I have a MPPT 75|10 solar charger and when using it on the default getting to charge a 18650 24v pack i can get 100 to 175 watts at my battery. But when I select the LiFePo4 setting for the battery it drops the watts down to 30 to 45. Is it okay to use the default GEL battery setting for the 18650 pack or do i need to use the LiFePo4 setting and if so why does the watts decrease on that setting.
Hi N. This is like a loaded question. Your "18650" is simply a cell size, and nobody can help you without *much* more information.
And the first question would be 'what BMS do you have?'.
Thanks John,
Just to be clear on the subject. I am referring to the watts coming from the solar panel to the solar charger then inputting to the battery. The BMS i am using is from a Jehu 18650 kit.
https://kit.com/jehu/jehu-s-diy-powerwall-pcb-project
Thanks,
Nathan
Ok, so it seems this is a 'diy' system, to at least some degree.
What you need to know is what the bms expects, along with what the batts expect. Your little 75/10 is configurable via the onboard algorithms, which might do, but you could also set specifics if you can determine what you want.
From here, we don't even know what your nominal system V is, nor what batts you're using. Presumably they're Li-ions?, which can be quite dangerous if not treated correctly.
Perhaps go back to your supplier for the deeper info you seek, and ask here how to set your Victron kit to achieve that?
Sorry if I seem to be fobbing you off, but it's likely your supplier is the best to ask about this issue.
Presumably they're Li-ions?, which can be quite dangerous if not treated correctly.
Assuming a typical 10Wh 18650, approximately 28 of them have rated energy (which is less than total energy) equivalent to 1 stick of dynamite. The Li chemistry can't release the energy quite as quickly as dynamite, but it can do it extremely quickly in certain failure modes (which can be triggered by mishandling).
So, yeah, treat loose Li cells with great care. They are significantly more dangerous than the 1.5V AA cells that people are used to abusing.
Clearly I think you should stick with store bought battery systems. You should be aware that the term Li Ion is like saying all Kleenex and Q tips are the same.
The charging profile of a LiFePO4 chemistry is different than the LiNiCoAlO2 of the Panasonic 18650 cell. Not to mention that who knows what the chemistry is of Chinese 18650 cells. 18650 only identifies the physical dimensions of the cell.
It also depends on your physical construction of your battery cell on the number of cells in parallel and in series. So you really have not provided the needed information to answer your question.
I would safely say the make up of your battery consisting of a handfull of 18650 cells requires a custom charge profile to keep them from over charging and protect you from fire or explosion.
Hopefully you have a data sheet for the type of cells you are using so you can research and do the math to determine a safe charge profile. The nice thing about Victron MPPTs is you can program them for custom charge profiles.
So to answer your basic question, no you can not use the Lead Acid Gel charge profile to charge your 24 volt 18650 constructed battery.
