Breaker vs Battery disconnect switch

[rogerdw]

I don't know if it's wise to disconnect using a relay/contactor while under load.

Yes I agree. In my case I have a standard large 300A DC cct breaker, along with this solenoid in series ... and under normal circumstances I turn off the AC output from the inverter ... then switch off the DC supply via the kilovac.

If you must do this under load, you should use a proper DC breaker with an arc chute, that will pull the arc away from the contacts while the power is being broken.

These solenoids are used widely in the EV industry and switch huge DC currents constantly.

They're rated for 500A+ between 12-900V DC ... and 2,000A interrupt at 320V DC. The contacts are hermetically sealed, so far less likely to oxidise and arc etc. I'm certainly more comfortable in flicking this off in an emergency if I had to, than the DC cct breaker.

 

[BarracudaBob]

Yes I agree. In my case I have a standard large 300A DC cct breaker, along with this solenoid in series ... and under normal circumstances I turn off the AC output from the inverter ... then switch off the DC supply via the kilovac.




These solenoids are used widely in the EV industry and switch huge DC currents constantly.

They're rated for 500A+ between 12-900V DC ... and 2,000A interrupt at 320V DC. The contacts are hermetically sealed, so far less likely to oxidise and arc etc. I'm certainly more comfortable in flicking this off in an emergency if I had to, than the DC cct breaker.

Little losses in there but hard to beat the K.I.S.S. Logic for a part that is designed for just this task. 0.03A@48V = 38W per day.. Ok, I'll do it.

 

[meetyg]

Yes I agree. In my case I have a standard large 300A DC cct breaker, along with this solenoid in series ... and under normal circumstances I turn off the AC output from the inverter ... then switch off the DC supply via the kilovac.




These solenoids are used widely in the EV industry and switch huge DC currents constantly.

They're rated for 500A+ between 12-900V DC ... and 2,000A interrupt at 320V DC. The contacts are hermetically sealed, so far less likely to oxidise and arc etc. I'm certainly more comfortable in flicking this off in an emergency if I had to, than the DC cct breaker.

AFAIK, the contactors in EVs do not normally switch under high load. They switch on when you power the car, and switch off when your parked and turn off the car. The current during these actions isn't supposed to be significant (especially because it's high voltage).

Of course they need to support the higher continous currents when the EV is being driven. But not so when switching on/off.

 

[robbob2112]

Here is the full spec sheet on the contactor. I have a number of them. Basically you try not to switch them under load. Under a low load (200 amps or less) you can get 12 disconnects. Under high load they have exactly one switch cycle and they need to be replaced.

 

[rogerdw]

Here is the full spec sheet on the contactor. I have a number of them. Basically you try not to switch them under load. Under a low load (200 amps or less) you can get 12 disconnects. Under high load they have exactly one switch cycle and they need to be replaced.

Understood, of course you never want to have to switch them under load if possible.

Having said that ... I'm running 48VDC and not 320 ... so that should buy me a few extra cycles ... and my 300A fuse should blow at some stage before it gets to 2,000 amps.

 

[robbob2112]

My plan is to install them as emergency disconnects and never use them unless current is at zero or there is an emergency. At $15 each they are cheaper than some fuses.

 

[rogerdw]

My plan is to install them as emergency disconnects and never use them unless current is at zero or there is an emergency. At $15 each they are cheaper than some fuses.

Exactly ... same conclusion I had come to.

 

[BarracudaBob]

Exactly why I didn't want to spend to much for one. Still like my solenoid idea on the breaker.

 

[Brucey]

I can't seem to get myself to pay $200 for the motorized battery switch. I am getting close to pulling the trigger on this one

Batteryhookup has them (used, pulled from EV packs) for $15.

TE Connectivity EV200AAANA 500a 0-900vdc Tyco 12/24v

These were recovered from EV battery modules. These are VERY EXPENSIVE online. If you have any project that needs a high current relay this is your chance to save some money. Make a cheap 30a BMS into a 500a BMS. This will work for batteries in the 9-36v range so perfect for Lifepo4 and Lithium...

batteryhookup.com

 

[Skypower]

Batteryhookup has them (used, pulled from EV packs) for $15.

