Classic / Kid Boost mode : Stealing from the XW MPPT 60

[ChrisOlson]

Does your XW system know what is going into the battery ?

Yes, it displays battery net amps on the SCP.  Even though it does not measure it with a shunt it agrees with our TriMetric within +/- 0.5A

Why don't they just limit the current and thus the rise to EQ voltage by looking at the battery temperature ?
That might work pretty good.

Because there is no need to make something more complicated than it has to be.

Manually doing an equalize is fine if you're around to do it.  The idea was to use the auto EQ to simulate three-stage bulk/absorb/finish charging.  Unfortunately, auto EQ in the Classic does not work properly.  Or at least not according to the charging recommendations from any battery manufacturer I have ever encountered.  That was the issue.

[boB]

Does your XW system know what is going into the battery ?

Yes, it displays battery net amps on the SCP.  Even though it does not measure it with a shunt it agrees with our TriMetric within +/- 0.5A

How does it know the battery current aside from other DC loads without its own shunt or sensor ?

How does it take into account the current coming from the wind system for example ?

[ChrisOlson]

How does it know the battery current aside from other DC loads without its own shunt or sensor ?

How does it take into account the current coming from the wind system for example ?

The controllers have shunts on their outputs so each one is measured.  The XW inverter has a hall effect sensor mounted on the main processor board in the upper right of the DC section of the inverter.  It measures DC current in or out of the inverter.  The whole system communicates what they're doing over Xanbus and either the SCP or the ComBox does the calculations to determine net current and reports the results back to the devices.  So they all know what battery current is (along with other information that they communicate with each other).

It does not communicate with the wind system.  During absorb charging our RD-1 Relay Driver shuts the wind system down so it doesn't interfere with the XW system measuring its end amps, and the battery gets charged correctly.  The wind is not needed at that point anyway when there's adequate solar to charge the battery and carry loads.  If the voltage "sags" more than 0.5V below the Absorb V setting, either due to excessive loads on the system or solar insolation dropping off, then the RD-1 lets the wind system start back up.

The XW System's method of measuring end amps is pretty accurate.  It agrees with the TriMetric +/-0.5A during finish stage near end amps for charging.  At higher amp draws the XW system is a little more off compared to what the TriMetric says - like at 100A actual current draw by the inverter (as shown by the TriMetric) the XW system says 104-105A.  With the inverter overloaded at 200A draw on the battery as shown by the TriMetric, the XW system says 218-220A.

[dgd]

Oooh.. can't wait for this new feature in the Classic. (and KID)
Two absorb stages so that pre-absorb boost or post-absorb boost or neither can be selected
I assume this would need to be part of the follow-me logic where there are two or more Classics charging the battery bank.
And of course configuarable by the local app 

dgd

[DMJ72]

Oooh.. can't wait for this new feature in the Classic. (and KID)
Two absorb stages so that pre-absorb boost or post-absorb boost or neither can be selected
I assume this would need to be part of the follow-me logic where there are two or more Classics charging the battery bank.
And of course configuarable by the local app 

dgd

Sounds good.

[ChrisOlson]

pre-absorb boost charging is not recommended by any battery manufacturers that I know of.  It only works on batteries that have been moderately cycled where it can be used to take advantage of peak solar conditions at solar noon, and without excessive heating of the battery.  For batteries that have been discharged to 50% SOC it will get your battery way too hot by forcing too many amps into it at the higher boost voltage for the first hour.

Finish charging (delayed boost) is different.  It is an algorithm designed to limit current to the battery to no more than C/10 to prevent excessive water use and heating of the battery.  And at the same time provide a high voltage finish stage that fully desulfates the negative plates.  It is now almost the industry standard recommend charge profile (Trojan, US Battery, Surrette, and all industrial forklift/floor maintenance, locomotive and marine batteries).  Industrial grid-powered forklift/floor maintenance and marine chargers have used it for years (IUIa with no float).  Currently there are only two RE chargers that I know of that can do it - the XW from Schneider and the SC-2030 from Bogart.  Of the two, only the Bogart SC-2030 does it correctly.

