OK, so I got this thing rigged up here, 72v with right around 30 amps

N

n00b

100 mW
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Alright, so here's what I'm doing:

I got this 12-fet 26-32A controller with 100v caps inside that look decent quality and a throttle with a key that registers the voltage boogered into said controller.

What I'm worried about is the power supply is 2 36v 30A batteries in series to get 72v with 30A.

The battery packs are the same and have a 30A BMS.

It's supplying a 1000W cheapy hub DD motor, and thus far it seems OK.

Is there anything I should be worrying about?
 
The BMS systems in the packs? Are they 36v ( 10s) BMS systems? The danger being one BMS might fail, in circuit, and then short open, allowing full pack voltage across the now single BMS.. which designed for 36v, will not typically take 72v well, and may very well immediately fry too. In a chain. One goes and takes the other out.

Its the failure you plan for, in the end, and make concession to protect agains.
 
DogDipstick said:
The BMS systems in the packs? Are they 36v ( 10s) BMS systems? The danger being one BMS might fail, in circuit, and then short open, allowing full pack voltage across the now single BMS.. which designed for 36v, will not typically take 72v well, and may very well immediately fry too. In a chain. One goes and takes the other out.

Its the failure you plan for, in the end, and make concession to protect agains.
Click to expand...
I'm kinda not testing the BMSs in the packs, but I'm pretty sure they'e of decent quality.
I may have gimped the controller a little too much by filing too much of the shunts off.
If I was to leave the controller stock, what are my chances?
So you're saying if the controller tries to draw 2 more amps than the battery BMS, there could be..problems? Fire?
 
Shunts? Why are you removing the metal form the shunt? to get less current? The 32A controller should be fine with the 30A packs at 72v. 30A @ 72v is good for 2160w.. and it only takes 6-8 Amp to move bicycle speeds on 72v... ( 10-15mph, 400-500w, 6-8A)
 
DogDipstick said:
Shunts? Why are you removing the metal form the shunt? to get less current? The 32A controller should be fine with the 30A packs at 72v. 30A @ 72v is good for 2160w.. and it only takes 6-8 Amp to move bicycle speeds on 72v... ( 10-15mph, 400-500w, 6-8A)
Click to expand...
So I don't need to file the shunts to keep the batteries from catching on fire?
 
DogDipstick said:
Shunts? Why are you removing the metal form the shunt? to get less current? The 32A controller should be fine with the 30A packs at 72v. 30A @ 72v is good for 2160w.. and it only takes 6-8 Amp to move bicycle speeds on 72v... ( 10-15mph, 400-500w, 6-8A)
Click to expand...
Because I heard (read) it's not good to have the controller trying to pull more amps from the battery than what it can put out.

I kinda know how to fix that. Especially if it's just a 2A discrepancy.

I'm of the opinion it's not the voltage, it's the amperage.
 
DogDipstick said:
The BMS systems in the packs? Are they 36v ( 10s) BMS systems? The danger being one BMS might fail, in circuit, and then short open, allowing full pack voltage across the now single BMS.. which designed for 36v, will not typically take 72v well, and may very well immediately fry too. In a chain. One goes and takes the other out.

Its the failure you plan for, in the end, and make concession to protect agains.
Click to expand...
Why would the 1st BMS fail? The BMSes might just take take 72v no problem.
 
n00b said:
So I don't need to file the shunts to keep the batteries from catching on fire?
Click to expand...
Yes the 32A max controller... if manufactured correctly... should not overwhelm the 30A battery... a battery rated for (X) amps contin can usually push a little more upon peak. If the controller is 32A... it should be fine without a mod limiting current. Friend.

yes, might, take 72v no problm. Might not. Electronics are designed around price points.. and typically the lower the voltage a rated part, the cheaper it is.. so they would NOT use 132V rated FET banks in the BMS designed for 36v... they might use 60V max rated cause its cheaper... and

Why do BMS systems fail? IDK I dont use em. However, i work for fusion and fission engineers and they got me covered.. so.... special case I am. Use one. for sure. I dont know why people use " Battery Murder Systems" but they do and think its safer yet shit still burns. Sometimes it doesnt. Sometimes the BMS is well designed and does its job for years and it is built with parts that can easily take 2x the voltage of the operational range.. but .. sometimes this is not the case. Just telling you what to look out for.

FET banks of transistors in a ttypical BMS system fail either open circuit or closed circuit.. no in between. Its job is a large switch... and ... it loses the funtion of stopping the current if it failes in teh " closed " state.. and stays there.. and does not " open " the circuit and stop the fault current downstream. Like a short or a kid who walked up to your bike goo gaa baby that tried to grab the wires and got shocked. is getting shocked. is burning. Is crying and burning. Stupid baby should not have grabbed the wire its the fault of the baby but the working BMS might stop the current.. the broken BMS might not.

...nothing like the smell of fried babe in the morning let me tell ya. Noffin' like it on earth.
 
DogDipstick said:
Yes the 32A max controller... if manufactured correctly... should not overwhelm the 30A battery... a battery rated for (X) amps contin can usually push a little more upon peak. If the controller is 32A... it should be fine without a mod limiting current. Friend.

yes, might, take 72v no problm. Might not. Electronics are designed around price points.. and typically the lower the voltage a rated part, the cheaper it is.. so they would NOT use 132V rated FET banks in the BMS designed for 36v... they might use 60V max rated cause its cheaper... and

Why do BMS systems fail? IDK I dont use em. However, i work for fusion and fission engineers and they got me covered.. so.... special case I am. Use one. for sure. I dont know why people use " Battery Murder Systems" but they do and think its safer yet shit still burns. Sometimes it doesnt. Sometimes the BMS is well designed and does its job for years and it is built with parts that can easily take 2x the voltage of the operational range.. but .. sometimes this is not the case. Just telling you what to look out for.

FET banks of transistors in a ttypical BMS system fail either open circuit or closed circuit.. no in between. Its job is a large switch... and ... it loses the funtion of stopping the current if it failes in teh " closed " state.. and stays there.. and does not " open " the circuit and stop the fault current downstream. Like a short or a kid who walked up to your bike goo gaa baby that tried to grab the wires and got shocked. is getting shocked. is burning. Is crying and burning. Stupid baby should not have grabbed the wire its the fault of the baby but the working BMS might stop the current.. the broken BMS might not.

...nothing like the smell of fried babe in the morning let me tell ya. Noffin' like it on earth.
Click to expand...
Al-righty then. :oop:

I'm not checkin' the fets in the BMS, the batteries are sealed up and it's supposed to be the best cells this company makes.
They make good batteries. Been using some AAA rechargables they made for years.
I did open up the controller, obviously. I may try an unmodded one on the system next.
Could be I shaved too much off of this one. Idk 'bout all that fried baby stuff, that's pretty weird, bro.
 
n00b said:
Al-righty then. :oop:

...that's pretty weird, bro.
Click to expand...
A great electrical engineer of the world today, by the name of Bruce Bowling, board designer and electrical genius ... standing, next to the man.. Phil Tobin... who programmed ALL the GM cars from 1980 through about 1998... wrote every program .. the cars ran... said to me:

... And his is the best electrical engineering advice i have ever had in my entire life. ...

He said...

Quote: (Sic)

"..Noise?.... well... if you strike your baby with a stick: It will make noise. " " Remember this, because it will solve all your electrical design problems "

_Bruce Bowling, circa 2004
 
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