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Post by Telemachus on Jan 11, 2021 16:13:09 GMT
You can do that but in the case of the flip flop relay you posted, it could get out of sync. In the case of the Tyco relay it needs 3A for 50-100mS so that is one pretty huge capacitor, and of course the waveform would be asymptotic not square. And you have the holding current of the relay used to drive the bistable relay to consider when it is in one of its states. A brute force way of doing it as would be designed by a ... (you get the picture). Whereas in my case I have a microprocessor driving one small MOSFET for switching on, and one for switching off, giving a waveform exactly as the relay manufacturer intended. All very small, neat, elegant and cheap. When I said it was the method we used, I mean a method that was used on several custom built units, I do not recall any complaints as regards things getting out of sync on any of them. It worked and worked well, the relays concerned were actually GE DIN rail relays very simillar to the one in the RS catalogue.
A relay is not particularly critical about the waveform that you feed it .... it either is good enough or not .... that method was good enough. To be honest if it ever did get out of sync, it would be fairly obvious and could be reset by simply turning off and back on again the control driving it. as regards your method of drive certainly it's fine but you do realise that your one small MOSFET would just as happily drive the relay I described
just to add .... the reason I was using a c/o relay contact as the drive was because that is what the module from ebay uses as one of it's outputs
As I said, the fundamental flaw of a flip flop relay is that it is a fundamentally bad design that will go wrong at some point if it is an open loop system. If there is some sort of feedback such that the controlling system knows which state the relay is in, then it’s fine. But you don’t propose that. I would never contemplate such an atrocious design. If you can’t see that point then it is a bit like having an argument with someone who is adamant that 2 and 2 makes 5, or that he really did win the election when he didn’t. The problem with the capacitor solution is that you start off applying the correct voltage to the relay and instantly the voltage starts decaying, at a rate determined by the size of the capacitor. How low the voltage can get and still continue to operate the relay to finish its switching, depends on course on the specifics of the relay and isn’t something described in the spec sheet so straight away you are fudging a solution without any data to back it up. But let’s say for the sake of argument that it can tolerate going down to 60% voltage (7.2v) after 100mS, what size of capacitor do we need to operate the Tyco relay? C = t/r where t is 0.1s and r is 4 ohms, so C is 25,000 microfarads. The voltage rating needs to be able to tolerate a spike, say around 35v which is the normal sort of automotive spike. So let’s have a look at the RS catalogue for tantalum capacitors with a 35v rating. Oh dear the biggest is 220 microfarads, so we are going to need 113 of them in parallel. Each one is £2.20 plus vat so that will be £298. And another £298 for the other coil to flip the relay the other way. So at a total of £596 just for the capacitors, and they are surface mount devices so we are going to need a pcb. Yes, I can see now that this is a really good idea. NOT. This is the difference between us, I can immediately see the problem and quantify it, whereas you just look for a bigger hammer.
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Post by Telemachus on Jan 11, 2021 16:13:35 GMT
I like simple engineering Yes, big hammers are very satisfying to use.
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Post by JohnV on Jan 11, 2021 16:45:06 GMT
I like simple engineering Yes, big hammers are very satisfying to use. on thick heads
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Post by Telemachus on Jan 11, 2021 16:49:38 GMT
Yes, big hammers are very satisfying to use. on thick heads If you are considering self-harm (and I wouldn’t blame you!) perhaps you should first consider counselling?
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Post by kris on Jan 11, 2021 16:52:44 GMT
Haven’t you two kicked shins enough yet?
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Post by Telemachus on Jan 11, 2021 16:54:07 GMT
Haven’t you two kicked shins enough yet? please sir, she pulled my hair and I squeamed and squeamed and I just pulled her hair back. Oh and scratched her eyes out too I suppose. Yes I think we are probably getting bored with it now. Well, it is dark and raining here.
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Post by JohnV on Jan 11, 2021 17:10:18 GMT
When I said it was the method we used, I mean a method that was used on several custom built units, I do not recall any complaints as regards things getting out of sync on any of them. It worked and worked well, the relays concerned were actually GE DIN rail relays very simillar to the one in the RS catalogue.