[dgd]

pre-absorb boost charging is not recommended by any battery manufacturers that I know of.  It only works on batteries that have been moderately cycled where it can be used to take advantage of peak solar conditions at solar noon, and without excessive heating of the battery.  For batteries that have been discharged to 50% SOC it will get your battery way too hot by forcing too many amps into it at the higher boost voltage for the first hour.

There does not seem to be too many battery manufacturers who recommend their deep cycle batteries are only partially discharged then recharged as seems to occur in many RE systems.
My own 1025Ah bank gets to about 20% dod maximum but more often 10 to 15% daily.
40 to 60% dod very  very occasionally when weather turns to custard, maybe once every 2 years.

This is where I though a pre-absorb boost would be of advantage and reduce stratification before absorb. A fixed one hour time I don't like so a configurable time up to an hour would be nice.
Finish charging boost where PV is the charging source may be wishful thinking as end day PV input diminishes.

Finish charging (delayed boost) is different.  It is an algorithm designed to limit current to the battery to no more than C/10 to prevent excessive water use and heating of the battery.  And at the same time provide a high voltage finish stage that fully desulfates the negative plates.  It is now almost the industry standard recommend charge profile (Trojan, US Battery, Surrette, and all industrial forklift/floor maintenance, locomotive and marine batteries).  Industrial grid-powered forklift/floor maintenance and marine chargers have used it for years (IUIa with no float).  Currently there are only two RE chargers that I know of that can do it - the XW from Schneider and the SC-2030 from Bogart.  Of the two, only the Bogart SC-2030 does it correctly.

Ok, but what is the difference for desulfating purposes to just doing a regular EQ cycle?
Is it more efficient or better for the batteries to do a finish stage and perhaps not bother with a float stage? I'm thinking RE not very deep dod system here.

dgd

[ChrisOlson]

Ok, but what is the difference for desulfating purposes to just doing a regular EQ cycle?
Is it more efficient or better for the batteries to do a finish stage and perhaps not bother with a float stage? I'm thinking RE not very deep dod system here.

The only reason industrial chargers use IUIa (no float) is because it's more efficient and doesn't waste power floating batteries that are going back to work during the next shift. 

The finish stage is different than EQ.  It is a constant-current stage designed to fully de-sulfate the battery as part of the normal charging process instead of relying on periodic EQ charges that severely abuse the battery.  During EQ the battery is held at high voltage for a long period of time.  Finish charging with IUI holds the battery at a constant current and lets the voltage rise above Absorb V until it reaches the recommended finish voltage at the constant current.  Then the charger shuts off.

[boB]

  Finish charging with IUI holds the battery at a constant current and lets the voltage rise above Absorb V until it reaches the recommended finish voltage at the constant current.  Then the charger shuts off.

What voltage and current is that though ?

The stage will most likely stay at a high voltage at a high current very long unless the voltage is VERY high.
I would think that battery temperature would also play a role but voltage times current together kind of do
relate to temperature after the battery has been fully charged.

Also, chargers for fork lifts etc are normally plugged into the grid so they will have a lot of energy available whereas off grid may not be so lucky.

But if it's only every so often (week or two) then it's probably OK to let them cook, but watch the battery temperature as well as voltage and current.

[vtmaps]

What voltage and current is that though ?

Good question... in a few battery specs that I have looked at, the Vboost, Veq and Vfinish are often the same or within a few tenths of volt.  I think the whole rationale for any of these high voltages is to stir the electrolyte. 

Makes me wonder about other ways to achieve the same ends with a flooded LA battery.  Maybe shorter, but wider batteries that are less prone to stratification.   I think with an electrolyte circulation system there is no need to exceed gassing voltage. 

--vtMaps

[ChrisOlson]

What voltage and current is that though ?

