What type of relay turns things OFF when the ignition 12v comes on? [SOLVED]

[uksuntimes]

This was solved thanks to everyone's help. Details and items are in all the posts below for anyone else that might arrive here one day

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ORIGINAL MESSAGE
Hey everyone!

I am struggling to know what to search for and would love a little guidance as I suspect there is a special type of name involved

I can find lots of relays (e.g. voltage sensing relays) that will turn things ON when they are sent a 12v ignition signal, but in my case I want to turn things OFF while the ignition is live, and turn back on when the ignition is gone.

Might there be a different kind of relay or device I can use to do this?

My use case is as follows

1. I have 2 x 170w solar panels, connected in parallel
2. I have a smart alternator
3. Both of these go into the 50A Renogy MPPT smart controller (yes yes, I NOW know about Renogy, but it's what I have).
4. When I have the car running/alternator signal ON, I want to DISCONNECT the solar/PV input. When the car ignition goes off again, I want to RECONNECT the solar/pv input

My reason for this is that I can get a full 50A charge from my alternator while driving but only if the solar is disconnected. At the moment I manually flip the breaker, but I would like to automate this instead so I can get full charging juice while driving.

I will keep searching around, but so far everything I am finding is about connecting when 12v is detected, but not disconnecting.

Thank you all in advance!

 

[uksuntimes]

Much like the Rubber Duck method for coding, I think I've just managed to solve my problem simply by posting here. Maybe

Is what I am looking for called a "Normally Closed Relay" / "Normally Closed Switch" ?

Or might there be a smarter component to use?

 

[Rednecktek]

What you're looking for is a Normally Closed (NC) relay so when the power is shut off the contacts close. Many smaller relay bricks will have a set of pins for Normally Open (NO) and Normally Closed (NC) on them. The larger higher amperage ones are usually NO so you'll have to do some digging and figure out what kind of amperage range you need for that.

Edit: Beat me by 2 seconds! ?

 

[uksuntimes]

@Rednecktek I really appreciate you taking the time to reply, and so quickly as well!

Regardless of if I posted, it means a lot to get confirmation of my assumption. Assumptions are something I really don't want to make when playing with electricity so thank you for building my confidence in my system building skills.

Now to find one that is rated to handled the 17v 340w and cable sizes I have while still taking a 12v signal to know when to open/close.

 

[Rednecktek]

So you need something listed for 25+ amps to be safe. Shouldn't be too hard if you can find NC contactors for DC in the first place.

You'll be looking for a relay with multiple terminals like this one or a more basic version like this guy and your best bet honestly is to head to your local auto parts store, they probably have something that has the right ports and ratings.

 

[mikefitz]

Try this,

Maxi (High Power) Change Over Relay - 12V 60/70A

High power 12V 60/70A maxi changeover relay from Durite. 2x 6.3mm & 3x 9.5mm blade terminals in type B layout. Commonly used in starter circuits.

www.12voltplanet.co.uk

You need 6mm2 cable and yellow crimp terminals for the high current connections,

Female Blade Terminals - 3.0 - 6.0mm² Cable (Yellow)

High quality yellow pre-insulated female blade crimp terminals (3.0-6.0mm² cable). 6.3 & 9.5mm blade widths. Tinned copper conductor & PVC insulation.

www.12voltplanet.co.uk

Mike

 

[uksuntimes]

Thank you for taking the time to reply.

My solar would be putting down more than 12v though (17 I believe) would this still be suitable? As ultimately that charging current would be going through the relay is my understanding.

Or does the 12v just relate to the switching aspect?

 

[DIYrich]

The relay can power (switch) a larger relay that is capable of handling the power.

 

[Rednecktek]

The 12v is the switching power.

 

[uksuntimes]

Wonderful! Thank you - that is something I have remained stuck on for some time. Duly noted!

 

[mikefitz]

12v is the voltage to operate the relay. There should be no issue with switching 16 amps at 18 volts from the panels.

 

[uksuntimes]

So if I see this, it means 'normally open' ?

And as such I would want to find one that is normally closed.

I already have this relay here, but looks to me that it would be a normally open relay.

 

[uksuntimes]

Try this,

Maxi (High Power) Change Over Relay - 12V 60/70A

High power 12V 60/70A maxi changeover relay from Durite. 2x 6.3mm & 3x 9.5mm blade terminals in type B layout. Commonly used in starter circuits.

www.12voltplanet.co.uk

You need 6mm2 cable and yellow crimp terminals for the high current connections,

Female Blade Terminals - 3.0 - 6.0mm² Cable (Yellow)

High quality yellow pre-insulated female blade crimp terminals (3.0-6.0mm² cable). 6.3 & 9.5mm blade widths. Tinned copper conductor & PVC insulation.

www.12voltplanet.co.uk

Mike

So how do we know that this 'change over relay' is 'normally closed' ? Or is this another name for that type of relay?

 

[mikefitz]

The relay I suggested can be used as either normally closed or normally open, see diagram,

https://www.autosparks.co.uk/5-pin-change-over-relay-12v-30a-with-detachable-bracket

With no power to the energisation coil the contact 30 is made to pin 87a, when power is applied pin 30 connects to pin 87.

In your application connect pin 30 to the DCC50 solar input, and pin 87a to the panel input positive.
Your ignition on signal is applied to pin 85 with 86 to 0 volts.

Use one of these in the vehicle fuse box, you are looking for for a 'key on' signal, what vehicle do you have ?

Add-A-Circuit Mini Blade Fuse Holder

Easily create an additional circuit without the need to splice into existing cables. Plugs into an existing fusebox location, turning one fuse slot into two.

www.12voltplanet.co.uk

Mike

 

[Mike 134]

Idec RH2B-U DC12V Relay | eBay

Find many great new & used options and get the best deals for Idec RH2B-U DC12V Relay at the best online prices at eBay! Free shipping for many products!

www.ebay.com

 

[uksuntimes]

Thank you so much for all the answers on this.

I had to leave the project for a while due to some personal issues, but am now picking this up again and excited to implement the solution.

I wondered, is it possible/advisable to get a pre wired relay holder to use in my project? At the moment, I am not sure how best to attach this to my wiring board without it all being a bit of a mess.

To that end, is there a size/style/name I should look for to find a compatible relay holder/socket for https://www.12voltplanet.co.uk/maxi-high-power-change-over-relay-12v-6070a.html ?

Keeping in mind the voltage/amperage with regard to any pre wired aspects

 

[uksuntimes]

Ah, I may have just answered my own question in their product description
"Note: This relay has 3 x 9.5mm terminals and will not fit in a relay socket or box"

Any advice on good ways to add this relay into a project are welcome.

 

[pollenface]

1. When I have the car running/alternator signal ON, I want to DISCONNECT the solar/PV input. When the car ignition goes off again, I want to RECONNECT the solar/pv input

Sounds like you just need a 5-pin relay.

The 5th pin is normally closed, when voltage is supplied it "OPENS"

easy peasy

 

[uksuntimes]

Thank you all for your help and input!

Finally got this installed today.

Got it wrong on the first try, but once I switched the pin, it works exactly as intended!

Now when I drive the car, the solar gets disconnected and I can get the full 50amp charging from the alternator instead of it being restricted to 25 because the solar is attached.

Wonderful!

Need to cable everything in nicely now that I have proven it works, but I am delighted with the result and I couldn't have done it without all your help.