High amp output bms

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maarkmohamed

100 W
Joined
Jan 10, 2019
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114
Hey guys as you may or may not know ive been trying to figure out exactly which cells and what size battery back ill be doing for my build and ive concluded that i want to do a 20s 20p battery pack with 3000mah cells. And each cell is capable of 20A discharge continuous and 30A for a short few seconds. That being said i would like to draw from my pack 400+ amps. Been looking for a bms to work with this kind of battery but a bit troubling trying to find one, and it also needs to support regen. Anyone got any ideas? Do you think i should get a regular bms that fits my battery configuration and then bypass the output leads and just put a 400A+ circuit breaker?
 
maarkmohamed said:
Hey guys as you may or may not know ive been trying to figure out exactly which cells and what size battery back ill be doing for my build and ive concluded that i want to do a 20s 20p battery pack with 3000mah cells. And each cell is capable of 20A discharge continuous and 30A for a short few seconds. That being said i would like to draw from my pack 400+ amps. Been looking for a bms to work with this kind of battery but a bit troubling trying to find one, and it also needs to support regen. Anyone got any ideas? Do you think i should get a regular bms that fits my battery configuration and then bypass the output leads and just put a 400A+ circuit breaker?
Click to expand...
I would point out that the switch on the BMS and the BMS itself are two somewhat different things. Also I doubt you'll be drawing 400 amps; you'd need to double up on 4/0 wiring (and protection devices) to really support those kinds of draws for any length of time.

I would get a remote trip 250 amp DC breaker (rated for at least 80 volts) and have the BMS trip the breaker on a fault. For that you can use almost any BMS; you just have to intercept the signal to the DC switch that it uses.

If you want more current, get two 200 amp remote trip breakers and parallel everything.
 
I was a bit confused on the awg wire carrying capacity. On one page they say 4/0 can handle about only 250a, and on another welding awg chart, it says that for 600a at a 100% duty cycle you would need 2 1/0 wires, which wouldnt be to far from one 4/0 wire. Take a look links below. Im aware that length matters. I shouldnt need the wire to be more than 5ft.



https://www.lincolnelectric.com/en-us/support/welding-solutions/Pages/selecting-proper-size-welding-cables.aspx



https://www.cerrowire.com/products/resources/tables-calculators/ampacity-charts/
 
maarkmohamed said:
I was a bit confused on the awg wire carrying capacity. On one page they say 4/0 can handle about only 250a, and on another welding awg chart, it says that for 600a at a 100% duty cycle you would need 2 1/0 wires, which wouldnt be to far from one 4/0 wire. Take a look links below. Im aware that length matters. I shouldnt need the wire to be more than 5ft.
Click to expand...
NEC wiring charts are for wiring installed in conduits and walls. These are conservative values that ensure there won't be any fires.

Welding tables are for wires that are exposed (i.e. easier to cool) and are continuously monitored by the welder. So their current ratings are far higher.

If you are going to run wires inside a bike or vehicle, then I'd stick closer to the NEC tables. If all the wiring is fully exposed to airflow you might be able to get away with the welding specs if you keep an eye on it. I'd err on the conservative side, both for safety and because you lose less performance that way.
 
I agree i would much rather play it safe. However the wires should run from the battery and lay on the frame of the bike which would be exposed to plenty of air/cooling when riding and the controller as well. If i use the 4/0 wire i will monitor it very carefully when drawing such high amps. On the other hand im more concerned about the bms issue, hoping someone has experience with this and can provide some additional advice.
 
I hope your not planning on drawing 400 amps on a bike... Forget flip cup...how about flip bike...
 
maarkmohamed said:
On the other hand im more concerned about the bms issue, hoping someone has experience with this and can provide some additional advice.
Click to expand...
Do you not want to use a circuit breaker?
 
billvon said:
maarkmohamed said:
On the other hand im more concerned about the bms issue, hoping someone has experience with this and can provide some additional advice.
Click to expand...
Do you not want to use a circuit breaker?
Click to expand...


Yea i was thinking about using a 400-500 amp fuse or circuit breaker but had trouble finding one that matched my Volts. Found a lot that matched the amps i was using but not the volts, unless u know of one insert the link.
 
maarkmohamed said:
Yea i was thinking about using a 400-500 amp fuse or circuit breaker but had trouble finding one that matched my Volts. Found a lot that matched the amps i was using but not the volts, unless u know of one insert the link.
Click to expand...
OK, again, a 400 amp breaker is a mistake for the reasons listed above.