TE Connectivity EV200AAANA 500a 0-900vdc Tyco 12/24v

These were recovered from EV battery modules. These are VERY EXPENSIVE online. If you have any project that needs a high current relay this is your chance to save some money. Make a cheap 30a BMS into a 500a BMS. This will work for batteries in the 9-36v range so perfect for Lifepo4 and Lithium...

batteryhookup.com

I’m actually surprised about how low the hold down current is. Only about 1.5 watts. This is great in terms of battery usage but makes me wonder how strong the return spring is. Too weak and even the slightest of arc could potentially weld the contacts in place without enough force to pull it apart. Suggest that you reduce current as much as possible before switching. If the device to power the coil is a transistor, remember to protect it the transistor from the coil’s “back EMF” .

 

[BarracudaBob]

I ordered the contactor yesterday. Will enjoy a little torture testing

Mint Mobile getting into batteries ?

Mint Block Rack Battery

Mint Block

EV Grade Lithium Batteries: These lithium iron phosphate battery boxes come in a compact and sleek design that provides consistent performance & great power. Unlike regular lead acid batteries, you can mount or stack your 100Ah LiFePO4 battery in any position that works for your setup. Built-in...

mintenergy.us

On Sale at:

https://batteryhookup.com/products/new-mint-energy-51-2v-100ah-5-12kwh-lifepo4-battery

 

[meetyg]

I’m actually surprised about how low the hold down current is. Only about 1.5 watts. This is great in terms of battery usage but makes me wonder how strong the return spring is. Too weak and even the slightest of arc could potentially weld the contacts in place without enough force to pull it apart. Suggest that you reduce current as much as possible before switching. If the device to power the coil is a transistor, remember to protect it the transistor from the coil’s “back EMF” .

This specific model has an "economizer", which draws less power after initial contact is made. I don't think it affects the disconnect strength. Also, they claim it protects from back EMF:


I think it's a great product, got some myself, but used them sporadically.

 

[rogerdw]

Still like my solenoid idea on the breaker.

Yeah, I always think of that too when I turn one off ... so little force needed to make it click off.

 

[BarracudaBob]

Yeah, I always think of that too when I turn one off ... so little force needed to make it click off.

Just an itch I'll have to scratch. I wish I could find some old videos of a really cool antenna disconnector we made. Disconnected multiple coaxes via linear actuator.

 

[rogerdw]

Haha, I'm picturing a metal weight on a piece of string ... with the weight stuck to a tiny electromagnet. Cut the current to the electromagnet and the weight drops ... pulling down the cct breaker.

 

[robbob2112]

Just get the midnite solar breakers that can be remote tripped by a signal.

 

[Hedges]

They're rated for 500A+ between 12-900V DC ... and 2,000A interrupt at 320V DC. The contacts are hermetically sealed, so far less likely to oxidise and arc etc. I'm certainly more comfortable in flicking this off in an emergency if I had to, than the DC cct breaker.

There are DC breakers rated 50,000 AIC. Why would you prefer a relay rated 2000 AIC as emergency disconnect?
I would expect these to just sit and burn under fault currents.

I ordered the contactor yesterday. Will enjoy a little torture testing

How high a DC current, at pack voltage, can you go?

AFAIK, the contactors in EVs do not normally switch under high load. They switch on when you power the car, and switch off when your parked and turn off the car. The current during these actions isn't supposed to be significant (especially because it's high voltage).

Of course they need to support the higher continous currents when the EV is being driven. But not so when switching on/off.

Exactly.

 

[Brucey]

There are DC breakers rated 50,000 AIC. Why would you prefer a relay rated 2000 AIC as emergency disconnect?
I would expect these to just sit and burn under fault currents.



How high a DC current, at pack voltage, can you go?



Exactly.

I think the Tesla packs have replaceable pyro fuses for emergency disconnect purposes.

 

[BarracudaBob]

I think the Tesla packs have replaceable pyro fuses for emergency disconnect purposes.

I didn't know they had it in the vehicles. I figured it was a spring loaded fuse, once it blows it moves out of the way asap. Learned something new.

Pyro Safety Switches

www.autoliv.com

 

[rogerdw]

Just get the midnite solar breakers that can be remote tripped by a signal.

I wasn't aware they made them. With a quick look I can only find them up to 250A ... do they make 300A or higher? Only need up to 60V ... not 150 or 300.

Certainly if I can get one it will kill two birds with one stone.

There are DC breakers rated 50,000 AIC. Why would you prefer a relay rated 2000 AIC as emergency disconnect?
I would expect these to just sit and burn under fault currents.

It was fitted in series with a 300A DC breaker to add a remote switching function and there is already a 300A fuse in line as well.

I know you weren't asking me but my pack is 48V 980aH.