Relay to disconnect large inverter (Will's latest video)

yes, never heard about such wire before.

JeepHammer said:

I wonder where the idea for a SCRAM came from?

An over/under voltage disconnect/safety switch to kick a SPDT or DPDT will work without the continuous on (Normally Open) to save the batteries.
There is virtually no draw (.03W) until the protection is triggered, then the draw is whatever the relay draws.

I'm working on my first BMS, and I speculated about using it to SCRAM my battery protection relay already in place, but I just don't know enough about BMSs to recommend it for anyone yet... Good to see Will running with some last ditch battery disconnect since big versions of these batteries cost so much and are so easily damaged by low voltage!
You gave me a starting point for my 24V, 4.5kWh batteries headed for a 48 Volt system (notice the coil voltage on the relays below).

Since Will is getting shocked, that relay isn't blowout protected, bad news should the contacts wear much at all, you WILL get welding since the differential is so high, good way to get serious arc problems.

There is a reason I don't use closed high amp relays anymore, and I"ve been using them for nearly 20 years ti do exactly what he's doing,
And I started out with with a NC, continuous draw system, but it didn't take me long to figure it out and go to DPDT, blowout protected relay. I run it NC (normally closed) until something goes horribly wrong...

View attachment 5307

Under/Over voltage switch, 12, 24, 48 volt versions, $20
NO (Normally Open) allows the system to draw .03W until the under/over voltage is triggered, samples the battery line voltage.

View attachment 5308

View attachment 5309

Voltage Monitoring Relay DC 12V/24V/36V/48V Over-Voltage and Under-Voltage Protection Relay 35MM Guide Rail 13-17V 10-14V(DC24V): Amazon.com: Industrial & Scientific

Voltage Monitoring Relay DC 12V/24V/36V/48V Over-Voltage and Under-Voltage Protection Relay 35MM Guide Rail 13-17V 10-14V(DC24V): Amazon.com: Industrial & Scientific

www.amazon.com

I bet I just sent a bunch of people off on google searches...
Differential? Blowout?...
Maybe I misspelled something or used the wrong terminology for someone?

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Got links to the products?

you find such device known as fridge protector. They just cut the line if voltage goes to hig or too low and put a delay (about a minute) when power comes back to normal range.
a 555 IC combined with a relay or triac is very simple to build.

nosys70 said:

yes, never heard about such wire before.

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No offense, but that's what I figued and why I pointed it out.
DO THIS STUFF about 20 years and IKSS (I Know Some Shyte)

FilterGuy said:

Got links to the products?

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According to gnubie we aren't supposed to 'Spoon Feed' or 'Serve Up On A Silver Platter' or whatever it was he wrote when someone was looking for a 65 amp breaker.

BIG RED WARNING, DO NOT, UNDER ANY CIRCUMSTANCES USE ANY OF THIS FOR YOUR SYSTEM.
According to 'Internet Experts' ALL of this will burn your house down, knock down the mailbox, knock up your dog, and none of it will work anyway since it's not sold through a vendor for 'Solar Equipment'.
Warning required by moderators...

But, I'm all about DIY and helping out, so what products are in question?
Some I still have the links for, some I ordered a while back and probably don't.
I have a tendency to delete things once the item comes in.

Fusible Link, scroll down for the size you think you might want...

Under/Over Voltage Monitor, DPDT so you can run a Normally Closed or Normally open.
Make sure you pick the right voltage and use a test light to set your OPEN/CLOSE points before hooking up to the battery line contactor.

Panel Strings,
*IF* you want to use an upper/lower limit on the panel side, the appropriate high/low (Set low to zero or disable) and these for the panel strings. Get yours in your battery voltage, this one is 48 volt coil.

Latching The Relay.
If you run a normally closed protection, activation opens the relays, and you can latch any of the relays open with some 5 amp diodes, but they are everywhere and cheap, you shouldn't have to look for them very far.
Stays open once 'SCRAM' happens until you reset it.

Contactor,
And here is the rub about posting specific links, they are out of stock, but this one is 48 volt coil anyway.
It will give you a place to start a search for your battery voltage.

