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24v Large Super Capacitors

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Phil B View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Phil B Quote  Post ReplyReply Direct Link To This Post Topic: 24v Large Super Capacitors
    Posted: 06 December 2016 at 12:26pm
Ok so I have a problem that I can't work around.

On our solar rig we use a few large 240v class D smps amps ( FFa and C-Audio Pulse)  Usually not a problem with our new inverter. Loads of power available 3000 watt rms with a 6000 watt peak. All good and we never pull more than 1/4- 1/2 of the RMS capacity.

BUT it sends the inverter into a warning mode due to voltage ripple on the DC side. This is probably due to the fast & high current demand on bass notes which the inverter tries to pull out of the batteries. We have upped the cable size and made sure we have good tight connections at all times. It also seems to happen at 80% or less of battery charge state, which can catch us out when running hard from a full 100% start off.  And finally last weekend it tripped out during a gig.. very dull.

So would fitting some very big ( scary) 30v say 6-10 Farad caps before the inverter help things ? I'm beyond my skill level when talking about smoothing out DC ripple by introducing more capacitance before an inverter?? In theory it should work to reduce the ripple on the dc side of things but thought I better ask ! The inverter is one of these....CP 3000 24v


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Post Options Post Options   Thanks (0) Thanks(0)   Quote carlosdelondres Quote  Post ReplyReply Direct Link To This Post Posted: 06 December 2016 at 2:04pm
not 100% sure it's the same issue, but adding caps is a recognised solution for voltage ripple causing ESC (speed controller) failure - this thread at rcgroups might shed a bit of light https://www.rcgroups.com/forums/showthread.php?952523-too-long-battery-wires-will-kill-ESC-over-time-precautions-solutions-amp-workarounds
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Sapro2 Quote  Post ReplyReply Direct Link To This Post Posted: 06 December 2016 at 4:04pm
Have a chat with the guys from bimble solar:

http://www.bimblesolar.com/

They run the Bimble Inn at Glastonbury festival and a few other festivals. They also supply solar related gubbins but they also run a reasonably large solar rig in their festival venue. They sell those sorts of Caps and I am sure would be up for having a chat with you and should know their stuff.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote snowflake Quote  Post ReplyReply Direct Link To This Post Posted: 06 December 2016 at 5:41pm
what batteries are you using? deep-cycle batteries might not be designed for high current but would have thought any standard car battery should deal with it.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote slaz Quote  Post ReplyReply Direct Link To This Post Posted: 06 December 2016 at 10:22pm
Originally posted by snowflake snowflake wrote:

what batteries are you using? deep-cycle batteries might not be designed for high current but would have thought any standard car battery should deal with it.


Don't know details of type .... but - big ones - lots of em AFAIK - pics of this rig were up on here a while ago. Wondering if a single battery (mebbe even one cell in one battery)  has degraded with high internal resistance could cause a voltage drop on heavy load.

Another thought - might be worth (if poss) trying a non switch-mode amp or two - see if behaviour is any different.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote mk2_ginger_biscuit69 Quote  Post ReplyReply Direct Link To This Post Posted: 06 December 2016 at 11:21pm
im thinking that above, one cell having issues - its a problem with have with a 48V traction battery on a work forklift, trying to get the lease company to admit there is a problem is another matter. Try using much juice at once [say driving off whilst lifting a heavy load, and it trips out].

regardless, having a bigass capacitor bank would certainly help - but would have to be attached in a clever way. A softstart type resister circuit would need to be added for when they initially charge or you would risk a MASSIVE current surge which could screw your traction cells, blow breakers/fuses, and arc like a bugger when you connect the battery/flick the switch. You could of course have it 'on' the battery bank so its always charged, meaning you'd only have to 'soft' charge it on the initial run, but any short circuit would make a spectacular boom.... certainly have to be bloomin' careful with that kind of capacitance, its really dangerous.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote ceharden Quote  Post ReplyReply Direct Link To This Post Posted: 06 December 2016 at 11:22pm
Adding some bulk capacitance close to the inverter is not necessarily a bad idea but I'm not sure you need to go for as high a value as you're suggesting.  Might not need to be Supercaps either, some decent high ripple current Electrolytics might also do the job.

