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Post by Deleted on Jan 18, 2021 19:50:52 GMT
Maybe she was concerned about the contents of the fridge.
ETA you have a 230v fridge driven by the inverter so in the event of batteries being removed from circuit and inverter switching off the contents of the fridge could go off quite quickly.
Obviously to quote someone "you wouldn't want a warm beer"
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Post by Deleted on Jan 18, 2021 20:19:14 GMT
Maybe she was concerned about the contents of the fridge. ETA you have a 230v fridge driven by the inverter so in the event of batteries being removed from circuit and inverter switching off the contents of the fridge could go off quite quickly. Obviously to quote someone "you wouldn't want a warm beer" From my admittedly very unhealthy perspective, the presence and the temperature of beer are the two primary boating issues to address, other than ensuring the boat actually stays above water. As distressing as it is to contemplate, I have to accept the possibility that the electrician has not taken this mission statement on board, and is perhaps indifferent to the fate of my beer supply. My current theory- to which I will hold unless proven wrong- is that her reservations are technical in nature, rather than being driven by empathy for my beer.
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Post by Telemachus on Jan 18, 2021 20:40:02 GMT
It is a bit of a faff, but something you may only have to do once, or very occasionally. But yes it might be helpful to have a push button or switch wired in to make it easier, it will be very low current so nothing fancy needed. I'd be very grateful for your thoughts on a related issue: I outlined the relay-based solution to my electrician and she was pessimistic about it. In trying to describe my idea over the phone, I started by saying that in using the relay, I would 'pretend' that the lithiums were the vehicle battery (i.e. the battery that needed to be protected from over-discharging). So I would connect the relay into the wire that carried the output from the lithiums to the inverter. There is a sensor wire that would normally be connected to the battery that is the source of the charge (normally the vehicle battery). So normally, this sensor would monitor the vehicle battery voltage. In my setup, this sensor would instead be connected to an appropriate position on the lithium battery bank. So when the sensor detects the lithium battery voltage has fallen below say 12v, the relay disconnects the output/load that is being taken from the lithiums. When I explained this, the electrician suggested that a further battery would be required after the relay (in other words, between then relay and the inverter). I dont understand why she would have said this, unless I described the relay setup in a confusing way. I'm hoping it is that, because I thought I had a simple and cheap protection against over-discharging, and I dont want to have to go back to the drawing board. I'm pretty sure the batteries will survive without an over discharge cut off (unless I let other people use the boat), and 99% of the time I'll be watching the batteries' SoC manually, but it would be a nice thing to have if it can be done cheaply and simply. To save me trawling back through pages of dross, can you remind me exactly which relay you are planning on installing?
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Post by Deleted on Jan 18, 2021 20:43:17 GMT
You may call it "dross" as a deliberate attempt to aggregate the cesspit of god's mistakes but other than that well I suppose quite a lot of it is dross.
Quality dross though. None of your common or garden dross.
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Post by Deleted on Jan 18, 2021 21:47:54 GMT
To save me trawling back through pages of dross, can you remind me exactly which relay you are planning on installing? Its this one, and I must apologise- my ignorance of all things relay-related led me to misleadingly refer to sensors that dont exist on the item. www.splitcharge.co.uk/product/durite-0-727-43-200a-smart-programmable-relay/The way I think this will work is as follows: The relay will sit between the lithiums and the inverter. The voltage-sensing is done on the charge that comes into the relay from the lithiums, via the 6mm bolt terminal. When that voltage drops below 11.5v (factory set value), the link from the lithiums to the inverter will be cut by the relay switching off. When the lithium batteries have got some charge back in them from the B2B, the voltage from them into the relay will rise above 12.8v, and the relay will switch on automatically, and the lithiums will thus be reconnected to the inverter. So no need for the override switch I mentioned in an earlier post.
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Post by Deleted on Jan 18, 2021 21:55:14 GMT
I still think that some people view the contents of the fridge as important.
Plus perhaps there is something about the inverter being switched off at the source rather than using its own on/off switch.
If you did have a small battery as suggested by the electrician then it would take both of those potential issues out at least for a short time.
