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Post by kris on Mar 5, 2021 13:09:36 GMT
So I got round to testing the relay. Since I fitted the batteries they’ve just been between 13.2v and 12.9v but today I plugged an angle grinder in which when switched on took the voltage down to 12.7 which should have closed the relay but it didn’t. I kept trying to no avail, I’ve checked the settings on the bmv app. The relay is set to close at 12.8, the relay setting is default so basically it should have worked. I’ve checked the wiring between the bmv and relay all connected and connected as suggested. Com on bmv to battery -ve and No on bmv to the remote connector on the relay. So I’ve run out of things to check. Any ideas?
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Post by Telemachus on Mar 5, 2021 13:15:23 GMT
So I got round to testing the relay. Since I fitted the batteries they’ve just been between 13.2v and 12.9v but today I plugged an angle grinder in which when switched on took the voltage down to 12.7 which should have closed the relay but it didn’t. I kept trying to no avail, I’ve checked the settings on the bmv app. The relay is set to close at 12.8, the relay setting is default so basically it should have worked. I’ve checked the wiring between the bmv and relay all connected and connected as suggested. Com on bmv to battery -ve and No on bmv to the remote connector on the relay. So I’ve run out of things to check. Any ideas? Well firstly, is the BMV relay actually operating? At the bottom of the App it shows you the state of the relay, either open (off) or closed (on). Is this changing? If not, it’s a problem with the BMV settings. If it is, it’s something to do with the wiring and the BGB. Report back and we’ll take it from there.
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Post by Telemachus on Mar 5, 2021 13:31:09 GMT
Oh and don’t forget there is a 10 second delay - the voltage has to be continuously low for 10 seconds before the relay operates.
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Post by kris on Mar 5, 2021 13:45:06 GMT
Oh and don’t forget there is a 10 second delay - the voltage has to be continuously low for 10 seconds before the relay operates. It’s this I wasn’t taking account of. So it works fine, at least I know the relay works now.
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Post by kris on Mar 5, 2021 18:11:43 GMT
So today as well as testing the relay, I wired in the battery charger. It has a lifepo4 setting but I think the voltages are a little high. Anyway I wired it in and ran a generator to test it for a while. It seems to work okay, but the cable from the main fuse seems to get warm, not really hot but quite warm. The strange thing is it’s just this bit of cable. The wire from the battery charger to the switch stays cool, as does the cable from the switch to the relay and the cable from the relay to the fuse stays cool. It’s just the cable from the battery side of the fuse. I checked all the connections etc all seems fine. Anyway as I say the cable isn’t really hot, but the temp differential is a little bit worrying. Anybody got any ideas?
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Post by Telemachus on Mar 5, 2021 18:49:36 GMT
So today as well as testing the relay, I wired in the battery charger. It has a lifepo4 setting but I think the voltages are a little high. Anyway I wired it in and ran a generator to test it for a while. It seems to work okay, but the cable from the main fuse seems to get warm, not really hot but quite warm. The strange thing is it’s just this bit of cable. The wire from the battery charger to the switch stays cool, as does the cable from the switch to the relay and the cable from the relay to the fuse stays cool. It’s just the cable from the battery side of the fuse. I checked all the connections etc all seems fine. Anyway as I say the cable isn’t really hot, but the temp differential is a little bit worrying. Anybody got any ideas? If they all have the same current in them, then the one that is getting warm has higher resistance for some reason - thinner cable or a high resistance connection with the heat spreading along the cable. Are the connections at either end of the cable hot? You could test the voltage drop at various places near the cable to see where voltage is being dropped with the current flowing, because in order for heat to be generated there must be some voltage being dropped somewhere. Alternatively it could just be that this cable has less effective heat dissipation due to being in a bundle or other such congested place without good air circulation. Anyway, if it is only warm it isn’t a safety problem, but as I said it is indicative of voltage being dropped.
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Post by Deleted on Mar 5, 2021 18:52:40 GMT
I wonder if it could be a dodgy cell.
It's well known for batteries to have dodgy cells and I don't see why lithium batteries would be any different in this respect. Yes they have massively higher effective capacity and cycle life but they can't be infallible.
