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jetzi

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7 hours ago, Tony1 said:

 

Hi Nick, just an quick update- the rewiring in series as described hasnt resolved the issue, so what I've done is unplug the wires from the second BMV (except for the live wire into NO port), so its just acting as a monitor only. 

My thinking is that before trying to wire up a second BMV, I need to resolve the problem that has recently arisen with the first BMV (the one I set up as a high SoC disconnect). 

 

The MPPTs are not responding to this BMV in the way they did a few days ago, before I started messing about with a second one. 

Before my sabotage, all the MPPTs and B2Bs would switch off and on correctly as per the relay setting changes on the BMV. 

Since my experiments, only one of the MPPTs can successfully be controlled- if I even plug in the cable to the second MPPT, both switch off. Both units behave this way- I reversed their roles and it doesnt matter which unit has the control cable plugged in. If either one of them is plugged in, it works as expected. If the other cable is plugged in, they both switch off. 

 

Another thing I noticed is that if the B2Bs are running, both of the MPPTs will behave correctly, as they used to do (ie both respond to the BMV in unison).

But when the B2Bs switch fully off, the MPPTs go back to the incorrect behaviour. 

 

So before even considering wiring in the second BMV again, I wonder if you can work out why- with a single BMV connected- I can only control one of the MPPTs at a time, even though my wiring setup has been returned to its original state of a few days ago? 

 

The wiring setup is as described above- I tried removing the negative wire from the bus bar that goes into the NC port, but if I do that, the chargers no longer respond to the BMV at all. 

 

I'm now thinking that your view of a few weeks ago was very valid- it might not be wise to rely on the control cables to switch off chargers in the event of a high voltage.

I think what I need, as Richard suggested, is a Victron battery protect unit, which will provide a physical disconnection, and which I can control remotely using one of my BMV712s.  

 


You need to check the voltage on the control wire connected to the B2B and MPPTs when you are expecting them to be on, and off. My suspicion is that you might have blown the fuse that feeds the battery positive supply to the first BMV relay. Have you checked the fuse?

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19 minutes ago, nicknorman said:


You need to check the voltage on the control wire connected to the B2B and MPPTs when you are expecting them to be on, and off. My suspicion is that you might have blown the fuse that feeds the battery positive supply to the first BMV relay. Have you checked the fuse?

 

Thanks Nick, just checked the fuse leading into the NO port and the fuse on the wire into the BMV, and both look visually perfect, but I replaced the one going into the BMV just in case. 

 

Unfortunately the MPPT is so clever that it switches itself off at night, so I cant test switching the MPPTs on and off after I replaced the fuse, and I'm out travelling all day tomorrow.

 

To check the voltage on the B2B cable I placed the black probe onto one of the shunts, and the red probe I inserted into the socket of one of the B2Bs, and it is reading 13, which I assume is correct because the B2Bs are working correctly. 

Also, the B2Bs are located further down the cable than the MPPTs (travelling away from the BMV, so to speak)- so I dont think there is a problem with the voltage on that cable as such..

 

The MPPT cables have four pins on the socket that inserts into the MPPT unit, and both cables gave the same readings, in that one pin read zero, two read about 11.95v, and the fourth pin read a bit over 12v, maybe 12.35 I think.

So the voltage in the MPPT cables is a bit less than the 13.25v at the B2B, would that be enough to cause an issue? Certainly it didnt up till I messed about trying out  the other BMV.

 

 

 

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35 minutes ago, Tony1 said:

 

Thanks Nick, just checked the fuse leading into the NO port and the fuse on the wire into the BMV, and both look visually perfect, but I replaced the one going into the BMV just in case. 

 

Unfortunately the MPPT is so clever that it switches itself off at night, so I cant test switching the MPPTs on and off after I replaced the fuse, and I'm out travelling all day tomorrow.

 

To check the voltage on the B2B cable I placed the black probe onto one of the shunts, and the red probe I inserted into the socket of one of the B2Bs, and it is reading 13, which I assume is correct because the B2Bs are working correctly. 

