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 > Your search for posts made by 'FWC' found 78 matches.

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RE: Calling on Solar Techies

It is 5V for Victron MPPT devices (by design). It varies by manufacturer/implementation. https://www.youtube.com/watch?v=uTMVmW7GTus&ab_channel=VictronEnergy
FWC 01/29/21 09:06am Tech Issues
RE: Calling on Solar Techies

I am sure Pianotuna and BFL get it, as do I. MPPT primarily gets you more power when the battery voltage is less than Vmp, as Pianotuna succinctly explains. The extra charging early and late is a secondary and minor effect. In your example below with Vmp 17.9V and 11.5A assuming your battery is in bulk charge (14V) with a PWM charge controller you can harvest 11.5A x 14v = 161W. With an MPPT controller you can harvest 11.5A x 17.9V = 205W, so an extra 25% or so more power. With MPPT you absolutely can control the current. You can't produce more current than is available from the solar panel, or more than the battery will accept, but within those limits you can set what current you want. This is useful because it allows you to over-panel your system. Wrong, you cannot "control" the current even with MPPT. You are "assuming" that the battery is like a fixed resistor, it is not. You cannot FORCE more current into the battery than what it can "absorb". The ONLY real advantages to using MPPT is it allows you to use mismatched panel voltages from the battery voltage, allows panel voltages twice or higher than the battery voltage, the higher panel voltage allows for use of smaller ga wire but yet yield more panel wattage, allows charging to commence EARLIER in the day and to continue LATER toward evening which allows you to harvest longer and netting a bit more yield. Example, two 100W "12V" panels (17.9V VMP) in parallel gets you about 11.5A (about 5.75A each panel) same panels in series now gets 35.8V VMP at 5.75A.. Both add up to 200W.. 17.9 x 11.5 = 205.85W 38.8 x 5.75 = 205.85W The difference with MPPT is once the series panel gets at least 2V higher than the battery voltage it can start charging.. While it may start charging, it may not have enough current from the panel to be able to harvest full 200W until later when the sun is more direct on the panel. MPPT has ZERO to do with how or what "modes" it is in for battery charging but more with getting enough voltage from the panels to start charging FASTER and LONGER over the entire day.. Your arguments are not valid because you are ASSUMING that the MPPT cares about the load attached and is regulating the load current attached, it is not. In reality, MPPT is regulating the VOLTAGE just like PWM does to the load which regulates the CURRENT but the CURRENT is HIGHLY DEPENDENT ON THE BATTERY STATE OF DISCHARGE (IE voltage of the battery) and or load.. Voltage AND current work hand in hand, you cannot separate the relationship without affecting the other.. The battery adds in an unknown dynamic to the whole mess. Watts is watts, you can't get more watts with MPPT only a bit longer charging cycle. Piano gets it, BFL gets it, I get it, you don't get it..
FWC 01/28/21 08:07pm Tech Issues
RE: Calling on Solar Techies

Ok, In simple english. MPPT takes the "extra" voltage from the panel, changes it to pulse dc (or is it ac at that point?), transforms it down in voltage and delivers more amps out, than amps in. While doing so, it has an overhead (loss) of about 4%. PWM does nothing with the extra voltage so that is "wasted" power. The most famous example of MPPT was a unit called "heliotrope" It worked so poorly that it consumed more power doing MPPT than it produced. The unit was heavily marketed by AM Solar. It was the early days of MPPT at the consumer level. Does MPPT work better than PWM and harvest more watts? The answer is a resounding "It depend". Often it does. But sometimes, it does not. If you want to go MPPT, then go high voltage on the panel side, the higher the better so long as you don't exceed the input voltage. The trade off is the higher the voltage, the more loss at the charge controller. But the higher the voltage, the earlier and later in the day charging will be presented to our ever hungry batteries. If you want PWM then go with panels that do around about 19 volts (plus or minus 2 volts). What ever choice you make--enjoy having the nearest thing to a free lunch you are likely to find for as long as you have the system. Mine is now 15 years old and still producing its rated output. I'm as happy as a clam--even if it is rather small by today's standards. Nice simple description. I would add that MPPT always produces more power than PWM, how much more is variable. Contrary to the bunk from Bogart, unless the Vmp is < 4% above Vbattery (which would be a vanishingly rare situation in a properly configured system) then MPPT will produce more power. The other advantage of MPPT is that you have much more control - you can regulate both voltage and current.
FWC 01/28/21 05:29pm Tech Issues
RE: Calling on Solar Techies

