MPPT vs PWM Solar Regulators

[noelex 77]

Originally Posted by onestepcsy37

belizesailor -
and yet i never see voltage over about 13.7 or so when charging.
.

The battery voltage is dependent on SOC and the current.
If the voltage is never over 13.7 you don't need any regulation.

Batteries do need charging at least occasionally, to 100% for maximum life.

[Captain Bill]

Originally Posted by Sumner

That is interesting. I don't have a PWM controller to compare against, but we bought the Blue Sky 2512iX for our Mac that had 180 watts on it (now 200) and in 3 months of cruising with it I don't remember the cloud thing being an issue. The amps would drop as the battery came up on charge. Most of the time in good sun about 9-12 amps and felt that was good due to the low sun angles (Nov.-Dec) and (Mar.-Apr.).


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That is interesting information. I was getting almost 13 at 28.5N a week before the summer solstice from 300 Watts of panels on a clear sunny day. In previous years at that same time of year I had seen 15-16a at 35N. The tech had me check the version of firmware in my unit and pronounced it the latest and greatest. I suspect it has a bug, but he said that was the way it was supposed to work. The tech did say I could send it back to them and they would check it out under warranty. I asked what the turn around time was and he told me 3 to 4 weeks. I asked if they could send me a loaner unit while the checked out mine. No they couldn't. So I was supposed to go without a controller for 3 to 4 weeks while they checked out my unit. Not to mention I am cruising full time and I would have to wait until I got it back to continue my journey. I did an overnighter last night with a lot of motoring and finished late this morning so the batteries had a pretty good charge on them. I tried to do an equalize, but the system refuses to go in to equalize mode. Some message flashes on the screen, but it goes away so fast I can't tell what it says. I'm quite convinced that this unit is defective, but I can't be without a controller for a month waiting on Bluesky. I may buy a cheap PWM unit somewhere to hold me for a month. Now if I can just find a cheap place to stay for a month while I'm waiting, it's not like I'm going anywhere.... or was I.

[Sumner]

Originally Posted by Captain Bill

.... The tech did say I could send it back to them and they would check it out under warranty. I asked what the turn around time was and he told me 3 to 4 weeks. I asked if they could send me a loaner unit while the checked out mine. No they couldn't. So I was supposed to go without a controller for 3 to 4 weeks while they checked out my unit. Not to mention I am cruising full time and I would have to wait until I got it back to continue my journey.....

I think that I might e-mail them a link to this thread and tell them that this would be of great benefit to their company if they could possibly act quicker on this deal. They could have UPS do a pickup on it at say a marina, they check it out, and either return it or replace it on their dime with a turnaround of maybe 1 week. It would be great for their customer relations and I'll bet sell some more controllers for them.

I've had good luck with questions to the tech dept. but so far things have worked. I've been very happy with Solar Blvd where we bought both of ours and all of our panels. We broke a panel on a piling in Florida and they got one out the same day (from Calif). and we were back in business about 3 days later. Not sure what they would do in this situation.

I had a computer store for a number of years selling mostly to businesses in Wyoming, Montana and South Dakota and they never waited for a warranty item and that got me a lot more sales through referrals hundreds of miles from the store.

Good luck and maybe there is someone on here that might be near you that might have a controller they aren't using,

Sum

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[T1 Terry]

Originally Posted by onestepcsy37

belizesailor -

hadn't thought about that one - panel output voltage is about 22 volts and i've wired it directly to the battery bank. i'm no electrical genius but i can see where, if i have no load drawing down the battery bank the panel could quickly fry it. and yet i never see voltage over about 13.7 or so when charging.

an example. i have all loads turned off. this is strictly panel to battery bank. before i turn the panel on i measure 12.5 on my digital voltmeter. turn on the panel. the voltage begins climbing slowly for the next half hour until it reaches about 13.7, and then it stays there for quite a while. after several hours i get nervous and shut it down. the next morning (still no load on the battery bank) i measure 12.7 on my battery bank. i can't say for certain if the high voltage charge is hurting the batteries because even though the voltage is high the amperage is only about 7.5 max. the battery bank is four golf carts or about 450 amp hours, so the charge rate is less than 2% of the battery capacity, which i've been told is a safe rate.

ok, that's all i know. this amp/volt/watt stuff makes my head spin...

