When to end absorb

stephendv

I've been watching the charging amps during absorb and was wondering when would be the best point to end absorb. The batteries are 1.5 year old traction bats 867Ah C20.
The often quoted 2% for end amps seems far too soon to me as that would be where the dot is in the graph, about halfway to where the charge starts levelling off.
My gut feeling is to end it at whatever the amps are at 14:00 on the graph. Thoughts?

Attachment not found.

Vic

Re: When to end absorb

Hi Stephen,

My Surrettes like close to 1% into the batteries as EA.

Would use SG as THE indicator of where to stop Absorb. Nice graph! Vic

BB.

Re: When to end absorb

Stephen, are these sealed batteries where you cannot take SG readings?

If so, it might be interesting graphing the battery temperature (or even rate of temperature change) vs time... At some point, most of the energy would go into heating the batteries rather than charging them. You might see a temperature inflection point at the point the batteries are "full".

If these are sealed batteries with a catalyst--You might measure temperature near the catalyst (in battery cap?) (or even battery pressure--if you have that capability) if the body of the cell is not showing temperature variations (too much mass, air cooling, etc.).

-Bill

stephendv

Re: When to end absorb

Vic yes I can try SG readings, there's a small problem in that the cells suffer from stratification so I only ever see the fully charged 1.28 SG at the end of an EQ charge. But I could take that into account and just watch for when the SG stops rising as use that as end amps.

Bill, luckily they're flooded so SG will be my first port of call. Interesting idea with the temps, they hardly change during charging. The batts are snug in a semi-underground bunker so they start the morning at about 15 degrees C and end the day at 16, after the absorb in the graph. If I want temps to rise then I need to do an EQ.

BB.

Re: When to end absorb

You are running a fairly low rate of charge--Which is leading to stratification issues? You might want to see what the curves look like if you bump up the charging voltage a volt or so.

Do you have a comparison between AH/WH load vs charging per day?

If you are having stratification--Your plates tend to discharge at the base of the cell and recharge near the top--Not a good way to ensure long battery life. Forced mixing by adding heat/more gassing (from higher charging voltage--if more charging current is not available) may be a viable option (don't like the idea of too much gassing--But what can you do?).

-Bill

stephendv

Re: When to end absorb

BB. wrote: »

You are running a fairly low rate of charge--Which is leading to stratification issues? You might want to see what the curves look like if you bump up the charging voltage a volt or so.

Yeah, I've tried experimenting with an absorb voltage of 2.45V instead of 2.4V, the curve bottoms out like the one above but the cells still don't reach the fully charged SG value. They reach 1.27 SG instead of 1.29. The only thing that seems to bring them up to 1.29 is EQ style voltages 2.6V and higher.

Vic

Re: When to end absorb

BB,

Seems to me that charge current has little to do with mixing and de-straitfication. Absorption V does seem to be the thing that encourages mixing via gassing. Longer Absorption times at lower voltage are not as effective at mixing as are higher Abs voltage, in my experience. Higher rates should increase diffusion flows, but gassing seems to be the thing that mixes the electrolyte.

No shortage of opinions here, Vic

BB.

Re: When to end absorb

One of the papers I referenced mentioned (sort of) that high discharging currents warmed the electrolyte/plate boundaries and (significantly?) increased the electrical activity of the battery in very cold weather...

Since the "boundary" for high current discharge seems to be around C/8 (12.5%) for flooded cell batteries--I was wondering if that was also the boundary for "high current" charging which could increase the battery temperature enough to help with mixing.

-Bill

Vic

Re: When to end absorb

Hi BB Bill,

Well about all that I know is that I know very little of the ins and outs of batteries.

Did two hours of Bulk at 10% of 20 Capacity yesterday ... was monitoring electrolyte temp with a thermometer in electrolyte of one cell. The temp went up one degree F in this Bulk, but as Absorb V approached the rate of temp rise increased significantly (wow, what a surprise!). This is, of course, not at the boundary of the plate/H2SO4, and there is some lag time, especially in Bulk when there seems (to me) to be less mixing.

Batteries are interesting creatures, and it is easy to obsess too much about their care and feeding.