MICRO VOLTAGE CONTROL,
If you want micro voltage control, and some of us do, try this with a 'Kicker' relay for higher amperage to the big contactor.
Just use it with a kicker relay for about 10 amps to open the SCRAM DPDT relays.

DIN Tray, (I like DIN rail boxes)



Make sure you pick the right size for the circuit board you order, there are a BUNCH of sizes...

Responding to the original post ..... I am retired now, but worked many years doing commercial building controls ..... and installed and thousands of relays / contactors. The only time I ever saw the contacts fuse was when the system was struck by lightning.
If really concerned about the contacts sticking closed .... just put a 2nd relay in series with the first. The odds of 2 relays fusing at the same time is exponentially less likely ... the problem of a single failure is already EXTREMELY unlikely.

FilterGuy said:

Got links to the products?

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Weren't you in on the Fuse/SCRAM conversation?
I posted everything including wiring diagrams there...
Even posted some pictures of component pieces as they trickle in from 'China Mart'.

SCRAM solar panels on overvolt panel overvolt situation. (Set Under Volt To Zero),
Protecting the Batteries with Panel/Charge Controller SCRAM, Over Volt on the battery line is fixed by opening panels, panels and charge controller are taken off line in one stroke.
I'm more concerned with undervolt on the batteries, I REALLY don't want to damage those expensive batteries!
Take out latching Diodes and and the circuit will close when voltage comes back into tolerance.

You could use MOSFETs instead of electromechanical relays, I simply prefer relays.
Since in a well balanced system this should never trip, but it's insurace to keep those expensive batteries alive.

Bob B said:

Responding to the original post ..... I am retired now, but worked many years doing commercial building controls ..... and installed and thousands of relays / contactors. The only time I ever saw the contacts fuse was when the system was struck by lightning.
If really concerned about the contacts sticking closed .... just put a 2nd relay in series with the first. The odds of 2 relays fusing at the same time is exponentially less likely ... the problem of a single failure is already EXTREMELY unlikely.

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With no fuse and no blowout protection, lets hope...

I might have missed it, but I havent seen any mention of a flyback diode yet. You need one on large (50A+) relays/contactors to provide a path for the spike of voltage and current the relay coils generate when the relay de-activates. Otherwise the spike hits your equipment and causes premature wear on components or can cause things to fail.

nosys70 said:

you find such device known as fridge protector. They just cut the line if voltage goes to hig or too low and put a delay (about a minute) when power comes back to normal range.
a 555 IC combined with a relay or triac is very simple to build.

Click to expand...

Why not just get an Over/Under Volt protection relay and set the timer for the delay, again, about $20

Maast said:

I might have missed it, but I havent seen any mention of a flyback diode yet. You need one on large (50A+) relays/contactors to provide a path for the spike of voltage and current the relay coils generate when the relay de-activates. Otherwise the spike hits your equipment and causes premature wear on components or can cause things to fail.

View attachment 5328

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And there it is!
I was waiting from my first post for someone to argue terminology...

JeepHammer said:

I bet I just sent a bunch of people off on google searches...
Differential? Blowout?...
Maybe I misspelled something or used the wrong terminology for someone?

Click to expand...

Maast said:

I might have missed it, but I havent seen any mention of a flyback diode yet. You need one on large (50A+) relays/contactors to provide a path for the spike of voltage and current the relay coils generate when the relay de-activates. Otherwise the spike hits your equipment and causes premature wear on components or can cause things to fail.

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It's normal for snubbers to be used across coils to prevent the kick from killing drive components. In this case it would be protecting the FETs in the BMS. The body diode in the FETs may not be capable of handling the voltage involved and break down. I imagine several people posting here are quite familiar with the use of diodes to prevent this but just hadn't thought to post it.

JeepHammer said:

I'm glad YOU said that, I get in trouble for arguing with the 'Experts', fan boys and salesmen...
I even tried to get some of the guys most active and pretty well knew what they were talking about, mentioned fusing and protection circuits (SCRAM) and got mostly crickets...

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You may find that people you involved in your group private message may well have been going to add some information to it but your snarky comments has resulted in them abandoning that because they no longer want to know about it. Attitude is a miraculous thing.

