For switching between two poles with a 40A do I use Relay or contactor?

[ferbo]

Hello,

I have a 12s battery pack (48v) that I need to connect to my load of max continous current of 40 A. I want to be able to connect and disconnect them with a command from a CAN transceiver. To explain more, I want my battery to either be connected to the load or the charger portals. Should I use a relay on a PCB or a different solution.

Thank you!

 

[barry]

It doesn't matter if your relay is sitting on a PCB or mounted to a pole. What matters is the rating of the relay. Can it break 40 Amps? And, FYI, a contactor IS a relay. It's generally just a term applied to relays that handle higher power.

 

[ZASto]

And, of course, it should be rated for DC load, with spark/flame extinguisher.

 

[KlausST]

Hi,

48V DC, 40A .... why not using a Mosfet?

Klaus

 

[c_mitra]

I think #4 is the best solution because an electronic switch MOSFET is perhaps safer and more reliable. Not to talk about the cost.

Switching DC at 40A is not going to be cheap with an electromechnical relay. If you love the relay, I suggest a SSR.

 

[barry]

The problem with a mosfet is that they don’t come in a SPDT configuration, which is what the OP wants. You have to use two mosfets and some logic, or two separate control lines. But a SPDT SSR sounds like a good solution.

 

[KlausST]

Hi,

True.
Maybe the OP can tell where the "charger EXCLUSIVE OR load" requirement comes from.
Why disconnect the load during charging? Why disconnect the charger during load operation?

Klaus

 

[ferbo]

It doesn't matter if your relay is sitting on a PCB or mounted to a pole. What matters is the rating of the relay. Can it break 40 Amps? And, FYI, a contactor IS a relay. It's generally just a term applied to relays that handle higher power.

Thank you! my problem is that I'm not sure if it's wise to direct such a power on a PCB and if it's better to use mosfets instead of a relay. how I can find the best solution and component.

 

[ferbo]

Hi,

True.
Maybe the OP can tell where the "charger EXCLUSIVE OR load" requirement comes from.
Why disconnect the load during charging? Why disconnect the charger during load operation?

Klaus

Hi

My load is a bunch of motor drivers that are connected to motors and a another charger that is connected to computers and a backup battery (LTC4020) and I thought maybe it's not wise for them to be connected while the battery is being charged. am I wrong?

 

[d123]

Hi,

Maybe these will help to decide about the power-handling capacity of your PCB:

PCB Trace Width vs Current Table

PCB Trace Width vs. Current Table

Calculate the maximum current of a trace

PCB Trace Width Calculator

The best solution is a relative concept. Maybe one viewpoint could be considering the safest solution, and then the smallest one that dissipates the least power besides the power drawn by the load. Junction temperature rise in the selected MOSFET(s) is an indicator of how appropriate the device is for the task. An SSR is a nice solution - isolating the (small) control signal from the (large) power path.

Best regards.

 

[KlausST]

HI,

My load is a bunch of motor drivers that are connected to motors and a another charger that is connected to computers and a backup battery (LTC4020) and I thought maybe it's not wise for them to be connected while the battery is being charged. am I wrong?

The very most devices do charge and operate at the same time.
Just imagine if there was a laptop only either charging or operating. Impossible to work with...

Klaus

 

[ferbo]

HI,

The very most devices do charge and operate at the same time.
Just imagine if there was a laptop only either charging or operating. Impossible to work with...

Klaus

thank you I just thought there is always a circuit in between like ltc4020 to work and charge at the same time.