However, a 250 amp breaker would work well. The MNEDC250RT, for example, is good to 250 amps and 125 volts, and has a remote trip that the BMS can drive. And if 400-500 amps is really important to you, then get two of them and parallel them. But I'd start with 250 amps - you are very likely overestimating what you will draw.
 
billvon said:
maarkmohamed said:
Yea i was thinking about using a 400-500 amp fuse or circuit breaker but had trouble finding one that matched my Volts. Found a lot that matched the amps i was using but not the volts, unless u know of one insert the link.
Click to expand...
OK, again, a 400 amp breaker is a mistake for the reasons listed above.

However, a 250 amp breaker would work well. The MNEDC250RT, for example, is good to 250 amps and 125 volts, and has a remote trip that the BMS can drive. And if 400-500 amps is really important to you, then get two of them and parallel them. But I'd start with 250 amps - you are very likely overestimating what you will draw.
Click to expand...

Ok so plan is ill bypass the bms output leads and connect my output lead to the 250a circuit breaker and maybe your right, i probably wont draw more than that but if i do ill put two of them in parallel. But dam a bit expensive for a circuit breaker lol.
 
maarkmohamed said:
Ok so plan is ill bypass the bms output leads and connect my output lead to the 250a circuit breaker
Click to expand...
Great. You also have to take the shutdown output and route it to the remote trip of the breaker. That way if a cell goes bad (over/undervoltage) the breaker will trip and disconnect the battery. The breaker solenoid takes 24 volts but will usually work with 12 volts. A small 5V/12V relay, driven by the output of the BMS, can switch the higher current 12 (or 24) volts to the breaker.
But dam a bit expensive for a circuit breaker lol.
Click to expand...
At those currents/voltages things do get expensive. (And don't forget the 4/0 wire - that stuff can cost almost a dollar per INCH.)
 
billvon said:
maarkmohamed said:
Ok so plan is ill bypass the bms output leads and connect my output lead to the 250a circuit breaker
Click to expand...
Great. You also have to take the shutdown output and route it to the remote trip of the breaker. That way if a cell goes bad (over/undervoltage) the breaker will trip and disconnect the battery. The breaker solenoid takes 24 volts but will usually work with 12 volts. A small 5V/12V relay, driven by the output of the BMS, can switch the higher current 12 (or 24) volts to the breaker.
But dam a bit expensive for a circuit breaker lol.
Click to expand...
At those currents/voltages things do get expensive. (And don't forget the 4/0 wire - that stuff can cost almost a dollar per INCH.)
Click to expand...

If im not mistaken the bms will protect me from overcharging, and then the controller has a low voltage cut off which would shut it down when to low. And what exactly do you mean by the shutdown output? You have the c- which is for the negative end of the charge cable, then you have p- for negative end of output and b- which goes to negative end of cell, and then the sens wires.
 
maarkmohamed said:
If im not mistaken the bms will protect me from overcharging, and then the controller has a low voltage cut off which would shut it down when to low.
Click to expand...
Normally it does. You are bypassing that part of the BMS so it won't work. You therefore need another means to shut it down. The remote trip on the 250 amp breaker provides that means to shut it down.
And what exactly do you mean by the shutdown output? You have the c- which is for the negative end of the charge cable, then you have p- for negative end of output and b- which goes to negative end of cell, and then the sens wires.
Click to expand...
Inside the BMS there is a line that goes to the internal FETs that shut off the power. They are usually N channel and are usually on the - terminal. You have to find what's driving those FETs and use it to drive the breaker's remote trip instead. Usually you can just look at the FET's gate pin and see what that signal looks like.
 
maarkmohamed said:
Hey guys as you may or may not know ive been trying to figure out exactly which cells and what size battery back ill be doing for my build and ive concluded that i want to do a 20s 20p battery pack with 3000mah cells. And each cell is capable of 20A discharge continuous and 30A for a short few seconds. That being said i would like to draw from my pack 400+ amps. Been looking for a bms to work with this kind of battery but a bit troubling trying to find one, and it also needs to support regen. Anyone got any ideas? Do you think i should get a regular bms that fits my battery configuration and then bypass the output leads and just put a 400A+ circuit breaker?
Click to expand...

Do you have pack photo ? Im about to build 20S20P also . Wonder what you use to connect cells for that 400amp continous ? Nickel or copper ?
 
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