Beware that if you do go for such high value supercaps that the initial charge current when you connect them across the battery will be massive, they'll appear like a short circuit.  You'd probably need to charge them slowly through some big power resistors, then short the resistors out once the caps have reached the same potential as the batteries.

Internal resistance of your batteries could be an issue as mentioned.  One option would be to use some high current starting batteries close to the inverter in parallel with your main deep-cycle storage ones.

That inverter looks really cool though, especially all the features to run in parallel with a current limited mains supply etc.  It's almost more of a UPS than an inverter.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote valve head777 Quote  Post ReplyReply Direct Link To This Post Posted: 06 December 2016 at 11:51pm
As above,
Is there any way of loading the bank with a typical current load for test purposes? If you can rig this up and you have flooded cells, its relatively easy to spot a dying cell as it will gas before the rest. Imho if you are using big sealed batteries (vrla) they're not really suited for your application. In my experience vrla sulphate really quickly when in partial charge. They're only really good for applications where they get charged fully directly after discharge such as ups. At 80% soc, a good bank should hold its voltage under reasonable (related to ah capacity of the bank) current demand. Obviously diagnosing a weak cell on vrla is more difficult.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote davey t Quote  Post ReplyReply Direct Link To This Post Posted: 07 December 2016 at 9:50am
Inverting to 240V then using AC amplifiers seems like the wrong way to do things. I would invest in some pro car audio class D amps. They are designed to run from batteries and have lots of energy storage built in. That said... most only go up to 14.4V DC. We have a 3.6k rms 12V rig which runs for ages no problem from 2 or 3 110Ah leisure batteries. Plenty of power. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote valve head777 Quote  Post ReplyReply Direct Link To This Post Posted: 07 December 2016 at 2:17pm
Erm, 3.5kw is a 330ish amp draw. From 2x 110ah batteries?????
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Phil B View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Phil B Quote  Post ReplyReply Direct Link To This Post Posted: 07 December 2016 at 9:47pm
Ok...thanks for some ideas there..

Firstly its not a voltage drop but a ripple. The inverter detects the ripple 

a) Davey T... not going to swap to car audio amps now, invested too much in 240v ones and we are adding more subs as well. Also we run 24v so would need a step down of some kind.

b) Snowflake ...batts are 12 x Yuasa 1100 amh SLA 2v cells. Came from a UPS system. Run in series to get a 24v bank.

c) Valvehead. We have tested all the cells a few months ago, getting voltage readings on resting cells over a 2 day period, none seemed to be low. They have always coped well up till now and spend 99% of the time at float resting. That's why I was thinking of the capacitors in-line with the bank to smooth out the peaks that the amps are demanding. The voltage under load can sag to 23.3 - 23.5 when about 80% of charge and a heavy load, thats when the voltage ripple alarm starts up. The low voltage shut off is set to 22v and we've never gone that deep.

d) Chris... yep like the starting battery idea, would do the same job as some big caps. Not sure how that would work with charging from solar though... At the moment we run 1.5kw of panels through a Midnight Solar 150.. means we can sometimes be pushing 40-50 amps @ 24v back into the bank? The equalise mode with a different type of battery would be all over the place.

Food for thought..

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Post Options Post Options   Thanks (0) Thanks(0)   Quote snowflake Quote  Post ReplyReply Direct Link To This Post Posted: 07 December 2016 at 10:03pm
Originally posted by davey t davey t wrote:

Inverting to 240V then using AC amplifiers seems like the wrong way to do things. I would invest in some pro car audio class D amps. They are designed to run from batteries and have lots of energy storage built in. That said... most only go up to 14.4V DC. We have a 3.6k rms 12V rig which runs for ages no problem from 2 or 3 110Ah leisure batteries. Plenty of power. 

or there are lots of amp modules that run on 24, 36 or 48V DC. converting DC to AC and back to DC it going to waste at least 25% of your power, possibly more.

if you are going to stick with the inverter just try a few odd capacitors and see if any of them solve the problem. if you think you might have a duff battery it will probably have a slightly higher temperature than the other ones after running for a few hours..
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