BigRed

Maplin are selling off there 1 farad cap(UZ87U) with display at half price £49.99 instead of £99.99, i think this is a bargain and it will not be avaliable for long, just reserved mine.

DJ140

Thanks for sharing that, what does a 1 farad cap do, do I need one?!!

I guess if I don't even know what one is the answer's no, but an explanation would be good anyway.

BigRed

OK, a 'cap' as commonly know in the ICE world helps to clean up bass by giving the amps a good source to drain heavy current from, this can crispen up bass response and keep bass tighter and more under control. You only need these if you are running a good sub and amp, if not running a sub don't bother. The cap has connections on it for +12v and earth and are connected accordingly and also have a display for voltage input ETC, these units can kick out some serious amperage and can be of great risk if misused,they must be charged/discharged according to there instructions. When i was a kid i used to 'reverse charge' electroliytic capacitors and believe me they go with a good pop, these were tiny compared to these monster caps. 1 farad is the capacitors value, in the electronics world this is an enormous capacitive value, probably the highest avaliable.

[Edited by BigRed - 4/21/2003 11:52:23 AM]

john_s

iTrader: (1)

I've been thinking about trying a cap for a while. This might just be the excuse i need :d

Do they make much difference in a small (single amp & sub) setup, or are they only really necessary for more serious sized installs?

Cheers,

John

Shifty

IIRC, rule of thumb is one farad per RMS kilowatt. It might not make much difference to a small install, but at the price I'd be tempted to get one anyway, ready for when you upgrade

Steve.

UHF

thanks for the info, mighty interesting

john_s

iTrader: (1)

My thoughts exactly. Will nip up tomorrow & grab one.

John.

UHF

I have 800w @ 2Ohms with two 12" inifity subs, the lights dim when they hit, i take it that the cap will eliminate this?

BigRed

UHF, at this price i think it is probably worth giving one a try, it will improve the weight of bass and might stop your lights dimming.
The cap will help iron out the 'Bumps' in the supply to you amp/amps, and also help your alternator/battery from sudden heavy current needs.

[Edited by BigRed - 4/21/2003 11:10:56 AM]

UHF

yeah, was thinking at £50 I cant go far wrong?

Take it that I should wire it up battery side of my rear distribution block? and then into the two amps?

Or isnt it worth using on the 4 channel mid/high amp?

BigRed

Wire it up to both your amps, it will provide enough current. I have mine wired to my second battery in the boot , so if you keep it as close to your amps as poss you can't go wrong. It will need a +12v feed (main feed from your battery) and a good earth.Also I have a 60amp fuse in the +12v side on mine, just incase!!!

[Edited by BigRed - 4/21/2003 11:17:27 AM]

Shifty

It should be wired in parallel to the amp, as close to it as possible. In my install there will be be less than six inches of cable between the sub amp & the cap.

Hopefully these things will come with good instructions, but be very careful when working with it. Capacitors have nominally no internal resistance, so a discharged one will suck a huge initial current when hooked up to the power supply, and a fully charged one will discharge with a hell of a kick if you short it out. Initial charging should be done with a resistor in line to drop the current. Hopefully there's one supplied. Discharging should be done with a 12 volt bulb so that you can see when it's done.

Steve.

BigRed

My old cap was discharged with a resistor, can't remember what value now, but it worked very well.Charging was don the same way, resistor in line with the +12v to SLOWLY charge the cap up over a period of around 10 mins, then it can be connected diredtly to the +12v feed without a high current draw.
THESE CAPACITORS CAN BE A POTENTIAL BOMB, DO NOT SHORT CIRCUIT THEM THEY CAN AND WILL EXPLODE CAUSING INJURY TO POEPLE INSTALLING THEM AND DAMAGE THE CAR THEY ARE WORKING ON, ALSO DO NOT REVERSE CHARGE THEM THIS WILL HAVE THE SAME EFFECT. MOST OF THESE CAPS DO HAVE A SAFETY RELEASE VALVE BUT I WOULD NOT LIKE TO FIND OUT IF IT WORKING CORRECTLY.