Maybe a 25ah golf buggy battery or something.
Although thinking about it (impossible at this point as I have been up since 3am) would the relay still work if there was a battery the other side of it ?
Bedtime !
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Post by patty on Jan 18, 2021 22:03:25 GMT
We are in the process of fitting a 12v fridge in the van.. It did not quite go according to plan.. there is no such thing as a 30 minute d-i-y task..... Sense of humour a must when a son relies on mums help.....
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Post by Deleted on Jan 18, 2021 22:15:03 GMT
I still think that some people view the contents of the fridge as important. Plus perhaps there is something about the inverter being switched off at the source rather than using its own on/off switch. If you did have a small battery as suggested by the electrician then it would take both of those potential issues out at least for a short time. Maybe a 25ah golf buggy battery or something. Although thinking about it (impossible at this point as I have been up since 3am) would the relay still work if there was a battery the other side of it ? Bedtime ! I think the point the electrician might have been making was that there HAS to be a battery on the 'output' side of the relay, and that I cant just connect it to the inverter. I guess that would make sense- I mean sitting in between two batteries is the situation that the thing is designed to fit into. Maybe it needs to sense some kind of charge even on its output side...
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Post by Deleted on Jan 18, 2021 22:20:44 GMT
We are in the process of fitting a 12v fridge in the van.. It did not quite go according to plan.. there is no such thing as a 30 minute d-i-y task..... Sense of humour a must when a son relies on mums help..... You have my sympathy Patty. And yet, in theory the principles of electricity would seem to be straightforward... I might be tempted to have a go on a part time dwelling, but I rang a couple of sparks today and there's no chance of one attending in less than 10 days. The problem is that if I try a DIY job and screw up the B2B install and disconnect something I shouldn't, I could be without electricity (and therefore pumped water too) for almost 2 weeks before I can get someone in t fix it. And in winter as well. I'm thinking I might wait till the electrician is free to do the job.
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Post by Telemachus on Jan 18, 2021 22:23:46 GMT
To save me trawling back through pages of dross, can you remind me exactly which relay you are planning on installing? Its this one, and I must apologise- my ignorance of all things relay-related led me to misleadingly refer to sensors that dont exist on the item. www.splitcharge.co.uk/product/durite-0-727-43-200a-smart-programmable-relay/The way I think this will work is as follows: The relay will sit between the lithiums and the inverter. The voltage-sensing is done on the charge that comes into the relay from the lithiums, via the 6mm bolt terminal. When that voltage drops below 11.5v (factory set value), the link from the lithiums to the inverter will be cut by the relay switching off. When the lithium batteries have got some charge back in them from the B2B, the voltage from them into the relay will rise above 12.8v, and the relay will switch on automatically, and the lithiums will thus be reconnected to the inverter. So no need for the override switch I mentioned in an earlier post. Ah yes, I remember now! Although the instructions are rather scant, I don't think a battery will be needed on the downstream side of the relay. The instructions say "Terminal 87 to secondary battery or separate circuit +12V" and in your case, it is the "separate circuit". My slight concern is that once the inverter is de-powered, the large input capacitors will discharge and thus when the relay closes again, the capacitors will suddenly have 12v applied to them and a very large current will momentarily flow to recharge them. Although it will only be milliseconds, the current will exceed the rating of the relay. If it is a mechanical relay then I doubt it will be a problem due to the very short duration of the overload, and bearing in mind the infrequency of switching (we hope!). If it is electronically switched, I would be a bit more worried.
And the other problem is that if it is mechanically switched, how much current does it use 24/7 with the relay activated to send power to the inverter?
Is the intention only to de-power the inverter in the event of low voltage, or the entire boat's 12v dc system including lights etc. I would have thought that, although it might seem a bit drastic, the latter would be better since the whole point is to protect the batteries from over-discharge and if lighting etc has been left on you will still eventually over-discharge the Li. Or is the inverter the only thing connected to that side of the B2B / the Li batteries?
I agree that you don't need an override button / switch to reconnect, but it would make programming it easier.
