If there is a BMS, why do I need a solar panel controller?


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ynot

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The title says it all:
The BMS will not accept power from the PV panels if the batteries are fully charged, so why complicate things?
 

ynot

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A little enigmatic Wolf, why does the BMS not handle the voltage.
It is going to accept volts as long as they are in range & not allow overcharging.
 

Cheap 4-life

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A little enigmatic Wolf, why does the BMS not handle the voltage.
It is going to accept volts as long as they are in range & not allow overcharging.
A bms has completely different functionality compared to a chargecontroller. Do some searches on here for a bms and also search charge controller. Or google.
Solar mppt chargecontrollers take the pv panels varied voltage and keep it just above the batteries voltage so the battery can properly charge.
Bms manages the battery
 

daromer

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A chargecontroller is not the same as a batterymanagement system. One does not replace the other

Chargecontroller makes sure you have a proper CC CV routine built in and if you run one with MPPT it also makes sure that you get the max out of the solar panels. A charge controller does not care aboute the health of the battery.


A BMS on other hand is to maintain and protect the battery. It looks at voltage on the pack, on cells and current. it also manages the temperature of the battery. See this as a secondary deffense if the chargecontroller fails or something else happens. It will then disconnect. Note that disconnecting for high voltage is not the same as regulating charge current or voltage.
A BMS can also let you know whats going on and to some degree balance the cells to get longer runtime overall before its totally out of balance.

Yes you can potentially have the solar panel go directly to the battery through the bms and so does cheap ass electronics do to save some bucks. But you loose alot of total energy available due to not optimizing and the fact that the bms shuts down it shuts down both in and outgoing power. (Unless we talk about some ebike BMS systems where they have in and out ports)
 

ynot

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A chargecontroller is not the same as a batterymanagement system. One does not replace the other

Chargecontroller makes sure you have a proper CC CV routine built in and if you run one with MPPT it also makes sure that you get the max out of the solar panels. A charge controller does not care aboute the health of the battery.


A BMS on other hand is to maintain and protect the battery. It looks at voltage on the pack, on cells and current. it also manages the temperature of the battery.
A BMS can also let you know whats going on and to some degree balance the cells to get longer runtime overall before its totally out of balance.

Yes you can potentially have the solar panel go directly to the battery through the bms

Thanks Daromar, I guess this is the experts section with no time for people who are not well steeped in BMS/lithium technologies.
Installed my first solar panel in 1982, along with my first wind turbine, in those days no one had heard of charge controllers, we did the controlling manually. Monitoring water levels was sufficient for years.
Installed my first charge controller in 2002, at that time felt that if you had a sufficient battery ratio to PV, (so that the PV would not deliver anything the battery could not handle) a controller was a gimmick KISS, .ie 6 - 200 amp golf cart batteries and a 100 watt panel.
Now as the ratio of batteries to panels has changed due to panel prices things have changed.
BMS's are new to me, so I come here for information, in the last month have switched an electric garden tractor which I built in 2010, from LA to lithium batteries, studying like mad to learn about solid state batteries and BMS's. Am waiting for the 3 BMS's I have ordered to arrive, so that I can build battery packs for my tractor, my RV and the freighter trike I am building.
Am not likely to live long enough to take my house off grid economically, but have lived off grid for a total of 18 years since 1980.
Can you steer me to a source of BMS information that describes the functions in a little more depth than the sites I have found with goggling and youtubing?
Tony
 
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daromer

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With a wind turbine you do have a charge controller as well. You have always had a charge controller but they of course work and look differently.
For a early Lead acid system and then with wind you basically control the voltage and dump the excess. A solar panel you dont need to dump the excess but regulate what goes into the battery. Once again LA generally dont need BMS since they like to be over charged a bit.

In the beginning you often did have the voltage of the solar panel closely to the battery and thus used PWM controllers mainly. They just turn it on/off. The new MPPT is more smart and you gain 20% or more in increase and you can also run HVDC inputs instead saving money on wiring.

BMS is something that exist on Lithium and have done so since the start. A BMS doesnt have to be complex and they differ based on what you are going to use them for and of course what function you want.

A BMS generally do:
1. Protection
2. Notification
3. Maintenance (Balancing)

Protection consists of
Under and over voltage of full pack
Under and over voltage on a specific cell
over current
Temperature.

And of course can do more :)

You can find some information in the FAQ here and i have also done some vidoes roughly talking about it.

