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Old 09-23-2013, 01:49 PM   #1
rickst29
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Cool MPPT Upgrade

Voltage of my Panels at maximum Amps is 19.1 VDC. And Voltage stays near this level whenever they are putting out a significant, useful level of Amps through the entire daytime. Thus, with a cheap PWM, my '200 watts' really works, at the best possible moment in "Bulk" charging, with no wiring losses , at about 200 * 14.4 / 19.1 (more like 150W). In the "Real World", I'm seeing only about 135 average for a "perfect" cycle of Bulk + PWM charging.

Why not a 3rd panel?

There is no question that I would get more energy into the battery, at slightly over half the cost of a decent MPPT, by simply adding a third "100 watt" panel to the roof (staying with the current "PWM", or upgrading to a somewhat better one.) But there is a problem with that idea:
Having tuned my torsion bars for "adequate" lifting power against the two panels I already have, (while not making it too hard to collapse the shell and clip into the brackets), there is substantial resistance for getting it started when collapsing- the sideways motion back to the Trailer Body, before gravity becomes "my friend" and helps to take it down the rest of the way. I feel that an increase in lifting power, to handle the increase shell weight of a 3rd panel, will create a significant increase in resistance at the beginning of the motion - my sideways push against torsion bar resistance on the way down. It's already quite an "mmmph!" to start pushing sideways, into an area where gravity helps to take it down the rest of the way.

So, Spend almost 2x more on a decent (== "high end") MPPT controller?

Aside from adding a bit more charge capability (maybe 1/2 as much as 3rd panel used inefficiently) a good one would appear to have other have benefits for my use of the battery bank:
  1. In camp on sunny days, achieving 90 - 100% battery SOC (instead of 80%-85% with my stupid PWM). Its got a high quality temp sensor, where my PWM has none at all.
  2. Anti-Sulfation per my specification instead of the bad PWM logic.
  3. Accurate readings for Battery and Solar charge Amps and Volts, instead of nearly-always-green "idiot lights".
No reading of power being delivered from the battery, in the setup which I'm considering.

Right now, my battery gets to about 80% SOC during a sunny day with the PWM. That gives me about 30% of the 'nominal' total battery capacity (before reaching a red-line value of 50% SOC.) With a really smart controller, completely aside from the fact that it's creating MPPT levels of current to begin with, I think that I could get about 1/3 more useful SOC into the batteries.

Since it can probably double the lifespan of my batteries (which I have been using down to less than 50% SOC, on occasion) by reaching a much higher max SOC during the charging day (without a lot of "playing around") there's probably a payback in one set fewer batteries to buy over the next 1012 years. Between the battery lifespan improvement, the improvement in usable capacity (with no additional batteries, cabling, or weight), push-button Anti-Sulfation, and decent logic to switch back from "Float" into MPPT "Bulk" or "Absorb" operation, I'm seriously considering that acquisition for reasons which seem defensible. Completely aside from getting a really "kewl upgrade".

Mounting in the 2619 would be a bit awkward - the cheap PWM sits outside, but the expensive MPPT would need to be inside (Maybe along the "front" wall of the fixed-size Trailer Box, next to the collapsing dinette.)
- - - - -

Done. Rogue model "2024", now discontinued, bought from remaining inventory and installed 5/2015.
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TM='06 2619 w/5K axle, 15" Maxxis "E" tires. Plumbing protector. 630 watts solar. 450AH LiFePO4 batteries, 3500 watt inverter. CR-1110 E-F/S fridge (compressor).
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Old 09-24-2013, 05:24 AM   #2
scrubjaysnest
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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.
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Old 11-02-2013, 09:04 AM   #3
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I don't know electricity like some of you do, so I'll ask for your expertise.

Currently, I have a 100w solar panel, with a PWM controller. It is connected to a single 12v battery.

If I go with 2 6v batteries, instead of a single 12v, do I need to change anything regarding my solar? Is my PWM controller still sufficient?

My electric use is LED lights, the water pump, and, in the winter, the furnace fan. I don't use much electricity (so maybe I don't really need to go with 2 6v batteries, but I would like to be covered, in case I have to go 4 days with no sun).
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Old 11-02-2013, 09:42 AM   #4
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LoveToCamp -

Does your current setup meet your needs? If so, nothing needs to change. The two 6-volt batteries will charge just like a single 12-volt battery. Assuming that your panel provides as much power as you need, then the new batteries will simply keep a larger reserve for you - which was your purpose in upgrading your battery, I imagine.

