cap w/digital voltage display

i got this scosche 500k cap with a sweet red led readout an blue led backlight, im sure most know what im talkng about
im not really wantin to use the capacitor part of this thing just the volt display,

what do u guys think if i were to use a relay off my remote turn-on an run a pair of wires from my amp + an - to my cap ? to use my display which id like to mount around my drivers seat. i kinda wish there was a way to seperate the 2 from each other.

is there a way to disable the capacitance? would i be gettin a accurate voltage reading?

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1000 watts of lp, now need sum hp an mids

Just buy a 3-digit voltmeter from eBay, you can get blue LEDs or backlit blue LCDs for around $10.   

Otherwise just hack the meter off the cap, it should only have 2 wires (ground & +12V).
The cap is probably useless unless you know why you need it...

sell the cap and buy a digital volt meter. that's my 2 cents

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@0 Hertz Xpertz/Team SPL

well the top of the cap does unbolt an seperate, its really easy to do i just need sumthin to mount it to now, probly end up boltin rite too the dash of my car,
a bolt on meter who woulda thought

an as far why i need it old spark, it filters the voltage spikes but adds load to ur alternator so its not really needed cause alts have a built in regulator

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1000 watts of lp, now need sum hp an mids

sthrnbmpn wrote:

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...but adds load to ur alternator so its not really needed cause alts have a built in regulator

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Ah yes, the same old crap! Who told you that?

A cap does not add a load to the alternator other than when charging (much the same as a battery). But it LESSENS the alleged "strain" on the alternator by providing a store of electricity (much like a battery, only a heck of a lot smaller).


All alternators have voltage regulators. The cap is irrelevant.

And batteries filter spikes - that is the main reason you shouldn't disconnect the battery with the engine (alternator) running. (It used to be because batteries provided a voltage reference for the regulator (alternator), but nowadays they provide their own voltage reference.)

well it doesnt add load unless its charging, an if ur amp discharges the cap alot while playin music thats a lot of discharge/recharge

im not tryin to open an old can of worms but im just goin by what majority rules about caps, an it seemed to make sense when i think about it, a 500k farad is a smaller cap in the car audio realm, so maybe it would help clean up the the voltage goin to the amp

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1000 watts of lp, now need sum hp an mids

Your not opening a can of worms. But you may be stressing those that simply don't know and don't or can't think too hard.

Think about what you said - the capacitor supplies energy when the alternator can't. Then the alternator replaces that energy.

So, has that saved the alternator or stressed & damaged it?

Without the cap, the alternator would have to supply that same energy/power.

So the cap saves the alternator from having to supply the burst of power, and the alternator thanks the cap in return by recharging it.

If that whole bullsh "extra load" argument were true, we'd be using the smallest battery we could get just to "save the load".


Do those same people put bigger batteries on their system? I bet if it's an audio forum the answer is yes.
And yet the battery is worse from that POV than a cap. In part because it is so much bigger (electrically) than a cap, but more so because of the charge & discharge inefficiency - you put about 30% more electricity in to the battery than you get out. (I'm not sure of the figure(s), but I think that is a conservative estimate.)

Compare that to a cap which has essentially 100% efficiency - eg, over 99%.
So why aren't those dorks using caps instead of batteries if "alternator load" is such an issue? Oh yeah, I forget, caps lower peak SPL - so they use low ESR AGM batteries instead. (Of course if they placed their AGMs in the engine bay - or better still - used flooded batteries, they'd get even higher peak SPLs if the low-ESR caps are the reason for the lower SPLs.)


Don't worry, though there are many audio-forum contributor's that excel in stupidity, there are a few that understand the basics.
LOL - if you don't know what I am talking about, see the poo chucking between floridaspl and caraudioclassifieds regarding "How many batteries do I need?" (as linked).

Not that the OP is the brightest of kids, viz: "Why would it work harder to recharge 10 batts versus 1 batt? Its constantly charging at a certain rate based on RPM (this case being 160A max). I'm just confused by electrical systems I suppose. I'll ask my EE/Physics degree'd father what he thinks tomorrow" (see extra batteries like extra caps apparently does NOT load the alternator!), but he calls the knowledgeable people dorks, nurds & ridiculous despite his admission that he knows squat.

But floridaSPL is another site that reckons to add more batteries rather than upgrade the alternator (first).
I can only assume that despite their assertions that voltage is important for an amplifier that they don't use the amps they often refer to (which increase output with increasing voltage) and that they actually have high-quality amps whose output does NOT vary with input voltage - ie, whether you have 12V or 14.4V will not effect the max power output.


Alas I ramble, but for people like that, ANYTHING is a can of worms. That's because they aspire to that level of intelligence. They may be smarter than a worm, but a can of them would indeed be a challenge.

I guess my suggestion or warning is to be careful where you get your info from. And I'd suggest when it comes to "power", you should ignore the majority of the stuff from similar audioforums (as per floridaSPL - unless it is from one of their good people).

There is some truth in there. By your own arguments:

1 you put more energy into a battery (or capacitor) than you can get out because of efficiency loss
2 the capacitor supplies energy when the alternator can't
3 the alternator replaces that energy

Therefore, adding a capacitor increases the energy required from the alternator because of some loss of efficiency when storing and discharging through the capacitor.

