Headway LiFePO4 starter battery

[evm1024]

Currently my boat has a 700 AH LiFePO4 house bank along with an AGM start battery and SLA windless battery. I've picked up 8 Headway 8 AH cells to give them a try as a start battery.

These 38120HP cells are 8 AH cells and rated at 2000 cycles and a 15C discharge rate. I've seen a number of discharge rates spec'd including 200 amps for 30 seconds.

The first set I'm going to play with are 8 cells so I end up with 16 AH @ 13.2 volts and a 400 amp 30 second rate. It would be easy to increase the cell count to 12 or 24 to get 24 AH or 32 AH.

I note that 32 AH is roughly equal to 64 AH lead acid (at 50% capacity) and that my current AGM start battery is spec'd at 72 AH @ the 20 hour rate. Not too different even if they are apples and oranges.

Two aspects jump out at me to start with.

First is that the supplied bus bars are a bit wimpy for the demands of a start battery. Likely they could work fine but it is easy to double or triple them for greater conductor cross section.

The second is the needs of a BMS. Being that the house battery is LiFePO4 and that the charging system is set for the house battery the charging profile will be fine. A somewhat simplistic charge relay could be use to isolate the Headway cells from the charge system when not charging and when fully charged.

Given that this would be a dedicated start battery I would not expect it to become "fully" discharged and thus no LVD would be "needed". Of course Poo poo happens...

I think that the first test that i want to do is to wire the 8 cell battery up and then start the engine to get the peak amperage and total AH consumed per start.

Then just see how many starts that battery can do before pulling the SOC down to 20% or so. With repeated starts I could get a temp reading on the battery buss bars and thus get a feel for the sizing needs.

This photo shows the cell I have configured for top balancing. The battery measures about 6.5" x 6" x 3.25".

I'll also be looking at trying a larger battery made out of 16 of these cells for a replacement for the windless battery. (gotta finish the icebox rebuild first)

[Q Xopa]

Thanks for sharing. I'm watching with interest.

I have also been looking at doing a Windlass LFP batt. I've been thinking of the Fortune 25A cells. But the Headway 8A also look interesting.

I was thinking I would keep FLA for my Starter to help suck up any Alternator diode damaging surges in the event of a HVD. Doesn't sound like you consider this a issue?

[evm1024]

Originally Posted by Q Xopa

Thanks for sharing. I'm watching with interest.

I have also been looking at doing a Windlass LFP batt. I've been thinking of the Fortune 25A cells. But the Headway 8A also look interesting.

I was thinking I would keep FLA for my Starter to help suck up any Alternator diode damaging surges in the event of a HVD. Doesn't sound like you consider this a issue?

I'm only working on proof of concept at this time. The Headway cells provide a common platform that can be scaled to the application. How about just 4 cells at the input to your SSB for example (and 24 at your 12 volt windless).

I am not too concerned with HVD in general - there are diode protection devices (which I think are needed). HVD "should" shutdown your field current as part of the disconnect process. And should your alternator to battery cable disconnect you will need voltage clamping anyway regardless of your battery chemistry.

I've been toying with a bit of logic that implements a "charge enable" signal based on a number of inputs. Not ready for primetime.