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Post by Telemachus on Jan 18, 2021 22:24:39 GMT
I still think that some people view the contents of the fridge as important. Plus perhaps there is something about the inverter being switched off at the source rather than using its own on/off switch. If you did have a small battery as suggested by the electrician then it would take both of those potential issues out at least for a short time. Maybe a 25ah golf buggy battery or something. Although thinking about it (impossible at this point as I have been up since 3am) would the relay still work if there was a battery the other side of it ? Bedtime ! I think the point the electrician might have been making was that there HAS to be a battery on the 'output' side of the relay, and that I cant just connect it to the inverter. No I don't think so, see my previous post.
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Post by Deleted on Jan 18, 2021 22:57:29 GMT
Ah yes, I remember now! Although the instructions are rather scant, I don't think a battery will be needed on the downstream side of the relay. The instructions say "Terminal 87 to secondary battery or separate circuit +12V" and in your case, it is the "separate circuit". My slight concern is that once the inverter is de-powered, the large input capacitors will discharge and thus when the relay closes again, the capacitors will suddenly have 12v applied to them and a very large current will momentarily flow to recharge them. Although it will only be milliseconds, the current will exceed the rating of the relay. If it is a mechanical relay then I doubt it will be a problem due to the very short duration of the overload, and bearing in mind the infrequency of switching (we hope!). If it is electronically switched, I would be a bit more worried.
And the other problem is that if it is mechanically switched, how much current does it use 24/7 with the relay activated to send power to the inverter?
Is the intention only to de-power the inverter in the event of low voltage, or the entire boat's 12v dc system including lights etc. I would have thought that, although it might seem a bit drastic, the latter would be better since the whole point is to protect the batteries from over-discharge and if lighting etc has been left on you will still eventually over-discharge the Li. Or is the inverter the only thing connected to that side of the B2B / the Li batteries?
I agree that you don't need an override button / switch to reconnect, but it would make programming it easier.
Ah, I had forgotten about it needing a current 24/7 to keep it open and 'running', so to speak. The leaflet refers to standby current of 2mA, and if that's what it means, then I can live with that. I'll have to make sure I've understood that correctly though. I was wrong to refer to it outputting to an inverter. Truth be told, I don't have a particularly clear idea of where the output wire from the lithiums goes, but I guess it will effectively be powering everything- inverter and 12v electrics? I'm going to be pretty bloody disappointed if I go to the trouble of wiring it in, or paying for the electrician to do it, and then it overloads and breaks the first time it disconnects and comes back on. That said, it will be a very, very rare event that the voltage will get that low, and as long as it doesnt break the inverter in its death throes, I can probably let it be sacrificed in preference to damaging the batteries. I dont really need the smart version, there are ones for £30 that will cut the discharge at around 12v, so its not that expensive to replace anyway (and certainly much less than replacing damaged batteries). I just don't want collateral damage to the other electrics. In terms of the settings, the factory default is 11.8v, and to be honest I'm wondering whether to just leave it at that rather than faff around programming it. If the low voltage event is as rare as I think it will be, going down to 11.8v as a one-off would probably be ok.
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Post by Telemachus on Jan 18, 2021 23:08:19 GMT
Ah yes, I remember now! Although the instructions are rather scant, I don't think a battery will be needed on the downstream side of the relay. The instructions say "Terminal 87 to secondary battery or separate circuit +12V" and in your case, it is the "separate circuit". My slight concern is that once the inverter is de-powered, the large input capacitors will discharge and thus when the relay closes again, the capacitors will suddenly have 12v applied to them and a very large current will momentarily flow to recharge them. Although it will only be milliseconds, the current will exceed the rating of the relay. If it is a mechanical relay then I doubt it will be a problem due to the very short duration of the overload, and bearing in mind the infrequency of switching (we hope!). If it is electronically switched, I would be a bit more worried.
And the other problem is that if it is mechanically switched, how much current does it use 24/7 with the relay activated to send power to the inverter?
