Alternator and LiFePo battery question

Duty cycle is usually 1/3

Example 120 amp alternator--continuous load 40 amps.

I don’t use my TV to recharge my TT Lithium battery.

A typical automotive alternator can NOT properly charge a LiFePO4 battery. The only way to properly get a full charge LiFePO4 battery from an automotive alternator is use a DC-DC charger.

I would run 50% maybe 60% however that is total draw not just battery charging.

Don’t need a “proper” charge with LFP like is needed with lead-acid. Just get it close to 14 volts and it is charged.

I have a Redarc 40 amp DC to DC charger but apparently there is a solenoid that sends current from my alternator to the house battery when the ignition is on. I was unaware of this when my mechanic installed the charger. I just finished a 1500 mile road trip and was seeing a lot more than 40 amps on my shunt while driving. Fortunately I have a very robust alternator. I just found out about this solenoid so I will try and straighten it out so only the DC to DC charger is charging the battery.

pianotuna wrote:
Duty cycle is usually 1/3

Example 120 amp alternator--continuous load 40 amps.

Don - Is your rating what you feel a standard gas engine alternator should be capable of? I ask because I have Leece Neville 165 amp heavy duty alternators on a lot of equipment with diesel engines Nodwells and Tucker Snocats). 33% of 165 amps would be about 55 amps. When running them in the late fall or winter with all of the lights, heaters and engine fans on, I can easily pull 90 to 100 amps. If I'm using the electric winches, I'll run more than that. I haven't had an alternator fail yet, but your post made me curious.

Bill

Trackrig wrote:

pianotuna wrote:
Duty cycle is usually 1/3

Example 120 amp alternator--continuous load 40 amps.

Don - Is your rating what you feel a standard gas engine alternator should be capable of? I ask because I have Leece Neville 165 amp heavy duty alternators on a lot of equipment with diesel engines Nodwells and Tucker Snocats). 33% of 165 amps would be about 55 amps. When running them in the late fall or winter with all of the lights, heaters and engine fans on, I can easily pull 90 to 100 amps. If I'm using the electric winches, I'll run more than that. I haven't had an alternator fail yet, but your post made me curious.

Bill

It is for the Ford alternator on the E-450. Full rated output is 130 amps. Your alternator is far more robust.

I believe Mexicowanderer may have designed the Ford 130 amp unit.

That said, I did get peak loads of greater than 70 amps as I have dual charging paths with 50 amp self resetting circuit breakers. The meter would not go higher than 70--but the breakers would switch off and on.

I'm still on the OEM alternator. On a cold winter night, with the dash heater full on with the headlights, the "house" bank will send power back to the engine. Even so the fan ran slow.

I'm planning on adding a 20 amp dc to DC unit and hope to do that this summer, after I get the SiO2 batteries that I've been wanting for so long.

Teleman wrote:
I have a Redarc 40 amp DC to DC charger but apparently there is a solenoid that sends current from my alternator to the house battery when the ignition is on. I was unaware of this when my mechanic installed the charger. I just finished a 1500 mile road trip and was seeing a lot more than 40 amps on my shunt while driving. Fortunately I have a very robust alternator. I just found out about this solenoid so I will try and straighten it out so only the DC to DC charger is charging the battery.

Not clear how it was done from that. If part of the plan was to isolate the LFP from the alternator in case of way high draw from low SOC LFP (which is in dispute how much of a threat that is, but let's say it is valid for now) then leaving the OEM charging in place was wrong.

Next, the DC-DC itself will draw more than its 40 amps output as its input. Depending on the wiring from engine batt to DC-DC, if long and thin, could be 60 amps. If short and fat could be 45 amps.

So you need to pick the DC-DC output amps size to go with what your alternator can do, which depends on the input amps that you can only guess at.

If the amps are too high you could perhaps fatten that wiring to bring it within spec, or else before buying the DC-DC just assume 50% higher input over the output amps and match that to the alternator amps

BFL13 wrote:

Teleman wrote:
I have a Redarc 40 amp DC to DC charger but apparently there is a solenoid that sends current from my alternator to the house battery when the ignition is on. I was unaware of this when my mechanic installed the charger. I just finished a 1500 mile road trip and was seeing a lot more than 40 amps on my shunt while driving. Fortunately I have a very robust alternator. I just found out about this solenoid so I will try and straighten it out so only the DC to DC charger is charging the battery.

Not clear how it was done from that. If part of the plan was to isolate the LFP from the alternator in case of way high draw from low SOC LFP (which is in dispute how much of a threat that is, but let's say it is valid for now) then leaving the OEM charging in place was wrong.

Next, the DC-DC itself will draw more than its 40 amps output as its input. Depending on the wiring from engine batt to DC-DC, if long and thin, could be 60 amps. If short and fat could be 45 amps.

So you need to pick the DC-DC output amps size to go with what your alternator can do, which depends on the input amps that you can only guess at.

If the amps are too high you could perhaps fatten that wiring to bring it within spec, or else before buying the DC-DC just assume 50% higher input over the output amps and match that to the alternator amps

It was an oversight. I was unaware of the solenoid that connected the alternator to the house battery. Obviously my alternator survived the high current draw which topped 100 amps at one point. The DC to DC charger is very close to both batteries with 6 ga cables recommended by Redarc for their length so that is not a problem.

One thing with the DC-DC is you can set its output voltage and do the same with your solar controller's to get them about the same so they add their amps while you are driving.

With ordinary alternator charging in newer vehicles, the alternator voltage gets lower than the solar's, and you mostly only see what the solar is doing.