Viewing: Capacitor

**Chippy657** · 14-03-2009, 02:18 PM

Right another question from me (shock)

I have installed my sub and such and when i have the engine running and the lights on they start to flicker when the sub kicks in, i know i need a capacitor but not sure what farad i need.

I have this sub running of this amp, it is bridged so any ideas?

hope thats all the info you need!!!

**pgarner** · 14-03-2009, 02:25 PM

give 1/2 farad for every 500w RMS (NOT PEAK).
the amp shows 900w, is that peak or RMS ?

1 farad should proberly do you alright, 2 tops

**Chippy657** · 14-03-2009, 07:07 PM

900w peak so i would only need a 1 farad at most? or is it dangerous to get a higher one? will it damage my gear???

**turbonutter69** · 15-03-2009, 11:53 AM

You will only need 1 farad. It is also safe to use a bigger capacitor. If you planning on more subs I'd go for a 2 farad.

***HDi fun*** · 15-03-2009, 12:03 PM

Why not just buy another battery and mount it right next to the power amplifiers

**turbonutter69** · 15-03-2009, 01:08 PM

Quote:

Originally Posted by HDi fun

Why not just buy another battery and mount it right next to the power amplifiers

A capacitor would be much easier to install and will work just as good as a separate battery.

***HDi fun*** · 15-03-2009, 01:38 PM

OK - good answer. A battery is only a very large, polarised, electrolytic capacitor anyway.

**turbonutter69** · 15-03-2009, 02:48 PM

I'd be checking all the wiring to the amp before investing in a Power Cap. 900 watts peak shouldn't really affect the lights on the car unless the battery and alternator are weak. Make sure you have a good short earth cable. The shorter the earth cable the better. Bad connections will make your lights dim but you may well just need to reinstall the system with better quality cable.

***HDi fun*** · 15-03-2009, 03:04 PM

900 watts is about 75 amps load at 12 volts!!

**Chippy657** · 15-03-2009, 04:32 PM

So a 1 farad capacitor will be sufficient for what i need and thanks for the replies

Turbonutter- My earth cable is only 15cm long, my connections are all very good and i have a Juice wiring kit so the quality should be there. I understand what you are saying about bad connections because i come across them all the time in my day job!

p.s. Is juice any good? i have heard thay are but just need an experienced opinion!!!

**pgarner** · 15-03-2009, 04:40 PM

dont know mate, i allways mad my own wiring kits much cheaper.
could be the altinator is unable to produce enough power. not going to be running full whack but even at 500w thats still 42amps if youve got lights etc on it could be pulling too much.
what size altinators on it?

**Chippy657** · 15-03-2009, 04:41 PM

whats the altinator? I am not the greatest mechanicly lol as you can probably tell

**pgarner** · 15-03-2009, 04:49 PM

the thing that charges the battery. basically a generator that is turned by belt, along with the regulator ( most are inbuilt to the alternator) it provides around 13-14v constant to provide power for the car and recharge the battery

follow the power lead on the battery there should be 2. one leads to the fuse box the other should go to the alternator.

**turbonutter69** · 15-03-2009, 05:41 PM

Quote:

Originally Posted by HDi fun

900 watts is about 75 amps load at 12 volts!!

I had a 1200 watt D-class amp running 2 12 inch subs and the amp was running at 1ohm stable which boosted the amps power to 2400 watts. I didn't need the capacitor but I bought it so the bass stayed strong however loud it is played. A 900 watt amp should not make the light's flicker. What engine is in the car?
Juice are a good name but there is better out there.

**Chippy657** · 15-03-2009, 09:29 PM

Engine is only a 1.2

I must have explained wrong, when the sub is on and a really demanding part comes in (not very often but enough to annoy me) the headlights dim ever so slightly.

Also another question, when i was setting up the amp and sub, setting the gain
and all that, i must have had the system on for 20-30 mins and then i couldnt start the engine afterwards the battery had died, i charged the battery and everything was fine, so would a capacitor allow me to play music with the engine off and still be able to start the car afterwards?

Cheers pgarner i found the alternator so i learned one thing today.

***HDi fun*** · 15-03-2009, 11:20 PM

The battery itself will take over when the alternator can't deliver enough current. Perhaps the battery itself is in need of replacement if lights are dimming slightly. If its internal resistance is going up, as is typical when a battery failing then this is a likely symptom.

CLASS D AMPLIFIERS

CLASS D AMPLIFIERS are not linear devices. They operate the output devices (whether BJTs or MOSFETs) in switched mode. This ensures that the devices are either fully on fully off, thereby increasing efficiency as there is no partial conduction.

Despite the fact that semiconductors don't obey Ohm's law all the time they do so fairly well when operated in their linear region. As such, the source and load see the output device as a simple resistance. And the same rules apply as to simple resistors ie Power (WATTS)=I x I x R.

This power is dissipated as heat within the output device and makes NO contribution whatsoever to the signal output power.

Class D amplifiers rely heavily upon low pass filtering before driving the final load in order to get rid of quantization noise. They are not necessarily of high audio quality and their frequency response is highly dependent upon the impedance of the final load.

