500amp overkill bms

[rodrick]

Looking to build a contactor type bms using a overkill bms they have on clearance due to lugs being to small and a tyco 500amp contactor that battery hookup has

the whole setup is about $120 for a Bluetooth 500amp bms if it works well

my question is does anyone know of any issues that could cause a problem using the c- to just control the contactor coil

 

[SeaGal]

Do Overkill sell a 500A BMS ?

Or are you looking to make a 500A BMS by some odd wiring? If so, how would you stop the BMS's FETs from blowing?

 

[rodrick]

Do Overkill sell a 500A BMS ?

Or are you looking to make a 500A BMS by some odd wiring? If so, how would you stop the BMS's FETs from blowing?

I’m planning on using there bms to control the tyco contactor which is rated for 500 amp but the load on the bms is only a couple of watts controlling the coil on the contactor

 

[SeaGal]

I see... Then posting a schematic might help others more familiar with attempting that give their input.

 

[Lt.Dan]

I'm more curious what you are trying to power at 500a? Could stepping up in voltage be an option?

500a is no small amount of power...

 

[sunshine_eggo]

DIY starter battery?

 

[SeaGal]

DIY starter battery?

High performance golf buggy to be used in a hilly area?

 

[rodrick]

The reason I went with the 500 amp is because they were cheap I'll probably never pull more than a hundred to 150 off of one but I thought it was just a cheap way to make a contactor type BMS

 

[hwy17]

Can you be more specific about the BMS, with a link or something? Are you building a 12/24v battery or a 48v battery with 12/24v controls?

One thing about the battery hookup contactors is they are polar, meaning they are designed to break current in one direction. If you use them for bidirectional breaking of charge and discharge then they can only do a couple highly loaded breaks in one of the directions.

 

[rodrick]

Can you be more specific about the BMS, with a link or something? Are you building a 12/24v battery or a 48v battery with 12/24v controls?

One thing about the battery hookup contactors is they are polar, meaning they are designed to break current in one direction. If you use them for bidirectional breaking of charge and discharge then they can only do a couple highly loaded breaks in one of the directions.

Looking to use them on a 24 volt battery system the BMS is an Overkill 8s they have on clearance because it had small lugs and so they derated them to 80 amp so I just figured I'd use them as a control for the contactor

 

[hwy17]

Do you already know the output does the action you want it to and it's a question of power?

I'm going to use these relays to power the contactors for my build. But I can't say for sure that they work well yet, still building.

https://www.digikey.com/en/products/detail/cit-relay-and-switch/J115F31A24VDCS-9/12503413

That's a 24v coil, I don't know exactly what kind of signal you're dealing with from your BMS. I'm using 12v controls and a 12v coil relay and contactor.

 

[grizzzman]

Can you do it? Yes....But.
There will be a lot of features that will not work.
Bidirectional control will be gone.
safety features will not work ( If that matters to you)
All you will have will be cell voltage control.
It will not know how full or empty it is.

 

[rodrick]

Do you already know the output does the action you want it to and it's a question of power?

I'm going to use these relays to power the contactors for my build. But I can't say for sure that they work well yet, still building.

https://www.digikey.com/en/products/detail/cit-relay-and-switch/J115F31A24VDCS-9/12503413

That's a 24v coil, I don't know exactly what kind of signal you're dealing with from your BMS. I'm using 12v controls and a 12v coil relay and contactor.

I'm going to use the p- to the coil which will be 24 volt battery voltage that will operate the contactor which in turn closes the negative circuit and at that point completes the circuit from battery negative to contactor to negative bus bar all of the load is through the contactor and the BMS fets will only have the coil load so all functions of the BMS except for state of charge should be functional

 

[grizzzman]

I'm going to use the p- to the coil which will be 24 volt battery voltage that will operate the contactor which in turn closes the negative circuit and at that point completes the circuit from battery negative to contactor to negative bus bar all of the load is through the contactor and the BMS fets will only have the coil load so all functions of the BMS except for state of charge should be functional

So........what happens when you hit a low voltage disconnect during charging? The BMS shuts down the relay and you can no longer put a charge back into the battery?

 

[hwy17]

I'm going to use the p- to the coil which will be 24 volt battery voltage that will operate the contactor which in turn closes the negative circuit and at that point completes the circuit from battery negative to contactor to negative bus bar all of the load is through the contactor and the BMS fets will only have the coil load so all functions of the BMS except for state of charge should be functional

Oh I get it now. You certainly don't need a relay then lol.

I wonder if that will definitely release the contactor though, they only take milliamps to hold and afaik I thought mosfets had some way to leak a little voltage out even when they're open so that devices can still detect the battery. That leakage might hold the contactor. Or correct me if I'm still not getting it. I've never built a pack with a fet BMS.

 

[rodrick]

Oh I get it now. You certainly don't need a relay then lol.

I wonder if that will definitely release the contactor though, they only take milliamps to hold and afaik I thought mosfets had some way to leak a little voltage out even when they're open so that devices can still detect the battery. That leakage might hold the contactor. Or correct me if I'm still not getting it. I've never built a pack with a fet BMS.

I’m hoping it will on a video I watched it took .5 amps to make it chatter but not lock up but that was at 9 volts so at 27 volts I’m thinking .2 amps minimum to even make it chatter I’ll know more when I get the parts here and start playing hopefully this won’t get move to the up in smoke section

 

[rodrick]

So........what happens when you hit a low voltage disconnect during charging? The BMS shuts down the relay and you can no longer put a charge back into the battery?

Good point I’m thinking a over ride switch to close the contactor something like a push button momentary switch for safety reasons

 

[Rocketman]

I would have your charging go through the bms. That way you can always just plug it in and charge. The load (motor) goes through the contactor. If low voltage happens the bms shuts off the contactor and you stop.

I would consider a shunt based battery monitor- I like Victron BMV712 - but there are others (that way you don’t run out of power).

Good Luck

 

[rodrick]

I would have your charging go through the bms. That way you can always just plug it in and charge. The load (motor) goes through the contactor. If low voltage happens the bms shuts off the contactor and you stop.

I would consider a shunt based battery monitor- I like Victron BMV712 - but there are others (that way you don’t run out of power).

Good Luck

The problem with that is the charge voltage would keep the contactor energized rendering the bms protection features useless

I run victron 500 amp smart shunts on all my systems I’m a fan also

 

[Rocketman]

The problem with that is the charge voltage would keep the contactor energized rendering the bms protection features useless

I agree that could happen, however this is for a Golf Cart, so you will need a rule that you cannot charge the golf cart while you are driving it (or the cart is turned on).

It will be easy to leave the long cord that attaches to the solar panel at home. ?