Attempt to replace a 4.5Ah 12V Pb battery with LiFePO4 for a Profoto Acute B flash generator I have a detailed writeup here...
Previously I had used a Tenergy drop in Li replacement which worked for a few years but is reaching EOL as well as my Pb versions. It is no longer available.
I am looking to avoid building a Li pack from components and modify an existing pack to do the job by adding capacitor(s) parallel to the battery in order to reduce the peak current by at least 10A to prevent the PCB on the LiFePO4 from cutting out.
-Acute B 600 generator (load) outputs 600 joules -load is primarily large capacitor bank -load in turn discharges to circuit powering Xenon tube -Recycle time is under 2 sec -Pb Battery is rated 4.5Ah 12V -Approx Peak Draw is 30A -battery is fused at 40A (slow blow) -Attempt with [CTC LiFePO4] -failed: PCB cuts out at 22A and it did -Battery Box is 89mm x 69m x 106mm
-[Bienno stock cell:] 4.5AH LiFePO4 rated 4C peak (18A) -Bienno opt 2 6Ah LiFePO4 rated 4C peak (24A)
I don't have a true measurement of the peak draw, a figure of 30A was given to me by a repair tech.
Looking at a goal of reducing the 30A draw down below the trigger point for either Bienno LiFePO4 pack above noted, I calculated using C=Q/V respectively for the packs noted above.
- Q=12A/S V=15 C=0.8F - Q=8A/S V=15 C=0.5
In either case, I should be able to get the Pack and a pair of caps in Series or parallel depending on available values and build to fit existing battery box spec.
If someone would chime in on my calculations, it would be nice to know. I don't see where any additional circuitry is necessary on this, the generator only sees a source of V & A beyond it's input terminals.