Also, the B2Bs are located further down the cable than the MPPTs (travelling away from the BMV, so to speak)- so I dont think there is a problem with the voltage on that cable as such..

 

The MPPT cables have four pins on the socket that inserts into the MPPT unit, and both cables gave the same readings, in that one pin read zero, two read about 11.95v, and the fourth pin read a bit over 12v, maybe 12.35 I think.

So the voltage in the MPPT cables is a bit less than the 13.25v at the B2B, would that be enough to cause an issue? Certainly it didnt up till I messed about trying out  the other BMV.

 

I wouldn’t be the fuse feeding the BMV, otherwise the BMV display would be off. I meant the fuse feeding the relay NO contact. You need to check this fuse with a meter.

 

But anyway, the acid test will be to check the voltage on the control wires to the various devices, either 0v or battery positive voltage according to whether on or off. If the voltage 

 

The slightly different voltages on the MPPT plug is not relevant. That socket/plug is nominally designed for the VE.direct digital communications (power, ground, data in, data out), and is “repurposed” for  the remote control function by means of their special cable.

 

I am made nervous by your mention of a live wire on the second relay NO a contact. The original relay has a positive wire on one contact and a negative on the other. If you add either a positive or negative wire to the second BMV you can end up with a short circuit. Hence why I suspect the fuse feeding positive to the first BMV relay.

 

The MPPT’s have weak pull down to negative, and it seems as though the B2Bs when operating have weak pull-up to 12v. So I think you are seeing some battle between these weak pull-ups and pull-downs. When there is only 1 MPPT, the B2B pull-ups win, when there are 2, the MPPT pull downs win. And when the B2Bs are off their weak pull-up is lost so one or both MPPTs pull the wire down to 0v. All arising because the aforementioned fuse is blown. Maybe. Well that’s a theory anyway!

 

You said there was 12v or so on the control line, but was this with the B2Bs off, or when they were operating? It would be good to know the voltage on the control wire with the B2Bs off and the MPPTs in daylight. I seems unlikely that it will be 12v or so and if not, it points to the fuse feeding the first BMV NO contact being blown.

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46 minutes ago, nicknorman said:

I wouldn’t be the fuse feeding the BMV, otherwise the BMV display would be off. I meant the fuse feeding the relay NO contact. You need to check this fuse with a meter.

 

But anyway, the acid test will be to check the voltage on the control wires to the various devices, either 0v or battery positive voltage according to whether on or off. If the voltage 

 

The slightly different voltages on the MPPT plug is not relevant. That socket/plug is nominally designed for the VE.direct digital communications (power, ground, data in, data out), and is “repurposed” for  the remote control function by means of their special cable.

 

I am made nervous by your mention of a live wire on the second relay NO a contact. The original relay has a positive wire on one contact and a negative on the other. If you add either a positive or negative wire to the second BMV you can end up with a short circuit. Hence why I suspect the fuse feeding positive to the first BMV relay.

 

The MPPT’s have weak pull down to negative, and it seems as though the B2Bs when operating have weak pull-up to 12v. So I think you are seeing some battle between these weak pull-ups and pull-downs. When there is only 1 MPPT, the B2B pull-ups win, when there are 2, the MPPT pull downs win. And when the B2Bs are off their weak pull-up is lost so one or both MPPTs pull the wire down to 0v. All arising because the aforementioned fuse is blown. Maybe. Well that’s a theory anyway!

 

You said there was 12v or so on the control line, but was this with the B2Bs off, or when they were operating? It would be good to know the voltage on the control wire with the B2Bs off and the MPPTs in daylight. I seems unlikely that it will be 12v or so and if not, it points to the fuse feeding the first BMV NO contact being blown.

 

 

Cheers Nick- I replaced the fuse leading into the first BMV, and the voltage at the BMV in the NO socket (with the neg on the shunt) is about 13v.

 

Fingers crossed the fuse will sort it out (and the two victron cables are showing a voltage when the relay was set to closed.

Although I didnt check their voltage before replacing the fuse, I could test that scenario by removing the pos wire.

 

I'm off out first thing so I wont get a chance to test it until tomorrow evening- hopefully I'll be back whilst its light enough to keep the panels active. 

