Removing Battery Connection

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feudalkaos
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Removing Battery Connection

Post by feudalkaos » Fri Dec 06, 2019 12:13 pm

I have an Outback VFX2812 and a Flexmax 60 with 1110 watts of solar.

I have been using 675 ah of flooded lead acid batteries for my system but am not going to switch out to Lithium batteries.

I have concluded that I need 400ah of lithium and have sourced 16 LiFePO4 100ah cells which I will configure as a 12V bank.

I am aware that for my lithium cells I will need a BMS that will open the charging side on a high voltage event and the load side for a low voltage.

With my outback charges, if I were to be charging at any given time and suddenly open the high voltage relay what would happen to the charges?

This should only happen if something malfunctions since the chargers will be configured to stop charging long before a high voltage event however I am looking for failure modes. I would like to be able to protect the chargers in this event. I know some chargers are capable of handling opening the battery connection mid charge, (>100A) in some cases, but I am not sure if these will.

My backup plan is to open the PV circuit with a relay to stop incoming power to the Flexmax 60 and open the AC source with a relay to stop the incoming power to the VFX2812. Thoughts?

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Gwendoly Espe
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Re: Removing Battery Connection

Post by Gwendoly Espe » Fri Dec 06, 2019 1:07 pm

From the VFXR manual: VFXRA
The inverter is also controlled by a high battery cut-out limit. If the DC voltage rises above this limit,
the inverter immediately stops functioning and gives a High Battery V error. This function is intended
to protect the inverter’s output and loads. Continuing to invert on a high DC voltage may produce a
distorted waveform. Note that the inverter’s high battery cut-out does not alleviate the high battery
state. The cause is an external condition which could damage the inverter.
 The high battery cut-out voltages for each model are shown in Table 18 on page 63. This voltage is not a changeable set point.
 If the voltage drops below this point, the inverter automatically recovers.
 This is one of the errors on page 52. It appears as an event on a MATE3-class system display. The low battery and high battery functions are summarized in Table 18 on page 63
On Page 57 has the electrical specs including the DC max's that might help you with your question.


I hope this helps!
Gwendoly Espe
Applications Engineer


Alpha Technologies Inc. / OutBack Power Technologies
3767 Alpha Way Bellingham WA 98226 USA
http://www.alpha.com

feudalkaos
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Re: Removing Battery Connection

Post by feudalkaos » Fri Dec 06, 2019 3:25 pm

Thank you for the reply however this is not what I was looking for.

When I said high voltage event I meant for the batteries not for the Flexmax 60 or VFX2812.

My question is, what happens to the Flexmax 60 and VFX2812 when they are outputting power to the connected batteries and suddenly the batteries are disconnected? Are they able to handle this?

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Re: Removing Battery Connection

Post by SandyP » Sat Dec 07, 2019 5:24 am

feudalkaos wrote:
Fri Dec 06, 2019 3:25 pm
My question is, what happens to the Flexmax 60 and VFX2812 when they are outputting power to the connected batteries and suddenly the batteries are disconnected? Are they able to handle this?
Probably should not have an issue, didn't your installer post on the wall a system shut down & start up sequence.

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Re: Removing Battery Connection

Post by raysun » Sat Dec 07, 2019 6:42 am

The question is a bit like asking what will happen to a car if its stopped by driving it into a ditch. It may not do mechanical damage, but it isn't going to help the paint job either.

The proper sequence for shutting down the inverter is to disconnect the AC load, then disconnect the battery.

The correct procedure for the charge controllers is to disconnect the PV source, then disconnect the battery.

The proper start up procedures are the reverse of the disconnect procedures.

You will want to make sure the controllers and inverter are shut down in an orderly manner in order to assure damage is not inflicted upon them or equipment connected to them.

More than that, you will want to assure the system never reaches a battery condition where an abnormal shutdown would occur.

Out of curiosity, every charge controller I've ever worked with states unequivocally that there must be battery power connected prior to connecting PV power. What controller is referenced that would allow the controller to disconnect from the battery at a > 100A load?

feudalkaos
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Re: Removing Battery Connection

Post by feudalkaos » Sat Dec 07, 2019 3:38 pm

I do not entirely agree with your comparison to driving a car into a ditch. If a system is designed to handle such a change in load then it can do as much. My question is only if it is designed to handle it.

