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Mitchs PV and battery system disapoints.

 
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Mitch



Joined: 04 Aug 2006
Posts: 458
Location: Grand Union Canal, London

PostPosted: Sat Jun 28, 2008 5:27 pm    Post subject: Reply with quote

Yes, most interesting indeed. Sorry for all the questions guy's, but I am wondering what I have done wrong here.

When I did up the boat, I installed 20 x 110 a/h Elecsol batteries. They were well expensive, but the blurb called them "carbon-fibre" and went to great length's to explain why they were so much better. They even came with a 5 year warrauntee! I run a 12v system, (mistake I know, should have gone 48v), with a 3Kw inverter. At full clout on the inverter, I imagine a current draw of around 300 amps. The batt's are all in parallel, so that's about 15 amps per batt. I didn't think that was stressing them in any way. Average use is 20 amps per hour, and the batt's lasted 90 hours from full to flat. My charger is a 20 amp regulated power supply and is set for 13.9 volts open circuit voltage. I re-charged all week and used the batteries every weekend. This is a 48 hour, or 50% discharge cycle, with a 120 hour charge cycle, with the voltage limited to 13.8v across the batt's. Slow charge rate of 1 amp per battery, so again, I was sure this was not harmful. Within 18 month's - 75 cycles - they were only lasting 50 - 55 hours, so were now getting nearly a 100% discharge over a weekend. At three years - 150 cycles - they were totally wrecked, giving me less than 10 mins, and all blown and swollen. Obviously I didn't get a couple of thousand pounds new batteries under warauntee - that wasn't going to happen without huge legal expenses, but what went wrong? I topped them up every 6 month's, but by the third top-up, I was putting in 30 litres of water between the 20 batteries. Why did they gas that much? I really didn't think I broke them. Reasonable discharge rate, nice slow charge rate, DOD of 50% - hell I should have 7 - 10 years out of them. They were, after all, almost twice the price of the nearest competitor!!

Have now replaced them with "Energy" 100a/h batteries - it's quite strange though, because the 110 a/h ones lasted me about 90 hours at a 1 amp per battery discharge rate - yet brand new 100 a/h batteries last me 40 hours, at the same discharge rate! Oh, well I suppose "chinese watts" apply to everything these days, I no longer believe anything I'm told in advertising blurb - or by salesman for that matter.
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adam2
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Joined: 02 Jul 2007
Posts: 6559
Location: North Somerset

PostPosted: Thu Jul 03, 2008 9:05 am    Post subject: Reply with quote

Mitch wrote:
Yes, most interesting indeed. Sorry for all the questions guy's, but I am wondering what I have done wrong here.

When I did up the boat, I installed 20 x 110 a/h Elecsol batteries. They were well expensive, but the blurb called them "carbon-fibre" and went to great length's to explain why they were so much better. They even came with a 5 year warrauntee! I run a 12v system, (mistake I know, should have gone 48v), with a 3Kw inverter. At full clout on the inverter, I imagine a current draw of around 300 amps. The batt's are all in parallel, so that's about 15 amps per batt. I didn't think that was stressing them in any way. Average use is 20 amps per hour, and the batt's lasted 90 hours from full to flat. My charger is a 20 amp regulated power supply and is set for 13.9 volts open circuit voltage. I re-charged all week and used the batteries every weekend. This is a 48 hour, or 50% discharge cycle, with a 120 hour charge cycle, with the voltage limited to 13.8v across the batt's. Slow charge rate of 1 amp per battery, so again, I was sure this was not harmful. Within 18 month's - 75 cycles - they were only lasting 50 - 55 hours, so were now getting nearly a 100% discharge over a weekend. At three years - 150 cycles - they were totally wrecked, giving me less than 10 mins, and all blown and swollen. Obviously I didn't get a couple of thousand pounds new batteries under warauntee - that wasn't going to happen without huge legal expenses, but what went wrong? I topped them up every 6 month's, but by the third top-up, I was putting in 30 litres of water between the 20 batteries. Why did they gas that much? I really didn't think I broke them. Reasonable discharge rate, nice slow charge rate, DOD of 50% - hell I should have 7 - 10 years out of them. They were, after all, almost twice the price of the nearest competitor!!

Have now replaced them with "Energy" 100a/h batteries - it's quite strange though, because the 110 a/h ones lasted me about 90 hours at a 1 amp per battery discharge rate - yet brand new 100 a/h batteries last me 40 hours, at the same discharge rate! Oh, well I suppose "chinese watts" apply to everything these days, I no longer believe anything I'm told in advertising blurb - or by salesman for that matter.


