End Amps

[plongson]

At the risk of beating a dead horse, I'm trying to get up to speed on END AMPS. I've searched here, on NAWS, the Rolls site and even the 'net with limited results. Any links would be appreciated but here's my deal...

Right now I have the classic 250 set to absorb for 4 hours and 59 volts. It seems to be working pretty good, SG is acceptable with water usage topping off about every 6 to 8 weeks. Never being one to leave well enough alone, what do you guys think of the End Amps feature/setting? Should it be employed and how should I go about setting it up correctly? Is it really any better than a set time?

I know all this is subjective but I am open to all opinions.

THANKS for the help!

Paul

[Westbranch]

Hi Paul, I assume you are still using the protocol settings determined in the previous string? 

If so have you thought of 'dialing back a bit' on the time &/or volts now that you have brought your bank up to a point that  you are happy with, since summer will bring more (longer) charging time than achieved in winter.

Eric

[plongson]

That's exactly what I was thinking. Kind'a why I was looking in into the end amps option...but in the absorb setting,  4 hours is 4 hours whether it's summer or winter...right??? I Dun'no??

[Vic]

Hi Paul,

A fixted Asorb time is fine if you have a fairly constant DOD of the batteries.  EA can be the perfect solution,  once you determine the correct amount ending current,  if your DOD varies quite a bit.  As you know the required Asorb time really depends on the DOD.  This EA value  is not difficult to determine with FLAs.

Howerer,  as you probably know,  the CC cannot determine just how much of the CC current is going into the batts as charge and how much is being used by Inverters (and possibly other battery loads).  So,  if you have fairly low loads near the end for a typical day,  or fairly constant Inverter loads,  which you can add to the desired EA value,  EA is still a very good way to end Asorb.

In an active household,  with folks turning of/off appliances,  water pumping systems coming on/off at random times,  EA from a CC is prob not the best way to end Asorb.

If you have a shunt in your system between the Neg batt lead,  and inverters,  you can measure the ACTUAL currents charging the batts.  This can help you determine EA,  but it is no help with significant and varying loads near the Asorb end.

A Battery Monitor could measure this Net Charge current,  and perhaps some day command a CC to end Asorb.  I do not know of a BM with this function.  Some of the commands that are available in the Classic comm set could allow this - like Force Float -  But there would need to be a BM that had this control function built-in.

Would bet that the MN BM will have this function,  and many more.  I cannot wait for such a product.

I DO use EA here,  as the day-time loads are light,  well known,  and random loads are under the control of a single individual.  Agree with WB about Asorb time,  altho,  if is what the system needs (that is,  if your SGs are not creeping up now),  then keeping it as it is should be OK.  You are using water,  but not too much etc.  Have Fun,  Vic

[plongson]

Hey Vic, thanks for the reply.

I can see what you are saying about the CC and a BM. It seems the CC would almost require a BM for EA to be optimal. Too bad one is not available yet. Going by what you are saying (yes, my loads are light and predictable at the end of the day and my DOD is only about 10% to 13% by morning even in winter) so for now I'll leave it on a set time.

Even though I seem to have a handle on SG, what confuses me is, with the 4hr/59vdc absorb I still have a variance in SG. At the end of the day, after an hour or two of float, several cells are at 1.250/5 and the rest are closer to 1.260/5. Is that an acceptable spread? Maybe I need to EQ more often?

If I had it to do all over again, I would commission the system totally different. Live and learn... I'd fully charge for days on on end, EQ before throwing a load on them and get an initial SG reading from the get-go. like I said...live and learn.

Just for giggles, what is your EA setting?

Paul

[Westbranch]

Maybe I need to EQ more often?

If I had it to do all over again, I would commission the system totally different. Live and learn... I'd fully charge for days on on end, EQ before throwing a load on them and get an initial SG reading from the get-go. like I said...live and learn.

AH HA!  how often are you EQing?  that might be the key to those variant numbers... Can you summarize your protocol since you got the SGs up (way back when)

[plongson]

EQ has not really been on a regimented schedule but has been done about once every 4 to 5  weeks or so. The entire system was commissioned about a week before Thanksgiving 2011.

I've done one or two 4 hour EQ's using the genset very early on (which burns plenty of fuel) and the rest have been done via solar, as soon as possible after hitting float usually about 1300hrs. The Classic is set for a 2 hour EQ. I get plenty of gassing and the cells all come up together but never really EQUALIZE. In other words they'll come up say 10 points but the gap never really closes and some stop at say 1.265 and the low ones stop at at 1.255.

I'd love to see the whole bank at 1.265 across the board. Ya think they just need a longer/more frequent EQ session?

[Vic]

Hi Paul,

Well, EQ should bring up the SG on the lagging cells,  and unfortunately,  it also brings up the SG on cells that do not really need it.  Having a 10 point spread is actually good IMHO.

