DALY BMS 200A

gehowi said:

In my case my MPPT chargers lose their ground reference since the batt minus is interrupted, the output rises to the same voltage as the PV: 120V.

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Can you advise which MPPT controller you have?

I was thinking about active balancers as well, not the ones with capacitors but those with coils and energy transfer. The Daly just use resistors to put a load on the highest cells which is wasted energy every day.
But member "electric" here in this forum says that such balancing is not needed for good cells after the initial balancing is done. He is very experienced..
But for my 8*110Ah Lead acid banks it was really necessary to use active balancers up to 6A. Without I got huge voltage differences in only 1 week.

You're probably right if you have good cells, but my recent purchase from ali were within 10ma of each other but when the charging got to 14.1v one cell went out of balance by 250mv, which took me around 20 hours to balance back again. I'm still doing the top/bottom balancing so perhaps it will be better once this is done, but the daly bms just kept cutting my charger out as it couldn't balance that large of a difference.

@gnubie
I use 4 cheap chinese "Makeskyblue" MPPT chargers (55$) 12V -48V automatically; 120V input 30A output.
There are several minor issues with these controllers but the MPPT works perfect. I prefer cheaper separate controllers over 1 expensive controller.
I have some redundancy and it's cheaper to replace one.

@ScoTTyBEEE
I am in the same situation. I bought 16 200AH from chinese seller BLS Battery and got old crap. I bought a new set of 16 cells and got good ones.
These are always in balance but the first 16 are always unbalanced whatever I try.
"electric" said it's better to do top balance only: means charge it up until some cells reaches 3.65V and bring this cells down until the same level as the other cells. But if cell capacity does not match, imbalance comes back fast.

@Deno
I use HA02 balancers from Aliexpress They are made for LA not for Liion. I use for 2 years; 1 per group of 4 batteries, very effective.
HA02 24-48V 2-4 batteries. 10A bal current +-35$
For LA batteries in series, a balancer is really necessary to get max battery life and max total capacity.

Deno said:

yep. I never understood the 'logic' of why anyone would design a circuit layout for their discrete components, that would include disconnecting the BATTERY from the SOLAR CHARGE CONTROLLER, while solar is connected, when every dingus knows you hook up the battery first, and solar last, and disconnect the battery last... the SCC ALWAYS has a direct battery connection while solar panels are hooked up.

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It' s very easy (cheap) to disconnect the low side (-) with some parallel mosfets but it is not so easy to do it for the high side (+).
Disconnecting ground reference is never a good idea but in case of such BMS, yes they stop the current flow and don't care about your other circuitry.
I disconnect PV +inputs, that's only 5.5A @ 100V per group of 6 panels. Any decent small relay 250V 16A with NC contact can do without burn in. It's only active in summertime so the relays are almost never activated. During other seasons my 30KW batteries cannot get overcharged in one day.

What bothers me the most is the lack of full and informative data on some of these Chinese products. (Daly BMS for example) I’m not interested in buying and testing things just in order to figure out exactly how they operate. Some people may enjoy reverse engineering but I have other things to do with my time. It is more of an experiment than a build. Back when I designed and built control systems the product documentation would give you a full understanding of the component you were looking at. For example, anybody ever see a ‘mean time between failure’ rating on one of these Chinese BMS units? I guess you find that out at some point - surprise!

@Klspahr
If your product is decent and you are sure about your specs, then you make decent product documentation.
If not, like Daly, then you make your electronics invisible by moulding and give a minimum specs. On my Daly they do not even printed the 30A for the separate port. And I cannot check the mosfets to see if it's true. As soon as it fails I will cut it open.
Chinese don't care about MTBF, after 2 weeks you can't open a dispute and you even don't know the real manufacturer or the seller.
And silly enough, everyone is so happy to receive their cheap package from China that 80% gives 4-5 stars without even testing it.
Low prices have a reason.