Solar Upgrade verse Running the Generator

[john61ct]

Originally Posted by Exile

can run them down to as low as 20% SOC without harming them.

Much lower, no problem.

A BMS system will define "empty" as ~5% remaining, isolates from loads so no damage.

With bare cells you are responsible for figuring that out, multiple protective devices set at say 15% then 10%.

[john61ct]

Originally Posted by sailorboy1

The problem is that my 100-amp charger once it gets to only supplying 10-amps goes into float. But that's only really around 97% charged. If I run the generator in the day for say the air conditioner the batteries stop charging and it's kind of a waste. So a small charger that can be programed to stay in absorption would be a plus to get fully charged.

The smallest available Sterling ProCharge Ultra or ProMariner Pronautic P will give you fine adjustable settings.

But I would replace the badly designed charger myself.

If you're watching Amps in with a shunt-based BM at the bank, you could set FloatV = AbsorbV and end charging when current gets down to under say 3-4A.

[Kenomac]

Lithium batteries? Now you're talking big bucks when $500 turns quickly into chump change.

[a64pilot]

Originally Posted by sailorboy1

The problem is that my 100-amp charger once it gets to only supplying 10-amps goes into float. But that's only really around 97% charged. If I run the generator in the day for say the air conditioner the batteries stop charging and it's kind of a waste. So a small charger that can be programed to stay in absorption would be a plus to get fully charged.

If your curious, I have a Sterling pro charge ultra and can show it to you.
However what makes the most sense is to hit the batteries with as high a charge rate as is possible with the generator in the morning when they are low and can accept high charge current, then program your Solar to stay in absorption and not run the generator in the afternoon.

I can tell you based on your earlier posts about not having to babysit and obsess over your battery bank, that LifePo is not for you, as that is still a science experiment and will require both big $$$ and constant monitoring / fiddling with at least until you get everything dialed in.
I believe LifePo is not ready for prime time yet, there is no solution that I know of that is a plug and play, install and forget solution, and get it wrong and that is big $$$ down the drain.

A lot of chargers, the Sterling Pro Charge Ultra being one of them, if you cycle the circuit breaker they start over in absorption, run the cycle and go to float. If my bank is down and I am relying only on it to charge the bank, I have to cycle the circuit breaker a coup,e of times to get to full charge. I do that as opposed to setting float voltage at absorption rates so O don't forget when I'm plugged into shorepower.

[Exile]

Originally Posted by john61ct

Much lower, no problem.

A BMS system will define "empty" as ~5% remaining, isolates from loads so no damage.

With bare cells you are responsible for figuring that out, multiple protective devices set at say 15% then 10%.

With their ability to drain down as low as 5% or so, then theoretically you could size them much lower than what you have with your LA capacity. If correct, then this could lower the initial cost. Is there a general rule of thumb on how much you can safely downsize, or for most is it more likely defined by the size of their battery boxes (or just wanting the extra capacity)?

[sailorboy1]

Originally Posted by john61ct

But I would replace the badly designed charger myself.

You must be pretty rich then. That's probably at least a $2,000 project to replace a well working charger/inverter and remote control panel just to get 3% of battery capacity charging.

Hope on next month's budget thread you post I'm not spending near enough money.

I think some posts on this thread highlight just how crazy some people are about their batteries. I expect to get at least 5 years out of my current house batteries and they were $550. I'm not spending $1000s to get an extra 1-2 years out of them.

[john61ct]

Originally Posted by Exile

Is there a general rule of thumb on how much you can safely downsize

Lead bank (AH capacity * .55) will give you around the LFP equivalent.

Note quality LFP cells usually have greater capacity than spec'd, sometimes by as much as 10%.

If well cared for and no disaster, they can come out cheaper than lead in the long run because they don't walk down capacity for many years, thousands of cycles.

But yes such a large investment and long ROI makes it risky.

Right now the marine market is mostly racers where hundreds per every kg saved is worth it.

[john61ct]

Originally Posted by sailorboy1

That's probably at least a $2,000 project to replace a well working charger/inverter and remote control panel just to get 3% of battery capacity charging.

I would phrase that as "just to get a proper Full charge.

But yes that sort of investment would not make sense with such an inexpensive bank.

I also don't buy Kombi inverter/chargers.

Side note, you should consider doing a 20-hour load test on the bank if unexpected failure at sea would be more than inconvenient.

