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Registered Member #509
Joined: Sat Feb 10 2007, 07:02AM
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Posts: 329
Hello all, I'm in the planning steps of a project which is going to use a few LiFePO4 battery packs, and like any good lithium pack, cell balancing is needed, but using 10AH cells, simple shunt balancing is either painfully slow, or dissipates an annoying amount of power.
I found this article which seems like a good principal
However rather than for purely balancing, I'd like to use the transformer that would be required for balancing for charging also. My device will have a 48V bus internally, normally generated by DC-DC converters powered by said batteries, but when its on an external power source, and idle, I'd like to be able to charge the batteries off the 48V bus, which would only be 144W with a 10A charging current, which doesnt seem too excessive to make.
The gate drive transfomer winding article in the 4HV wiki seem relevant with the math and formulas I'll need for the transformer, However I have a few questions.
The article says this operates as a flyback converter, so the core is going to need to store the energy, which means I'm going to need to use ferrite cores? (as opposed to iron powdered?)
For effiency purposes would a forward converter be more desirable, or more suited to this application? I'm going to be winding a transfomer either way, so I might as well go with what works best. I'm not too familiar with forward converters, but seems like a decent start. What sort of core materials/size/frequency would be desireable for a forward converter? I'm guessing I'd be shooting for the 25k-100khz reigion to keep switching losses low and iron losses lowish too?
I'd like to use a PIC with PWM module for the gate drive of the primary, and a micropower comparitor + mosfet for cutting off the charging current when the cell reaches 3.6v (CV phase of charging doesnt gain much capacity LiFe cells iirc.)
Does it looks like I'm barking up the right tree for this? Thanks for any thoughts/comments.
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Winding a battery charging/balancing transfomer.
