[hyundave]

As some of you know I'm now at Virginia Tech and sadly don't have my 2008 elantra with me =[. It's back at home in my dads garage. Every week or two, he goes and takes it out for a bit just to keep the engine moving occasionally. Well the past three times he's gone to start the car, it's been dead so he has to jump it. One person has said it's because I have a subwoofer. I don't think that's right at all.

What I do think it could be is my capacitor. It's a 2 farad cap that's hooked up to the battery (and the 2 amps are hooked to that). Do you guys think my problem is the cap sucking up power? I never had a dead battery before but I also drove my car almost every day so it would have gotten a charge.

What do you guys recommend I do? Get the battery checked? (it's only 1 1/2 years old) Or should I just remove the cap? (If so, whats the best way of discharging it? Or do I even need to if it hasn't gotten power?)

Hopefully I'll be bringing my car down after Thanksgiving and having her here. Thanks guys

 

[left channel]

If he doesn't drive it very long the battery will not get a full charge. Do you have a charger that he can hook it up to?

 

[qwertydude]

Well one thing is the battery may have been on its last legs considering it's already 4 years old. And generally taking a car out for a quick spin every now and then is actually worse than letting it sit. The reason is quick spins don't let the engine fully warm up so you end up letting water, and combustion chamber byproducts build up in the oil raising its acidity levels.

Not only that but the amount of energy it takes to start a car isn't fully recovered til about 15 minutes or so of driving so that could also have been exacerbated with the quick spins.

Lastly, once a car battery has dies, it never is the same again. The plates can warp and lead can flake off and settle at the bottom of the battery thus creating a low level shorting in the cells that can drain the battery even when sitting. It's likely not you subwoofer just a confluence of those two previous events.

 

[JeremyC]

I've been through that before. The battery is probably still ok.

Being prior military I had to leave my car parked for 1 to 4 months pretty often.

A new battery will make it a couple of months without a problem. give it a couple years of use, and it won't last that long.

As for your dad starting it. Once its dead it takes a while to get charged back up. Add in a few more months of setting, and it will take even more to get it powered back up.

Have him hook up a charger and leave it setting for a while. Or start it and let it run for at least an hour. (charger would be better)

And if you have to park it in the future, look into one of these.

Northern Tool - NPower Battery Charger/Maintainer - 2 Amp customer reviews - product reviews - read top consumer ratings

 

[MarkZ]

It's not the capacitor, unless it's broken. But that's probably unlikely.

I think the other guys are right. You could consider installing a high current knife switch or a battery buddy to disconnect your battery when the vehicle is going to sit.

 

[hyundave]

Well I just bought one of these guys as a just in case... Amazon.com: Stanley J309 300 Amp Jump Starter: Car Electronics

 

[RNBRAD]

It is absolutely your capacitor, or at least partly if not mostly to blame. Capacitors will bleed or dissipate energy based on their low internal resistance just as a battery does or anything that stores energy. I have about 5 farads of capacitance and my vehicle will last about a week if im very lucky. I have to keep it on a charger constantly cause caps will drain your battery(s) quick. This is one of the reasons I quit using caps or reluctant to do so in some of my other systems. It's a benefit vs advantage that needs to be weighed. Love the benefits but this is a real disadvantage most people don't know about.

On a side note, get a Battery Tender JR, best small charger made. I hard wired a plug for easy plug access in my fender well. Something to think about when you don't drive daily and use capacitance.

 

[MarkZ]

It is absolutely your capacitor, or at least partly if not mostly to blame. Capacitors will bleed or dissipate energy based on their low internal resistance just as a battery does or anything that stores energy. I have about 5 farads of capacitance and my vehicle will last about a week if im very lucky. I have to keep it on a charger constantly cause caps will drain your battery(s) quick.

A capacitor has a very small leakage current. Typically on the order of microAmps. If your capacitor's leakage current is high, I suspect that it's faulty.

BTW, this is easy to measure. Go out and measure your leakage current and you'll know if your capacitor is functional or not.

 

[RNBRAD]

A capacitor has a very small leakage current. Typically on the order of microAmps. If your capacitor's leakage current is high, I suspect that it's faulty.

BTW, this is easy to measure. Go out and measure your leakage current and you'll know if your capacitor is functional or not.

How about 5-20 micro-amps per micro-farad? This is average range for the large caps we use in car audio. So if your running 2,000,000 uF, do the math. I'm sure that anyone that runs any amount of capacitance beyond 1 farad or so can attest to the standby longevity of their batteries charge. I'm sure some of these cheaper caps are even worse.

 

[MarkZ]

How about 5-20 micro-amps per micro-farad? This is average range for the large caps we use in car audio.

No, you got that number off a website that was talking about small electrolytics in general. I have google too.

Have you ever actually measured it? Or are you just relying on an irrelevant number from some random website? Seriously dude, GO OUT AND MEASURE IT. All you need is a DMM and a little know-how.

 

[SHAGGS]

Trickle charger, aka Battery tender, and a simple breaker style switch to the cap/amps. Or just pull the fuse.

https://www.google.com/#hl=en&tbo=d...79c1db411a11f2&bpcl=38093640&biw=1688&bih=818

 

[chad]

Toss a battery tender on it /done.

