Before solar panels became interesting for people that are on the grid, there were only 36-cell ones for charging 12 Volt batteries (and if you had a 24V battery you’d need two panels in series, to make 72 cells). With 36 cells the panel runs at about 18 Volt, and when it gets warm in summer, the Voltage will drop but still be enough to charge a 12 Volt battery (which really takes about 15 Volt).
Charge controllers were developed for these 36-cell panels, to prevent overcharging and damage to the battery. These charge controller are essentially just switches that rapidly (many times per second) connect the panels to the batteries, and then disconnect them. By changing how long the panels are connected vs. disconnected the effective charge current changes, and that’s how the controller keeps the battery Voltage in check. These controllers are called Pulse Width Modulation controllers, or PWM controllers for short, because that’s how they do the charging.
Then solar became interesting for people that are on the grid, and the standard there is for 60-cell panels. Almost all the panels you see on rooftops are 60-cell. These panels have an open Voltage of about 38 Volt, and run at about 30 Volt (though on a hot day in the sun they’ll run as low as 24 Volt). You can hook them up to a 12 Volt battery with a PWM controller, but since those controllers directly connect the panel to the battery (they’re just a switch), it forces the panel to run at 14 or 15 Volt, half of what it can do, and power output will be half as well. So by using a PWM controller with a 60-cell panel you will get about 100 – 130 Watt out of a 260 Watt panel.
To make 60-cell panels work with batteries a different type of charge controller was developed, called Maximum Power Point Tracking or MPPT charge controllers. Those run the panel at whatever Voltage it takes to make the most power, and then convert that Voltage down to the battery Voltage. So, with a 60-cell 260 Watt panel and an MPPT controller the panel could be running at 30 Volt – 8 Amp, while charging the battery at 14 Volt and 17 Amp!
To charge a 24 Volt battery takes at least 2 x 36 = 72 solar cells. That means you need two of the 60-cell panels in series (120 cells), and an MPPT charge controller. Likewise, a 48 Volt battery bank needs 3 of the 60-cell panels in series to reach a Voltage that’s high enough to consistently charge the batteries.
Now, MPPT type charge controllers have much more electronics inside and are much more complex than PWM type charge controllers. That means a 40 Amp MPPT controller is quite a bit more expensive than a 40 Amp PWM controller. But 60-cell panels are MUCH cheaper per Watt vs. 36-cell panels, and that more than makes up for the price difference in charge controllers.
You’ll find a variety of PWM and MPPT type charge controllers on our Web site.
Hopefully this helped clear up the mysteries around charge controllers!
Rob Beckers
I was hoping you would continue the presentation with controllers that would transfer the maximum power for both situations when the input voltage is also lower then the output voltage. So there is no need to add another panel for a 24V battery – just select another output voltage on the controller. And I bet the schematics are known since such controllers are used for recovering break energy on EVs and hybrid cars. The breaking generator may deliver a large span of voltages (and powers) to be supplied to a relatively constant voltage battery.
Daniel, it’s indeed possible with electronics to make what’s called a “boost converter” where the output Voltage is higher than the input Voltage. Unfortunately I don’t know any brand/type of MPPT charge controller that uses this. They are all fairly simple “buck converters”, that can only lower the Voltage from input to output.
So, for all intends and purposes, all the MPPT controllers on the market need an input Voltage from the panels that is higher than the battery Voltage.
-Rob-
Nice Post. Thanks!
If I want to have a electric fencing 60w solar panel, which one is better?Using Charge control or MPPT?
Ahmad, almost all 60W panels are made from 36 solar cells. You can use a (cheaper) PWM type charge controller for those. There is very little benefit in going with an MPPT controller, save yourself the money.
-Rob-
Hi Rob
Thanks for the info , I have three Coleman 150 watt panels that I am going to hook up to a 12 volt battery bank off grid , the panels from what I can tell are 30 cell ,so if Iam taking your info correct there is no advantage into getting the MPPT controller
Thanks you in advance
Bill
Bill, those would be 36-cell panels, and they work at (around) 18 Volt. You can connect all three in parallel (positives to positives, and negatives to negatives), and use a cheap PWM controller. Alternatively you can connect all three in series (positive to negative of the next panel), have just two wires come from the panels, and use an MPPT controller to convert the higher Voltage (54 Volt or so) down to 12 Volt for the batteries. If you need to run a long wire between panels and charge controller the latter would have the advantage that it’s only 1/3 of the current going through those wires, and 1/9 of the line losses, so you can use thinner wires.
Hi Rob
Thanks again for the info much appreciated , the distance is about 15 to 20 feet max that the panels will be away from the charge control unit ,I haven’t bought a controller as of yet so I can go either way , I will buy and hook up the panels whatever gives the best performance to charging the batteries any info you share is greatly appreciated to a novice guy hooking up a off grid solar array
Thanks again !
Bill
Thanks for the info on controllers.
