Normally Open (NO) vs Normally Closed (NC)

[Mark]

Hi All

Just wanting to get an idea of your views on the NO vs NC to control an appliance (old freezer) via relay connected to the BMV 700/2.

I have the relay (AC: 220V 10A; DC: 12V) currently wired as NO to the BMV (Default Relay / NOT Inverted) and so when SOC is above X the relay is not energised (STAYS CLOSED) and when SOC is below X it is energised and then OPENS.

What are your thoughts:

• OPEN by default (NO), or
• CLOSED by default (NC) 

[Chris Hobson]

I would have it so that under normal operation the contactor/relay is not energised. When the exception occurs then energise the relay/contactor. So in my geyser case when battery voltage is over 53.5V  contactor closes and geyser is on. Geyser is off more than it is on therefore contactor energised when geyser is on.

[Mark]

53 minutes ago, Chris Hobson said:

I would have it so that under normal operation the contactor/relay is not energised. When the exception occurs then energise the relay/contactor. So in my geyser case when battery voltage is over 53.5V  contactor closes and geyser is on. Geyser is off more than it is on therefore contactor energised when geyser is on.

Are you using the Axpert relay or BMV . I am using the BMV to drive a 12V circuit which switches a seperate 10A 220V relay.  Scared of using the BMV direct given the 60V limit

[___]

I think the choice of whether you  want to use NO or NC depends on what condition you want it to fail in. If the system fails, do you want the freezer to run (and save whatever is in there, which could be important), or is it okay if the freezer stops running?

Reason for this line of thinking: Every two years I have to replace the IR beam at my gate because something in the filter fails and suddenly sunlight falling directly onto the receiver causes the gate to remain open, and this weekend was that weekend again. I had to AGAIN replace the IR receiver (the sender is 5 years old and just keeps on going). So this thing works on the basis that a closed circuit means all is clear and the gate may move, while an open circuit means there is an obstruction. Having had 12k worth of damage once when the gate closed on my vehicle, it is important to me that a failure should rather disable the gate (fail safe). So the NC relay contact is used and an obstruction opens the circuit. Any failure in the wiring therefore makes it fail safely.

The new receiver is now inside an enclosure with a hole drilled in the lid to allow the IR-beam in, so that the sun cannot shine on it directly. Yes, off-topic, but that's what drives my current thinking :-)

[SilverNodashi]

18 minutes ago, plonkster said:

I think the choice of whether you  want to use NO or NC depends on what condition you want it to fail in. If the system fails, do you want the freezer to run (and save whatever is in there, which could be important), or is it okay if the freezer stops running?

Reason for this line of thinking: Every two years I have to replace the IR beam at my gate because something in the filter fails and suddenly sunlight falling directly onto the receiver causes the gate to remain open, and this weekend was that weekend again. I had to AGAIN replace the IR receiver (the sender is 5 years old and just keeps on going). So this thing works on the basis that a closed circuit means all is clear and the gate may move, while an open circuit means there is an obstruction. Having had 12k worth of damage once when the gate closed on my vehicle, it is important to me that a failure should rather disable the gate (fail safe). So the NC relay contact is used and an obstruction opens the circuit. Any failure in the wiring therefore makes it fail safely.

The new receiver is now inside an enclosure with a hole drilled in the lid to allow the IR-beam in, so that the sun cannot shine on it directly. Yes, off-topic, but that's what drives my current thinking :-)

Agreed. Any relay should be wired up in such a way that under a failed condition you'll suffer the least losses. On a compressor, if the relay had to stay close due to a PLC failure, it would mean a blown tank! But if the relay contacts opened up when the PLC / MCU failed, a pressure release safety valve could automatically be triggered. 

 

wire it up so that if power fails (low battery / no sun?) the least amount of damage could occur. I would rather take a cold shower, than damage my battery bank if need. Or shower tomorrow. 

[Mark]

That was my thinking.  I would rather have the relay on if something goes wrong so that freezer doesn't go off.  The SOC is then monitored by software (SolWeb) to switch to Grid if needed. And my Low Voltage cutoff is also a third damage limitation option. 

[___]

2 hours ago, Mark said:

That was my thinking.

Great minds think alike! Fools never differ :-)

[Chris Hobson]

14 hours ago, Mark said:

Are you using the Axpert relay or BMV . I am using the BMV to drive a 12V circuit which switches a seperate 10A 220V relay.  Scared of using the BMV direct given the 60V limit

One of my posts has gone missing. Using the BMV relay directly. We had a raging debate after which we conceded that TTT was correct the BMV can switch  220V using the relay. If my BMV ever fails I'll touch TTT for a new one . 

[Mark]

Ha... TTT - I'm nervous... when the chaps put this in the manual...!

Especially a high amps appliance = geyser...

[___]

I think the consensus was that the 60V rating is a DC rating, so it can handle an AC voltage that is higher BUT.... you are obviously still limited to 1 ampere. So you'd switch a 230V contactor with that and let that switch the geyser.

