Single Chip BMS Research + DALY Pin Compatible BMS's

methods

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Aug 8, 2008
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This is like my 1 day off a year.
Time here is 0330 and I have already been up an hour and a half.

What I am talking about is this sort of thing
TI.png

They are well documented and dirt cheap
https://www.mouser.com/ProductDetail/Texas-Instruments/BQ7790518PW?qs=OlC7AqGiEDlYTjB/0WSTTA==

That came from the Google Search: "Single Chip BMS"

and

The Second Topic is BMS compatible with the DALY whip
DALY_Whip.png

I have absolutely no interest in perfectly parsing my blog to narrow down on whatever specific topic (cough) so we will talk about AT LEAST 5 things at once here. If you dont like it, click the next blog.

-methods
 
So What I see along the right is a row of NTC Thermistor inputs. They are all referenced to the same Vref. Each has an independent LPF.

Pretty Standard
You should ask yourself why they add the LPF and if you need it. Yes you do.

-methods
 
I am not reading the datasheet, just pulling images off of pages 2/3. All these things are the same.

ST.png
 
Ok
All that checks out

The next step is to get a Demo Design... but that is after Down Select. Down select is after Requirements & Rational.

Requirement
- 16S in 1 or more chunks
- LiFePO4 compatible limits
- Balance 50mA or better every channel
- Common Port ready (2 mosfet arrays)
- Low Power (super low power)
- Hardware or Software programmable
- Well documented, Available, Legit
....

I am going to pair this with the best mosfets on the planet, so... I do not NOT need any jenky-ass Chinese-Translated mystery chips. No Sir. I am done with that. I will pay my extra dollar and get something with a 180 page datasheet built to ISO standards

ya know?

...
- Requires no heat sink
- Handles 21A continuous
- Handles 42A burst
- Handles 84A peak
- Handles Transient currents**

.... we could go on

- Has internal temperature protection
- Has shared-thermal design (potted)
- Has 1/2 External temperature probes
- Has UART, SPI, or other AVAILABLE but not required
....

- Is not incompatible with an IP67 design
- Low Pass Filters on all read lines
- TVS diodes on every single bit of it
- 1mOhm ON for Charge or Discharge

... Then it all starts getting expensive eh? I got the quotes for a big clunky BMS that I know will work. Call it a hundred bucks in quantity tens not hundreds. Maybe half that in quantity hundreds not tens.

-methods

-methods
 

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DALY.png

So even if that thing has Short Circuit Protection, I would have to fuse-up or run mega-wires as 100A is a ton. So basically assume you get no overcurrent protection from the BMS (Which is wise anyway).

Yea - so for about double the price you step into a much larger class of BMS. Tempting, as that is a better price (by half) and better rating (by almost double)....

But is it?

-methods
 
I have one of this style, 4S.
I have beat on it pretty hard including total meltdown of my inverter at 2KW. It definitely survived a short!

JDB.png

Shorts happen
Quite often in the grand scheme of things. If you are only building one battery and taking your time, whatever. If you are building 40 batteries and banging them around ---> Going to happen. Either direct short or some kind of Instrument Short.

Riiiiight - We all have fuses running (rolls eyes)

Should but more often than not we tie the BMS directly to our appliance and wait for it to go bangers.

-methods
 
Here is the exact 4S LiFe model I burned in. This was for a <2KW mobile setup. Pack was about 90Ah

Inverter was a $42 special from CL. It would let you draw about 300W over continuous rating then blow its fuses, which were internally soldered to the PCB. I fixed that with some 12AWG then forgot about it (lol). Later I ran it H A R D and lit off the inverter something fierce. BMS was fine. Inverter was not at all.

JDB.png

-methods
 
Anyhow, that is a fair standard for:

* Actually Works

Yah know?

-methods
 
So along the way I also bought this bad-boy. It is currently in service. My primary gripe is that the battery is so TRUCKING heavy that I simply can not work with it. 90Ah of 16S is a wicked brick.

JDB.png

This one has never seen any real testing. I made sure its features worked (LVC and HVC) but I never hammered on it.

-methods
 
You have got to understand than when you H A M M E R on something, ,.......