I have 5 panels in total, 2old 60 watt panels (24 years old) running through a 10 amp Morningstar, 2 130 watt panels through a 20 amp Morningstar sunlight and a 4 year old 130 panel running through a Coleman 30 amp digital controller.
The system grew from a single gell cell “Enerpac” power supply to the present system with 4 deep cycle solar batteries.
I’m thinking of bringing all the panels (say 500 watts) together, splicing all panels together and running through a 60 amp controller. I think this would leave room to add 2 more panels and 2 more batteries. We use th cottage 5 months a year and leave the cottage alone in winter with the system looking after itself.
I’d appreciate any comments or advice you can give me re the 60 amp controller or any other thoughts.
Thanks,
Terry.
Terry, are all the panels 36-cell (they likely are, I’m just not sure about 130W panel)? And is your battery bank 12 Volt? That would allow you to connect them all in parallel (positive to positive, and negative to negative). Doing so keeps the Voltage the same, it just increase current to the sum total of all the panels.
With dissimilar panels like yours that would be the only option to combine them all (connecting in parallel). In a more general sense, if you have panels that work at the same current they can be connected in series, and panels that work at the same Voltage can go in parallel.
You can then connect them all to a single charge controller. While you could save a bit of money by using a PWM controller, I would suggest going with an MPPT type charge controller (see the story above!). Though for 36-cell panels into a 12V battery bank there is not much gain from an MPPT controller, they do allow you to oversize the PV side, add more panels, even more than 60A would allow, because MPPT controllers actively control the current coming out and going into the batteries. If you have more panels it may simply clip at 60A on a sunny day, but on a cloudy day when it doesn’t reach 60A you get the benefit of the extra panels.
We have had very good experiences with the EP Solar brand charge controllers. Their 60A MPPT controller is new for us, but if their other models are a guide it should work very well and very reliably. It is by far the cheapest 60A MPPT controller around (that is still decent), the next step up would be an Outback, or top-of-the-line would be a MidNite Classic charge controller.
For the EP Solar 60A one have a look at https://www.solacity.com/product/epsolar-epever-it6415nd/
If you prefer to stick with a PWM controller, then Morningstar makes great ones: https://www.solacity.com/product/morningstar-tristar/
Keep in mind though that you have to make sure NOT to exceed 60A in case of a PWM controller, they don’t protect themselves.
Hope this helps!
-Rob-
Bonjour,je trouve très intéressant. moi j’ai 4panneaux et 8 batterie. Il manque quoi pour les utiliser. Merci
Very helpful explanation and amswers. Based on this it sounds like I can save my money and stick with the pwm controller for my camper van. Thanks.
Hi, I have a single 100 watt panel with these specs. :
Rated power: 100W
Open circuit voltage (Voc): 21.6V
Max power voltage (Vpm): 18V
Short circuit current (Isc): 6.11A
Working current (Iop): 5.55A
Output Tolerance: ±3%
Temperature range:-40℃ to +80℃
I paired this panel with a cheaper 20A PWM controller not fully understanding PWM controllers limitations (wasted power) at the time. I was able to get it to deliver on a sunny day a max of 2.2 amps at around 14.2 volts to my 95 AH 12V deep cycle battery to charge it. I use the battery to power a trolling motor on my canoe. The 12V motor draws around 20 amps at the speed I typically use. My hopes was to use the solar panel on long camping trips to keep the battery charged while I was trolling (if it was sunny of course) and also after I was done trolling, to re-charge the battery fully. If the PWM is delivering 2.2 amps and Motor is drawing 20 amps, then it can only provide 11% of the power needs of the motor, which is something,, but not quite enough. Also, if I had used as an example 50% of the capacity of the battery, then it would take 21.5 hours in direct sun to recharge to battery fully (not accounting for other losses that are most likely present). My question is, If I bought a 20 amp mppt controller would that mean that it would give me the full 5.55amps from the same panel ? If yes, this would be an increase of 2.5X the amps and would speed up recharging my battery after trolling, and also not cause it to run out of power as quick as it would charge at a higher rate while I’m trolling as well. This would theoretically bring down the recharge time for 50% depleted 95AH battery to around 8 hours, which is much more manageable for me. I mounted the panel to my canoe so it is connected while I’m trolling. Thanks for the help!
Hi Michael,
The PWM controller should be fine for the panel you have. Yours is a 36-cell panel, that runs only slightly above the charge Voltage of your battery. There is little to be gained by using an MPPT controller.
If you’re not seeing the charge current it should be producing there must be something else going on. Shading would be my first suspect, since that kills panel output. Also, a charge controller will taper down the current as the battery approaches full. If yours is set to keep the Voltage at 14.2V then it may be working fine, and what you see is just the tail-end of the charge process. It would be more informative to see what current it produces when the battery is known to be empty and the Voltage (while charging) is still below 14 Volt.
