precision shunt/resistor, and measure the v drop of the shunt, why would you need a good PS? Wouldn't the various measurements account for any PS deficiencies?

You will be better with precision PS then shunt. You can improve your measurements with Kelvin type resistors but it is much easier with PS.

[pipeous]

I just wanted to update. I finally ran my RC8 today with the Neu 1512 2.5D. The caps worked awesome. I checked it a few times and ran for quite a while at a BMX track. Not even close to getting warm on 4s lipo. motor or esc. I'll never waste time with fans again. In fact, I am going to add caps to my Sidewinder now to cool the B44 down a bit.

[Cain]

Saw pipeous other post, he is running 4 of the 440 caps. So with my simple logic, would that mean its basically similar to running 1760 cap? If so, Then running the 1 novak 2700 cap could lead to even better cooling seen on a mamba max ESC?

Thoughts on this? Thinking of picking up 1 novak cap, maybe 2, and ditching the fan.

[BrianG]

Yes, if running caps in parallel, you just add the values up. So, 4 x 440uF caps (what an odd value) is the same as 1 x 1760uF cap.

However, there is a point where you get smaller gains. Sure, you can add 20 caps and it would be cool, but would be a waste. Approximately doubling whatever is on the ESC would make the most difference and still be easy to fit on/near the ESC. Adding more certainly won't hurt (although it does make the initial hook-up spark bigger), but you just don't get the same amount of gain for the effort and cost. If your setup NEEDs the extra caps just to function and not overheat, maybe it's time for a different ESC choice.

Also, since these caps heat up, it's better to use several smaller ones in parallel because there is more surface area to help the air cool them. Plus, transient response is typically faster.

[Cain]

Thanks for the response.

The main thing I am looking for is the ability to eliminate the fan currently used with the Mamba max on 4S. I am curious based on pipeous experience, using 1 Novak HV cap will basically give the same or even more benefit that he is seeing.

I think I may give it a shot.

[pipeous]

I do notice the caps get warm, about the same as everything else. The MM works good on the 8th scale with 4s. it's smooth. I can crawl along with no cogging, burn laps and it is just such a consistent feel. I could come arund a corner onto a table top and keep the throttle on enough to keep speed in the corner and roll the table for the next double. carving such tight lines to the big o too. I can't see spending 4 times the money when $5 worth of caps fixes the heat issue. I am getting about 30 mins runtime too.

I let quite a few guys drive it at the track yesterday. pretty soon all the questions of where, how much started coming up. We just had a new electric only track open up. the property owner has a brushless 8th scale, b44, 10th truck... all brushless. Sat night racing under lights will be awesome. big track

[lutach]

My Mtroniks truck controller has a huge 10,000uF, 85C capacitor and I'm just wondering, what's tha max amount of capacitance do you guys recommend?