A Forum run by Enthusiasts of MidNite Solar

Charge Controllers and Clippers => The "Classic" charge controller => Topic started by: bigal on September 11, 2018, 06:11:08 PM

Title: Lithium charge cutout with Classic
Post by: bigal on September 11, 2018, 06:11:08 PM
Getting ready to  deploy,  48v@200 ah  lithium battery. 32 Fortune prismatic cells, metal case , 100ah.

For protection against over voltage, solenoid disconnect seems the standard for lithium chargers.

Simple question, if I use a solenoid disconnect, will Classic tolerate a quick disconnect without damage? Charging current would be low, perhaps 10amps@48v

From reading here it seems that the Classic does not have a suitable relay contact, and the software to initiate this disconnect.

I am aware of the  whiz bang ending amps possibility but would rather not do it that way.

I have a stand-alone controller that can be configured to do the disconnect without any control by the classic.





Title: Re: Lithium charge cutout with Classic
Post by: ClassicCrazy on September 11, 2018, 06:45:21 PM
You can set high and low voltage limits in the Classic .

Not sure what other protections you have on your batteries - a BMS ? If so that should take care of your batteries.

I would use the disconnect to protect  your batteries from going too low .

Larry
Title: Re: Lithium charge cutout with Classic
Post by: bigal on September 11, 2018, 07:14:06 PM
Thanks Larry,
Using high and low disconnect.

Not sure what you  mean by setting lw and hi  voltage on classic...could you explain?

Picture shows active battery balancers .. little black boxes
1 per cell or pair of cells, depending on your plan.

Title: Re: Lithium charge cutout with Classic
Post by: Vic on September 11, 2018, 07:31:28 PM
Hi bigal,

I am NOT Larry,   but when he said,  "You can set high and low voltage limits in the Classic",  am sure that he was saying,   that in the Classic Charge>Limits Menu,  there is a Low Voltage Limit,   and a High Voltage Limit setting to Limit the Classic's range of charge voltage.

IMO,   Vic
Title: Re: Lithium charge cutout with Classic
Post by: ClassicCrazy on September 11, 2018, 08:03:51 PM
Yes - as Vic said that is what I meant about the voltage limits.

Larry
Title: Re: Lithium charge cutout with Classic
Post by: ClassicCrazy on September 11, 2018, 08:08:28 PM
What I did with my lithium was use ending amps to cut off the absorb and go to float which wouldn't charge up the batteries any longer - I have whizbang.  I was using bottom balancing so had voltage set to a point  in absorb where it couldn't fill them up all the way.
You should probably consult your battery supplier and ask them what they recommend for setpoints for you batteries.
The problem I had was things messed up for me a couple times and I did not have anything that would disconnect the batteries from everything on a low voltage point. 

Larry
Title: Re: Lithium charge cutout with Classic
Post by: bigal on September 11, 2018, 08:57:51 PM
 
Didn't mean to start a Lithium charging topic here. Maybe we can get back to the original question inmyfirstpost.

I'm using a charge  cut off solenoid that is controlled by
a stand alone controller.

Question is, if I use a solenoid disconnect, will Classic tolerate a quick disconnect without damage? Charging current would be low, perhaps 10amps@48v.

Alternators for example, can be damaged by being disconnected from the battery when charging.

Title: Re: Lithium charge cutout with Classic
Post by: mike90045 on September 12, 2018, 02:47:19 AM
I suppose it depends on how the Classic generates it's internal source power, and what happens while it's running, has solar and the battery "disappears".    Will the electronics go ape ?  Will some PV power sneak into the battery side and keep the controller properly powered ? 
The engineers should know, and maybe there is a mod for "future proofing" that can address this, so that a BMS can safely halt charging from the Classic.

Or, there is worse case, the battery "disappears", the sun is shining and the Classic goes "pop".
Title: Re: Lithium charge cutout with Classic
Post by: bigal on September 12, 2018, 03:32:02 PM
Mike you stated the issue perfectly...I want to avoid POP!!

On boats , charging is often  done by engine alternator, and when lithium batteries are full and disconnected, a small lead acid  battery is left connected across the alternator to avoid damage.

Maybe something like that is necessary??
Title: Re: Lithium charge cutout with Classic
Post by: Westbranch on September 12, 2018, 08:08:39 PM
Al, maybe my limited electrical knowledge, but wouldn't the FLA  battery have to be disconnected while the Lithium is being charged? I am imagining that there needs to be more than a solenoid, say like an  auto transfer switch in an Inverter?

No idea if the Classic would survive a 'drop gate' solenoid driven disconnect that leaves the PV power flowing.... wouldn't it be better to shut off the PV input?  Classics tolerate that every time we do a VMM (factory reset)
Title: Re: Lithium charge cutout with Classic
Post by: mike90045 on September 12, 2018, 08:40:27 PM
Quote from: Westbranch on September 12, 2018, 08:08:39 PM
.......

