Depth of Discharge Myth?

[newhaul]

Originally Posted by evm1024

Well the model I've been working on is starting to show some interesting results. Of course it is a model so it is somewhere between total nonsense and reality.



Solar output follows an irradiance profile that I picked up off some solar website. Not as good at the irradiance figures we used back when I had something to do with modeling the oceans and rivers but a start.

Power consumption is also an hourly table that ends up with 133 ah used per day.

The generator only kicks in when the SOC is less than 50% for FLA batteries. Solar is cut off at 100% SOC for FLA.

I should note that I have not included a charge acceptance/efficiency on the charge side (just straight amps in at the moment). I'll get around to that and vary those parameters based on SOC and current. Also, no peukert yet too.

This of course means that even thoe the model says 100% it does not really mean that. It just says that if it were a perfect world then the battery would be 100%. I'll have to factor in charge taper and float at some point.

This all works in FLA's favor.

On to the data.

Runs are for 50 days and the time step is 1 hour, the battery starts at 100% SOC.

With the model set to 300 watts of solar, 400 ah of FLA, and an 80 amp alternator on the engine, 133.6 AH daily usage I see that the battery has only 28 hours (well time-steps) where it is 100%SOC.

50 days at 24 hours a day is 1200 hours. So to be at 100% even in this model only 28 times is bad. 39 hours (out of 1200) between 90% and 99% SOC, 236 hours between 80% and 89% SOC, 550 hours between 70 and 79% SOC, 347 hours between 60% and 69% SOC.

The range for FLA is set fro 100% to 50% which means that the model will run the alternator for an hour (80 ah charge in a perfect world) anytime it gets to 50% SOC. In total 1280 AH (16 hours run time) added by the alternator.

Of course there is a lot to do to make this model useful.

With that in mind it appears that 300 watts of solar on a boat that uses 134 ah per day will require running the engine. And that the batteries will be spending a lot of time in the 70%SOC range while not getting to 100% SOC very often and likely never really getting truly full. That boat better do some long motering days.

sounds like a situation where Lfp would excell

[evm1024]

Originally Posted by newhaul

sounds like a situation where Lfp would excell

I have some parameters for LiFePO4 in the model. Runt show that it get to the target voltages and just cycles comfortably.

I'll post those results later.

[john61ct]

Originally Posted by botanybay

Interestingly my golf cart batteries continue to take full generator output up to about 90% SOC. I am putting about 140A into a 440AH bank. (About .3 C) when on genset.

You guys use sealed batts for golf cars there?

[four winds]

Glad this thread dodged the closure bullet, so far. So I have a chance to say how well I've enjoyed the information. Very well.

For my needs I can now see where lithium storage could be considered. money aside, sadly.

No,, solar, genset, windgen, bimini, dodger, windlass,..watermaker, ect.

Two banks, (1)- 200 Ahr Li, charged via dc-dc from (2)- 220 Ahr gc2 FLA charged via alternator.

FLA Bank for starting, bildge, salon lighting, nav lights ..... expect to be topped off easily and often. Buffers the Li charging, but what happens to SOC when the dc-dc is charging the Li, and it can take more than the FLA? Could one get 100a to the Li bank if the FLA can only accept say 50a? I'm guessing FLA SOC is going down if so.

Li Bank for Fridge, autopilot, nav instruments, VHF, FM, inverter loads. Would get me through an overnighter with good stable voltage. if it gets low in the wee hours, maybe pull from the dc-dc and the FLA backup. Start the engine when FLA SOC advises, preferably when heading for anchor.

Enough dreaming.



The original question, discharge myth? That part was an interesting discussion. Learned stuff. But knew, at least for me, deep discharge kills FLA early. Killed my 230 Ahr bank in three years anchoring out, at about 150-170 Ahr daily use. guessing. Batteries (Deka) cost $230 US. I could live with that, but plan is to use 440 Ahr gc2's and a new Delco 120a alternator (awaiting install).

[ramblinrod]

Originally Posted by four winds

But knew, at least for me, deep discharge kills FLA early. Killed my 230 Ahr bank in three years anchoring out, at about 150-170 Ahr daily use. guessing. Batteries (Deka) cost $230 US. I could live with that, but plan is to use 440 Ahr gc2's and a new Delco 120a alternator (awaiting install).

Glad you've enjoyed the thread.

Yes 230 A-hr bank for ~150 A-hr daily consumption is too small. Should be around 450 A-hr bank, so your 4 x GC2's should serve well. Your 120 A alternator is right-sized as well. Add in 600W of solar and/or wind, and you will have a great system. You will rarely require charging with the alternator, but when you do (poor sun and/or wind yesterday in todays forecast) an hour in the morning will suffice.

