MPPT Charge Controller for LifePO4 Batteries

[dennisail]

Originally Posted by dennisail

I have been looking at controllers to charge a proposed lithium bank. Seems the good MPPT controllers are very expensive, huge, heavy and possibly not all that much better than PWM (well not as good as spending that extra money on one more panel).

Here is a $41 adjustable 30A PWM controller which is small and light. So you could easily buy 2 or 3 to power your panels, and having multiple controllers has its benefits anyway. The fact you can adjust it should mean it will work fine with lithium. It has a separate temp sensor which you could easily rig up to a variable resistor to disable it.

30A LCD Solar Battery Regulator Charge Discharge Controller 12V 24V CE Certify | eBay

I see a many cheap supposed MPPT controllers but I am not convinced they will work as desired.

Thoughts?

I decided that MPPT was not worth it at this stage and went with a single 60A PWM controller of this kind. I will be using it on my lead bank. I will have a go at disabling temp comp in preparation for lithium.

I still believe that MPPT controllers can not function efficiently as designed on a boat with multiple panels per one controller. If you want to do it right you must use one per panel. Had victron bothered to get back to me I might have done it though.

[Maine Sail]

Originally Posted by dennisail

I still believe that MPPT controllers can not function efficiently as designed on a boat with multiple panels per one controller. If you want to do it right you must use one per panel. Had victron bothered to get back to me I might have done it though.

I have done lots of testing that shows they do perform just fine on multiple panels..... I use a PentaMetric analyzer with a computer data recording interface. I can track multiple shunts & voltages at the same time. Allows me to do A/B comparisons..

Not a tool everyone would have but when you do solar installs you need to understand and know what you are talking about. The analyzers don't fib and they have given me some great info over the years...... I bought this tool because a real lack of any solid data exists for the way solar arrays are installed on boats. Plenty of information for stationary land based arrays but very little for marine systems.

MPPT on boats usually does best with parallel panels but in some cases series wins if shading is not an issue.... If shading is a big issue then one controller per panel can also help. The new generation of MPPT controllers are very fast and react to the changes very, very rapidly. The Rogue, MidNite etc. are all excellent if you need custom programing options..

If you have space, then add more panel, if you are out of space go MPPT. MPPT's generally have more custom programing options than do PWM's but the Morningstar PWM's are very good.

[dennisail]

The whole point I am trying to make is that shading WILL be an issue on most boats. Therefore you WILL need separate controllers for the MPPT to work to its full potential. Of course MPPT will work fine on multiple panels if they are electrically similar and all have the same sun hitting them since the Vmp will be the same for all.

I would love to see the results if you randomly and actively shaded some of the panels in your MPPT tests, them compared the output to parallel wiring with PWM.

[senormechanico]

Originally Posted by dennisail

Yeah. I would run individual cell voltage displays too. For under $2 why not. Self powered to as low as 2.7V. So if it turns off you know you are in trouble.

Mini DC 0 32V LED Panel Voltage Meter 3 Digital Display Voltmeter Motorcycle | eBay

Seems a BMS is not really required if you set it up correctly, IE make sure no charge devices can exceed the max voltage, plus use a low voltage disconnect relay, and periodically check cell balance.

I ordered four of these.
One was shorted, but the others work great down to about 2.6 volts.
There's a tiny pot on the back side if you want to calibrate it.
The seller promised to send a replacement for the bad one.
I ordered 8 more for individual cell monitoring on my home's bank as well.
They draw approximately 20 ma each.

[dennisail]

Glad I could be of help!

BTW the panels I ended up going with are 4 x 200W 12V panels (18-22V).

My panels are rated to 11.1A @ 18V which is 200W. But the max current is still 11.1A at 13V which is only 145W. I certainly get the 11.1 amps out of them though! But MPPT does promise a decent potential power increase.

[SV THIRD DAY]

Originally Posted by dennisail

GBut MPPT does promise a decent potential power increase.

Even with shading of my multiple panels (the typical boat reality), I still see a 20% boost in current on a regular basis with our MPPTcontroler, so for my dollar it's worth the added cost because a cruising boat can never have too much solar!

[noelex 77]

Originally Posted by dennisail

My panels are rated to 11.1A @ 18V which is 200W. But the max current is still 11.1A at 13V which is only 145W. I certainly get the 11.1 amps out of them though! But MPPT does promise a decent potential power increase.

A brief reading of the specifications is a bit deceptive. The Vmp is measured with a flash of light, keeping the cell temperature low. In practice the cell temperature will be much higher and the Vmp will be significantly lower.

The current will also rise slightly at 13v. These factors need to considered (together with the effieciency of the voltage conversion and self consumption) when estimating the gain from MPPT technology.

