PzS plate no/size

liamg

Hello,

I've seen that every manufacturer has a wide range of (PzS) cells available, with variable number of plates and plate size.

That's it, I've seen 250Ah cells with two plates (125Ah per plate), three plates (80Ah per plate) and so on.

A lower number of plates usually increase the plate height. Is that prone to electrolyte stratification?

A larger number of plates means more chances to develop a inter-plate shortcircuit (imho).   

FWIW, I'll go with the thicker plates (though that parameter is not always available).

From reliability point of view, what's the best choice? Thank you in advance for any oppinion.

liamg

Any thoughts about the width (the number of plates) vs height ratio?

mvas

Yes, stratification is an issue with any stationary batteries.
It would seem that the taller battery would aggravate the stratification issue.
But, if you regularly charge your batteries to 14.8 Volts then you will get some bubbling to stir the electrolyte.
An Equalization Charge will mix the electrolyte even more.
Some tall PzS batteries ( Varta? ) have an electrolyte re-circulation path built-in,
which they claim solves this issue.

Tall PzS batteries do not appear to be very common for small scale RE projects, yet.
A secondary case is usually available to solve the "tipping" issue with tall 2V cells.

See message #147 in this thread ...
http://forum.solar-electric.com/discussion/comment/308705#Comment_308705
Contact @stephendv  for info regarding PzS batteries

liamg

Thank you very much, @mvas! I knew about the electrolyte recirculation (I guess every reputable manufacturer has this option already) but I dont's think it is quite effective. 

They just insert some air through a single/small pipe down to the bottom of the case but I doubt there's a homogeneous recirculation of the entire electrolyte (especially if the cell has many plates).

Speaking of that, what about the number of plates? Should I worry about the increasing chances of interplate shortcircuits or that's not an issue with the PzS topology?

mvas

liamg said:

Speaking of that, what about the number of plates? Should I worry about the increasing chances of interplate shortcircuits or that's not an issue with the PzS topology?

PSOC / under-charging (#1), over-charging (#2), under-watering (#3) are the top reasons batteries have early failure.
Is there really any difference between "taller / fewer plates" vs "shorter / more plates" re: interplate short circuits?
Do see a high rate of early failure from "inter palte short ciruit" ?

liamg said:

They just insert some air through a single/small pipe down to the bottom of the case but I doubt there's a homogeneous recirculation of the entire electrolyte (especially if the cell has many plates).

Have you ever see how "rising bubbles in a tube" can cause the water in a fish tank to thoroughly circulate?
A very similar principle is used by Hawker and others:
"... The Hawker Perfect Plus electrolyte circulation system, using the Air System principle, consists of a pipe system which is fitted in the cells. A diaphragm pump sends a low rate airflow into the cell which creates a circulating air stream inside the cell box. This system prevents electrolyte stratification and the battery charging is optimized ..."
Is this better than over-charging the cell to create randomly located bubbles?
Only time will tell.

liamg

Like I've just said, I knew about the recirculation systems but you can't compare a fish bowl full of clean water with a tight mixture of Pb plates, separators and electrolyte.

The air bubble will try to escape up to the top following the easiest paths so it would rather "climb" the case walls (there's more clearance) instead of interplate regions. Does EnerSys (Hawker/FIAMM) posted any real-life video of what's actually happen inside there?

The techonlogy should work with a proper designed (bottom) case, to allow an even distribution of air bubbles around every plate. In practice, they just insert a small tube from the upper lid to the bottom of a regular case. 

Btw, what about the extra oxygen entering the electrolyte during recirculation? Maybe a true recirculation (electrolyte only) would have been better (but not easier, I must admit).

Later edit:

I've just found a similar thread (about the electrolyte recirculation): http://forum.solar-electric.com/discussion/8362/air-pumps-for-better-battery-charging/p1

mvas

Not a fish bowl, a large fish tank with dirty water - more water than your battery.
Have you never seen that little tube with bubbles that can pull the dirty water completely out of the tank and
into an external filter and then the cleaned water flows back into the tank - the water is thoroughly mixed.
Also, an underground fish tank filter can use a "bubbler tube" to thoroughly circulate the water inside tank.
Bubbles are amazing efficient at moving water.

OPzS - The air tube is at the bottom of the cell where it can move the heavy electrolyte from BELOW THE PLATES
to force it above the plates, where it mixes with the most dilute electrolyte and finally washes over the plates.