A relay is not particularly critical about the waveform that you feed it .... it either is good enough or not .... that method was good enough. To be honest if it ever did get out of sync, it would be fairly obvious and could be reset by simply turning off and back on again the control driving it. as regards your method of drive certainly it's fine but you do realise that your one small MOSFET would just as happily drive the relay I described
just to add .... the reason I was using a c/o relay contact as the drive was because that is what the module from ebay uses as one of it's outputs
As I said, the fundamental flaw of a flip flop relay is that it is a fundamentally bad design that will go wrong at some point if it is an open loop system. If there is some sort of feedback such that the controlling system knows which state the relay is in, then it’s fine. But you don’t propose that. I would never contemplate such an atrocious design. If you can’t see that point then it is a bit like having an argument with someone who is adamant that 2 and 2 makes 5, or that he really did win the election when he didn’t. This is the difference between us, I can immediately see the problem and quantify it, whereas you just look for a bigger hammer. The difference is you can't see the fact that you are calculating the figures for a Tyco relay which is a high power contactor I was talking of a relay to switch 4A for a fridge
Anyway I don't believe anything more than the Inverter is needed as a warning and what is more for the fridge you could simply use a relay normally on to run the fridge that switches off with the low voltage trigger for the inverter ....... for people without an inverter an energised relay that could supply the fridge would only draw maybe 0.1 A and could be driven from the same voltage sensing module but again why? If you have an alarm that notifies you when your batteries are getting to say 25% that gives you plenty of warning to do something about it manually. It's a boat it doesn't have to be super duper highly technical fully automatic bells and whistles ...... it's a canal boat not a state of the art transport system
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Post by Deleted on Jan 11, 2021 17:18:51 GMT
a brave man letting novices loose on your pride and joy ..... a very brave man The thing is, when I made those rash offers the boat was more simple to use... With the advent of the new batteries there will be a bit more checking of things needed, and more risk of expensive damage if they dont follow the instructions. I think I'll wait until one of them asks me about it, rather than proactively mention it again. It would be a unique experience for them (one that they probably wouldn't seek out and pay for of their own volition), and so it would be a lovely and unique gift to be able to give. But if and when it happens, I'll probably have most of the risks under control. I'll have a cheap relay acting as a low voltage cut off (the one you suggested!), and my B2B will keep charge current and voltages within safe limits. So the only risk I can see will be them leaving the lithiums connected up and being fully charged all day every day for two weeks whilst they cruise. The kind of damage that sustained periods at full charge might inflict is not as critical as the damage from sustained high voltage, but it could easily happen. I will go to great lengths to explain the risk of keeping the batteries fully charged, and I'll get their agreement to pay for any damage of any kind that the boat suffers. I'll also insist on spending an afternoon cruising and doing a couple of locks so I'm happy they're fairly safe. Luckily the people I'm talking about are not random pissed-up hirers- they will be very careful if I ask them to be. All of that said, if it happens it will be a pretty anxious week or two that I'm away from the boat....
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Post by Telemachus on Jan 11, 2021 17:36:54 GMT
As I said, the fundamental flaw of a flip flop relay is that it is a fundamentally bad design that will go wrong at some point if it is an open loop system. If there is some sort of feedback such that the controlling system knows which state the relay is in, then it’s fine. But you don’t propose that. I would never contemplate such an atrocious design. If you can’t see that point then it is a bit like having an argument with someone who is adamant that 2 and 2 makes 5, or that he really did win the election when he didn’t. This is the difference between us, I can immediately see the problem and quantify it, whereas you just look for a bigger hammer. The difference is you can't see the fact that you are calculating the figures for a Tyco relay which is a high power contactor I was talking of a relay to switch 4A for a fridge
Anyway I don't believe anything more than the Inverter is needed as a warning and what is more for the fridge you could simply use a relay normally on to run the fridge that switches off with the low voltage trigger for the inverter ....... for people without an inverter an energised relay that could supply the fridge would only draw maybe 0.1 A and could be driven from the same voltage sensing module but again why? If you have an alarm that notifies you when your batteries are getting to say 25% that gives you plenty of warning to do something about it manually. It's a boat it doesn't have to be super duper highly technical fully automatic bells and whistles ...... it's a canal boat not a state of the art transport system In normal routine operation it is unlikely that an “emergency disconnect” device would be needed. The whole point of having it is for when the unexpected happens, for example you go shopping and crash the car. Or in your case, hit yourself over the head with a large hammer and end up in hospital for a week. Under those circumstances, no amount of beeping warnings is going to help.
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Post by JohnV on Jan 11, 2021 17:55:01 GMT
The difference is you can't see the fact that you are calculating the figures for a Tyco relay which is a high power contactor I was talking of a relay to switch 4A for a fridge
Anyway I don't believe anything more than the Inverter is needed as a warning and what is more for the fridge you could simply use a relay normally on to run the fridge that switches off with the low voltage trigger for the inverter ....... for people without an inverter an energised relay that could supply the fridge would only draw maybe 0.1 A and could be driven from the same voltage sensing module but again why? If you have an alarm that notifies you when your batteries are getting to say 25% that gives you plenty of warning to do something about it manually. It's a boat it doesn't have to be super duper highly technical fully automatic bells and whistles ...... it's a canal boat not a state of the art transport system In normal routine operation it is unlikely that an “emergency disconnect” device would be needed. The whole point of having it is for when the unexpected happens, for example you go shopping and crash the car. Or in your case, hit yourself over the head with a large hammer and end up in hospital for a week. Under those circumstances, no amount of beeping warnings is going to help. In summer my boat will quite happily look after itself for months at a time, in winter it's plugged in to shore power, if that fails it will probably last a week then the inverter will stop (and so will the fridge freezer) without the inverter/fridge running even in winter the solar panels will supply enough to gradually recharge the batteries (the inverter will not restart, it requires a manual reset for that) I will lose all the food in the freezer and it will make a mess ..... but that is all
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Post by Telemachus on Jan 11, 2021 18:12:35 GMT
In normal routine operation it is unlikely that an “emergency disconnect” device would be needed. The whole point of having it is for when the unexpected happens, for example you go shopping and crash the car. Or in your case, hit yourself over the head with a large hammer and end up in hospital for a week. Under those circumstances, no amount of beeping warnings is going to help. In summer my boat will quite happily look after itself for months at a time, in winter it's plugged in to shore power, if that fails it will probably last a week then the inverter will stop (and so will the fridge freezer) without the inverter/fridge running even in winter the solar panels will supply enough to gradually recharge the batteries (the inverter will not restart, it requires a manual reset for that) I will lose all the food in the freezer and it will make a mess ..... but that is all Nobody is telling you how you should operate your batteries / your boat. But just like Peter has done, it isn’t helpful to project your own specific choices made under your specific circumstances, onto other people with different circumstances.
