LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

[Lagoon4us]

Does the choice of running the charge from the Alternators through the existing lead acid start batteries exist or is the requirements of charge too different?

Don't electric vehicles have a freewheeling charger in them to give some back on hills, coasting etc?

[Lagoon4us]

When a Lithium goes into an over or under voltage situation and the alarm has gone off, what timing do you have to do a manual disconnect before damage is done?

[mcarling]

Originally Posted by Lagoon4us

Does the choice of running the charge from the Alternators through the existing lead acid start batteries exist or is the requirements of charge too different?

I guess you mean putting lead acid batteries in parallel to act as a capacitor. I would not connect lead acid and lithium phosphate batteries in parallel.

Originally Posted by Lagoon4us

Don't electric vehicles have a freewheeling charger in them to give some back on hills, coasting etc?

I guess you mean regenerative charging.

Originally Posted by Lagoon4us

When a Lithium goes into an over or under voltage situation and the alarm has gone off, what timing do you have to do a manual disconnect before damage is done?

Depends on the voltage thresholds at which the alarms are set and the charge / discharge rate (as a function of C).

[Lagoon4us]

Would the solution be then to have two lithium banks so the one shuts itself down leaving the other to absorb the charge?

[deckofficer]

I have regenerative braking on my electric car. It is two stage, both are adjustable. Stage one is just lifting off the "go" pedal, stage two is triggered by the brake lights coming on. Unless someone forces me to panic stop, I hardly ever use my friction brakes.

[mcarling]

Originally Posted by Lagoon4us

Would the solution be then to have two lithium banks so the one shuts itself down leaving the other to absorb the charge?

I wouldn't. I think an audible alarm should be sufficient, but separate disconnection of the loads (and charging sources) upon low (or high) voltage would be fine. I'm just arguing against disconnecting both the loads and the charging sources from the batteries at the same time while leaving the charging sources connected to the loads.

[deckofficer]

Originally Posted by Lagoon4us

Would the solution be then to have two lithium banks so the one shuts itself down leaving the other to absorb the charge?

If your concerned about an overcharge while away from the boat for an extended time period, the solar charge controller will take care of that and disable the wind turbine. If your concerned about overcharge on the hook because your daily usage is less than what you collect via wind and solar, well lucky you. If this is the case, I hate to waste energy, so how about using the high level sense circuit to energize a relay that has contacts rated for an electric hot water heating element?

[Lagoon4us]

Yep i see where your coming from just trying to find a workable solution for us.

If we leave the boat and go to town for the day, then the only charging will be via Solar and or Shore power. IF the sensor shuts the pack down no harm should be done as the MPPT will cope and i would think the charger should as the scenario would be no different to either switching the battery isolator off whilst the charger was running and/or a fuse blowing, the effect would/should be the same.

BUT if we are ashore no electronics would be activated so a surge would/should not harm. The only items on would be bilge circuit, water pumps and cheapish security sensors.

It would almost be best to run the mains isolated to the Lithiums, perhaps a second high output alternator (Balmar) that can be manually controlled when required? So there's just no risk of losing boat handling.

[Lagoon4us]

Yes the Morningstar can do that, we are taking it slowly preparing everything for the installation so unsure of demands for now, a 12volt element for the Quick boiler is a definite. Cheers

[ebaugh]

Frank,

Even if you add a second alternator, if something disconnects it suddenly from from the lithium, and it's only battery, the alternator won't be happy unless the field is also disconnected at the same time. In fact, the field may need to be disconnected a second or two before the battery, Im not sure, someone will know.

This is why I paralleled AGM and my Lithium. If the alternator is the only concern for a disconnect, you can use the ignition on circuit to activate a solenoid to parallel the battery. I don't think there is any reason that can't be done with a lead acid start battery. The only drawback is the lead acid might not fully charge on a Li charge voltage. If there is any other technical reason this wont work OK, I'd like to hear it.

As previously mentioned, check you shore power charger for compatibility if the opportunity exists for it to power your house loads in a disconnect situation.

[Maine Sail]

Originally Posted by mcarling

My biggest concern with the setup described would be the possibility of the alternator being directly connected to any electronics without the capacitance of the battery bank. If you have an MPPT for the solar, that should be safe. The battery charger might also fry electronics without a battery connected, but it depends on the charger (some are fine).

The charge sources would ideally be separated by a charging and load bus. This ensures that when there is an HVE the disconnect of any charging devices does not directly allow them to be connected to other "loads".

[hellosailor]

e-
"the field may need to be disconnected a second or two before the battery,"
There's no universal answer. Some alternators can run without damage. Most will take damage, but the damage is from overheating, so ambient temperature, airflow, all that good stuff makes the time it takes for damage variable. It won't be instant so before/after is not critical. From what I've been told it can be a matter of 30 seconds before the alternator is toast, so the disconnect should be as fast as possible. Simply switching the load (i.e. throwing a battery switch) isn't supposed to cause damage, from what I was told. Leaving it flipped, disconnected, will cause the damage fast enough.
Bottom line is that you either have to know your equipment intimately, or assume it will be damaged and just "don't do that".

[daddle]

Opening the field connection of an alternator will instantly reduce its output to some very small current. The same cannot be said for opening the sense wire of a regulator, either internal or external. It that case the alternator may go to full power or to low power depending on the design.

[Lagoon4us]

Apologies wrong link this is correct one :-http://www.gsl.com.au/tl_files/pdf-solar-products/MPPT30-2L.pdf

[goboatingnow]

Originally Posted by hellosailor

e-
"the field may need to be disconnected a second or two before the battery,"
There's no universal answer. Some alternators can run without damage. Most will take damage, but the damage is from overheating, so ambient temperature, airflow, all that good stuff makes the time it takes for damage variable. It won't be instant so before/after is not critical. From what I've been told it can be a matter of 30 seconds before the alternator is toast, so the disconnect should be as fast as possible. Simply switching the load (i.e. throwing a battery switch) isn't supposed to cause damage, from what I was told. Leaving it flipped, disconnected, will cause the damage fast enough.
Bottom line is that you either have to know your equipment intimately, or assume it will be damaged and just "don't do that".

There damage to alternators is from its inductance. Reducing the current to zero in an inductor causes the voltage to rise towards infinity. In practice many hundreds of volts. This usually destroys the rectifier diodes. In car type alternators the voltage can reach about 150v and decays in about 400ms

In fact many alternators can now handle load dumping. Anyway either switch the field , or make before break in a power resistor or other load. No need to parallel AGMs in , there far less expensive ways

Many alternators today actually can handle such load dumps. In fact European cars must survive load dumps to IEC 7637

Dave