 

PS- the B2Bs are showing 13.25v now, when they are fully off, and the BMV relay is closed. 

 

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1 hour ago, nicknorman said:

I wouldn’t be the fuse feeding the BMV, otherwise the BMV display would be off. I meant the fuse feeding the relay NO contact. You need to check this fuse with a meter.

 

But anyway, the acid test will be to check the voltage on the control wires to the various devices, either 0v or battery positive voltage according to whether on or off. If the voltage 

 

The slightly different voltages on the MPPT plug is not relevant. That socket/plug is nominally designed for the VE.direct digital communications (power, ground, data in, data out), and is “repurposed” for  the remote control function by means of their special cable.

 

I am made nervous by your mention of a live wire on the second relay NO a contact. The original relay has a positive wire on one contact and a negative on the other. If you add either a positive or negative wire to the second BMV you can end up with a short circuit. Hence why I suspect the fuse feeding positive to the first BMV relay.

 

The MPPT’s have weak pull down to negative, and it seems as though the B2Bs when operating have weak pull-up to 12v. So I think you are seeing some battle between these weak pull-ups and pull-downs. When there is only 1 MPPT, the B2B pull-ups win, when there are 2, the MPPT pull downs win. And when the B2Bs are off their weak pull-up is lost so one or both MPPTs pull the wire down to 0v. All arising because the aforementioned fuse is blown. Maybe. Well that’s a theory anyway!

 

You said there was 12v or so on the control line, but was this with the B2Bs off, or when they were operating? It would be good to know the voltage on the control wire with the B2Bs off and the MPPTs in daylight. I seems unlikely that it will be 12v or so and if not, it points to the fuse feeding the first BMV NO contact being blown.

 

Apologies for hassling, just a quick follow up- I'm coming round the the idea that for the emergency high voltage disconnect, (the event that should never actually happen if all other elements are set up properly), a BMS-style charger switch off is not reliable enough. Its ok for a day-to-day SoC limiter, as a high SoC wont kill the batteries. 

But for the high voltage protection I feel more reliability is a good idea.

The BEP switches are a bit expensive, and I dont know for sure that I can use a BMV to switch off a victron battery protect unit at high voltage, by plugging into the remote control switch socket. 

 

So I was wondering- would one of these simple 200 amp relays do the job? 

https://www.amazon.co.uk/gp/product/B07FKXFWSQ/ref=ox_sc_act_title_2?smid=A1MEUEEKSUPDHQ&psc=1

 

I looks like it just needs a 12v signal to control it, and I can set the BMV to send either +12v or zero, right? 

So why not use a £15 unit like this, instead of paying £150 for a BEP, or $100 for a victron unit that I only need the remote option for anyway?

I remember you saying the tyco relays are good because they are bistable and dont drain current when not in use, but in my case I have 1.4kw of solar, so there will always be enough of a charge in the lithiums to operate the relay, even if its just a trickle. 

 

 

 

 

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23 hours ago, Tony1 said:

 

Apologies for hassling, just a quick follow up- I'm coming round the the idea that for the emergency high voltage disconnect, (the event that should never actually happen if all other elements are set up properly), a BMS-style charger switch off is not reliable enough. Its ok for a day-to-day SoC limiter, as a high SoC wont kill the batteries. 

But for the high voltage protection I feel more reliability is a good idea.

The BEP switches are a bit expensive, and I dont know for sure that I can use a BMV to switch off a victron battery protect unit at high voltage, by plugging into the remote control switch socket. 

 

So I was wondering- would one of these simple 200 amp relays do the job? 

https://www.amazon.co.uk/gp/product/B07FKXFWSQ/ref=ox_sc_act_title_2?smid=A1MEUEEKSUPDHQ&psc=1

 

I looks like it just needs a 12v signal to control it, and I can set the BMV to send either +12v or zero, right? 

So why not use a £15 unit like this, instead of paying £150 for a BEP, or $100 for a victron unit that I only need the remote option for anyway?

I remember you saying the tyco relays are good because they are bistable and dont drain current when not in use, but in my case I have 1.4kw of solar, so there will always be enough of a charge in the lithiums to operate the relay, even if its just a trickle. 

