Here is some news in the supercap/battery dept. It is old but essentially:
“These guys have built high-performance supercapacitors out of graphene that store almost as much energy as a lithium-ion battery. They can charge and discharge in seconds and maintain all this over many tens of thousands of charging cycles.”
You might want to get some graphene oxide, hydroazine, and a ultrasonic jewelry cleaner. 
It looks like resistors can be used for very slow rates of charge but for this application an active balancer is needed. I think some of the packs sold do not have balancing but that can greatly reduce their life span. And that’s the main reason behind building my own pack. Maxwell’s look like a good brand.
Jeff
Maxwell is a good brand for sure. I thought you only shortened the lifespan if you went overvoltage, and you are more likely to do that since you could in theory have an oddball low voltage cap. I could be wrong, but that is what I remember reading, along with Maxwell’s ± number was more on the postive rather then the negative side because they had improved manufacturing capabilities…
However, I missed this announcement.
http://finance.yahoo.com/news/sunvault-energy-graphene-based-supercapacitor-151000747.html
I didn’t see when they said they were going to start production though.
Sean, nice article. It’s may understanding that caps can not be made exactly the same so a small difference in leakage current, for example, can cause one cap to have a higher voltage than another cap. No problem until you exceed the voltage rating. At that point the life span of that cap is going to be shortened. Remember that we want our bank to last 20 or 30 years.
But I agree a better built cap will make a better bank of caps. All the balancing schemes have their problems, dang it! The active balancer works better at moderate to low charge rates. It looks like over rating the bank will work the best for this application and that might explain why I don’t see a balance circuit in this type of bank. So just add an extra cap or two for safety. That lowers the average voltage that all the caps see and gives a bit more room for that one or two caps that will see a higher valtage.
I’m tapped out for tonight…
Jeff
That is my understanding too.
With 6 caps you have a 16.2v rated potential ± 10 or 20%… Maxell was saying it was more likely to be on the + side because of improvements in their manufacturing. But if you are charging at <14.58v you are outside the -10%
Since it is a 1 off project, and you want it to last 30 years. Rather then derate the array, it might be easier just to test the caps.
I would email Maxell tell them what you are doing, and ask if that is the correct/best way to accomplish it and ask how you check if you are within tolerances. I assume you just charge them to 2.43v and hold them there to see if they bulge or overheat.
They will know for sure.
Well, I’ve been burning up scratch paper on math equations and they vary in complexity but this one is the simplest one that I found on Maxwell’s web page. It doesn’t account for RC so I would consider it a less than minimal capacitance.
WARNING: I don’t know what I’m doing here… Just winging it with some equations I found on the Internet…
Csys ------- is stack capacitance
dt ---------- is discharge time
Imax ------ is Power / Vmin
Imin ------- is Power / Vmax
Iave -------- is (Imax + Imin) / 2
W ---------- is Watt
f ------------ is farad
Vmin ------ is the lowest voltage the inverter will work at
Vmax ----- is the highest alternator voltage but not higher than the highest inverter input voltage
I recall that some alternators can produce 80A and charge at 14.2Vdc. But lets be optimistic and call it 14.5Vdc.
So:
W = A x V
W = 80 x 14.5
W = 1160
So if we had a a extremely efficient inverter we could call out a 1000w inverter. For the sake of calculating that’s what we will do. The clone engine may not be able to supply the needed power at this level but it might be possible to have two engine/alternator units powering the inverter/supercapacitors.
Bellow are the specs for a Xantrex (sounds like some kind of ED medication) inverter:
Item 806-1210
Input V = 10.5 to 15.5Vdc
W = 1000W but some times 900X is written.
W surge = 2000W but some times 1800 is stated
It would be a nice advantage to modify the alternator regulator to put out 15Vdc because that would increase the usable capacity of the stack. The usable power in the stack is only from 10.5 to 14.5Vdc, ouch! All the power below 10.5vdc can not be used in this application but that stored energy can be used for another application like charging a brainiack phone, led lighting or a blower fan. The specs state that the inverter has an over-voltage shut down at 15.5Vdc. This would allow a simple over-voltage protection scheme with the addition of an interposing relay before the supercapacitors. This would need to be shunted during start up.
Back to the math…
2200W = surge
2000W is the inverter surge but I added 200W for inefficiency. I’m also assuming that the surge will only last one second. On the plus side the alternator should contribute some current during the surge.
dt = 1 second (that’s how long I’m guessing the surge will last)
Vmax = 14.5
Vmin = 10.5
Imax = 2200 / 10.5 = 210
Imin = 2200 / 14.5 = 152
Iave = (210 + 152) / 2 = 181
Csys = Iave x (dt / (Vmax - Vmin))
Csys = 181 x ( ( 1 / (14.5 - 10.5 ) )
Csys = 181 x ( 1 / 4 )
Csys = 181 x 0.25
Csys = 45f
I was planning to use seven capacitors. So:
7 x 45 = 315f supercapacitor.
