diy solar

diy solar

New PowerMax Lithium Series Converter/Chargers

LFP batteries can benefit from some level of absorption.
They typically should not be held in cv until current approaches zero though.

CC ~= bulk
CV ~= absorption

I found a graph on page 43 in my SPF 3000TL LVM-24P 3.0 manual that agrees with your pdf and the 3-stage NPB.

ChargingCurve.png

There is a formula for calculating the ABS time in Utility Charging Mode.

Time in ABS can vary between 10min and 8hrs. There is no setting for ABS time.

I can't tell if this graph applies to Solar Charging Mode. I can log into a RPi and graph later.

Does the NPB calculate ABS time?
 
No time calculation. Float is triggered when current equals 10% of Bulk. If the system has significant loads this level may never be reached.
I don't understand the 10% Bulk phrase.

The Growatt is my second Inverter/Charger that calculates ABS time. I believe that is a good way to do ABS. I believe that there needs to be some time limit on ABS. Otherwise the ABS Voltage could continue indefinitely. Wouldn't that be a bad thing?

If the load can be maintained at Float Voltage, why not switch? If the Float Voltage cannot carry the load, then consider re-bulk.

Is there a situation where the '10% Bulk' might continue ABS too long?
 
I don't understand the 10% Bulk phrase.

The Growatt is my second Inverter/Charger that calculates ABS time. I believe that is a good way to do ABS. I believe that there needs to be some time limit on ABS. Otherwise the ABS Voltage could continue indefinitely. Wouldn't that be a bad thing?

If the load can be maintained at Float Voltage, why not switch? If the Float Voltage cannot carry the load, then consider re-bulk.

Is there a situation where the '10% Bulk' might continue ABS too long?
10% bulk means absorption until the current drops to 10% of the configured rate.
For a 50 amp charger that would be 5 amps.
The popular big blue 280ah cells have a recommended tail current of .05c(14 amps).
In reality optimal tail current will depend on both the bulk voltage, bulk current and probably cell temperature.
 
10% bulk means absorption until the current drops to 10% of the configured rate.
For a 50 amp charger that would be 5 amps.
The popular big blue 280ah cells have a recommended tail current of .05c(14 amps).
In reality optimal tail current will depend on both the bulk voltage, bulk current and probably cell temperature.
If there is a 6A parasitic draw, then ABS would continue indefinitely because charge Amps would never fall below 5A.

An ABS timer is a good thing.
 
Any updates on the MeanWell charger??

The other one I have saved in my cart is the Victron Energy Blue IP22 Smart - they have a 30A option - $195. Ouch.
 
Too busy and out of town.
Interesting that it does not come with a cord. Had to grab a surplus computer cord from work.

I assume it does what it says.
 
IIRC the concern was charge termination at 10% of current and if there’s a load that it would never terminate.
I don’t think it re-boosts either, the assumption is you unplug from shorepower at some point and it starts over the next time you plug in.

Just curious. I still have not used the powermax charger - solar covers it.

2 week trip coming up though, 3K miles. I finally get to really test it all out.
 
I'm using a PM3-30 for my home brew 4S-2P pack. First I dropped down the peak voltage to 14.2v and selected 3 stage charging mode. After settling in at around a 13.2v "float" voltage overnight the unit quit working (LED light off). Unplugged and re-plugged it in. Unit started working again until mid day, then LED went off.
Gulp - looks like sunshine_eggo basically said what I did ...

Not unusual. Your bank is fully charged, and assuming it did a great job, the terminal voltage would settle to about 3.38v (13.52v total rested like after 12 hours, higher if less hours).

When it dropped into the 13.2v float mode, that voltage is LESS then the battery terminal voltage, and no current into the battery will flow. (The voltage differential for charging is basically backwards) You won't measure 13.2v of course because that would be the internal CV of the charger at that point.

Charger gets confused in float when no current is actually flowing and may consider itself disconnected, extinguishing the light. :)

Resetting the charger just quickly goes into this cycle again. So unless you have loads you need to run, I'd just simply NOT let the batt sit there at the 14.1v static setpoint. If you do, you are trying to push the cells to zero absorb (aka tail current), which is unnecessary and damaging long run.

Ie, at a static 14.1v when it fully charges, if allowed to go to zero tail-amps, it is basically trying to push the cells beyond capacity - which it can't do and just creates more secondary reactions prematurely aging the bank.
 
Any FLA charger that does equalize is out for AGM or lifepo.

Definitely out for LiFePO4, but the "never equalize agm" is often misconstrued with flooded lead acid batts that go to a very high voltage EQ, like 15.6v

In many solar controllers where you ARE using agm's, say where the CV is 14.4v, if you look at the specs where the controller says it will "EQ" for something 1 hour at only .2v above your set CV point. like 14.6v, this can actually be ok - because agm's are notoriously UNDERcharged in a solar application.

The problem is most solar controller manufacturers confused the issue by using the EQ nomenclature for what should really be called a "refresh". For agm's at least.

On the other hand, some of those who run flooded, and don't check the controller spec for a "TRUE" higher voltage EQ (which takes many hours actually) just *think* they are doing an EQ because the controller says so, but is actually doing a relatively mild refresh instead.