READ BIGREDS POST EARLIER

[Edited by BigRed - 4/21/2003 11:41:35 AM]

chiark

Two points here:

- A cap won't stop your lights dimming. You need a different approach to solve that, if you can solve it at all . Upgrade wiring, in particular the earth wiring from battery to chassis, plus b+ to alternator and alternator ground.;

- "Read the friendly manual" that comes with a cap. The ESR (equivalent series resistance) of these babies is measured in milliohms. Current equals Voltage / Resistance, so hook this up to your battery straight and you'll find it tries to draw literally thousands of amps. That doesn't do much good. Hopefully your fuses blow, but...

Saying all that, 50 quid for this cap is a bargain

Shifty

Mine arrived this morning :-)

Looks quite nice. The bracket supplied with it is much better than the extra ones Maplin sell. And apparently the whizzy electronics in the display mean that you don't need a resistor to charge it up. I'm not taking any chances though !

Still tempted to buy another one though, just for symmetry you understand......

Steve.

john_s

iTrader: (1)

I got mine at weekend. Read the bit about not needing to charge through a resistor, but not made my mind up about that yet!

The thing about it that is quite worrying though is that there is no cover over the terminals to protect from anything metal that might short them out. I'll have to see what i can come up with.

John

Shifty

I was just thinking the exact same thing ! And they're only about an inch apart, something loose in the boot could easily bridge that gap.

I was planning on having everything (amps + cap) recessed into a panel so it shouldn't be too much of a problem for me, but I'll still have to be very careful working near it.

Steve.

BigRed

Picked mine up tuesday, have to agree on the terminals maybe use some heatshirnk tubing on them. Nice looking unit and it does not require a resistor to charge it up, i have tried it on a 12v supply and the electronis provide the cap with a 'soft start' so a sudden current rush does not occur, the only problem is that i have a split charge system and the display on the cap is on ALL the time , even when the ignition is switched off but it only takes around 35 milliamps when left connected so maybe not a problem if you don't leave the car standing too long. Will have to disconnect or remove the fuse when i go on holiday for two weeks.

CraigRA

Just bought one of these off a friends friend (havent collected it yet,+ it's not a Maplin cap), trouble is he cant tell me how to wire it. After reading this thread have now got a bit paranoid.
so anyone want to give me an idiots guide to safe fitting.

john_s

iTrader: (1)

Big Red: I've been wondering about the display being on all the time and making a small drain if the cap is connected to a perm +12V feed. Or are the electronics smart enough to notice a lack of drain from the amp and turn the display off after a while?

Shifty: Not decided what to do about covering the terminals yet. I'd planned on fixing my amp & cap to the sub box to keep things tidy. Perhaps point the terminals against the side of the boot to keep things from touching across. Might just have to resort to some mk1 sticky tape to keep things covered though.

John.

chiark

The electronics should turn the display off "in around 8 minutes" according to the manual. Laughable as the manual is

Anyhow, one thing concerns me: is the soft start bidirectional? ie, if the amp tries to draw a load of current will the cap increase its resistance to drop the current?

I'll find out when I get it installed

BigRed

CraigA, connect the +12v terminal to your amps main feed (+12) and the - nagative terminal to a good earth point try to keep the cap as close to your amp as possible.Hope this is easy enough for you!!

This cap has reverse protection in the form of an audiable warning 'buzzer', and as for the manual , it is pi55 poor.LOL

[Edited by BigRed - 4/25/2003 8:13:03 PM]

Shifty

CraigA - if it's not one of these with a pack of electronics on the top, then you'll need something in series with it to charge it up. A resistor or a 12V bulb will do the job. To do the initial charge, you want something like this:

(battery)+......(bulb).......+(cap)-.....(ground)

When the bulb goes out completely the cap is charged. Shouldn't take more than a minute, but it's not dangerous to leave it longer. A 5W bulb will do fine.

After that, it needs to be wired in parallel with the supply to the amp. So (+) power from the battery goes to (+) on the cap and then on to (+) on the amp. Similarly, (-) on the amp to (-) on the cap to ground.

HTH,

Steve.