Trouble understanding battery DOD & shutdown voltage.

90cummins · December 2014

I have a new 24v Zantrex XW4024 with 4 Trojan L16RE-B 370ah batteries and they should supply 600 watts for 6 hours according to Trojans sizing calculator but I'm getting only 2hrs before the low battery voltage warning goes off and I could also use advice on the charging voltage, amps and time to properly recharge them.
What voltage should the batteries maintain with a 25 to 30 amp load (600 watts) at 50% DOD? My batteries are operating at 46 degrees.
90cummins

Vic · December 2014

Re: Trouble understanding battery DOD & shutdown voltage.

Hi 90..,

Well, it looks like the battery bank needs to be fully recharged.

Using YOUR Hydrometer, what are the SG readings of your battery, after this full recharge? If there is a variation of more than about 25 SG points, you should probably EQ the battery bank.

You have Flooded batteries, and a huge advantage of these batteries is that you can actually measure the SG of each cell.
It looks like you are trying to cycle the bank, which is good. Just be careful that you do not over-discharge any cell.

Please remind us what you are using to charge the batteries -- PV, Grid, etc. What are the voltage settings for Absorb, and Float, and how is the Absorption stage ended -- by time, or current?

FWIW, Thanks! Vic

90cummins · December 2014

Re: Trouble understanding battery DOD & shutdown voltage.

The Xantrex XW 4024 has a built in charger capable of a 150amp charge rate. I entered the battery type and ah/rating into the programmer when I energized the system.
I recorded the SG levels and voltage after 12 hours off charge on 12/1/14.
I sent the data below to my supplier along with discharge data under load and they said they may be under charged but otherwise said they looked OK.
I pointed out that battery B1 is off from the others and the pack voltage drops and does not support a load of 400 to 600 watts for the 6 to 7 hours according to Trojans calculator.
I changed the charging parameters yesterday to 29.6v bulk, 29.6 absorb and 27.5 float. Battery temperature is still 46 degrees.
I’m thinking k I need to bring them to the Trojan outlet for testing but want to understand and test them more so I know what I’m talking about and have hard data to present them.
I will continue to cycle them and gather data but suggestions would be appreciated.
Thanks
90cummins

Monday 12/1/2014 9am battery idle for 12 hours (off charge)
Pack voltage 26.1v @ 53 deg

9:00am SGr.

B1 A 1250
6.46v B1 B 1250
B1 C 1245

B2 A 1260
6.5v B2 B 1260
B2 C 1260

B3 A 1260
6.5v B3 B 1260
B3 C 1260

B4 A 1260
6.5v B4 B 1260
B4 C 1260

Cariboocoot · December 2014

Re: Trouble understanding battery DOD & shutdown voltage.

This question looks very familiar. I think its twin came up just a few days ago, complete with explanation about real battery capacity vs. load demand and temperature variation. Seems to be a common problem.

Batteries will not maintain Voltage against current draw; Voltage drops. How much so ranges from immeasurable over time by standard meters to fairly drastic and instantaneous. It is directly related to the draw.

25-30 Amps from 370 Amp hours is about 7-8% and should be manageable for a short time. But batteries are not linear. The longer the draw goes on the less capacity the battery has and the greater percentage that draw represents which pulls it down faster and lessens the capacity even more. Having them at a cold 42 (Fahrenheit one would assume) reduces the capacity further. If they are new batteries and have not been cycled several times that will reduced the capacity. If they are not being fully charged ... same thing. Almost everything works against battery capacity. The current here is more than would be used to test them to dead over the 20 hour rating period. That would be as much as 500 to 600 Amp hours would use, and remember that is to DEAD.

Oh and if it is 600 Watts AC it will be more like 700 Watts DC depending on the efficiency and tare of the inverter.

Should I bother to mention that small/long cables drop Voltage under load? Or that loose connections can do the same thing?

Anyway, what Vic said. Be sure they're charged to begin with.

Cariboocoot · December 2014

Re: Trouble understanding battery DOD & shutdown voltage.

Those aren't fully charged SG's and that first battery definitely has a problem.

Definitely need to do an EQ on them.

Also what is the amount of time spent in Absorb?

Blackcherry04 · December 2014

Re: Trouble understanding battery DOD & shutdown voltage.

From the Trojan Battery manual since you don't like opinions, here is the documentation as requested.