This dual-use of the "EQ" nomenclature has caused SOO much confusion over the years.
 
In reality optimal tail current will depend on both the bulk voltage, bulk current and probably cell temperature.
Equally important to LFP and lead-acid both, but ESPECIALLY dangerous with lead-acid if you never go to float and stay in CV forever due to thermal runaway.

Ideally, you follow the manufacturer's recommendation on what C/n rate at which to trigger the switch to float.

AND - crucially, if you cannot reach that stated value, but instead observe a "stall" or no further improvement in the tail-current drop say from 10-30 minutes, you switch to float.

Not watching for the "stall" has destroyed banks, because unless the cells are factory new when the manufacturers guidance was pretty easy to obtain, age and use increase the internal resistance, and the wise battery manager guy will observe say 6 months to a year later if a stall is occuring, note the amperage, and change the new amperage trigger for float a bit beyond that.

Thermal runaway lead-acid:
1) Battery stays in CV and never gets trigger to go into float.
2) At high CV, and very low current, this last part of the phase is very inefficient chemically.
3) If left on too long, that inefficiency turns into heat. You can't feel it at first, but give it a week or so. If you could actually feel the plates themselves, you'd know quicker.
4) When lead-acid gets warmer, the chemical reaction itself is more efficient.
5) Even though the battery is already nearly totally charged, this lingering heat increases the battery's demand for more current. But it is already charged!
6) Charger obeys, more unnecessary charging current flows into an already charged battery, creating more heat, creating more demand... you see where this is going.

For a consumer, usually this is in the form of bulged out gels or agms, tops of cases popped, vents blowing, terminals bending off at angles.

In a commercial environment, lets just say you don't want to drive up to your vault doors blown wide open, halon going off, firemen on the scene ...

All this from just a weeny little tail current. Just saying - don't discount the damage just a "little" current can do.
 
The term equalize, in relation to LA chemistry, has two definitions, desulfate and destratify.

Desulfate is charging, the act of un-discharging, which basically changes lead sulphate back into lead oxide. The process takes a long time to complete. The S molecules are returned to the water and that re-constitutes the sulfuric acid in solution. It is critical that the S not remain attached to the Pb too long or it will be sulfated as crystals.

Destratify is stirring, the act of mixing acid that may have settled in the water. It requires enough Voltage to cause electrolysis where the bubbling acts to mix the solution in a FLA. Mixing time is minutes in contrast to the hours needed for desulfate. There is NO mixing with gel and AGM.

With LFP, charging is basically returning enough energy into the battery to last until the next charge event.

IMHO and YMMV.
 
I have read the thread but still don´t understand what´s the consensus, are these Powermax recommended chargers for lifepo4, ( big amperage ) or not for any safety issues? I wanted the Victron IP22 30amp but one with 100amp would be great if is ok. But I want something that I can set up and forget about it, I don´t want to be disconnecting the charger because some voltage problem arises from this charger. Any thoughts?
 
The default 'lithium' charge voltage is too high - at least for my cells, they will hit bms over-volt. And the default 2-stage voltages are not adjustable.
In fixed voltage output IS adjustable, it works fine, but you would have to set it to a float level to set it and forget it. I'm not so sure that's such a great idea with any lithium battery. And at a lower charge voltage the differential between charge voltage and battery voltage would be so low as to be very slow charging. Constant volt charging drops current as the battery voltage rises.

Frankly I would go with the Victron, that's on the top of my list to replace my Powermax. But I am still using it, in fixed voltage set to 14.1V, with a switched power source, and I simply switch it off when charge current reaches 11A. It will put out the full 55A until very close to full, and when the CV current starts to drop then the battery is full. So far I have not had to use it, my solar panels recharge the battery to full each day, even on cloudy days with some sun breaks.

We've been two weeks out on a trip, several days travelling, then parked for several days, some cold temps, and still have not used more than half of our capacity. Solar recharges, or if we're driving then the Victron Orion supplies 18A to get it topped back up. I have it set to 13.8 boost and 13.4 float, it has a minimum 10 minute boost duration which restarts every time you start the engine, so I didn't want it over-floating the battery.

The biggest problem is there is no charge termination - it drops to float, which would be fine, but the boost voltage is too high.

We were hoping to get a full report from Time2Roll on the MeanWell charger - it had a better charge logic, but does not have a reboost function, so it resets each time you plug in, settable charge voltage, and drop to float. There is a question whether it would drop to float if there are any loads that keep the battery voltage below full charge level, so will it actually drop to float?

If you have a really big battery supplying large loads then surely you'll be looking for a high-power charging option. I find my 230A battery to be very easy to maintain. We just don't have large loads to supply.

Also, be sure to consider the input current to your converter/charger - a 100A charger is gonna pull more amps than a standard 110v 15 or 20 amp circuit can supply. The 55A charger pulls 11A at full draw. I have it on a shared 20A circuit, so that's about all I would want a charger to use. Fortunately my other circuits cover the high-amp loads, like coffee maker at the galley, microwave, AC, gas-absorption refer on AC, and etc.
 
Back
Top