Author Topic: Absorb timer starting point question Classic 150  (Read 175 times)

Gordon

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Absorb timer starting point question Classic 150
« on: November 13, 2021, 11:22:42 AM »
Hi Folks,

Just wondering if anyone may know if it is possible to get the absorption timer to start its countdown when the target voltage is reached rather than .3 volts below target?

I've recently switched from FLA to LFP technology and noticed something very interesting. As bulk voltage is rising and approaching the absorb set point, the absorb timer will actually start at .3 volts below the set point and at .2 volts below the set point the display will switch from bulk to absorb. This has never been an issue with FLA since absorb is long enough for the voltage to rise up to the set point. However now I'm in a situation where I need to come up with a work-around since the battery manufacturer states all you need to do is bring it up to the set point and go straight to float, no time for the voltage to rise up the extra few tenths of a volt. And yes, I definitely have the temp compensation turned completely off.

My Classic 150 was purchased in April of 2108 and has the following revision info on the screen:

2186: 11/29/2017  MNGP
2128:  1/11/2017   Classic

I'm wondering if a more recent version of the firmware may have this as an option since I have not been able to figure out how to do it with the options I have currently. I did try to reduce absorb time down to zero and see it that would make it come up to the set point, but the lowest you can go is 3 minutes.

Any suggestions would be appreciated.

Thanks,

Gordon


Steve_S

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Re: Absorb timer starting point question Classic 150
« Reply #1 on: November 13, 2021, 11:56:18 AM »
Have you corrected for the Voltage Difference / Drop from Battery Pack Terminals to SCC ?
Even a .3 Difference can play funny games with the results.
Same applies to Inverter.  For example if you want it to cutoff @ 20.0V you don't want it cut off @ 20.5 or 19.5 because it thinks sees 20.0 at it's terminals.

Picky Voltage calibration is not a Huge Deal with any Lead battery but with Lithium which is Millivolt Sensitive (including BMS') a half volt could be nasty...  IE LFP absolute 0%SOC = 2.500Vpc, for 24V cutoff is 20.0 below that and damage is occurring.

Using a quality DMM/DVOM check your Battery terminal voltage during "Normal Regular" discharge, same during a Typical Charge is being applied.  At the same time as checking that, do the same at the SCC & Inverter.  You will likely see a different level voltage between Load & Charge. 

For the CLASSIC, in the TWEAKS Sub-Menu there is a setting for OFFSET VBATT for adding the voltage correction value.

WORST CASE SCENARIO as I don't know what Inverter etc you have.  There maybe no "correction for offsets" so you woudl have to change the actual value.  IF if Discharge difference in reading is 0.3V and you want to cutoff @ 20.0 then you'd have to change that to 19.7V which would be 20.0 @ Batt Terminals.
Classic-200, Samlex EVO-4024 Inverter/Charger, 1190AH/30kWh of LiFePO4 & 856Ah of Rolls Surette LEAD.

Gordon

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Re: Absorb timer starting point question Classic 150
« Reply #2 on: November 13, 2021, 12:36:58 PM »
Hey Steve,

Thanks for the reply. The issue I'm facing is something slightly different than what it appears you are addressing. My CL150 is using the voltage it sees at its terminals to determine when to begin the absorb timer. I don't have any way to directly use battery voltage to initiate the change from bulk to absorb, but I have taken this into account as I will describe later. So when you set the CL150 absorb voltage to say 28.0, what the CL150 does is start the absorb timer when it sees the 28.0 minus .3, ie. 27.7. And then appears to switch to constant voltage mode at 27.8, presumably to rise up to the set point of 28.0 in a more controlled manner, instead of riding full current up to 28.0 and then switching to absorb once it already gets there.

Now that being the case I have two option of how to get the batteries up to 28.0 before the CL150 switches to float; 1) extend the absorb time or 2) increase the absorb voltage and limit absorb time. Right now I'm doing the latter since it seems to have less chance of causing problems.