Equalizing
Equalizing is an overcharge performed on flooded/wet batteries after they have been fully charged.
Trojan recommends equalizing only when fully charged batteries have a low specific gravity reading
below 1.230, or wide ranging specific gravity 0.050 between the battery’s cells.

http://www.trojanbattery.com/pdf/TRJN0169_UsersGuide.pdf

Surfpath · December 2014

Re: Trouble understanding battery DOD & shutdown voltage.

Blackcherry04 wrote: »

From the Trojan Battery manual since you don't like opinions, here is the documentation as requested.

Equalizing
Equalizing is an overcharge performed on flooded/wet batteries after they have been fully charged.
Trojan recommends equalizing only when fully charged batteries have a low specific gravity reading
below 1.230, or wide ranging specific gravity 0.050 between the battery’s cells.

http://www.trojanbattery.com/pdf/TRJN0169_UsersGuide.pdf

Howdy Blackcherry,
On a side note, it's somewhat challenging to really know what Trojan recommends in regards to EQ. On a video on their youtube site, called Trojan: Equalization is Key to Extending Battery Life and Performancethey recommend "equalizing batteries every 30 days, or when SG is less than 1.235, or when there is a difference in SG's of more than .030 between the cells". Here it is (click on link below to go to the exact point in the video):

https://www.youtube.com/watch?feature=player_detailpage&v=jCl5klSF4tE#t=89

Perhaps the "ONLY" equalize advice is more recent, and maybe it only applies to certain Trojan batteries, but it seems to me that their instructions are inconsistent.

Blackcherry04 · December 2014

Re: Trouble understanding battery DOD & shutdown voltage.

Surfpath wrote: »

Howdy Blackcherry,
On a side note, it's somewhat challenging to really know what Trojan recommends in regards to EQ. On a video on their youtube site, called Trojan: Equalization is Key to Extending Battery Life and Performancethey recommend "equalizing batteries every 30 days, or when SG is less than 1.235, or when there is a difference in SG's of more than .030 between the cells". Here it is (click on link below to go to the exact point in the video):

https://www.youtube.com/watch?feature=player_detailpage&v=jCl5klSF4tE#t=89

Perhaps the "ONLY" equalize advice is more recent, and maybe it only applies to certain Trojan batteries, but it seems to me that their instructions are inconsistent.

They can be different depending on what battery your talking about, Trojan makes many kind of batteries. There is a difference in Maintenance Equalization and Corrective Equalization. One is to keep from having a problem and one is to correct a problem. When you get down to .005, it's better to have a range in mind and not some exact trigger point.

The 30 days probably doesn't apply to everyone, some RE systems are able to return to full SG levels ( daily / weekly ) and may never need a maintenance / corrective EQ.

90cummins · December 2014

Re: Trouble understanding battery DOD & shutdown voltage.

I did another test today and hopefully have some good data.
At start of test voltage was floating at 28.2v
The following specific gravity and volts data are towards end of test;
SG. VOLTS
B1 C1 1250 5.99V
B1 c2 1250 Battery temp 48deg
B1 C3 1250
B2 C1 1265 6.05V
B2 C2 1260
B2 C3 1260
B3 C1 1260 6.04V
B3 C2 1260
B3 C3 1260
B4 C1 1260 6.04V
B4 C2 1260
B4 C3 1260 Battery temp 48deg, voltage 24 with load, 24.5v without load

Test was performed with battery temp at 48deg and a steady 613va / 516 watts load.
9:18 25.8v 19.4a Test started
9:24 24.6v 25.7a
11:03 24.3v 25.1a
11:12 24.2v 26a
11:52 24.1v 26.1a
12:01 24v 26.9a
12:21 23.9v 26.2a End of test voltage reading under load
12:22 24.5v 2.9a No load voltage reading
12:24 Start charge cycle 112a @ 28.3v
1:02 charging 49.2a 29.7v

The charger is set up as follows;
Equalize 31v
Bulk 29.6v
Absorb 29.6v (300 minutes)
Float 27.5v
The following data is after the test and after the charge cycle. There is a BTS to monitor & adjust charge rate according to temperature.
At 6pm batteries at float I recorded SG & voltage again battery temp 53 deg ;
B1 C1 1270 7.1v
B1 C2 1270
B1 C3 1265
B2 C1 1280 6.98v
B2 C2 1280
B2 C3 1280
B3 C1 1280 7.04V
B3 C2 1280
B3 C3 1280
B4 C1 1275 7.02
B4 C2 1280
B4 C3 1280
During the test which lasted 3 hours 3 minutes the load was steady.
This is the first time I looked at the event log and it does not appear the charge events last very long.
The event log shows very short times for the various stages of charge;
I set the absorb time for 300 minutes.
12:24 charge cycle starts Bulk
12:32 Absorb cycle starts
1:59 Equalize starts
2:59 System Floats
I must be missing something?