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Post by kris on Mar 5, 2021 19:21:40 GMT
So today as well as testing the relay, I wired in the battery charger. It has a lifepo4 setting but I think the voltages are a little high. Anyway I wired it in and ran a generator to test it for a while. It seems to work okay, but the cable from the main fuse seems to get warm, not really hot but quite warm. The strange thing is it’s just this bit of cable. The wire from the battery charger to the switch stays cool, as does the cable from the switch to the relay and the cable from the relay to the fuse stays cool. It’s just the cable from the battery side of the fuse. I checked all the connections etc all seems fine. Anyway as I say the cable isn’t really hot, but the temp differential is a little bit worrying. Anybody got any ideas? If they all have the same current in them, then the one that is getting warm has higher resistance for some reason - thinner cable or a high resistance connection with the heat spreading along the cable. Are the connections at either end of the cable hot? You could test the voltage drop at various places near the cable to see where voltage is being dropped with the current flowing, because in order for heat to be generated there must be some voltage being dropped somewhere. Alternatively it could just be that this cable has less effective heat dissipation due to being in a bundle or other such congested place without good air circulation. Anyway, if it is only warm it isn’t a safety problem, but as I said it is indicative of voltage being dropped. The cable from the switch through the relay onto the fuse and then the batteries is all the same. I’ll check all the connections again tmw and see if I can trace it.
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Post by kris on Mar 5, 2021 19:46:19 GMT
I wonder if it could be a dodgy cell. It's well known for batteries to have dodgy cells and I don't see why lithium batteries would be any different in this respect. Yes they have massively higher effective capacity and cycle life but they can't be infallible. I don’t think so as I connected these to a laptop and checked out the balence between cells, all are fine. Also if it was a cell in one battery I would have thought that battery would get warm?
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Post by kris on Mar 6, 2021 13:45:46 GMT
So I had another go with the battery charger. The cable from the battery side of the mega fuse heats up quite quickly. I checked all the connections tightened them down etc. I measured the voltage drop at 0.2v across the fuse. I’m puzzled to what could be causing it, the only thing I can think of is a badly crimped connector? It’s definitely bad enough that I wouldn’t leave it to run un attended.
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Post by Telemachus on Mar 6, 2021 16:09:36 GMT
So I had another go with the battery charger. The cable from the battery side of the mega fuse heats up quite quickly. I checked all the connections tightened them down etc. I measured the voltage drop at 0.2v across the fuse. I’m puzzled to what could be causing it, the only thing I can think of is a badly crimped connector? It’s definitely bad enough that I wouldn’t leave it to run un attended. Yes could be a crimping issue. Does one of the fuse terminals get hotter than the other? What is the fuse rated at vs the charging current? Maybe the fuse is operating near its limit?
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Post by kris on Mar 6, 2021 16:14:01 GMT
So I had another go with the battery charger. The cable from the battery side of the mega fuse heats up quite quickly. I checked all the connections tightened them down etc. I measured the voltage drop at 0.2v across the fuse. I’m puzzled to what could be causing it, the only thing I can think of is a badly crimped connector? It’s definitely bad enough that I wouldn’t leave it to run un attended. Yes could be a crimping issue. Does one of the fuse terminals get hotter than the other? What is the fuse rated at vs the charging current? Maybe the fuse is operating near its limit? The fuse is 250amps and the charging current is 60amps. Yes the battery side of the fuse gets warm the relay side of the fuse stays cool. The battery side of the fuse is where the heat is originating from, it spreads from here along the battery cable there are no other places on the batteries near the batteries that are getting warm. So the only thing I can think is it’s an issue with the crimp.
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Post by Telemachus on Mar 6, 2021 17:02:18 GMT
Yes could be a crimping issue. Does one of the fuse terminals get hotter than the other? What is the fuse rated at vs the charging current? Maybe the fuse is operating near its limit? The fuse is 250amps and the charging current is 60amps. Yes the battery side of the fuse gets warm the relay side of the fuse stays cool. The battery side of the fuse is where the heat is originating from, it spreads from here along the battery cable there are no other places on the batteries near the batteries that are getting warm. So the only thing I can think is it’s an issue with the crimp. Yes that sounds likely.
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Post by kris on Mar 6, 2021 17:13:47 GMT
The fuse is 250amps and the charging current is 60amps. Yes the battery side of the fuse gets warm the relay side of the fuse stays cool. The battery side of the fuse is where the heat is originating from, it spreads from here along the battery cable there are no other places on the batteries near the batteries that are getting warm. So the only thing I can think is it’s an issue with the crimp. Yes that sounds likely. it’s a bit of a pig to replace the crimp but it looks like that’s what I’m going to have to do. At the moment I can quite easily live of the amount the solar is generating.
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Post by Telemachus on Mar 6, 2021 19:42:53 GMT
it’s a bit of a pig to replace the crimp but it looks like that’s what I’m going to have to do. At the moment I can quite easily live of the amount the solar is generating. Could you not just try to compress the crimp a bit more? Maybe hit it with a punch/hammer to make a notch, which reduces the internal volume and thus squishes the cable more. You would have to have something heavy behind it to absorb the blow, of course.
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