Navitron Renewable Energy and Sustainability Forum

Energy/Electricity Storage and Use/Grid Connection => Off-Grid, Batteries & Inverters => Topic started by: Nickel2 on October 12, 2019, 04:13:03 PM

Title: Nickel2 power wall batteries
Post by: Nickel2 on October 12, 2019, 04:13:03 PM
Service time on the batteries today. They are getting on 6 years old so performance is sagging.
I have 4 x 12v 200Ah units in series/parallel.
2 of the batteries have a tired cell each, with SG of 1.17 and 1.19 respectively; the rest are all about 1.28 except for 1 at 1.21.
I am going to rearrange them so that the two tired batteries are in one series pair, and the good ones are in the other series pair.
These series pairs will then be connected in parallel, with a balance lead between the series pair junctions.
Now the silly questions  :P
Do FLA batteries go open circuit or short circuit as they age?
I know they are overdue for replacement, but due to the current financial constraints, I'd like them to see me through another winter. They live at 15 - 20 degrees, and being starter batteries only get used to 10-15% DOD.
Can I recover the low cells? The tops of some plates look a bit sulphated (whitish). Would a large dollop of amps sort them out? My mains 'battery doctor' can supply 25 Amps.
All advice gratefully received, ta!

Title: Re: Nickel2 power wall batteries
Post by: A.L. on October 12, 2019, 05:01:57 PM

Ignore if obvious,

Dendrites growing from one plate can penetrate any separator and contact the next plate, crud at the bottom can build up and touch two or more plates.

Title: Re: Nickel2 power wall batteries
Post by: Philip R on October 12, 2019, 08:13:25 PM
Do your batteries have a clear case, which allows you to see the plates and fullness of the mud space below the plates?
If this space is not full, then I would try some single cell recharging, equalisation. To bring on some light gassing at about 2.3 volts per cell upwards. Don't go mad with the current or you will knock off active material off the plates or rods( if tubular type). This should hopefully bring up the volts and sg of the electrolyte. Sulphation will kill a lead acid if left too long in a low charge state. Gassing also de stratifies the acid in the space below the plates.
Philip R

Title: Re: Nickel2 power wall batteries
Post by: Nickel2 on October 13, 2019, 10:52:25 AM
They were starter batteries recovered from a 2MW generator plant when new ones were fitted. They were 4+ years old when I got them and had been on 13.25V (!?) float all their working lives, only used to start the engines for testing once per month. I've had them working for 15 months.
Others of the type on different sites were found to 'explode' sometimes when test starting, so they were all replaced. I don't have clods of cash to wave at forklift batteries or Li batts, so these have had to do for the time being. (Currently looking for a leaf in a ditch  whistle)
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Title: Re: Nickel2 power wall batteries
Post by: JohnS on October 13, 2019, 12:02:41 PM
Hi Nickel2

It is difficult to tell from your photos, but it looks to be that you have got the wiring of the batteries wrong. 
The top and bottom pair are each wired together to give a 24v battery.
However, the bottom pair have more cable going to them and thus the voltage supplied to them when charging will be slightly lower as there is voltage drop across the extra cable.
The result is that the bottom pair will never get a full charge.

These folks explain the issue much more elegantly than I can

Apologies if the wiring is correct and I did not see it properly.


Title: Re: Nickel2 power wall batteries
Post by: Nickel2 on October 13, 2019, 01:28:48 PM
Hi John, I totally understand what you mean, but I have taken that into account. The top pair are connected in series using 50^2 mm to give nominal 24v  . The bottom pair are in series to give 24v. The two pairs are then connected in parallel, using 50^2 mm copper from top to bottom at the 0v end, and top to bottom at the 24v end. The junctions  of the batteries at the 12v points are joined together using 16^2 mm.
At full current I'd expect to see 7.7 mV difference between top and bottom, but in this application typical current is 10 A top, 10 A bottom, so 3.87 mV difference calculated is not far from what I have measured with the fluke 75. The red and black leads from the MPPT to the batteries are 16^2 mm; the grey leads from battery to Henley block are 50^2 mm.
Briefly, There is so much copper between the two that charge/discharge-current difference is almost negligible. They are all as tired as me, but we both need to eke out a few more months! Thanks for your reply :)

Title: Re: Nickel2 power wall batteries
Post by: Philip R on October 13, 2019, 01:57:26 PM
You mentioned 13.25v float. That is a tad less than 2.21 volts per cell. If these cells were not properly brought up to charge, the acid will stratify.float needs o be a bit higher, we did 2.25 vpc on the Plante,s, in my previous workplace, not Faure cells that you have. Try a boost,equalisation charge.
Philip R

Title: Re: Nickel2 power wall batteries
Post by: TT on October 13, 2019, 07:12:40 PM
Hi Nickel2,

If you have time to share a rough schematic of your set up, that would be awesome,
Just plugging away at buys some bits and bobs for my own solar PV Install- DIY.
Interested in the fans, the filter? Etc

Thanks in advance

Title: Re: Nickel2 power wall batteries
Post by: Nickel2 on October 13, 2019, 08:11:39 PM
Right. :(
Had a play this pm with the battery charger. Started at 28.5V for 1 hour ~ 20A. (adjusting to keep voltage as constant as possible). After 1 hour at 2.375V per cell, upped the voltage to 29V for another hour ~ 25A, 2.42V per cell. All the good cells were gassing freely with the visible part at the top of the plates chocolate brown.
After the 2 hours were up, SG tested the two bad cells, they were only up by a percentage point, (on the border of the green and white area of the float).
This evening I've drawn less than 300Wh and the battery off-load voltage has dropped to 25.07V from sundown to 20:00. facepalm
Unless I can awake those two cells, the poor old batteries will go back into the pot to make new ones, and I shall be back on full-grid til I find more old carp to nurse into their leaden dotage.
Edit: It's all gone horribly wrong now. Batteries do not like the new arrangement and have flattened each other. I shall revert to the original setup and try one last time. If no workee, then I'll take em all to the scrappy and put the weight towards another set. from somewhere. :fume

Title: Re: Nickel2 power wall batteries
Post by: Philip R on October 14, 2019, 09:35:05 AM
When I suggested cell voltages, I omitted charge rate. When I mentioned the boost charge, the manufacturers, suggested via the old BS440 spec, the rate of C/7 upto 2.3 vpc and the down to C/14 afterwards. So for the 200Ah cells, about 14A.
The specific gravities should come up if the played are in circuit and not sulphated beyond redemption. I recall my first station battery discharge test, it took over a 2shifts to bring the SGs  back. That was without being sulphated.
On another occasion, a cell was removed from the battery for a teardown test. The replacement cell had not had its plates conditioned like an older cell, therefore of lower capacity.
I charged it on a single cell charger for two days and the on a coutant lab psu, voltage limit of 2.35 vpc and a current limit of 2A for a few days. The sgs came up and the plates coloured up nicely.
The cell went into the battery and when discharge tested on the next routine, ot behaved like the other cells.