Lithium charge cutout with Classic

[bigal]

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.

[ClassicCrazy]

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

[bigal]

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.

[Vic]

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

[ClassicCrazy]

Yes - as Vic said that is what I meant about the voltage limits.

Larry

[ClassicCrazy]

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

[bigal]

 
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.

[mike90045]

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".

[bigal]

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??

[Westbranch]

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)

[mike90045]

.......

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.

[bigal]

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.

[dgd]

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

[bigal]

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.

[RossW]

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.