I would prefer mixing the electrolyte with external bubbles vs over-charging my cells.
Bubbling the plates will increase active material shedding, which is lost capacity forever.

liamg

I don't want to argue, but still a fish bowl/tank is a different animal. Put a bank of Pb-separator-Pb plates (as in a real battery) inside that fish tank and I bet the bubbles will avoid the interplate regions.

In theory, the whole principle looks right. I just wonder why it's not used as default on every PzS (at least) battery these days. There's at least one thing it could do for sure: recirculating the shedding material from the bottom of the case, to avoid interplate shortcircuits.

mvas

The Hoppecke system shows the electrolyte flowing up one end of the plates and down the other end of the plates.
They say, "Circulation of the electrolyte", as in flowing in a circular path,
 not random mixing like regular over-charging bubbling.

It does not matter how the bubbles drag the heavier electrolyte back up to the top,
but once at the top, the bubbles come out of solution and
now the heavier electrolyte can mix with dilute electrolyte and/or wash back down over the plates.

The bubbles should not recirculate any shedded (dead) lead material = "mud".
The mud must stay at the bottom where it belongs, in the mud bin.
That is why the plates stand on ribs (see photo below).
The plates must not touch the bottom of the battery.
Too much shedding = too much mud = shorted cell.

liamg

Okay, I'll take it for granted.. that's how it supposed to work (in theory), anyway.

I must say that I was actually asking few vendors about this feature and they kind of disappointed me.

First, this feature must be preordered to factory (no stocks available) hence a very large delay in delivery time.

Second, they were quite pessimistic about the real advantage for my application (off grid system).

Beside, they kept on asking me if I have the appropiate charger for that. I guess that's another weak point: one could destroy the battery if the air pressure is just too high thus any vendor will try to avoid such a twilight situation.

Later edit:

Do you believe in last picture you've posted? Do you have that large space between two plates for those violet bubble upstreams? It's rather the small blue line between them..

mvas

liamg said:

Okay, I'll take it for granted.. that's how it supposed to work (in theory), anyway.

I must say that I was actually asking few vendors about this feature and they kind of disappointed me.

First, this feature must be preordered to factory (no stocks available) hence a very large delay in delivery time.

Second, they were quite pessimistic about the real advantage for my application (off grid system).

Beside, they kept on asking me if I have the appropiate charger for that. I guess that's another weak point: one could destroy the battery if the air pressure is just too high thus any vendor will try to avoid such a twilight situation.

Later edit:

Do you believe in last picture you've posted? Do you have that large space between two plates for those violet bubble upstreams? It's rather the small blue line between them..

Yes, in theory.  

On the website the very first Typical Application is Solar / Off-Grid
I think, a stationary off-grid application is more applicable than any motive application = constant mixing from motion
What application does the vendor think is more applicable than yours?

How about the green arrows in these two (2) images here ...
https://www.mare-solar.com/shop/myfiles/ECS_en.pdf
Circular path of green arows:
1) Across the bottom the plates
2) Up the opposite side wall
3) Across the top of the plates
4) Down the side with the bubbler tube

Looks like the bubbler tube is in the corner.
I would like to see a video of the bubbles!

Both Trojan and Rolls state, do not Equalize unless needed.
We should not equalize on a regular basis per a so-called "Smart" Charge Controller.
So, could the bubbler prevent any unnecessary Equalizing that we've been do just to un-stratify the electrolyte?
Hydrometer shows, "SG is LOW" therefore Batteries must always require charging, right?
Wrong, what if the acid is mostly concentrated at the bottom and battery is fully charged?
How much extra life / more cycles can we get by not shedding active material, by elimating some over-charging?
That is the $64,000 question.

liamg

The vendors (and the manufacturers) claim the reduced bulk charging time (by simultaneous mass reaction over the entire plate surface) and a lower average temperature thus one could use higher charging currents (so they could use the battery twice per day for a forklift, by example).

Anyway, I've always wanted to stir the electrolyte up using a stick (through the venting holes) so yeah, a legit recirculation system would be more than welcome!

Now serious: the electrolyte recirculation it's the best innovation for this old technology but they could have been using a better design to be effective.

But, once again, I believe in manufacturers conspiracy: an immortal battery will close their business; instead, a "gentle touch" of a bare recirculating system will improve their market share.

BB.

OK, here is a long thread with links to various studies about Lead Acid Battery Stratification:

http://forum.solar-electric.com/discussion/16664/when-does-electrolyte-stratification-occur?p=210105#post210105

And we had a member with access to a laboratory that would do various interesting tests:

http://forum.solar-electric.com/discussion/8362/air-pumps-for-better-battery-charging/p1

-Bill