 

I guess you could do. A permanent 0.25 amp drain goes against my principles but as you say, you have plenty of solar. Ditto relying on something to be powered in order for the boat’s services to operate (ie the failure mode is that the lights go out). I just wonder how it will cope with being on 24/7 dissipating 4 watts plus some heat generated by flowing current through the contacts. But then again presumably it’s designed to be on for hours on end.

 

I’d worry slightly about the back-emf generated when the BMV relay opens, since the stored magnetic energy in the fairly chunky relay coil has to go somewhere and it’s likely to be dissipated by arcing across the BMV relay contacts, burning them. V=L*dI/dt and all that. I’d want to put a freewheel diode across the relay coil to dissipate this energy and prevent arcing. But then again, how often is this relay going to open? Hopefully never, once testing is complete.

Edited by nicknorman
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10 hours ago, nicknorman said:

I guess you could do. A permanent 0.25 amp drain goes against my principles but as you say, you have plenty of solar. Ditto relying on something to be powered in order for the boat’s services to operate (ie the failure mode is that the lights go out). I just wonder how it will cope with being on 24/7 dissipating 4 watts plus some heat generated by flowing current through the contacts. But then again presumably it’s designed to be on for hours on end.

 

I’d worry slightly about the back-emf generated when the BMV relay opens, since the stored magnetic energy in the fairly chunky relay coil has to go somewhere and it’s likely to be dissipated by arcing across the BMV relay contacts, burning them. V=L*dI/dt and all that. I’d want to put a freewheel diode across the relay coil to dissipate this energy and prevent arcing. But then again, how often is this relay going to open? Hopefully never, once testing is complete.

 

Thanks Nick, that is a valid point about the amount of background current drain on a 24/7 basis.

The BEP switch uses I think 0.15 amps, the inverter uses 0.5 amps, and the toilet fan maybe 0.1 amps, so there is already about 18 Ah of charge needed every day, just as a baseline- and that's without the mobile signal booster thing that uses almost 2amps, and is on most of the day and evening.

That relay would add another 6Ah to the daily drain, which is not great.

 

The thing is, I dont mind paying more for a bistable relay- in fact I would consider replacing the BEP with the same sort of thing.

The potential snag for me is whether a bistable relay is more complicated to wire up to the BMV? 

The appeal of the cheapo unit is that I can get it tomorrow from Amazon and have it wired up to the BMV in the next few days. Bish bosh, as they say. 

 

PS - I dont suppose there is an example of a bistable relay you would recommend for a boat, that is simple to wire in? 

 

 

 

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23 minutes ago, Tony1 said:

 

Thanks Nick, that is a valid point about the amount of background current drain on a 24/7 basis.

The BEP switch uses I think 0.15 amps, the inverter uses 0.5 amps, and the toilet fan maybe 0.1 amps, so there is already about 18 Ah of charge needed every day, just as a baseline- and that's without the mobile signal booster thing that uses almost 2amps, and is on most of the day and evening.

That relay would add another 6Ah to the daily drain, which is not great.

 

The thing is, I dont mind paying more for a bistable relay- in fact I would consider replacing the BEP with the same sort of thing.

The potential snag for me is whether a bistable relay is more complicated to wire up to the BMV? 

The appeal of the cheapo unit is that I can get it tomorrow from Amazon and have it wired up to the BMV in the next few days. Bish bosh, as they say. 

 

PS - I dont suppose there is an example of a bistable relay you would recommend for a boat, that is simple to wire in? 

A bistable relay has the complication that it must be driven by a very short duration  ( 1/10th second) high current (3A) pulse to turn on, and ditto on different wires to turn off. So it can’t be directly connected to a BMV a relay. I use the Tyco BDS-A, but with my own electronics to operate it.

You might consider what Kris on the other channel has been using, the BG 250.

 

https://www.samlex.com/product/bgb-250/

 

This can be programmed with some low voltage cutouts, but the high voltage cutout is fixed and much too high. He therefore uses a BMV relay connected to the thing’s Remote terminal, to control it. Seems to work well, but it’s not cheap.