I agree that most things are not designed to handle a sudden drop in load but not all are this way. As a comparison that may not be as direct, I have worked with variable frequency drives outputting hundreds of amps to a motor at much higher voltages that are perfectly capable of handling the motor being disconnected or even shorted mid output. This is merely a design feature in which they have included a large dissipation system such as a DC brake to handle the sudden change in load.

I do not have specific examples of inverters or charge controllers that are capable of this at high output loads but have only been told of them by others who own them. It is certainly possible that these people are mistaken but it is irrelevant since I was only asking about my inverter and charge controller from those who may know.

I did not ask for a critique of the question or for direction on the proper way to start it up or shut it down. I am more than aware that the goal is to avoid any event in which the batteries are suddenly disconnected. I am seeking information regarding the result of such as sudden disconnect if one were to happen.

I am not sure if it was your intention or not however your message comes across as unhelpful and somewhat pompous. If you only intend on trying to reduce questions that you feel are beneath you then please refrain from responding. If I am misreading your response and misjudging your (always possible with text based discussion) then I apologize and please feel free to respond further.

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Re: Removing Battery Connection

Post by raysun » Sat Dec 07, 2019 7:26 pm

You can read into it what you choose. The information you need is there.

Be sure to shut down loads before removing battery voltage from inverters. Be sure to shut off PV before removing battery voltage from charge controllers.

Apply battery voltage before connecting loads to inverters. Apply battery voltage before connecting PV to charge controllers.

The FNDC relay has the fastest response and the widest voltage trigger points.

Avoid conditions that would cause battery voltage to reach limits that would damage cells.

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Re: Removing Battery Connection

Post by James Wilson » Sun Dec 08, 2019 4:35 am

I just replaced my lead acid batteries with Battle Born batteries. I have same concern.

The batteries' internal BMS is supposed to disconnect th batteries when they are below 25 degrees F, their charge drops too low, or their charge is too high.

It's not good engineering, but I'm just counting on the charge controllers to function properly and not overcharge the batteries. And the inverter's Low Voltage Disconnect to keep the batteries from getting too low. And the batteries are in the basement where I don't expect it to go below freezing.

feudalkaos
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Re: Removing Battery Connection

Post by feudalkaos » Sun Dec 08, 2019 9:06 am

James

I considered using Battleborn but decided against for this very reason. I know that you have no insight into the BMS on Battleborn batteries so I am building my own bank using Sinopoly cells.

My ultimate plan is to disconnect AC side and PV side for my charge controllers before disconnecting the battery load but I was looking to find out what would happen if the load was disconnected. Wanted to know from someone who has actually had this happen or has tested it themselves. Unfortunately, it seems I am only getting speculation and a bit of berating for asking the wrong question apparently.

If I happen to get better information from someone on another forum I will be sure to let you know!

James Wilson
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My RE system: 4 - Sharp ND-167U3A 167 Watt solar panels
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Re: Removing Battery Connection

Post by James Wilson » Sun Dec 08, 2019 9:31 am

Yes there were some obtuse replies! :)

I decided on the Battle Borns because I don't need any more 'science experiments' in my life right now. Otherwise I would have gotten some much less expensive batteries and worked out a BMS for it.

raysun
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Re: Removing Battery Connection

Post by raysun » Sun Dec 08, 2019 9:40 am

James Wilson wrote:
Sun Dec 08, 2019 9:31 am
Yes there were some obtuse replies! :)

I decided on the Battle Borns because I don't need any more 'science experiments' in my life right now. Otherwise I would have gotten some much less expensive batteries and worked out a BMS for it.
You might want to search the forum for integrating SimpliPhi LiFePo4 batteries with Outback inverters for some hints on how to safely manage the voltage limits. The Battle Borne batteries could be handled a similar way.

The best strategy, which has been tested in the field, is to use the FNDC to monitor voltage and to use its relay to shut down AC loads and PV in under volt and over volt conditions. Ideally, the settings used should be within the range that would cause the BMS to disconnect the battery.

There's an application note floating around that will provide guidance.

feudalkaos
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Re: Removing Battery Connection

Post by feudalkaos » Sun Dec 08, 2019 9:56 am

James Wilson wrote:
Sun Dec 08, 2019 9:31 am
Yes there were some obtuse replies! :)

I decided on the Battle Borns because I don't need any more 'science experiments' in my life right now. Otherwise I would have gotten some much less expensive batteries and worked out a BMS for it.
I understand that completely. Honestly, I am wishing I had done the same. I always have too many experiments going and this one is only adding to that stress. Unfortunately, I have already purchased the cells so I am committed at this point.

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