With the wind and sun, I predict your batteries will last 6 years, without 3-4.

If you forget the wind and sun, you will be forced to run the alternator about 3 hours every day and will get no where near 100%, hence reduced battery life expectancy.

If you change FLA to LFP, that will reduce the runt time to about 1.5 hours every day.

If you dislike running the engine for charging, (noise, smell, and cabin heat) forget the LFP and add solar and wind.

[ramblinrod]

Originally Posted by evm1024

Switching over to 400 watts solar with all the other conditions being the same and the model ends up with no alternator charging required and no real time below 80% SOC. Most of the time around 90% SOC.

I'll take some time over the weekend to go over the math to be sure that the model is "doing the right thing" (tm).

If you use the ratio I recommend,
100 A-hr consumption
300 A-hr FLA
200 W wind
200 W solar

and your model provides accurate results, then ICE charging is rarely if ever required on a typical sunny, sunny with clouds, or partly cloudy day.

On the worst of days, no sun, no wind, one can run the alternator for an hour for 2 days, without really harming the batteries (due to extended and deeper PSOC)

Total cost to add wind and solar is about $800-$3000 DIY depending on mounting requirements and product quality. Solar (rigid panels) will last pretty much forever unless damaged, wind about 10 years avg.

Cost is completely compensated by reduced engine run time (diesel fuel, maintenance, and engine depreciation)

[newhaul]

Originally Posted by ramblinrod

Glad you've enjoyed the thread.

Yes 230 A-hr bank for ~150 A-hr daily consumption is too small. Should be around 450 A-hr bank, so your 4 x GC2's should serve well. Your 120 A alternator is right-sized as well. Add in 600W of solar and/or wind, and you will have a great system. You will rarely require charging with the alternator, but when you do (poor sun and/or wind yesterday in todays forecast) an hour in the morning will suffice.

With the wind and sun, I predict your batteries will last 6 years, without 3-4.

If you forget the wind and sun, you will be forced to run the alternator about 3 hours every day and will get no where near 100%, hence reduced battery life expectancy.

If you change FLA to LFP, that will reduce the runt time to about 1.5 hours every day.

If you dislike running the engine for charging, (noise, smell, and cabin heat) forget the LFP and add solar and wind.

that was actually a good post right up in till the last sentence.

[four winds]

Originally Posted by newhaul

that was actually a good post right up in till the last sentence.

I do dislike engine charging, but I accept it. Because I dislike the idea of solar and wind much more. No solar plans.

So yes, I'll kill the 440 Ahr gc2s also. It will just take longer than three years hopefully. Longer to get to a point of diminished capacity, that necessitates a change in use habits. While a plan for new batteries begins.


I like the hybrid banks idea though. I think it might be a way of taking better care of the batteries, in my use pattern (alt only, on the hook). Specifically, I think it would result in the PSOC condition would dominate in the Li bank. And the FLA bank would spend more time closer to 100% SOC.

Was hoping someone might comment on the FLA-dcdc-Li charging question in the prior post. No matter, can't afford such a bank.

[evm1024]

Originally Posted by four winds

I do dislike engine charging, but I accept it. Because I dislike the idea of solar and wind much more. No solar plans.

So yes, I'll kill the 440 Ahr gc2s also. It will just take longer than three years hopefully. Longer to get to a point of diminished capacity, that necessitates a change in use habits. While a plan for new batteries begins.


I like the hybrid banks idea though. I think it might be a way of taking better care of the batteries, in my use pattern (alt only, on the hook). Specifically, I think it would result in the PSOC condition would dominate in the Li bank. And the FLA bank would spend more time closer to 100% SOC.

Was hoping someone might comment on the FLA-dcdc-Li charging question in the prior post. No matter, can't afford such a bank.

I'll work on my model a bit more and try to get the numbers to be more accurate.

What is clear is that the model predicts (at least in this stage) that FLA will be in PSOC most of the time and is likely to have significant lifespan reductions.

The model runs I've done with LiFePO4 show them just cruising along. They cycle between 70 and about 60% SOC (70% is what the forcings say the max charge on the bank should be).

What this means is that the LiFePO4 bank could easily have 2000 to 4000 cycles without breaking a sweat. If the FLA bank is reduced to even as high as 500 cycles then the LiFePO4 bank outlives the FLA bank by a factor of 4 to 8. Which means that the FLA bank has be be 1/4th to 1/8th the cost of the LiFePO4 bank to break even.

