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Old 14-11-2014, 17:06   #1
Jd1
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Some More Lithium Thoughts And Questions

I was going to use the existing thread "LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks" but for reasons unknown to me I was unable to display the last page (405) on that thread. Maybe it's suffering overload ?
Anyhow, I am getting close to actually using the new system and I had a couple of thoughts I would like input on.
I am using the House Power BMS and at 3.6V*4 (14.4V) the system disconnects the charge bus to avoid overcharging the lithiums. In my research, I have come across references of 3.33 to 3.4V being 100% charged and if charged to 3.6V, the cells will drift back down to the 3.33 to 3.4V range. I don't recall at what voltage the House Power BMS will cancel the high voltage alert signal but what I am envisioning is the battery voltage goes to 14.4, the charge bus disconnects, the voltage gradually drifts downwards, the charge bus gets enabled again and the whole thing repeats.
In itself that doesn't seem like a bad thing as the common thinking is the battery does not get damaged by 3.6V cell voltages. On the other hand though, I have read many times that people will avoid leaving lithiums fully charged as that somehow seems to damage them over the long range. This could be a problem in this setup.
What actually happens that damages the lithiums when they sit fully charged ? How badly are the cells affected - will they only loose a tiny amount of charge capacity per year or is it a much more significant figure ?
In other words, is this something to worry about ?
My second question is in regard to charge voltage. I am currently set up to charge at 14.4 V with my Balmar alternator and MC614 external regulator. This is fine for the lead acid batteries still in the system (but isolated from the lithiums via a FET isolator) but it cramps my style for charge current for the lithiums. My goal is to charge the lithiums at around 160A to almost full charge so I am thinking of upping the charge voltage a bit. What bulk charge voltage can I get away with for lead acid cells without causing damage? Would a diode in series with the lead acids be necessary ?
I would very much appreciate if somebody could post the MC 614 parameters they are using if they are charging both lithiums and lead acid cells with the same settings.

A bonus question: is anybody using a DC-DC power supply or charger to charge their lead acids from lithiums in a mixed cell system ? I don't believe a standard charge relay (or automatic charger for a second battery) will work for this as it's voltage sensing circuits are not suitable.
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Old 14-11-2014, 17:23   #2
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Re: Some more lithium thoughts and questions

Have you read Maine Sail's article on life po4 batteries?
LiFePO4 Batteries - Thoughts & Musings Photo Gallery by Compass Marine How To at pbase.com
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Old 14-11-2014, 18:20   #3
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Re: Some more lithium thoughts and questions

What reduces capacity of lithium batteries over time is heat.
The best way to increase their life is to keep them cool.

The higher the voltage, the more heat is created.
The higher the discharge rates, the more heat is created.
The hotter the environment they are in, the more heat is created.

The charging voltage must be higher than resting voltage for current to flow into the batteries. The final 10% of charge requires higher voltage which creates more heat that is not in proportion to its benefit, i.e. it 'wears them' more than 10% of their lifetime. So generally they should not be charged more than 90% full, unless of course, you need 100% of the capacity.
In a boat, just get a bigger battery and don't use all of its capacity.
So to be specific, 14.4v if left to charge until full is going past 90%.

If you look at the charge curve, you can find where the voltage is at 90%.

Some research has shown just using the middle 20%, i.e. keeping them half-full, 40-60 they last 5 times longer. While this is nice, notice that this size battery is 5x more expensive than one 1/5 the size that lasts 1/5 as long (not exactly, but you get the point)
In my view, batteries will be cheaper/better in five years, so it isn't wise spending a fortune to get a big one today that you barely use to make it last longer.

But the key is not to keep the batteries 90% full unless you really need to.
It is better to let them run down to 20% and then recharge back to 90%.
I often hear people top them off every day, which isn't ideal.
In a car, we recharge them to full everyday because the range of an EV needs the full capacity everyday.

