MPPT Upgrade?

[rickst29]

Originally Posted by scrubjaysnest

I'm surprised you are only getting to 80% SOC. We reach 100% after two to four hours of full sun with the morningstar 10 PWM. With full sun We have 10 amps into the batteries with two 80 watt panels. Now it could be the difference in batteries since we don't use golf cart batts; but two 12 volt 95 aH. They should charge at 8 to 9 amps, while the golf cart really need about 20 amps @ 14.8 to 15.5 volts for a 225 aH battery.

10 amps (continuous "bulk" charging, which I can't get from my "cheapo" PWM) into a pair of 95 aH batteries is only 5A per battery. 4hrs * 5A = 20Ah per battery. So, if you're reaching 100% in only 4 hours, you're not burning them down below about 80% through the night. My electric usage is much worse than yours.

[LoveToCamp]

As far as battery capacity, I currently have one 12v, with (I assume) about 95 aH of capacity. While I didn't draw it down below 12.4v (according to a Battery Bug) during either of our two weeks out this summer, we also had full sun one week, and a couple hours of good sun most days the second week.

I don't know the maximum amps coming from my panel, as I only have lights, not meters. According to the info on Windy Nation, it is 10 amp output for the panel.

[Bill]

I am an electrical engineer, and I am fascinated by the idea behind MPPT and the circuitry that accomplishes it. If an MPPT controller is what you need, then it is worth every penny. Having said that, it should be clear that if you don't need MPPT, then the extra cost is wasted.

Let me be a devil's advocate for a moment. Suppose you have some panels, and battery(ies), and a cheap PWM controller. And suppose that your usage habits are such that your setup brings your battery back to full charge by 2 PM every day. A controller - any controller - must stop charging when the battery is full, so the PWM controller stops charging (or backs off the charge rate to a trickle) at 2 PM.

Now suppose that you replace your cheap PWM controller with a nice MPPT controller. This controller gets more amps out of your panels, so your batteries charge faster. And now, instead of being fully charged at 2 PM, your battery is fully charged at 1 PM, and the MPPT controller stops charging at 1 PM.

Either way, the batteries are fully charged by mid-afternoon, and either way, you go into the evening with a full charge. Yes, it is nice to look at that ammeter in the morning and see the higher charge current. But if it simply means that charging is completed earlier, then it really doesn't accomplish anything.

Of course, the above argument applies only if you already have a system that is adequate to your needs. If your system is marginal, and you often go into the evening without a full charge, then an upgrade to MPPT is a great idea. Or if you camp a lot under cloud cover, and the simple system doesn't quite get there when it is cloudy, then MPPT can help. Or if you want to increase your daytime power use (not evening power use!), then an MPPT controller will let you do that.

My conclusion is simply to be sure you need MPPT before you lay out the added cost.

Hope that made sense, and not too preachy.

Bill

[LoveToCamp]

Thanks to all for your input. I understand the difference between the two types now, and the types of use that each is good for. I appreciate your patience.

[scrubjaysnest]

Originally Posted by rickst29

10 amps (continuous "bulk" charging, which I can't get from my "cheapo" PWM) into a pair of 95 aH batteries is only 5A per battery. 4hrs * 5A = 20Ah per battery. So, if you're reaching 100% in only 4 hours, you're not burning them down below about 80% through the night. My electric usage is much worse than yours.

This is correct especially if the two 12 volt batteries are identically matched.
Since one is a year older then the other, the newer is most likely getting less charge over the 4 hour charge period. Over the long haul this isn't good for long life; but is a trade off when you put two batteries in parallel. Also with the two batteries in parallel and using voltage to indicate SOC you are seeing the weaker battery. In an ideal world the two batteries would be isolated from each other with the controller selecting which battery needed charging the most. Again ideally load would be switched to the battery having the highest SOC. Besides becoming a high cost charging system for benefit gained; to be truly effective it requires matched batteries. For those with a high current usage, ie inverter running a hair dryer, 6 volt batteries in series with about 200 watts of solar plus mppt may be the better choice.

[rickst29]

Originally Posted by LoveToCamp

AS far as battery capacity, I currently have one 12v, with (I assume) about 95 aH of capacity. While I didn't draw it down below 12.4v (according to a Battery Bug) during either of our two weeks out this summer, we also had full sun one week, and a couple hours of good sun most days the second week.

I don't know the maximum amps coming from my panel, as I only have lights, not meters. According to the info on Windy Nation, it is 10 amp output for the panel.