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6 minutes ago, nicknorman said:

A bistable relay has the complication that it must be driven by a very short duration  ( 1/10th second) high current (3A) pulse to turn on, and ditto on different wires to turn off. So it can’t be directly connected to a BMV a relay. I use the Tyco BDS-A, but with my own electronics to operate it.

You might consider what Kris on the other channel has been using, the BG 250.

 

https://www.samlex.com/product/bgb-250/

 

This can be programmed with some low voltage cutouts, but the high voltage cutout is fixed and much too high. He therefore uses a BMV relay connected to the thing’s Remote terminal, to control it. Seems to work well, but it’s not cheap.

 

Cheers Nick, looks like that would be perfect, but they seem to be out of stock everywhere at the moment. 

I might just get one of the £15 cheapos for now so I can just finish the job and move on.

 

I dont like the idea that it might burn out part of the BMV when it opens, I must say that, so I'll use your diode suggestion. 

 

Bear in mind I'm only using this relay to disconnect the chargers- the load cables are separated, and they have their own BMV which is set to disconnect at low voltage/low SoC, but in that scenario the chargers all stay connected.

Conversely, if the chargers are disconnected due to high voltage, the loads will all stay functioning- my cunning plan is that this will allow the voltage to more quickly reduce to safer levels. 

 

 

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21 minutes ago, Detling said:

Could you not use a small relay controlled by the bmv, then the relay contacts get burned not the bmv relay.

 

Forgive me, my understanding of the detail is very sketchy- are you suggesting to insert a second small relay (similar in size to the one within the BMV)- so that it takes the brunt of any damaging energy coming back from the big relay?

 

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3 hours ago, Detling said:

Could you not use a small relay controlled by the bmv, then the relay contacts get burned not the bmv relay.

 

No need, a freewheel diode will absorb all the energy for a few pennies and not use any power. Any relay coil really needs a freewheel diode to absorb the energy, so if another relay was to be inserted i'd recommend such a diode on that too. The current taken by the proposed big relay (0.25A) is well within the capabilities of the BMV relay (1A)

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50 minutes ago, nicknorman said:

 

 

No need, a freewheel diode will absorb all the energy for a few pennies and not use any power. Any relay coil really needs a freewheel diode to absorb the energy, so if another relay was to be inserted i'd recommend such a diode on that too. The current taken by the proposed big relay (0.25A) is well within the capabilities of the BMV relay (1A)

 

Sorry to pester Nick, but is there a specific rating or type needed for this task? 

 

I can see things called flyback diodes on ebay, like this, but I'm not sure its the right thing:

 

https://www.ebay.co.uk/itm/192634537176?epid=1747602058&hash=item2cd9e9c4d8:g:WtcAAMXQqC9SMDja

 

On Amazon there are multipacks with dozens of the things, like this: 

 

https://www.amazon.co.uk/BOJACK-Assortment-Rectifier-Recovery-Switching/dp/B07Q8RPBVY/ref=sr_1_3_sspa?crid=26CGWG0E6E3&dchild=1&keywords=flyback+diode&qid=1633711442&sprefix=flyback+%2Caps%2C229&sr=8-3-spons&psc=1&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUEyU1ZXT0xHOVRWWUZEJmVuY3J5cHRlZElkPUEwMzgxNjYwWVRLNThWRVNTODNNJmVuY3J5cHRlZEFkSWQ9QTAwNzM4OTVQVVFEMVkzSkhMOVQmd2lkZ2V0TmFtZT1zcF9hdGYmYWN0aW9uPWNsaWNrUmVkaXJlY3QmZG9Ob3RMb2dDbGljaz10cnVl

 

Would one of those do the job?

 

And is the diode soldered in series somewhere on the COM control cable,i.e. somewhere between the BMV and the relay?

 

 

 

 

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1 hour ago, nicknorman said:

 

 

No need, a freewheel diode will absorb all the energy for a few pennies and not use any power. Any relay coil really needs a freewheel diode to absorb the energy, so if another relay was to be inserted i'd recommend such a diode on that too. The current taken by the proposed big relay (0.25A) is well within the capabilities of the BMV relay (1A)

 

Assuming this is a "thing", are there any relays that have these diodes built in?