Hope that helps.
That 4,300 post thread usefulness as archive is almost nil.
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Old 14-11-2014, 18:25   #4
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Re: Some more lithium thoughts and questions

Yes, I have - thanks!
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Old 14-11-2014, 18:53   #5
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Re: Some more lithium thoughts and questions

Thanks Jack, interesting view on things. I wonder if it would be worthwhile to over-ride the charge relay control in such a way as to disable re-charge until the battery is down to let's say 50% capacity - something I could probably do with the alarm function of the Cellog8 or the SOC meter - both of these are part of the setup.
Based on re-reading mainSail's article and what you have mentioned in your post, I will not be increasing my charge voltage. This means the current will taper off by itself when the battery reaches a full charge and the charge relay cut-out stage will never be reached. I think I might even try dropping the voltage just a bit to see how the charging rate is affected when the SOC is at 50% or less. At this reduced SOC I would want to be up at a 160A charge rate.
Looks like some more experimentation is in order!
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Old 14-11-2014, 20:02   #6
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Re: Some more lithium thoughts and questions

bing..bing..bing.

winner...win....winner....

But they also have a shelf-life some where about 5-7 years.

So if you don't have a cycle count that equals shelf life, then you leave something on the table.

The big Q...? what is a cycle

Lloyd

Lead is dead...but it still might be cheaper then Li....whatever..

It all depends on system design, and of course use.


On a big O'jet airliner then max is best.... but on a boat it may not be true.


Moving to the next best-thing as an early adopter means you are paying for R$D so when the industry matures, it becomes viable.

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Quote:
Originally Posted by nimblemotors View Post
What reduces capacity of lithium batteries over time is heat.
The best way to increase their life is to keep them cool.

The higher the voltage, the more heat is created.
The higher the discharge rates, the more heat is created.
The hotter the environment they are in, the more heat is created.

The charging voltage must be higher than resting voltage for current to flow into the batteries. The final 10% of charge requires higher voltage which creates more heat that is not in proportion to its benefit, i.e. it 'wears them' more than 10% of their lifetime. So generally they should not be charged more than 90% full, unless of course, you need 100% of the capacity.
In a boat, just get a bigger battery and don't use all of its capacity.
So to be specific, 14.4v if left to charge until full is going past 90%.

If you look at the charge curve, you can find where the voltage is at 90%.

Some research has shown just using the middle 20%, i.e. keeping them half-full, 40-60 they last 5 times longer. While this is nice, notice that this size battery is 5x more expensive than one 1/5 the size that lasts 1/5 as long (not exactly, but you get the point)
In my view, batteries will be cheaper/better in five years, so it isn't wise spending a fortune to get a big one today that you barely use to make it last longer.

But the key is not to keep the batteries 90% full unless you really need to.
It is better to let them run down to 20% and then recharge back to 90%.
I often hear people top them off every day, which isn't ideal.
In a car, we recharge them to full everyday because the range of an EV needs the full capacity everyday.

Hope that helps.
That 4,300 post thread usefulness as archive is almost nil.
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Old 14-11-2014, 20:09   #7
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Re: Some more lithium thoughts and questions

JD1=R$D untill the bat tech matures.//

Yipeeee.

Lloyd

Quote:
Originally Posted by Jd1 View Post
Thanks Jack, interesting view on things. I wonder if it would be worthwhile to over-ride the charge relay control in such a way as to disable re-charge until the battery is down to let's say 50% capacity - something I could probably do with the alarm function of the Cellog8 or the SOC meter - both of these are part of the setup.
Based on re-reading mainSail's article and what you have mentioned in your post, I will not be increasing my charge voltage. This means the current will taper off by itself when the battery reaches a full charge and the charge relay cut-out stage will never be reached. I think I might even try dropping the voltage just a bit to see how the charging rate is affected when the SOC is at 50% or less. At this reduced SOC I would want to be up at a 160A charge rate.
Looks like some more experimentation is in order!
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Old 15-11-2014, 05:09   #8
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Re: Some more lithium thoughts and questions

Something to remember about Li "shelf life", is that it's not like they suddenly stop working or have a Pb-like capacity crash. Li (at least the LiFePO4's we have been working with) simply have a slow steady decline in capacity (of course depending on heat, average cycles DOD, etc.). The theoretical shelf life standard is when the capacity has declined to 80% of the original (same as "cycle life").