A 3KW invertor at 12 volt input would indeed draw about 300 amps if fully loaded, which as you point out is about 15 amps per battery, that should not present a problem.
What size were the cables linking the batteries to each other? if insufficient in size, this could result in the batteries nearest the inverter taking most of the load, and failing.
(Idealy when a number of batteries are wired in parralell, the cables should be arranged such that the path to each battery is the same length, this is especialy desirable when very large currents are innvolved)

The great consumption of distilled water may suggest overcharging, what was the exact charging voltage ? 13.9 is perhaps a little high but not that bad, was it checked with an accurate voltmeter?

Batteries dont like high temps, they wernt near too near a stove, boiler, engine, engine exhaust, solar HWS or other heat source were they?

It might be worth trying to claim on the warrenty, dont raise your hopes, but silly not to try.
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Mitch



Joined: 04 Aug 2006
Posts: 458
Location: Grand Union Canal, London

PostPosted: Thu Jul 03, 2008 10:25 am    Post subject: Reply with quote

Thanks Adam2, I did try the warrenty thing with no success. Just for interest, the batt's are situated inside the living area, (breather hoses run to the outside), in two rows of 10. They should be at, or just under, room temperature. The batt. boxes are situated each side of the boat. I have two 10mm x 30mm x 2mtr copper bus-bars - one for neg, one for pos - in each box. The batts are connected to the bus-bars with 35 sq.mm, 225 amp welding cable, of about 30cm long between the terminal and bus-bar. The neg bus-bars are chassis grounded using 2 x 35mm cables each of around 70cm long. The inverter is mounted at the back of the boat, and I have run two 35sq.mm cables from each pos bus-bar to the inverter. (4x cables in total carring pos. - neg. grounded). This distance is around 10 metres - not ideal, I know, but at full clout on the inverter the volt drop is .4 volts. (E.G. 12.8v across the batteries = 12.4v at the inverter. (This has increased to around .6/.7 volts over time - some contact cleaning is required). The 13.9 volts at full charge is accurately measured on the batt. sense wires I have run independantly back to the electrical cupboard, and which are connected to the sense terminals on the power supply.

I honestly cannot see what it is that killed the batteries. The only thing could be lack of maintenance, perhaps they need checking once a week, rather than once every 6 month's. Problem is that I literally have to dis-assemble cupboards and couches to get at them - hence my purchasing "ultra low maintenance" batteries. This time I have bought SFL's - let's see what they do.
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adam2
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Location: North Somerset

PostPosted: Thu Jul 03, 2008 11:01 am    Post subject: Reply with quote

With the layout described, the batteries nearest the inverter connections would supply a greater share of the current, however with such large busbars the effect should not be significant.

I suspect that with batteries in regular use, the six monthly topping up may not have been sufficient, monthly checking might have been better.

A charging voltage of 13.9 volts is a little high if long continued, fine for recharging after a discharge but a bit high for continual use.

Was this a three stage battery charger? or a true constant voltage power supply?

Three stage battery chargers can be "confused" by a battery bigger than they were designed for, and this can lead to overcharging, contrary to what might be expected.

A true constant voltage power supply can be used with any sixe battery, though of course it takes a long while with a large battery.
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Mitch



Joined: 04 Aug 2006
Posts: 458
Location: Grand Union Canal, London

PostPosted: Thu Jul 03, 2008 11:28 am    Post subject: Reply with quote

True constant voltage switch-mode PSU, with the the sense inputs connected. Initially it took 5 day's to reach 13.9, from complete discharge. I was only dis-charging 50% normally though. I would disconnect from shore power at around 5 pm on Fri, and run on the batt's till Sunday 5 or 6pm. For the first few month's it reached 13.6/7 by Wed. morning, with charge current down to about 2 amps. Hit 13.9 by Fri evening with charge current down to 4 or 5 hundred milli-amps. Initial charge current is limited to 20 amps by the PSU - approx. 1 amp per battery.

Other charging is via 3 x 100 amp alternators on the engine, modified so that an Adverc 4 stage controller could overide the provided regulators. I have never had chance to see the Adverc work - 7 hours of running the engine didn't get the batt's anywhere near full, from flat, so the Adverc just sat wide open, pumping around 15 amps per battery. Highest I ever got was 13.3 across the batt's - and that was only twice that I used the engine to charge when away on my holiday's. The alternators have blown up twice - short circuit diodes - but each alternator was fed via a seperate 120 amp blocking diode, which are still fine, so no A.C. componant managed to get to the batteries. The alternators are controlled by individual switches, and I only ever run one when cruising. I only fire up all three when standing still and needing some extra charging. (The engine is too small to run all three and push the boat along - choice, charge or cruise, not both).
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