JeepHammer said:

And there it is!
I was waiting from my first post for someone to argue terminology...

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I can't see anyone arguing the terminology, especially not Maast who merely used a correct term. I guess me calling it a snubber must also be an argument.

gnubie said:

It's normal for snubbers to be used across coils to prevent the kick from killing drive components. In this case it would be protecting the FETs in the BMS. The body diode in the FETs may not be capable of handling the voltage involved and break down. I imagine several people posting here are quite familiar with the use of diodes to prevent this but just hadn't thought to post it.

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Where EXACTLY is the 'FET' in what was posted?

And what EXACTLY does it do when not protecting a 'Fet'?

I wonder why they didn't mention it?
Seems important enough that about all high amp contactors have them installed, Will looked for contunity between coil posts, so clearly this battery protector intended for self jump starting doesn't have one...
Fairly important detail to leave out, particularly for people that are familiar with with it...

gnubie said:

You may find that people you involved in your group private message may well have been going to add some information to it but your snarky comments has resulted in them abandoning that because they no longer want to know about it. Attitude is a miraculous thing.

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That's a report, I'm not going to argue with you yet again.
Condensation yet again and we just went through this, Argumentative, counter productive, particularly when I contributed to the conversation...

God knows why I bother but given that the application is the coil being switched by the BMS and that the BMS uses FETs to control the load I'm suggesting that in this application the diode would be protecting the FETs. I know, what a leap!

Perhaps you should read the wiki article to understand the application and function of the flyback (snubber) diode.

gnubie said:

God knows why I bother but given that the application is the coil being switched by the BMS and that the BMS uses FETs to control the load I'm suggesting that in this application the diode would be protecting the FETs. I know, what a leap!

Perhaps you should read the wiki article to understand the application and function of the flyback (snubber) diode.

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First off, like I pointed out and you refuse to acknowledge, Will checked for continuity between posts. No diode.
So, No diode, no 'Fly Back' or 'Snubber' position.

*IF* there is no diode, that non-existent diode can't function as a blow out diode either.

Second, Diodes are a device/component, they do a LOT of functions in different positions.
I know you struggled with diodes in bypass position, and the blocking positions,, you wouldn't comment on Isolation position for diodes so i assumed you understood that...

Is that what you are upset about? The function of the position of a diode?

ghostwriter66 said:

Hi. The Relay does not affect charging at all. All it is doing is allowing literally a high amperage direct circuit from the battery to the inverter bypassing the BMS.

Going to over simplify this but we normally run 600aH 12V banks consisting of (3) 200aH batteries ... The 200A BMS we use runs us about $70. Not the best one in the world but does 100% of what we need. We put one on each battery bank.

Then we use a 12V 500A RELAY between the last battery and the inverter. Our power draw is no more than 400A at a time with no surge. Its cheaper for us to do it that way - with literally the same results - then buying 600A BMS's for each of the battery banks.

Our batteries are rated at 2C discharge.
We have buss bars that are rated at 600A
We use 4/0 from the last battery to the relay to the inverter. (slight overkill)
We fuse it

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Clear and concise explanation with no razzle dazzle, thank you.

You know as I read all of these many wonderful articles that you all contribute to Will's DIY, the technical depth is impressive and even sometimes so mind boggling that I sometimes flirt with the idea of just giving in and building the $15,000, (that's a huge number for me at this point in my life), power line in from the main road to my tajmahcabin, then paying too much for grid power for the rest of my days. Then I say, "nah".

offgriddle said:

You know as I read all of these many wonderful articles that you all contribute to Will's DIY, the technical depth is impressive and even sometimes so mind boggling that I sometimes flirt with the idea of just giving in and building the $15,000, (that's a huge number for me at this point in my life), power line in from the main road to my tajmahcabin, then paying too much for grid power for the rest of my days. Then I say, "nah".

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That's the "I'm Overwhelmed" and Overloaded feeling with too much info a hand, which get's folks exasperated and stressed. Sometimes too much info is just detrimental if it's too fast and can't be digested & understood.