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Victron 150/35, Outback
#31
Good deal..
so what about u not using a bms.. I’m trying to figure out if I need one.. I read so many places that a bms is needed with lithium... I understand that since u are not charging to full battery capacity that u arent worried about overcharging your individual cells.. but what about if a cell starts to deteriorate or goes bad?.. how would u know without a bms? I seen u said that u use the rc charger thing so I guess u just check periodically with that?

So if I’m understanding all this correctly,... to charge lithium (the pack in the pic) not lifepo, I can use charge controller that I can shut off equalization and battery temp, and adjust absorption voltage and float voltage.,
what if the charge controller has a bulk stage? Would I shut off bulk by voltage adjustment?
Is the reason hughf said it’s a pain in the arse to use a charge controller that is not controllable by bms due to him charging his cells to max?

Hugf are u saying I need to use float mode for lithium to allow the charge from charge controller to bypass my bats to supply loads?
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#32
You should probably use a BMS.  I've been dealing with lithium batteries for at least 10 years by now... I've just developed a certain comfort level with how I do things.  I'm not recommending NOT to use a BMS, I just take a different approach at times.

I have used low voltage disconnect which is based on voltage in some of my portables.  I also have used BMS units plenty of times as well, like those inexpensive PCB boards to the Chinese Bluetooth BMS units.  I’ve just done it a bunch of different ways over the years.

All my cells are pretty well matched, new, or often times the same exact cell.  Everything I use is fully tested.  I also monitor my cells pretty closely.  I top balance my batteries and am pretty conservative with cycle depth. Running into a problem is pretty unlikely, but that doesn’t mean it cant happen.  You could say I am running at a higher risk than someone who has a well setup Batrium system.

Most of my smaller packs or portables are not charged in the field.  I charge them using a balance charger, no different than how things are done in an RC car or plane.  They don’t use active BMS as its done externally at the charger.  If I need to charge in the field I have a balance charger with me and can charge off my car battery without a problem.  I probably have about 5-6 different chargers I’ve collected over the years.  Multiple Accucell 6 units, iCharger 206B, iCharger 3010b, iCharger 4010 Duo, iCharger

The more consistent your batteries are, the less reliance you will have on your BMS to actually do something.  Just as an example, none of my cells came from used laptop packs.  Med packs yes, EV car yes, new cells yes, but never cells that were already marked end of life in a serious project.

Why not start with a small system, inexpensive charge controller, play with it until you get it right, and then scale up?  Its pretty much how I learned all this stuff.

Solar charge controller is just a glorified DC-DC converter with too many settings.  You can charge batteries with a cheap Chinese DC-DC buck converter and pretty much get the same result.  If you just set every settings to the max charge voltage, it would basically do the same thing.

I think the bluetooth BMS units are great for monitoring large system as well... I took this pic when I was testing the unit.  Cell 5 was intentionally high for testing.

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#33
Ok I will use a bms..
correct me if I’m wrong, it seems as if I can use the outback in the pic for my lithium pack since the absorption and float voltages can be adjusted and equalization and battery temp can be turned off. Also the outbacks charge current can be set for a constant current.
U said something about some charge controller tapering off current near full. Does the charge controller I need to use have to have this
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#34
I don’t know why you would want to set a CC value on a solar charge controller. You won’t take full advantage of the PV power coming in by limiting it.

Perhaps if you needed to limit the current because your battery bank can’t handle the charge rate, or if there is another system component that can’t then I would understand, but I would just get a bigger battery or more capable component at that point.

Any reduction in charge rate should be cause you are losing daylight at the panel.
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#35
Ok then.. I thought lithium would charge more like it’s supposed to with a constant current
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#36
You use CC charging to not exceed the maximum current the battery can safely accept.

You use CV charging to not exceed the maximum voltage the battery can safely accept.

This graphic should help you visualize what happens in a CC/CV charger at the individual cell level...  

