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SamV 
Old Croc
Joined: 21 October 2008
Location: London
Status: Offline
Points: 8711
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 Posted: 23 November 2009 at 4:37pm |
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I once connected my 12v battery to my distribution block and it sparked, melting a blob off the metal distribution block. Since then I use at least 4awg cable for most of my systems over 400w
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james folkes
Old Croc
Joined: 08 January 2005
Location: United Kingdom
Status: Offline
Points: 3064
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Posted: 25 November 2009 at 12:35am |
 SamV wrote:
Also from experience a cap would make little to no difference. |
right... now i've been mulling this over for a while and i think i've come up with an explanation.
your system runs from static battery voltage, that being in the order of 12.5 volts. the only thing that stops the voltage sagging when the bas kicks is the battery's ability to deliver current. since this is nothing like the order of magnitude of cranking current, even deep cycle batteries can probably manage it with ease, especially if you've been a good boy and wired your system with fatty boom-batty cable. which you have...
however, if your system is running at charging voltage of around 14.6, the only thing that is holding the fort for those last couple of volts is the charging system itself, namely the alternator and by extension of thus, the person pedalling's legs! this is where your capacitor bank comes in, it's there to stop the voltage dropping from that higher value and correspondingly to lighten the load on the alternator and associated circuits, charging up again in times of surplus.
hence you are right: if you are running a static voltage system then no, a cap won't make any difference.
james.
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mardy hippy.
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SamV
Old Croc
Joined: 21 October 2008
Location: London
Status: Offline
Points: 8711
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Posted: 25 November 2009 at 1:16am |
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Aye that's pretty much it. However my battery being a decent deep cycle floats at 13.6v and has just over 1000 cranking amps.
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rich_gale
Old Croc
Joined: 18 February 2008
Status: Offline
Points: 2697
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Posted: 25 November 2009 at 7:31pm |
SamV wrote:
Aye that's pretty much it. However my battery being a decent deep cycle floats at 13.6v and has just over 1000 cranking amps. |
so it would be right to assume that any portable system where a capacitor may indeed have a positive effect on the sound quality would probably gain a benefit because their actual battery is unable to perform?
so a system capable of drawing more current (during its intended use) than its fully charged battery can deliver would ideally benefit a lot more from an increase in battery cranking power and capacity instead of adding a cap?
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REFLEX ALL THE WAY.... (however, im playing with horns again...) That ok Mister Valiant? :)
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SamV
Old Croc
Joined: 21 October 2008
Location: London
Status: Offline
Points: 8711
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Posted: 25 November 2009 at 8:08pm |
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Trouble is if the battery isn't upto spec it won't be able to recharge the caps fast enough depending on the cap.
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james folkes
Old Croc
Joined: 08 January 2005
Location: United Kingdom
Status: Offline
Points: 3064
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Posted: 25 November 2009 at 8:15pm |
i think that's fair to say rich, a better battery is always a good thing... in the grand scheme of things most battery systems probably can deliver the current required for most needs, the weak point as you pointed out earlier is more likely to be the cabling. i think the cap only makes sense when you are running at charging voltage, but if you are it makes a lot of sense.
having said that, if rapid draw is bad for your battery system the capacitor might well take some of the strain off it. it'll still use the same amount of power of course, but that power might be spread out in a beneficial way.
that leisure battery sounds a peach sam, a wise investment.
james. |
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mardy hippy.
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rich_gale
Old Croc
Joined: 18 February 2008
Status: Offline
Points: 2697
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Posted: 25 November 2009 at 9:09pm |
mota man has some good prices on leisure batteries at the mo.
@ sam and james-
i thought about this a lot and was wondering if a cap has any noticable loss in terms of heatup or leakage? if it is near 100% efficient could it be assumed that a cap will add to the running times of a smaller sla that has its capacity rating measured at a lower current draw than how it is being used in the real world? will the slight smoothing of the current draw have a noticeable positive effect on the discharge rate (assuming most battery capacities are measured at a discharge rate lower than the rate we are probably going to use them at in portable audio)
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REFLEX ALL THE WAY.... (however, im playing with horns again...) That ok Mister Valiant? :)
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james folkes
Old Croc
Joined: 08 January 2005
Location: United Kingdom
Status: Offline
Points: 3064
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Posted: 25 November 2009 at 10:09pm |
rich_gale wrote:
will the slight smoothing of the current draw have a noticeable positive effect on the discharge rate? |
that indeed is the question. as sam pointed out the cap will be recharged by the battery too, so is the smoothing effect even there? i guess it has to be as the amps will draw power from both sources during the transient and only when it has passed will the cap recharge, but as to what real world difference it might make to run time, you'd have to proper science it to find out.
