Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 06-03-2014, 22:32   #106
Moderator
 
noelex 77's Avatar

Cruisers Forum Supporter

Join Date: Jul 2007
Location: Living on dirt waiting for our new yacht to be built.
Boat: Half built Bestevaer.
Posts: 10,618
Re: MPPT Charge Controller for LifePO4 Batteries

Quote:
Originally Posted by T1 Terry View Post
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.
There is no fundemental difference between how MPPT controllers and PWM manage these issues.

Some controllers have better adjustability and suitability than others, but this is not a feature that is dependent on if the controller is MPPT or not.
__________________

__________________
noelex 77 is offline   Reply With Quote
Old 06-03-2014, 23:01   #107
Do… or do not
 
s/v Jedi's Avatar

Cruisers Forum Supporter

Join Date: Feb 2009
Location: in paradise
Boat: Sundeer 64
Posts: 9,198
Re: MPPT Charge Controller for LifePO4 Batteries

Quote:
Originally Posted by noelex 77 View Post
There is no fundemental difference between how MPPT controllers and PWM manage these issues.

Some controllers have better adjustability and suitability than others, but this is not a feature that is dependent on if the controller is MPPT or not.
It is for people who recently bought a PWM controller. It doesn't work for them if their choice wasn't the most optimal, so MPPT must be bad, PWM good.
This is the way it works for most on the forum.
__________________

__________________
s/v Jedi is offline   Reply With Quote
Old 06-03-2014, 23:58   #108
Registered User

Join Date: Jul 2011
Location: Australia NSW south coast
Posts: 633
Re: MPPT Charge Controller for LifePO4 Batteries

Quote:
Originally Posted by noelex 77 View Post
There is no fundemental difference between how MPPT controllers and PWM manage these issues.

Some controllers have better adjustability and suitability than others, but this is not a feature that is dependent on if the controller is MPPT or not.
I'm open to be corrected, have you found MPPT controllers that can do better than a PWM controller once the controllers have moved from the boost mode to absorption or float mode?
With Li batteries, getting them to 96% plus SOC is only part of the requirement, there is still at least half a day of solar output available than could be used for other purposes. MPPT controllers, in the right conditions, can harvest more while in bulk mode, but once they reach the absorption mode and float mode, they don't seem to be any better than a PWM controller, well at least the units I've tried, and granted, they were not Outback or Midnite units either. No one wants to give me one of those to play with :lol:
With Li batteries, if you can harvest another 5% or even 10% (a big push of the reality boundaries with Li) more than PWM during bulk mode by using an MPPT controller simply means you spent a lot of money being the first one to have fully charged batteries, not that you weren't going to get fully charged batteries if you didn't spend the extra $$.
Now, if the MPPT unit could harvest more than the PWM controller during the absorption or float mode to power say an air con system or water heater or deep freezer, then there may be some justification for the added expense, but I'm yet to see it.

T1 Terry
__________________
T1 Terry is offline   Reply With Quote
Old 07-03-2014, 00:08   #109
cruiser

Join Date: May 2007
Location: Brisbane AUS
Boat: Cowther 43 - Hunter 40.5
Posts: 1,006
Re: MPPT Charge Controller for LifePO4 Batteries

I don't get it Terry. What do you expect will happen when you turn the air con or HWS on with an MPPT controller going? Surely as long as it has the same max voltage setpoint it will increase current to compensate for the slight voltage drop at the battery terminals. I know that lithium batteries will not reduce voltage under load anywhere near as much as lead, but there will still be some drop, and surely any decent controller will notice this?

As far as I know the lithium batteries being discussed here are 99% full at 13.9-14V. Surely as long as the controller does not let terminal voltage fall below this the batteries will remain 99% full no matter what loads are turned on right?
__________________
dennisail is offline   Reply With Quote
Old 07-03-2014, 01:10   #110
Moderator
 
noelex 77's Avatar

Cruisers Forum Supporter

Join Date: Jul 2007
Location: Living on dirt waiting for our new yacht to be built.
Boat: Half built Bestevaer.
Posts: 10,618
Re: MPPT Charge Controller for LifePO4 Batteries

Quote:
Originally Posted by T1 Terry View Post
I'm open to be corrected, have you found MPPT controllers that can do better than a PWM controller once the controllers have moved from the boost mode to absorption or float mode?
If the solar panels are producing more power than the combined demands of the loads and battery acceptance then the controller will be regulating and MPPT technology makes no difference.

