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Post by kris on Feb 25, 2021 17:08:43 GMT
So just to be clear BMV com connects to battery negative . Bmv no connects to bgb remote. Sorry to be a pain Correct. Thank you.
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Post by duncan on Feb 25, 2021 18:14:56 GMT
I’d like to get into electric cooking, these induction hobs are supposed to be good. Once I’ve got 2.4 kw of solar then I’ll need them. Just got an induction hob, to complement the air source heat pump coming next week. Turn the gas off completely. Max power is 7kwh, got to be wired into the 32a cooker supply. Some of the rings have a boost function. But, while looking around I did see some 13a 2 ring ones. Thinking about doing the same. Which hob did you go for Jim?
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Post by Jim on Feb 25, 2021 18:49:25 GMT
Just got an induction hob, to complement the air source heat pump coming next week. Turn the gas off completely. Max power is 7kwh, got to be wired into the 32a cooker supply. Some of the rings have a boost function. But, while looking around I did see some 13a 2 ring ones. Thinking about doing the same. Which hob did you go for Jim? One from IKEA with a name that sounds like a good cough. Just over £200.
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Post by kris on Feb 26, 2021 12:48:39 GMT
As a starting point set Peukert (item 5) to 1.05 and the charge efficiency (item 6) to 99%. Plus of course set the battery capacity (item 1). You will also need to set up the fully charged detection (items 2,3 and 4) so that the meter synchronises to 100% when fully charged. To give advice on how to set that up, you’d need to remind me how you are planning to charge them. Then there is the relay to set up. If you want to operate the relay on low voltage, items 18 and 19 maybe to 12v and 12.5v (or lower, if you like) and for high voltage it’s 20 and 21, maybe 14.6 and 14.1 or whatever you want to risk. And I would put in a significant delay time in 14 to stop relay chatter, maybe 30 seconds. Oh and best to connect the power wire for the BMV to the battery side of the relay, otherwise SoC will be lost, and reset to 100%, when the power fails and is restored. I’ve set the capacity 1040amp/hr, I’ve set the peukert to 1.05 and charge efficiency to 99%. I will be mainly charging through a tri star mppt which will be set to gel settings which equate to an absorb voltage of 14v and a float voltage of 13.7v. So I’m thinking of setting the high voltage cutout to 14.1v and the low Volta age cutout as 12.3v. Exciting stuff when I’ve finally got this relay voltage set I can start using them and get rid of my lead acid domestics
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Post by Telemachus on Feb 26, 2021 14:16:55 GMT
I expect that will be ok, but if it were me I’d go for a slightly lower float voltage, maybe 13.5. The thing with Li is to avoid holding them at a highish voltage for long periods, and in mid summer if you are a light user, they are going to be held at over 3.4v per cell for long periods. The other thing is to consider is if there is temperature compensation (increasing voltage at low temperature) by the MPPT - Li cells don’t want any temperature compensation.
I suggest setting the voltage limits on the BMV relay settings to a test value (high voltage quite low, and low voltage quite high) to check the thing operates as expected, then set back to such as you suggest once you know it works.
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Post by kris on Feb 26, 2021 14:48:07 GMT
So I’ve set the voltage limits, 18, 12.2v 19, 12.5v 20, 14.2v 21, 14.1v
The relay mode is set to remote?
14, Relay minimum closed time, is set to 1min as it wouldn’t allow me to set for 30secs.
I don’t really know what to set section 2,3 and 4 to? I was also thinking how can l check the relay is working?
I’m going to get used to this set up and test it before going further with the install
im stuck with the gel settings on the mppt for the moment, but James the guy who all these valences came from has done the same for quite a while with no issues.
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Post by kris on Feb 26, 2021 15:02:54 GMT
So with those settings input and the battery voltage at 13.2v, the relay isn’t open.? Which I would expect it to be.
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Post by kris on Feb 26, 2021 15:18:29 GMT
Doh my bad, I haven’t put power to the relay. What should the fuse on the ground be rated at?