The buck converter controls the output voltage. How exactly it does it depends on the topology of the converter design. One common way to do it is to use two interleaved buck converters, and you change the transistor drive duty cycle to control the output. However, this is how the buck converters always work - so if you want to argue that makes it 'PWM Mode' then the discussion becomes pointless as by that definition all MPPT charge controller are always in 'PWM Mode'. Getting a little bit out of the weeds here, my point having designed and built MPPT chargers is that an MPPT controller can be more efficient and can provide more energy in all phases of charging relative to a PWM controller. The example above of the controller providing power to the load during float is pretty solid evidence of this.
FWC 01/28/21 03:52pm Tech Issues
RE: Calling on Solar Techies

Ok, what specifically do you mean by 'uses PWM when in Float and Absorb'? As I have explained numerous times now - it is clearly not doing the same thing as a PWM controller when in float and absorb. When necessary it has the ability to boost the current in float and absorb, which a PWM controller by definition cannot do. I just walked out and turned the fans on in my camper (5A load), it is afternoon, the Victron MPPT 20/100 is in float mode, solar panel is producing 18.5V at 4.0A, charge controller is outputing 13.4V (float for my LiFePO4) at 5.4A (0.5A to the battery, 4.9A to the fans). Right now my MPPT controller is producing ~30% more power in float than a PWM controller could. I don't know how else to explain this to you.
FWC 01/28/21 02:35pm Tech Issues
RE: Calling on Solar Techies

IMO (maybe not understanding) question not answered---- AFAIK, that is what the MPPT controller also does in Absorb and Float. AFAIK that is called PWM, without considering whether current in equals current out. If you just switching a switch on and off (ie PWM) then you cannot increase the current, you can only decrease the average voltage. Therefore, if the current is being increased by the controller is not acting like PWM controller. As the photo of the Victron parameters showed earlier - it is clearly boosting the output current while in float, therefore it is acting as a DC-DC buck converter, not a PWM regulator. I think the misunderstanding may be that a switch mode power converter (eg an MPPT controller or any type of DC-DC converter) internally uses switching transistors, it is therefore a PWM controller. It may be worth reading up on how DC-DC converters work: Buck Converter
FWC 01/28/21 01:45pm Tech Issues
RE: Calling on Solar Techies

I think we need to start with a basic understanding of what a PWM solar controller is and what it does and how it is different from an MPPT solar controller. In simplified terms the PWM controller is just a switch (a MOSFET transistor) and a micro controller that measures voltage and controls the switch. In bulk charge a PWM controller isn't doing anything - the switch is on all the time and the panels put what ever current they can produce into the battery at the voltage of the battery. In Absorb and Float, the controller starts turning the switch on and off (rapidly) while varying the ratio of time the switch is on relative to when it is off in order to reduce the *average* voltage at the programmed level (eg 13.6 V for float). The current is determined by the battery/load and the controller does not regulate or modify the current in anyway. *This is PWM and the current out always equals the current into the controller* In an MPPT charge controller you have a switch mode power supply, commonly a buck converter. This is different to a PWM system because in addition to the switching MOSFET it also has a large inductor and a diode (and a bunch of other stuff, but that is not important). This allows the the controller to do two things, control the impedance it presents the solar panel to match the maximum power point from the panel AND to convert the voltage from the panel in excess of the battery voltage to extra current. *This is NOT PWM as the controller is doing more than just switching on and off*. Now if the battery is drawing less power than the panel can supply, then the controller does not need to track the maximum power point and can just present a fixed impedance to the panel. This can be the case when the controller is operating in constant voltage mode (absorb and float), but even in this mode the power could exceed what is available from the controller without MPPT, in which case a well designed controller will begin hunting for the maximum power point again to provide the battery and loads with the power they need. It is easy to tell if a controller is operating as a PWM controller - if the current out of the controller is not equal to the current in then it is NOT operating as a PWM controller.
FWC 01/28/21 12:16pm Tech Issues
RE: SiO2 Batteries

You want to make sure you use LiFePO4 cells, not lithium cobalt (which is what Tesla uses). I can't speak to these specific cells as I haven't used them, but many other folks have with good luck: EVE 280Ah LiFePO4 Cells I use this BMS: Bluetooth BMS Which is also resold in the US by these folks: Overkill Solar BMS
FWC 01/28/21 09:03am Truck Campers
RE: Calling on Solar Techies

Apologies to the OP for the thread drift here. Sounds like you have a good plan, and 400 - 500W of solar and PWM controller will work well for you. However, one of the issues with a forum is that it can act as an echo chamber and incorrect information gets repeated and amplified unless it is corrected. There are a bunch of statements in this thread that really aren't correct, and while these don't matter in your situation, it may be important for the next guy. Part of the reason that solar and energy management systems seem so confusing and complicates is that there is so much dodgy information floating around.
FWC 01/28/21 07:34am Tech Issues
RE: SiO2 Batteries