If I had a ForkLift battery, think that I'd be on the high end of the recommended charge voltages, and if it looked like there was still stratification, would try to use one of the more exotic charger profiles, that Stephen has noted for EU chargers.

Stephen, believe that you can now make that MidNite Classic stand up and dance, so bet you can program a microcontroller to do some of these different charge profiles.

Good thing that FLAs are fairly forgiving. Good Luck, Vic

stephendv

Re: When to end absorb

Vic wrote: »

Batteries are interesting creatures, and it is easy to obsess too much about their care and feeding.

If there's a support group for battery obsessives, please let me know

Vic wrote: »

If I had a ForkLift battery, think that I'd be on the high end of the recommended charge voltages, and if it looked like there was still stratification, would try to use one of the more exotic charger profiles, that Stephen has noted for EU chargers.

Stephen, believe that you can now make that MidNite Classic stand up and dance, so bet you can program a microcontroller to do some of these different charge profiles.

The communication link between PC and classic isn't reliable enough to use it to control the charge profile. Still looking for a solution to that... so in the meantime, I do opportunity short-EQ's every week or so. This is where the Classic's PC software really shines, I can start and stop EQ from the comfort of my desk without walking down to the batteries Just 10 minutes at EQ voltage to get the mixing going, but haven't done any proper tests to see whether this works well or not.

Rngr275

Re: When to end absorb

stephendv wrote: »

If there's a support group for battery obsessives, please let me know
.

You mean I am not alone? I just went off grid this summer and I am being accused of having an affair with the batteries... which in a way I am!;) Will it get better?

niel

Re: When to end absorb

Rngr275 wrote: »

You mean I am not alone? I just went off grid this summer and I am being accused of having an affair with the batteries... which in a way I am!;) Will it get better?

how shocking.:p i think you're safe as long as you don't take them out to dinner and sleep with them.:roll::p

unicornio

Re: When to end absorb

stephendv wrote: »

If there's a support group for battery obsessives, please let me know

The battery itself is an obsession. is variable and fickle as a good girlfriend ... hehehehe

The absorption step is as how to treat a girlfriend, there are thousands of ways and each in its way expresses his nature, his personality, so I do not think there's only one way to do well the absorption stage but there will be many ... so yes, all the more that we can deepen our relationship which is necessary to find what is our way ...

to the extent that we succeed or fail in the way, give long as we maintain our battery with us...
as well as a girlfriend (or boyfriend) ... lol

westbranch

Re: When to end absorb

Stephen, try this doc, its focus is LA battery chemistry and then applying it to AGM and Gel, but lots to be gleaned re this discussion I think.
ps lots of small typos...
http://www.cdtechno.com/pdf/ref/41_2128_1199.pdf

there are 2 points I see applicable here:

1 the graph of Abs V and temp rise and
2 the reference to a higher Abs V and the higher current that accompanies it.

pps I am still re-reading this doc and 'absorbing' it vis-a-vis my battery and choosing the proper charge settings for Bulk, Absorb and Float so no expert here...

stephendv

Re: When to end absorb

westbranch wrote: »

Stephen, try this doc, its focus is LA battery chemistry and then applying it to AGM and Gel, but lots to be gleaned re this discussion I think.
ps lots of small typos...
http://www.cdtechno.com/pdf/ref/41_2128_1199.pdf

Thanks westbranch, lots of interesting docs and graphs on that site! Will have to take some time to study.

boB

Re: When to end absorb

I can't seem to find that document. Is there a name on the document I might be able to look for instead of that link ??

Also, this company has some very interesting products !

boB

stephendv

Re: When to end absorb

From here: http://www.cdtechno.com/resource/support_doc.html

You can look at the number at the start of the doc: 41_2128 to find it in the page. Direct linking seems not to work.

westbranch

Re: When to end absorb

thanks Stephen, I came to it from another link, that is a great list of interesting docs..
Muchas Gracias

Eric

ps they must have your 'name ' on a block list, I can get it straight away

jtdiesel65

Re: When to end absorb

So the process here is to watch SG and when SG reaches ideal amps going in becomes end amps? How does one figure in the load given there might be differences at different time?