charge parameters for 450Amp/hr battery bank on VFX3024E

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charge parameters for 450Amp/hr battery bank on VFX3024E

Postby cuteajax on Sun Dec 03, 2017 10:17 am

I just procured 6 units of 150Amp/hr AGM batteries (Varta Lad150) which i intend to connect to my 24V Outback VFX3024E inverter (230v output) in a series/parallel configuration (for a total combined capacity of 450Amp/hr @ 24 volts). Can someone help me with the most optimal charge parameters (i.e. absorb voltage, absorb time, float voltage, float time, Equalize voltage, Equalize time) to enable me optimize my battery bank (i.e. striking a balance between maximizing my battery life and shortening charge cycle). If it helps, I maintained the charge rate on the default (9 AAC). I use mate 2 and i am still connected to national grid (not yet on solar). The manufacturers of the batteries did not give any information about their charging requirements except that the maximum voltage = 14.8V. Thanks in advance.
cuteajax
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My RE system: Outback VFX 3024 Inverter (230V), 6 units of 150Amp/hr AGM batteries.

Re: charge parameters for 450Amp/hr battery bank on VFX3024E

Postby Mike Curran on Sun Dec 03, 2017 5:14 pm

Your battery specs only give C5 discharge rate (123Ah) but judging from the discharge curves it looks like the C20 rate is 7.5A × 20hr = 150Ah.

(Fyi, Rolls Battery manual link: http://rollsbattery.com/wp-content/plug ... Manual.pdf)

Not sure what you meant
cuteajax wrote:I maintained the charge rate on the default (9 AAC).
Most charge parameters are set on the DC (battery) side of things.

Following Rolls Battery's recommended AGM battery charging parameters, bulk charge rate = 0.25 × C20 = 37.5A and is maintained (if you reach it - this isn't a settable parameter) until battery voltage =2.45 V/cell × 12cells = 29.4 volts (which is within your 14.8 × 2 = 29.6V limit). This is your absorb voltage setpoint. Maintain that voltage until charge rate declines to 0.007 × C20 = 1.05A, at which point absorb should stop and batteries set up to float at 2.3V/cell × 12 = 27.6 volts. Again, these are all Rolls' AGM battery recommendations. YMMV.

You will have to experiment to see what absorb time gets you down to 1.05A charge rate while holding voltage at 29.4. If your charge rate tapers off to something greater than 1.05A and it looks like it'll never get there, then I would note that elapsed time as your absorb time and revert to float at that point. As your battery ages absorb time will change so you can't "set and forget" it. Since you're still grid connected your float time can be something minimal like 1 hour.

I'm no (AGM battery, or any other kind of) expert so take a look at Rolls' manual and draw your own conclusions.

One final note: 3 parallel strings of batteries make it likely some batteries will charge differently than others, resulting in possible premature failure of the weakest batteries in a string, then that string itself. My understanding is one string is optimum, 2 strings maximum/marginal, and anything more is problematic.

Hope this helps. - Mike

PS Perhaps the best thing about this post will be that it promotes other, probably more helpful comments :smile:
Mike Curran
OutBack Guru
 
Posts: 378
Joined: Sat Aug 28, 2004 6:28 pm
Location: Chagrin Falls, Ohio
My RE system: Outback:
- 8 (2x4) Evergreen 180's into one MX60
- 6 (2×3) ALEO S79-300's into one FM80
- 2 grid-tied GVFX3524's classic stacked for 120/240VAC
- 12 Surrette/Rolls 2V x 1766Ah
- Hub10.3, Mate3, FNDC, RTS, OpticsRE. Tigo Energy ES maximizers on each PV module.

Westinghouse Solar:
- 30 (2x15) 235W panels with Enphase M215 microinverters, grid-tied.