Cariboocoot · December 2014

Re: Trouble understanding battery DOD & shutdown voltage.

90cummins wrote: »

The event log shows very short times for the various stages of charge;
I set the absorb time for 300 minutes.
12:24 charge cycle starts Bulk
12:32 Absorb cycle starts
1:59 Equalize starts
2:59 System Floats
I must be missing something?

Am I reading that right: eight minutes in Bulk? That is pretty far away from making any sense at all, especially if the batteries are being drawn down to 24.5 (near 50% SOC).

Another thing: Equalization is not a normal charge cycle. It should not be occurring during the Bulk/Absorb/Float regimen. Shut it off.

Vic · December 2014

Re: Trouble understanding battery DOD & shutdown voltage.

Hi 90 ..,

Thanks for the data. B1 seems to be a bit of a laggard.

Did you measure the SGs of B1 or the whole bank after the EQ?
Did you notice the battery current at or near the end of the EQ?

And on which battery is the RTS? Does Schneider still use a battery terminal-mounted RTS?

It is a good idea to monitor the EQ as it proceeds -- watching the SGs of the lowest cells, and if the EQ is long, the battery temperatures.

A one-hour EQ is fairly short, and also, watching the current (into the battery via a Shunt or perhaps on the Combox) when the EQ voltage is just reached at the beginning of the EQ, and then the current into the battery current at or near the end of the EQ, can tell you weather the EQ should be extended in time.

Opinions, Thanks, Vic

90cummins · December 2014

Re: Trouble understanding battery DOD & shutdown voltage.

Am I reading that right: eight minutes in Bulk? That is pretty far away from making any sense at all, especially if the batteries are being drawn down to 24.5 (near 50% SOC).

Another thing: Equalization is not a normal charge cycle. It should not be occurring during the Bulk/Absorb/Float regimen. Shut it off.

Yes 8 minutes Bulk is what I see and no the Equalization does not run every charge cycle.
I scheduled it for this charge cycle only.

Hi 90

Thanks for the data. B1 seems to be a bit of a laggard.

Did you measure the SGs of B1 or the whole bank after the EQ?
Did you notice the battery current at or near the end of the EQ?

And on which battery is the RTS? Does Schneider still use a battery terminal-mounted RTS?

It is a good idea to monitor the EQ as it proceeds -- watching the SGs of the lowest cells, and if the EQ is long, the battery temperatures.

A one-hour EQ is fairly short, and also, watching the current (into the battery via a Shunt or perhaps on the Combox) when the EQ voltage is just reached at the beginning of the EQ, and then the current into the battery current at or near the end of the EQ, can tell you weather the EQ should be extended in time.

Opinions, Thanks, Vic

Yes B1 is always abnormal in comparison to the others.
Yes I measured the SG & voltages of the whole bank (12 cells) at the end of the load test and after the charge cycle.
The RTS is on the B3 terminal.
No I didn’t monitor the EQ current or volts.
Guess I’ll do another load test & try to record additional parameters.
Thank you;
90cummins

Vic · December 2014

Re: Trouble understanding battery DOD & shutdown voltage.

OK, 90, thanks for the added info.

WAS trying to ask if you had measured SGs after the EQUALIZATION.

The EQ, primarily to try to equalize the spread in SGs, and also, it helps mix the electrolyte, which is often part of getting the SGs back to where they should be.

And monitoring the SGs, as the EQ proceeds will help you know when the EQ ahs done its job, or as much as you can expect it to do, when the SGs stop rising.

That is why automatic EQs are not a great idea, unless short, and perhaps at the lower range EQ voltages, just to mix things up, a bit.

Short EQs usually raise the battery temps little, even at relatively high EQ voltages, but you should think about the need to compensate the SG readings for temperature rise from extended EQs. Usually, the compensation would be small, and can be ignored, unless the temperature rise is large.

Again, just my opinions. FWIW. Vic

90cummins · December 2014

Re: Trouble understanding battery DOD & shutdown voltage.

Just a thought ; could the short charge cycle be caused by the charge controller receiving incorrect feedback from the batteries specifically B1?
90cummins

Cariboocoot · December 2014

Re: Trouble understanding battery DOD & shutdown voltage.