Something that also is common and is wrong is that peope think that you can replace a BMS with an active balancer and thats wrong. If you look at my list above the maintenance aka balancing part come on 3rd place of what a BMS main function is.

Hope that explains. A BMS aint something magical making it 100% safe. It makes it "safer" :)
 

ynot

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Thanks Daromer, we were cross posting, I would have written things slightly differently had I seen your post.
Seems to me the boffins could do well to incorporate BMS's and charge controllers assuming a large enough market.
Tony
 

hbpowerwall

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Seems to me the boffins could do well to incorporate BMS's and charge controllers
The issue there is the vast amount of different chemistries, heat management, ease of replacement/upgrade, voltages etc.
 

ynot

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The issue there is the vast amount of different chemistries, heat management, ease of replacement/upgrade, voltages etc.
Of course, but chemistries are liable to settle into a few preferred types, but the market may never be large enough to pay for the development costs.

PS when I was building wind turbines, (600+ 200 watt machines) none of us even knew of any such thing as a charge controller, we lived with the machine and did the controlling.
Tony.
 

hbpowerwall

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PS when I was building wind turbines, (600+ 200 watt machines) none of us even knew of any such thing as a charge controller, we lived with the machine and did the controlling.
Tony.
Back in the day we had real lead batteries with proper amounts of lead inside - as long as they were topped off they were the charge controller lol
 

ajw22

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The BMS will not accept power from the PV panels if the batteries are fully charged, so why complicate things?

Ah, not quite. The generally accepted maximum voltage of Li-Ion cells is 4.20V. But if you directly attach a solar panel to the BMS set to cut off at 4.20V, it will cut off at around 80% charge (even less, as the cell ages).
To fully charge, the voltage needs to be held steady at 4.20V for quite some time longer. The exact reaction of the BMS will differ in specific cases, but it will be far from the optimal fast/safe/accurate charge profile a charge controller can be programmed to perform.

Another major issue, as others have noted, is efficiency.
Let's look at this specific 335W panel:
datasheet: https://www.lg.com/us/business/download/resources/BT00002151/LG335N1C-V5_AUS.pdf
Attached directly to a hypothetical 9S battery (thus, minimum voltage 3.0V x 9 = 27.0V ; max 4.2V x 9 = 37.8V )

The panel has a short circuit current of 8.44Amps. That's the maximum it can ever deliver.
When the battery is empty (27.0V), the charging power will thus be limited to just 27.0V x 8.44A = 227.88 Watt. Far cry from the 335W a good charge controller could eek out of it.
Similar problem as the battery is reached full state (37.8V). As the panel approaches its maximum voltage, the current it can deliver starts to plummet. Looking at the chart in the datasheet, it'll output just 8Amps at 37.8V = 302.4 Watt. Not that bad in this case, but that's just by luck.
 

ynot

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Thank you, am getting the kind of information was hoping for.
The situation seems to have reversed again.
Used to be that batteries were cheaper than panels,
then panels became cheaper than batteries, so we needed PV controllers.
Now batteries are getting cheaper so the paradigm is shifting,
and of course we see folks running big parallel packs with no BMS.
Tony.
 

daromer

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I hope noone running Lithium batteries run without BMS. That have never been manufacturer standards. BMS have always been incorprated into BMS systems in one way or another.

It have nothing todo with cost. Its not like you have cheaper panels thats why you have controllers... You have controllers because its safer and you get more energy out of a panel in the long term.
So dont connect that together because its not relevant in the equation here.
 