It is much less than manufacturers would have us believe.

[dennisail]

That's pretty much why I went with PWM and 12V panels. When the time comes I will get individual controllers as I am sure price will come down

[goboatingnow]

Originally Posted by dennisail

That's pretty much why I went with PWM and 12V panels. When the time comes I will get individual controllers as I am sure price will come down

LTC are just sampling a new integrated mppt chip , $ 4 in quantity. It integrates a full tracking mppt logic, switching power conversion and a full CC/CV battery charger algorithm. Should provide the basis of some interesting small current mppt per panel designs. I'm trying to get a few to start playing

Dave


Sent from my iPad using Tapatalk

[T1 Terry]

Originally Posted by noelex 77

A brief reading of the specifications is a bit deceptive. The Vmp is measured with a flash of light, keeping the cell temperature low. In practice the cell temperature will be much higher and the Vmp will be significantly lower.

The current will also rise slightly at 13v. These factors need to considered (together with the effieciency of the voltage conversion and self consumption) when estimating the gain from MPPT technology.

It is much less than manufacturers would have us believe.

Haven't been here for a while I found the bad side of MPPT controllers far outweighed the good side when I tried using the on Li batteries. The battery voltage is always higher, there is very little iternal resistance to over come, pulse charging when the PWM control kicks in speeds the last bit of charging up significantly, providing a useable piece of battery capacity from auxiliary uses, like heating water or running an air con unit. Both these type loads can be heavy but short term, the water heating can be set up to do this, air con does it by itself, these small bits of capacity can be recovered very quickly with the PWM pulse charging effect, MPPT does seem to have this advantage due to the way it functions.

the constant voltage seems to be an issue with MPPT controllers, they don't have reference of when to drop back into boost mode and most controllers run a reduced float voltage they refer to as a maintenance voltage, they seem to drop into this mode and get stuck there till the batery capacity is seriuosly depeted.
Maybe someone will redesign an MPPT to suit Li batteries, not just a cosmetic preset charging parameter setting with a new menu spot, none of them understand what is involved with Li battery charging anyway, still stuck in the lead haze.

T1 Terry

[goboatingnow]

Originally Posted by T1 Terry

Haven't been here for a while I found the bad side of MPPT controllers far outweighed the good side when I tried using the on Li batteries. The battery voltage is always higher, there is very little iternal resistance to over come, pulse charging when the PWM control kicks in speeds the last bit of charging up significantly, providing a useable piece of battery capacity from auxiliary uses, like heating water or running an air con unit. Both these type loads can be heavy but short term, the water heating can be set up to do this, air con does it by itself, these small bits of capacity can be recovered very quickly with the PWM pulse charging effect, MPPT does seem to have this advantage due to the way it functions.

the constant voltage seems to be an issue with MPPT controllers, they don't have reference of when to drop back into boost mode and most controllers run a reduced float voltage they refer to as a maintenance voltage, they seem to drop into this mode and get stuck there till the batery capacity is seriuosly depeted.
Maybe someone will redesign an MPPT to suit Li batteries, not just a cosmetic preset charging parameter setting with a new menu spot, none of them understand what is involved with Li battery charging anyway, still stuck in the lead haze.

T1 Terry

Mppt in itself has nothing to do with charging batteries and many combined mppt/battery chargers are as you point out not well set up for Li. Often they enter CV mode and throttle back the current because the internal algorithm assumes its a current limited absorption mode LA . This is true even if the voltage limits are adjustable to " Li settings"

Pwm works on Li cause it's too dump to care, hardly a good engineering solution in the long term, but you are stressing the batteries with that method if you get close to the upper knee. ( which I know your not )

Dave


Sent from my iPad using Tapatalk

[noelex 77]

Originally Posted by T1 Terry

the constant voltage seems to be an issue with MPPT controllers, they don't have reference of when to drop back into boost mode and most controllers run a reduced float voltage they refer to as a maintenance voltage, they seem to drop into this mode and get stuck there till the batery capacity is seriuosly depeted.

As Dave says there is no fundamental difference in battery management between MPPT controllers and controllers that are not MPPT.

The best controllers of both types (MPPT and none MPPT) are quite adjustable and should be suitable for lithium even if they have been originally designed for lead acid.

The difficulty comes from the medium quality controllers that often have limited adjustability, preventing a suitable battery algorithm for lithium.