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Old 11-03-2013, 04:27 AM   #5
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Quote:
Originally Posted by LoveToCamp View Post
I don't know electricity like some of you do, so I'll ask for your expertise.

Currently, I have a 100w solar panel, with a PWM controller. It is connected to a single 12v battery.

If I go with 2 6v batteries, instead of a single 12v, do I need to change anything regarding my solar? Is my PWM controller still sufficient?

My electric use is LED lights, the water pump, and, in the winter, the furnace fan. I don't use much electricity (so maybe I don't really need to go with 2 5v batteries, but I would like to be covered, in case I have to go 4 days with no sun).
For us two 12 volt 95 aH batteries is more then enough, our usage is similar to yours; although we most likely use the heat less. We use the 12 volt batteries because of slightly lower weight and if need be I can pull one out and charge it will out exploring the area in the TV. For us 4 days without sun drops the batteries to about 65 or 70 % SOC
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Old 11-03-2013, 01:12 PM   #6
rickst29
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Quote:
Originally Posted by scrubjaysnest View Post
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.
My stupid, $15 Chinese PWM falls down to "trickle charge" mode far too early - according to some extremely conservative, built-in timer. It also lacks ANY temperature measurement and compensation, and that's kinda important for calculating SOC properly. It can't do that, and so it "quits" too early.

So, I needed to make some kind of upgrade. I could have gotten a Morningstar 20 for about $80 (that's barely more than 1/3 the cost of the MPPT I bought) But for late season camping with less favorable sunlight (Sep-Oct), the extra "oomph!" from MPPT could be useful, because my all-electric Fridge (mostly daytime load) and CPAP (mostly nighttime load) consume "significant" power. Here's the one I bought: http://www.roguepowertech.com/photos...24A1PrevSM.png

Gory details:
* Supports 12v and 24v battery banks
* 100v max Voc PV limit
* Very low standby power consumption
* Auto fault resolution (faults will not require the user to restart the controller)
* Reverse battery and input short protection (without using relays or blocking diodes)
* User-upgradable firmware (with optional data converter)
* Fully automatic startup
* Extensive data logging and real-time data accessible with the PC connection and software utility
* Historical data log accessible via PC
* Modified MPP tracking algorithm with new triggers for sweep and user-adjustable options
* LED display for battery voltage - can be turned on or off from front panel at the press of a button
* LED indicators for charging mode and fault status
* Adjustable battery temperature compensation
* Adjustable current limiting
* User-adjustable calibration
* DIP switch for selecting startup charging profile - profile and setpoints can be changed at any time with a remote display or computer interface
* Smaller footprint, lighter weight, robust thermal design (no fan)
* Conformal coated circuit board
* 18-ga steel enclosure with black textured powder coat finish

It operates in 6 modes: MPPT "Bulk"; Voltage limited MPPT "Absorb"; PWM Mode when the battery circuit won't take all the current during "Absorb"; "Float" mode at 13.6V; and two kinds of "inactive standby": One happening during daytime (when the battery line stops taking current in "Float" mode, but the Panel Voltage is above 13.6V and capable of offering more charge); and another, ultra-low power "sleep" mode for night (when the panel voltage drops below minimum requirements to support any battery charging at all).

In 2015, Rogue stopped making this device - because cheaper devices have become available from China are available, and (unlike 2013 models) they work pretty well. Rogue can't build the 2024 and sell it at a profitable price.
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TM='06 2619 w/5K axle, 15" Maxxis "E" tires. Plumbing protector. 630 watts solar. 450AH LiFePO4 batteries, 3500 watt inverter. CR-1110 E-F/S fridge (compressor).
TV = 2007 4runner sport, with a 36 volt "power boost".
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Old 11-03-2013, 01:56 PM   #7
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Quote:
Originally Posted by rickst29 View Post
Mounting in the 2619 would be a bit awkward - the cheap PWM sits outside, but the expensive MPPT would need to be inside (Maybe along the "front" wall of the fixed-size Trailer Box, next to the collapsing dinette.)
I also went with an MPPT Controller on our 2619 for many of the same reasons (weight, space on the roof, etc.). When camping with HarveyRV a few years ago with identical panels and identical sun conditions, and close to identical batteries/charge state, I was getting about 20% more amps to the batteries than he did with his regular controller.