No idea if the Classic would survive a 'drop gate' solenoid driven disconnect that leaves the PV power flowing.... wouldn't it be better to shut off the PV input?  Classics tolerate that every time we do a VMM (factory reset)

Yes, much better, but that is going to need a 200V DC switch, and the BMS has to activate it, not the classic.
Title: Re: Lithium charge cutout with Classic
Post by: bigal on September 12, 2018, 09:07:03 PM
So I'm not really trying to reinvent this whole thing, but I would like to look at a little different twist at charging lithium's. Standard practice is to leave them connected and just make sure the voltage doesn't go too high. In off-grid application this is great since we're going to be using lots of power during the day and of course there has to be a battery connected to the PV and the inverter for this to work.

Been doing this for almost 7 years with my forklift battery. Of course it likes to be on float and there has never been any issue with overcharging.

It seems likely that I might end up with using the Wiz bang 2 and ending amps to cut the charging back. I'm not entirely happy with that because it's not foolproof. Perhaps I need to use my BMS to allow for an additional cut off, if it senses voltage too high. of course that still leaves me with the problem of how to cut off the charging entirely without cutting off the classics from the battery.

I've considered retaining my old 48 volt battery system and leaving it in parallel with the lithium's. Of course that opens up a whole new can of worms. I could use contactors and cut One battery in and another one out. Again not a very elegant solution.

I just need to be able to shut off the charging of the classic with a with a logic control or something along that order.
I'm not a programmer so that leaves me a little out in the cold from some of the folks that can do that sort of thing.
Title: Re: Lithium charge cutout with Classic
Post by: dgd on September 13, 2018, 12:11:52 AM
Quote from: bigal on September 11, 2018, 06:11:08 PM

Simple question, if I use a solenoid disconnect, will Classic tolerate a quick disconnect without damage? Charging current would be low, perhaps 10amps@48v

I have had battery bank disconnected from a Classic when in bulkmppt charging. No problems and the classic  continued to power an AC inverter. On another system when a battery breaker tripped the Classic again suffered no ill effects and with nowhere for output current to flow to the PV input current just dropped to near zero.
Dgd
Title: Re: Lithium charge cutout with Classic
Post by: bigal on September 14, 2018, 11:20:50 PM
Pretty interesting observations! Thanks!

When you have 5k wrapped in a lithium battery, ya gotta have some serious saftey features...

Sounds like I could have an emergency disconnect without damage to Classic.

Title: Re: Lithium charge cutout with Classic
Post by: RossW on September 15, 2018, 08:25:17 AM
Quote from: bigal on September 14, 2018, 11:20:50 PM
When you have 5k wrapped in a lithium battery, ya gotta have some serious saftey features...

I have 900 AH @ 52V of LFP, live entirely off-grid... have set the Classic to a maximum charge voltage of 55.5V, my inverter has LVD should volts ever get down to 2.875V/cell, but will kick in the genset at 3V/cell or 30% SoC.

Granted, it's only been a short time (March 2014), but not even looked like any hint of a problem. So far, it's superior to the AGM I had before in every regard.
Title: Re: Lithium charge cutout with Classic
Post by: bigal on October 07, 2018, 09:42:42 AM
I've done more reading from group of early lifepo4 users in Australia. To prolong cell life, they finally adopted a charging plan that shuts off charge at preset voltage near 3.45 volts (HVD).  When cells drop to 3.3, bulk charging is resumed.

No system that used a form of float voltage was successful LONG TERM. These batteries are not tolerant of being kept at or near 100% charge . It shortens the number of charge cycles.

This brings me back to my original premise of disconnecting the Classic at a preset voltage, and reconnecting at a lower voltage.

This could occur multiple times a day.

I'd like the Midnite Brains to comment on the wisdom of the using a Classic in this manner!! Am I going to have problems?  How could I safely do this??
Title: Re: Lithium charge cutout with Classic
Post by: FNG on October 10, 2018, 05:09:09 PM
Quote from: dgd on September 13, 2018, 12:11:52 AM
Quote from: bigal on September 11, 2018, 06:11:08 PM

Simple question, if I use a solenoid disconnect, will Classic tolerate a quick disconnect without damage? Charging current would be low, perhaps 10amps@48v

I have had battery bank disconnected from a Classic when in bulkmppt charging. No problems and the classic  continued to power an AC inverter. On another system when a battery breaker tripped the Classic again suffered no ill effects and with nowhere for output current to flow to the PV input current just dropped to near zero.
Dgd

Correct, The classic couldnt care if the battery goes away it will just set in absorb or float and power itself from the pv. if a sweep is forced it will of course then drop out do to 0 amps during the sweep but it will not hurt anything at all
Title: Re: Lithium charge cutout with Classic
Post by: australsolarier on October 14, 2018, 01:51:28 AM
bigal, it seems to me to you are still a bit confused.  HVD disconnects the battery via a breaker or relay. (to protect the battery from being overcharged.

in the midnite classic you can set the max voltage that it ever permits. and low. it has nothing to do with bulk and float settings. or HVD or LVD.

my bulk setting is 56V. end amp 8A. so in the morning it charges to at max 56V and then tapers out. after end amp kicks in, the midnite switches to float and keeps it there abouts at 53.6V.