I do wonder what is your EQ voltage,  tho.  Active bubbling is good during EQ.  Surrette specs the minimum EQ  voltage of 61.9 V

When comissioning the banks here,  chose the Pilot cell in the traditional manner -- chose the cell with the lowest SG.  In the oldest bank,  that Pilot is still the lowest SG cell.  Have set the charge parameters to bring that cell to 1.265 on a good sunny day.  So, other cells run a bit higher SG than that.   Just like to get every cell "fully charged"  It is possible that I should lower the target SG for the Pilot to something like 1.260,  allowing some of the hotter cells to run at a bit lower SG.

Hydrometers do have some tolerance of +/- 3 to 5 points,  for most of them.  And some say that it is not possible to read closer than 5 points,  which I do not agree with.

Also,  regarding the Float voltage setting,  it should be adjusted just high enough to maintain the fully charged SG of the Pilot cell -- it should maintain the SG of that cell when Asorb stage ended EDIT: For the duration of Float.  Once Float MPPT begins,  then there is not enough power afailable to maintain the Float voltage,  so,  the SG would slowly decrease.

The 4 hour EQ seems long to me.  The two factors for an EQ is the voltage and time spent at that voltage.  The Classic has the option to Temp Compensate the EQ,  which IMHO we should use.

Nothing can be perfect,  at least not for long regarding off grid battery banks.  FLA are forgiving,  and we all do our best to do our best for the batteries.

And,  BTW,  I use an EA value of 16 amps.  It would be about 14 A,  but 16 allows for the inverters,  and parascitic loads,  and also the times the refer runs.  In monitoring the SG at end of Asorb a number of times,  16 A is correct for my systems.
EDIT: Of course the amount of charging accomplished at a certain EA current value does depent upon the Asorb voltage setting.

OK,  better post this.  Obviously,  the above is what I believe works for my system.  Others might do things a bit differently.   Good Luck,  Vic

[plongson]

The EQ voltage is set to 62 on the Classic. Ya, a 4 hour EQ seems to go on for ever! It drove me nuts to be running the genset for that long with diesel pushing $4.00 (We run red dyed with no road tax) so I really try to get the EQ duty done on solar, and that is set for 2 hours. I've been going over the Rolls manual again and they recommend longer stretches between EQ, like several months to twice a year.

If not time based, when do you EQ? When you see a large disparity between cells? As a general rule is a 10pt spread not too bad? I remember reading somewhere here or at NAWS that sometimes some cells never come up to textbook spec's.

I really wish I had better understanding on all this when I commissioned. Dang, I was building the house one day and started my trial by fire into the murky world of Solar Administrator of this system at the flick of that proverbial switch the next.  LOL  I've only been in the big-time for about 5 months.

Actually I really believe I'm in decent shape overall. I have an old neighbor down the road who just can't understand why his system will just shut down in the evening watching Perry Mason. Come to find out it's tripping on LVCO. The old boy is just slamming his system everyday, The local solar installer finally gave up on coming out to help because he'd never listen...

Anyway...The knowledge gleaned here has been invaluable. Just an unbelievable willingness on everyone's part to share and help. It is truly, truly appreciated.

Thanks to all

Paul

[Vic]

Paul,

Yes,  Surrette has begun recommending less frequent EQs,  unless there is a specific issue that an EQ could help resolve.

I probably EQ every 4-5 months now -- used to EQ more frequently. I think that a 10 SG point spread is fine and dandy.  And,  yes,  divergant SG is one of the main reasons I EQ.

The deeper the average discharge of the bank,  the more frequent EQ is required (in general).

If you EQ,  and essentially see NO increase in SGs on the cells that you want to increase,  after 4 hours,  then IMHO,  no rational amount of EQ will improve things.  The one thing is after a few hours of EQ,  batt temps can rise,  which depresses the SG readings a bit.  Another thing that you know is that EQing can consume some additional water.  THis water loss increases SGs.  At times, here,    run the high SG cells with a bit higher water level,  and any laggard a bit lower.  Probably too obsessive on my part.

There is no better learning,  than doing.  We are all learning,  and some of us with we could go back a bit and do things a bit differently.  Too bad that batteries have gotten so much more expensive ... it makes all of these details seem more important than in times past.

AND,  yes,  I believe that you are in very good shape.  Have mentioned before.  Most folks simply do not pay attention to batteries until the power goes OFF.  When batteries are new,  things can seem to be OK for some time,  some folks  go along paying them no heed at all.   You are paying close attention,  wondering,  and asking questions.  THis is not the normal behavior for many off gridders,  but should allow you to get very good batt performance.

Again,  am no expert here.  Am making mistakes myself,  and hopefully learning something from them.  Good Luck,  enjoy Spring,  Vic

[plongson]

Enjoy spring ... Hahaha...it just finished snowing. Oh well, it will be here soon enough. Lol