 

[RNBRAD]

No, you got that number off a website that was talking about small electrolytics in general. I have google too.

Have you ever actually measured it? Or are you just relying on an irrelevant number from some random website? Seriously dude, GO OUT AND MEASURE IT. All you need is a DMM and a little know-how.

Good idea: Though not sure it really matters or a need to prove measure anything. I have real application experience and this subject is common knowledge other than to those that don't have much experience with capacitors. Get some guys in here that use a few farads of capacitance on a single battery and have let their cars sit a few days off charge and our conversation is mute. I started using caps in the early 90's which was after Richard Clark first used them in his GN. I've alway used Mallory and Esoteric, so I don't use junk. Anyone that's been an installer and has dealt with caps knows that a cap thats sits for just a few days in some cases hours, knows it's going to spark if you don't charge it with a resistor "right before install". I've experience the exact problem the OP is having and have for 20yrs. Remove the caps, problem gone!!! Most cars will sit 3 to 4 weeks without a problem. Add some caps, cut that in half if not less.

Just for the sake of conversation and because I have a test bench, thought I'd pull out a cap and test it. Not sure the accuracy of the testing but interesting non-the-less. Here I have a Mallory cap, 31,000uF, 25vdc rating. I use these on solely on every processor as well as the head unit. I also have a small AGU Interstate 12v battery charged and ready to go.

Battery and cap voltage (made sure cap held full voltage of the battery)

I'm leaving battery hooked up to cap and monitoring the amperage pull of the cap. This is the stabilized reading I got after I held in place for a litter over a minute. It spiked initially, not sure why. It stopped around 27.8 and fluctuated up and down at that point for several minutes.

I let the cap sit in place for 1 minute minus the constant charge of the battery. Starting voltage was 14.86, after 1 minuted it dropped to 14.75.

So saying a capacitor has a very small leakage current, while this may be true in the short scheme of things, but long term it will become a problem such as the case for the OP. So when he asks if this is the problem, no doubt in my mind. Also, this is something car manufacturers have payed close attention to with all the electronics in the newer cars, as capaicitance with electronics has increased so has battery leaching as the car sits. Mercedes Benz with all their accessories and electronics on their loaded cars use 2 batteries to overcome this problem.

Here's some more irrelevant numbers from a random website.

 

[MarkZ]

Interesting results, but I don't understand them. First of all, CGS is crap. So, fine, we can examine the properties of this capacitor, but it doesn't necessarily extend to a better one. Second, Mallory rates leakage current for that capacitor to be 4mA with 14.8V applied, so I suspect you might have a dud on your hands. And third, leakage current usually increases with the square root of capacitance in cans... so if we extrapolate to 3F, that brings you to about 40 mA. Which is about an order of magnitude higher than what I've seen... but regardless, if that number is right, it's still not much to lay the blame on the capacitor (again, unless it's faulty). A reasonable car battery should be able to withstand 40mA for weeks.

 

[GlasSman]

Well to OP.....my suggestion is to return the electrical system to STOCK by removing the main power wire fuse until the problem is sorted out....could be a problem with the cap wiring or any number of things causing a draw.

I haven't used caps since 1996 when I realized they didn't much except make cap manufacturers generate sales.

I would go one step further and remove all after market gear.

If the vehicle is stranded somewhere or needs service your friend will appreciate having his gear safe.

 

[sqshoestring]

So pull the fuse(s) to the amps, mine is on the battery and 2 seconds to pull out. Better yet pull the battery cable but it can trash your HU and processor settings.

Batteries do loose charge in storage naturally, all the time.

Yes best way is a maintainer I bought one at walmart and it works fine, iirc it is 1 or 2 amps you can set it to. It shuts down at full charge by itself so you can leave it on indefinitely. Or you can plug it in every 2-4 weeks for a day/etc.

I do care for stored cars in the winter at times, I start them and let them run about 15-20min then drive them around a short trip. I don't worry about driving them much if they are stored in a dry place and just move them some to use the transmission and brakes. Most people don't insure cars for road use when in storage lol.

I've had all stock cars deplete the battery in storage, not knowing why. Sometimes a battery just is not that good for whatever reason as well. With that you either charge it all the time and/or disconnect the battery. Some of my own cars I take the battery out and store it in an area that does not freeze, it is much nicer to the battery. I always do that with boats for example, lawn equipment, etc.

Seems like it would be easy enough to unhook the cap for storage anyway, if you think or test that to be the issue.

 

[RNBRAD]

Interesting results, but I don't understand them. First of all, CGS is crap. So, fine, we can examine the properties of this capacitor, but it doesn't necessarily extend to a better one. Second, Mallory rates leakage current for that capacitor to be 4mA with 14.8V applied, so I suspect you might have a dud on your hands. And third, leakage current usually increases with the square root of capacitance in cans... so if we extrapolate to 3F, that brings you to about 40 mA. Which is about an order of magnitude higher than what I've seen... but regardless, if that number is right, it's still not much to lay the blame on the capacitor (again, unless it's faulty). A reasonable car battery should be able to withstand 40mA for weeks.