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Post by peterboat on Feb 26, 2021 15:48:31 GMT
I expect that will be ok, but if it were me I’d go for a slightly lower float voltage, maybe 13.5. The thing with Li is to avoid holding them at a highish voltage for long periods, and in mid summer if you are a light user, they are going to be held at over 3.4v per cell for long periods. The other thing is to consider is if there is temperature compensation (increasing voltage at low temperature) by the MPPT - Li cells don’t want any temperature compensation. I suggest setting the voltage limits on the BMV relay settings to a test value (high voltage quite low, and low voltage quite high) to check the thing operates as expected, then set back to such as you suggest once you know it works. Nick these are the same as Johns, Tony and mine and full charge is 14.6 and float is the same so float should be ok at 13.6 its what I have settled at, the cutoff is the one I worry about as I ran mine down last year and 12.8 downward is very fast this is the second time I have done it with the same results it like falling off a cliff
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Post by kris on Feb 26, 2021 15:52:40 GMT
I expect that will be ok, but if it were me I’d go for a slightly lower float voltage, maybe 13.5. The thing with Li is to avoid holding them at a highish voltage for long periods, and in mid summer if you are a light user, they are going to be held at over 3.4v per cell for long periods. The other thing is to consider is if there is temperature compensation (increasing voltage at low temperature) by the MPPT - Li cells don’t want any temperature compensation. I suggest setting the voltage limits on the BMV relay settings to a test value (high voltage quite low, and low voltage quite high) to check the thing operates as expected, then set back to such as you suggest once you know it works. Nick these are the same as Johns, Tony and mine and full charge is 14.6 and float is the same so float should be ok at 13.6 its what I have settled at, the cutoff is the one I worry about as I ran mine down last year and 12.8 downward is very fast this is the second time I have done it with the same results it like falling off a cliff
so what would you set the cut out voltage at peter?
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Post by peterboat on Feb 26, 2021 16:08:38 GMT
Nick these are the same as Johns, Tony and mine and full charge is 14.6 and float is the same so float should be ok at 13.6 its what I have settled at, the cutoff is the one I worry about as I ran mine down last year and 12.8 downward is very fast this is the second time I have done it with the same results it like falling off a cliff
so what would you set the cut out voltage at peter? 12.8 Kris when these batteries are flat LAs are considered fully charged very weird its another world. I was at the boat wed, thurs this week, I switched all solar to the drive batteries and lived on the Valence batteries for 2 days, they were at 13.4 at the start and 13.2 yesterday evening, fridge freezer running, tv, electric kettle, toaster etc. I have dropped the float to 13.4 as I am not on the boat much at the moment as I am decorating at Jaynes, when I get back I will up it to 13.6 again. Mine is a 24 volt system but I am halving my numbers to help normal users. If we were using these batteries as intended 14,6 volts down to 12.8 is where all the energy is, I have only had mine up at the top a couple of times for top balancing purposes and thats in 4 years I think?
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Post by kris on Feb 26, 2021 16:13:56 GMT
So I need to reset my values. I’ll do that now. I need an in line fuse before I can finish wiring it up, so tmw.
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Post by Telemachus on Feb 26, 2021 16:49:22 GMT
I expect that will be ok, but if it were me I’d go for a slightly lower float voltage, maybe 13.5. The thing with Li is to avoid holding them at a highish voltage for long periods, and in mid summer if you are a light user, they are going to be held at over 3.4v per cell for long periods. The other thing is to consider is if there is temperature compensation (increasing voltage at low temperature) by the MPPT - Li cells don’t want any temperature compensation. I suggest setting the voltage limits on the BMV relay settings to a test value (high voltage quite low, and low voltage quite high) to check the thing operates as expected, then set back to such as you suggest once you know it works. Nick these are the same as Johns, Tony and mine and full charge is 14.6 and float is the same so float should be ok at 13.6 its what I have settled at, the cutoff is the one I worry about as I ran mine down last year and 12.8 downward is very fast this is the second time I have done it with the same results it like falling off a cliff
I think you should check the spec sheet. The one I’m looking at says 14.6 maximum charge voltage, and 13.8 float. This means that Kris’ initial settings are within limits, however the point is that this value of float voltage holds them at very close to 100% SoC. In order to maximise life I suggest that it would be better to back the voltage off slightly such that they are held at perhaps 97% SoC, especially as with solar this voltage will be held for long periods every day in summer. Minimum discharge voltage on the spec sheet is 10v which is clearly right at the bottom of the knee. As you say there isn’t a huge amount of charge left below a static voltage of 12.8 but you have to bear in mind that the voltage dips under heavy load. If you set the relay to open at 12.8v it will open under heavy load when there is still quite a bit of charge left. The point of this relay is not to set the point where the batteries are routinely taken down to, but to set an emergency cut off limit. So one could in theory set it to 10v but that seems a bit drastic and assumes the cells are well bottom-balanced. So as a compromise I’d set it to 12v. In my system with per-cell monitoring im going to set the shut off at 2.6v on the lowest cell (2.5 being the minimum) as I don’t want the thing tripping off when I put the kettle on.
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Post by Telemachus on Feb 26, 2021 16:51:52 GMT
People historically suffer from lead acid syndrome. They think that taking a Li battery down to a low SoC is worse for it than taking them to a high SoC. But in fact both are equally bad for an Li battery - 95% or 5% are the same in terms of stress.
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Post by Telemachus on Feb 26, 2021 16:52:50 GMT
Doh my bad, I haven’t put power to the relay. What should the fuse on the ground be rated at? Fuses are not needed on ground wires, only on wires connected to battery positive.
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