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Message |
    
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 2105
Registered: 9-2004
| | Posted on Tuesday, September 26, 2006 - 10:31 pm: | 
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i would like to add a 22,000uF 40volt elec. cap. between my power supply and my KL300p amplifier to provide some "headroom".
does anyone know of any problems, or special instructions on doing so?
just never messed with a cap this big, and want to be safe.
matt |
Tech833
Moderator
Username: Tech833
Post Number: 1459
Registered: 8-2002
| | Posted on Wednesday, September 27, 2006 - 11:26 am: |
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That capacitor will short out your power supply on startup, so you would need to add a series resistor between the PS and the cap. Say, 2 ohms. Also, you would need to bleed off the charge after use so you don't kill yourself, so you need a parallel bleeder resistor too. Say around 1K. |
Hotwire
Senior Member
Username: Hotwire
Post Number: 1804
Registered: 1-2005
| | Posted on Wednesday, September 27, 2006 - 12:01 pm: |
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KV, I can picture your shack now. You would'nt happen to have a big green guy with 2 bolts sticking out on the sides of his neck hidden under a white sheet do you?
Need an assistant? |
Chad
Senior Member
Username: Chad
Post Number: 1116
Registered: 11-2004
| | Posted on Wednesday, September 27, 2006 - 12:02 pm: |
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You can use something in the order of a .5 to 1 Farad intended for car audio use (although I do not condone the use in that app)
But honestly, I tried it and saw no difference in output. Nothing beats appropriately sized supply wiring.
Paul, it's a 12V amp, he won't need a bleeder resistor, just DON"T SHORT IT!!! In fact many caps for the application mentioned above actually have a charging circuit built in. (sort of a soft start relay that takes the resistor out of line after charging)
Chad
*** Tech 833 note ***
I disagree. It may be 'only 12 volts', but that is a TON of storage, and when it discharges, it will be WAY more that 12 volts flying around there. A bleeder would be mandatory for safety.
You can charge a cap with as low voltage as you like, but when it discharges, it will be at whatever voltage IT likes! |
Chad
Senior Member
Username: Chad
Post Number: 1118
Registered: 11-2004
| | Posted on Wednesday, September 27, 2006 - 2:52 pm: |
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I may be wrong but I'm pretty darn sure that a cap will only discharge at it's last charged voltage minus some parasitic drain. It's the current that will approach a gazillion if it is discharged in a low impedance manner. I'd be willing to bet my finger across a cap charged at 12V with no EMF pulses going on. In fact I have man-handled fully charged 12 and 24V industrial caps and never felt a thing. I have seen HV caps want to climb back up, but usually the internal resistance on these are rising and need replaced due to the fact that they no longer filter properly and act as cells in a battery. But they never float up ABOVE their last charged state or working voltage. Simply stated A 16V cap will not float up above it's rated voltage at a state of rest while disconnected from the charging apparatus.
If a cap would discharge at a higher voltage than it's charge then we would have big problems in power supplies floating up to whatever IT likes and damaging voltage regulation when in a rest state, many said power supplies do not have bleeder resistors.
Chad |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 2109
Registered: 9-2004
| | Posted on Wednesday, September 27, 2006 - 3:47 pm: |
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then how do they get away with selling 1 to 2 farad capacitors for car stereo use, that are intended to sit right near your car battery?
if shorting out the power supply would be a problem, wouldnt shorting out a car battery be an even bigger problem?
yet just about every comeptition stereo system has one if not more of these under the hood.
interesting.
well, either way, i may be stupid, but i tried it last night.
it did not short out the power suppy, and it seemed to work fine.
i just left the amp on, and shut off the power supply, so the amp drained the cap.
now, from what im reading here, am i to understand that i may be doing damage to my amp by allowing the cap to bleed off by leaving the amp on, and shutting off the power supply?
i also see caps like the one i have in the base station versions of the "competition" style amps.
i appreciate the replys guys, my head is like a big capacitor, and is storing all the info im learing on here.LOL
matt |
Wildrat
Senior Member
Username: Wildrat
Post Number: 1058
Registered: 12-2003
| | Posted on Wednesday, September 27, 2006 - 4:11 pm: |
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There are some good articles on the farad caps if you Google them. The cap from what I have read in the articles is to take that initial jolt when ya first key up or in the car audio use when ever there is a surge in power use if you now what I mean. Wally World sells farad caps for around 45 - 50 bucks. I was going to use them in my Jeep but I refuse to pay that much for a capacitor. Whats worse is the 3/4/5 farad caps, they think they are gold.
WR |
Moonraker
Intermediate Member
Username: Moonraker
Post Number: 250
Registered: 3-2005
| | Posted on Wednesday, September 27, 2006 - 7:13 pm: |
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I use a 1.5 farad car audio cap on my base power supply. It does help when using ssb but it is no replacement for the proper size power supply.
I did worry about damaging my radio by letting the cap drain back through it so I put a switch inline between the radio and cap.
Kid, I think what 833 is means by "shorting" is the large ammount of current the cap will draw to charge up when you first turn on the power supply. The resistors will let the cap charge slowly with low amp draw from the power supply.