you will have to adjust the voltage that the midnite shows with a good quality volt meter. (in the menu, they have excellent manuals) and then it might  still be out a tenth of a volt or so. that does not seem much for lead acid batteries, but it is much for lithium. in my case to absorb at 56, one midnite classic is programmed to 56.2V,, the float for 53.6, is programmed 53.7. it then DOES float and absorb in the demanded voltages) (after the voltages have been adjusted.)

generally you should not have a low voltage disconnect. i am not usually going underneath 60% SOC. but i have tested down to 10% with both systems. the large 400ah system did trigger a programmable disconnect. now,  a low voltage disconnect should only happen when there is none or little solar input anyway. it is the last of the defenses, before the battery will be destroyed. in my opinion, a disconnect should not harm the midnite classic. there are 10s of thousands of midnite classics out there and it is the least of the problems or questions thrown up. similar say you have a 10kw inverter running at full capacity and turn off a switch to disconnect a 10kw load. should just turn off without problem.

Title: Re: Lithium charge cutout with Classic
Post by: Ron Swanson on October 14, 2018, 11:35:53 AM
Are you doing all this with the BTS disconnected or what?
Title: Re: Lithium charge cutout with Classic
Post by: Aravilla on January 03, 2019, 04:54:47 PM
This thread is a bit old now but I thought I'd throw a couple of comments in as the OP seemed to be slightly misaligned on either terminology or strategy. Most importantly - disconnects are not operational, they are emergency. And in an emergency, if you lose a solar controller vs burn the whole place down, take the dead solar controller 100% of the time. That said:

1) HV/LV/HC disconnects are just that - disconnect actions. Throw a switch, the connection is broken, hard and without remorse. If one is planning to use this strategy for anything other than "holy @*#&, the power @*#& has really hit the shittin' fan" type disconnect, that's insane. It's potentially dangerous, operationally disruptive, and is gonna be expensive. With this type of disconnect, it's programatically planning for the scenario where all other failsafes and settings have been violated. Operational vs emergency. But...

2) On that note, I would never want the controller itself determining when a battery bank HV/LV/HC disconnection is to take place. The controller should operate within the configuration given to it which prevents the need for emergency disconnects. No knock on the Midnite product line, however they lack a few important things that are vital in determining when a disconnect is required, and furthermore, the product is designed for a single (non-related) purpose.
2a) First, the controller is only responsible for the charging (and possibly coordinating/monitoring) aspect of the battery lifecycle. Asking a solar controller to perform a HVD/LVD is, in two words, operationally wrong. Your BMS is responsible for this.
2b) Secondly, in the HVD/LVD scenario, the Midnite products lack a voltage sense feature, meaning whatever voltage the controller is seeing is not actual battery voltage. The resolution the controllers have is not sufficient for LFP management when they are at or near 100% SoC - this requires cell level monitoring and very accurate voltages typically to two decimal places. And you cannot be 100% sure that the solar controller has the entire battery picture especially with other sources of charging or load. The BMS is installed at the cell level and sees all this.

3) Back to the BMS concept - the BMS is what should determine when a disconnect is required, and then trigger action(s). This can (and should) be very quick. There are other steps that can be taken in the pre-disconnect process to either eliminate the need or gracefully take things offline. In the case of alternators, for example, a pre-process that helps prevent the destruction of the alternator (field disconnect will save it from killing diodes) is a nice to have. Same with a solar controller in a HV/HC disconnect scenario being told to turn off gracefully and possible mitigate the issue. But, if the secondary process either doesn't eliminate the problem or complete in a reasonable timeframe, the hard disconnect needs to be executed. This is why we typically wire into charge and load bus bars. Each bus is configured with a disconnect that is programmatically controlled. The nice thing with dual buses is that just because charging was disconnected, doesn't mean the load side stops functioning. Highly useful in a boat house bank scenario, for example.

Properly setup equipment should rarely present a problem (and that's what the disconnect is for) and I can't say I've heard of a Midnite controller, for example, programmed to 14.5v running away to 15.0v on its own. In fact, when we charge our LFP bank, we can watch the bulk voltage stay very steady throughout the day and climb slowly...until it doesn't...right around 99%. At this point the controller jumps to absorb quickly, and amps back-off rapidly and in less than 1 minute, the controller will move from bulk to float, with voltage never going higher than we've configured. Should it do that, the BMS takes over and would disconnect the whole battery.

One thing owners strive for is the notion of "getting everything possible out of the setup". I've had conversations with folks when setting up systems that goes something along the lines of "but the batteries never get to 100%, only 99%, what's wrong?". They feel like they're being ripped off that last 1% or something. But in reality, it's an installer protecting your assets and giving some wiggle room in case "the worst" should happen.

Anyway, hope this helped someone.
Title: Re: Lithium charge cutout with Classic
Post by: australsolarier on January 03, 2019, 05:37:17 PM
aravilla,

well said.
and yes it would be nice if the midnite classics would have voltage sensors at the battery terminals. this is particularly beneficial for lithium batteries.