So, even at the so-called end of rated cycle life or shelf life, you still have more useable capacity than a brand new Pb bank of the same rated capacity. So with good care (or good BMS), the useable life could be greater than the 5-7 year figure if the system capacity is still enough for the tasks at hand.

How long until a good Li system is down to...say 60% of the original capacity, do to age? With the GLi systems, we don't know yet, as not a single system has "aged out" so far!
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Old 15-11-2014, 14:37   #9
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Re: Some more lithium thoughts and questions

New to this forum. We were told that Cruisers Forum was the best forum on the web for solar and LFP. It definitely is. Wondered why the LFP thread ended about 6 months ago and from a few comments above, it appears that it is filled.

We are full time RV'ers and primarily boondock. Our 5th wheel is solar autonomous. Weight and cube is important for us and our system is basically the following.

1.4 kW in panels. There are six panels ganged in two groups of three in series
and then in parallel to TriStar controller at about 90 V max.
Four batteries of 4 CALB (180 A-hr cells in series). The batteries are in series
for a 48 nominal battery bank of 180 A-hr at 48 V.
4.0 PSW inverter (Magnum)

Am working through the main thread and it make take some time. There is much to learn. Discussions seem to be quite civil and informative.

Reed and Elaine
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Old 15-11-2014, 14:52   #10
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Re: Some more lithium thoughts and questions

Welcome Reed and Elaine
I think the previous thread kinda died out because most people that wanted to convert have done so and the rest are sitting on the fence waiting for prices to come down (or to acquire knowledge). It was slow going towards the end of that thread.
I am also just about ready with things - 4 cells in series, 700Ah each. I am just waiting for a relay board that was ordered more than three weeks ago from China to finish off the last bit. Then it is a question of tuning things and doing some more capacity testing.
There is one locker that is a beautiful example of wire spaghetti that I will have to fix eventually but not until I have all things worked out (Lots of 2/0 wires in there) .
One example is what was discussed at the top of the thread - I am thinking of changing my charge routine to activate at 50% SOC and deactivate at about 90% SOC. The BMV-700 SOC meter fortunately allows for just that functionality!
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Old 15-11-2014, 15:27   #11
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Re: Some more lithium thoughts and questions

Quote:
Originally Posted by Jd1 View Post
One example is what was discussed at the top of the thread - I am thinking of changing my charge routine to activate at 50% SOC and deactivate at about 90% SOC. The BMV-700 SOC meter fortunately allows for just that functionality!
Why stop at 50%??? 20% SOC to 90% is fine...

Our bank is close to 550 cycles, most to 80% DOD with no loss of capacity. Even the best lead acid banks would have been dead long ago doing this..

Most coastal cruisers won't do this many cycles even in 5 years.. At 80% DOD you should expect to see 1500 - 2000+ cycles.. Course with a 700Ah bank that is going to take some serious time to recharge especially at a .22C charge rate. If you are hitting absorption voltage, even at 13.8V to 14.0V, before the high 90's, there is something wrong.

50% is lead acid mentality there really is no need for this mentality with LFP.

Discharge to 20% SOC recharge to 13.8V - 14.0V and about 20-30A net accepted current and your bank will likely outlast you...

Be very careful relying on an Ah counter for continual cycle monitoring. You will still want to do manual synching every time the bank meets your chosen "full" parameters... Even on LFP they drift if not kept on top of..

Just this afternoon I was finally getting around to removing the bank from the boat for the winter. It hit 18F last night so no charging today.......

In the next week or so I will have it reassembled in the shop and will do another capacity test..

Today's removal procedure:
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Old 15-11-2014, 16:56   #12
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Re: Some more lithium thoughts and questions

Maine Sail - Lead mentality is hard to overcome. Finally, after 18 months of cycling (we are full time RV'ers that primarily boondock), I am able to accept 30% SOC.