[Maine Sail]

Originally Posted by T1 Terry

Haven't been here for a while I found the bad side of MPPT controllers far outweighed the good side when I tried using the on Li batteries. The battery voltage is always higher, there is very little iternal resistance to over come, pulse charging when the PWM control kicks in speeds the last bit of charging up significantly, providing a useable piece of battery capacity from auxiliary uses, like heating water or running an air con unit. Both these type loads can be heavy but short term, the water heating can be set up to do this, air con does it by itself, these small bits of capacity can be recovered very quickly with the PWM pulse charging effect, MPPT does seem to have this advantage due to the way it functions.

the constant voltage seems to be an issue with MPPT controllers, they don't have reference of when to drop back into boost mode and most controllers run a reduced float voltage they refer to as a maintenance voltage, they seem to drop into this mode and get stuck there till the batery capacity is seriuosly depeted.
Maybe someone will redesign an MPPT to suit Li batteries, not just a cosmetic preset charging parameter setting with a new menu spot, none of them understand what is involved with Li battery charging anyway, still stuck in the lead haze.

T1 Terry

When they go back into boost/bulk mode?

My MPPT is always in bulk to about 99% SOC.. Due to the high acceptance and the relatively small current source of the array. My MPPT never hits voltage limiting until the battery is pretty much full. The rest of the time it is in bulk where MPPT is most efficient.

Lead acid batteries quickly drives beyond 13.4V with solar but getting LFP there is tough with a small current source thus my MPPT stays in bulk longer than with LA batts.

My MPPT's beat PWM as measured by cumulative watt hours and ampere hours.. I have tested Genasun, Rogue and even an old Aurinco MPPT and each and every one had better Ah/Watt hour input into the LFP bank.

I have been able to do A/B comparisons using my dual shunt Pentametric monitoring system and tracking Ah's with MPPT on one panel and PWM on the other. Both panels were identical brand size and wattage. I have even swapped controllers and panels and still got the same results. These results are not huge 10-17% but good enough that when you run out of real estate it can make a difference. As of yet I have not been able to get PWM to beat MPPT on LFP.

When most MPPT controllers reach absorption voltage they essentially turn into a quasi PWM controller. The nice thing about LFP is that reaching target voltage does not occur until about 99% SOC for us, which keeps the MPPT in MPPT boost mode for nearly the entire charge cycle.....

With a much larger array then you could hit target voltage perhaps as low as 95-96% SOC (we can do this with a large alternator) but at that point a good MPPT essentially becomes PWM anyway...

[dennisail]

You guys talk of medium price controllers not having enough adjustability for lithium. If you can set the max voltage on the controller to 13.9V, then have a low voltage cutoff relay for the whole bank. Is there really much more you need?

[T1 Terry]

Originally Posted by Maine Sail

When they go back into boost/bulk mode?

My MPPT is always in bulk to about 99% SOC.. Due to the high acceptance and the relatively small current source of the array. My MPPT never hits voltage limiting until the battery is pretty much full. The rest of the time it is in bulk where MPPT is most efficient.

Lead acid batteries quickly drives beyond 13.4V with solar but getting LFP there is tough with a small current source thus my MPPT stays in bulk longer than with LA batts.

My MPPT's beat PWM as measured by cumulative watt hours and ampere hours.. I have tested Genasun, Rogue and even an old Aurinco MPPT and each and every one had better Ah/Watt hour input into the LFP bank.

I have been able to do A/B comparisons using my dual shunt Pentametric monitoring system and tracking Ah's with MPPT on one panel and PWM on the other. Both panels were identical brand size and wattage. I have even swapped controllers and panels and still got the same results. These results are not huge 10-17% but good enough that when you run out of real estate it can make a difference. As of yet I have not been able to get PWM to beat MPPT on LFP.

When most MPPT controllers reach absorption voltage they essentially turn into a quasi PWM controller. The nice thing about LFP is that reaching target voltage does not occur until about 99% SOC for us, which keeps the MPPT in MPPT boost mode for nearly the entire charge cycle.....

With a much larger array then you could hit target voltage perhaps as low as 95-96% SOC (we can do this with a large alternator) but at that point a good MPPT essentially becomes PWM anyway...

The issue is not the fact they stay in bulk mode till they reach 96% to 99% charged, depending on the size of the array and how far up the knee you are prepared to go, it's the inability to get an MPPT controller to change back out of absorption of float mode when needed automatically. A PWM controller with good programmability doesn't have these issues, even if it's in float mode and set to 13.8v, it will use all that's available to maintain that 13.8v, more often than not, MPPT controllers fall down in this area. The problem is most likely to be in the algorithm for absorption and float modes as has already been mentioned, it can't be fixed with a few voltage parameter changes, it requires serious reprogramming and that requires a serious understanding of Li battery requirements.
It's obvious that a charge controller of any sort is not genuinely Li compatible if it can't sense cell voltages and simply relies on averaged terminal voltage, this is simply not good enough for Li batteries.
Look after the cell voltages and the terminal voltage will look after itself, ignore the cell voltages and pay the price of reduced battery life.

T1 Terry