Maxwell Ultra-Cap's/Lithium cells hybrid pack - Page 4 - RC-Monster Forums

BrianG · 12.04.2006, 06:02 PM

Yeah, or a high-output alternator and a second battery. :(

I was actually looking at regulating the lights to a solid 12v even though they won't be quite as bright. That way, they won't dim when the electrical system goes from ~14.4v to ~12v when the bass hits. But a linear regulator would be large and toasty.

zeropointbug · 12.04.2006, 08:55 PM

Brian, i have been thinking. You know when you said all that matters is the average power for a ultra cap... that still didn't sit right with me. So i was thinking is it the term 'mean', the mathematical term, it's kind of like average. Only in this app, I would be higher than average power output (from battery).

Do you know what i mean when i say the 'mean' discharge, not the average discharge? It would be a little higher than average.

I am not totally sure if thats the term, so if you think you know what im talking about, if you could help out?

BrianG · 12.04.2006, 09:13 PM

Well, IIRC, "mean" is the physical center value of a dataset, whereas "average" is the sum of the values of the dataset divided by the count of numbers in the dataset. If this is correct (and please let me know it it's not), what do you mean (no pun intended :))?

BTW: Where did I say that? I'm trying to think what I might have been talking about...

zeropointbug · 12.04.2006, 10:50 PM

(no pun intended) lol i was going to say that :005:

I guess it's not mean, it must be called something else. It will come to me, some like RMS, but not...

BrianG · 12.04.2006, 11:03 PM

Quote:

Originally Posted by BrianG

OK, I think I'm going to order several of these caps and make a "2s2p" bank for a total of 11v and 1F and install it on my Jato for giggles. All I need is an Eagletree to take some readings on voltage drop. I guess I could strap my Fluke meter on top and set it to record min/max/average voltages...

Well, scratch that idea. After looking at those caps a little more closely, I started to wonder if the terminals and internal conductors could pass the kind of current I'm looking for. So, I finally found a datasheet and found that the rated continuous current is so low that it would be all but useless. They are designed for long, very low current discharge (in the mA range).

zeropointbug · 12.05.2006, 12:27 AM

Really? I would have thought that they would do fine as far as current.

Maxwell Technologies haven't replied yet on the email about the 120,140,310,and 350 Farad medium size cells. Im starting to think that the smallest cell, the 120 Farad cell should be enough. Enough to keep the voltage of my pack at least 16.0 volts (16.5volts nom.) under normal driving, which is bashing for me. But you know what, it would be so cool, cuz if you let the truck sit a couple seconds you would be able to bring the system up to no load voltage, which would be 17.25 volts (around 3.45 volts/cell), and then get a huge burst of NOS. :026:

I just hope the caps are around 20-25 dollars a cell.

BrianG · 12.05.2006, 12:49 AM

Quote:

Originally Posted by zeropointbug

Really? I would have thought that they would do fine as far as current.

Yeah, and it makes sense really. Look at the caps used for car audio. They are only 1-1.5F typical and rated for 20v, and they are huge and heavy. Well, the connections and the internal plates are designed to pass heavy amounts of current. The small caps I was looking at are WAYYYY smaller and lighter even discounting the voltage rating. This is due to the thinner conductors used internally. High burst current was compromised in favor of small size and weight. Makes sense since these are designed for memory backup applications. This datasheet is what I was looking at (page 2, table at the bottom headed by "Standard Ratings").

zeropointbug · 12.05.2006, 02:15 AM

Well, what are you saying? That a few mA isn't enough to throw around your Jato?
LOL

I really want to try this, it appears so promising for my setup. The A123's cells will last and last, they will run super cool and low discharge; this would allow them to easily reach over 3000 cycles. At 25 degrees, after 1000 cycles at 100% DOD they are still at 95% capacity retention, and they say the internal cell resistance goes down over use!

aqwut · 12.05.2006, 03:10 PM

woah... 1 farad can be that small cap... that is cool

BrianG · 12.05.2006, 04:12 PM

Quote:

Originally Posted by aqwut

woah... 1 farad can be that small cap... that is cool

Yeah, it is quite small. Because it is rated for such a low voltage, the plates can be very close together; and because the current rating is so low, the thickness of the plates can be ultra-thin.

I think that if I tried to use these, they would heat up and expand/pop before too long. Plus, if you look at the ESR, it is kinda high compared to caops designed for high currents...

zeropointbug · 12.05.2006, 09:45 PM

Have you ever had a cap blow on you?! I have, it's not fun, reverse polarity... the end vent opened right up, filled a large portion of my room with steam from the electrolyte. Very stinky :020: :036:

Ya, the new Super-Ubar-Ultra Caps from that group from MIT uses Nano carbon tubes like hair that drastically increase capacity and current. They claim 60Wh/kg gravimetric density. EStor, another company claim i think ~120-150 Wh/kg, IMPRESSIVE. For a capacitor.

BrianG · 12.05.2006, 09:57 PM

Oh yes, I've had a couple pop. One was because of too high voltage - I could actually see it expand until it vented. It happened before I could shut the power off. The other was from reverse polarity. That was a 1,000uF 50v cap in a power supply. Yes, they do stink.

zeropointbug · 12.06.2006, 09:52 AM

BTW, I now going to give in and get the DX 2 Spektrum Radio. I don't really like running out of room after one small town block. How are they for range?

BrianG · 12.06.2006, 11:04 AM

I've had good luck with my DX3 system. The range is about as far as I can effectively control it; ~100 yards at a guess give or take. Although, I always try to make sure the receiver is as far away as possible from the noisy motor wires to avoid potential interference problems.

glassdoctor · 12.06.2006, 11:38 AM

I have never had a problem with range with any FM or my Spektrum system... you lose perspective on the car before you run out of range as Brian said.

But, long range is not the Spektrum's strong suit actually. A good regular FM system should have better range. That's why the plane guys are not converting to DSM. That's what i am told by the plane guys at the LHS, when I asked why they aren't using it.