PWM compared to MPPT controllers ... (2 Viewers)

[spressomon]

Thought I'd make a dedicated thread for this discussion rather than bastardize a couple other pseudo related threads.

Specific to our off-road application: Anyone have direct experience with durability/reliability apart of our rough and tumble (think washboard) world of boon docking: Typical MPPT (<$300) and PWM controllers?

Does, in general terms, an MPPT controller have additional circuitry/electronic complexity that would make it any less reliable/dependable/suitable due to vibration for our typical application compared to PWM controllers?

 

[LAMBCRUSHER]

IIMU...that you utilize an MPPT type controller when you have source voltages that differ from your sink voltages. IE, an mppt controller can be used to feed a 12 volt system from voltages just above your sink voltage all the way up to the controllers max allowable input voltage, providing the current rating also supports your source/sink specs...PWM controllers are limited to their voltage ranges both in and out. I'm guessing that the circuitry of a PWM controller is simpler and therefore also more durable than am MPPT. An MPPT will be more universally useful to an end user...that panel on the roof of your house would require an MPPT controller to use with you 12 or 24 volt LC...

 

[LandCruiserPhil]

Professionals will tell you any system under 300w a MPPT controller is not worth the additional cost. I have run and tested several controller from basic low cost to full programmable units and see very little difference in terms of performance. Programmable are nice giving you the ability to adjust voltage to adapt to batteries for Bulk, absorption, and float needs. I have several years and well over 20K in off road testing and never a controller failure.

 

[george_tlc]

The MPPT controllers I've seen or used (around the US$100 mark, China units) are well made and internally conformal coated using a thick material. The conformal coating provides protection against condensation/dirt/fog/raindrops etc. I'd not be expecting long term survival in harsh weather conditions - e.g. I wouldn't mount them outside or in the engine bay where high wind speeds, mud, salt, etc will spray on them often.

Many PWM controllers are also not weather proof. So, I wouldn't expect any weather related reliability differences.

Consider that vehicle manufacturers mount their ECUs in the cabin, that would be a good location for a permanently mounted solar charge controller. Heat/mud/salt/water etc environment conditions are the enemy of electronics.

From an circuitry/component perspective, MPPT will be more complicated since it contains a DC DC converter that needs to handle 10/20/etc Amps. Many MPPT controllers have built in displays (typically LCD) and membrane actuated switches. Construction I've seen is surface mount (other than connectors) which is very rugged.

A higher end PWM controller will also have a display and some switches. So comparing similar units would have no reliability differences.

The major 'difference' in reliability is the PWM controller will basically just have a high power FET (or similar switching device) to pulse on/off to connect the solar panel output to the battery/load per the charging algorithm/profile. An MPPT controller will have a DC DC converter that is used to connect the solar panel output to battery/load as directed by the MPPT algorithm (software). The number of failure points (due to high current, power dissipation etc) will be higher in an MPPT controller than the simple PWM FET. So, here we are comparing reliability of the design and whether the designer chose components with sufficient capability to handle those currents/power and provide suitable thermal paths in the layout of the board and heatsink.

Finally, given that worst case (PWM or MPPT controller failure) you can just connect the solar panel direct to the battery and use a multimeter to terminate the connection when the battery is fully charged, I'd not be worrying about what to do with a failure in the field.

Australia is the land of corrugations (1000's of km of them) and I've not had electronics suffer/fail due to vibration - even in leaf sprung vehicles... But that just means you need to be sensible where you store/mount things - i.e. not directly to the chassis/frame... What feels like horrific corrugations to us, is actually quite mild if you ignore the sound of them and put you hand on the body of the vehicle to feel what is going on. Air filled rubber tyres and rubber body mounts do a wonderful job of removing the high energy G forces. I've seen (one of my designs) suffer through NASA inflicted high G force lab testing (lighting unit used on a shuttle launch tower facility), ALL the small surface mount components had no issues - but larger components ripped themselves off the PCB (we had to revise the construction and POT the entire board to 'retain' the large components (larger inertial forces). All the equipment in the launch monitoring buildings (remote buildings near the tower) where mounted in racks that were sitting on air suspension assemblies. From the video in those buildings you would NOT want to be in them during launch

cheers,
george.

 

[Cruiserdrew]

I assume this thread was prompted by the discussion on this thread:
Why such low amps from 150w solar panel?

From that, it's clear that many people do not understand the finer points, so maybe this thread can help sort that out. I don't want to be in the position of telling people what is or isn't worth it for them, but up front I will say, that if PWM controllers and MPPT controllers cost exactly the same price, that few PWM controllers would be sold.

For the purposes of this discussion, I will assume we are talking about relatively small camping systems like might be useful on offroad trips. RV discussions with huge battery banks, multiple panels, etc are a different discussion.