the internal resistance of the batteries is probably not a million miles off that of the cap, although that is speculation, whatever it's bound to be significantly less than that of the charging system so i'm quite sure the amps will draw more from the cap than the alternator. i need to do some research on alternator speeds and cadences, see if i can't figure out a gear range that will offer usable power across the optimal voltage range for the system. i think the trick is going to be making sure that even in the lowest gear you are running at about 13 volts at a sustainably relaxed yet purposeful pace.
ironically, the complexities of the pedal generator have now far outstripped those of the audio system, but i've totally sold myself on the idea. i need to get a kWh meter in there somewhere to calibrate shift changes during parties... but yeah, the extra power is one thing, however the leap to true sustainability is the winning hand.
james.
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mardy hippy.
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SamV
Old Croc
Joined: 21 October 2008
Location: London
Status: Offline
Points: 8711
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Posted: 25 November 2009 at 10:17pm |
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I get my batts from tanya.co.uk, excellent service and great prices.
Caps do get warm but sadly I don't know in terms of loss. Rich I had the same idea for my wheeley case system which was powered by a 12v 14ah (or 24ah) Yuasa wheelchair batt. Cap made no difference to anything bar the weight.
If you do really want smoothing then the best best is a battery/cap hybrid like the Xstatic Batcap. Which are essentially small batts with extremely fast in/out current, or see it as a cap that can store upto about 24ah of current. They ain't cheap though.
The king of the 12v will be whoever best uses this: http://www.batcap.net/Products/BatCapExtreme/tabid/91/Default.aspx
Edited by SamV - 25 November 2009 at 10:22pm
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SamV
Old Croc
Joined: 21 October 2008
Location: London
Status: Offline
Points: 8711
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Posted: 25 November 2009 at 10:25pm |
james folkes wrote:
rich_gale wrote:
will the slight smoothing of the current draw have a noticeable positive effect on the discharge rate? |
that indeed is the question. as sam pointed out the cap will be recharged by the battery too, so is the smoothing effect even there? i guess it has to be as the amps will draw power from both sources during the transient and only when it has passed will the cap recharge, but as to what real world difference it might make to run time, you'd have to proper science it to find out.
the internal resistance of the batteries is probably not a million miles off that of the cap, although that is speculation, whatever it's bound to be significantly less than that of the charging system so i'm quite sure the amps will draw more from the cap than the alternator. i need to do some research on alternator speeds and cadences, see if i can't figure out a gear range that will offer usable power across the optimal voltage range for the system. i think the trick is going to be making sure that even in the lowest gear you are running at about 13 volts at a sustainably relaxed yet purposeful pace.
ironically, the complexities of the pedal generator have now far outstripped those of the audio system, but i've totally sold myself on the idea. i need to get a kWh meter in there somewhere to calibrate shift changes during parties... but yeah, the extra power is one thing, however the leap to true sustainability is the winning hand.
james. |
Let me know if you make any progress, when I did the maths not so long ago it wasn't worth the cost/drag or effort compared to the achievable outputs unless yours is for use when static? My plan was to charge/supplement power as I cycled around.
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james folkes
Old Croc
Joined: 08 January 2005
Location: United Kingdom
Status: Offline
Points: 3064
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Posted: 26 November 2009 at 11:52am |
whilst i do intend for the system to work on the move (there are plenty of critical mass style events and the like going off up here), the main application as we see it now is small scale free parties out in some of the more inaccessible reaches of the peak district. frankly, if the police can be arsed to hike 1 mile from any navigable byeways then fair play to them, we'll move someplace else.
so yes, predominantly static, possibly having to power an inverter for decks and a bit of led lighting on top of the amplifiers at times too. it is likely that we might be set up at these locations for over 12 hours at a time, that being the case the choices boil down to: pussyo stereo with long battery life, nails stereo with laughably short run time, nails stereo with all the batteries in the world, or nails stereo and power generation system.
those batcaps are the coolest thing... plus they do a 25 farad capacitor, yikes! if we ever get to the point of doing spl comps with our 12 volt rigs that kind of thing is going to be essential tackle.
james.
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mardy hippy.
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rich_gale
Old Croc
Joined: 18 February 2008
Status: Offline
Points: 2697
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Posted: 26 November 2009 at 12:56pm |
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i cant wait till the summer. im going for 4x 100ah batteries. 2 per sack trolley so about 60kg per 200ah. the system, dual cd/mixer and power supply should be a breeze off road with 5 people (1 person with a sack trolley loaded with the booze).
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REFLEX ALL THE WAY.... (however, im playing with horns again...) That ok Mister Valiant? :)
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-=SHOW OFF YOUR 12V SYSTEM!!!!=-