Is the intention only to de-power the inverter in the event of low voltage, or the entire boat's 12v dc system including lights etc. I would have thought that, although it might seem a bit drastic, the latter would be better since the whole point is to protect the batteries from over-discharge and if lighting etc has been left on you will still eventually over-discharge the Li. Or is the inverter the only thing connected to that side of the B2B / the Li batteries?
I agree that you don't need an override button / switch to reconnect, but it would make programming it easier.
Ah, I had forgotten about it needing a current 24/7 to keep it open and 'running', so to speak. The leaflet refers to standby current of 2mA, and if that's what it means, then I can live with that. I'll have to make sure I've understood that correctly though. I was wrong to refer to it outputting to an inverter. Truth be told, I don't have a particularly clear idea of where the output wire from the lithiums goes, but I guess it will effectively be powering everything- inverter and 12v electrics? I'm going to be pretty bloody disappointed if I go to the trouble of wiring it in, or paying for the electrician to do it, and then it overloads and breaks the first time it disconnects and comes back on. That said, it will be a very, very rare event that the voltage will get that low, and as long as it doesnt break the inverter in its death throes, I can probably let it be sacrificed in preference to damaging the batteries. I dont really need the smart version, there are ones for £30 that will cut the discharge at around 12v, so its not that expensive to replace anyway (and certainly much less than replacing damaged batteries). I just don't want collateral damage to the other electrics. In terms of the settings, the factory default is 11.8v, and to be honest I'm wondering whether to just leave it at that rather than faff around programming it. If the low voltage event is as rare as I think it will be, going down to 11.8v as a one-off would probably be ok. My suspicion is the 2mA refers to when the relay is disconnected. When it is connected, as per its intended use the engine would be running so I suspect the current drain might be a lot more, but impossible to know for sure. Well yes ultimately if it breaks but saves your expensive Li batteries, it’s not the end of the world. I can’t see how it could damage the inverter.
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Post by Deleted on Jan 18, 2021 23:29:02 GMT
Ah, I had forgotten about it needing a current 24/7 to keep it open and 'running', so to speak. The leaflet refers to standby current of 2mA, and if that's what it means, then I can live with that. I'll have to make sure I've understood that correctly though. I was wrong to refer to it outputting to an inverter. Truth be told, I don't have a particularly clear idea of where the output wire from the lithiums goes, but I guess it will effectively be powering everything- inverter and 12v electrics? I'm going to be pretty bloody disappointed if I go to the trouble of wiring it in, or paying for the electrician to do it, and then it overloads and breaks the first time it disconnects and comes back on. That said, it will be a very, very rare event that the voltage will get that low, and as long as it doesnt break the inverter in its death throes, I can probably let it be sacrificed in preference to damaging the batteries. I dont really need the smart version, there are ones for £30 that will cut the discharge at around 12v, so its not that expensive to replace anyway (and certainly much less than replacing damaged batteries). I just don't want collateral damage to the other electrics. In terms of the settings, the factory default is 11.8v, and to be honest I'm wondering whether to just leave it at that rather than faff around programming it. If the low voltage event is as rare as I think it will be, going down to 11.8v as a one-off would probably be ok. My suspicion is the 2mA refers to when the relay is disconnected. When it is connected, as per its intended use the engine would be running so I suspect the current drain might be a lot more, but impossible to know for sure. Well yes ultimately if it breaks but saves your expensive Li batteries, it’s not the end of the world. I can’t see how it could damage the inverter. I'll have to email the supplier and see if they can tell me what the operating current draw is. If it turns out to be more than an amp, I'm not going to connect it. After all that's 24Ah in day, right? My B2B is rated at 60amps, so if I understand it right (which is by no means certain), the B2B will put about 1Ah into the batteries every minute, so even a single extra amp over 24 hours would mean an extra 24 mins of engine charging every day. So yes, I need to find out....
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Post by Deleted on Jan 19, 2021 7:56:23 GMT
Surely the inverter has a low voltage disconnect anyway built into it.
This would probably be something like 11.8v which is well above the minimum safe voltage for LFP battery.
I probably missed a bit but why would you need a relay to do a job the thing is designed to do by itself?
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