LiFePO4 battery & no alternator

[bubruins]

With the decreasing cost and improved performance of lithium iron phosphate batteries I'm surprised we don't see more builds using only a lithium battery and no alternator. My plan at this moment is to run a 12v 200ah lifepo4 and no alternator on the lakester, charging it overnight. It seems like it would reduce complexity and give ever so slightly less parasitic drag on the drivetrain. Is there any reason not to do this?

[SPARKY]

not at all  I would have dual switchable systems as a back up  also depends on your systems requirements

[sabat]

Just be double sure you have enough juice to keep your fuel pump going at the big end.

[Mike Borders]

We have extensive experience running a zero-loss system which you are interested in.  We used it on our 8-Record Roadster and are currently using it on our new F/BFMR Roadster.  Shoot me a PM and I'll be happy to discuss it with you.

Mike

[bubruins]

DM sent. Thanks in advance Mike!

[1leg]

With todays modern electronic ignition and EFI we have found that everything runs just a little bit better with a alt. putting out 13.8-14v.

If you are running a magneto and mechanical fuel injection or carb you might be fine. You may want to look at a 16v system alot of drag racer use it without a alt.

[Mike Borders]

Steven, PM sent.  M

[deepindebt]

We run no alternator, mechanical injection and MSD, we went from two 12 volt to one 16 volt, non lithium and its a game changer

[bubruins]

After some back and forth with Mike Borders I did more research about IGN1A coils. This tech article by haltech has a great table about coil power replenishment at different voltages. https://support.haltech.com/portal/en/kb/articles/ign-1a-ignition-coils

It looks like most lifepo4 batteries have a 12.8 nominal volts or basically 50% charge. 100% charge is 13.6v. There will be some transmission losses in the length and gauge of cable, but it seems like the coils are happy at anything above 12.0v. It'll be interesting to see if a 12v 200a battery can maintain that while also seeing other loads.

In my circumstance 6x IGN1A coils could draw a max of 90 amps at peak rpm.
2x davies Craig 150 electric water pumps could max out at 20 amps peak.
1x electriconic wastegate can draw 20 amps peak, 5 continously
1x drive by wire throttle body 10 amps
1x walboro 255 priming fuel pump draws 10 amps.
1x standalone pcm is 1 amp
In total that 151 amps might be a lot for a 12v 100ah battery to maintain voltage at, though it could possibly provide it for 30 seconds. I think the safer route for me will be a 12v 200ah lifepo4 to have more rated capacity and overhead not creating voltage loss while providing power. Fortunately the lakester has a perfect place for that size battery. I plan to run a hybrid electric priming pump, but majority mechanical fuel pump to ease in regulation, and this appears may also help keep max battery requirements in the realm of reason. Am I missing anything?

[sabat]

Just so I'm clear on the tradeoffs, what are the drawbacks of running an alternator?

[deepindebt]

HP loss! Every extra thing spun by the engine is a HP eater.

[sabat]

Do you have a sense of how much? 5-10hp?

[deepindebt]

Good question, i do not, but i bet your guess is close and if you add water pumps, fuel pumps ect, it adds up!

[1leg]

The standard guess is about 1hp per 25amps.

A 50-70amp will use around 2-3 HP, For me in a 12volt system I wouldn't run without a alternator. if you are running EFI.

We get so few runs in this sport, why would you risk an aborted run because you didn't have enough battery.

[Mike Borders]

The standard guess is about 1hp per 25amps.

A 50-70amp will use around 2-3 HP, For me in a 12volt system I wouldn't run without a alternator. if you are running EFI.

We get so few runs in this sport, why would you risk an aborted run because you didn't have enough battery.

We've been doing it for years, and there is no danger of that if you prep the car properly (which we do anyway).  Less parts, less space needed, and we even ran two batteries in parallel for the extra weight plus the extra capacity, and low voltage was never a problem.  Our results speak for themselves.