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Old 10-15-2015, 09:11 AM   #201 (permalink)
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Quote:
Originally Posted by oldtamiyaphile View Post
How long did you get out of if? I've got 14,000km and roughly 7300 starts on my supercap/ lead acid combo so far (from new).
I installed the lithium battery about two years ago and had the bridge rectifier failure about a month ago after replacing some slipping belts and one worn pulley that were basically limiting the alternator output. It always did that, but it was just getting worse to the point it would slip for a minute after every start (and I do many in London). After this I modded the alternator to supply 30A at idle, rather than trying to bump 120A.

Years ago I had a van and used to work as a mobile mechanic. I had a sealed deep cycle battery to start the car, power the tools and a mini fridge, which was good for about 2 years or 50000KM (they were about the same). Never had one dying, the capacity would just go down to the point the battery was no longer viable for my needs and this could be detected months earlier as the starting power would slowly go down. Starter batteries on the other side are normally fine one day and die unexpectedly overnight with a shorted cell.

My point is that super capacitors are viable if they replace the battery altogether, I don't think I would pay the premium just for the added longevity of the starter battery, when a smaller size deep cycle VRLA or lithium would achieve just as much, unless it was the case for extreme low temperatures.

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Old 10-15-2015, 01:04 PM   #202 (permalink)
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Keep in mind that as you get closer to peak capacity, the charging rate (amps/sec) on the caps tapers off. They're usually only a dead short when bone dry of capacity.
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Old 10-15-2015, 02:30 PM   #203 (permalink)
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Quote:
Originally Posted by cts_casemod View Post
The alternator will most likely be subject to a bit of s strain while charging a capacitor from 9V to 14V, for example. It's a 'dead on' short circuit.

I currently have 12.8V LiFePO4 battery on my car and even that ended up blowing the bridge rectifier due to the CV charge employed.

I say a hybrid would be the best approach. Say 10Ah lithium battery than can be had for $60 coupled with the capacitors to aid on starts. Probably a 200F would suffice.

I like the idea of a small solar panel to trickle charge... never used use, but I'm seriously considering it.
Alternator output is regulated, so the strain should not exceed rated output. Perhaps the rectifier blowing was coincidence.

I like the 10 Ah paired with the capacitor idea the best. I'd go with 6x 350 farad caps since they are most common and cheap kits are available on Ebay.

Solar charging would require a balance circuit since neither caps or LiFePO4 is tolerant of even slight overcharges. A small solar panel can easily exceed the parasitic drain of vehicle electronics plus self-discharge and over-volt both the caps and the battery.

I had a small solar panel over-run the LED balancers I have installed on my caps, but fortunately I discovered the problem before the voltage went much above rated.

Quote:
Originally Posted by cts_casemod View Post
My point is that super capacitors are viable if they replace the battery altogether, I don't think I would pay the premium just for the added longevity of the starter battery, when a smaller size deep cycle VRLA or lithium would achieve just as much, unless it was the case for extreme low temperatures.
I tend to agree. Supercaps can replace a battery on cars with extremely low parasitic drain, which is almost no current vehicle due to remote entry, car alarms, and radio. My truck has a 0.0057 Amp draw due entirely to the radio memory. If I took the radio out, I think there would be zero parasitic draw. A small solar panel can keep it topped off.

A supercap/LiFePO4 combo makes sense if the goal is to reduce weight, but LiFePO4 is not tolerant of charging in sub-freezing conditions.

When my Prius battery finally dies, I'll replace it with a LiFePO4 since it's located in the temperature controlled cabin, and the OEM replacement cost is something absurd like $250.
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Old 10-15-2015, 03:13 PM   #204 (permalink)
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For those interested in my self-discharge numbers:


8-31-2015 (posted earlier in this thread)
14.25v

9-02-2015 (posted earlier in this thread)
14.10v

10-15-2015 (today)
13.64v

45 days passed
0.61v lost
0.013v/day; .075v/day lost in first two days...Checking this time tomorrow will probably *NOT* show another .01v lost.
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Old 10-15-2015, 03:58 PM   #205 (permalink)
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Old 10-16-2015, 08:48 AM   #206 (permalink)
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Quote:
Originally Posted by Enki View Post
Keep in mind that as you get closer to peak capacity, the charging rate (amps/sec) on the caps tapers off. They're usually only a dead short when bone dry of capacity.
I was just looking at one in farnell:

XB3550-2R5307-R - BUSSMANN BY EATON - CAP, SUPER, 300F, 2.5V, SNAP IN | Farnell element14

...with 0.006Ohm, if the capacitor is at 11V after a start I = U/R

I = (14.4-11)/0.006
I = 566A

I don't suppose many car alternators can provide that nominally. Of course there are many other losses on the system, but those can't be quantified, they vary widely (alternator impedance, engine speed, cabling...)


Quote:
Originally Posted by redpoint5 View Post
Alternator output is regulated, so the strain should not exceed rated output. Perhaps the rectifier blowing was coincidence.
Standard alternators (excluding special vehicles and marine applications) are voltage regulated, not current. They rely on the high impedance of lead acid batteries for protection. Current is reduced if the regulator temperature is too high, but provide no protection against short term overload conditions.