Plus the other advantages of the LifePO4 bank are there as well. Expensive in the short term but frugal in the long term.

Of course to switch from FLA to LiFePO4 requires a complete mindset change. This is somewhat difficult and does take more effort than doing it like we always have.

Imagine getting up in the morning and seeing that your bank is sitting at 30% and NOT having a heart attack. You know that with LiFePO4 the bank is fine and able to produce full amperage without breaking a sweat. And that solar or an alternator run later in the day will bring the bank up in SOC.

For me this is priceless.

[kmacdonald]

I think the biggest cost savings with lithium is less engine or generator run time to charge them. The other savings, real or imagined, pale in comparison.

[john61ct]

Originally Posted by four winds

but what happens to SOC when the dc-dc is charging the Li, and it can take more than the FLA? Could one get 100a to the Li bank if the FLA can only accept say 50a?

I'm guessing FLA SOC is going down if so.

I would try but have a hard time understanding.

One bank gets the output directly from the primary source. Say that's a 400A FLA one, charged from a 200A alternator.

The LFP is then getting fed by a DCDC charger, say an 80A Sterling BB.

The FLA may at first accept (draw) say 60A, tgen later this drops to 20A as SoC climbs.

The DCDC will draw its say 70A for the LFP, pretty much constantly until the bank is full.

The alt/vr will gear up and down the amps output as needed.

Neither bank's acceptance rate will affect the other.

[four winds]

Originally Posted by john61ct

I would try but have a hard time understanding.

One bank gets the output directly from the primary source. Say that's a 400A FLA one, charged from a 200A alternator.

The LFP is then getting fed by a DCDC charger, say an 80A Sterling BB.

The FLA may at first accept (draw) say 60A, tgen later this drops to 20A as SoC climbs.

The DCDC will draw its say 70A for the LFP, pretty much constantly until the bank is full.

The alt/vr will gear up and down the amps output as needed.

Neither bank's acceptance rate will affect the other.

Thanks for the reply John (and others). I think you do understand what I'm wondering about. I'd like to ask different question, or in a different way at least.

Let's say the Li is accepting (wanting) 70a from the dcdc charger, getting it from the FLA bank. And the FLA bank is accepting (wanting) 60a at the same time. Would the system be requiring 130a total from the alternator?

If so....... let's say the alternator will do 90a continuous without melting down. ok... I visualize the Li bank getting it needs filled at 70a. Because the lead bank will give it up without hesitation. But the lead bank state of charge is dropping, needing 60a, but only 30a left for the alt to give.

If that is bad, then is it possible a hybrid Li/FLA system, with alt only charging, must be able to support charging at max combined acceptance of both banks?

[Dockhead]

Originally Posted by ramblinrod

. . . If you dislike running the engine for charging, (noise, smell, and cabin heat) forget the LFP and add solar and wind.

Again, the false dichotomy between more solar vs. lithium. This sentence is nonsensical. More solar will reduce running engines, with or without lead. There is no scenario where lead batteries vs. lithium will reduce engine running time so a desire to run engines less is simply NOT an argument for lead batteries - it's an argument for more solar.




And for anyone who CAN'T add more solar (or have any solar at all, or doesn't want to), then lithium, not lead, is the way to reduce engine run time.


Lithium reduces engine run time in two powerful ways:


1. You don't run any engine to put on a finish charge, a matter of life and death for lead, but which lithium does not require or even want.


2. You can add more charging capacity (bigger alternator, bigger AC chargers) to take advantage of lithium's much greater acceptance rate.




Why is this something to argue about? I don't understand -- these are clear and obvious facts, and based on them, and others, some people will make one choice and others will make a different choice. I really don't understand why that bothers anyone, unless arguing itself is a kind of sport.

[Dockhead]

Originally Posted by four winds

Thanks for the reply John (and others). I think you do understand what I'm wondering about. I'd like to ask different question, or in a different way at least.

Let's say the Li is accepting (wanting) 70a from the dcdc charger, getting it from the FLA bank. And the FLA bank is accepting (wanting) 60a at the same time. Would the system be requiring 130a total from the alternator?

If so....... let's say the alternator will do 90a continuous without melting down. ok... I visualize the Li bank getting it needs filled at 70a. Because the lead bank will give it up without hesitation. But the lead bank state of charge is dropping, needing 60a, but only 30a left for the alt to give.

If that is bad, then is it possible a hybrid Li/FLA system, with alt only charging, must be able to support charging at max combined acceptance of both banks?