Read your article on LFP several weeks ago after being guided to it by some others. I have noted it on several fora.

Have read there are problems with charging at low temperatures. We left our rig at son's place at 8000' in mountains of northern NM for three months when we flew down and spent that time traveling in Guatemala and Honduras. We just let everything continue and the LFP bank was at 3.4 V per cell when we returned. It did get down to -20 F at times.

The batteries are CALB cells fabricated by Manzanita Micro and the bank came with a BMS that has worked extremely well. Being OCD at times, I have observed the monitor as it shows the 16 cells going through balance.

LFP is apparently well accepted in the cruising community but is very new in the RV and house bank regimes. There is a great deal of confusion and ignorance and the discussions get vituperative very fast. However, there are a large number of boondocking RVers that are following developments and cost reductions very closely.
Reed and Elaine
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Old 15-11-2014, 17:26   #13
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Re: Some more lithium thoughts and questions

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Originally Posted by Maine Sail View Post
Why stop at 50%??? 20% SOC to 90% is fine...
You would start a sail cruise with a battery that's down at 20%???

The actual parameters will have to be worked out yet but the 50% figure happens to be the default with the SOC meter plus I do not want to get into a situation where I am forced to charge before I can settle down at an anchorage. At 50% charge I have enough power and don't need to worry.

Going below that probably only makes sense if you know what your itinerary is for the next few days and you'd be controlling that manually which I don't want to get into.

Of course if you are into motoring that's a different kettle of seaweed!
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Old 15-11-2014, 20:10   #14
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Re: Some more lithium thoughts and questions

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You would start a sail cruise with a battery that's down at 20%???
We actually do that with pretty good regularity. 20% SOC means two days + of energy left in our bank if I take it to 0%. I have never had to go there but have been down to 5% SOC and have had zero qualms about doing so. On those occasions it was usually because we were in a peaceful quiet cove and wanted a couple days more of quiet. On one occasion I flipped the solar back on at 30% SOC and we got 2.5 more days in that anchorage without the motor...

With lead I would never do that but with LFP I could care less about the occasional dip to 5% SOC.. This summer we spent nearly an entire week at less than 60% SOC due to minimizing motor run times.

At 20% SOC on a 700Ah bank you still have 140 amp hours. If you set an "occasional" oops floor of 5% then you still have 105Ah's to use, if needed. 80% is not by any means an absolute with LFP. I know some guys in the LFP world who think I am crazy to not use all 100%...

This last 15% on your bank is the equivalent to an entire cruising usable capacity, in lead acid, (cycling 50% SOC to 85% SOC) to a 300 Ah lead bank. Only occasionally dipping to 5% for LFP is like Mike Tyson picking up a feather.. No skin off its back.

On our way back from trips we usually wait for the wind to come up then have a nice afternoon sail home and often don't get to run the motor. Our SOC is what ever it is when we get back.

I have also been leaving solar off so I can cycle to 80% DOD as frequently as possible, for testing purposes. As such we very often leave the boat on the mooring at approx 15-40% SOC and go home. During the week I will sometimes try and sneak another cycle (for my cycle testing) but that again usually puts me back at 20% SOC before we head off again.

If I run the motor for just one hour, we have engine driven refrigeration for quick chill downs, as well as DC refridge, that 1 hour gives us three full days of energy independence. Because the batteries charge so fast and can be cycled so deeply it is a very differnt mind set.

I am confident you will eventually see and come to understand exactly what I am talking about. I know this sounds counter intuitive but I no longer worry about charging. Talk to me in two years and we can compare notes again... I know that is very, very, very hard for folks to wrap their heads around but LFP is NOT lead acid. Breaking that long time engrained mind set is very difficult. It was difficult for me too....

I had a good friend row over this summer and ask what our solar array was putting out? He wanted to compare notes. He was shocked when I said I had no idea because it was turned off. I flipped it on for him but he could not, for the life of him, understand how or why I had solar off.