The controller is throttling back the solar panels under these conditions, throwing away power, so any extra power that can be produced by the voltage conversion inherent in the MPPT tracking process is irrelevant. The same is true if we fitted a larger solar array it is of no benefit if the controller is regulating.

However, the equation is still simple more power from the solar panels whether from MPPT conversion or a larger solar array the more power we can use (on average)
__________________
noelex 77 is offline   Reply With Quote
Old 07-03-2014, 01:47   #111
Nearly an old salt
 
goboatingnow's Avatar

Cruisers Forum Supporter

Join Date: Jun 2009
Posts: 13,649
Images: 3
Re: MPPT Charge Controller for LifePO4 Batteries

Quote:
Originally Posted by dennisail View Post
I don't get it Terry. What do you expect will happen when you turn the air con or HWS on with an MPPT controller going? Surely as long as it has the same max voltage setpoint it will increase current to compensate for the slight voltage drop at the battery terminals. I know that lithium batteries will not reduce voltage under load anywhere near as much as lead, but there will still be some drop, and surely any decent controller will notice this?

As far as I know the lithium batteries being discussed here are 99% full at 13.9-14V. Surely as long as the controller does not let terminal voltage fall below this the batteries will remain 99% full no matter what loads are turned on right?

Exactly, if either see pwm or mppt , if you have spare solar capacity. Turn on another load. !!!

Dave
__________________
Check out my new blog on smart boat technology, networking and gadgets for the connected sailor! - http://smartboats.tumblr.com
goboatingnow is offline   Reply With Quote
Old 07-03-2014, 04:46   #112
Marine Service Provider
 
Maine Sail's Avatar

Join Date: Jan 2007
Location: Maine
Boat: CS-36T - Cupecoy
Posts: 3,060
Re: MPPT Charge Controller for LifePO4 Batteries

Quote:
Originally Posted by T1 Terry View Post
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
Terry,

I have no idea what "MPPT" controller you are using, sounds like more of a fancy sticker than an actual MPPT, but what you describe is not how any MPPT controller I've ever used or installed works. At least none of the good quality products I have used work that way... If the voltage drops below set point they go back into bulk. Simple stuff.... They work similarly to a PWM in absorption but in bulk you get some more out of them...

I have used/tested three different MPPT's on my own LFP bank. A Genasun, an Aurinco and a Rogue. None exhibit any of what you describe...

Quote:
Originally Posted by T1 Terry View Post
I'm open to be corrected, have you found MPPT controllers that can do better than a PWM controller once the controllers have moved from the boost mode to absorption or float mode?
Huh....? They are both doing PWM once they hit absorption.... Once you are at a "limiting voltage" the batteries decide how much current they take not the controller. Boost in MPPT only occurs before you hit voltage limiting or in bulk mode.

If a Li battery comes up to 14.0V and right at that point can take 40A or needs 40A to maintain 14V then that is all the battery will take, MPPT or PWM.. If the voltage starts to climb either MPPT or PWM will regulate it to prevent an overshoot of the target set point.

We don't have a massive array so our time in absorption is extremely short and the batteries are nearly as full as they will get by the time our array gets it there. This means that when on solar we are maximizing our MPPT gains longer than if we were using LA batteries because the LFP bank keeps the MPPT in bulk far longer that does a lead acid bank..
__________________
Marine How To Articles
Maine Sail is online now   Reply With Quote
Old 07-03-2014, 11:31   #113
Senior Cruiser
 
senormechanico's Avatar

Cruisers Forum Supporter

Join Date: Aug 2003
Boat: Dragonfly 1000 trimaran
Posts: 5,823
Re: MPPT Charge Controller for LifePO4 Batteries

Both our Midnite Solar 150 (home's system) and the Blue Sky 2512/IPN Pro Remote on the boat are programmable and act the same as Mainsail just described.

When we hit float on the boat, we turn on the hot water tank via the inverter.
Hot showers...ahhh !!
__________________
Memento,homo, quia pulvis es, et in pulverem reverteris.
senormechanico is offline   Reply With Quote
Old 07-03-2014, 18:15   #114
Nearly an old salt
 
goboatingnow's Avatar

Cruisers Forum Supporter

Join Date: Jun 2009
Posts: 13,649
Images: 3
MPPT Charge Controller for LifePO4 Batteries

We need to be careful about bandying around terms like PWM and MPPT. solar regulators that use MPPT in the main do not use PWM as the output charging regime. They use pure DC derived from a switched mode power convertor.