For the absolute best explanation of how a capacitor functions in a car audio application, this thread is fantastic. Highly recommended, read the whole thing!

https://web.archive.org/web/20080117064421/https://forum.realmofexcursion.com/showthread.php?t=17970

oldspark wrote:

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Compare that to a cap which has essentially 100% efficiency - eg, over 99%.
So why aren't those dorks using caps instead of batteries if "alternator load" is such an issue?

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Caps suffer a voltage drop proportional to the current it supplies by Ohm's law V=IR. With currents (I) running upwards of 50 or 100 amps or more, a tiny internal resistance (R) of only 0.02 ohms would lower the voltage (V) at the capacitor's terminals by 2 volts or more.

The alternator would have to drop it's voltage due to an extreme load for the cap to begin discharging, and if the cap is helping supply a significant current its voltage will also drop as shown above, which leaves the humble battery to help supply current starting at about 12 volts.

The amount of energy that can be supplied by a capacitor at high currents, is a tiny fraction of the amount of energy that can stored in a capacitor, which is in turn a tiny fraction of the energy that can be stored in a battery. Read that link to see all the details.

-J

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Malcom: "This is the captain. We have a...little problem with our engine sequence, so we may experience some slight turbulence and then...explode."
Jayne: "We're gonna explode? I don't wanna explode.

sthrnbmpn wrote:

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i got this scosche 500k cap with a sweet red led readout an blue led backlight, im sure most know what im talkng about
im not really wantin to use the capacitor part of this thing just the volt display,

what do u guys think if i were to use a relay off my remote turn-on an run a pair of wires from my amp + an - to my cap ? to use my display which id like to mount around my drivers seat. i kinda wish there was a way to seperate the 2 from each other.

is there a way to disable the capacitance? would i be gettin a accurate voltage reading?

---

Lots of good suggestions above.

The voltage reading would be reasonably accurate, should be just fine for your needs.

-J

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Malcom: "This is the captain. We have a...little problem with our engine sequence, so we may experience some slight turbulence and then...explode."
Jayne: "We're gonna explode? I don't wanna explode.

teenkertoy wrote:

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Therefore, adding a capacitor increases the energy required from the alternator because of some loss of efficiency when storing and discharging through the capacitor.

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What inefficiency?

Are you saying that a cap resistance is similar to vehicle wiring?
In comparison, a cap is close enough to 100% efficiency.

And if a cap has a resistance of 0.02 ohms, then I would certainly ditch it and use an AGM battery (as far as ESR & resistance is concerned).

You could draw a circuit or schematic for a vehicle's charging system. Show the stator winding resistance as well as the distribution resistance, the battery and its resistance (assume it is to spec & fully charged), and that of the load.
If you come up with a something profound, I'll change my stance.
Remember that the cap is a parallel device - it is not a (say, 0.02 ohm) series resistance. (Its terminal voltage will always equal its circuit voltage - there is no voltage drop, but feel free to model and ideal capacitor etc.)
Or do some rough power dissipation calcs for the cap, the protection (fuses) and wiring.   


However, you should realise the above "efficiency" is irrelevant. A battery "saves" the alternator and it has way more overhead than a cap. (You might find around ~100-fold more "inefficiency" with a battery.)
And, is it more efficient to not have a cap (or battery) and let the alternator provide the load(s)? (And do you like dipping headlights and stalling engines?)   


I put it to you - do you recommend a bigger battery for its increased capacity (as well as lower resistance) to offload the alternator, or a small battery (to offload the alternator)?

I eagerly await your response.

It cannot be denied that when a cap charges, it places load on the electrical system equal to the amount of charge it can store.  It also cannot be denied that any cap will discharge its stored energy when system voltage drops.  The amount of energy that can be stored by even the largest caps is only sufficient to compensate for minor fluctuations in system voltage, so they do help eliminate voltage ripples and provide instantaneous surge capacity for amplifiers, and they can discharge at much faster rates than any battery.  This is why caps are used in all amplifier power supplies.

There is no way to supply long-term (more than one second) power to an amplifier or any other electrical system using capacitors unless they are very large indeed.  But they do have a place in all audio systems.

As to the OPs question concerning using the cap-top voltage meter in some other location, as long as the connections are made safely there is no reason why it wouldn't work.  But as other people have suggested, there are far better solutions that you wouldn't have to ghetto-rig if all you want is a voltage display on your dash.

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Support the12volt.com

ghetto-rig lmao, that pretty much sums it up, that would make a gd sig

i was just tryin to put it use it, lites up the inside of my car bright blue an im not really into the brite lite type stuff, imma try an come up with something a little creative for a mount nothin too ghetto lol

my 90 amp alt is puttin out its max with both my amps , at least i hope it is, so imma go capless for now

thanx every one for all your input

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1000 watts of lp, now need sum hp an mids

Sorry for the bump, but guess who just installed a new alternator on floridaSPL?
Geez (pun intended), all that bashing for nothing. And I'll bet caraudio won't be thanked.
But it was good seeing some talented repliers - those Tasmanian Devils are smart.
But I like the comment that an alternator "is for the rich kids". Funny, but here an alternator is almost cheaper than a battery. But with the prices I have seen stateside, even an expensive alternator will be cheaper than multiple batteries in the long run (ie, after a few battery replacements).