You are manually doing what a PWM controller does. It connects the panels directly to the battery till the voltage reaches the preset boost/bulk voltage, then it rapidly turns the switch on and off to hold the voltage at the preset absorption voltage for the preset length of time, then drops the voltage back to the preset float voltage and turns it on and off to maintain that voltage. Somewhere in it's programming is a set of circumstances that returns the system to boost voltage and the whole cycle starts again.
The better the regulator the more adjustments that can be made to each of these preset levels.
An MPPT controller does the absorption and float exactly the same way, the only time the MPPT part works is during the boost or bulk charge phase.

Sooo.... you are safe to let the battery voltage get up to 14.4v before you switch it off, this will bring the battery up to around 80% SOC if it's a flooded type and 90% id it's an AGM type.... and overcharged if it's a lithium ferrous type but you would be very heroic to use the manual switch method on lithium batteries, the climb from 12v 0% SOC to 13.8v 100% SOC is very slow near flat but very quick once the cells hit fully charged, almost vertical if viewed on a graph.
The difference between using a PWM regulator and no regulator with the size panels you have would be 1ah a day maybe, but the regulator controlling the absorption and float stage would get a lot more into the battery anyway so really you are not better off without a regulator other than the system being simple.
It does show that a regulator is not essential though, just a lot easier.

T1 Terry

[onestepcsy37]

for what it's worth, i plan on adding a second 135 watt panel in the near future, and then i'll have to use a regulator because it would be possible to produce more amps than i draw. still undecided between pwm and mppt, but, being cheap and seeing no overwhelming advantage to mppt i'm leaning towards pwm....

[cfarrar]

Captn Bill, I believe something is wrong with your Blue Sky controller or your setup. We have a 2512ix, IPN remote and 220 watts wired in parallel (~10 ft of 12 gauge and 15 ft of 4 gauge cable). I've never seen the problems you describe. Typically the controller provides our panels' rated output, sometimes .5 amps less, sometimes an amp more (summertime in New England).

[OceanPlanet]

Some info that may be interesting to the folks here. Attached are results from testing that Nigel Calder and I did this summer, comparing MPPT vs. PWM, and parallel vs series wiring. No big surprises, however good to have actual data.

[noelex 77]

That's great information OceanPlanet many thanks for posting it.

[Sumner]

Originally Posted by OceanPlanet

Some info that may be interesting to the folks here. Attached are results from testing that Nigel Calder and I did this summer, comparing MPPT vs. PWM, and parallel vs series wiring. No big surprises, however good to have actual data.

Yep, thanks also.

I started to panic when on the second to last page I saw that the 3024i that we have was doing very poorly against the Genasun GVB-24 in shaded conditions. Then I finally read the whole thing and saw where you were using two MPPT controllers to show the high losses due to shading when panels are in series vs. parallel. Felt better after finally realizing that it wasn't the 3024i, but the series wiring that accounted for the big difference. They both produced the same amperage in full sun.

You guys did a good job. Did you try and collect any data between the MPPT and PWM at lower battery voltages? I can see where that would be hard to do. Possibly have the controllers on the same batteries and panels and switch back and forth between them for some length of time as the batteries took a charge. Say maybe 3 minutes on one and then the other and take the average output from the beginning to end of each 3 minute timed period. Start at possibly 50% charge and stop when the batteries go into acceptance.

Anyway thanks for the work you did do and sharing it,

Sum

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[Dsanduril]

Bruce,

thanks to you and Nigel for doing all the work. I think the conclusions you reached are pretty much in line with what has been discussed on this and other forums. A couple of small things:

First slide, MPPT = Maximum Power Point Tracking (even on the GenaSun website) The whole point it that the controller finds the point that delivers the maximum power.

Conclusions:

● Always use a controller to prevent overcharge, unless small panels with large batteries.

As has been discussed here, the human can be the controller, with very wide pulses and susceptible to failure.

● On boats (usually shading issues), use a good MPPT controller vs. PWM

● Ideally, use one controller with each panel, especially if charging 24V or higher batts

Completely agree, although I suspect the cost (and maybe even the cost/benefit) will kill this idea for most sailors.

● If possible, with multiple panels to one controller, wire in parallel not in series

Again, for 99% of boating cases agree. Series only works when all panels in the series are exposed to identical solar radiation conditions.

[OceanPlanet]

Hi Sum,

I've been kicking myself ever since the test that we didn't think to do the lower-voltage comparison of MPPT vs. PWM. Would have shown much greater gains for the MPPT That's my semi-educated guess, anyway...;-)

Oh well, Nigel is out of town for the season. Perhaps next year!

B