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Post by Deleted on Oct 29, 2021 10:48:38 GMT
Yep. Cleaned all 144 of them. With a light sanding block And then cleaned them with contact cleaner? the issue is sometimes grains from the sanding block are left on the surface and can give a poor connection. remember points on cars? if you used glasspaper to clean them up the glass could be left behind stopping them making a contact and working No, I didn't use contact cleaner. 120 grit sanding block. Maybe I just didn't get some of them clean enough. Cell 3 is certainly behaving more as I would expect. Though I have now changed the leads for shorter ones. Eta. Contact cleaner added to shopping list
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Post by Deleted on Nov 12, 2021 11:06:42 GMT
I had another go at balancing my cells yesterday. I think they may be a bit closer than my first attempt. I bought a wire wound resistor in the end, as it seemed easier taking a bit out than putting a bit in. Time will tell I spose.
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Post by Telemachus on Nov 12, 2021 11:41:54 GMT
Looks good to me! All you really need is for it to be sufficiently balanced so that you can charge at a reasonable voltage like 14.3 and not have any of the cells hit 3.65v
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Post by Deleted on Nov 12, 2021 11:57:02 GMT
Looks good to me! All you really need is for it to be sufficiently balanced so that you can charge at a reasonable voltage like 14.3 and not have any of the cells hit 3.65v I suppose if I only charge to 80 % capacity, the need for perfect balancing becomes less crucial, and possibly not required at all. Next job is to determine why the Battery monitor is reading slightly higher than the BMS software is reporting.
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Post by Telemachus on Nov 12, 2021 12:32:39 GMT
Looks good to me! All you really need is for it to be sufficiently balanced so that you can charge at a reasonable voltage like 14.3 and not have any of the cells hit 3.65v I suppose if I only charge to 80 % capacity, the need for perfect balancing becomes less crucial, and possibly not required at all. Next job is to determine why the Battery monitor is reading slightly higher than the BMS software is reporting. I think there is some misinformation floating around. If you charge to 13.8v and hold until the current subsides, you are at about 98% SoC. You barely get any more into the batteries by increasing to 14.3v, maybe up to 99.5% or more. And if you want to go up to the max of 3.65x4= 14.6v, you barely get any more charge in, just the last 0.5% or whatever. Its quite difficult to charge only to 80% because very slight changes in voltage have a major effect. The only way to do it is to approximate the SoC using an Ah-counting battery monitor like a BMV712, and even then after a week or two it will have drifted off because of the inherent error prone nature of integrating current to get Ah. What I do is to charge to 80% based on the BMV, then when necessary every couple of weeks I charge to (very nearly) 100% by applying 14.3v. When the current subsides to 5% capacity, the BMV resets to 100% and the charge stops. I also have a “stop charge” trigger if a cell voltage gets to 3.65, but so far it hasn’t. I suspect the reason why the BMS and the Battery Monitor disagree slightly is because of the reasons I gave earlier - Ah counting is inherently inaccurate, with error increasing with time. You need to synchronise at a known point (normally 100% SoC) to set them back in agreement with each other from time to time.
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Post by kris on Nov 12, 2021 12:37:32 GMT
I tend to ignore the soc reading on the bmv and just use the voltage reading. It got boring synchronising it all the time.
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Post by Deleted on Nov 12, 2021 12:43:11 GMT
I suppose if I only charge to 80 % capacity, the need for perfect balancing becomes less crucial, and possibly not required at all. Next job is to determine why the Battery monitor is reading slightly higher than the BMS software is reporting. I think there is some misinformation floating around. If you charge to 13.8v and hold until the current subsides, you are at about 98% SoC. You barely get any more into the batteries by increasing to 14.3v, maybe up to 99.5% or more. And if you want to go up to the max of 3.65x4= 14.6v, you barely get any more charge in, just the last 0.5% or whatever. Its quite difficult to charge only to 80% because very slight changes in voltage have a major effect. The only way to do it is to approximate the SoC using an Ah-counting battery monitor like a BMV712, and even then after a week or two it will have drifted off because of the inherent error prone nature of integrating current to get Ah. What I do is to charge to 80% based on the BMV, then when necessary every couple of weeks I charge to (very nearly) 100% by applying 14.3v. When the current subsides to 5% capacity, the BMV resets to 100% and the charge stops. I also have a “stop charge” trigger if a cell voltage gets to 3.65, but so far it hasn’t. I suspect the reason why the BMS and the Battery Monitor disagree slightly is because of the reasons I gave earlier - Ah counting is inherently inaccurate, with error increasing with time. You need to synchronise at a known point (normally 100% SoC) to set them back in agreement with each other from time to time. I clearly need to give it some more thought. I will only be charging using solar for the time being. I guess using the BMS as a charge cut off is not best practice, and I should set my solar charge levels at something around 13.6 boost/float.
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Post by Telemachus on Nov 12, 2021 12:47:36 GMT
I think there is some misinformation floating around. If you charge to 13.8v and hold until the current subsides, you are at about 98% SoC. You barely get any more into the batteries by increasing to 14.3v, maybe up to 99.5% or more. And if you want to go up to the max of 3.65x4= 14.6v, you barely get any more charge in, just the last 0.5% or whatever. Its quite difficult to charge only to 80% because very slight changes in voltage have a major effect. The only way to do it is to approximate the SoC using an Ah-counting battery monitor like a BMV712, and even then after a week or two it will have drifted off because of the inherent error prone nature of integrating current to get Ah. What I do is to charge to 80% based on the BMV, then when necessary every couple of weeks I charge to (very nearly) 100% by applying 14.3v. When the current subsides to 5% capacity, the BMV resets to 100% and the charge stops. I also have a “stop charge” trigger if a cell voltage gets to 3.65, but so far it hasn’t. I suspect the reason why the BMS and the Battery Monitor disagree slightly is because of the reasons I gave earlier - Ah counting is inherently inaccurate, with error increasing with time. You need to synchronise at a known point (normally 100% SoC) to set them back in agreement with each other from time to time. I clearly need to give it some more thought. I will only be charging using solar for the time being. I guess using the BMS as a charge cut off is not best practice, and I should set my solar charge levels at something around 13.6 boost/float. I’m not a great expert on solar but I think you want to have a much lower float voltage. Holding 13.6v for long periods will get you pretty close to 100% SoC. Into the mid-90s anyway. I’d say take it up to maybe 13.6, hold for 30 mins or so (absorption time) then revert to 13.35 or so, which is the voltage that will hold the cells at around 80%.
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