If you want a stiffening cap for £25, hie thee hither to your local maplin electronics where you may be lucky to find the QK81 0.5F capacitor on special offer at £24.99.

(I've just bought the last one in Leeds, so phone your local store to check first...)

 

How useful are these?

I have a 1.5 Farad which is supposed to cover me for 750wrms - and so a 0.5 farad would be good for a small sub?

 

I *think* the recommendation is 1F for 1kW of amplification. I'll see if it makes a difference.

I've never been a fully paid up believer in caps, so this is sorta sticking my toe in the water on the cheap

 

Has saved my speaker magnets from self destructing - as the amps have not clipped with the load.. destroyed 2 sets of Dyn's I think from not having a Farad - but if your not running much bass who knows..

But does'nt stop the lights from dimming.. need a decent battery

 

Right.

Anyone got a 1F capacitor for sale? (Kryten? )

Cheers Steve.

Nick.

 

Steve....

get a bigger alternator... + something like an Optima Battery.. Im assuming you have decent sized cable 2Awg or similar?? + Uprated the ground on the car??

David

 

Whats a cap (capacitor ?)? why do I need one? And how do I do it ?

 

It's a capacitor.

You need one because it will keep your amplifiers fed with juice better than your battery, apparently.

You charge the capacitor using a resistor (otherwise biiig current draw!) whack the positive terminal onto the battery cable and the positive terminal of your amp using a short cable, and ground the negative terminal.

Also, "RTFM" really does apply here. You *must* use a resistor to initially charge and also to discharge the cap, otherwise you can really do damage. These things have an equivalent series resistance of around 0.001 ohms, which means with a 12V difference in potential it'll draw upwards of 12000 A. This will, if you're sensible and fused correctly, blow the fuse. If you're not fused, I wouldn't like to think what would happen.

 

Thanks Nick

 

Similarly on the discharge - its basically a HUGE cattleprod and you really don't want to be touching those nice gold terminals..... (Hint: they will be BLACK afterwards)!

Nick - YHM

 

Dave

Optima is next on list - I've been told to get the most expensive!

Ground??

Otherwise fine

I have'nt destroyed any speakers lately..... - the previous Dyns - the spider glue came lose - whatever that means - apparently I destroyed the magnet - from Amp clipping... the Genesis amps could'nt hack the current draw....

I only have about 1000 wrms of subs.. I'm gradually getting there..

Martin

Round at Bobs a few weeks ago - as the Farad is situated very close to my rear strut brace and I was removing things in the boot to get at the fuel pump, bob was very, very nervous.......

 

what do you mean by "ground???"

I meant that you need equally big fxuk off cable from alternator to chassis or battery. Battery to Chassis. Dist Block to chassis / or amp to Chassis..

If you have 1kwrms then I would suspect that you have allready done this... Have you had a clamp meter around your cable to see what current you are drawing when in spl mode??

David

 

nick my only concern is when a garage disconnect the battery for maintainence work..

David

 

Good point Mr Wallis, not thought of that! I guess removing the master fuse from the audio system will do the job.

 

You would possibly still have to recharge the cap when refitting the fuse though.

David

 

Steve - I bet he was nervous!

As long as the battery isn't disconnected for that long (ie weeks) and you have no problems with the wiring, there's no reason the cap would discharge. Now, if they short something out, there may be a problem.....

As for current draw, I've measured it before on a system with about 1kw RMS and the peak draw was about 175A IIRC. No way a standard alternator can cope with that! Sustained draw was far less, but when the Prodigy CD got going.....

 

most diesel alternators are about @100a I would go for a new alternator and possibly a split charging system... depends on listening would certainly measure current draw and take it from there... also montitor voltage...

David

 

Fitted a Honda Legend alternator to my old car (Corolla GTi) went from about 45Amps to 85Amps.... never had a charging problem agian