Solar regulators that use PWM as a battery charging regime , do so to avoid the cost of implementing a switch mode DC to DC convertor and employ the advantage of a PV panel being a current source.

A solar regulator could for example deploy a DC to DC converter that uses a PWM switched mode supply to do the voltage conversion. That does not make in a PWM solar regulator.


PWM charge controllers , or those that charge the battery using a PWM output waveform are very inefficient when in low duty cycle PWM. The vast majority of the panels potential output is being lost at that point due to duty cycle and pulling the panel away from Vmp.

Dave


Sent from my iPad using Tapatalk
__________________
Check out my new blog on smart boat technology, networking and gadgets for the connected sailor! - http://smartboats.tumblr.com
goboatingnow is offline   Reply With Quote
Old 07-03-2014, 18:35   #115
Moderator
 
noelex 77's Avatar

Cruisers Forum Supporter

Join Date: Jul 2007
Location: Living on dirt waiting for our new yacht to be built.
Boat: Half built Bestevaer.
Posts: 10,618
Re: MPPT Charge Controller for LifePO4 Batteries

Quote:
Originally Posted by goboatingnow View Post


PWM charge controllers , or those that charge the battery using a PWM output waveform are very inefficient when in low duty cycle PWM. The vast majority of the panels potential output is being lost at that point due to duty cycle and pulling the panel away from Vmp.
If the regulator is in low duty cycle PWM it is heavily regulating. Effeciency is not needed at this stage, in fact operating the panel outside its optimum parameters is a bonus.
__________________
noelex 77 is offline   Reply With Quote
Old 07-03-2014, 18:35   #116
Registered User

Join Date: Jul 2013
Location: San Diego, CA
Posts: 3,157
Re: MPPT Charge Controller for LifePO4 Batteries

Maybe I'm oversimplifying, or missing something here, but here's my understanding. Space for solar panels is very limited onboard, so boaters are buying very expensive panels for the extra efficiency over other, cheaper brands. Power is always in demand, so considering the cost of the panels and the increased yield from teh panels from MPPT controllers, even if the comparable MPPT controller was $300 more than the same amperage PWM controller, it's still worth it. From what I've seen on my 2 solar panel installations, the MPPT output appears to be higher, so it's well worth it from my point of view. If I were on a boat, I'd run all major electrical loads like water maker, laundry, water heater, etc. during the day while power is flowing. You may end up with batteries that aren't 100% charged at sunset, but then you've already consumed most of the power that was discretionary in terms of when you used it. Now you have nearly full or full batteries, the MPPT controller never went into float mode, and the only power you'll consume overnight are the regular loads - lights, refrigeration, navigation, etc.

The next day, the sun will rise again. If you've sized your system properly, you'll be able to power whatever you choose on a rotational basis. You shouldn't need to make water every day, or do laundry every day. So the problem about MPPT controllers not efficiently switching from float back to bulk mode can be dealt with by keeping it in bulk mode during peak daylight time with proper loading.
__________________
socaldmax is offline   Reply With Quote
Old 07-03-2014, 18:41   #117
Nearly an old salt
 
goboatingnow's Avatar

Cruisers Forum Supporter

Join Date: Jun 2009
Posts: 13,649
Images: 3
Re: MPPT Charge Controller for LifePO4 Batteries

Quote:
Originally Posted by noelex 77 View Post
If the regulator is in low duty cycle PWM it is heavily regulating. Effeciency is not needed at this stage, in fact operating the panel outside its optimum parameters is a bonus.

The term regulator is very confusing , as a PWM charging regime is not really a regulator in the sense of a linear or switch mode " regulator "

What I meant was that the panel has considerable output power available, especially under mppt, diversion regulation would actually be more useful and I'm surprised it's not implemented more.

Dave


Sent from my iPad using Tapatalk
__________________
Check out my new blog on smart boat technology, networking and gadgets for the connected sailor! - http://smartboats.tumblr.com
goboatingnow is offline   Reply With Quote
Old 07-03-2014, 20:17   #118
Do… or do not
 
s/v Jedi's Avatar

Cruisers Forum Supporter

Join Date: Feb 2009
Location: in paradise
Boat: Sundeer 64
Posts: 9,198
Re: MPPT Charge Controller for LifePO4 Batteries

I'm 100% with MaineSail on this; only the bulk mode matters; during absorption and float you are wasting array output and controller efficiency is irrelevant.