However, if I could get the voltage up to the set point before the timer begins then I have a better situation since I don't have to do either things mentioned above (extending absorb time or increasing absorb voltage). At that point, if can get the voltage that the CL150 sees to be equal to the set point before the timer starts I can set the timer to the lowest value and not have any possibilities of going over voltage. Then all I have to contend with is the voltage drop that you mentioned in your post. 

I don't plan on using any voltage correction at the CL150 for the following reason, at low current flow it is dead on with actual voltage at the batteries. However, I do know that I get a .1 VDC drop for every 20 amps of charge current. If I leave it the way it is, it's accurate at low current flow, if I correct for the .2 VDC drop at high current then I'm accurate under charge condition but off under low-flow conditions. Either way, you're right on during one condition and off under the other. I'm just choosing to be accurate under low-flow and adjust the charge voltage for the high-current charge condition.

If I get the absorb timer to start when voltage reaches the set point, then all I have to do is set the set point to 28.2 knowing that the .2 V drop will mean the batteries see 28.0 and set a low absorb timer and I'm good to go. That's where I was planning to do the voltage correction, in the setting of the set point. Then all you do is set the lowest absorb time and you don't give it a chance to get any voltage rise over the 28.0 that the batteries see when the timer is initiated. Much lower probability of any problems happening than any of the alternatives that I have now.

Thanks,

Gordon

Gordon

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Re: Absorb timer starting point question Classic 150
« Reply #3 on: November 13, 2021, 12:43:22 PM »
Oh, I should have mentioned that I have an ExelTech MX inverter system without any of the program features, so I have no way of setting an inverter cutout voltage. That's something I plan to do on my own since I have a real good feel for power usage and charge state and I just keep an eye on the battery voltage meter in the house. It's simple but it does work. If I have some cloudy days, I just go out there and run the generator for a few hours and I'm good to go until the sun comes back out.

boB

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Re: Absorb timer starting point question Classic 150
« Reply #4 on: November 13, 2021, 02:41:41 PM »
Is the voltage reading on the Classic close to a good volt meter reading ?

As I remember, the Classic requires the Absorb voltage to actually reach the Absorb set point and then it can fall as much as 0.2 or 0.3 volts below that before turning back into MPPT mode (bulk) again.

Could that voltage have reached the set point value when you weren't looking ?

I think we are going to try and make a change to the software so that it takes more time sitting at that set point before deciding it is actually in Absorb but I'm not sure.

Also, is there a temperature sensor that is possibly affecting the target set point ?   What does the "VIEW"  menu show in the charge menu ?

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Gordon

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Re: Absorb timer starting point question Classic 150
« Reply #5 on: November 13, 2021, 04:30:44 PM »
Hi Bob, thanks for the reply.

The Classic is reading the exact same voltage as my DMM and the meter I have in the house. The only time I have to make any kind of an adjustment is under full charge current when the CL will be reading correctly but the voltage is actually .2 less at the batteries. That's no problem since I account for that in the setting.

There is no temperature compensation set at all. So that's not a factor.

And yes, your first statement is correct, it will reach the set point when given ample time. The issue arises when you want to use a very short absorb time and the timer actually begins counting at set-point -.3 V. Then you don't have the time for it to reach the set point. Perfectly fine for FLA, but the LFP battery manufacturer wants the batteries to come up to a set-point, in this case 28.0 volts and then drop right down to a float voltage. So to answer your second question; no I'm positive the voltage didn't reach the set-point because I've done this now on multiple occasions making sure I was understanding what was going on. Even if it did, the timer would prevail and it would sit there until the timer ran out or until the end amps figure was reached.

To your fourth point; mine is actually saying "absorb" on the display when it is at set-point -.2 V.

Ideally for this to work and for me to only have one "fudge-factor" to deal with (the voltage drop under full-charge current), I would like to get it to start the timer when the voltage actually reaches the set-point. Then all I do is set that point at .2 over where the batteries need to get ie. 28.2 and set a very low timer value and I'm good to go. The worst thing that could happen since it is targeting a voltage over the truly desired voltage is that charging would go too long and current would drop and then voltage at the CLassic would equal that at the battery and I'd be at 28.2 on the battery. But the short timer setting combined with an end amps setting should ensure that never happens.

