Upgrading LiFePO4 280ah 48v to 560ah 2 batteries in parallel or double cells in parallel?
- Thread starter dswiggum
- Start date
MrM1
I'm Here, But I'm Not All There
Good plan. Just remember to plan your wire size for the anticipated load, BUT to plan your fuse size to appropriately protect that size wire. Fuse are to protect your wire.
John Frum
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On the feeder circuits(batteries to busbar) the fuse should go as close to the battery positive terminal as possible to minimize the chance of an upstream short.
On the branch circuits(between loads and charge sources other than the battery) the fuse should go as close to the busbar as possible.
Fused busbars like this https://www.victronenergy.com/dc-distribution-systems/lynx-distributor
and this https://www.bluesea.com/products/5196/MRBF_Surface_Mount_Fuse_Block_-_Common_Source
enforce best practice.
The branch circuits are fused at the positive busbar even if its a charging circuit because the source of the terrifiying dead short current is the battery.
Another pragmagtic side to this practice is hopefully the inexpensive branch fuses will blow instead of the expensive class-t fuses on the feeders.
On the branch circuits(between loads and charge sources other than the battery) the fuse should go as close to the busbar as possible.
Fused busbars like this https://www.victronenergy.com/dc-distribution-systems/lynx-distributor
and this https://www.bluesea.com/products/5196/MRBF_Surface_Mount_Fuse_Block_-_Common_Source
enforce best practice.
The branch circuits are fused at the positive busbar even if its a charging circuit because the source of the terrifiying dead short current is the battery.
Another pragmagtic side to this practice is hopefully the inexpensive branch fuses will blow instead of the expensive class-t fuses on the feeders.
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At the point of doubling the 16 to 32 too. All are 280ah 3.2v. My first batch was bought 12 months ago. 2021 cells say Internal Resistance (IR) 0.15 mohm, the latest say 0.18 milliohm.
I was told to parallel old with new and use one BMS that way.
Will the slight difference cause any issues down the road ?
I am told they are both Eve products. The latest are branded Docan Power. The old ones have no labeled brand. Both are the same dimensions and have M6 terminals. Terminal distance are different. 2021 are threads into terminal, 2022 have welded studs.
Hate to wire all up and find I have to reverse plans and get a second BMS with two totally separate stacks.
Any input would be great.
I was told to parallel old with new and use one BMS that way.
Will the slight difference cause any issues down the road ?
I am told they are both Eve products. The latest are branded Docan Power. The old ones have no labeled brand. Both are the same dimensions and have M6 terminals. Terminal distance are different. 2021 are threads into terminal, 2022 have welded studs.
Hate to wire all up and find I have to reverse plans and get a second BMS with two totally separate stacks.
Any input would be great.
TorC
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I'd just go with 2 BMS and two independent packs from the start. That gets you both every cell individually monitored and redundancy for failure/service - just shut down and remove one pack while the other keeps running your house. Just need to make sure both are at reasonably similar SoC when reconnecting. Shouldn't be too hard, as the one in service will swing more than normal working alone.
I cannot get the second BMS anytime soon. So the two packs in series are built. Different spacing so they are not adjacent to each other in the normal context. Busbars in each series from bottom to top. No bus bars between parallel cells at equal voltages. BMS is already wired to one bank. And I have small gauge (#18) cross-connecting to the other bank at each level. Seems to be happy for now.