In bulk phase, a good MPPT controller will outperform directly connected by 20-25%. On my Outback Flex60 I get 2200W avg and 2500W on a good day, while before it was 1800W avg and 2000W on a good day. This is all in bulk mode as we use more energy than the 660W solar array provides.

p.s. to bring it in simple numbers: with the MPPT controller, the controller output equals 4 hours of maximum array output; without MPPT this is 3 hours or 25% less energy produced. As soon as the controller (any controller) goes into absorption mode, it doesn't matter anymore what type you have and you're letting energy go to waste at that point.

__________________
s/v Jedi is offline   Reply With Quote
Old 08-03-2014, 03:05   #119
Registered User

Join Date: Jul 2011
Location: Australia NSW south coast
Posts: 633
Re: MPPT Charge Controller for LifePO4 Batteries

Quote:
Originally Posted by s/v Jedi View Post
I'm 100% with MaineSail on this; only the bulk mode matters; during absorption and float you are wasting array output and controller efficiency is irrelevant.

In bulk phase, a good MPPT controller will outperform directly connected by 20-25%. On my Outback Flex60 I get 2200W avg and 2500W on a good day, while before it was 1800W avg and 2000W on a good day. This is all in bulk mode as we use more energy than the 660W solar array provides.

p.s. to bring it in simple numbers: with the MPPT controller, the controller output equals 4 hours of maximum array output; without MPPT this is 3 hours or 25% less energy produced. As soon as the controller (any controller) goes into absorption mode, it doesn't matter anymore what type you have and you're letting energy go to waste at that point.

If you are getting 20% to 25% more because you changed controllers has little to do with it being an MPPt controller and far more likely to be a case of either crap wiring or the previous PWM regulator was crap.
If you can get more than a 5% improvement using MPPT compared to PWM in bulk mode, you have either a seriously badly match system or crap wiring.
The VPM of a panel at actual operating temp isn't 17v or 18v, it's more like 16v or less. In extreme sun and no cooling that can drop down below 15v. The difference between the 13.3v to 13.8v an Li battery charges at and 15v to 16v is sweet stuff all, for a 660w system solar array you'd be hard pressed to see an improvement at all.
As far as the B/S that MPPT starts charging before PWM and continues charging after PWM stops..... apply a bit of logic to that thought, PWM doesn't have much circuitry requiring current to power it, MPPT does, so logically, how can that be a true statement. Low voltage MPPT controllers do not have buck boost circuitry, if the panel voltage is even equal to battery voltage there will be no current flow.

Too much theory from mains feed solar and their MPPT controllers is taken as fact with low voltage MPPT controllers and the manufacturers make no attempt to dismiss this falicy, and why would they, if they actually tod the truth no one would buy one.

Take a propper look at the specs of your solar panels, the Vmp degrades by 0.462% per degree over 25 deg C, a solar panel temp (not ambient temp) will climb to 70 deg C very quickly in full sun and stay there while they are at their max efficiency. Do the math, compare the working Vmp to actual charging battery terminal voltage, factor in voltage drop across the cables, and suddenly the smoke and mirror theoretical gains an MPPT controller can give go out the window.

T1 Terry
T1 Terry
__________________
T1 Terry is offline   Reply With Quote
Old 08-03-2014, 03:44   #120
Moderator
 
noelex 77's Avatar

Cruisers Forum Supporter

Join Date: Jul 2007
Location: Living on dirt waiting for our new yacht to be built.
Boat: Half built Bestevaer.
Posts: 10,618
Re: MPPT Charge Controller for LifePO4 Batteries

Quote:
Originally Posted by T1 Terry View Post
The difference between the 13.3v to 13.8v an Li battery charges at and 15v to 16v is sweet stuff all, for a 660w system solar array you'd be hard pressed to see an improvement at all.
The improvement would be between 13 and 16% . A cell temperature of 70c is a high and a Vmp of between 15 and 16v is a little low, but factor in the self consumption of the controller and some loss in the wiring and I think the % numbers are close to the mark.
Say a 10-20% gain for lithium and 5-15% for LA.
__________________

__________________
noelex 77 is offline   Reply With Quote
Reply

Tags
battery, lifepo4, mppt

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
MPPT Charge Controller for LifePO4 Batteries s/v Holiday Electrical: Batteries, Generators & Solar 185 25-05-2014 16:43
Satphone & HF for Ocean Crossings? Sabbatical II Marine Electronics 106 08-07-2012 01:43
What Do You Do for a Living? xoxxx Off Topic Forum 329 07-06-2012 05:22



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 18:33.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.