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1 hour ago, Tony1 said:

 

Sorry to pester Nick, but is there a specific rating or type needed for this task? 

 

I can see things called flyback diodes on ebay, like this, but I'm not sure its the right thing:

 

https://www.ebay.co.uk/itm/192634537176?epid=1747602058&hash=item2cd9e9c4d8:g:WtcAAMXQqC9SMDja

 

On Amazon there are multipacks with dozens of the things, like this: 

 

https://www.amazon.co.uk/BOJACK-Assortment-Rectifier-Recovery-Switching/dp/B07Q8RPBVY/ref=sr_1_3_sspa?crid=26CGWG0E6E3&dchild=1&keywords=flyback+diode&qid=1633711442&sprefix=flyback+%2Caps%2C229&sr=8-3-spons&psc=1&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUEyU1ZXT0xHOVRWWUZEJmVuY3J5cHRlZElkPUEwMzgxNjYwWVRLNThWRVNTODNNJmVuY3J5cHRlZEFkSWQ9QTAwNzM4OTVQVVFEMVkzSkhMOVQmd2lkZ2V0TmFtZT1zcF9hdGYmYWN0aW9uPWNsaWNrUmVkaXJlY3QmZG9Ob3RMb2dDbGljaz10cnVl

 

Would one of those do the job?

 

And is the diode soldered in series somewhere on the COM control cable,i.e. somewhere between the BMV and the relay?

No just a bog standard silicon rectifier diode like a 1N4001.
eg https://www.ebay.co.uk/itm/111777815515

 

You connect it across the relay coil, cathode to the coil terminal you connect to positive, anode to the coil terminal you connect to negative. The cathode is the end with the white ring.

 

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12 minutes ago, Richard10002 said:

 

Assuming this is a "thing", are there any relays that have these diodes built in?

 

I don't know of course, but my guess would be that the high-end products probably do have this sort of protection built in, but my £15 unit clearly doesn't have it. 

 

But I do find it encouraging that for an extra few quid, I can add a diode that makes the cheap relay into an acceptable solution to provide battery protection, in conjunction with a BMV712. (Although I wouldnt have a cat in hells chance of doing that without some very specialised advice and info from Nick).

 

To be honest, I wish I'd cottoned on that there was a £15 solution before I bought my BEP motorised switch for £100 (and brand new they are almost £200, if you can even find one). 

 

I did look at the victron battery protect unit, but its high voltage disconnect is fixed at 15v, which is no use at all. It can be remotely switched, but I couldnt find any certain confirmation online that I could control that on/off switching using a BMV712. 

 

Part of the problem is that everyone has a different view on what is an acceptable level of protection for lithiums. 

In my case, I've put in a high-SoC limiter function using a BMV, in order to keep the batteries as healthy as possible, but the majority of folks probably think that is not necessary.

 

And a few days ago I tried something new- I wanted to use two BMVs together, both able to send signals through the same COM control wire, which would add in a high voltage disconnect to the high SoC limiter, but so far that hasnt worked.

It still feels like breaking new territory for many people getting into lithiums, but touch wood, mine have survived their first 6 months of cruising in my not very capable hands.

 

 

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39 minutes ago, Richard10002 said:

 

Assuming this is a "thing", are there any relays that have these diodes built in?

Some do, for example the Tyco BDS-A bistable relay that I use. Of course with any relay that has such a diode, you have to be careful to connect the coil to the right polarity (ie the right way round), otherwise the diode will present a short circuit.

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8 minutes ago, nicknorman said:

No just a bog standard silicon rectifier diode like a 1N4001.
eg https://www.ebay.co.uk/itm/111777815515

 

You connect it across the relay coil, cathode to the coil terminal you connect to positive, anode to the coil terminal you connect to negative. The cathode is the end with the white ring.

 

 

Sorry Nick, just to make sure, the coil terminals are the flat connectors where you attach the small control wires, right? 