Here's how today's charging went. I had two adjustments I had to factor in. So I set absorb to 28.5, knowing that the Classic would start the timer at 28.2 and that when it sees 28.2 and there is high charge current the batteries are actually at 28.0. Then the 3 minute timer started and during that time it came up to 28.1 briefly at the batteries and shut right off when the 3 minutes were up. I was still pushing a lot of current into the batteries so I had no issue with any of that.

That's the best I've come up with to get to the desired 28.0 under full current and then get out of that and into float right away. The other option is to go with a 28.0 set-point and an extended absorption time. But there is no way to know what that time should be especially under varying sun conditions. So it might get to 28.0 and stay there for a long time on a sunny day or it might not get there at all on a cloudy day. It will ensure one thing, and that is that I will never get more than 28.0 at the batteries. But it will do this under a constant voltage rather than a constant current, which is more like what the LFP battery munufacturer is looking for.

Thanks,

Gordon

 

Gordon

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Re: Absorb timer starting point question Classic 150
« Reply #6 on: November 13, 2021, 04:55:21 PM »

I think we are going to try and make a change to the software so that it takes more time sitting at that set point before deciding it is actually in Absorb but I'm not sure.

Also, is there a temperature sensor that is possibly affecting the target set point ?   What does the "VIEW"  menu show in the charge menu ?

This is an interesting statement since on mine, with the firmware version listed in my first post, it doesn't spend any time at the set point before starting the timer and the designation "absorb" comes on the display before it reaches the set point also. Depending on charge rate it will take time out of the absorb timer to actually reach the set point. Is it possible that there is a newer firmware version that does what you are saying? That may work very will for me.

Sorry I didn't answer your final question in the previous post. The view (in the temp comp menu) shows the same voltage as the voltage set in the voltage menu, verifying that there is no t-comp in effect. 

boB

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Re: Absorb timer starting point question Classic 150
« Reply #7 on: November 13, 2021, 11:29:51 PM »

Well dang.  I will have to have a closer look at the code now.

We also have another engineer working on Classic code now.

Thank you for the answers and input !

boB
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Gordon

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Re: Absorb timer starting point question Classic 150
« Reply #8 on: November 14, 2021, 09:56:05 AM »
Hi Bob,

That would be great!

It would be ideal if the voltage would come up to the set point under constant current and then start the timer and switch to absorb mode (constant voltage) at that time. And if we could go as low as 0 minutes on the timer too. That way anybody with the new LFP batteries could accomplish whatever the manufacturer may specify for charging parameters.

Then all the user has to think about is any voltage offsets to perform and they're good to go.

I'm very interested in hearing what your team comes up with.

Thanks Again,

Gordon

boB

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Re: Absorb timer starting point question Classic 150
« Reply #9 on: November 14, 2021, 01:04:16 PM »
One thing that will be added will be to allow the Absorb time to go to zero.

Zero isn't really quite zero though as it will require a few seconds at Absorb so that a "peak" voltage does not trigger the Absorb erroneously.

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Gordon

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Re: Absorb timer starting point question Classic 150
« Reply #10 on: November 25, 2021, 10:22:46 AM »
Yes, understood Bob. After a few weeks with this setup it appears that all that is needed is to have the timer start its counting when it reaches the set point. Not necessary to be able to go down to zero on the absorb timer.

Right now I'm having to use a set point that is .2 VDC above where I want it to be so that I'm in the range where these batteries start to rise rather quickly and predictably. Then I can use the absorb timer to have it reach the 28.0 VDC that SP calls for right about the time that it times out. Also have an End-Amps setting in there for a current-based absorption cut-off.

Thanks for your help.
« Last Edit: November 26, 2021, 05:14:27 PM by Gordon »