I really like the Morningstar PWM controllers. They seem very well made and robust, the built in firmware has a charging profile I like, and they are physically small, which helps with mounting options. If they have a down side, it's that they are not programmable. So if you want a different charge profile or a longer or higher voltage absorb stage, you are out of luck. This is a minor issue though, and it's mostly a plug in and forget situation. Mine has run off road on trips and for months at a time in my driveway.

I have the Ecoworthy MPPT controller as well. It's about $100, so double what the Morningstar PWM controller costs. But for that $50 you get a fully programmable charge controller, slightly better efficiency and a built in display. I changed my float voltage from 13.5 to 13.8 and raised my absorb voltage to 14.8. I recently used it on a 10 day trip to death valley and mounted the controller inside the truck, and left the 160 watt panel connected full time-ie even when underway, driving etc. So it was fully exposed to miles of washboard, alternator power spikes (if any) any and all loads. Not a single problem.


More generically, if you have a "12 volt" panel isn't really 12 volts. Your average '12 volt' panel will have an open circuit voltage (VOC) around 22volts, but will make it's maximum power (this is the point of maximum efficiency) around 17.5-18volts. A PWM controller works by intermittently connecting the panel directly to the battery. It does this very fast but the important concept is the direct connection. During the "pulse" (connected to the battery) the panel will be at battery voltage, and so is producing power lower on the power/voltage curve, and so is giving up a bit of panel's maximum power potential. With a "12 volt panel" this isn't a big difference (maybe 10-20%) and so a PWM controller works perfectly well, especially if you use less power overall, than your panel is capable of producing.

Take home point: with a 12 volt panel, PWM or MPPT controllers will both work fine, with the cost nod going to PWM, and the efficiency nod going to MPPT.


The real difference comes when not using 12 volt panels, or when using two 12 volt panels wired in series. Then the VOC (Voltage, open circuit) will be close to 40 volts. A PWM controller will still force the system to operate at 12 volts on the panel side. But the panel's maximum power point is more like 32-35 volts. An MPPT controller operates the panel side of the circuit at the maximum power point, and still allows the battery side to work in the 12 volt range. So in effect the panel can operate at the voltage where it is most efficient. Pretty cool, and in this case the entire system would be significantly more efficient.

An MPPT controller allows one other cool trick that will decrease line losses from the panel to the controller. Since the panel side can operate at a significantly higher voltage, the current to supply the same battery power will be less. Lower operating current (amps) means lower resistance losses in the wiring from the panel to the controller. So in effect, you could have a longer wire out to your controller or a smaller wire. It's the same concept that explains why long distance power lines operate at 500,000 Volts and your house operates at 115 volts.

Take home point: Use an MPPT controller if you use 24 or 36 volt panels, otherwise you're throwing 1/2 or more of your power out the window.


So where to go. From a practical perspective, especially if amps, volts and watts sound like gibberish, and you hated college physics, get a 12 volt panel and a PWM conttroller. But get a good PWM controller like a Morningstar. Monitor your battery with a volt meter, even the Harbor Freight $5 meter will do.

But if your power needs are greater than about 160 watts or you are right at the limit of your existing panel-ie your 60 watt panel barely keeps up with your fridge, an MPPT controller will be slightly more efficient. Slightly. You should probably just buy a bigger panel, but that's up to you.

Now if you just have to squeeze every possible watt out of your system, or you run 24 or 36 volt panels, you will want to use an MPPT controller.

But watch out if shopping on Ebay. The MPPT controllers that seem too cheap, are really PWM controllers with an MPPT sticker.

 

[spressomon]

Yes, Andy, the impetus for this thread came from the discussion in the "why so low amps from 150w solar panel" thread. I thought it would be a good resource to have a dedicated thread for controllers.

To add: From my limited understanding, all things being equal (which they seldom are), an MPPT controller is better suited for controlling the current from PV panel to a battery/batteries when the battery being charged has been more than moderately discharged. The ability to up-current, as needed, is valuable in this scenario when feeding from panels that operate at a higher nominal voltage.

 

[jonshonda]

Professionals will tell you any system under 300w a MPPT controller is not worth the additional cost. I have run and tested several controller from basic low cost to full programmable units and see very little difference in terms of performance.

OMG cruiserdrew and george_tlc are about to prove you soooo wrong.

 

[LandCruiserPhil]

OMG cruiserdrew and george_tlc are about to prove you soooo wrong.

Haha Do your research

 

[jonshonda]

Haha Do your research

Interesting they chose not to respond on this thread.

 

[LAMBCRUSHER]

you guys put too much thought into this type of stuff...as long as the smoke stays inside, it's working...

