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

[hellosailor]

KVB-
"getting about 10% more out of your pack.
However, why this would make sense in a marine application escapes me... "
You've half-answered your own question. If that approach allows someone to get 10% more capacity out of a battery/bank, they can either spend the extra bucks, or buy 10% more batteries--if they've got the room for them--and they need the extra capacity.
Assuming the claim is true, no matter how much room you have for batteries, "room" is always limited in a boat.

I wonder if anyone at Boeing is wondering, just how thick an armored titanium battery box would have to be...Or why they don't ask the FCC for a waiver allowing them to swap in LiFEPO4 battery systems to get those planes back in the air.

[mcarling]

Originally Posted by K_V_B

It looks like they put a DC/DC convertor on every cell (that's the only reason I can think of for the small transformers).

DC-DC converters use power electronics, not transformers. Transformers only work with AC.

[mbianka]

Originally Posted by K_V_B

It looks like they put a DC/DC convertor on every cell (that's the only reason I can think of for the small transformers). So they have what they call "active balancing".
(I got that from here: Li-Ion BMS - Lithium-Ion Battery Management Systems and large battery packs). This supposedly actively shuffles energy between the cells to keep them at the same SOC, thus enabling getting about 10% more out of your pack.
However, why this would make sense in a marine application escapes me...

A good point. The complexity and monitoring of these battery banks is what gives me pause. Things like additional BMS circuitry required to keep the cells balanced just scares me that it creates additional points of failure and additional $ replacement costs. Especially on boats that might frequently be exposed to lightning storms. Where some of these components might fail from induced currents in the wires and circuits from nearby strikes.
Until I see there is more of a track record on boats of several years of trouble free operation I'm on staying on the sidelines but, also keeping an eye on how they work in the real marine environment. What can I say I'm a Keep It Simple Sailor.

[mrm]

Originally Posted by mcarling

DC-DC converters use power electronics, not transformers...

Are you sure?
SMPS Power Supply Topologies: Comparison and Selection

[mcarling]

Originally Posted by mbianka

The complexity and monitoring of these battery banks is what gives me pause. Things like additional BMS circuitry required to keep the cells balanced just scares me that it creates additional points of failure and additional $ replacement costs.

My opinion, for whatever it may be worth, is that BMS circuitry is probably worthwhile for 144V to 750V propulsion battery banks, but a waste of money and perhaps more added risk than benefit in 12V and 24V house batteries. I especially would not want a BMS anywhere near a 12V or 24V starter battery -- even if the BMS were free.

[mcarling]

Originally Posted by mrm

Are you sure?

Yes. An understanding of the Maxwell Equations clarifies why. In short, it is the change in the current flow in the primary coil which induces the change of magnetic field which induces the current flow in the secondary coil.

In the usual case, the current alternates the direction of flow, but it is sufficient to alternate the magnitude of flow i.e. usually the voltages reverse but it is sufficient to alternate between high and low (typically about zero if not reversed) voltages.

[diugo]

All DC/DC converters require an energy storage device---either a capacitor or an inductor, of which transformers are a class. The things in the pic are definitely inductors of some sort.

[mrm]

Originally Posted by mcarling

Yes. An understanding of the Maxwell Equations clarifies why. In short, it is the change in the current flow in the primary coil which induces the change of magnetic field which induces the current flow in the secondary coil.

In the usual case, the current alternates the direction of flow, but it is sufficient to alternate the magnitude of flow i.e. usually the voltages reverse but it is sufficient to alternate between high and low (typically about zero if not reversed) voltages.

DC-DC converters use power electronics, not transformers...

To avoid further thread drift I will only make the following remarks and stop with this subject.

You asserted, that DC-DC do not use transformers. This is plain wrong and a study of typical SMPS topologies I linked to earlier will tell you why. Btw, SMPS is a DC-DC converter.

Had you written 'DC-DC converters use power electronics AND transformers/inductors' things would have be fine.

Maxwell equations are fine, but you seem to have forgotten core materials are not ideal and have both hysteresis and residual magnetisation, and core saturation is a bad thing in SMPS for obvious reasons. You'd better reverse that flux...