Well first off when you say a Mallory CGS capacitor is crap you don't know what your talking about. Your probably one of those ESR guys, lower is always better.

Here's a voltage reading on the same bad cap 9 hours later. Started out at 14.86. Not sure the total energy leakage over this period of time. I'm sure it would be greater if it would maintain a constant flow of energy to it. Your problem Mark is you try to take a number like 40uA and try to incorporate that into the big picture. You've never experienced it, your trying to imagine it. I'll show it to you in real time and I can do this test with any and all capacitors. Why? Caps are horrible storage devices. A battery on a shelf in a store will last many months if not years, in a car it will last a few weeks. Why? even with no active devices in a car, the caps in the electronics will deplete the battery quicker. I really don't care about numbers, means nothing to me cause like I said, I used caps for years, still use them and know exactly how a capacitors works. This cap below I bet sparks when I plug it up to the battery. I don't need numbers to explain it, it's reality, actuality, these things leak some real energy and this thing is a baby. All I can say for you is you need to hang out with some guys that use caps or you need to go buy some and play with them. Then that little 40uA constant number turns into one hellofa weld in a few hours. It happens time after time, cap after cap. I honestly think your experience comes from reading a book and not the laboratory. Like I said I've used caps for 20 years and have installed them in countless system over this time period. Take it from a guy that has real world experience with these things. I'm not here to BS you!! I can pull another capacitor I can do this test over weeks, doesn't matter to me. I can go buy a new one, cept these Mallory's are not cheap.

[/IMG]

 

[MarkZ]

Well first off when you say a Mallory CGS capacitor is crap you don't know what your talking about. Your probably one of those ESR guys, lower is always better.

Wait, doesn't Mallory even call it their budget line?

All I can say for you is you need to hang out with some guys that use caps or you need to go buy some and play with them.

I honestly think your experience comes from reading a book and not the laboratory.

I really don't care about numbers, means nothing to me cause like I said, I used caps for years, still use them and know exactly how a capacitors works.

And you're the only one here with first-hand experience.

We get you guys in here every so often. You think you're king **** because you're an engineer, but you don't realize that you're on a forum full of engineers. Take some of your Mallory money and buy some humility.

Anyway, it's a shame you don't care about numbers, including the numbers on Mallory's own data sheet. I found this on their own website:

2.6. LEAKAGE CURRENT -

(DCL) MAX 6 MA.



Leakage current (DCL) is the DC current flowing through the capacitor. During application of voltage to new capacitors the DCL decreases and will stabilize in from 1 to 10 days to a small fraction of the value measured after five minutes electrification.



DCL shall be tested under the conditions of Paragraph 2.8 as follows:



Pre-conditioning. Capacitors shall be preconditioned for DCL current measured by applying rated working voltage for 30 minutes minimum at least 24 hours and not more than 48 hours before test.



Measurement. Sufficient DC voltage shall be applied with a steady, regulated source of power across a series combination which includes the capacitor being tested, a milliammeter and a current limiting resistor of a value which permits rated DC voltage to appear across the capacitor within one minute. The maximum DCL current after five minutes electrification time at rated working voltage and 25°C + - 5°C shall not exceed the value as determined from the equation: I = .006ÖCV Where I is the DCL in milliamperes, C is the measured value of capacitance in µF, V is the rated DC voltage.



In no case, however, shall the DC leakage current exceed six milliamperes at +25°C.

 

[GlasSman]

I used caps for years, still use them and know exactly how a capacitors works. i

What TRUE benefits do you see in using a stiffening cap?

I blindly installed a 1 FARAD cap back in the 90's....but after doing some tests I could not see one bit of benefit....I prefer to keep electrical systems as simple as possible.

These devices have not been considered a neccesary component in a 12 volt electrical system for more than a decade now.

 

[MarkZ]

well, I'd like to hear from some of these regulars on here about how caps are draining their batteries, and not take either one of you guy's word for it, but some other random dudes who have used caps.

seems to me that a cap is an active drain, much like a digital clock or radio preset circuit, and the larger the cap the higher the potential for drain.

It is. But so is your head unit. So is your ECM. There's a lot of stuff in a car that's designed to draw current when the car is off, usually because it has to maintain a memory of some sort. What's important here is how much of a contribution the cap is providing to the total drain on the battery.

and I have heard that these big car audio caps "go bad" but then, that usually would mean shorting or an open condition, or plain exploding like smaller caps can do.

Yup! They go bad, they even explode with overvoltage. We've had a couple posts in this forum over the years that have talked about that.

and I am unaware of what hardware one might use to test a big cap if it still meets it's capacitance targets, or if it has excessive drain coming off of it. My multimeter craps out at 200uf, so....

V(t) = V(0)*exp(-t/RC)

That's how you can compute C with a meter, because the other variables are all known. Initial voltage: V(0), voltage at time t: V(t), R: drain resistance.

If you want to measure leakage resistance, you can use the same equation only solving for R. Unfortunately, R is a function of V(t) (among other things), which makes it much harder to solve, but if you ignore R's dependence on that other stuff it's easy.