* It Breaks
* You lose that money (LOL)

but more importantly!

* It breaks
* You find out your shit is not as good as you thought it was

Eh?

-methods
 
So here is the deal eh!

Can you get a powerful BMS this small? DEFINITELY
Is it going to cost $11? DEFINITLY NOT

You are looking at paying the same top dollar (higher) for something nice and small and compact. Let me show you some of the BOM cost here....

JDB.png

-methods
 
Start here: https://www.digikey.com/

Transistor Mosfet Single
In Stock
N-Channel
Vgs 80V-120V

That will get you a thousand results

RdsON 1-6mOhms

That will get you down to 250 results

NOW LISTENT... TRUST DIGIKEY OR TRUST MOUSER. JUST TAKE THE VERY FIRST OFF THE TOP BRO... OR THE TOP 3

https://www.digikey.com/en/products/detail/micro-commercial-co/MCAC100N08Y-TP/16032527
Beautiful mosfet
It is not really Logic Level tho, so be super careful. Remember that RDSON is usulaly at something like 10V gate drive... so if they say they can turn on at 4V, that is more like threshold. It may be conducting, but not at the target RDSON

If you need Gate Drive (like 2V) now is the time to enter it! Otherwise, assume standard.

If you need an easier or more traditional package, now is the time.

... ANYHOW
That aint my brand

-methods
 
Exclude Market Place (f-that)

(Prices spike after that)

Assume competitor companies are trumping up their specifications. Listen bruh, nobody is giving you like... a 100V 3mOhm on Mosfet for $2. LOL. If they do, it is a mixup or there is a hitch. This is a super competitive market, so if something is too good to be true then it is.

Just... STiCK To kNoWn BrAnDz pLeaSe!!!!

Infineon (Internal Rectum Fryer)
IXYS (I guess)

I dont use any other mosfets. I try to stick to IR (Infineon) because that extra $3 makes a BIG difference in margin and reliability. I ran a hell of a reliability program on their mosfets and they were super rock solid.

-methods
 
Filter by only IR, now down to 58 results
Get your wallet out buddy, now its time to start doing the math

JDB.png

Now look here son!
You can not just sort by cheapest every time. That is an idiots move and that is what roached Amazon in the future. Sorting by cheapest price is not what an Engineer does.

Requirement -> Targeting no heat creation

That means we need something like 1mOhm ON resistance

* 1pcs of these for $8
* 6pcs of 6mohm @ $4.20 each = $25 bones
* 3pcs of 3mohms @ $4.77 each = .....

See?
You need to consider your REQUIREMENTS and choosing carefully. You will N E V A R see a funky-ass China-Mainland BMS with the chip I selected above in it. . . but you will see that sort of thing around here

Cough

In the Chinese designs they use SUPER CRAPPY mosfets and gang them 4P, 6P, 8P... even more. The problem with that is that it takes only 1 bad nut to roach the boal.

Nah bruh

-methods
 
Never tried one.... About to LOL. That is not that expensive to me. I usually have to do Isolated designs so I pay that much for my gate drive alone.

JDB.png

Bro... That is what I was expecting for the Discharge Control of my 20A BMS. DOH -> 2pcs!!! so $15 in mosfet alone!

P = V * I
P = I^2 * R
P = V^2 / R

P = 20A * 20A * 2mOhms = 800mW

That is the sort of waste heat I find acceptable. Two of those in series, a couple watts.

-methods
 
Now... to go with that

* Isolated Gate Driver to hit the high side
* Mad TVS Diodes to eat that shit and protect our stuff
* Thermal Epoxy, the good stuff
* >..........

$10K project

Never going to happen

N E X T

-methods
 
I am not sure if guys like this just rebadge standard BMS or if they spec parts. It is not outside the realm of possibility that they are specifying higher grade parts for their BMS

https://overkillsolar.com/product/bms-100a-16s-lifepo4-12/

-methods
 
So how do I know this one is better?

Easy Dude
* PN,SN

Part Number, Serial Number
Without that, all the rest are absolute garbage. Zero Accountability. Zero Traceability. Zero Interest bruh.

Think ISO

JDB.png

-methods
 
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