BMS modding for more current

[ElectricGod]

I pulled up the HY3410 mosfets and moved them over to the C- buss. I had a bunch of AOT290 mosfets that I pulled off a dead BMS. They already had the center legs cut out of them which was exactly what I needed for the BMS. I left all the copper reinforcing where it was and then added wire to both sides of P-. The original .004 ohm .5w shunts came out and were replaced with 10 .005 ohm 2 watt shunts. I'll need to reset the shunt value so it reads current correctly.

 

[Dui ni shuo de dui]

Can someone explain to me, whats the point of this? I buy small bms'es, fit 10 usd relay, positive from the pack, negative from bms p- to drive coil and i switch controller ignotion to positive.
Discharging through bms mosfets is just another waistfull thing that subtracts from overal efficiency.

In this case it seems to me that you won't have current discharge control, since the current won't pass through the BMS. So basically your BMS will only manage cells voltages.
Also, your relay will need electricity to stay close since you need to feed its coil. I'm not really sure that is more efficient in the end, a proper BMS doesn't heat at all (well at least mine doesn't), and the inefficiency isn't constant, since it will only happen under discharge, while the relay will need current 100% of the time your ride will be on.

 

[agniusm]

Well, your discharge is controlled by your controller and doing it twice has bo benefit. Relays consume power but you only need tiny one and the levels there are miniscule. You are also adding another point of failure in your circuit. Just saying. There are no motorbikes or cars that are made to discharge trough bms and extra cost is just ridiculous. Better invest that 100 extra on branded reliable western bms.

 

[ElectricGod]

Well, your discharge is controlled by your controller and doing it twice has bo benefit. Relays consume power but you only need tiny one and the levels there are miniscule. You are also adding another point of failure in your circuit. Just saying. There are no motorbikes or cars that are made to discharge trough bms and extra cost is just ridiculous. Better invest that 100 extra on branded reliable western bms.

Thank you for your opinions.
These BMS's are already pretty good as is.
I just make them handle more current.
Reliability isn't really an issue with them.

 

[ElectricGod]

I've psoted a lot of stuff on modding several smart BMS's.
The ones that use the cute elephant app have an LCD.
I thought I'd get a couple of them to try out.
This would supposedly eliminate the need for a phone app or the USB/PC app.

I have to say...do NOT waste your time. This is the dashboard screen.
All the other pages of data are even worse than this.
Since I can't read squiggly, I don't know what is what.
I've gone through all the menus looking for something to select or change and maybe get an idea what things do.
It appears that you can't change anything via the LCD...disappointing!
Assuming it uses settings from the BMS, you should see the battery at nearly full.
There's zero documentation for the LCD so I'm 100% guessing at functions.
It has a connector labeled speed, but what you connect it to is a mystery...maybe a motor hall?
Doesn't matter really as none of the screens list kmh or mph or RPM.
This was a waste of money!

 

[rcpilot]

Hey there Electricgod, I see you haven't been online for a little while, I hope you are well.
I have a BMS that failed; two of the mosfets cracked and are missing chunks. I was reading this thread in hopes to repair and mod my BMS but unfortunately all of the pictures are broken and as they say a picture is worth a thousand words. Any chance these can be fixed?

 

[kdog]

I hope EG hasn't left the forum, I think some stuff went down late last year.
This was a great little how to thread for basic modding of bms's with some really good pics.

 

[fechter]

Hey there Electricgod, I see you haven't been online for a little while, I hope you are well.
I have a BMS that failed; two of the mosfets cracked and are missing chunks. I was reading this thread in hopes to repair and mod my BMS but unfortunately all of the pictures are broken and as they say a picture is worth a thousand words. Any chance these can be fixed?

Unfortunately EG is gone and took all his pictures with him.

It may be possible to repair the BMS if only the FETs blew. When they blow, they tend to short out, so there's a chance the gate driver is also damaged. Depending on the model, there are ways to test. First step would be to remove the blown parts. Then you can try to power the control circuit and see if the gate voltages look OK. If the gate voltages don't come up, then no point in installing new FETs.

Try posting a picture of the board.

 

[serginho007]

To improve current flow somebody tried to add copper strips on BMS (B- and C-)?

Found video on YouTube where man says that helps...



He's using low temperature solder paste which melts easy with any air gun with just 138C

https://www.amazon.co.uk/gp/product/B07B3WV5KN/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

Anyone tried? Is that really helps or useless?

 

[fechter]

I've done something similar with pieces of heavy copper wire. It helps.

 

[serginho007]

I've done something similar with pieces of heavy copper wire. It helps.

Used tick copper wire instead of a copper bar?

 

[monette999]

Will this mod work?

I want no Shunt functions

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[amberwolf]

As long as you don't mind the potential for blowing up the BMS FETs and possibly setting fire to the battery (since from another of your posts you also want to have no current limit in your controller, so there won't be *ANY* kind of current-limiting in your system) if it causes sufficient overcurrent to heat the battery cells enough, then you can do any mod you want--it's your stuff.

 

[monette999]

If wonder why my 30A Controller has 120V 100A FETs inside.

Copper Copper Bars soldered to the PCB.

The shunt line going to a resistor and then a transistor. I think it is the Base of the transistor to trigger the FET GATEs to ground.

So why only 30A when my Gets are rated 100A in full bridge configuration.


Why all that for 30A. False Lable???

Greetings.

 

[amberwolf]

30A *battery* current.

Phase currents (what the FETs see) can be MUCH higher than battery current, becuase the controller is a voltage/current converter.

 

[monette999]

Amberwolf,

do you know how to calculate the power of an 3phase motor with a phase shift of 120 degrees.

P= U*I square route 3 times cos phi.

So according my old knowledge the full bridge in good for more than 30 A.


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[amberwolf]

The point is the 30A doesnt' have anything to do with the 100A FEt rating. They're for different parts of the circuit.

 

[monette999]

You comment was not useful, but If I have 3 Full Bridges with 100A FETs what power max can I drive over the the phases.

120A per phase and max 100V

That's what's on the datasheet.

Each Phase can switch 6000watts

Can I put 2180W over the three phases in average?

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[john61ct]

As stated, the theoretical current rating of FETs using AC

has little relation to the real-life limit of the whole device.

Get rid of ALL BMS current limitations by simply using it for voltage sensing only, the cutoff protection accomplished by external contactors, rated however high you need (50% more current than they will ever see)

But you need to devise **some** way of limiting your current levels, even if you just use fuses.

Basing the limits on heat sensor input is better, e.g. CAv3

 

[Dinesh6252]

The point is the 30A doesnt' have anything to do with the 100A FEt rating. They're for different parts of the circuit.

Hi, I have a DALY 7S 20A bms in which 3 of the mosfets (Right row) got burned due to high discharge current. The MOSFETs used are Samwin sw056r68e7t (68V,120A). Can you tell me then, how many mosfets do I need in total for a 60A 7s bms. I want to use FDP075N15A (150V,120A) MOSFETs. Its a Common port 7s 20A BMS (same port for charging and discharging) so if anyone can tell if I need to change both charge and discharge MOSFETs or only the discharge MOSFETs will do the job?

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