Lithium Batteries (for the rest of us)

[EddieS]

ebaugh and Terry
Thanks for your responses. I read through the link that Terry sent and could not find the tall tales. I guess my alternative is to get off my lazy a** and start learning about this technology. Thanks again for the info. I'll be back. Ed

[vRUN]

Thanks for summary ebaugh

Originally Posted by ebaugh

(marine) inverter chargers can all be programmed to do this. So can many shore power chargers. But it's a not always a pre-programmed profile. You have to custom set the parameters you want in the chargers configuration.

Same with the Maxim IC. Currents and voltages are "programmed" with a couple of resistors selected and soldered into place. Sufficient for me since I do not think I'll change the bank that often.

(my) "small bank"
I believe it to be good engineering practice to first build a scalable model... especially since at the moment I do not really need 400 Ah
(I also believe that pressing old equipment into use for tasks it hasn't been designed for does too often result in failure - and then blamed to the new technology... so I for one am not going to use an old Pb charger, even with "fixes" - but then I don't have too )

[georgec]

How does the cell logger read the voltage of individual cells when they are in parallel to make the 12v bank? Also, if you need to bleed some voltage off to balance the cells wouldn't you have to isolate that cell from the bank?

[goboatingnow]

Just to address one issue.


Its bad practice to float Li. Hence when the selected voltage and optionally current set point are reached , charging should be discontinued. Charging should then only begin after a certain percentage of discharge has occurred.

Leaving an impressed voltage on a LI can cause plating of the anode and gradual loss of capacity over time.

This is actually an area , ie backup batteries , where Li is not ideally suited

In my view on larger boat banks, when charged disconnect the charge sources. For long unattended situations you have (a) no power requirement so shut down the bank and rely on the LVC to save the batteries

Or (b) ensure the charge sources can reconnect after certain discharge has occurred ( or even let the LVC restart the charge process)

On a Li battery every cycle is a cycle.

Dave

[goboatingnow]

Originally Posted by georgec

How does the cell logger read the voltage of individual cells when they are in parallel to make the 12v bank? Also, if you need to bleed some voltage off to balance the cells wouldn't you have to isolate that cell from the bank?

Cells in parallel by definition are balanced , even if they are not at identical SOC. hence you only need to read the series string voltages

DAVE

[T1 Terry]

Originally Posted by goboatingnow

Just to address one issue.


Its bad practice to float Li. Hence when the selected voltage and optionally current set point are reached , charging should be discontinued. Charging should then only begin after a certain percentage of discharge has occurred.

Leaving an impressed voltage on a LI can cause plating of the anode and gradual loss of capacity over time.

This is actually an area , ie backup batteries , where Li is not ideally suited

In my view on larger boat banks, when charged disconnect the charge sources. For long unattended situations you have (a) no power requirement so shut down the bank and rely on the LVC to save the batteries

Or (b) ensure the charge sources can reconnect after certain discharge has occurred ( or even let the LVC restart the charge process)

On a Li battery every cycle is a cycle.

Dave

Not sure where you got that information from Dave. What cell voltage do you call a float voltage?

T1 Terry

[goboatingnow]

Originally Posted by T1 Terry

Not sure where you got that information from Dave. What cell voltage do you call a float voltage?

T1 Terry

Its not a question of voltage, Good practice is that no long term impressed voltage is left on a Li cell after charging.

Floating is a concept from LA tech. It really doesnt have relevance in Li as the self discharge is minimal. ( which is what float charge was designed to counter). Hence after charging in Li, the charger should be disconnected.

The next issue is when to reconnect the charger

What we often have in boats is not float charging but load sharing. This is particularly problematic in Li, as it can generate lots of mini cycles. Two scenarios exist (a) Ie the charger resumes supplying current to the boat and hence impresses a charge voltage on the battery. or (b) a reconnect voltage is set so that when the battery discharges to that point the charge cycle begins. ( thats often what used in integrated IC circuits).

