Chargring SuperCap's with Step Down Module -Can charage caps in series?

Thread Starter

FubarI33t

Joined Dec 14, 2015
2
SuperCap's!!!! Fun little project I am working on that should become a permanent fixture in the trunk of my Wankel powered RX8.

Components: 6x 2.5V 700F Cap's, 2x 4-38V to 1.25-36V 5A adjustable step down modules(ebay 5$ special)

So, here is the purpose, 6x700F Caps in series(116.663F) for engine starting!!. Now I don't want to just feed 14V back into these caps for charging. I bought two(one each for 3 caps) of these 5A adjustable module's(with current limiting) and I hope they can limit the current enough so the caps don't burn them out. But question is- Wiring these up for recharge. I'm by-far no expert in wiring. But what I have so far, Positive of each cap wired to positive output of module(remember 3 caps per module set to 2.1-2.2V) and both NEG output of modules wired to NEG output of last cap(NEG that grounds to car) Now each Cap is in series, with solid copper connectors, will it hurt to have the modules wired in to each POS of caps? I wanted to ask BEFORE I apply power, I am well aware these things can pretty much kill me if they want.

Yes these caps have been insulated with extra thick HD rubber tape between the Alloy bars!
 

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Papabravo

Joined Feb 24, 2006
13,924
Capacitors in series are like resistors in parallel. You can't just add them up; it doesn't work that way. Ignoring that detail for a moment are you here to tell us that you can actually do this -- start a rotary engine from this rig?

BTW
700 || 700 || 700 ≈ 233.3 F

http://farside.ph.utexas.edu/teaching/302l/lectures/node46.html

You might want to undertake a basic review of electronics before you do kill yourself. You could proceed on your current path and win a Darwin Award.
 
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GopherT

Joined Nov 23, 2012
8,012
Capacitors in series are like resistors in parallel. You can't just add them up; it doesn't work that way. Ignoring that detail for a moment are you here to tell us that you can actually do this -- start a rotary engine from this rig?

BTW
700 || 700 || 700 ≈ 233.3 F

http://farside.ph.utexas.edu/teaching/302l/lectures/node46.html

You might want to undertake a basic review of electronics before you do kill yourself. You could proceed on your current path and win a Darwin Award.

That is what he said, hex pet the OP did the math correctly. You did the math correctly if the OP is willing to change his design to your newly specified 3 caps in series instead of 6.

Six caps in series at 700F each is 166 F (exactly as OP said)

Now, about that Darwin Award....
 

Alec_t

Joined Sep 17, 2013
11,398
It is unlikely that all six caps have identical capacities. Therefore, with the series arrangement, one or more may become reverse polarised when the caps discharge into the load. From my limited googling it seems the jury is out on whether that will damage a supercap, and it may be manufacturer-dependent.
If damage can occur, then some sort of charge-balancing may be necessary during charging and discharging.
 

DickCappels

Joined Aug 21, 2008
6,457
Perhaps rather than balancing, placing a very high current Schottky diode across each capacitor to limit the reverse voltage might be enough. Anybody know what half a volt reverse bias for a short time is likely to do to a supercap?
 

Denesius

Joined Feb 5, 2014
103
Super caps use a carbon coating along with an electrolyte immersion. Reverse polarity (low voltage), short-term will alter the electrolyte distribution, markedly diminishing capacity, and long-term will overheat and burst the casing.
They do make balance chargers for supercaps: they are available on ebay, cap specific, and for my Maxwells cost about $1.90 per cell, free shipping. They balance the charge, prevent overvolts, and block reverse charging. They dissipate the excess as heat, so you do need current limits during charge.
I have a bank of caps in series (12, for a 24 volt system) that I use to maintain power to an essential gauge (AHRS in an aircraft). The bank charges during power up, and will keep the data valid during interruptions of as long as 10 minutes. During normal power down the bank simply discharges down to around 8 volts, at which point a relay opens.
These suckers will easily start a Honda Ridgeline engine at least 3 times on a full charge! I know- I tried it. The starter motor spins faster than internal battery- however, on the 3rd try I burned out the trace on the circuit board, the weak point in the circuit.
(and no, it wasn't the 24v setup- I used only 1/2, or 12 volts)
 
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Thread Starter

FubarI33t

Joined Dec 14, 2015
2
I did find some Cap-Top protection boards for my 2.5V 700F Caps with reverse protection etc... They are on order, i'll just use the step down modules to take the 14V down to 12V since they also have current limit protection(5A each cont,) and let 1 feed 3, so both of my boards will still be used. I will deff keep this post updated with results or more questions.
 

Papabravo

Joined Feb 24, 2006
13,924
That is what he said, hex pet the OP did the math correctly. You did the math correctly if the OP is willing to change his design to your newly specified 3 caps in series instead of 6.

Six caps in series at 700F each is 166 F (exactly as OP said)

Now, about that Darwin Award....
He actually said 116.663 which is correct, not 166 which is incorrect, but I was misled into thinking he had added them up in some fashion. Closest I've come to a Darwin was pressing on into deteriorating weather conditions in my 7ECA. I was instrument rated, but the plane was not instrument equipped. I had needle-ball & airspeed.
 

GopherT

Joined Nov 23, 2012
8,012
He actually said 116.663 which was what misled me into thinking he had added them up in some fashion. Closest I've come to a Darwin was pressing on into deteriorating weather conditions in my 7ECA. I was instrument rated, but the plane was not instrument equipped. I had needle-ball & airspeed.
If you've already procreated, then you cannot get an award. If you've passed on your genetic material, you are only eligible for an honorable mention.
 

#12

Joined Nov 30, 2010
18,210
You guys creep me out. Flying into bad weather with a needle-ball? I'm so cautious I won't even get on a boat, and I start my lawn mower with a battery, but the, "yank here" rope is still in place.
 

Papabravo

Joined Feb 24, 2006
13,924
You guys creep me out. Flying into bad weather with a needle-ball? I'm so cautious I won't even get on a boat, and I start my lawn mower with a battery, but the, "yank here" rope is still in place.
Nothing creepy about it, training kicks in, you keep the wings level and the airspeed constant, you're flying straight and level at a constant altitude so you have time to decide what to do next. You call ATC, he asks if you have a VOR, you say yes, he says "tune 115.7 and fly direct". You comply and 10 minutes later you're out of the soup and it's CAVU. This is almost as bad as textspeak.
 

ScottWang

Joined Aug 23, 2012
6,909
Something you should care about when you using super capacitor:
1. Using voltage -- The rating voltage of cap, if you using 2.5V then you better not to over 2V and the Vcap_total = 2V*6 = 12V, over 2V or 2.5V may be damage the cap, but it is no good for the cap, and it will make the life time shorter.

2. Equal voltage -- Each cap needs to in parallel with a resistor, the current of resistor about 0.12 mA, if you didn't add the resistors may not change anything in the short time, but someday, one of the weakness cap may blow up then its normal life time.

3. More protection -- For each cap in parallel with a 2.5V zener diode, and choosing the watts as more higher.

4. Note : If you have added the resistors and zener diodes and found any parts was damaged then the cap was lost the balance then you should using the ESR meter to measure the caps and change the bad cap.
 

BR-549

Joined Sep 22, 2013
4,938
I have no experience with Scaps.

Why not charge them like you discharge them? In series.

Monitor each cap voltage. Won't this tell you how your stack is preforming?
 
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