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Old 23-03-2020, 15:39   #1
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Charge relay and 123Bms question

I have 200ah winston cells with 123Bms and the 123 dual relay. I have the “standard mode” and standard settings v-bypass=3,4v and v-max=3,6v. I thought that the v-bypass should be the start of the balancing and that charging should stop when one cell reached v-max. This isn’t the case. The charge stop criteria is always (at least for my bank) when all cells is above v-bypass. In my mind this allows for very little balancing since the charging normally stop at 3,4v. Any comments on this?
Is this a mistake in the design or have I just got it wrong?
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Old 24-03-2020, 09:57   #2
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Re: Charge relay and 123Bms question

Hi Flod.
I have finalised my installation of 4 x 300 cells this weekend in exactly the same set-up as you, and noticed the same behavior of the 123 Smart BMS, however the app tells me that the bank is full when all cells reach 3,40v. I have set full at 95% in the configuration


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Old 24-03-2020, 10:11   #3
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Re: Charge relay and 123Bms question

Hi yes that is another “design” feature that the coulomb counting reset at 100% when all cells are above v-max (in your and my case 3.40v) I suspect that voltage is a little to low to be “full” . According to the normal charge curves 3,6v is more like “full” but maybe that is to high to operate on a normal basis
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Old 24-03-2020, 10:46   #4
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Re: Charge relay and 123Bms question

Looks like the bms also errors on temperature. Min and max temperatures must have separate settings for charge and discharge... i.e. discharge while freezing is okay but not charging.
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Old 24-03-2020, 12:11   #5
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Re: Charge relay and 123Bms question

My boat is still put away for the winter and I don't remember the behavior. I have had good luck with their support by email, info@123electric.eu. They usually get back to me in a day. They also turned me on to larger but efficient relays for my system as I have a large bank. Let us know what they say.
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Old 19-04-2020, 13:52   #6
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Re: Charge relay and 123Bms question

Hi Flod

I have a 260ah bank with the 123 BMS and think the parameters you describe are the same as mine and I think correct. Been installed and running for last 12 months
Top balancing should have been carried out before use and the sort of use most yachties put battery banks through does not tend to take them out of balance quickly.
If the cells V are close together then balancing will be a very quick affair, as it should be.

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Old 19-04-2020, 14:19   #7
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Charge relay and 123Bms question

Yes and I realised that the bms is in fact balancing the cells. I started another thread on that but it seems to work. My only objection is really that the bms closes the charge relay at the same volt as the balancing starting point. I have put a manual switch in the system to override this. So I can continue to charge up towards 3,65 for the highest cell if I want and get a longer balancing period and a “fuller” battery
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