The correct way to share a Li battery and a load, is often referred to as Power Path Switching. For longest life, the Li battery should supply the load via a Diode sharing path ( either ordinary or MOSFET ideal) Once the power supply/charger load current is within the limits, No voltage is impressed on the Li battery. If the load is greater then the charger, both charger and battery share the load, with the battery slowly discharging.

Separately , behind the diode splitter, a Li charge circuit kicks in at a predetermined voltage threshold to recharge the battery and then disconnect. That recharge point should ideally be set at the low discharge point.

Thats what is in well designed Li power circuits in consumer devices that have to be operated while being charged ( iPhones etc)

Of course in a boat , using an existing charging schema, this is difficult to arrange ( which is why personally I would recommend a complete system redesign ) then all you can do is select a float voltage that reduces voltage stress in the Li battery. The problem comes when load sharing occurs and many chargers , come out of float mode and raise the voltage and supply the load and also stress the already charged Li battery.

No easy answer using existing systems.

PS A lot of this research is coming from GSM devices that use Li to handle the large current pulses ( 2-3A) that occur in class 10 devices. This causes lots of mini cycles and has lead to reduced life times , often unexpectedly so.

Dave

[Lagoon4us]

Our solar regulator applies 14.10 volts as a maintenance voltage, different terminology i guess and we don't leave our Dolphin charger on we instead manage our bank by being aware of it's content.

We use position '08' on the charger which gives a max of 13.60 volts and this seems to boost our days charge nicely allowing the solar to top up on cloudy or unproductive days due to sailing angles etc

When we store the boat it will be with the Lithium charged and isolated from the house.

Works for us and has for months now...

[goboatingnow]

Note , the other thing to bear in mind for some users, Its very unwise to charge Li at below freezing .
dave

[Lagoon4us]

Question has anyone experienced the Junsi reading a different total voltage to their meters?

I have two different albeit expensive monitors and the Junsie always reads higher? One a BEP the other a GSL Solar monitor which generally agree with each other.

Are $12:00 Junsie's accurate?

[transmitterdan]

Originally Posted by goboatingnow

Its not a question of voltage, Good practice is that no long term impressed voltage is left on a Li cell after charging.

Floating is a concept from LA tech. It really doesnt have relevance in Li as the self discharge is minimal. ( which is what float charge was designed to counter). Hence after charging in Li, the charger should be disconnected.

This isn't a technical answer If a charger is programmed to switch to a "float" voltage a couple tenths below the resting voltage of a fully charged bank I fail to see how this can be a bad thing. There will be no current from the charger and thus no "plating" or other ill effects can occur. In this case how can the bank even know the charger is powered on? From its point of view the charger is "off". It is infinitely easier to coerce a traditional battery charger to float at some lower voltage than to completely shut off shut and on based on SOC.

[georgec]

Originally Posted by goboatingnow

Cells in parallel by definition are balanced , even if they are not at identical SOC. hence you only need to read the series string voltages

DAVE

Is there a general consensus on the design of a house bank? I am looking at a 12 cell bank. Is it better to place the cells in parallel then in series? That would be 4 banks of 3 cells in parallel. Is the main reason less cells to monitor? In this design wouldn't you monitor each paralleled bank?

[chala]

Originally Posted by georgec

How does the cell logger read the voltage of individual cells when they are in parallel to make the 12v bank? Also, if you need to bleed some voltage off to balance the cells wouldn't you have to isolate that cell from the bank?

Originally Posted by goboatingnow

Cells in parallel by definition are balanced , even if they are not at identical SOC. hence you only need to read the series string voltages

DAVE

Is that a clear answer ???

[transmitterdan]

Originally Posted by chala

Is that a clear answer ???

Yes it is.

[ebaugh]

Originally Posted by georgec

Is there a general consensus on the design of a house bank? I am looking at a 12 cell bank. Is it better to place the cells in parallel then in series? That would be 4 banks of 3 cells in parallel. Is the main reason less cells to monitor? In this design wouldn't you monitor each paralleled bank?

Always connect first in parallel then in series, unless your application requires multiple banks.