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Old 05-14-2003, 06:39 AM   #1
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Default Power Capacitor

Hi guys. Greetings from Malta.

I have just read the article in RC Zone about Power Caps.

It sounds quite impressive. The writer recommends a cap of 10,000 uf. for most of today's speedos.

I picked one up at an electrical shop this morning, and yes it only cost me US$3 as opposed to the US$ 50 that people like LRP charge for theirs. Problem is that a 10000 cap is enormous.


Can anybody tell me if linking 2 x 4700 caps in parallel would give the same effect as a single 9400 uf cap. The reason I ask is that 2 x 4700 caps still take up less space and are much lighter than the 10000 one.

Thanks in anticipation for your constructive replies.

regards

Joe from sunny Malta.
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Old 05-14-2003, 07:01 AM   #2
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Yes, the capacitance goes up.


Just make sure that CAP you are getting is High Frequency Low impedance Capacitors.
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Old 05-14-2003, 08:58 AM   #3
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From a capacatance point of view yes 2x4700uf caps in parallel would be the same as a single 9400uf. However the 2 caps would have much higher impedance that the single cap. In capacitors impedance goes down as capacitance goes up.

For info the large cap in the LRP worlds kit is 4700uF, and certainly looks to me to be a Panasonic made cap.
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Old 05-14-2003, 09:17 AM   #4
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Hi Matt,

I've just soldered the 2 x 4700 caps in parallel and wired them up to my GT7.

They are 2 of the normal ones supplied by all the speedo manufacturers at vastly inflated prices.

I'll see how it goes and let you know. I'm just charging up some cells and should be running in about an hour.

I see the British championship is shaping up nicely. Chris Ashton did well for Schumacher. How are you doing?

Regards

Joe from sunny Malta.
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Old 05-14-2003, 09:22 AM   #5
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Default Re: Power Capacitor

Quote:
Originally posted by johnbull
Hi guys. Greetings from Malta.

Can anybody tell me if linking 2 x 4700 caps in parallel would give the same effect as a single 9400 uf cap. The reason I ask is that 2 x 4700 caps still take up less space and are much lighter than the 10000 one.

regards

Joe from sunny Malta.

Yes, same effect.

Before soldering that capacitor to the ESC permanently, try this.

Adjust the throttle trim until the car's wheels are turning slowly but smoothly. Then hold the capacitor by its body and touch the leads across the motor terminal (in parallel) observing correct polarity. The motor should speed up. I haven't tried soldering a cap on the motor then running the car on the track so I don't know if it gives more punch.

I'm hoping you'd try as you have your own track.

Do this only on high capacitance caps. 10000uF or more. lower capacitance caps burns (low impedance)

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Old 05-14-2003, 09:23 AM   #6
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john,

you can buy pretty small 10,000uF caps, the trick is to not overdo the voltage. a 10v cap will be substantially smaller than say a 35v.

and it should say "This article was kindly donated by Sanj's RC Homepage" but nonetheless.

sanj
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Old 05-14-2003, 09:51 AM   #7
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Sanj, Thanks! That article has been very helpful to me.

I do have a question regarding what is meant by "linking (the caps) in parallel" in order to do this, do you solder the negative of the 1st capacitor to the negative of the 2nd, then to the negative of the ESC, and the same routine for the positives or...? Please advise.

Thanks and cheers,
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Old 05-14-2003, 09:56 AM   #8
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Quote:
Originally posted by MattW
From a capacatance point of view yes 2x4700uf caps in parallel would be the same as a single 9400uf. However the 2 caps would have much higher impedance that the single cap. In capacitors impedance goes down as capacitance goes up.

For info the large cap in the LRP worlds kit is 4700uF, and certainly looks to me to be a Panasonic made cap.

That's ture.

The length of the capacitor and its construction determine the capacitor's self-inductance and thus its resonant frequency.

The lead length to the capacitor's external circuit load influences the incircuit performance, usually in a quite different manner from that which was calculated based upon ideal (that is, no inductance) conditions.
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Old 05-14-2003, 10:52 AM   #9
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so if i was to go to an electronic store to look for a capacitor, what should the specs be?
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Old 05-14-2003, 11:07 AM   #10
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I`m using 2 16v 4700uf caps and thats working for me
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Old 05-14-2003, 11:41 AM   #11
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Im gonna have a go at this, can sum 1 post a pic of there car with the caps soldered on.

Cheers
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Old 05-14-2003, 01:25 PM   #12
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working voltage of greater than 7.2v (usually the next one up is 10v)

high frequency, low impedance and you can pretty much pick the capacitance you want. the limiting factor will be the size.

sanj
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Old 05-14-2003, 02:24 PM   #13
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I picked up three 4700uF 10V. I was planning to wire all three, but the problem lies with space and protection. I don't have the space (Xray T1R) so I used two instead of three. Race it last night, lots of punch. Voltage ripple smoothed out nicely.
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Old 05-14-2003, 02:42 PM   #14
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just wondering, i hear a lot of people use it in mod class, but does it have an effect in stock class?
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Old 05-14-2003, 04:08 PM   #15
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JB, If they are the Novak ones, they are also Panasonics (or the last ones i looked at were!). Easily available, certainly in the UK.

1st national (stafford) i was on a B final run till i had something of a drive issue!! It was effectively single run qualifing as it had been wet right up until rd4.

This past weekend at Bedworth i was in the A for the 1st 3 rounds, but then got nudged out after round 4 by 0.9secs. Still my best qualifying to date - but how nice would it have been to actually make the final! The A was seperated by 8 secs, and Dave certainly seems to be back on it this year.
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