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

[deckofficer]

I goofed. New power supplies and chargers are using switching instead of heavy transformers. My charger only weighs 8 lbs, rated at 1200 watts. I have a switching power supply for my HF SSB and at 30 amps only weighs maybe 5 lbs. I also have a 75 amp 12 VDC supply for the HF amp, it uses a transformer and weighs 30 lbs.

[deckofficer]

Originally Posted by diugo

I like the idea of a good crimp, followed by tight heat shrink to keep moisture out. Soldering large cables is a lot of extra work!

I'm changing my mind after soldering up my parallel jumpers, and will finally embrace crimping over soldering and pony up the $250 for a crimper.

[diugo]

Bob, I got my cables crimped from some guy named genuinedealz on eBay, you buy the cable and lugs from his store, and for a dollar he will crimp the cable. No need to buy a $250 crimper.

[deckofficer]

Originally Posted by diugo

Bob, I got my cables crimped from some guy named genuinedealz on eBay, you buy the cable and lugs from his store, and for a dollar he will crimp the cable. No need to buy a $250 crimper.

That is a good reference, thanks. I've had crimping done for me on some of my EV projects, but for the boat I'll buy them. Nice way to warm up a new anchorage to your arrival, when someone puts the call out, having cables that have fried out of their lugs, your equipped to help if you have crimpers. Just a good tool to have onboard with so many cruisers having high current demands from their inverters in our nasty, salty world.

[catakate]

Originally Posted by deckofficer

Nice way to warm up a new anchorage to your arrival, when someone puts the call out, having cables that have fried out of their lugs, your equipped to help if you have crimpers. Just a good tool to have onboard with so many cruisers having high current demands from their inverters in our nasty, salty world.

Yet another good idea for when I'll hit the Med.

[ebaugh]

Awhile back we we looking at how to separate charging and discharging paths...especially inverter chargers. Anyone see a problem with this circuit?

[mrm]

What diode current ratings you propose?

Say, a charge solenoid opens and you use windlass or a bow thruster...

[ebaugh]

They would have to be battery isolator sized for the largest of your charge/discharge current expectations.

[diugo]

Originally Posted by ebaugh

Awhile back we we looking at how to separate charging and discharging paths...especially inverter chargers. Anyone see a problem with this circuit?

When an inductive load opens, it usually makes more sense to put the diode across the load (parallel to it, wired "backward") rather than the switch/solenoid. That way, the residual energy in the inductor is absorbed only by the diode, not the battery and everything wired to it.

[ebaugh]

These are not for the coils. The intent is to have one path to the battery, but be able to either stop charge or stop discharge individually. That way if a charger hits HVC, the loads remain connected. There would be a slight voltage drop to the loads, but the lights remain on.

I'm not sure how important it is on the LVC side to keep the charger connected. So you could eliminate one of the diode/rectifiers. But it would work both ways if you needed it.

[mrm]

Originally Posted by ebaugh

They would have to be battery isolator sized for the largest of your charge/discharge current expectations.

Technically, no problem, for example:

Vishay VSMD400AW60 | VSMD400AW60

or

Powerex LS410860 | LS410860

Only one of them has to be sized for above max. expected load current. The other has to be rated above max. possible charging current.

Heat will be a consideration. For example, 1.2V drop @ 300A will generate 360W of heat to be dissipated. Probably unrealistic and unnecessary to design for continuous loads of that magnitude though. More likely scenario is a passive radiator and a note to skipper 'use bow thruster sparingly when HVC active'.

[diugo]

I think, in the event of high voltage, it may be more practical to simply send a signal to the charger telling it to stop---avoiding that solenoid and diode altogether.

However, in the event of low voltage, your good idea---the solenoid and antiparallel diode---would disconnect the major loads, but still keep what might be the only charging source connected.

[ebaugh]

Originally Posted by diugo

I think, in the event of high voltage, it may be more practical to simply send a signal to the charger telling it to stop---avoiding that solenoid and diode altogether.

However, in the event of low voltage, your good idea---the solenoid and antiparallel diode---would disconnect the major loads, but still keep what might be the only charging source connected.

Good luck figuring out which charge source...solar, alternator, AC charger is causing high voltage event...and then finding a marine product with a signal based switch in each category. In normal operation, this event is much more likely than a low voltage event.

In a low voltage event, most likely there are no charging sources present, except perhaps solar or wind.

[diugo]

Originally Posted by ebaugh

Good luck figuring out which charge source...solar, alternator, AC charger is causing high voltage event...and then finding a marine product with a signal based switch in each category.

Nevertheless, it (signaling all charge sources to stop) is the preferred course of action. Otherwise your charge disconnect solenoid suddenly leaves multiple charging sources, all connected to each other, without a battery to take the load.

In a low voltage event, most likely there are no charging sources present

Then I am curious as to how you plan to correct the low voltage event without a charging source present?

[ebaugh]

Originally Posted by diugo

Nevertheless, it (signaling all charge sources to stop) is the preferred course of action. Otherwise your charge disconnect solenoid suddenly leaves multiple charging sources, all connected to each other, without a battery to take the load.

Then I am curious as to how you plan to correct the low voltage event without a charging source present?

Most charging sources are not too concerned about a load, the exception being an alternator. That would need to have the field pass through the aux contacts on a Tyco EV200 or some other mechanism to turn off the alternator.

The low voltage event would have to be cleared manually. I have a bypass switch on my installation that forces the solenoid to close, then charge, then reset the BMS. This bypass is intended only for manual observed use. But if you want it both ways, it just needs 2 diode rectifiers as shown.

Much depends on the battery monitor or BMS used and the specifics of other systems in the boat.