2 of 4 MX60s shutting down during absorption

Discussion about the MX60 Charge Controller

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judoal
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2 of 4 MX60s shutting down during absorption

Post by judoal » Tue Jun 09, 2020 12:42 pm

My system: 4 arrays totalling 10kW, 4 MX60s, 3 GVFX3648, (16-6 volt AGM batteries (2 strings in parallel), mate3s, hub10. The 3rd GVFX is connected directly to the grid bypassing the batteries.

1. The system goes into absorb mode about the same time every day (11:30 AM) when the system is producing full or nearly full power
2. Two MX60s consistently either go to sleep or greatly reduce their output.

I don't understand why the two MX60s go to sleep or reduce power. And why the system decides to go into aborb mode at the same time when there is full sun and the system reduces its power output.

Anyone have an idea about correcting this?

Thanks

raysun
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Re: 2 of 4 MX60s shutting down during absorption

Post by raysun » Tue Jun 09, 2020 1:26 pm

judoal wrote:
Tue Jun 09, 2020 12:42 pm
My system: 4 arrays totalling 10kW, 4 MX60s, 3 GVFX3648, (16-6 volt AGM batteries (2 strings in parallel), mate3s, hub10. The 3rd GVFX is connected directly to the grid bypassing the batteries.

1. The system goes into absorb mode about the same time every day (11:30 AM) when the system is producing full or nearly full power
2. Two MX60s consistently either go to sleep or greatly reduce their output.

I don't understand why the two MX60s go to sleep or reduce power. And why the system decides to go into aborb mode at the same time when there is full sun and the system reduces its power output.

Anyone have an idea about correcting this?

Thanks
The MX60 charge controllers sound like they are doing what they are supposed to do: charge the batteries from the PV arrays.

The battery charging process has three steps:
• Bulk - a constant current phase where the chargers deliver as much charge current as is available, and they are programmed to deliver. During the Bulk phase, the battery voltage will steadily rise.

• Absorb - a constant voltage phase where the battery is held at the Absorb voltage as set in the chargers' parameters. During the Absorb phase, the charge current will steadily decline to a minimum - the Charged Return Amps.

• Float - a constant voltage phase where the battery is held at the Float set point, and a small charge is applied to keep the battery at full charge.

During Absorb, the charge controllers will deliver only the amount of current needed to maintain the Absorb voltage. The chargers will also supply whatever current is needed to service the loads during this phase. If more PV power is available than is needed for Absorb charging and for load service, the charge controllers will scale back their delivered power so as not to overcharge the battery. In the case of 4 arrays producing near maximum power, it's likely there is excess.

pss
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Re: 2 of 4 MX60s shutting down during absorption

Post by pss » Tue Jun 09, 2020 1:29 pm

Let's assume all 4 mx60 have the same charge parameters and absorb times and the array output to each is equal. After an initial bulk charge period, the controllers will reduce the amperage into the battery bank as it charges. If your load is being supplied, batteries will continue to charge until the cycle completed. Often, the voltage of the battery bank is not equal among each controller unless they all go to a common charging buss bar, then to each string. Commonly, the times send some to absorb and the others are not far behind. Again, as load is met and Batts reach full charge, no problem. If inverters not grid tied selling, no place for PV to go

SandyP
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Re: 2 of 4 MX60s shutting down during absorption

Post by SandyP » Tue Jun 09, 2020 4:17 pm

judoal wrote:
Tue Jun 09, 2020 12:42 pm
../..

I don't understand why the two MX60s go to sleep or reduce power. And why the system decides to go into aborb mode at the same time when there is full sun and the system reduces its power output.

Anyone have an idea about correcting this?

Thanks
Are you asking as you want to sell power back to the grid?

judoal
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Re: 2 of 4 MX60s shutting down during absorption

Post by judoal » Wed Jun 10, 2020 8:16 am

Thank you all for your responses. I understand about not overcharging the batteries. So, my next question is why would the system go into absorb mode in the middle of the day under full sun. What triggers the initiation of this phase?

Thanks

raysun
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Re: 2 of 4 MX60s shutting down during absorption

Post by raysun » Wed Jun 10, 2020 9:22 am

judoal wrote:
Wed Jun 10, 2020 8:16 am
Thank you all for your responses. I understand about not overcharging the batteries. So, my next question is why would the system go into absorb mode in the middle of the day under full sun. What triggers the initiation of this phase?