The rectifier could very well be coincidence, but an empty lithium battery and a constant voltage charge source are asking for trouble, regardless.


Quote:
Originally Posted by redpoint5 View Post
I like the 10 Ah paired with the capacitor idea the best. I'd go with 6x 350 farad caps since they are most common and cheap kits are available on Ebay

Solar charging would require a balance circuit since neither caps or LiFePO4 is tolerant of even slight overcharges. A small solar panel can easily exceed the parasitic drain of vehicle electronics plus self-discharge and over-volt both the caps and the battery.

Curious if anyone tried audio caps for that purpose (the ones uses with subwoofer's)?

Solar panels often have a regulator circuit except the very smallest ones, for which the BMS can actively shunt the excess energy and balance the cells at the same time, so this isn't particularly troublesome.

Quote:
Originally Posted by redpoint5 View Post
A supercap/LiFePO4 combo makes sense if the goal is to reduce weight, but LiFePO4 is not tolerant of charging in sub-freezing conditions.
That depends how much the subfreezing is. My battery gets warm after 5seconds at 3C to pre heat the glow plugs and 2-3 seconds at 8C to crank the engine. Further charge will warm it up a bit more. This may cover the typical usage. If not ,there are ways around it. For minus 20C or below it might be troublesome, even for lead acids. Here the capacitor would be a welcome extra.
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Old 10-16-2015, 09:34 AM   #207 (permalink)
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Quote:
Originally Posted by cts_casemod View Post

...with 0.006Ohm, if the capacitor is at 11V after a start I = U/R

I = (14.4-11)/0.006
I = 566A
Is that the single capacitor impedance, or the total impedance of 6 capacitors added in series?

Quote:
Standard alternators (excluding special vehicles and marine applications) are voltage regulated, not current. They rely on the high impedance of lead acid batteries for protection. Current is reduced if the regulator temperature is too high, but provide no protection against short term overload conditions.
I believe you, but I'm going to verify this sometime when I am messing around with caps and starting again. The alternator in my TSX varies output modes depending on electrical demands including the state of battery charge.


Quote:
Curious if anyone tried audio caps for that purpose (the ones uses with subwoofer's)?
Audio caps tend to be much lower in capacity and much higher in price.

Quote:
Solar panels often have a regulator circuit except the very smallest ones, for which the BMS can actively shunt the excess energy and balance the cells at the same time, so this isn't particularly troublesome.
The cheapie panels I see on Amazon for $20 don't have any regulation, but balance circuits are fairly cheap for the common supercap sizes on the market and can easily handle a few watts of extra juice.

Quote:
That depends how much the subfreezing is. My battery gets warm after 5seconds at 3C to pre heat the glow plugs and 2-3 seconds at 8C to crank the engine. Further charge will warm it up a bit more. This may cover the typical usage. If not ,there are ways around it. For minus 20C or below it might be troublesome, even for lead acids. Here the capacitor would be a welcome extra.
I had wondered how much of an issue freezing was considering that the battery will quickly heat up with use. I'd still be hesitant to run it during the coldest days in the Portland area, which might be 15 F. I'd have no concern if with the battery in the passenger compartment.
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Old 10-16-2015, 11:25 AM   #208 (permalink)
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Here's a couple of ideas I was thinking of trying when I get around to putting caps on my Bug (I have to rebuild the engine first ).

First, why not hook the caps directly to the starter, but put some resistance between it and the alternator (and any battery). That way you get full power to your starter, but the caps don't put a strain on your alternator.

Also, why not have two resistances. One could be activated by a high power relay/contactor when you hit the brakes. This would be low resistance (or no resistance), and kind of work like a hybrid system, causing you to bog down your alternator, but only while stopping. The other route would be high resistance continuously (or no connection at all).

A head lamp or series of 12 or 6V incandescent lamps would likely work. The neat thing would be that it would offer more resistance when there's a high voltage difference since the lamps would heat up and cause more resistance. But as the voltage levels out they would heat up less and lose some of their resistance. The lamps would also allow you to charge your caps from 0V without effectively short circuiting your electrical system.

I do prefer the idea of using caps over lithium or lead acid, but because it gets very cold here. It's common to see temperatures as low as -40 F (-40 C). (Yes, that's forty degrees below zero !)
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Old 10-16-2015, 01:09 PM   #209 (permalink)
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+1 car audio caps being completely worthless, even in car audio applications.



There's just not enough capacity in car audio caps for them to do what they are supposed to do.
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Old 10-16-2015, 02:15 PM   #210 (permalink)
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Capacitors in audio. That makes me think of some kind of filter to filter low frequencies and keep high frequencies for tweeters. That way more low frequency power can be delivered to the woofers. Likewise you could put inductors on the woofers in order to filter out the high frequencies. But for maintaining a voltage due to excessive current draw... Ya, you'd need some ultracapacitors for that. And even then, sounds like a bandaid fix for not having a powerful enough alternator and would likely still not work unless you got a high amp alternator.

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