Alternator Charging LIFePO4

[lblt]

I am pretty sure charging a lifepo4 bank with my rig's alternator will quickly overheat and kill it. Can I safely and effectively limit the current demand and thus alternator temperature by just running smaller wire back to the house battery? Any gotchas with doing this? I can't afford the fancy regulator's that the boat people use for alternator charging lifepo4 banks

thanks

 

[SternWake]

Not knowing the range of voltage what your vehicle's voltage regulator allows is an issue.

Just do not idle to recharge, or just drive slow, and the alternator should stay below 220F.

I have alternator temperature data in my van showing Idling with a hot engine and maxed out alternator has the stator temp rising quickly to danger zone. At 65MPH, more amps much more airflow, and have yet to see more than 135F after half a mile at 65mph.

 

[lblt]

Not knowing the range of voltage what your vehicle's voltage regulator allows is an issue.

Just do not idle to recharge, or just drive slow, and the alternator should stay below 220F.

I have alternator temperature data in my van showing Idling with a hot engine and maxed out alternator has the stator temp rising quickly to danger zone.  At 65MPH, more amps much more airflow, and have yet to see more than 135F after half a mile at 65mph.

Thanks for the response. Its a 70amp alternator in a 1980's toyota van. They can get hot in the engine compartment under the driver seat. Not sure how to go about finding the voltage range of the regulator? thanks

 

[SternWake]

Attach voltmeter where it can be seen when driving. Take note of the voltage range it allows in different situations with an already fully charged battery. The max voltage seen in this situation should be the maximum allowed.

I think it would be very wise to add a thermocouple to your alternator and disconnect Lifepo4 house bank if it reaches 200F.

I use this handheld meter:
https://www.amazon.com/upHere-4-Cha...1487216434&sr=8-5&keywords=K+type+thermometer

And used arctic silver thermal epoxy to glue it to alternator stator(casing)

Why guess? Before I added the thermocouples, I guessed, and was very wrong about alternator and Battery temperature.

 

[John61CT]

Sorry to be that guy, but if you "can't afford" the ancillary hardware to properly charge and look after a LFP bank, you probably won't get the longevity that is required to make it a sensible investment.

Why do you think you need LFP?

Maybe better to just buy Sam's or Costco 6v at 80% cheaper per 100AH, they're also much more forgiving of varying charging voltages.

Or Firefly Oasis if you really need to PSOC abuse your bank, yes also expensive up front, but at least charging voltages more in line with normal lead parameters.

That said, another approach for LFP might be to "filter" your charge sources through a cheaper lead bank, use that as your Starter/reserve, and charge the LFP House bank precisely using an appropriate DC-DC battery to battery charger.

Also not cheap, depending on the Amps capacity, but that one DCDC unit can convert "rough charging" (through a cheap lead battery) from any source, shore power, solar charger, move to another alt or vehicle, etc without having to spend money on that custom voltage, staged charging intelligence from every source.

 

[blars]

Using undersized wire to limit current produces heat, wasting power. Alternators set for lead-acid can produce higher voltage than is good for LiFePO4, but most voltage regulators will cut it back after a short time charging the starter battery. You need to know the length and size of the wire to calculate it's resistance, then the voltage difference to calculate the current. Make sure you are not exceeding the maximum current carrying capacity for the wire.

In my setup, the small wire used by my RV manufacturer is limiting the alternator charging, but I plan on eliminating this as it can get my LiFePO4 up to 14.2v when it was already fully charged. Long drives could be a problem overcharging the LiFePO4, but I have not seen it. I'm also considering using a DC-DC converter to trickle charge my starter battery from my solar. (I sometimes need to use a battery charger on an inverter to charge the starter battery.)

 

[John61CT]

Using undersized wire to limit current produces heat, wasting power.

Not to mention potentially burning the whole rig down.

Really, saving pennies for a nice drop-in HO alt regulated by an MC-614 that lets you spec a custom voltage setpoint is a much better idea.

But IMO not as good on a budget as a nice big Sterling B2B if the LFP bank is large.

Might get away for a small bank with a couple hundred for one of the smaller non-customizable units like ABR Sidewinder, but for me I would never charge my LFP over 13.8V (3.45vpc).

And too low a charge rate relative to the bank capacity will be not only slow but likely bad for longevity.

 

[frater secessus]

And too low a charge rate relative to the bank capacity will be not only slow but likely bad for longevity.

LFP does not suffer from either slow charging or a partial charge state that could result from it.