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Old 12-03-2015, 19:20   #1
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Simplified & Practical Lithium Charging?

And when I say "Lithium" let's suppose that means only LiFePo4 types, since they're the only ones that can't fail and start an insane inferno from flammable electrolyte.

Don't get hung up on the exact numbers, since they'll vary a little with each manufacturer and improvement in chemistry.

But it seem that experimenter/owner/users and manufacturers are slowly coming to an agreement that these batteries can be charged pretty simply. Most cells are now being rated as "safe" to charge up to some 4.0 volts and discharge down to 2.0 volts without damage, and to "fully" charge and discharge if kept above 3.5V and not above 3.6V.

So, assuming a fixed voltage, constant current charger that was tightly and accurately limited to 3.6 volts per cell, (i.e. 14.4 for a "12" volt battery) with an amperage that couldn't stress the matched bank, and for the moment ignoring the decreasing-amperage taper charge along with charging to full capacity...

Couldn't one then get a fairly simple and fairly good charging protocol, rather easily?

This is also rashly assuming that either the cells were pretty well matched to start with, so a top balance was not critical, or that the top match (balance) was done as part of configuration.

And that from that time forward, a rather simple BMS was relied on to monitor the cells, cutting off the charging at perhaps 3.65V and the discharging at 3.45V, keeping the cells within working parameters.

Again the goal is to eliminate the rocket science and get "pretty good" results, especially since cycling a battery from 0-100% is apparently not best for longevity while 10-90% or something similar may be "good enough" to still be vastly superior to lead acid installations, with many players suggesting this will still provide 2000-5000 cycles, some arguing twice that much.

So...Maybe we're at the point where "good enough for government work" is feasible, and all the rest is, really, just for the guys who like to restore Porches and soup up their muscle cars now?

Are we near or perhaps at that point yet?

Motivated by other threads asking how big a battery anyone can lift or move these days, and the convenient way that switching from lead to lithium pretty much eliminates that problem. And with two or five thousand deep cycles, price is still a consideration, but economy no longer is.

If the charging and BMS can be simplified while the performance and safety and longevity are still that good...Are we there yet?
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Old 12-03-2015, 21:48   #2
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Re: Simplified & Practical Lithium Charging?

I think you've got it right.

I would suggest that before installing the cells, that you do a capacity test on each of them. This makes sure you start with good cells, and know how well they match up. Then fully charge each cell so they are balanced before connecting them in series.

The other consideration is to not always keep them fully charged if you don't need to. This is what you would normally want to do with lead acid batteries, but the lithiums should last longer to not always be fully charged.
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Old 12-03-2015, 22:09   #3
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Re: Simplified & Practical Lithium Charging?

Please forgive my ignorance but once all batteries are fully charged at time of installation aren't there electronic devices that can be used to automatically control a bank of Litho batteries?
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Old 12-03-2015, 22:31   #4
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Re: Simplified & Practical Lithium Charging?

Jack-
How far (% charge) to keep them would be almost a whole other issue. Again aiming for KISS...maybe that means using the same charger, but instead of charging, say, to 3.6V...dropping another tenth so it is a simple "switch" to throw? Or, since most batteries are rated to charge to ~4.0 volts, mightn't stopping the charge at 3.6 without the taper current be enough?


Holy mysteries remain.


Walkabout-
Yes, there's all sorts of stuff, aimed at all sorts of markets. I'm not well-read enough to know if there are any chargers aimed at the marine market, let alone how complex and expensive they might be.


Kinda like cars today: Airbags that turn into claymore mines?! This is progress? Sometimes, less would be more, and I can't help thinking were at the point where someone ought to treat these batteries like horseshoes. You know, close is good enough. Keeps things cheap & reliable.
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Old 12-03-2015, 22:59   #5
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Re: Simplified & Practical Lithium Charging?

Understood Hellosailor. I agree with you. Coming from the electronics industry I do also know how you can use electronics to do complex tasks simply.

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Old 12-03-2015, 23:12   #6
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Re: Simplified & Practical Lithium Charging?

Things are looking good down the road for voyagers I think ?

Gas/diesel/propane etc needs to be refilled but an unlimited supply of electricity is somewhat feasible !

Can't add more then that but I will be watching !
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Old 12-03-2015, 23:34   #7
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Re: Simplified & Practical Lithium Charging?

It looks like we will have a commercially available solution in about 18 months. Tesla is supposed to come out with lifepo battery packs for residential solar system's sometime next year. I have no idea how they work however.
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Old 12-03-2015, 23:45   #8
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Re: Simplified & Practical Lithium Charging?

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Jack-
How far (% charge) to keep them would be almost a whole other issue. Again aiming for KISS...maybe that means using the same charger, but instead of charging, say, to 3.6V...dropping another tenth so it is a simple "switch" to throw? Or, since most batteries are rated to charge to ~4.0 volts, mightn't stopping the charge at 3.6 without the taper current be enough?
The common wisdom is to use only the 'middle 80%' of capacity,
so don't charge above 90% full, and never below 10% full.
A simple way of doing that can be reducing the charge voltage to a lower voltage. It is my view that it is better to charge them faster at a higher voltage, and then stop charging them sooner, than spend more time charging them at lower voltages. Not everyone agrees.

I was saying to not keep them fully charged. Charge them to 90% full, then don't recharge them back to 90% full until they are discharged down to say 25% left. This isn't how you would do lead acid, lead acid you would want to keep them fully charged all the time if you could, like run the generator everyday to 'top them off'. So I'm saying don't 'top them off', let them discharge down before recharging them (assuming you don't need full batteries for a specific reason, for example, about to make a passage)
This might mean your solar panels don't charge today even though it is sunny. Find something else to do with that energy, perhaps heat up some water for showers.
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Old 12-03-2015, 23:51   #9
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Re: Simplified & Practical Lithium Charging?