 

[e9999]

wonder what will happen to all those controllers when in a few years from now we see new technology for batteries (starting with LiIon maybe?) becoming prevalent for vehicles... Seriously, flooded lead acid has been around for too long...

 

[Cruiserdrew]

I'm sure charge controllers will evolve too. It's just a matter of the proper voltage.

I'm stoked for lithium batteries, but not at $500-$1000 per battery. Lead acid is practical and well understood. It will be awhile before Lithium batteries displace them in practical applications.

 

[Bogo]

I'm sure charge controllers will evolve too. It's just a matter of the proper voltage.

I'm stoked for lithium batteries, but not at $500-$1000 per battery. Lead acid is practical and well understood. It will be awhile before Lithium batteries displace them in practical applications.

Charge controllers for solar with lithium iron batteries are already available. Some are being used on racing sailboats. Don't know who makes the solar charge controllers. Just that they are in use.

 

[e9999]

with LiIon cells you can't get close to 12.6V very easily. So, many of the current chargers and solar charge controllers intended for lead acid won't work with the former if the voltage levels and charging schemes can't be adjusted. It'll also be interesting to see if they will change the voltage ratings of car components, or instead stick with 12-14V and use a voltage modifier when having LiI batteries on board.

I'll start checking for solar charge controllers that can handle LiIon if I buy one.

 

[Cruiserdrew]

I'll start checking for solar charge controllers that can handle LiIon if I buy one.

Eric-you realize you are only looking at $50-$100 for an appropriate charge controller, so I wouldn't let waiting for a lithium charge controller be the deciding factor in setting up a basic system.

 

[spressomon]

Victron MPPT, among others, has a LiFePO4 charging and float profile setting. But budget controllers from what I've seen do not. At any rate unless you have very limited space AND need the big current draw down requirement AND have big $ budget you can forget about anything with the word "lithium" in it for the foreseeable future. Especially with Trump trumping relations with China

 

[george_tlc]

'Simple' charging a lifepo4 is relatively easy compared to an SLA. 4 of them also get you into that 12V - 14V sweet spot. They are quite common on motorbikes since they are light (about 4x the energy/weight density), provide plenty of kick for starting/running and very durable in terms of shock/vibration etc. They just cost tooo much (presently) for our use where we are looking at 70AH or more.

Lifepo4 are all much more tolerant (in fact happier) at higher temperatures, whereas SLA life deteriorates dramatically with higher ambient temperatures.

Given Lifepo4 are available as a direct replacement for motorbike 12V SLA they will charge happily in that environment. A solar charge would need to be adjustable for the float setting since 13.8V (nominal float) would not fully charge/top off a 4 pack Lifepo4. You also would want to disable the temperature compensating part of the SLA charge profile. Summary is that adding a Lifepo4 profile would not be hard for a manufacturer since it is simpler subset of a SLA/AGM profile. An MPPT would be the obvious choice since you want to do Voltage regulated charging/float without spiking like a PWM controller.

cheers,
george.

 

[e9999]

regular LiIon would not charge OK in a 12V motorcycle unfortunately, likely. At around 14.6V nominal there would not be a lot of excess voltage over that for charging, I imagine. But I think the LiPo are more like 3.2 or 3.3V each so their 13V is right on. Yup, should be an easy replacement.

Oddly, I do remember reading that folks are using LiPos for replacement in power tools, supposedly cheaper than usual LiIon, but that may no longer be true.

I'm curious also as to how much Lithium we have left if those batteries are going to be it. I remember an article where it said that the yearly Lithium need for the Tesla factory in NV would just about equal the global production. No idea if true.

 

[spressomon]

14.6v is the max charge recommended for long term health of LiFePO4 cells in a nominal 12v array.

 

[george_tlc]

regular LiIon would not charge OK in a 12V motorcycle unfortunately, likely. At around 14.6V nominal there would not be a lot of excess voltage over that for charging, I imagine. But I think the LiPo are more like 3.2 or 3.3V each so their 13V is right on. Yup, should be an easy replacement.

Oddly, I do remember reading that folks are using LiPos for replacement in power tools, supposedly cheaper than usual LiIon, but that may no longer be true.

I'm curious also as to how much Lithium we have left if those batteries are going to be it. I remember an article where it said that the yearly Lithium need for the Tesla factory in NV would just about equal the global production. No idea if true.

Given the numbers you wrote up top, I don't think you realize that a LiPo is NOT a Lifepo.... LiPo is Lithium Polymer, Lifepo is Lithium Ferrous Phosphate (LiFePO4). Totally different chemistries. The lifepo batteries are the nominal 3.2V cells, the lipo are very similar to the Lithium Ion cells.

There's likely just as much a lithium scarcity as there is a petroleum/oil scarcity...

cheers,
george.