Amortize the cost difference between a regular controller and an MPPT controller (that as you mention often have other beneficial features besides just the MPPT function) over 20 years (50 nights/year) and it works out to a couple of pennies a night (and that's with RS232 interface for custom programming the controller, LCD display and battery temp sensor). I already have two 80 watt panels...the roof doesn't have the space for another panel and I didn't want to add any more weight.

I figure if I nail the back-in into the site on the first attempt, the savings in gas pays for the MPPT controller.

As far as mounting, I mounted mine inside the dinette storage next to the water tank. I used liquid nails to attach a piece of plywood to the paneling on the inside and then mounted the controller to the plywood.

Pictures here: here
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Old 11-03-2013, 03:09 PM   #8
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Okay, rickst29, so the MPPT has lots of bells and whistles. How many of those will I need to adjust, to get one to work well with my system? Are they well-adjusted out-of-the-box? Or, will I spend a day reading a manual, then another day trying to make adjustments when the sun is shining?

Getting more charge to the battery in fall/winter/spring is definitely an argument for an MPPT. If I have to make seasonal adjustments to the unit, though, then I would shy away from that.

I read (what appears to be) a good write-up on the difference between MPPT controllers and PWM. It made a good case for MPPT, in order to optimize charging, but it used a 240w system as an example. Is a 12v battery system really worth the $250 for a MPPT controller?
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Old 11-03-2013, 03:24 PM   #9
rickst29
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Smile Thanks, MudDog!

MudDog, my device is fan-free, but it can't be installed in a tightly closed compartment. (2619 doesn't have the passively vented battery compartment out back; batteries are on the tongue). II put it under the table, front end of the base "box", close to dead center. We no longer fold the table down down in traveling.
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TV = 2007 4runner sport, with a 36 volt "power boost".
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Old 11-03-2013, 04:02 PM   #10
rickst29
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Quote:
Originally Posted by LoveToCamp View Post
Okay, rickst29, so the MPPT has lots of bells and whistles. How many of those will I need to adjust, to get one to work well with my system? Are they well-adjusted out-of-the-box? Or, will I spend a day reading a manual, then another day trying to make adjustments when the sun is shining?
The first of two "pre-programmed" options for FLA seems nearly perfect for my needs (option FLA #0). But my battery bank, loads, and Solar panels are a pretty decent match for each other. If I had a ton of "extra" battery capacity, I'd be programming. Or, if I had 300W on the roof (overwhelming my smaller pair of batteries), I could use the more conservative "pre-programmed" option FLA #1. There is also a pre-programmed profile for "typical" Gel/Sealed batteries, and a 4th for AGM/VRLA.

BTW the cost for 'pretty good' Chinese models is now $170 - $190. (May 2015)

With less battery capacity and lots of panel power, you can afford to let quite a bit of "extra" voltage go unused. In MudDog's configuration, on the other hand - lots of battery capacity, only 150 Watts of panel power - it becomes important to squeeze every bit Panel Power into the batteries. To the extent that an "unusual" match between Battery Bank and makes adjustments desirable, you would do that just once. it can be done with most any Windows PC. When I bought my "discontinued" model they threw in the adapters and cables for connecting to Windows PC for free.

Quote:
Originally Posted by LoveToCamp View Post
I read (what appears to be) a good write-up on the difference between MPPT controllers and PWM. It made a good case for MPPT, in order to optimize charging, but it used a 240w system as an example. Is a 12v battery system really worth the $250 for a MPPT controller?
It's not the battery voltage- rather it's the battery capacity versus the PV daily output. If your battery doesn't reach 100% charge when charged with a PWM controller, THEN the gain in power is useful. (The gain occurs by converting the excessive Voltage of power delivery into more Amps at the lower voltage the battery can actually take.) Therefore, I need to ask a question right back: How much battery capacity do you travel with, and what is the maximum Amps coming from your Panel(s)?
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