With LFP there is no need to worry about:

Getting back to 100% SOC

Worrying about dipping below 50% DOD

Worrying about dipping below 80% DOD

Worry about charging, it happens so fast

I have come to think of it not as charging but as simply placing energy in the bank. The term charging to me paints images of a long arduous process of an hour+ in bulk then 4-10 hours in absorption etc. etc... In LFP it is pretty much bulk almost all the time. heck I don't ever need to run to absorption and hold it there if I don't want to. The only real reason I do is to manually synch the Ah counter.

I can simply run the alt for what ever amount of Ah's I desire for the next day or two, or three, but no more than I care to... What point you get to in SOC does not matter, like it does with lead acid, so long as you don't go below 0% SOC, which is actually very hard to do....

Yes capitalize on opportunities to charge, when you can, but don't stress over it. You'll soon find that you don't need to..

Sure you take charging opportunities, when you have them, and we have, and do, recharge at 40% DOD or 30% but I don't think I have ever felt a pressing need to do so at 50% SOC when we are out enjoying cruising.


Quote:
Originally Posted by Jd1 View Post
The actual parameters will have to be worked out yet but the 50% figure happens to be the default with the SOC meter plus I do not want to get into a situation where I am forced to charge before I can settle down at an anchorage. At 50% charge I have enough power and don't need to worry.
You are still in a lead state of mind. Lead parameters don't apply well to LFP. I know this is very, very hard to grasp but you will come to see this and will likely look back and laugh....... As I have said many times before the biggest hurdles in LFP are about lead mindsets. Everyone, including myself, I feel underestimates this going into it.

Quote:
Originally Posted by Jd1 View Post
Going below that probably only makes sense if you know what your itinerary is for the next few days and you'd be controlling that manually which I don't want to get into.
We don't roll with much of an itinerary, not how we cruise, and so far charging LFP has not been a concern. Not thinking about batteries all the time is a actually a big relief..

It takes so little time to put multiple days worth of energy back into the bank that charging and focusing on battery management has literally become a non-issue for us.

My wife is even to the point of asking if I want her to flip on the alternator.

I occasionally glance at the Ah counter, and as we get close to 30% I may decide to flip the solar switch, if I don't want to hear the motor chilling the holding plate.

With lead we almost exclusively used the engine driven refrigeration. Because we needed to charge so much engine driven refrigeration was a good fit. With LFP it is now used very rarely.. Today we are almost all 12V DC refrigeration. Sure when running the motor I may boost the plate with the engine but we no longer find we need to run the engine for charging anywhere even close to what we had to with lead.

Our time at anchor is considerably quieter and considerably longer between engine charging events. I don't panic when I see we are close to 20% SOC but it admittedly took a while to get to that point.

Quote:
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Of course if you are into motoring that's a different kettle of seaweed!
We are not into motoring, though with sailboats and cruising Maine and the Maritimes, in the summer, it can be a necessary evil. Lack of motor running is the main reason we like LFP so much. My wife is a huge fan of the LFP bank...! Just getting the lead bank back to 85% SOC took so much longer and bought us a lot fewer days of peace & quiet on the hook.
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Old 15-11-2014, 21:44   #15
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Re: Some more lithium thoughts and questions

Lead prefers to stay fully charged and dies if left uncharged, where lithium prefers to be discharged, but not fully discharged.

This is a key point on why most BMS systems are actually harmful.
They are trying to keep cells 'balanced' by making sure every cell is completely charged up. This is just reduces the life of the cell, particularly if you have one that is weak, it ensures that it becomes even weaker.
I have given up arguing this point, but there you go.

When I created a charger for R/C cars I included a cooling fan in it and a temp sensor and pointed out batteries last longer if kept cooler. The reaction from the established industry was to create a 'battery heater' product and extoll the virtues of hot batteries. What can you do? If you are savvy, you sell a deluxe expensive battery heater that gets them hotter than the other products.
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