Set you solar controller, battery charger, wind generator controller, alternator regulatoe, hydrogen, and hampster wheel to let's say...13.4v to 13.6v and done. No drama, no over charge risk, simple and easy. Then move on and enjoy life. Its been working great for my 400ah bank now for 7 months. This ain't rocket science science folks, stop trying to make it harder than it is.
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Old 12-03-2015, 23:59   #10
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Re: Simplified & Practical Lithium Charging?

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Please forgive my ignorance but once all batteries are fully charged at time of installation aren't there electronic devices that can be used to automatically control a bank of Litho batteries?
Yes there are electronics that will 'balance' the individual 3v cells in a 12v series string, generally called a 'BMS' for Battery Management System. People that sell them say the sky will fall and your boat will explode if you don't have one.
I disagree. Particularly for a house bank because you don't ever fully charge the cells so they can be 'unbalanced' a little and it makes no difference. They will stay balanced unless a cell is given different treatment, in particular, one is kept hotter than the rest. Strapping them together can sometimes make the ones in the middle get hotter without airflow, or ones on the ends can be subject to heat from engines, so this is a consideration when you install them.

I am personally working on a Lithium charging system that charges each cell individually. It isn't really a BMS, but a battery charger designed specifically for lithium packs, and can take any charging voltage from any source, and regulates it down to a cell's charge voltage.
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Old 13-03-2015, 00:08   #11
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Re: Simplified & Practical Lithium Charging?

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I am personally working on a Lithium charging system that charges each cell individually. It isn't really a BMS, but a battery charger designed specifically for lithium packs, and can take any charging voltage from any source, and regulates it down to a cell's charge voltage.
Do you mind if I ask what's the point?
Isn't the simicity of charging the 4 cells with a single simple programable battery charger the easy way to go when the batteries are wired in series?
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Old 13-03-2015, 04:51   #12
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Re: Simplified & Practical Lithium Charging?

I personally think that individual battery level monitoring should be part of any lithium install, where there is series strings.

other then that I agree with the basics presented here. After initial pre-installation balancing, balancing rarely becomes an issue in fractional C systems

Obviously bear in mind the long term storage conditions, if you do leave the boat for long periods

I fully agree with the no float charging and avoiding mini cycle re-charging wherever possible

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Old 13-03-2015, 06:24   #13
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Re: Simplified & Practical Lithium Charging?

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Do you mind if I ask what's the point?
Isn't the simicity of charging the 4 cells with a single simple programable battery charger the easy way to go when the batteries are wired in series?
I believe Rich without a BMS, you will have some cells fail prematurely. I think you know this and are accepting some lower life cycle. It may be the difference between 4000 and 5000 cycles, I don't know.
But most of the people that are playing with these batteries are tinkerers as they pretty much have to be as you can't buy turn key yet. Tinkerers by their nature like to tinker, and it's fun maximizing anything, they will go through extraordinary measures to get an additional 10%, where you may say, heck with that, I'll just oversize the bank a little and end up at the same place without all the constant monitoring and work.

This won't become mainstream until someone markets a turn key bank and charger, and in my opinion a BMS ought to be in there, a BMS is a simple thing, not high speed electronics and has been in model airplane systems and other packs for years, without issue.
The model airplane chargers connect to each cell to balance the pack, the charger is the BMS, most other larger packs have a BMS as part of the pack.
Yes you can do without a BMS, just like way back in the day outboard motors had no voltage regulation, they just trickle charged the starting battery at a constant rate, regardless of its state of charge. It was simple and it worked, just it was really easy to greatly improve on that system so it has been improved.

Assuming a production battery, why not have a BMS as they are so simple?
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Old 13-03-2015, 06:43   #14
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Re: Simplified & Practical Lithium Charging?

But back to the original question, in my opinion, which is someone who has run zero LIFE house banks, ( No experience) you can in fact operate a bank very simply, just you will be leaving some capacity and possibly life on the table if you do so.
Completely different chemistry and use, but Toyota manages the battery pack on a Prius by not charging over 80% or discharging under 40%, they lose a lot of capacity by doing that, but have gained a long life pack with an extremely good service record for doing so.
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Old 13-03-2015, 11:06   #15
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Re: Simplified & Practical Lithium Charging?

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But back to the original question, in my opinion, which is someone who has run zero LIFE house banks, ( No experience) you can in fact operate a bank very simply, just you will be leaving some capacity and possibly life on the table if you do so.
Completely different chemistry and use, but Toyota manages the battery pack on a Prius by not charging over 80% or discharging under 40%, they lose a lot of capacity by doing that, but have gained a long life pack with an extremely good service record for doing so.
I wish these auto companies would release their research. I would find it very interesting to find out why the Prius cuts off the discharge at 40%. What testing was done with say a 20% cut off or even 10% and the effects this would have on battery life. I know it is not scientific but older phone litho batteries used to have what they called an inherent memory and you were told to fully discharge your phone battery before recharging. Now I understand this is not the case. When it comes to new batteries I would ere in not relying on old or past practices but rather rely on sound new scientific knowledge and valid comparative testing.

So let's have an independent test body like what I use in my electronics business like UL to do independent performance testing. Who knows we may find one brand that surpasses life cycles and max drain and top off way beyond current expectations. IMHO
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