capacitor help-- supposed to discharge itself?!?

[BerniniCaCO3 10+ year member]

Mind you I've never used a capacitor before, but I've read the literature, remember my high school electricity&magnetism, and believe I get it.

I just got a brandy new capacitor in the mail yesterday, was going to install it tomorrow, decided to charge it today. Err, apparently any sort of url link is prohibited, but the model is a Pyle Audio "PLMRCAP18 1.8 F 20V Round Marine Capacitor" bought from amazon.

It IS a bad sign that in several places on the package and on the capacitor itself, it calls itself a "maring" capacitor instead of a "marine" capacitor....

Anyway.

I charged it as directed: I hooked it up to my battery, in parallel, (positive to positive, neg. to neg.) with the resistor in series, which as I understand, limits a current spike especially when the capacitor is at 0V and 0ohms resistance and the battery is at 12.5x volts.

It very rapidly climbed to 10.2x volts and stopped there, presumably the resistor was consuming 2.3v.

At this point I took the resistor out and hooked the battery up directly, and the capacitor instantly came to equilibrium with battery voltage.

Now, I unhooked it, thinking it fully charged. I decided to check the voltage with my own voltmeter. It was , really just a few seconds after unhooking from the battery, now at 10.xx volts. I held the voltmeter to it, and watched the voltage drop quickly, to 9.xx volts, 8 volts... Just in case the voltmeter itself was consuming all the power this 1.8Farad capacitor could supply, I let it be and came back in 5 minutes. At this point it was down to .73 volts and holding steadyish.

So at the very least, open-circuit, NO load WHATSOEVER, terminals not connected in any way, my capacitor dropped of its own accord from 10 volts to less than 1 in between voltmeter measurements just minutes apart.

This makes the idea of precharging a capacitor absolutely laughable; it will discharge itself to .7 volts before I've even half finished soldering its connections!

Is this normal? For capacitors to leak this quickly internally? Or should that capacitor have held some charge for at least a few minutes... if not days, frankly, given a claimed 1.8Farads.

I'm fearing that there's an internal short that is both consuming energy, and perhaps seriously castrating the actual capacitance to be much less than 1.8F

I'm thinking I need to return this.

And buy a different capacitor (quite open to advice) that doesn't call itself a maring capacitor and sometimes a marine capacitor.

But I thought I'd check with you guys first before I cry for my money back, just in case this is normal behavior, seeing as I'm really not experienced working with capacitors.

And if I do need to return this, what brands/models have you found highest in quality and most durable?

In point of fact this is not going to supply an amp, but an electric fan, and it's going to live in the more hostile engine compartment; tucked behind the front fascia furthest from the engine's heat but not immune to moisture, if that influences advice.

I was also reading up on electrolytic capacitors, which this Pyle capacitor is, and apparently they're a little more delicate than solidstate (if that's the technical term-- not containing salt water anyway) capacitors?

Who makes a non-electrolytic capacitor, if in fact they're more durable?

Click to read more...

 

[Bettr n' Revrse 5,000+ posts]

Get rid of it... just add a batt

 

[CHEMMINS 10+ year member]

Dude...a cap charges and discharges instantly. And really.....it will not help your system. Unless you have a high output alternator, better batts, and upgraded wire size.....it is a waste of your time. Sell it and buy 1/0 wire and do the big 3.

 

[I Like Waffle]

You charged it incorrectly and now its screwed, thats what your ******* gets for buying a capacitor. It stayed at 10.3 volts because of the load on the charging system, it would have slowly charged if you let it be. Lucky it didnt explode on your *******

 

[BerniniCaCO3 10+ year member]

Should it discharge even without any draw on it?

I thought it would act like a battery, hold charge if there's no load-- even if it's not quite the deep ocean of amp-hours that a battery is.

It was a line item at the end of my previous post, but I should maybe explain how I'm using it more and you can tell me if it'll work or if it's the wrong fix.

Rather than powering bass notes, I'm trying to power an electric cooling fan mounted on the radiator, which I wired up last week to replace my ailing clutch fan.

This fan draws 30amps continuous at full draw. I upgraded the alternator to a 130amp alternator that keeps up just fine with all the lights and everything once the fan is up and running.

However, the fan has a cold/unloaded resistance of .2ohms, so the instant draw on startup is a theoretical 70amps.

