What would you do?

[grizzzman]

He He He you do have a point there about the script. Without question that is my weak point. I have a voltage triggered timer that has adjustable hiatus. Perhaps that would be a better choice. I will need to test it too see if it will be a Problem after the timer has triggered. Since my loads will low amps I am likely over thinking this
Thanks Terry

Why bother using a pwm solar controller at all? For just a few percent of AHs? Seems that a shunt type controller could run a SSR relay just fine and not deal with the on and off heat that is generated by pwm ? Is there any real need for absorption during all charge cycles? What am I missing?

Thanks
Now that I think on this, seems to me you would not see PWM until it reached absorption. So during Bulk (Boost) does the Dingo do it differently?

All PWM controllers basically work the same way, solar connected to battery until the target voltage is reached, voltage control from there on. The only difference to an MPPT controller is during the bulk phase of operation, after that all voltage control including shunt diversion is PWM control, a shunt diversion required a dump load equal to or greater than the charging capacity and needs to be available at all times. The hot water service is a great dump load, but once it reaches the thermostat cut off temp the load is no longer available, so what then?
Absorption mode not only puts those last few Ah in, it also gives the cells in a parallel string a chance to equalise capacity, a solar array that can pump out big amps will run the air con, but what about when there is no air con load? I posted earlier about the problems associated with high current charging as the top end of charge is approached, so if the DC to DC was to be combined with the solar then probably a bulk only then drop to float would be a good thing, let the solar do the last bit. This is not a long term suitable method for Li solar charging though and quite a few who have a very fringe understanding of Li charging requirements will learn that they really didn't know it all as the capacity starts to disappear. No doubt these will be the first to claim lithium batteries are no good, these type of people can not accept that they got it wrong

T1 Terry

So for the pack to stay healthy and balanced, they require time "at" the knee? You have also stated to cut charging. And here you talk of floating? Could you please explain?
Thanks

[T1 Terry]

Terminologies carried over from the lead acid battery technology do cause confusion eh Float charge for lead acid is 13.8v and means that if the battery will be held at that voltage a trickle charging will continue indefinitely, you have to remember that 12.8v is the really fully charged voltage, the higher voltage is to over come the internal resistance
LiFeP04 are fully charged at 3.4v per cell, perfectly balanced that equals 13.6v, they will not accept any more current unless the voltage exceeds their present voltage by 0.05v, or at the fully charged state that's 3.45v. Again if the pack is in perfect balance that adds up to 13.8v..... but the difference here is they are not trickle charging as the voltage must be greater than 13.8v (3.45v at each cell) for a perfectly balanced pack, so the suggested solar charging float voltage for a pack in use I still 13.8v, when not in use there is no need to charge at all. If not in use for more than 3 mths the battery should be discharged to around 3.3v per cell and disconnected, they can remain in this state of charge for yrs.
Lithium batteries do not like remaining on a constant "charge", but as long as the voltage is below the voltage they will accept more charge current they will not actually be on a constant charge but rather at a constant voltage waiting for any drop in the battery voltage for charging to resume. Once the cell is satuation charged the voltage will only drop if a load is applied.

As I say to anyone first trying to get their head around lithium batteries, don't compare anything about them to lead acid batteries or it will do your head in, the voltages are similar when fully charged but that is the only thing they have in common and they don't actually even share that as lead acid is really 12.8v fully charged and rested.... lithium would be at least 50% discharged if not more at that voltage.

T1 Terry

Missed the explanation for the need to cut charging. If a cell reaches 3.6v it is at a point it can not accept the charging current at the present rate it is being supplied, all charging needs to stop to allow the charge to settle throughout the cell or cell group, then charging can resume until either the primary control voltage is equal to the total voltage of all the cell groups in series, or, a cell or cell group again reaches 3.6v. How long the charging stops depends on the system, especially a continuous loads on the system as that will very quickly remove the over voltage charge on the high cell, yet a system that has no load applied will take quite a while for that over voltage to dissipate throughout the cell, in fact once saturation charged it will not dissipate at all until a load is applied.