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Post by JohnV on Jan 11, 2021 18:27:29 GMT
In summer my boat will quite happily look after itself for months at a time, in winter it's plugged in to shore power, if that fails it will probably last a week then the inverter will stop (and so will the fridge freezer) without the inverter/fridge running even in winter the solar panels will supply enough to gradually recharge the batteries (the inverter will not restart, it requires a manual reset for that) I will lose all the food in the freezer and it will make a mess ..... but that is all Nobody is telling you how you should operate your batteries / your boat. But just like Peter has done, it isn’t helpful to project your own specific choices made under your specific circumstances, onto other people with different circumstances. Then don't sell the high tech way as the only way .... it isn't, low tech can also work very well and at low cost especially if you have plenty of solar. The main reason I can't get more solar in winter is because my mooring is North South and my panels will only point to port or starboard. If I moored completely across the river I could double if not treble my solar collection. If I didn't have a mooring to go to in winter I would have to use my generator but that would not have to be sophisticated and as it is 6Kw it would not need to be run often and I would make damn sure I was moored where my solar panels would get the best of what sun there was. I would probably also up it to 2Kw or 3Kw but it would still not need anything fancy, a programmable MPPT controller is all the protection needed at the top end and as I have said, an alarm on the inverter is adequate bottom end protection
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Post by Telemachus on Jan 11, 2021 18:36:05 GMT
Nobody is telling you how you should operate your batteries / your boat. But just like Peter has done, it isn’t helpful to project your own specific choices made under your specific circumstances, onto other people with different circumstances. Then don't sell the high tech way as the only way .... it isn't, low tech can also work very well and at low cost especially if you have plenty of solar. The main reason I can't get more solar in winter is because my mooring is North South and my panels will only point to port or starboard. If I moored completely across the river I could double if not treble my solar collection. If I didn't have a mooring to go to in winter I would have to use my generator but that would not have to be sophisticated and as it is 6Kw it would not need to be run often and I would make damn sure I was moored where my solar panels would get the best of what sun there was. I would probably also up it to 2Kw or 3Kw but it would still not need anything fancy, a programmable MPPT controller is all the protection needed at the top end and as I have said, an alarm on the inverter is adequate bottom end protection I am offering my opinion on the best solution for TC. I am not suggesting he adopts my solution, which is definitely high tec. You have a very large amount of solar because you aren’t on a narrowboat. Lucky you, but not relevant to TC. And you have access to shore power whenever you want it. Again, not applicable to TC. You have made a few noises proposing ill thought out ideas that are not practical, and now your suggestion seems to be to not have any low or high voltage disconnect. That is one strategy. In my opinion it is a high risk strategy bearing in mind the cost of the batteries and the certainty that some unexpected event will crop up, given enough time. It will be up to TC to decide what he wants to do.
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Post by kris on Jan 11, 2021 18:47:22 GMT
Obviously you both still need to bang heads, carry on. Let the rest of us know when you’ve finished.
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Post by Deleted on Jan 11, 2021 19:01:27 GMT
Well chaps, I hope we can return to our normal civilised tone of discussion. I would hate to see any ill feeling arise between you guys from a difference in technical viewpoints.
For my part, I can say that I have been very grateful to hear all of the different approaches that have been described- both the simple and the complex.
I've ended up elements from both approaches, to be honest. John's £40 Durite split charge relay for example will be my low voltage disconnect, and I've had a few suggestions from Nick that are simple enough for me to want to employ.
I like the idea of an accurate battery monitor showing % SoC for example, so that my future boat guests will have something simple to read, and there will less risk of them damaging my batteries.
If I'd been sharper John I would've also picked up on your suggestion of using a big resistor to limit the current to the lithiums, as a cheap option to try out before I spent £270 on a B2B.
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