With another equation I came up with about 600f supercapacitor but another equation came up with about 300f. The equation that considered RC came up with the 600f but I just guessed at the internal resistance of the stack, the R part of RC…
Now after all that time put into the math I’m considering Maxwell’s super duper 3000f with very low internal resistance!!! No need to do much math at that capacity but they would cost about $$$$500… !!!
Ouch,
Jeff
I meant to reply earlier. I was going to go through all your math, but I haven’t had time so…
Xantrex is now owned by schneider electric of canada.
45F capacitors in series gives you 6.4F of capacitance, but a higher voltage.
In parallel it gives you 315F but at the 2.7v
This page explains it fairly well.
Hi Sean,
45F is for the stack. If seven caps are used they would need to be 7 x 45, hence 315F.
Jeff
Oh by stack you mean the whole array, like 7x7?
You would be better off to have 1 string of the 3000F caps, it is about the same price (maybe less) and gives you 428F.
The are 60.40/ea so about 422 vs ~467for the 350s (you get the volume discount for 50 that lowers the price)
Hi Sean,
We’re getting close now. I was going with 7 caps in series. Thinking about the big 3000 top of the line ones but $70 ea at Digakey or how ever they spell their name.
Time for me to pull the plug…
Good night everybody,
Jeff
Digikey. Thief River Falls Minnesota. Actually located next to Artic Cat.
This is the only thing I have understood about this thread. Hahaha But watching it closely because it has my curiosity.
I would probably wait for price drops too. I would only go with 6 though, the inverter can’t handle more then 15v, and it would increase the capacitance by 15%.
I forgot that, i wonder if you can pick them up from digikey and save a LOT on shipping. I think they have a hazardous material shipping charge.
Here is a guy with a do not try this at home demonstration on just making 120v with the alternator…
I wouldn’t try it, he is getting 300hz+ which could break a few things, although a rectifier should work…
The other important note is you can put resistance in the field coil circuit to bump up the voltage output. He is using a variable resistor… I saw another circuit that used a xenor diode too.
I think this scheme would work nice but I have to cross it off my list. A bit too expensive for me. Need the resources for other projects and don’t want to depend on an expensive (in my book) inverter.
For me, it’s best to leave the surge issues for the big gridster and I’ll focus more on electrical items that run on DC with no major surge and low power.
I do like the super cap idea and I might use them to power up the rotor coil so no need for a battery to get DC, or three phase ac, out of an alternator. Might even do that with a large common cap. More math needed. A super cap might be the ticket to power my small blower but more math and I need to measure the current draw of both items… Fun, fun, fun…
I wouldn’t cross it off my list. I would just put it at the bottom… Revisit it in a year or two. You will see more favourable numbers. The industry is going through a fairly major growth phase right now.
Some toys showed up for when the snow starts to pile up. I hope work slows down January and February.
Another new toy showed up…
Claimed to be NOS but maybe an old stock rebuilt. Odd that the older style is much easer to find and seems to be cloned. Sometimes the advertised 12si is really a mixed up 10si/12si…
Sweet, Jeff! Great find!
…
So what is it…?
It’s a blast from the past… 12si alternator. Not the best choice but fine for what I want… Pump up my smartphone with chartric and light some led lights.
The used 10si, that i was going to use, was used for an alternator conversion for my new 60 year old tractor… 
so that’s why this showed up.
These two responses seems to be saying opposite things, so which is it?
Obviously there is no point in installing a ‘supercap’ on a lawnmower, if it is truly going to leak down after 3 months, or even 3 days, as madflower69 seems to suggest~~~
If I’m going to jump-start my lawnmower, I may as well leave out the battery & the ‘supercap’, and save those expenses altogether. I’m not trying to become an electronics expert, but if the leakage is truly somewhere around 3 days, I see no point in having ‘supercaps’ in that application. It is true my lawnmower may sit for months at a time.
Another quick question, the video of the motorcycle mentioned ‘cold starting’ at 24F, which is great, but what about heated applications? as if ‘engine mounted’ next to the starter itself, temperature might be 300F in that location, would the ‘supercaps’ work well in that environment?
Just curious…
Oliver
I’ve been jumpstarting my mower for years. It’s saved me quite a bit of battery cost, and really not that hard to do…
