Classic retrofit A/C and a Lifepo4 battery?

[Duc Hunter]

Well it's time to resolve the battery in my Rat Rod, after a year in the body shop the current battery is not happy. I have been considering moving to LifePo4 battery’s for a while. The weight is nice, the longevity is also nice. I have the CR A/C though, along with their alternator (964 motor). I have heard that Lifepo4 batteries are not good in 4WD applications like my Jeep if you are winching, as a winch draws so much current that the battery’s short circuit protection will kick in. My winch can draw up to 400 amps on a max pull. The A/c wont get near that, but I think can easily draw 100 amps on its own.

I thought I would ask the question here and see if Jonny might reply, for the sake of al the CR customers out here.

And before someone says they would never you a lithium, battery so the car doesn’t catch fire….. Lifepo4 battery’s no more a fire hazard than AGM;s etc….as they are very different from regular lithium batteries.

[MeteorMetal86]

You can’t use a LifePO4 as a main battery in a car as when it nears 100% state of charge you need to stop charging and a generator won’t like being disconnected from the battery. The Li battery then needs to be used… or better is to never get near full and limit the voltage at 90% or so state of charge and that required precise voltage control. You need a small ”normal” battery in parallell and then either a disconnect that turns on and off the Li battery or a dc-dc charger. Very common setup in boats and I built one myself a few years back. Since the AC only runs when engine is on… all it really needs is a powerful generator. The battery is only for small balancing needs rather than storage, which is what an Li battery is good for, and thus the battery can be traditional.

Maybe I’m missing the point, others might have a different view

[andino]

Lithium ion and iron phosphate batteries have built in BMS’ that manage the power input and these batteries OP is talking about are hopefully specifically designed for use in a vehicle charged using an alternator.

OP, the battery you’re looking at should have load specifications that can guide you on whether 100A constant load will be suitable for the bms and cells inside. Depending on the size of battery you plan to use, you’ll find different speculations for what loads the battery can take.

[Jonny H]

I have been running a small LiFePO4 battery in our 993 dev mule for several years now. As per the above, most now have the BMS built in so there is no problem with charging from the alternator.

[Duc Hunter]

Originally Posted by Jonny H

I have been running a small LiFePO4 battery in our 993 dev mule for several years now. As per the above, most now have the BMS built in so there is no problem with charging from the alternator.

Jonny, why thank you. That answers that for me. I will prob run close to a H6, H7 size. I have never liked the terminals on the outboard side of the battery though, the positive is just too close to the inner wall of the frunk, etc. Not hard to change.

[PeteKz]

I'll go Jonny and andino one further: ALL vehicle batteries have BMS built in. They must have it just to contend with the varying voltages of the vehicle's charging system. I have opened up a motorcycle LiFePO battery, and, yes, it had circuitry inside the case. In fact, it had a lot of extra space inside the case.

Some vehicle lithium batteries are half the size of a conventional battery, and 20-25% of the weight. Good reasons to use one if you are trying to minimize weight and/or relocate the battery to a smaller space; say, inside the smugglers box.

[MeteorMetal86]

You’re all making good points about the BMS, absolutely required for automotive use. I wasn’t aware there was such a good application for LiFePO4 in our old vehicles, didn’t really cross my mind as we rarely need to store much energy, but the benefit isn’t storage, it’s weight and size, duh.

[47silver]

If constant draw is 100amp and peak load is 400 amp, you have 2 considerations:
Constant load with lights, ac, radio, engine management, add it up. By an alternator that gives a minimum 50% duty cycle, or buy a couple spares as auto alternators are not designed to run 100% of the time.
Your battery has to be able to handle the 400 amp surge, i would think that starting amps would be equivalent. Your winch would draw that current for a short time, but if you are winching your jeep a hundred feet, your battery will probably be depletrd.

[Duc Hunter]

My car has Classic Retrofit’s (Jonny’s) 964 alternator that is capable of 240amps, but will only do about 120-150 (if memory serves) with the standard fan belt setup. I am moving to a serpentine belt to enable all 240 amps (not that I need it). As a result I do not foresee a situation where the alternator cannot keep up with the car’s load, except at idle with the A/C running at 90-100 amps while at the VERY LONG Florida stoplights (sometimes north of 2 minutes). Also, that situation only comes up after the car has been heat soaked, as once it cooled off the A/C is not running that hard to keep it cool. My hope is that a LifePo4 will be more tolerant of taking up some of that load, enabling me to run the car longer and higher loads at idle, while cooling the car off.

Part of the reason I want to do this is longevity of the batteries, as LifePo4 battery’s last a lot longer than AGM’s. I also think it’s just better to go with new technology when to price to get in is not that high. In my case nice AGM;s are ~$250-300, and nice LifePo4’s are $350.

Thank you for all the great commentary. I will report back when I get it in and sorted.

[47silver]

Is it necessary to use a new pulley system for the 240 amp alternator?
the mechanical compressor would seem to require higher load on the fan belt than the 240 amp alternator?

[wazzz]

240 ampères multiplied by 14 volts is 3360 watts. I think the mechanical compressor is using less than that power. Probably no more than a couple of hp, or ~ 1500 watts.

[47silver]

My understanding is that the original york compressors where well over 5 horspepower.
That is why when the compressor clutch engages the rpm’s decrease substantially unless the ac accelerator solenoid pushes the throttle open to accommodate the increased load.

[wazzz]

Can't speak about the York as I have a 3.2 equipped with the factory Nippon Denso 10P15C compressor. The idle speed doesn't vary when it engages thanks to the ICV, but also because of its moderate power draw.

[Duc Hunter]

Originally Posted by 47silver

Is it necessary to use a new pulley system for the 240 amp alternator?
the mechanical compressor would seem to require higher load on the fan belt than the 240 amp alternator?

Per Jonny & Co at Classic Retrofit they say yes, you can only get the full 240amp out of the alternator if you use a serpentine. I believe it says so on their site.