LIFEPO4 Battery discussion thread

like wingnut said it will be fine, yes you will see some %soc differs near the mid range. But as soon as the voltage start dropping on the one pack the big pack will take more load. Just remember bigger cable to the bigger packs also helps it balance out better
 
denmendez65 said:
All that happens is the higher capacity one does more of the work in proportion to its ratio of its size in the overall bank. 100ah and 50ah, the 100ah will discharge twice the energy the 50ah. Nothing wrong with that. AI is not entirely accurate there.
Click to expand...
He also has all different cable lengths too.
 
DTBA said:
like wingnut said it will be fine, yes you will see some %soc differs near the mid range. But as soon as the voltage start dropping on the one pack the big pack will take more load. Just remember bigger cable to the bigger packs also helps it balance out better
Click to expand...
I'm not buying this one. We only drawing 5kW max. Maybe if the cable is longer, then go thicker.
 
wingnut771 said:
He also has all different cable lengths too.
Click to expand...
Do cable lengths really matter with Lithium batteries that have BMS? Th BMS will just cut off when full isnt it and the other will charge till full. Same with discharging?

I know with LA its important. Just not sure with BMS LIfepo4 batteries.
 
cavedog said:
So AI and general recommendations are do not parallel different capacities and batteries of different ages as they won't work well together.

What if I buy a 15kW omnivolt and parallel it with my 2 x 5.12kW batteries? Doesn't look like BMS does anything even if they communicate so if you mix battery brands up and just keep and eye on the cut off and full charge voltages you will be okay.

Click to expand...
Ask AI if its safe to parallel LFP with LA.

I would. @denmendez65 is too scared to.
 
wingnut771 said:
Its fine, the bigger battery does the heavy lifting. Andy has 100kWh parallelled together, all different Ah.

Here's an extreme example:
Click to expand...

denmendez65 said:
All that happens is the higher capacity one does more of the work in proportion to its ratio of its size in the overall bank. 100ah and 50ah, the 100ah will discharge twice the energy the 50ah. Nothing wrong with that. AI is not entirely accurate there.
Click to expand...

DTBA said:
like wingnut said it will be fine, yes you will see some %soc differs near the mid range. But as soon as the voltage start dropping on the one pack the big pack will take more load. Just remember bigger cable to the bigger packs also helps it balance out better
Click to expand...

Obviously not thinking about it as my max production even in good weather won't be enough to 100% them if I do but was just wondering what the forum members think on paralleling different sizes and brands etc.
 
denmendez65 said:
Do cable lengths really matter with Lithium batteries that have BMS? Th BMS will just cut off when full isnt it and the other will charge till full. Same with discharging?

I know with LA its important. Just not sure with BMS LIfepo4 batteries.
Click to expand...
Cable lengths affect voltage drop, but at the end of the day they all get to the same place in the end so not a trainsmash.
 
cavedog said:
Obviously not thinking about it as my max production even in good weather won't be enough to 100% them if I do but was just wondering what the forum members think on paralleling different sizes and brands etc.
Click to expand...
Again, all load dependent. If you generate 20kWh and have 40kWh. If some days you use 15 and other 25kWh etc, etc., overall the bank will be full. If you happen to pull the full 40kWh, then it if you consistently use 15kWh for the next couple of days, then the bank will be full.

The extra battery just acts as a buffer for bad weather. Some guys on the YouTube channels I followed, like the Old Jarhead, who were building off-grid cabins for their retirement and using old golf cart batteries (LA batteries), were doing that. Huge battery bank, but the generation could not fully charge the drained (below 50%) to full.

They were getting over 10 to 15 years from their LA batteries, btw, because of the oversizing. But yeah, it's all load dependent. One can have as many batteries as they want. Nowhere does it say you must generate enough to charge the batteries in one day from empty.
 
denmendez65 said:
Again, all load dependent. If you generate 20kWh and have 40kWh. If some days you use 15 and other 25kWh etc, etc., overall the bank will be full. If you happen to pull the full 40kWh, then it if you consistently use 15kWh for the next couple of days, then the bank will be full.

The extra battery just acts as a buffer for bad weather. Some guys on the YouTube channels I followed, like the Old Jarhead, who were building off-grid cabins for their retirement and using old golf cart batteries (LA batteries), were doing that. Huge battery bank, but the generation could not fully charge the drained (below 50%) to full.

They were getting over 10 to 15 years from their LA batteries, btw, because of the oversizing. But yeah, it's all load dependent. One can have as many batteries as they want. Nowhere does it say you must generate enough to charge the batteries in one day from empty.
Click to expand...
Andy has to wait for summer to fully charge his 100kWh.
 
Then again, I'm sure he doesn't pay for his batteries so ROI is not a thing.
 
wingnut771 said:
Then again, I'm sure he doesn't pay for his batteries so ROI is not a thing.
Click to expand...
Yeah, ROI is always a factor with this stuff. I am only adding upgrades up to the cost of the fixed charges from Citipower. If their fixed charges are 2k, for example, then I will budget for myself 24k that year for upgrades (if needed) since I don't pay them anymore.

So my next upgrade, even though I won't be staying at the house anymore, will be next year. I will add an additional 5kWh battery for 12k give or take, on the Omnivolt.

Won't spend anymore till something dies thereafter.
 
denmendez65 said:
Yeah, ROI is always a factor with this stuff. I am only adding upgrades up to the cost of the fixed charges from Citipower. If their fixed charges are 2k, for example, then I will budget for myself 24k that year for upgrades (if needed) since I don't pay them anymore.

So my next upgrade, even though I won't be staying at the house anymore, will be next year. I will add an additional 5kWh battery for 12k give or take, on the Omnivolt.

Won't spend anymore till something dies thereafter.
Click to expand...
Yeah, Pretoria and Durban have no fixed charges. Use 1 unit, pay 1 unit. Use 1000 units, pay 1000 units. Well in Durban at least. We don't have tiered billing.
 
Had a look at my cell voltages. All 16 cells are within 0.001V of each other. I don't think it can get better than this.
 
Self consumption is around 65 watts. Considering the sun is out between 8 and 4 that’s bad. 16 hours is about 1kWh of self drain. So only 3kWh really usable since it turns off at 20%
 
denmendez65 said:
Self consumption is around 65 watts. Considering the sun is out between 8 and 4 that’s bad. 16 hours is about 1kWh of self drain. So only 3kWh really usable since it turns off at 20%
Click to expand...
Makes me wonder if parallel inverters are worth it. People add 2 or 3 and each one is pulling 60 plus watts. Not worth it.
 
denmendez65 said:
Battery was at 98%. At the moment it’s at 3322mV or 84%
Click to expand...
Cell voltage only starts peaking above 3.45+V. I don't know what 98% means. You can only check cell deviation above 55.2V.

If you told me the cells are 0.001V apart at 58.4V (3.65V) then I would say its perfectly top balanced and the balancer is a good one.

3.32V is in the flat part of the curve. This is a meaningless voltage to check cell balance.
 
You must log in or register to reply here.
Back
Top
Sign up to the MyBroadband newsletter
X