That which one might assume, ain't necessarily so.

Results from my play time of using an automotive alternator to charge a 12 AH lithium deep cycle battery are below.

Results were not what I had expected.



Assumption being that the internal resistance of the battery is not changing (or does it?) is that as the lowered resistance allows greater current flow to the battery, that the voltage of the battery being charged is increasing. Resulting in less of a difference of potential between the power source voltage and the battery voltage.

Is this making any sense or am I off in the far left field?

 

Assumption being that the internal resistance of the battery is not changing (or does it?) is that as the lowered resistance allows greater current flow to the battery, that the voltage of the battery being charged is increasing. Resulting in less of a difference of potential between the power source voltage and the battery voltage.

Yes.
The higher the charging current, the higher the battery voltage, due to its internal resistance and the nature of the battery chemistry.

 

Is there a Battery Management System controlling the charging current to the battery?

 

Is there a Battery Management System controlling the charging current to the battery?

No.

 

using an automotive alternator to charge a 12 AH lithium deep cycle battery are below.

Is there a Battery Management System

No.

Keep a fire extinguisher near by. Lithium batteries need a carefully controlled charge profile. Ignore that and you could have a fire.

 

Is this a LiFePO₄ battery?
If so, it can be charged the same as a lead-acid battery, but the charging needs to be terminated when it is fully charged.
LiFePO₄ batteries do not tolerate trickle charging.

 

Yes to it being a LiFePO4 battery.

The BMS disconnects the power source when it is completely charged.

 

The BMS disconnects the power source when it is completely charged.

In post #4 you stated there was no battery management system (BMS).

 

Is there a Battery Management System

No.

The BMS disconnects the power source when it is completely charged.

Which is it? BMS? No BMS? We can't help you with accurate information if we don't have accurate information.

 

There is a BMS. It does not control current. Vary the current into the battery that is.

What it will do is stop current at some point.

 

If there was a way for the BMS to throttle the current to some specific amp value, to protect an alternator, that would solve the problem I am playing with.

 

If there was a way for the BMS to throttle the current to some specific amp value, to protect an alternator, that would solve the problem I am playing with.

Then an appropriate value series resistor should work for that.

 

Then an appropriate value series resistor should work for that.

That is what I am seeing.

 

There is a BMS. It does not control current.

How do you know it doesn't control current?

 

Good question. I am surmising that the BMS is not controlling current since if I change the voltage from the alternator the current changes accordingly. Only input charging control from the BMS according to the battery supplier is for high/low voltage, over current charging and low/high temperature charging.

 

over current charging

Isn't that controlling that current to avoid battery damage?

 

In a fashion yes. But any current below the maximum current does not seem to be controlled. That is the goal via the use of a resistor.

The concern is not with the battery. It is with the alternator. Some feel that running an alternator at high current flows are detrimental to the life of the alternator.

 

In a fashion yes. But any current below the maximum current does not seem to be controlled. That is the goal via the use of a resistor.

The concern is not with the battery. It is with the alternator. Some feel that running an alternator at high current flows are detrimental to the life of the alternator.

Never heard that.
If the alternator is running below its maximum current rating, there should be no significant effect on its life.

Who are these "some"?

 

Usually, alternators that are used for battery charging and also powering other loads are paired with a voltage regulator.
Consider that the common 55 amp MOPAR alternator, in 1969, when run with a solid battery connection and at quite high speeds, could produce almost 110 volts DC with a moderate load. Of course there was no claim that it would not eventually damage the alternator.

 

I am surmising that the BMS is not controlling current

It 100% does. A 100AH battery would charge at far more than 20A without input current limiting.