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24v Large Super Capacitors

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valve head777 View Drop Down
Young Croc
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Post Options Post Options   Thanks (0) Thanks(0)   Quote valve head777 Quote  Post ReplyReply Direct Link To This Post Posted: 08 December 2016 at 12:01am
@ Phil, do you equalize the banks? And at what voltage?
Im interested to know as i live off grid and use agm ups batteries.
I did wonder about voltage ripple. I still feel its the bank becoming weak. When charging i myself never let my system reach more than 27.8v as its gasing which will dry them out. The drawback is not really being able to equalize like you can for flooded, so very regular readings are taken and individual batteries charged. Tbn its a chore and makes me resent the lead acid technology. If only i could afford nife batteries.

Its sounds as if you should do a capacity test to get an accurate idea of how much capacity you actually have. Once below 80% original advertised capacity, performance drops quickly. In my experience the advertised advantage's of sealed don't bear out in reality. But they are reasonable safe (physically).

Edited by valve head777 - 08 December 2016 at 12:08am
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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: 08 December 2016 at 8:39am
Originally posted by valve head777 valve head777 wrote:

@ Phil, do you equalize the banks? And at what voltage?
Im interested to know as i live off grid and use agm ups batteries.
I did wonder about voltage ripple. I still feel its the bank becoming weak. When charging i myself never let my system reach more than 27.8v as its gasing which will dry them out. The drawback is not really being able to equalize like you can for flooded, so very regular readings are taken and individual batteries charged. Tbn its a chore and makes me resent the lead acid technology. If only i could afford nife batteries.

Its sounds as if you should do a capacity test to get an accurate idea of how much capacity you actually have. Once below 80% original advertised capacity, performance drops quickly. In my experience the advertised advantage's of sealed don't bear out in reality. But they are reasonable safe (physically).

Hi

I think you've hit the nail on the head there. We changed over solar controllers recently and it does an auto Eq once a week up to 28.4. Time to turn that off ! Slipped through the net of new panels, amps and inverters. Also gonna check density for each cell but not sure we'll be able to get in/out easily without damaging the vents.

These are the batts.....



Thnx !

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U.Viktor View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote U.Viktor Quote  Post ReplyReply Direct Link To This Post Posted: 08 December 2016 at 8:51am
If you use 230Vac powered amp, use PFC amp only.
Please keep in mind that most of conventional (non-PFC) amplifiers may generates 5x -- 10x of current peaks due mains current distortion than PFC amps.
These sharp current peaks means like your 3000W amp would look like 30000W amp for the inverter!
It easily triggers the output current protection of the inverter periodically or permanently.
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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: 08 December 2016 at 10:33am
Originally posted by U.Viktor U.Viktor wrote:

If you use 230Vac powered amp, use PFC amp only.
Please keep in mind that most of conventional (non-PFC) amplifiers may generates 5x -- 10x of current peaks due mains current distortion than PFC amps.
These sharp current peaks means like your 3000W amp would look like 30000W amp for the inverter!
It easily triggers the output current protection of the inverter periodically or permanently.

Yep well aware of all that and we swapped out our inuke 6000 for an FFa 6k to try help with PFC things. We are getting a ripple in the DC voltage though, the inverter can easily cope with the current draw so looking for ways to help the DC not AC side of things.

Ta

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valve head777 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote valve head777 Quote  Post ReplyReply Direct Link To This Post Posted: 08 December 2016 at 2:13pm
Hi Phil, I've tried in the past to put a small amount of deionised water back into sealed bats but with no success. Once the mat is dry its dead batt time...
You use large cells. How do you charge them? Ideally you'll need a rate at a minimum of c15 which for your bank is around 100amps for bulk charging. If you are relying on the panels, 40 amps is only a trickle.
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valve head777 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote valve head777 Quote  Post ReplyReply Direct Link To This Post Posted: 08 December 2016 at 2:24pm
In an ideal situation with all cells exactly the same in terms of voltage/capacity, 28.4 is ok (absolutely max) but in aging, cells become unbalanced so the weakest cell rises before the rest and begins drying out. This situation only gets worse over time. A lower voltage is a compromise but increases overall life. I hope your horse hasn't bolted just yet...

Edited by valve head777 - 08 December 2016 at 2:25pm
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minaximal View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote minaximal Quote  Post ReplyReply Direct Link To This Post Posted: 09 December 2016 at 8:26am
Hey Phil

Yeh i think equalizing SLA's will quickly kill them, unless it's possible to top up the water, or have a much lower eq voltage with temperature compensation.

Being off grid too, I had a very similar problem with our Victron Multi shutting down when battery voltage collapses with a heavy load, unfortunately it's normally a sign of cell degradation - lead paste falls off the plates over time leading to less capacity.