At any rate, when stuck in traffic, idling in drive at 700rpm idle speed, and the engine temperature climbs to where the fan turns on... even that upgraded alternator full-fields and causes a serious stumble for the engine, if not stalling it dead outright. I don't even get to lights-dimming point; it's not that the alternator can't keep up with the power demands, the engine can't keep up with the alternator at idle speeds when a huge amperage surge is just dumped on it. The engine's computer can't compensate with higher rpms fast enough to avoid stalling. If the fan had come stock with hte car, presumably the engine computer would be part of the system, and automatically bump the idle BEFORE the fan kicks on. But my ecu has no clue about what my aftermarket fan is going to do, so it's purely responsive; and it can't handle the surprise load.

Now, my single battery is the largest that fits, with a large cca rating of 1040amps, and obviously it can put out the 200amps needed to run my older-styled starter. So the battery shouldn't have any problem supplying 70amps to the fan.

What I was told however is that since the battery is at 12.5V, and the system voltage is at 14V, the draw will come from the alternator, as the highest voltage thing in town. So adding more batteries might not help me, if the power surge is still going to come from the alternator? And the alternator's load will still spike? And the engine will still stall?

So what I really need is a 14V battery-- or a capacitor, right in front of the fan, sitting at the line voltage of 14V, so that when that fan kicks up all of a sudden, the amperage rush will come from it and not from the alternator? It only needs to save the alternator for that second of peak draw when the fan first kicks, after that the system is stable.

 

[cyn 10+ year member]

okay... refer to what was posted... Caps are a waste of money.. get rid of it upgrade your batteries and add an additional battery if needed and upgrade all of your wires..

Big 3 do a search for it in the search bar

 

[BerniniCaCO3 10+ year member]

could you explain how exactly I charged it incorrectly, and whether it's still any good?

 

[cyn 10+ year member]

^^^ refer to posts above your post yet again.

 

[BerniniCaCO3 10+ year member]

I've got a brand new 130amp alternator with 0 gauge wire going to the battery, and a 1040cca battery. Not sure how much further I can upgrade those!

To the fan, admittedly, I have a sum 24" of smaller 10 gauge wire between the battery and the point that the wire enters the fan motor. There's a 30amp fuse in the middle, in front of the fan speed controller that acts as an intelligent fan relay, and that never blows. Guess the current spike is never for long enough to actually melt/blow the fuse. Would you suggest that that 2' of 10 gauge wire can be high-resistance enough to matter, and while unfortunately the tails right at the fan speed controller are fixed at 10 gauge, as is the wiring harness right at the fan, that beefing up the wire in between could help?

 

[BerniniCaCO3 10+ year member]

I thought that the resistance of a capacitor went up as it approached equilibrium with the line voltage.

It seemed really to stall at 10.2 volts.

I thought the resistor was only to slow the charging of the capacitor on the low end, when the capacitor was still at just 0V, and after that the capacitor would have its own resistance to not charge too traumatically.

After all, when I go to hardwire this into the car, it's not supposed to have that resistor in there anyway!

Or did I really need to let it sit for --how long, to give me an idea?-- with the resistor and truly reach battery voltage before I connect it into the circuit directly w/o a resistor?

At this point, did connecting it directly to the battery while it was still at 10.2 volts, burn/melt/damage some of the internal dielectric fluid and delicate foil, and is it ruined?

Or should I try again with more patience and hope it reaches 12.5 volts after, again, how much time should it take? With the resistor in place?

 

[BerniniCaCO3 10+ year member]

I could also consider an inductor to delay the current draw/ cut back the current spike to the fan.

 

[CHEMMINS 10+ year member]

Dude.....a cap will not help your fan issue. You need a 240 amp alt that puts out 140+ at idle. Your 140 amp alt is only doing 70-80 at idle.

 

[BerniniCaCO3 10+ year member]

yeah... I know that. In fact your estimates of 70-80amps are exactly what I came up with myself (80amps @2000rpm on the alternator, according to the manufacturer... and given 700rpm at hte crank and roughly a 3:1 pulley ratio...)

Which is enough to run the fan continuously but not enough to start the fan.

Why wouldn't a cap help with supplying the amperage surge to start the fan?

 

[I Like Waffle]

What the **** kind of car/fan do you have where the fan is pulling 30 amps of current?

 

[slvrado28z 10+ year member]

its a geo metro lmao