[zboss]

The advantage of lithium with any charging source, including solar, is that there is almost no resistance when charging above 80%. So at the end of your solar day, you are able to take advantage of every watt hitting the panels, increasing chances of fully charging your battery every day without increasing the size of your solar bank dramatically. It also doesn't matter if you run you engine in the morning and let the solar top off or at the end of the day, or at night. You will always be putting almost the full amount of your available charge source into the batteries.

This means less solar, less battery weight, less engine or genny run time, but at the expanse of some expensive batts.

300 Ah of smart battery is $3500 but the cost is mitigated over time by significantly longer battery life and less wear and tear on your diesel or gas charging sources.

Also, ships systems generally run much better without the voltage drop you get with lead acid batteries. The lithium battery always puts out its rated voltage until you are empty. This means your electronics stay cooler, use less heat, and generally operate better compared to when lead acid batteries are down in voltage.

So, just switching battery chemistries has significant overall advantages and no cost downside when amortized over 8 or 10 years.

Plus ... BTW... you can get a significant federal tax credit against the cost -30%. Making that $3500 battery around $2000 or roughly twice the cost of replacing my existing lead acid battery bank.

[Pizzazz]

Thread drift alert but it all ties together I guess.

Regarding lithium at 7x the cost of flooded batteries - it does not make sense financially. You can discharge lead acid down to 20% and recharge them up to 80% only, especially if they are golf cart cells. You will cut their life in half, to say $200 per 100 AHr. Still 3.5 times cheaper than lithium. Golf carts accept C/3 at these charge levels, so f you have 400 AHrs, you can charge them at 135A if your generator/charger supports that.

Regarding sizing of solar, I said 20% of battery capacity because you want to use solar charging in accept mode of charging. In the above example, you will switch off your generator at 80% SOC. The remaining 20% is approx. 80 AHrs. A 100W solar panel gives you around 30 AHrs per day. So you will need to have about 300 watts of solar to charge them to 100%. You do not need to go to 100% every day, may be twice a week would be fine.

This is why the OP system is quite good as it is. Anything else is just spending money for fun and we all do it but it does not mean it is needed. More solar clutters the boat, cannot be used effectively (i.e. it will not be enough to replace the genny) and costs money that should be saved to replace the batteries.

[zboss]

Where do you get 7x the cost. That is nonsense. My trojan t145s are about $1000 to replace and to get the same capacity in lithium is $2000 after tax credit.

[Kenomac]

Originally Posted by zboss

Where do you get 7x the cost. That is nonsense. My trojan t145s are about $1000 to replace and to get the same capacity in lithium is $2000 after tax credit.

By the time you also add in the new charger and alternator required for the lithium transformation, you'll be at least 4x the cost maybe 5x if labor is also included.

[john61ct]

People putting out LFP costs, **please** specify the system mfg/model/caacity range, ideally with links.

And at least mention whether you're talking bare cells or full bespoke BMS system.

7x is a lowball for the latter.

Even bare cells $700 per 12V/100AH was ballpark last time I looked at quality. And you do need specialized infrastructure, can cost more than the cells themselves.

[john61ct]

Originally Posted by Pizzazz

Thread drift alert but it all ties together I guess.

Regarding lithium at 7x the cost of flooded batteries - it does not make sense financially. You can discharge lead acid down to 20% and recharge them up to 80% only, especially if they are golf cart cells. You will cut their life in half, to say $200 per 100 AHr. Still 3.5 times cheaper than lithium. Golf carts accept C/3 at these charge levels, so f you have 400 AHrs, you can charge them at 135A if your generator/charger supports that.

Regarding sizing of solar, I said 20% of battery capacity because you want to use solar charging in accept mode of charging. In the above example, you will switch off your generator at 80% SOC. The remaining 20% is approx. 80 AHrs. A 100W solar panel gives you around 30 AHrs per day. So you will need to have about 300 watts of solar to charge them to 100%. You do not need to go to 100% every day, may be twice a week would be fine.

This is why the OP system is quite good as it is. Anything else is just spending money for fun and we all do it but it does not mean it is needed. More solar clutters the boat, cannot be used effectively (i.e. it will not be enough to replace the genny) and costs money that should be saved to replace the batteries.

There's more inaccuracies there than I've time to correct ATM, maybe others will help in the meantime. Not saying overall conclusion is wrong for the OP though, getting into the weeds on LFP should get a separate thread.

[Pizzazz]

I have been in these threads for over a year and it is the same arguments over and over.

Golf carts cost $1/AHr and is the best value for money for wet cells. This is why golf carts and heavy equipment runs on them. Point me to a lithium system that costs significantly less than $7/AHr installed.

Some people pay for more expensive wet cells, some get AGMs. More power to them.