Best Bang for buck is still FLA forklift style cells, i wish we'd gone for them originally, and they're much better at coping with continuous cycling with heavy loads than SLA's

To get around it, lower the inverter shut down voltage, that's what i did, but i also added a http://www.smartgauge.co.uk/smartgauge.html battery monitor and use that with relay output to tell the Victron when to shut down. It doesn't rely on voltage sensing alone, so it's a much more accurate way of knowing when SOC is low, and now i've set it so the batts can never get below 50% SOC, but it allows short term heavy loads which pull the voltage below 22v etc to pass through.

If the inverter can take an external relay input to tell it when to shut down or even the crude method to use a large contactor to disconnect it (only when SOC gets too low) and use something like the smartguage to trigger that, i think that's the best option without buying new batts or amps, and overall makes for a much more controllable and safe system.

What do you use to to know your batts are actually at <80% SOC when it happens, as it could be giving a rosier view of the batts, hence the voltage drop?

Whatever you do don't mix battery types! will be a world of pain and wasted money.

Really want to hear the system, i'll be over next year sometime...

Al

*Edit - As mentioned by Valvehead, if certain cells are less happy than others you could pull them out of the string and try to 'condition' / charge them seperately to bring voltage back up, but without a way to check SG of individual cells it's hard to tell whats happening. It could be worth exchanging cells at either end of the string for the central ones, as in a long string with cable resistances the cells at either end accept more charge and drain more quickly so 'wear out' more quickly.. lots of info on the smartguage website.





Edited by minaximal - 09 December 2016 at 8:41am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote carlosdelondres Quote  Post ReplyReply Direct Link To This Post Posted: 09 December 2016 at 8:44am
Yep, we have ~1000 Ah 48 volt forklift battery, 5 years old now and still going ok despite less than ideal usage. Can pull 7kW from the motor without fuss, never had a problem with running system off our inverter either (studer xtender 8000). But the inverter has PFC and can handle 24kVA 2 minute peaks.

Bigger battery and better inverter in the longvterm i'd have thought. Though multiple low ESR caps in parallel is what people use for speed controllers in multirotors - the vrip can be high enough to overvolt fets and cause burnout. Rule is to add caps if your're lengthening the battery wires over what the mfr supplies. Talking 22 volt systems pulling 100 amps plus DC and switching to 3 phase ac so not a million miles off in alectrickal terms perhaps...
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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: 09 December 2016 at 9:01am
Ok to answer a few questions...

Bank is charged by solar 99% of the time, we occasionally get a 240v feed into the Inverter / charger which I've limited to a 50 amp ( 24v) max. The solar charging is controlled by a midnite solar classic 150. The max I've seen is 47 amps so the batts aren't getting a huge amount and yes I know they can take 100amps but we haven't that many panels ( yet).

And Al ( hi fella) the midnite allows logging and using the Whizzbang shunt you can see real time system draw ( in fact almost all parameters). So I track SOC using a wifi router and a laptop.

And yep I'm hoping the horse hasn't bolted. I don't think it has, just using Class D amps has flagged something with the inverter. In all honesty I'd love to disable the ripple alarm and shutoff as the inverter can cope with the load fine, it's just an artifact of the way the amps draw that current!
I like the idea of a truck starting 24v batt in line to smooth things out. Not supposed to mix/ match but maybe we pop it in for gigs and charge separately afterwards?

.p.
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carlosdelondres View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote carlosdelondres Quote  Post ReplyReply Direct Link To This Post Posted: 09 December 2016 at 9:10am
Won't the different internal resistances of the batteries mean the load is drawn unevenly then?
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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: 09 December 2016 at 9:14am
Originally posted by carlosdelondres carlosdelondres wrote:

Won't the different internal resistances of the batteries mean the load is drawn unevenly then?

Maybe ? The truck batt might just take out the peaks that the amps are demanding, allowing the dc voltage across the bank to stabilize? 

And just to clarify...this is only when the system is maxxed out .. subs and low mids at -10 on the amps, limited by a multi band compressor. 

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minaximal View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote minaximal Quote  Post ReplyReply Direct Link To This Post Posted: 09 December 2016 at 9:23am
Hey Phil Smile

The Midnight has relay outputs i think doesn't it?

So just disable the inverter low voltage disconnect, (is that possible?) and use the midnight to trigger a big contactor to disconnect batteries at low SOC instead of the crude low voltage. Albright make proper contactors just for the job.

I can't remember how accurate the Whizzbang shunt SOC is, (think they're meant to be fairly accurate tho'?) hopefully it also uses Peukert calculations with a clever algorithm, as shunts logging just amps in and out don't tell the whole picture and go out of snyc.

If you do try adding odd batteries, treat them as expendable, and only connect them into the system for gigs, to make sure both banks get charged seperatley (properly)

The Navitron Forum has quite a few threads about battery mixing, and general consensus is it's a false economy.





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