What is your intended use? Boondocking. I have 220W of solar with a MPPT charger. No AC appliances. I have two 100AH deep-cycle AGM batteries now. I am attracted by the LiFePo4 batteries for their reducted weight and current capability but not their need for a special charger. The SiO2 evidently can use a standard charger. LiFePO4 does not necessarily need a special charger. You may get a slightly longer lifetime out of them with a charger exactly dialed in to their settings, but their lifetime is so long under normal use that if they last 4000 or 5000 cycles is immaterial. In a truck camper the weight savings of LiFePO4 is killer. Also look beyond battleborn, there are a bunch of others coming out at 50 - 70% the price of battleborn, or if you are adventurous go the DIY route which is about the cheapest battery you can buy.
FWC 01/28/21 07:27am Truck Campers
RE: Calling on Solar Techies

That bit in the previous post about the controller limiting its amps in Absorption is not right--the controller holds its voltage and the battery limits the amps.The effect is the same. The controller stops and starts the electric flow to control the voltage but the actual function that is happening is the current flow (amps) is stopped momentarily. https://cdn.sparkfun.com/assets/f/9/c/8/a/512e869bce395fbc64000002.JPG width=450 Note the voltage does not change, the total current (amps) is what changes. This is the difference between talking about the effect vs what is actually happening digitally. PWM is a strategy to control the average voltage - by changing the duty cycle you are controlling the average voltage. For PWM charge controller the battery is acting as an extremely large capacitor - ie it's voltage can only change slowly, so if you modulate the incoming voltage at frequency many orders of magnitude higher than the time constant of the battery (say 10 - 100's of kHz) the battery is in effect seeing the average voltage. A PWM charge controller measures the battery voltage and then uses a feedback loop to control the duty cycle on the transistor 'switch' in order to achieve the desired voltage (say 13.7V) - it does not regulate the current.
FWC 01/27/21 03:10pm Tech Issues
RE: Calling on Solar Techies

Why did the MPPT charge controller struggle to work? The MPPT controller itself introduces more voltage drop into the circuit due to the increase in complexity. It also needs more “voltage-overhead” to operate than the PWM controller due to the ‘switching’ circuit within the MPPT controller. So when the voltage drop along the cables becomes significant the MPPT cannot function as expected. When the voltage overhead is not high enough for the MPPT to function correctly it reverts to PWM operation. The MPPT controller also reverts to PWM operation when in absorption or float modes. During these two important charge modes the controller must reduce the current to the battery to avoid overcharging. So in these critical stages of charging the MPPT function has no benefit. https://sunworks.co.uk/improve-mppt-charge-controllers Who ever wrote this has no clue what they are talking about. The controller does nothing to regulate the current during absorption of float - in both these phases of the charge it is the battery limiting the current, the controller regulates the voltage. You will note in the settings for your controller there is no limit for absorb or float current, only voltage. The MPPT may have no benefit if the battery is drawing less current than is available from the panel at absorb/float voltage. However if the battery is drawing more current than is available from the panel at absorb/float voltage then MPPT will help. Many PWM charge controllers don't measure current at all - they are only regulating voltage.
FWC 01/27/21 03:00pm Tech Issues
RE: Calling on Solar Techies

I think you will need an oscilloscope to see the PWM. And yes as you load up the controller it will go back to converting wattage to maintain voltage. More pronounced with higher input voltage. An MPPT charge controller is a switched mode power converter, so it is always switching and varying the duty cycle. Depending on the quality of the filtering, you may be able to see some ripple with a scope, but this is true all the time, in bulk, absorb and float. The concept that it changes into a PWM charge controller and operates like one in absorb and float is just not true.
FWC 01/27/21 12:39pm Tech Issues
RE: Calling on Solar Techies

Thanks for all the great information. I will install the system as it is now except for going to 8ga wire from the panel junction to the Charge Controller at the batteries. According to the low voltage calculator this helps to lower voltage drop over 30 feet to 5.76%. Speaking of the low voltage calculator. I put in the parameters of the 500 watt kit as it came from the manufacture and it still came in at 4.5% voltage drop which is above the 3% recommended goal. Makes me wonder about the accuracy of the calculator. The kit comes with a 15 foot run to the Charger Controller and 10ga wire. As far as MPPT vs PWM the PWM came with the kit and just did not want to throw it away. The difference in price between the was only $100. In the future I will probably go MPPT just because you seem to have more options. Thanks again There is no issue with a greater than 3% voltage drop in the wiring between the panels and controller. In fact as long as the voltage drop is less than the difference between the panel maximum power voltage (~18V) and the battery voltage (~14.7V), or about 25%, then nothing is lost as the PWM charger doesn't use this voltage anyway.
FWC 01/27/21 12:16pm Tech Issues
RE: Calling on Solar Techies