My background: computer science as a job, Electronics as a long standing hobby. In SMPS area: I designed and built a 100W 12VDC -> 19VDC converter for my laptop for use on a boat. Also designed and built various SMPS power supplies for home use.

OK, hope it was not a complete thread drift, as it was in context of BMS boards.

[mcarling]

Originally Posted by mrm

You asserted, that DC-DC do not use transformers. This is plain wrong and a study of typical SMPS topologies I linked to earlier will tell you why. Btw, SMPS is a DC-DC converter.

Had you written 'DC-DC converters use power electronics AND transformers/inductors' things would have be fine.

DC-DC converters use power electronics and some additionally use inductors. They do not use transformers.

[Saltyhog]

Originally Posted by mcarling

DC-DC converters use power electronics and some additionally use inductors. They do not use transformers.

Not to get any further off topic, but I've designed countless DC-DC converters for use in various industries. I can assure you, with absolute certainty, some DC-DC converters do make use of transformers. See Flyback Converter. Just sayin' BTW, this is a great thread. Characterizing these cells performance and nuance's really only will happen with hours on road so to speak. To those folks here who are basically doing the heavy lifting for the rest of us, thanks for sharing!!!

[hellosailor]

I suppose adding active electronics directly at the battery also provides a great new way to provide RFI on the power system. One more reason for a big metal battery box, I suppose.

[noelex 77]

My start/ winch battery bank is getting on its last legs. The current batteries are Gel 200AHR. Overkill, but the "start batteries" also power the large 3500 anchor windlass. I anchor all the time and would like a reasonable reserve to anchor multiple times if needed.

I think LA would be the sensible choice, but having used small cylindrical lithium batteries for many years I think the time is right to boat system.

I need to order from European distributers. The customs problems here when dealing with Chinese, or USA imports are just not worth contemplating.

This company looks promising and I considering ordering 4 cells probably about 100Ahrs.
EV-Power | LiFePO4 Battery Pack (12V/17Ah PCM)

My questions.
1. Any opinion on the quality of these cells
2.Sinopoly, or winston
3.I plan on no BMS but I will manual balance as required. I would like a cell logger. This one, or is something else better?
EV-Power | Cell Logger 8 cells / 1 battery (USB port)
4. What happens if I parallel the house bank and the start bank?. I can see the potential for very high currents flowing from a charged house bank (400AHr gel) into a depleted lithium bank.

Thoughts?

[deckofficer]

Originally Posted by noelex 77

My start/ winch battery bank is getting on its last legs. The current batteries are Gel 200AHR. Overkill, but the "start batteries" also power the large 3500 anchor windlass. I anchor all the time and would like a reasonable reserve to anchor multiple times if needed.

I think LA would be the sensible choice, but having used small cylindrical lithium batteries for many years I think the time is right to boat system.

I need to order from European distributers. The customs problems here when dealing with Chinese, or USA imports are just not worth contemplating.

This company looks promising and I considering ordering 4 cells probably about 100Ahrs.
EV-Power | LiFePO4 Battery Pack (12V/17Ah PCM)

My questions.
1. Any opinion on the quality of these cells
2.Sinopoly, or winston
3.I plan on no BMS but I will manual balance as required. I would like a cell logger. This one, or is something else better?
EV-Power | Cell Logger 8 cells / 1 battery (USB port)
4. What happens if I parallel the house bank and the start bank?. I can see the potential for very high currents flowing from a charged house bank (400AHr gel) into a depleted lithium bank.

Thoughts?

For that battery it specs a max discharge current of 34 amps. That isn't suitable to the loads of engine start or 1500 watt windlass.

I clicked on your link and it showed the 17 a-hr battery. (4) 100 a-hr cells will work fine.

[noelex 77]

Sorry that was just a general link to the company.
These are the actual cells I am thinkink of
EV-Power | WB-LYP100AHA LiFeYPO4 (3.2V/100Ah)

[deckofficer]

And I revised my last post.