90cummins wrote: »

Just a thought ; could the short charge cycle be caused by the charge controller receiving incorrect feedback from the batteries specifically B1?
90cummins

No.
But it could be caused by the Bulk and Absorb Voltages being the same value if your charging source has separate settings for each. It depends on what triggers the switch from Bulk to Absorb. It is Voltage on most chargers, but they do not have two different V settings then just a threshold for the change. If it has two Voltages then current or time should be the determining factor for going to Absorb.

It would help if you put the details of your system in your signature line. Not all are the same and it's difficult to remember the specs on every piece of equipment. Impossible to remember who's got what.

Vic · December 2014

Re: Trouble understanding battery DOD & shutdown voltage.

90 ..,

In looking at the data in post #9, I had thought that you had done a second recharge with no discharge in between. There is a lot of data in that post, but that was what it seemed to say ...

If that was the case, then beginning a new charge cycle on a just charged battery, without increasing the charger voltage settings, should normally lead to a short Bulk, and if Absorb is ended by charge current, then the Absorb should also be relatively short.

That was just the way I had read that data.

Creating a Signature with the details of your system, including weather it is off-grid, as Marc/coot mentioned would be a big help. Vic

Cariboocoot · December 2014

Re: Trouble understanding battery DOD & shutdown voltage.

Seems Rossman has just said the Xantrex has separate number settings for Bulk and Absorb Voltage. I advised him to have them at different levels. This may be the reason for the extremely short Bulk stage. I am not certain; Xantrex equipment has many illogical aspects.

Vic · December 2014

Re: Trouble understanding battery DOD & shutdown voltage.

Cariboocoot wrote: »

Seems Rossman has just said the Xantrex has separate number settings for Bulk and Absorb Voltage. I advised him to have them at different levels. This may be the reason for the extremely short Bulk stage. I am not certain; Xantrex equipment has many illogical aspects.

Yea, saw that, separate Bulk voltage setting has come up a number of times before, and the customary advice for RE-charged systems has been to set both the Bulk and Absorb V the same. Have never heard of anyone else having this cause a short charge cycle.

The 90cummins data on post #9 can be a bit ambiguous as to just how many charges are there, and the exact sequence, but if there was one full recharge, followed soon-after by another, then my system would do a short Bulk, and a short Absorb, because the Absorbs here are terminated by End Amps into the battery.

As you know, there has been one school that thinks that the Bulk V should be set somewhat higher than the Vabs, but am not in that school.

FWIW, Seasons Greetings! Vic

Blackcherry04 · December 2014

Re: Trouble understanding battery DOD & shutdown voltage.

The Xantrex EQ algorithm has a automatic force charge cycle of Bulk and Absorb built in. When you start the EQ it will run the Bulk / Absorb and then instead of going to float it starts the EQ, It is at that time the count down timer will run for the EQ and the voltage will rise to the EQ setting. If you run out of time and retrigger the EQ it will run the Bulk / Absorb again, since you have just been at EQ voltage, it will go through the sequence very fast the second time and each time it's retriggered.

The same will happen if you'v completed a Full Re-charge cycle before triggering a EQ, but it goes through the Bulk / Absorb pretty fast, so a 8 minute Bulk and short Absorb would not be out of the question.

Here is the Custom Menu with separate Bulk / Absorb voltage settings.

Attachment not found.

As per OP's request for no opinions.

http://dealer.sunwize.com/emart_documents/237/Manual-2-Xantrex_XW_Inverter_Charger.pdf
.

Cariboocoot · December 2014

Re: Trouble understanding battery DOD & shutdown voltage.

Can you shut the EQ off?
Really there's no sense in running it if you can't 'prove' a full charge cycle.

Blackcherry04 · December 2014

Re: Trouble understanding battery DOD & shutdown voltage.

Cariboocoot wrote: »

Can you shut the EQ off?
Really there's no sense in running it if you can't 'prove' a full charge cycle.

On the EQ screen there is a cancel arrow at the bottom where you use the Right button to stop the EQ. Of course there has been some changes in the firmware, so some could be different.

90cummins · December 2014

Re: Trouble understanding battery DOD & shutdown voltage.

As requested I have created a Signature.
There's a lot of new information (thank you) I've yet to fully understand.
I'm digesting the info/suggestions and will attempt another better organized test.
90cummins

Trouble understanding battery DOD & shutdown voltage.

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Trouble understanding battery DOD &amp; shutdown voltage.

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Trouble understanding battery DOD & shutdown voltage.