Re: charge parameters for 450Amp/hr battery bank on VFX3024E

Postby blackswan555 on Mon Dec 04, 2017 12:37 am

I am not an AGM expert, But a couple of things to keep in mind,
You MUST NOT overvoltage AGM as it will kill them very quickly so it is important to have battery temp sensor about half way down what will be your hottest cell and your charge voltage and max current set correctly,
You do not equalise AGM, Some AGM manufactures are loosely calling it EQ, But it is not, A more correct term would be conditioning charge, same as absorb voltage but for extended time ( EQ is a controlled over-voltage charge, Try it on AGM and you will get a nasty hissing sound closely followed by your wallet crying, :smile: )

I maintained the charge rate on the default (9 AAC).
This number the the amount of AC the charger will use to charge batteries, Refer to manufacturers max charge current allowed for your batteries,
9AAC will give about 9amps x 230v / 24v without any losses would be 85 amps, probably more like high 70s in real world, (can not remember max, 10AAC iirc ? anyone ? but max does give 85a,)

Tim
My comments are based on my experience and research, They are not endorsed or checked by Outback.I am an independent British electrician living in Spain, So please take this into account when reading /acting on my post`s.
blackswan555
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Re: charge parameters for 450Amp/hr battery bank on VFX3024E

Postby cuteajax on Tue Dec 05, 2017 12:41 pm

Mike Curran wrote:Your battery specs only give C5 discharge rate (123Ah) but judging from the discharge curves it looks like the C20 rate is 7.5A × 20hr = 150Ah.

(Fyi, Rolls Battery manual link: http://rollsbattery.com/wp-content/plug ... Manual.pdf)

Not sure what you meant
cuteajax wrote:I maintained the charge rate on the default (9 AAC).
Most charge parameters are set on the DC (battery) side of things.

Following Rolls Battery's recommended AGM battery charging parameters, bulk charge rate = 0.25 × C20 = 37.5A and is maintained (if you reach it - this isn't a settable parameter) until battery voltage =2.45 V/cell × 12cells = 29.4 volts (which is within your 14.8 × 2 = 29.6V limit). This is your absorb voltage setpoint. Maintain that voltage until charge rate declines to 0.007 × C20 = 1.05A, at which point absorb should stop and batteries set up to float at 2.3V/cell × 12 = 27.6 volts. Again, these are all Rolls' AGM battery recommendations. YMMV.

You will have to experiment to see what absorb time gets you down to 1.05A charge rate while holding voltage at 29.4. If your charge rate tapers off to something greater than 1.05A and it looks like it'll never get there, then I would note that elapsed time as your absorb time and revert to float at that point. As your battery ages absorb time will change so you can't "set and forget" it. Since you're still grid connected your float time can be something minimal like 1 hour.

I'm no (AGM battery, or any other kind of) expert so take a look at Rolls' manual and draw your own conclusions.

One final note: 3 parallel strings of batteries make it likely some batteries will charge differently than others, resulting in possible premature failure of the weakest batteries in a string, then that string itself. My understanding is one string is optimum, 2 strings maximum/marginal, and anything more is problematic.

Hope this helps. - Mike

PS Perhaps the best thing about this post will be that it promotes other, probably more helpful comments :smile:


Thanks a lot Mike for your post. The "Rolls_Battery_Manual.pdf" is especially very valuable. One very key take-away from the document is that charge parameters (ie. absorb voltage, float voltage, time etc) depend to a great extent on the ambient temperature (the parameters actually varied among different temperature value). I live in the tropics where ambient temperature can vary significantly depending on the time of the day and the prevailing whether condition. It can go as low as 15 degree Celcius during rainstorms and as high as 40 degrees Celcius during peak summer months. My question is what is the safest charging setting for my peculiar situation? I don't want to undercharge my batteries and i definitely don't want to overcharge them either.
cuteajax
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Posts: 5
Joined: Sun Dec 03, 2017 7:56 am
My RE system: Outback VFX 3024 Inverter (230V), 6 units of 150Amp/hr AGM batteries.