Also, I and J (teenkertoy) and I have exchanged a few PMs. (Multi-discipline & short as usual LOL! Yep, another "sticky" with basic system and design principles.)
I explained that I was replying to the "cap (or battery) adds an extra load" which I look at from the overall POV. teenkertoy referred to "energy" (in his second last post in this thread) as I was doing from the overall wasted energy POV, and that of overall strain or load on the alternator. (Not that alternators should strain per se.)


But sthrnbmpn, IMO you are doing the right thing having a dash voltmeter. I find it amazing that people ask if they need a bigger alternator for their loads when a dash voltmeter will indicate that.

Plus it's a nice way to monitor the state and condition of your battery AND electrical system.
Just make sure you wire it across the battery, both poles.
Mine is simply relay switched by the ignition, but I'm working on mum's voltmeter which currently has a 3-way switch for Ignition, off, and momentary on. I'm adding a timer so that for both IGN and momentary on, there is a (say) 1 to 3 minute delay before the voltmeter relay turn off.   (The momentary on is to display voltage at any time - not IGN key required.)

(The momentary on is to display voltage at any time - not IGN key required.)
that would be real conveniant, is it a simple type circuit? i got relays down pretty gd , but momentary on , imma study up on that one

sumthin about push buttons, intersts me

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1000 watts of lp, now need sum hp an mids

A present it's a 3 position switch - on-off-momentary_on (ie, spring return to the central off position) - a not uncommon mini-switch.

I use a small relay whose coil is about 1k Ohms.
The switch & relay and voltmeter are housed in a dash blanking plate - just a quick prototype a this stage.      

I'm intending to use a MOSFET for the delay, but I need to get a round tuit first. (A round tuit in not a uniquely Aussie expression is it?)
And I have until September to complete the job, so it should be done by 2112 (no - not 2012!).

I should do that after I replace my faulty alternator (no charge lamp since February) and add MOSFET to buffer my UIBI relay (battery isolator).

ok now i feel kinda noobish again, i know what a momentary on is its just that u made it sound real hi tech an i had a blonde moment an couldnt picture it, lol i can make this happen

thanx old spark for the ideas, i dont really want the volt meter to be on everytime the ign is on, just whenevr i wanna check it out
1st position is closed, 2nd position is open an 3rd is momentary

now i feel smart again

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1000 watts of lp, now need sum hp an mids

You always were smart - you want a voltmeter!
How many people wonder if their alternator is big enough or they require a priority charging battery isolator (LOL - a bit of a joke, but I just posted elsewhere about WHY have them anyhow - if they did exist!), yet do they have a suitable voltmeter?

I think that's why caps have voltmeters - make the user think they have a voltmeter, but make sure it isn't in the dash so that they can see what actually goes on... That way they think they are ok but are really none the wiser.


Maybe I should post a pic of my (mum's) meter and switch assembly....
The switch might be this one...
from Altronics Switch Mini Toggle SPDT Centre Off Mom; noting that it is On-off-mom not mom-off-mom where mom is ON but spring loaded to return to center - the other positions are latching (or stay in place or whatever "not spring loaded" is - I don't want to use the term "locking" - that's another switch!)


Although the switch could switch the voltmeter direct, I used a relay to ensure I had the BATTERY terminal voltage at the voltmeter.
Hence the circuit is batt- to relay coil ground (#85) and voltmeter -ve, voltmeter +ve to the NO relay contact (#87) and batt+12V to the Common relay contact (ie, #30) and the momentary switch contact, and whatever "ON" source like IGN or ACC +12V to switch ON contact.
The common switch contact goes to the relay coil+ (#86).
(Not that I've used a HUGE relay with those terminal labels!)

I intend to have the switch-common feed a cap & FET that keeps the relay turned on after it is switched off. The relay coil is ~1kOhms but even then, I prefer a small cap with a FET or transistor to control it.   
But that delay circuit is a "cut & insert" that can be added any time withing the next few centuries. (Unless it's not that urgent in which case I'll relax a bit more....)


Yeah... maybe a pic, and a circuit....?

so after posting this ive really been doin alot of thinking on this subject, an the term gheto-rigged is the whole goal of my switch/meter install

i also have a amp fan wired to a switch under my seat an i was thinkin i could use a clean looking switch bank for accy's. such as meter, fan. so yes pics would help . my post count should be up hi enuff to were i can post sum pics also

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1000 watts of lp, now need sum hp an mids

sthrnbmpn wrote:

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 ...my post count should be up hi enuff to were i can post sum pics also

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All active members regardless of post count can upload images.

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the12volt • Support the12volt.com

what do you think ol spark ineed a way to mount in my ashtray or just buy a voltmeter, its just not doin anything sittin on my parts shelf

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1000 watts of lp, now need sum hp an mids

I'd rather spend the handful of dollars and buy one off eBay etc.