[grizzzman]

Dang Terry that is good info! My problem with "float" is leaving the charge at the upper level 100% range (for the very reason during storage you drop the charge to 50%) But then again whats the point if ya can't have the battery do your bidding If you don't mind lets discuss solar charging spec's (I am still pondering the cell level controls/disconnects) Bulk (Boost) at 14.0 to start then when it hits absorption time 15 min.(adjusting upwards until upper cell limit trips then backing off a bit. I can also set a % of the pack AH amps (say 5 amps as a back up termination point on a 100AH pack) then set float to 13.8 . Does this sound reasonable?
Thanks Terry

[T1 Terry]

Solar float 4 cell balanced at 13.8v is suited to a battery that is working, not for a battery in storage, why would you want to be charging a battery while it is in storage if you don't have to? 5% is a good safety margin for battery isolation but you would want to set a warning alarm at say 20% SOC so you know to keep an eye on what you really need to turn on until you get a chance to recharge by solar or DC to DC or mains or generator.... or SWMBO on the exercise bike.
Absorption time is really only required when multiple cells in parallel are used to build up the capacity, a single 100Ah cell will do its absorption stage while at the 13.8v (3.45v per cell) float. Multiple cells in parallel will too, but it just takes longer and the sun only shines for a limited time each day. As a general rule of thumb, 14v bulk, 13.9v absorption and 13.8v float will work well for solar with a lithium battery in use as the battery will be discharging throughout the night supplying the load and recharging each day the sun shines.
Lithium batteries are the complete opposite to lead acid batteries when it comes to charging. They don't like to sit at a high voltage unused, the harder they work the longer they live, they don't die because they were left un charged or not fully charged. The advertised capacity means just that, you can have 100Ah from a 100Ah battery, but that doesn't mean you can discharge it to 0V or even much below 2.8v without doing harm, the 100% depth of discharge will occur before the 2.8v is reached, so an accurate battery monitor is a must have and it must be programmed to the type of battery you are using and in 10 out of 9 cases that isn't the figures given in the product brochure or those given by the armchair experts
Unless you have a monitor that can split down to 0.01% and adjustable in 0.01% increments, the charge efficiency is 100% and the Peukert factor is 1.00, the accuracy suffers by around 0.03% but if that is a problem then maybe off grid power using lithium batteries is not for you and a quality monitor like the Victron 700BMV can be programmed to auto reset the 100% SOC when the required parameters are met anyway. I only added this bit because a certain book writer says the alarm bells ring when anyone claims 100% efficiency, LiFeP04 is not 100% efficient, they just don't make monitors for RV use that can cope with the 99.8% charging efficiency and 99.98% to 101% discharge efficiency at the loads likely to be encountered in RV house battery use. (that'll get him going, a claim of 101% discharge efficiency, I'll let him workout how that can occur )

T1 Terry

[grizzzman]

Terry I had to look up SWMBO....... It could not be truer you misunderstand my 5% ending amps example to terminate charging. Thanks for clearing up absorption issues. My battery monitor does not use Peukert is not used with this system. It has voltage compensation and temp compensation (this can be easily defeated) I realize now I can do bulk (boost) at 14.0 but I can not change absorption voltage. But I can set the time in absorption (like to 0 if needed) that would send it right to float 13.8. charging efficiency is adjustable with my FLAs it is at 94%. So that's not a problem. The monitor resets the AH counter when the battery is deemed charged... 101% discharge efficiency.....Hmmmm well ok

Thanks Terry

[grizzzman]

Hi ya Terry
With adapting a higher voltage for use to charge lithium (as an example say dc to dc charger that outputs 14.8 volts), do you just cut charging when the source hits 14.0? When do you allow the charge to start back up?

Thanks

[Dot]

Hi Grizz, how come you are on here at this time of the day?

[grizzzman]

Hi Grizz, how come you are on here at this time of the day?

Well Dot it is a bit after 8:00 PM here. What time is it there?

[Dot]

Oh, it is 1330hrs here in SA, too hot to go outside just yet but shall be heading out for tea so watch out for proof later tonight

[T1 Terry]

Hi Grizz, how come you are on here at this time of the day?

Well Dot it is a bit after 8:00 PM here. What time is it there?

It's lunch time Jan 5th 2017, roughly 1:30pm in South Australia, 11:30am in Perth WA, 2:30pm in Tasmania, Victoria and NSW, still 1990 something in Qld as they still can't understand how day light saving works

T1 Terry