For our batteries, after absorb is complete at 2.45 VPC, the recommended current for finish stage is 2% C/20 and held at that current until voltage rises to 2.58 VPC.  Different battery manufacturers have different recs.  For instance, US Battery recommends 2.40 VPC absorb and 3% C/20 to 2.58 VPC

[boB]

What voltage and current is that though ?

For our batteries, after absorb is complete at 2.45 VPC, the recommended current for finish stage is 2% C/20 and held at that current until voltage rises to 2.58 VPC.  Different battery manufacturers have different recs.  For instance, US Battery recommends 2.40 VPC absorb and 3% C/20 to 2.58 VPC

OK, so in your case it's 58.8V  up to  61.92 volts.    That makes sense.

So, how long does it take to go from, say, 60V to 61.92 volts ?
I wouldn't think it would be there long enough to do much good but, maybe...

[ChrisOlson]

So, how long does it take to go from, say, 60V to 61.92 volts ?
I wouldn't think it would be there long enough to do much good but, maybe...

boB, it depends on depth and length of cycle.  On shallow cycles like down to 20-30% DoD where the battery is being charged every day the finish stage will be done in about 20 minutes usually.  If the battery has been cycled below 50% DoD and hasn't been fully charged in a week I have seen the finish stage take 2-3 hours.

BUT - our XW controllers do not do IUI correctly.  They are IUU.  The things have a timed 1 hour absorb stage, then they transition to finish stage with constant voltage instead of constant current.  This seems to work fine, and I don't know what the difference is between using IUI as recommended, vs IUU like our XW controllers do.

I have told Schneider that instead of the timed 1 hour absorb the controller SHOULD stay at absorb voltage until current falls to 2% C/20, THEN go to 2.58VPC finish and again exit at 2% C/20.  The XW algorithm (according to Schneider engineering) is designed to make maximum use of peak solar insolation during the day with the assumption that there may not be enough solar later in the day to complete the finish stage.  And they may be right, as in most cases there is not going to be enough hours of solar to do a true IUI charging.

Ralph Hiesey's SC-2030 does true IUI, but I have not heard any results on how that matches available solar insolation to get the charging done before the solar runs out for the day.  My gut feeling is that doing true IUI is going to be touch and go in most cases, because unlike grid-powered chargers for industrial batteries, solar does not have a flat power curve during the day.  With RE charging using solar I think you have to "push" the battery as hard as feasible early while you got decent insolation to get the job done.  And that seems to be the algorithm that Schneider has chosen for the XW systems.

This all being said, the one hour absorb before transition to finish voltage (with our XW system) does help keep amps down to the battery when it's still "hungry", and thereby keep its temperature and water use down for the whole charge cycle.  And it makes pretty good use of available solar capacity.  But without a whole bunch of experimenting with this, I don't know who's right.  It's easy enough to implement IUI charging with a solar controller (according to Ralph Heisey).  But whether or not it works time after time in the world of RE remains to be seen.

[inetdog]

Hi Chris,
This may be common notation in this forum, but the way you are using "C/20" seems a little strange to me and potentially confusing to others.

To me the letter C represents the amp hour capacity of the battery or battery bank. But by itself, as characterized in Peukert's Law, that does not actually specify a characteristic of the battery. You have to add a specification of the time period at constant current over which you perform the discharge.
For RE, the standard is the 20 hour rate, and that is usually written C₂₀, or for the typographically challenged C20 or C(20).
A current which is some fraction of the amp hour capacity of the battery would then be something like 5C or C/5.
I think you are using C/20 to indicate C₂₀, yes?

Otherwise for a 100AH battery a finish current of 2% C/20 would be .1A instead of 2A. A very big difference!

PS: Fortunately this and most other forums do allow you to enter subscripts and superscripts, even though in some you have to go into Advanced entry mode first.

[vtmaps]

Fortunately this and most other forums ...

Hi Dave,  Welcome to the Midnite forum... I'm really glad to see you here! 

--vtMaps  (aka mapmaker on that forum you moderate)