Re: charge parameters for 450Amp/hr battery bank on VFX3024E

Postby Mike Curran on Wed Dec 06, 2017 8:28 am

Hey Ajax - With those temperature variations, you should consider getting a remote temperature sensor (RTS) from Outback. It mounts on the side of one of the batteries in your bank, preferably in a central location indicative of your overall battery temperature, and connects to your FX via ethernet cable. It will automatically provide temperature compensation so that the proper charging voltage is being applied at all temperatures.

http://outbackpower.com/outback-product ... ory_id=451
Mike Curran
OutBack Guru
 
Posts: 378
Joined: Sat Aug 28, 2004 6:28 pm
Location: Chagrin Falls, Ohio
My RE system: Outback:
- 8 (2x4) Evergreen 180's into one MX60
- 6 (2×3) ALEO S79-300's into one FM80
- 2 grid-tied GVFX3524's classic stacked for 120/240VAC
- 12 Surrette/Rolls 2V x 1766Ah
- Hub10.3, Mate3, FNDC, RTS, OpticsRE. Tigo Energy ES maximizers on each PV module.

Westinghouse Solar:
- 30 (2x15) 235W panels with Enphase M215 microinverters, grid-tied.

Re: charge parameters for 450Amp/hr battery bank on VFX3024E

Postby cuteajax on Wed Dec 06, 2017 1:09 pm

Mike Curran wrote:Hey Ajax - With those temperature variations, you should consider getting a remote temperature sensor (RTS) from Outback. It mounts on the side of one of the batteries in your bank, preferably in a central location indicative of your overall battery temperature, and connects to your FX via ethernet cable. It will automatically provide temperature compensation so that the proper charging voltage is being applied at all temperatures.

http://outbackpower.com/outback-product ... ory_id=451


Does it mean with an RTS, I may not worry about the charge parameters i set as the inverter and the RTS will figure it out for themselves automatically? Or do i still have to set some parameters that are "reasonable" before trusting the RTS to refine it further?
cuteajax
Member
 
Posts: 5
Joined: Sun Dec 03, 2017 7:56 am
My RE system: Outback VFX 3024 Inverter (230V), 6 units of 150Amp/hr AGM batteries.

Re: charge parameters for 450Amp/hr battery bank on VFX3024E

Postby Mike Curran on Wed Dec 06, 2017 1:37 pm

You still must set them, you just don't have to worry about temperature variations affecting your charging. The RTS and your FX will adjust them for you. For a 24V bank like yours, the correction factor with an Outback RTS is 0.06V/°C above or below the battery manufacturer's standard 25°C charge voltage recommendation. (I got the RTS correction factor from my 10 year old GVFX manual. I suspect it hasn't changed.)

So for example if you set float voltage to 26.4V and your batteries are at 30°C, the RTS + FX will reduce the actual measured voltage applied to your 24V bank by (30-25)×(0.06V/°C) = 0.3V. That would be 26.4 - 0.3 = 26.1V. A warm battery needs less voltage to accomplish charging (and vice-versa).

On the other hand, if battery temperature is 20°C, actual applied float voltage would be increased by (25-20)×(0.06V/°C) = (again) 0.3V, making your actual battery voltage 24.7V.

But bottom line is you must set your desired float, absorb, etc. voltages using a Mate.
Mike Curran
OutBack Guru
 
Posts: 378
Joined: Sat Aug 28, 2004 6:28 pm
Location: Chagrin Falls, Ohio
My RE system: Outback:
- 8 (2x4) Evergreen 180's into one MX60
- 6 (2×3) ALEO S79-300's into one FM80
- 2 grid-tied GVFX3524's classic stacked for 120/240VAC
- 12 Surrette/Rolls 2V x 1766Ah
- Hub10.3, Mate3, FNDC, RTS, OpticsRE. Tigo Energy ES maximizers on each PV module.

Westinghouse Solar:
- 30 (2x15) 235W panels with Enphase M215 microinverters, grid-tied.


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