LifePo4.. Yes AGAIN!

[travellerw]

Originally Posted by kcj

As to getting out of bulk---have you done an energy audit? Do you know, roughly, what your daily ah demand is? Do you know your solar ah generation?
If the later does not exceed the former by more than 10% I doubt it is really getting out of bulk.

If you are off the boat for stretches with no loads I would consider shutting the solar down. The LFPs don't like being stored full, or so I've read

If you really have solar to spare you can do like I did and wire your water maker and hwh to run off the inverter....

Yup, we use an average of 175AH/Day.. We can easily generate 250AH/day (more in the summer months. I have seen as much as 350AH). Currently we burn the extra power with either the washing machine or our hot water heater (or just throw it away). Unfortunately, running our watermaker off the inverter is not supported by the manufacturer. I'm not sure my inverter could actually cover the inrush current and actually start the water maker.

Even before this upgrade, I have been considering adding an Engle freezer. Seems like that might be a good use of the extra juice.

As to leaving the boat for an extended time. We plan to disconnect the LFP pack completely (at about 50 SOC) and hook up one of our LA start batts (they are deep cycle). A single solar controller will be left to charge that battery to just run the bilge pumps. Our boat is wired so that a single switch can be thrown an everything except the bilge pumps is disconnected.

[john61ct]

I would stick with good strap&plate.

The big prismatics still last years past a minor bulge event, but maybe not if the case is allowed to deform too much?

[john61ct]

With a conservative charging strategy, the whole idea of Bulk vs Absorb goes out the window with routine usage cycling.

Just charge to a setpoint and stop.

And with "too much" solar, fuggedaboudit who cares? You size panelage if possible for worst case cloudy or winter or latitudes or all three, not best case.

So of course you produce "too much" most of the time, especially with no lead long tail anymore, just put in what you need for a day or two and stop.

Remember, with LFP, getting to Full and staying there is not just not the goal, it's **harmful**!

Only go to your defined 100% if you have significant loads that will pull SoC back down from there right away.

Which means, if you want to carry loads from the SC "excess", do so before crossing 13.6V, and then resume charging X time before sunset.

If you happen to miss getting to Full, no big deal, concern over that is just leftover Lead thinking, unlearn it.

And of course if "wasting" excess power really bothers you, it can always be used for eutectic fridge plates, heating water, feeding a slow cooker, a dehumidifier, making ice etc.

[senormechanico]

john61ct,

I salute you. That's IT in a nutshell.

People need to experience LiFePo4 and live with it for quite awhile before they finally GET IT !

[arsenelupiga]

Originally Posted by john61ct

With a conservative charging strategy, the whole idea of Bulk vs Absorb goes out the window with routine usage cycling.

Just charge to a setpoint and stop.

And with "too much" solar, fuggedaboudit who cares? You size panelage if possible for worst case cloudy or winter or latitudes or all three, not best case.

So of course you produce "too much" most of the time, especially with no lead long tail anymore, just put in what you need for a day or two and stop.

Remember, with LFP, getting to Full and staying there is not just not the goal, it's **harmful**!

Only go to your defined 100% if you have significant loads that will pull SoC back down from there right away.

Which means, if you want to carry loads from the SC "excess", do so before crossing 13.6V, and then resume charging X time before sunset.

If you happen to miss getting to Full, no big deal, concern over that is just leftover Lead thinking, unlearn it.

And of course if "wasting" excess power really bothers you, it can always be used for eutectic fridge plates, heating water, feeding a slow cooker, a dehumidifier, making ice etc.

like your thinking

How would one go about balancing. My plan is to simply have charger for single LFP battery & monitoring system for each battery, and victron SOC integrator to get % SOC, and correct voltages if discrepancy. If SOC is not reset regularly, values probably get less and less accurate but not much one can do..

Top balancing looks unreliable as one can harm batteries. Bottom balancing, well I will not be at bottom or full often.

What is the criteria to say this battery is out of step - voltage during load, voltage when no load, voltage when say 30 min no load?

Then one notices discrepancy say 0.1V, how much charging is required to compensate, or is this best trial and error method ?

I assume even if batteries are out of step but within min and max voltage, there is no harm ?

[travellerw]

Originally Posted by john61ct

And with "too much" solar, fuggedaboudit who cares? You size panelage if possible for worst case cloudy or winter or latitudes or all three, not best case.

This is where I think weekend warriors and full time liveaboards might differ. For us, its just painful to know we are throwing usable power away. We try to eek as much as we can, as more power equals a better quality of life.

I just need to change my mindset. Instead of doing our high draw activities in the late afternoon, we will do them in the early morning. Leaving more of an empty bank for the late afternoon sun to pour into. We plan our %100 SOC to be about %85-%90 of the actual rated capacity of the bank.

The standard items (fridge, freezer, fans) should be sufficient to pull on the bank after charging stops.

[john61ct]

Originally Posted by travellerw

Instead of doing our high draw activities in the late afternoon, we will do them in the early morning. Leaving more of an empty bank for the late afternoon sun to pour into.

The standard items (fridge, freezer, fans) should be sufficient to pull on the bank after charging stops.

Sounds good.

> We plan our %100 SOC to be about %85-%90 of the actual rated capacity of the bank.

I would just pick a top charging **voltage** you feel is best for day to day cycling.

To get a consistent Full SoC point, Absorb at that V until trailing amps drop to .02C (2A per 100 AH), there's your 100%.

Yes your BM needs to be reset at that specific point frequently, ideally every cycle if you really need accuracy. (I don't)

_____
As for cell-level gear, my **personal** take is most of what people obsess about is unnecessary, as long as your usage is gentle current rates and you avoid both top and bottom shoulders in normal use.

Check for imbalance issues manually, more frequently in the early days, if you see none every time then relax, maybe quarterly or six months.

If you do see problems, maybe start researching solutions with people that know more than me.

But don't just accept conventional wisdom that IMO over-engineered solutions are required from the start, lots of cell-level hardware has been reported to be the **cause** of problems, so if you can, keep it minimal.

_____
wrt balancing:

I **never** go near the bottom, way too scary for me. Maybe with better equipment.

Going above 3.5Vpc for occasional maintenance causes no harm, with the thousands of extra cycles I believe I'll get losing a few off the back end is nothing.

Going closer and closer to a point where my whole investment is instantly destroyed, sorry but Nope, not for me.