absorption stage for lithium

[native pepper]

As Bruce S says, a bulk charge to your set voltage is all you need, plus in my opinion, an active cell equaliser. Then you have a hassle free system and don't need to look at it for months.

Have 6 x 60amp single stage bulk mppt chargers on my house, set to cut off at 14v, 2x 40amp on my bus and 3 x 60amp supposed mppt bulk controllers which got made in India because of their cheap price. They are pwm and useless for my mate, so he gave them to me and they are crap, have repaired one twice and the last one didn't work from the beginning, it arrived in bits and have yet to have a go at fixing it. Have them on my workshop with an array of different wattage 12v panels from 10w to 250w, The house has 24v panels and so will the bus when it finally stops raining for a few days.

We've had little sun over the last few weeks and yet the 700ah on the house has yet to get below 13v. Yesterday we came home to the bank full, after just a few hours of sun in the morning, after 10 years living on lifepo4 at home and about 5 on the bus, just love them.

[T1 Terry]

A separate sense wire would be handy but even then if the regulator is set at 14v the amps will still slow down as it gets near 14v. I am waiting for the battery to run down atm but the next charge will be from the dc/dc set at 20amps and 14.4 volts but I have the bmv relay blocking the dc/dc when terminal volts reach 14v. I will see if it puts back the same amp/hr as the solar set on 13.9v.
Also Terry I guess once a year carefully charging to 14.4 should control any memory loss although between 13.9 and 12.5v I am getting 160amp/hr atm which is above what I was haoping for anyway. When I saw some of your graphs Terry in another thread you seem to get full amps to full and then stop are you using a higher voltage to push the amps in and a separate controller to stop it at a set terminal voltage?
Sorry about all the questions but I guess I am in the early stages with lithium where I am playing with settings every cycle and watching what happens like a hawk.

The higher voltage is the solar panel output via a PWM controller, no taper as it approaches the target voltage, only current tapering once it reaches that voltage to hold it there for 6 mins, then the Dingo drops back to absorption mode at a lower voltage to allow for that saturation charging to occur.
The secondary system watches for a cell voltage run away, cutting the charge for a set time and then checking it the over voltage signal has cleared, charging resumes if it has or another charge cut cycle starts and the whole cycle repeats.
Charging to 14v then stopping the charge completely until a lower battery voltage is sensed can also be programmed into the Dingo using the non PWM control option and setting the hysteresis to the desired difference between end of charge and commencement of the next charge cycle. It works ok if the battery capacity is sufficient to carry the system load for a few days but after that period the battery packs true condition will become evident and a serious 100% SOC error will become clearly evident.
Only a top end balanced battery will have all cells arriving close to the same voltage at the tail end of the charging cycle. top balancing is not the same as continuous balancing, without monitoring the cell voltage on a full time basis and recording the voltage at 30 sec intervals max there is no way of knowing just what is happening when the end of the charge cycle is reached.
There are variations in the primary/secondary control system that can be used such as a charge cut when a cell reaches 3.6v and not resume until a specified battery voltage is reached, sort of a hybrid between the 2 control methods, also possible to be programmed into the Dingo and maybe the Victron MPPT but I won't know that until I've had a chance to test and evaluate this control method but it could be an alternate control method for higher voltage (more cell groups in a series string) battery system that can have a few cell runaway problems, the 48v system is a good example of this feral cat hearding problem but something that just doesn't happen with 12v (4 cell groups in series) battery.
Trying to use multiple 12v batteries in parallel is simply asking for trouble so the charge to a lower voltage and stop would at least minimise the potential damage.

T1 Terry

[exscott]

well I just got back home and put the battery on charge at about 18amps from 50% charged. I was a bit surprised at that many amps and going right up to 14.1v at the terminals the doc only got to 90% so I knocked the input volts down from 14.4 to 14.2 and the amps dropped down to 3amps once it hit 14.1 volts and stopped the charger. So I guess some absorption is needed for them to get the last bit in.