Not my image - but this should prove the point: https://community.victronenergy.com/storage/attachments/4911-2.jpg width=640
FWC 01/27/21 12:01pm Tech Issues
RE: Calling on Solar Techies

"Re: MPPT vs PWM controllers? MPPT - you only gain it's wattage conversion efficency while it is in BULK mode, once the controller eases off when switching to Absorb, all the ones I know of, revert to PWM mode for absorb and float. Mike that is the very point that I find is hardest to get across to everyone.And its the very reason you dont get 50% and above gains from them as most people claim.On another similar site a well know poster talked about |the mysteries of MPPTversus PWM" He never ever mentions that fact only give figures to show theory gains. You are also correct with "all the ones I know of, revert to PWM mode for absorb and floatOt of dozens I regularly test have never found one not to be like that." https://forum.solar-electric.com/discussion/13231/mppt-vs-pwm-controllers #25 Again - this is really not true. An MPPT controller does not switch to PWM mode in Absorb and Float. This is super easy to demonstrate if you have an MPPT charge controller. When it is in float and there is still plenty of solar, turn on a load that is around the same as the output you would expect from your solar controller. Watch the panel current and the output current. If output current > panel current (which it will be with series panels) then it is clearly NOT in PWM mode as it is converting 'extra voltage' to extra current.
FWC 01/27/21 12:01pm Tech Issues
RE: Calling on Solar Techies

The MPPT is operating as it always does - as a buck (or in some cases a boost) converter, regardless of the charging phase. The difference between this and PWM is that current in != current out. With PWM I_in = I_out, always. This is often not a big deal, but if you have loads running while in float, it can be. You want to support the loads off of the solar as much as possible. If you can't convert the extra panels volts to current then you are throwing away power that then has to be put back into the batteries by the solar panels. So in short, MPPT is working even in float. On technical note, a buck converter has a large inductor in it, so while you are PWM'ing a transistor on the input side, as long as the inductor isn't saturated you won't see the voltage move as the field collapse in the inductor is holding the voltage up. This is different from PWM where you will see the voltage oscillate up and down based on the state of the transistor. In Float the MPPT controller keeps the voltage to the battery at the Float set-point, but the issue is the controller wrt the panel voltage. The panel voltage that you can measure is actually a sort of average between on and off farther down (higher voltage) the IV curve knee than Vp and it varies with the load changes during Float. If you don't want to call that on/off "PWM" give it another name, but some or all MPPT controller booklets call it PWM.
FWC 01/27/21 09:45am Tech Issues
RE: Calling on Solar Techies

Well said Steve. There are several misconceptions in this thread. As stated well designed MPPT does not switch to PWM in absorption and float. It switches to CV (constant voltage) mode. Consider the edge case for a second - a 100V string of panels feeding a 12V battery, for half of the absorption phase the charge current is > 50% of the bulk current, if it was in PWM mode the current would be limited to about 15% of the bulk charge current. Secondly in float charge the current is very low, so you typically don't get any extra power out of an MPPT, but it is still not acting as a PWM charger. Consider if you turn a load on - the charger will ramp up the current to carry the load while keeping the voltage at the float set point (until it maxes out the available power). The other thing to consider is that solar panels are NOT constant voltage sources, they are closer to constant current sources. This is hard to conceptualize, but will help understand how MPPT harvests 'lost power'. For the OP, this doesn't make a huge difference as his panels are in parallel and it is a small system, but it is important to provide accurate information. I tdhink people need to learn more about MPPT chargers before they recomend against them..... yes they benifit more during bulk charging, no they do not switch to PWM mode, they are a three stage MPPT charger so basicly a DC_DC charger that converts DC to AC then back to DC at the most efficent combination ov voltage vs current. in the summer on a nice day they may only give you an aditional 10% but in the winter when it is cold that number can go up to 40% or when its raining or overcast it will be inbetween. also you could basicly run pannels in series lowering the current while raising the voltage which allows you to get away with a small cable and less loss than running in parallel. if you can aford it it is always worth getting a MPPT controler, if you cant then dont worry about it, but you can always upgrade later, would just mean reconfiguring your pannels to take advantage of a series setup. Steve
FWC 01/27/21 08:59am Tech Issues
RE: SiO2 Batteries

What is your intended use?
FWC 01/26/21 04:42pm Truck Campers
RE: Calling on Solar Techies

That article only applies for large (likely residential) installations when you have a large number of strings of panels in parallel and the wiring (or other panels) is not rated for a short circuit current of the strings. This wouldn't apply in this situation or 90% of RV based solar installs. So in short (hah!) there is no need for a fuse between the panels and controller in the installation being discussed here. Although it won't cause any harm.
FWC 01/23/21 08:46am Tech Issues
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