That's a very good question, but despite my limited EE knowledge, I think I actually know the answer to it.



The B2B charger acts as a load just like an inverter or anything else. If you read the Sterling manual, you'll see that this charger works by pulling the system voltage down to the point that the regulator will put full field on the alternator and force it to put out full output, as if you have an inverter or some other kind of big load on the system. So as long as the B2B charger is pulling enough current to keep the voltage below what will allow much current to flow into the lead batteries, then the lithium will be getting charged but not the lead. Once the lithium is charged and the B2B charger stops taking current, then the voltage will rise and the lead will get whatever charging profile the regulator has programmed. It's just like as if you were running the inverter off the alternator.


So I would not do it like you propose. I did post a diagram of the hybrid bank I am thinking about -- I would put the alternator on the lithium, not the lead bank, and on the contrary charge the lead bank via the B2B charger. This leaves open the question of how to protect the alternator in case of a LVC event, but this should be solvable (Sterling make an "alternator saver" -- maybe that would work).


So that way it would work in reverse -- the lead would get charged first UNTIL IT GOES INTO ABSORPTION and stops taking a big current, then the lithium will get a large current in parallel with the lead getting the small, long, low current absorption charge.


That's more synergistic and I believe that is what you want -- get the bulk charge on the lead done FIRST so that you get more finishing charge on the lead in a given motoring run.


Also, with the B2B charger set up to charge the lead, you can complete the finishing charge on battery power from the lithium. This would be key, I think, to giving the lead bank an ideal use profile, giving it a finishing charge EVERY CYCLE. If the B2B charger is pointing the other way, you can't do this.


BTW, the Sterling B2B charger will ordinarily NOT charge from battery power -- it is intended to charge only when an alternator is producing power. It has a manual override which will allow this ("regenerative braking mode") and might be programmable to allow this to be done automatically, but a requirement to do this manually doesn't seem like such a bad thing to me.




The more I think about it, the more I like the hybrid bank despite its complexity. It really knocks out the drawbacks of both types of battery chemistry, and provides redundancy we can't have in simple power systems. If you have room for a lot of lead batteries, this approach could work to ideally exploit the lead capacity, using a relatively small lithium bank which is used primarily to give the lead an ideal finishing charge every cycle.


This relatively small lithium bank could also be used to run high current devices like bow thrusters and windlasses, which greatly benefit from the lack of voltage sag. I figure my 10hp bow thruster would gain 25% power and run cooler, if I ran it off lithium batteries -- a really significant advantage possibly worth the price of lithium all by itself, for me.


What this means also is that for a boat which has a separate bow thruster bank already, something like this could be implemented very easily, with little net increase of complexity.



My boat is this case -- I have a separate "technical loads" battery bank, for thruster, windlass, and electric winches. If I go with lithium, I will put the lithium there, and leave the house loads on the existing lead bank, and charge the lead with a Sterling B2B charger. I will bypass the existing diode splitter and connect the alternator to the lithium, and add as second mains power battery charger, so each bank has its own charger. The increase of complexity is really not significant.

[Dockhead]

Originally Posted by john61ct

. . .
If that is bad, then is it possible a hybrid Li/FLA system, with alt only charging, must be able to support charging at max combined acceptance of both banks?

No, this is not necessary. It's unlikely to even be possible, unless the lithium bank is very small, considering the very high maximum acceptance rate of lithium (several x of C, at least).





The bank which is being charged by the B2B charger (let's call it the "secondary bank") will have priority, because the B2B charger acts as a load. The other bank (the "primary bank", the one directly connected to the alternator) will get charged only to the extent that the load produced by the B2B charger is small enough as a percentage of alternator capacity that the voltage can rise to the level where the primary bank can accept current.



So you can use any size alternator with any combination of banks -- no problem.


But you don't want the primary bank to be the lead one -- this could greatly increase the time required to achieve full charge on both banks. Because the lithium will get priority, then only after the lithium is charged will the lead bank start its whole charging cycle beginning with bulk.


Also, you would limit the charging of the lithium to the maximum capacity of the B2B charger and lose the benefit of getting full output into the lithium, in case the alternator is bigger than the largest B2B charger.




In all of this keep in mind that lithium melts alternators which are not designed for bulk power production and/or which are not derated, and all the more in a configuration like this. I think the Balmar Belt Saver function will be essential for this kind of bank, and I also think that such a bank makes little sense if you don't have or can't fit a large frame alternator (or at least one of those souped up Grasser jobs like MaineSail uses on his own boat).