10A doesn't equal a 100W panel. At 18-19V, the typical Voltage at Max current, the rating of a Panel which cold put out 10A would be 180-190W.

If Windy's panel is 100W @ 18V (which is lower voltage than mine, and more favorable to PWM), then the max current would be about 5.5 Amps. My panels run at 19.1V, so each of my two panels creates just 5.2 Amps at max. Instead of 10.4A total at maximum output, minus wiring losses, an MPPT would dish out up to 13.8A, (That would also be subject to wiring losses, but wiring losses would also be slightly reduced by re-wiring the two panels in Series.)
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5.5A into a single 85 Ah battery (95A is quite a bit more costly, and probably not what you have) -- that would need need about 7 hours, at full sun, to go from 50% SOC to 100% SOC. But your 12.4V minimum Voltage reading might be closer to 75% SOC, it depends on the battery in question. And so, even on that day, 3 hours @ 5.5A is sufficient. I think that your PWM setup sounds good enough to handle your needs without any upgrade, because your nighttime power use isn't anywhere near as high as mine.

[rickst29]

There are much (much!) cheaper Chinese-built "MPPT" controllers on Amazon and Ebay, but I just ordered a Rogue '2024'. (The most popular of those Chinese MPPT products are the same brand as my PWM Controller, and I got real tired of staring at my $20 PWM and saying to myself, "What the Heck is it Doing now?")

If I were as strong as an Ox, then the money could have been spent on another panel instead. But I'm not... so MPPT seems like a much less painful upgrade than adding more weight to the Shell. I'll re-wire my existing panel in series. The "net gain" should be roughly 2/3 of one panel (at full power), and will also be a little more effective in part-shade conditions.

It's to help with the new Fridge.

[rickst29]

I wwrite this post as notes for myself, and also for anyone who creates similar issues with such a heat-generating device.

My first comment is: How can they make and sell something like this for only $225, with any profit at all? The inductor is huge, the board layout is superb, and the components are costly. It "reeks" of quality.

Unfortunately, the "high end" quality is obvious - to even a casual observer. I can't mount this on the outside of TM, because it would be stolen in short order. It's also very large, and possibly wouldn't fit on the front of the "base box" anyway - while still leaving sufficient room for the shell to come down.
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It also generates some heat during operation. Roughly 95% efficient (at highest power: 38V converted into 14.8V on the battery cable) it's heat loss is 6-10 watts. That seems to be enough power loss to overheat the device in an enclosed spot with no fan.

My most likely location in the 2619 (with batteries on the hitch A-frame) is within the under-seat storage compartment, curb side. battery in back I'll need to add some fan-powered ventilation, with power while the Shell is DOWN, for that compartment: If it has power while the Shell is down, I can tap into the heater 12V supply line to run the switched fan.

The fan won't be creating any noise while sleeping, because it can be turned "off" when the Sun goes down, and turned "on" in the morning. I note that owners of older 2720 models, with the batteries in back could install such a device in the same compartment, with added ventilation).

[tentcamper]

I get it with the foot print reduction and that there are many days you don't get enough sun to full charge the batteries, so lets get as much amps as we can with the MPPT. But i'm not sure on an RV you get the numbers?

I have been reading a lot on the MPPT. I'm getting the impression you get the large gain in efficiency when your are running much higher voltage differences between the panes and battery banks, then a typical RV setup. If I understand it correctly, I may get 10% more with my low voltage system that I have??

[scrubjaysnest]

My understanding is mppt breaks even with 400 watts of panel. That said with the TS-45 morningstar pwm and 160 watts in winter full sun conditions we are only seeing panel ratings which means a longer charge time to reach 100% soc. What this means is 4.5 amps per battery when they really would like to 5+ amps. Summer we can do this but not in winter with sun angles. We went with the ts-45 expecting this and will add one or maybe two more panels in the 100 to 150 watt range. At this point Monday morning quarter backing says we should have gone with about 300 watts of solar, 24 volt panels and a morningstar pro 30. With a pro 30 pwm and two 150 watt 24 volt panels the system would still be portable but you could drop from 8 awg wire to 10 awg for a little savings. A mppt controller might give you C/20, battery capacity in aH divided by 20 gives the minimum boost charging current, under winter conditions full sun. That is the first 80 % of charge and after that when the CC goes to absorb, holding battery voltage at 14.8 or higher, there seems to be no problem with the mppt. Hope fully we will get some better day once Rickst29 gets his up and running.