-Rob-
I thought I ought to leave a comment about PWM vs MPPT charge controllers as there is a lot of inaccurate information on the web, much of which I believed and it misled me greatly.
Often people are lumping PWM charge controllers in with shunt on/off controllers — many of these call themselves PWM but they aren’t.
A good PWM charge controller, like the one I now have (Morningstar TriStar TS-45) will draw out the same watts from a panel, in full sun, that an MPPT will. They just do it differently. The TriStar puts a load on the panel till that load decreases the voltage to the battery’s voltage. Thus my 100 watt panel, on the TriStar PWM, will usually be putting in 6.6-7.5 amps @ ~13-14+ volts — usually around 95 watts per 100 watt panel, remember line voltage drop which adds to about the same loss as MPPT has for conversion. I’ve tested my 200 watt system with several charger controllers — Allpowers PWM, EPever MPPT, Victron MPPT, and TriStar PWM. The Allpowers maximum input was less than the panel’s max rated input, always, ~5.1 amps or less whereas the max rating is 5.49 amps. That’s because it’s most likely a shunt based on/off controller.
Where all the others pulled out maximum wattage per the conditions — all three of the others do nearly identical on harvesting wattage when in FULL SUN.
That above example is for clear sun, no clouds. This is where MPPT and PWM really diverge. MPPT do much better in cloudy conditions, where I’ll see my TriStar fall to 30% or lower a good MPPT would be doing 60% or better with the same cloudy conditions.
This is really the main difference between the two, along with, of course, the fact that MPPT allows you to run higher voltage and therefore smaller wire however, you can always go 24, 36, or 48 volts on a PWM and get similar effects.
Far too many people are comparing cheap “PWM” charge controllers that are really shunt on/off controllers to MPPT and making the 30%+ claim. This is very inaccurate information. Quality charge controllers harvest the maximum watts from the panel regardless of the charging technology used — PWM is a charging technology, not harvesting technology. In fact many MPPT use PWM as their charging technology because MPPT is a harvesting technology that greatly increases harvesting efficiency in certain conditions — those being mainly cloudy weather and very cold temperatures.
As for size of array and other things, they don’t matter with a quality controller PWM or MPPT, use what best fits your climate, available space, harvesting needs, budget, etc. In an area like Arizona where cloudy conditions aren’t a major concern PWM is all one needs, but in the northwest I would only use MPPT because you’re dealing with clouds more often than not.
Furthermore, the charging technology each controller uses is of great importance — search for Morningstar’s paper on “why PWM” written back in the 1990s. It goes into the differences of pulsing technologies and how they affect battery charging, sulfation, and desulfation. Very interesting and an important read — I’ve tested MPPT charge controllers that could NOT get my batteries equalized, yet the TriStar PWM did it quickly — all charge controllers are not created equal regardless if they are MPPT or PWM.
Cheap PWM controllers or cheap MPPT controllers most likely will either not harvest energy efficiently or not charge your battery effectively. I was floored when I installed the TriStar, first seeing how much energy it pulled down — I believed PWM were like what many say, they just cut off the voltage, like the allpowers, thus wasting 20+ percentage of available power, and then how it got my batteries back to full charge and baked in a day when the other controllers didn’t do it in a month each.
I would rate the four controllers I’ve used:
1. Morningstar TriStar
2. Victron 100/20
3. Epever tracer 20A — not an effective charger imo
4. Allpowers — waste of money imo
I hope this helps noobs like myself when first getting started.
CJ, thank you for the feedback, just one note: PWM controllers (regardless of brand, and I agree with your that Morningstar is a VERY good brand!) all work by switching the connection between panel and batteries on and off rapidly. There’s no in between, the connection is either “on”, with the panel fully connected to the batteries, or “off”. When a solar panel is connected to batteries the panel will run at the battery Voltage, it doesn’t have much internal capacitance to do anything else, and a battery bank is a near-infinite current sink. So, if the batteries at that point in the charge cycle are at 13.5 Volt, the solar panel will be at 13.5 Volt when the PWM controller is in its “on” part of the cycle. There’s no magic, it can’t do anything else, and PWM controllers would burn up if they tried going ‘in between’ on or off (the controller would have to dissipate the heat generated from the Voltage differential between panel and battery times the current). Usually a PWM controller uses a MOSFET for doing the switching, and they can switch hundreds of times per second between on and off. PWM controllers have no control over the power-point on the solar panel’s MPPT curve that they work at, they just run the panel at battery Voltage no matter what, due to the way they are built.
For solar panels the current vs. Voltage curve is nearly flat from zero Volt to the MPPT Voltage (which for a 12V panel is somewhere around 18 Volt), and so PWM controllers loose a little bit vs. an MPPT controller, since they have to run the panel at battery Voltage. The difference is small though, as you note, since charge controllers and battery banks spend much of their time charging near/at bulk-absorb Voltage, and for a 12V bank of flooded lead-acid that’s around 14.5 Volt (and up).
-Rob-