Thanks
Its the programmed response of the charging cycle - Bulk -> Absorb -> Float. The chargers exit Bulk and enter Absorb when the battery voltage rises to the Absorb Voltage set point programmed into the chargers.

Are you saying the battery had already been fully charged for the day and this is a 2nd charge cycle being executed?

judoal
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Re: 2 of 4 MX60s shutting down during absorption

Post by judoal » Thu Jun 11, 2020 4:37 am

My question should have been “what initiates the bulking phase? We have not had a power outage (loss of grid power). So the batteries are not being discharged. So why would they need to go through A bulking/absorb cycle. I’ve seen the battery voltage to the absorb voltage more than once during the day under full or partial sun.

raysun
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Re: 2 of 4 MX60s shutting down during absorption

Post by raysun » Thu Jun 11, 2020 4:55 am

judoal wrote:
Thu Jun 11, 2020 4:37 am
My question should have been “what initiates the bulking phase? We have not had a power outage (loss of grid power). So the batteries are not being discharged. So why would they need to go through A bulking/absorb cycle. I’ve seen the battery voltage to the absorb voltage more than once during the day under full or partial sun.
The principal trigger is the Rebulk voltage. If the battery drops below Rebulk, a new charge cycle is triggered.

provo
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Re: 2 of 4 MX60s shutting down during absorption

Post by provo » Thu Jun 11, 2020 6:29 am

raysun wrote:
Thu Jun 11, 2020 4:55 am

The principal trigger is the Rebulk voltage. If the battery drops below Rebulk, a new charge cycle is triggered.
You know, I've heard that, but it doesn't seem to be true for my FM80. I can go through the night on grid power holding float (24/7), and the FM80 will start bulk and go into an absorb phase shortly after the sun comes up, without getting anywhere near the rebulk setting of 24V.

Maybe you're talking about the VFXR charging rather than the FM -- I often have to manually Start Bulk on the charger before it will "wake up."

raysun
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Hyundai 355 watt panels (6 - 3 strings of 2 in series)
Honda EU7000is gas fuel generator

Re: 2 of 4 MX60s shutting down during absorption

Post by raysun » Thu Jun 11, 2020 8:54 am

Paraphrasing the FlexMax manual -
If, during Float, the battery falls below the Rebulk voltage, the charge controller will immediately start another Bulk cycle.

From another post (on charge controller behavior) -

From Outback support:

"The batteries will initiate a bulk charge in the morning (after sunrise) when the sun comes back up regardless of the battery voltage.

Unfortunately there is no way to disable this functionality. You can configure your absorb end amps to only allow a specific amount of current into your batteries but that's about it."
Last edited by raysun on Thu Jun 11, 2020 9:34 am, edited 1 time in total.

provo
Forum Czar
Posts: 529
Joined: Thu Jul 27, 2006 4:34 pm
My RE system: Sixteen Evergreen EC-120
(4 strings, total 1920W)
Eight Rolls S-550 (2 strings, total ~800Ah @ 24V)
One FM80
One VFXR3524A
Hub 10
Mate3s
FNDC and Trimetric
Location: Sierra foothills

Re: 2 of 4 MX60s shutting down during absorption

Post by provo » Thu Jun 11, 2020 9:16 am

raysun wrote:
Thu Jun 11, 2020 8:54 am

"If, during Float, the battery falls below the Rebulk voltage, the charge controller will immediately start another Bulk cycle."

and

"The batteries will initiate a bulk charge in the morning (after sunrise) when the sun comes back up regardless of the battery voltage.

You know, once a year or so I RTFM just for fun -- but I'm getting so ancient I only remember it for a few weeks :lol: .... Thanks!

judoal
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Posts: 30
Joined: Tue Mar 24, 2009 3:24 pm
My RE system: 3 GVFX3648, 4 MX60, mate3s, 16 Crown AGM, 2 series strings in parallel, grid-tie
Location: Nederland, CO
Contact:

Re: 2 of 4 MX60s shutting down during absorption

Post by judoal » Fri Jun 12, 2020 8:33 am

Thanks for the tip. I had forgotten about the rebulk voltage. I had set it too high. Will update this when I have more info about the results of lowering this voltage level.

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