If your goal is to fully charge a lithium battery as fast as possible at it's max acceptable charge current, you must use CC/CV otherwise you could have bigger problems on your hands.

If you never exceed the max charge current of your battery, or the max voltage, then you can charge without strict adherence to the CC/CV profile.  This is typical of many projects on this forum.


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#37
Ok well Ik I’m under the max amps the battery can accept.. only probably 30amps from my 99v 20amp array when mppt does its thing..
As for CV I just set the absorb volts conservatively under max charge so that takes care of that?
Hey man I’d just like to say thx for taking the time to help me with all these detailed explanations
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#38
It should, but I would revert to monitoring and testing to confirm.

Throw a volt meter on it and watch what your equipment does.  If you are comfortable with what you see then you should be good.  Fine tune as needed.

I think most people here are pretty conservative with charge voltage... usually for two reasons.  1. they want to try and make their batteries last longer by not fully charging or discharging.  2. margin of saftey.
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#39
(09-26-2019, 12:49 AM)Crimp Daddy Wrote: I don’t know why you would want to set a CC value on a solar charge controller.  You won’t take full advantage of the PV power coming in by limiting it.

Perhaps if you needed to limit the current because your battery bank can’t handle the charge rate, or if there is another system component that can’t then I would understand, but I would just get a bigger battery or more capable component at that point.

Any reduction in charge rate should be cause you are losing daylight at the panel.
You would set a current limit if you had far larger an array and hence far larger charge currents than your batteries could accept - rare I know, but they put that current limit in there for folks who need it.

(09-25-2019, 04:11 PM)Doin it Wrote: Why does the charge controller need to be controlled by a bms.. I thought a bms keeps the cells equal. Wouldn’t the charge controllers float allow for the reduced charge
When you are balancing your cells, you need to have a reduced charge current going into the pack or you will just burn out your balancing components.
The Batrium documentation for the cellmons states:

While charging, one cell eventually reaches the end-of-charge voltage and the charging controller (PacMon) sets a low bypass charge current. Low current is continually applied allowing all cells to equalise to end-of-charge state. Use a low bypass charger current setting to prevent overheating the CellMons. If the bypass currents are too high, the “shunt” heating will continue to increase, until the CellMon PCB temperature limit is reached (75°C). At this point, a CellMon will “self-protect” and stop bypassing. PacMon will command a controlled charger to throttle back or shut down (if unsuccessful)

If you never plan to do any balancing/bypassing by having perfectly matched cells then you can ignore the above paragraph and just hope things don't drift out at the top end.

Batrium has a 'limited power' mode for the charge current - this can be used to communicate to a canbus connected AC charger or MPPT.

If you don't want to do this communication then you need to tune your absorption setpoint and absorption timer along with your bypass voltage so that the balancing happens at the end of the CV phase when the charge current is naturally low.

(09-26-2019, 12:21 AM)Doin it Wrote: Ok I will use a bms..
correct me if I’m wrong, it seems as if I can use the outback in the pic for my lithium pack since the absorption and float voltages can be adjusted and equalization and battery temp can be turned off. Also the outbacks charge current can be set for a constant current.
U said something about some charge controller tapering off current near full. Does the charge controller I need to use have to have this

Every solar charge controller that can be programmed for a bulk/absorption/float cycle will taper the current at the end of the absorption phase, that's just the natural behaviour of things.

If you don't understand these basics, you shouldn't really be messing with this stuff till you do.
Current system: 9.6kWh wet Nicad batteries, 16S1P Calb LiFePo4 210aH, Batrium WM4, Outback vfx3048 inverter, mx60 mppt controller, flexware 500 mounting hardware, 2.4kW solar array, 6kW lister diesel genset. MY'13 Vauxhall Ampera
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#40
Hughf there’s only one way to understand this stuff.. by asking - research and Doin it
Crimp and your advice has helped me understand a lot more..
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