I have had my cap wired straight into the power supply for about a year and it hasn't caused any problems. But who knows, it may blow up tomorrow and if it does...thats what I get for being so hard headed. |
Chad
Senior Member
Username: Chad
Post Number: 1120
Registered: 11-2004
| | Posted on Wednesday, September 27, 2006 - 7:30 pm: |
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Wildrat DOES have a point, there is a quick current consumption spike before the ALC kicks in on some radios. Others attack pretty quick. I owned both of such radios and simply did not notice an increase in performance in amplification. They sag down to supply voltage and everything resumes as normal.
One the receiving end it would make NO difference unless the power supply is sagging in a bad way or inappropriate wiring is used to the amplifier for too long of a distance. It just took up space on the bench and is dismantled till the next project  Muah ha ha ha
Chad |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 2112
Registered: 9-2004
| | Posted on Wednesday, September 27, 2006 - 9:17 pm: |
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would an "in rush" current limiter be of any use in this capacity?
at this point i am just interested in learning, as i really dont notice any difference when using it or not, so if there is a risk of burning something up, im just going to take it out of line.
again, this is only going on a power supply that only powers an amp.
thanks for taking an interest guys,
matt |
Tech833
Moderator
Username: Tech833
Post Number: 1462
Registered: 8-2002
| | Posted on Wednesday, September 27, 2006 - 10:42 pm: |
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Keep in mind- The car stereo guys are not always the smartest individuals you could meet. They hear their buddy say something, then they repeat it, and call it truth.
Obviously, there are a few exceptions, but I advise you VERY few... |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 2120
Registered: 9-2004
| | Posted on Monday, October 02, 2006 - 12:40 am: |
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sounds like the car stereo guys and CB guys have a lot in common! J/K! LOL!
thanks for all the responses,
matt |
Hollowpoint445
Senior Member
Username: Hollowpoint445
Post Number: 1369
Registered: 6-2004
| | Posted on Monday, October 02, 2006 - 12:10 pm: |
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I've used an 85,000 uf cap with a 10 amp power supply for a long time. It's not exactly a great power supply, but it seems to work fine. It's connected directly to the power supply output. No series resistance, or parallel resistance to bleed off the charge after it's turned off. The power supply bleeds off it's own caps, so it does the same for the one I put in line too. The only downside is the alarm sound until it's bled off.
I actually started using it when a 12v gel cell went south and wouldn't charge anymore. It was connected to the power supply as a charger and worked well for many years, but because of infrequent use, I guess the gel cell sulfated too much to take a good charge anymore. Bummer.
Because I already had the cables run, I needed a way to connect them, so I used a cap that I had used in my car right at my radio's installation point. It worked fine, and it's been there since.
I don't really know if there is any performance increase, but when I checked the power supply output with a multimeter, I saw some AC. Adding the capacitor totally got rid of that AC in the output. If anything, I think it helps keep the voltage up on SSB peaks to prevent warble. |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 2126
Registered: 9-2004
| | Posted on Monday, October 02, 2006 - 10:30 pm: |
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thanks very much for the response hollowpoint!
i thought i remembered you saying before that you used a cap the size of a beer can on your power supply, so i was hoping you would chime in with some details.
the SSB peaks are the exact reason i added the cap.
also, it makes my 2000GTL solid as a rock on SSB, it doesnt drift a bit!
JUST KIDDING!!!
i thought you'd get a kick out of that.
later,
matt |
Wildrat
Senior Member
Username: Wildrat
Post Number: 1079
Registered: 12-2003
| | Posted on Tuesday, October 03, 2006 - 10:56 am: |
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KV hid to Wally World and get one of those farad caps they sell for around 45 bucks, or get a bigger one say 2-3 farad. Those car audio guys may not be bright but the articles I read on the net about using the farad caps made a whole lot of sense to me. I never thought of putting one on my PR-60 but I may consider it. I don't need it really though as all it's powering is my Magnum most times, but it won't hurt either and may actually extend the life of that expensive power supply when it does take a hit from something else I may be testing. I already know I'm going to use one in the Jeep, but I just don't drive it or use the radio enough to make it cost effective yet.
WR |
Hollowpoint445
Senior Member
Username: Hollowpoint445
Post Number: 1375
Registered: 6-2004
| | Posted on Tuesday, October 03, 2006 - 11:37 am: |
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Yes, it's about the size of a 16oz. frosty beverage can. Like I mentioned before, I don't really know that it helps, but I do know it totally eliminated the AC from the output of my power supply, and just that is reason enough for me to use it.
The voltage rock solid, but that's mostly because the power supply is rated at 10 amps constant/12 amps surge, and I only use it for my SSB CBs and 25 watt HR2600s/2510s.
Nice joke Matt. Please don't ever say that again! |
Wildrat
Senior Member
Username: Wildrat
Post Number: 1080
Registered: 12-2003
| | Posted on Tuesday, October 03, 2006 - 1:19 pm: |
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What size ca are you using HP445? Not the physical size, it's rating.
WR |