 

The coil terminals are not those M6 studs that holds the main cable? There's no obvious permanent place to solder the diode onto the studs (unless onto the flat ends)

 

https://www.amazon.co.uk/gp/product/B08TTV1VZB/ref=ppx_yo_dt_b_asin_image_o01_s00?ie=UTF8&psc=1

 

In my case, post 30 will connect to the chargers, post 87 connects to the main fuse and then into the battery pos, flat connector 86 goes to the BMV, and flat connector 85 goes to the neg bus bar.

The diode goes between between 85 and 86 (white ring nearest to 86). Do I have that right?

 

 

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3 minutes ago, Tony1 said:

 

Sorry Nick, just to make sure, the coil terminals are the flat connectors where you attach the small control wires, right? 

 

The coil terminals are not those M6 studs that holds the main cable? There's no obvious permanent place to solder the diode onto the studs (unless onto the flat ends)

 

https://www.amazon.co.uk/gp/product/B08TTV1VZB/ref=ppx_yo_dt_b_asin_image_o01_s00?ie=UTF8&psc=1

 

In my case, post 30 will connect to the chargers, post 87 connects to the main fuse and then into the battery pos, flat connector 86 goes to the BMV, and flat connector 85 goes to the neg bus bar.

The diode goes between between 85 and 86 (white ring nearest to 86). Do I have that right?

Yes. Obviously the other end of the BMV relay has to go to battery positive, via a small fuse.

Edited by nicknorman
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4 minutes ago, nicknorman said:

Yes. Obviously the other end of the BMV relay has to go to battery positive, via a small fuse.

 

Great, thanks so much for your advice Nick. 

I have another spare fused victron cable from my old BMV700, so I'll use that as the pos for the BMV712.

 

I might have the choice of running the BMV relay either reversed or not reversed.

 

If possible, I'd prefer not to reverse everything as I did with the high SoC limiter, as that gets confusing. 

So am I right in thinking I can invert the BMV relay, and use the high voltage parameter to trigger the opening of the relay?

And if I do that, I need to insert the pos feed into the NC port?

 

 

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44 minutes ago, Tony1 said:

 

Great, thanks so much for your advice Nick. 

I have another spare fused victron cable from my old BMV700, so I'll use that as the pos for the BMV712.

 

I might have the choice of running the BMV relay either reversed or not reversed.

 

If possible, I'd prefer not to reverse everything as I did with the high SoC limiter, as that gets confusing. 

So am I right in thinking I can invert the BMV relay, and use the high voltage parameter to trigger the opening of the relay?

And if I do that, I need to insert the pos feed into the NC port?

You don’t need to invert the relay, although you could (but it just complicates things!). With the relay not inverted, you connect positive to the NC terminal, then it will open (and turn off the big relay) when the high voltage parameter triggers.

  • Greenie 1
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There is a type of latching relay, called a "Carpenter" relay, that changes state with each impulse on a single wire. The duration is not important as long as it is enough to make the relay operate. They are not very common in the UK, but are used extensively in France for lighting installations that need to be controlled from more than two positions: the intermediate switch normally used in the UK is unknown there, where multiple switches for staircases or long corridors are normally spring-biassed push-to-make switches conected to the same terminal of a Carpenter relay. 

Edited by Ronaldo47
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1 minute ago, Ronaldo47 said:

There is a type of latching relay, called a "Carpenter" relay, that changes state with each impulse on a single wire. The duration is not important as long as it is enough to make the relay operate. They are not very common in the UK, but are used extensively in France for lighting installations that need to be controlled from more than one position: the intermediate switch normally used in the UK is unknown there, where switches for staircases or long corridors are normally spring-biassed push-to-make switches conected to the same terminal of a Carpenter relay. 

Yes. But unfortunately the BMV doesn’t have the option for a pulse, it is just a level output. 

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10 minutes ago, nicknorman said:

Yes. But unfortunately the BMV doesn’t have the option for a pulse, it is just a level output. 

 

Didn't another poster here design and build a circuit to convert a level output into a pulse, specifically to operate a bistable relay? 

 

Simon IIRC, but I can't recall his username.

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