A later development is the CLASS H amplifier. In this arrangement the amps supply rails' voltages themselves are continuously modulated to ensure that the output devices foward current can nearly always be at maximum. These, too, rely upon LPF networks for driving a loudspeaker.

Impedance is nowhere near as straightfoward as simple resistance. as such, the linearity of frequency response from a switched mode amplifier can be quite poor.

**turbonutter69** · 16-03-2009, 01:53 AM

I understand what your saying there HDI. But an you knew there was gonna be a but Class D amps where developed for driving subwoofers. A class d amp will deliver the power a hell of alot better and stronger than your normal Mosfet amp. I know the class d is more efficient than a standard mosfet but mine was delivering 2400 watts of pure bass and didn't affect the lights at all. But in a 1.2 it may well be that because i'd emagine that a 2.0 litre engine has a more powerfull battery and alternator than a 1.2 .
And yes Chippy you would be able to have the stereo on and the battery should be fine. But it will drain eventually if say constant all day with the engine switched off.

**pgarner** · 16-03-2009, 08:02 AM

mmm going to diagree there TN
the capacitor is basically a small battery just with lower resistance, this is why it can discharge itself quicker than the main battery when alot of current is required. the battery will basically die just as quick.

chippy did you look closely at the altinator ? it should have had a rating on it somewhere. on a 1.2 i wouldnt be looking high it might only be 60 amp compared to 120amp on a bigger engine

***HDi fun*** · 16-03-2009, 09:45 AM

I doubt the 2400 watts claim, That's over 200 amps at 12 volts. Class D amplifiers are more efficient that linear amplifiers but even so you can never get more than you put in.

**turbonutter69** · 16-03-2009, 11:54 AM

The capacitor will hold alot of charge when the ignotion is off. Please just trust me on this 1. Before I had the cap I needed the engine running to turn up the volume as the amps where drawing that much power the stereo kept switching itself off. Now with the cap installed I can sit without the engine running and crank up the volume without the stereo cutting out. No it won't last forever but will last longer than a battery on it's own. Plus the fact that the caps readout will tell if the power levels are dropping then just restart the engine before it's drained.
As far as 2400 watts. This is a true power figure as it is setup to run at 1 ohm stable. (it may be 2ohm but i'll check and then update but i'm sure it's 1 ohm) I don't know how to explain but in lamen terms the lower the ohms the more power an amplfier can produce. I'll try an find some info for you. But my amp is now running 2400 watts of pure Bass and this is fact!

**turbonutter69** · 16-03-2009, 12:00 PM

Sorry my mistake my amp is 1200 watts @ 4ohm and 2400 watts @ 2ohm stable. True power figure.

**pgarner** · 16-03-2009, 05:07 PM

Quote:

Originally Posted by turbonutter69

The capacitor will hold alot of charge when the ignotion is off. Please just trust me on this 1. Before I had the cap I needed the engine running to turn up the volume as the amps where drawing that much power the stereo kept switching itself off. Now with the cap installed I can sit without the engine running and crank up the volume without the stereo cutting out. No it won't last forever but will last longer than a battery on it's own. Plus the fact that the caps readout will tell if the power levels are dropping then just restart the engine before it's drained.

correct to a point, i had the same problem my HU would flash without the cap when i had something with alot of bass in it. after installing the cap it never did it again. this was due to the cap being able to supply the current quickly. the battery didnt last any longer however after around 50mins that was it had to restart the car. i had a low battery alarm that sounded when the battery dropped below 11v

**Chippy657** · 16-03-2009, 10:15 PM

Cheers for all your help!

pgarner i didnt look that closely but your probably right about the 60 amp thing although my amp cannot take more than 40A due to the inline fuse.

I am going to invest in a capacitor even if it has no affect on the headlights dimming ever so slightly, it will put my mind at rest knowing i can have my music on for 10 minutes and know that i will be able to start the car afterwards!!!

**pgarner** · 16-03-2009, 10:25 PM

you should be able to have it on for 10 mins without any problem.
if your going to be parked up blaring for a while look at installing another battery in the boot and power the amp off this. to charge it get an split charger

the cheap split chargers use a relay that connects to the ignition when the engines on the relay is closed and the latinator charges both battery. when the engines switched off the relay is open so it just uses the spare battery.
just make sure you go for a gel battery incase the worst happens

**turbonutter69** · 16-03-2009, 11:12 PM

Quote:

Originally Posted by pgarner

you should be able to have it on for 10 mins without any problem.
if your going to be parked up blaring for a while look at installing another battery in the boot and power the amp off this. to charge it get an split charger

the cheap split chargers use a relay that connects to the ignition when the engines on the relay is closed and the latinator charges both battery. when the engines switched off the relay is open so it just uses the spare battery.
just make sure you go for a gel battery incase the worst happens

I understand multiple batteries being installed when there is say a MTX Jackhammer that needs that kind of juice. But for a simple install a power cap will suffice. I have a 2 Farad power cap and it will last longer than 50 minutes without the engine running.