MisterSandals
Participation Medalist
I dunno why they designed BMS's the way they did. Glad you are able to make it work for your setup!
Dual 4S in parallel or 2P4S Configuration
- Thread starter Nigel Snook
- Start date
Thanks for your input, I will update as we get more time in the RV this spring.
Nigel Snook
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- Nov 18, 2020
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Gosh - I thought the Rec was expensive.........
Colin.Leake
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- Jul 13, 2021
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Nigel Snook
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- Nov 18, 2020
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As there is some interest about this configuration and seemingly very few adopters I thought it worthwhile offering some feedback after living with the kit for a few months now.
I have gone for the 2 x 4S set up but went with the Chargery 4S BMS - I couldn't bring myself to parting with the cash for 2 off REC.
1. The batteries played nicely when connected in parallel, it was clear that some current was flowing but very little. I guess when you are talking millivolts difference across the charge curve this will be the case. In my workshop with a short discharge test, they appeared to share the load (and subsequent charge) really well. Once installed on the boat however they do discharge and charge at different rates, not significant enough for me to take any action yet but will remove them at end of season to see if I can balance everything better.
2. I have a strange fault which demonstrates the value of 2 x 4S redundancy. When charging with solar and a large load applied e.g. electric kettle, a BMS sometimes trips charge relay on charge over current. Seemingly random batteries and always a single. The only way I can reset is by switching off BMS and subsequently output. This is clearly fine with this configuration.
In conclusion, I am very happy with decision to go for this configuration.......
I have gone for the 2 x 4S set up but went with the Chargery 4S BMS - I couldn't bring myself to parting with the cash for 2 off REC.
1. The batteries played nicely when connected in parallel, it was clear that some current was flowing but very little. I guess when you are talking millivolts difference across the charge curve this will be the case. In my workshop with a short discharge test, they appeared to share the load (and subsequent charge) really well. Once installed on the boat however they do discharge and charge at different rates, not significant enough for me to take any action yet but will remove them at end of season to see if I can balance everything better.
2. I have a strange fault which demonstrates the value of 2 x 4S redundancy. When charging with solar and a large load applied e.g. electric kettle, a BMS sometimes trips charge relay on charge over current. Seemingly random batteries and always a single. The only way I can reset is by switching off BMS and subsequently output. This is clearly fine with this configuration.
In conclusion, I am very happy with decision to go for this configuration.......
I've been through this issue before as well. I ended up going with a single 2p4s pack and a Renogy DC-DC charger to fill my second (2p4s) battery bank. This thread might help too.
diysolarforum.com
If your loads are "pulling" unequally from the batteries, I would suggest hooking both up in parallel, then hook the main positive to the + terminal on battery #1, and the main negative on the - terminal of batt #2.
That way you aren't using battery #1 for your loads, and filling it back up from batt#2, you would be pulling (more or less) equally from each pack.
Limiting current when a full second battery bank is put in parallel with a somewhat dead first bank.
I built a mobile solar generator box, it is 12 volt, and capable of 150 amps discharge. It has all kinds of 12 volt accessory ports (xt60, Anderson, barrel plugs, etc), and a shunt for monitoring AH's. I'm in the process of building a second "external" battery bank to add capacity when needed...
diysolarforum.com
If your loads are "pulling" unequally from the batteries, I would suggest hooking both up in parallel, then hook the main positive to the + terminal on battery #1, and the main negative on the - terminal of batt #2.
That way you aren't using battery #1 for your loads, and filling it back up from batt#2, you would be pulling (more or less) equally from each pack.
I to'd and fro'd on this a lot also.
I ended up going a single 2p4s with large BMS on my boat. It keeps it simple. I went with 163ah Calb Cells and a 250A Daly smart BMS (total of 326ah capable of 1c charge and discharge). If I went 4s only i'd still need the 250a BMS on each pack to carry the load of the inverter, should 1 bms die.. we dont do any massively offshore stuff so are generally an hour or 2 away from land max. Worst case I can carry a spare BMS (quite cheap) I can expand the pack easily if needed or can add a second complete battery identical, further in the future if I wish.. with minimal complexity.
Each situation is different.. but i weighed the risks and decided it was good for me..
Steve
I ended up going a single 2p4s with large BMS on my boat. It keeps it simple. I went with 163ah Calb Cells and a 250A Daly smart BMS (total of 326ah capable of 1c charge and discharge). If I went 4s only i'd still need the 250a BMS on each pack to carry the load of the inverter, should 1 bms die.. we dont do any massively offshore stuff so are generally an hour or 2 away from land max. Worst case I can carry a spare BMS (quite cheap) I can expand the pack easily if needed or can add a second complete battery identical, further in the future if I wish.. with minimal complexity.
Each situation is different.. but i weighed the risks and decided it was good for me..
Steve