[Guest]

That BMV it was done on is now going wot, 7-8 years(?), and still switching my 220v relays at least twice a day, sometimes more.

As I said at the time, as I was ignoring that heated debate, mine was done by a electrical engineer who was familiar with Victron devices, as I wanted something that at the time did not exist. I am pretty sure I am one of the 1st, if not the 1st person in the world, (yes I can brag  ) to use a BMV's relay to switch between power sources based on a BMV's SOC.

FWIW, at the time, Victron did respond, confirmed it was fine.

It is like we discovered recently, Victron tends to under spec their documentation ... that is why they can give a 5 year guarantee we suspect. Protecting their users by leaving a whopping amount of "oeps" leeway. Happy customer and less warranty repairs / replacements.

[Mark]

@TTT But you are switching using a relay not directly the load?

[Czauto]

@TTT But you are switching using a relay not directly the load?

I would assume at 1A the bmv relay was ever intended to switching a load directly?

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[Guest]

30 minutes ago, Mark said:

@TTT But you are switching using a relay not directly the load?

Correct.

The BMV's relay are triggering these relays.

[Guest]

To have this functionality to switch between a off-grid inverter and Eskom - without using any software.

[Guest]

And it is TTT proof ... smokeless in other words - for not only are there tripps on both sides, I can connect stuff with ease.

[Mark]

Do you have a wiring diagram for your fancy pants switch [emoji12]

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[Guest]

50 minutes ago, Mark said:

Do you have a wiring diagram for your fancy pants switch

Nope, I don't. Just pictures.

No, I am not disassembling it either. It works and looks very impressive and neat as is. 

[incagarcilaso]

On 30/4/2017 at 8:52 PM, Mark said:

Are you using the Axpert relay or BMV . I am using the BMV to drive a 12V circuit which switches a seperate 10A 220V relay.  Scared of using the BMV direct given the 60V limit

Mark, I see you have some experience with wiring the BMV relay to activate appliances on a "standard" 220V circuit. Can you help with this post of mine? 

 

[incagarcilaso]

On 1/5/2017 at 1:05 PM, The Terrible Triplett said:

That BMV it was done on is now going wot, 7-8 years(?), and still switching my 220v relays at least twice a day, sometimes more.

As I said at the time, as I was ignoring that heated debate, mine was done by a electrical engineer who was familiar with Victron devices, as I wanted something that at the time did not exist. I am pretty sure I am one of the 1st, if not the 1st person in the world, (yes I can brag  ) to use a BMV's relay to switch between power sources based on a BMV's SOC.

FWIW, at the time, Victron did respond, confirmed it was fine.

It is like we discovered recently, Victron tends to under spec their documentation ... that is why they can give a 5 year guarantee we suspect. Protecting their users by leaving a whopping amount of "oeps" leeway. Happy customer and less warranty repairs / replacements.

Hi TTT. I notice you looked into this at the time. Can you help me with this post of mine? Is it possible for me to use a BMV 702 relay to trigger a signal on a 230VAC appliance or do I need an intermediate relay? Please see this post and the documentation I added. 

 

[Guest]

47 minutes ago, incagarcilaso said:

Is it possible for me to use a BMV 702 relay to trigger a signal on a 230VAC appliance or do I need an intermediate relay?

Jip, been reading it all.

Am not a clever person when it comes to making things work and explain - am a ideas man who talks to clever people to make it for me.

Am good at blowing things up though.

So to answer your question, Yes, it is possible but I would not connect anything direct to a BMV's relay no. 

BMV's are very expensive compared to fuses and relays. To this effect my BMV relay is the trigger for separate 220v AC relays that are used to switch the current from, in my case, solar to Eskom and back.

Here is the pic of what the BMV is triggering. Left is solar power, right is Eskom. Design is such that it is impossible for even me to get Eskom and solar mixed - up ever. Trust me, I tried. :-) 

 

[Guest]

Here is the BMV mounted.

[incagarcilaso]

1 hour ago, The Terrible Triplett said:

Quote

 

Am good at blowing things up though.

So to answer your question, Yes, it is possible but I would not connect anything direct to a BMV's relay no.

 

Thanks TTT, that's what I thought might be safer. I'm not good at that either (not an electrician). I'll see if I can work out exactly what kind of secondary relay I need between the BMV and the appliance in order for this to work and also work out how it has to be wired. What I don't fully get is how the current isn't passed from one circuit to another (even with an intermidiary relay) when the relay is energised, because in that state of energised the circuit is made between the BMV and the appliance.

The appliance's relay input is rated 230VAC and 2A max, so I don't get how an intermediary relay translated the signal from the BMV rated at 60VDC and 1A max to that of the appliance.

 

 

[Guest]

@incagarcilaso I believe those Finder relays I use, model 62.33.8.230.0040 - 16A 250v relay for 230v AC is international. (?)

As far as I guess the Finder relay is switching the current, the BMV is just triggering the Finder relay.