Wolf

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we see folks running big parallel packs with no BMS
I'm glad you are getting the information you require and that is good. That's what this board is all about. I was not trying to be snide or enigmatic with my first answer but it does in essence boil down to voltage. You see initially solar panels were matched to batteries so you could hook a bunch of them up in parallel get your 14.8 to 15 volts and charge a bunch of deep cycle flooded cell 12V batteries in parallel and everything was good. Many were 6V in series to get the 12V. Inverters were 12 volt, copper was cheap as you needed to run some serious 00 or even 000 cable to support the amperage.
Well things have changed. Panels now run at ≈ 30 to 40 volts and we now wire them in series (Usually 3s) which increases the voltage to ≈100 to 120 volts. The benefit of this is that we get to use smaller wire as the amperage is reduced, With a Solar controller we can recoup that amperage by convert the voltage to a usable 48V and thus increasing the amperage with a minimal loss. My initial comment should have included wattage with the voltage. Wattage is the final product of all the work done by the voltage and amperage. 12V x 100 Amps =1200W, 48V x 25A =1200W and 120V x 10A = 1200W
I can get the same amount of work done '1200W' with each scenario the only thing changes is voltage which allows us, if we increase it, to use less amperage.
What does that have to do with a BMS and solar controller you ask. Assuming you have 4500W of solar panels on your roof and you want to utilize the output to charge a 12V battery bank you would have a current of 375A that is a wire size(in copper) of 600 which is just a bit over an inch in diameter. Just imagine the circuit breaker! Kind of ludicrous right? So what if we take that 4500W and increase the voltage to 100V? Now we have a manageable 45 Amps of current.
We can run 1 array of 3 panels in series X 6 and combine them all into an AWG 6 run. We can even split the array if we have an easterly and westerly attitude and just run (4) AWG 10 wires.
That leaves us with 100V just waiting to be hooked up to something. The BMS isn't going to allow that voltage is way to high unless you are running a 100V or so battery. The problem is that your solar output won't be consistent and the BMS has no way to regulate it. In comes the charge controller. It can take that 100V and 45A regulate it and turn it into something more manageable as in 48V at 93.75A. So we have reduced our primary wire size to AWG 10 and now we just need AWG 3 if we run at 100% for the secondary wiring. The BMS is now happy with a consistent voltage and can make sure each pack stays in balance with the others.
I would like to see the folks than run big parallel packs without a BMS. Pictures please.
Wolf
 
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ynot

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Wolf here is one, there are more if you ask youtube for leaf modules with no BMS.


Tony.
 

daromer

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Yes and there are plenty of people doing it so wrong. Above is one good example of it. Just because something works for one person one time doesnt make it good practice nor safe.
Above is a VERY good example of someone that doesnt know what a BMS is for and what the balancing function is for. Its 2 different things and please read back to the 3 points i listed where balancing is the last function. BMS is so much more and its a protective unit. It protects for WHEN shit hits the fan...

Lithium batteries without BMS is not the proper way of doing it. And it does not get justified because others do it! Running without balancing is something else and yes that can be done but since most BMS systems include balancer its not really worth it.
 

ynot

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?Yes and there are plenty of people doing it so wrong. Above is one good example of it. Just because something works for one person one time doesnt make it good practice nor safe.
Above is a VERY good example of someone that doesnt know what a BMS is for and what the balancing function is for. Its 2 different things and please read back to the 3 points i listed where balancing is the last function. BMS is so much more and its a protective unit. It protects for WHEN shit hits the fan...

Lithium batteries without BMS is not the proper way of doing it. And it does not get justified because others do it! Running without balancing is something else and yes that can be done but since most BMS systems include balancer its not really worth it.
Daromer, I appear to have set off a firestorm, unintended I assure you.
For myself am trying to learn, am currently using a 5s pac to run my tractor no controller, no BMS, while I wait for the BMS to arrive so that I can build a 5s 2p or 3p pack. My 5s pack may be damaged by having no BMS, but I have the modules and can afford to lose 5 if they become damaged, I do find it interesting that there are people who claim a BMS is not needed, for myself I decided that I will use BMS's for my packs.

My questions are on the level of, if the BMS sees volts higher than it is set for, it shuts down the charging, how does it do that? It would seem that it must either put the voltage input line (panel charger etc) into an open circuit, or a dead short, if a short it will have to have a pretty fancy arrangement of diodes to stop any damage to either the battery or the charging system.
So in the absence of a charge controller what happens when the battery is not fully charged, if the charger tries to deliver a voltage that is too high for the battery at an amperage that is too high for the battery What does the BMS do?.
In my old LA wind turbine days, with no controller or BMS the battery simply accepted the current and boiled off the water.

My mention of the cost ratio's between batteries, PV panels and controllers is nothing more than a simple observation/opinion, not one I would present for argument./ More of an 'it seems to me' statement. Though charted on a graph might agree with my observation.
Please regard my questions as those of perhaps a 5 year old wanting to know
"daddy whats a square, and can I have that big elephant over there".
Tony.
 

daromer

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A bms disconnect IF needed. Thats what the protection is about. Its not a Charge controller. Either you have a bms with mosfets. Often know and used for ebikes or smaller Evs. Or you have shunt trip breakers or contactors.
As Said bms Main function is protection when shit hit the fan. You dont want to overcharge lithium.




You cant compare la with lithium. I also Said this in thd beginning.
 
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