Series/Parallel Panel to Charge Controller questions

Re: Running 60v (5 12v Panels) in series with Morningstar MPPT60?

Yes, you can. But to do this efficiently, you need a MPPT type charge controller which takes "high voltage/low current" and efficiently "down converts" to the
"low voltage/high current" needed to recharge the battery bank.

A MPPT charge controller, more or less, sort of acts like the DC version of a variable AC transformer.

The down side is that MPPT charge controllers are 3-4x more expensive vs a PWM charge controller.

But for larger systems, almost all >100 VDC solar panels are not designed to charge a 12 volt battery bank through a PWM controller--They need Vmp~17.5 to 18.6 volts or so for efficient use of solar array power into 12 volt battery bank. The have Vmp~24-40 volts DC, or even more, and you need a MPPT charge controller to make an effective system.

Also--the best cost solar panels ($$$/Watt), have Vmp>>17.5 volts... So the extra money you pay for MPPT charge controller is saved in the price of less expensive solar panels and copper wiring.

With a typical/large MPPT charge controller, they can take an Vmp-array in the range of 17.5 volts to ~100 volts (or even higher for some controllers) and efficiently down convert to the ~12-15 VDC needed to recharge your battery bank.

-Bill

Re: Running 60v (5 12v Panels) in series with Morningstar MPPT60?

Cam,

I moved your question to its own thread--Keep everything less confusing this way.

If this is your charge controller:

Manson 12V 30A * Suitable for most types of heavy duty 12V battery.
* Microprocessor control PWM and 3 stage charging algorithms.
* Bulk, Absorption & Float Charge status on LCD Display.
* Ampere Hour logging read outs in 3 sets, today and last 2 days.
* 5 State LED Indications of battery levels.
* Electronic Overcharge Protection & Back Current Blocking to PV panel.
* Battery voltage: 12V
* Maximum PV panel open circuit voltage: 26V
* Continuous load / charge current: 30A

Then, you cannot use this charge controller to take "24 volt panels" (really 2*18.5=37 volt Vmp-array) and effectively charge a 12 volt battery bank.

However, if you get a "good quality" MPPT type charge controller, then you are correct. You can connect your 4 panels (identical Vmp/Imp?) in 2xseries and then 2xparallel strings and use the existing cable just fine (assuming your present 6.9mm² cable is appropriate for the current--Aprox 10 AWG and recommend around 25-30 amps maximum--but probably a lot less to keep voltage drop low).

The "Load Terminals" on a solar charge controller should be at the battery bank voltage, 12 volts in this case. There is usually no conversion involved from battery to Load Terminals--just the addition of a switch to turn of the loads if the battery falls below 10.5 volts or so.

Note the "Load Terminals" are typically fairly low current and it is not a good idea to attach heavy loads to these terminals (such as larger AC inverter, etc.).

-Bill

Re: Series/Parallel Panel to Charge Controller questions

basewindow wrote: »

When you say 'good quality' MPPT controller, I was looking at a 'Powertech 30A 12/24v' on e-bay. Would that be any good.

Errr... I don't know anything about that controller.

There is a link to an RV website where somebody tested the controller--and from their testing, it does appear to be doing MPPT type operation.

But there are so many unknowns there--I could not have much trust in the output measurements.

I looked up the Shinsung 240 watt panel--and the PDF has the Voc/Isc numbers reversed with the Vmp/Imp for the panel (not that I would do better in Korean typing these glossies up).

I bought the current one from e-bay and that has done the job faultless for 2 years.

Glad to hear that... Perhaps that speaks well for taking a chance on their MPPT verson.

My inverter runs directly from the battery bus bars, with the appropriate breakers in between.

Good.

My DC loads are LED lights (5w x7), 4w fan for my composting toilet, and 12v water pump (3.9a) with 25a breaker. I assume it's limited to 30a by my current controller, but it would be lucky to pull 12a with everything on.

Some charge controllers will current limit their Load Terminals (fault/turn off power), and others will make smoke.

In reality--You may be just as happy to connect your loads directly to the battery bus and skip the load terminals (unless you can program the to "turn off" at ~11.5 to 12.0 volts or so--which really would better protect the battery bank).

As a side question, Obviously there is voltage variation as the batteries are charged (12v up to 14.9) is that going to effect my 12v appliances or does my current Reg limit the voltage? I have noticed my Inverter sometimes/rarely shuts down momentarily due to over voltage during charging.

It can... There are many "12 volt devices" that are designed for use in automobiles/trucks/etc... A typical vehicle charging system outputs around ~13.8 to 14.2 volts.

A typical deep cycle battery based system will output around 14.5 to 14.8 volts when charging, and even ~15.0 to 15.5 volts when equalizing the battery bank (and even higher if sub freezing temperatures).

We have a few reports here of 12 volt automotive adapters (such as for laptop computers) failing when subjected to ~14.5 to 15.0+ volts.

If you have to use "expensive" 12 volt appliances, you probably should keep the battery charging voltage below ~14.5 volts, and disconnect your critical DC loads if/when you equalize at ~15+ volts.

-Bill

Re: Series/Parallel Panel to Charge Controller questions

Do you need/want AGM/Sealed batteries, or would you be OK with a standard flooded cell type battery bank?

AGMs are very nice, and expensive. But maintenance (distilled water, cleaning battery top+connections) is a bit of a pain too.

There are DC to DC converters you can use--But they do consume extra power.

At some point, just getting an AC Inverter is about the same thing, and gives you have advantage of a 120 or 230 VAC inverter to run your loads (much lower current, less copper wiring costs, you can send power much longer distances, and use standard devices regardless of battery bank voltage.

In my humble opinion, smaller systems can make sense with direct loads in native DC form (12 volt, perhaps 24 volt).

But as systems increase in size, it usually makes sense to go with an AC inverter and forget trying to run DC loads at all. You hardly gain anything from efficiency point of view vs the extra cost/issues of running DC loads.

Depending on your needs (and inverter availability/cost in your location), there is a very nice MorningStar 300 watt (600 watts for 10 minutes) 12 VDC TSW Inverter (120 VAC 60 Hz or a 230 VAC 50 Hz model) that can work very well on the smaller systems. It has a remote On/Off control input and a "search mode"--Both which save a lot of power if your AC loads are intermittent.

-Bill

Re: Series/Parallel Panel to Charge Controller questions

For powering a typical Energy Star full size frost free fridge, you need around a 1,500 watt AC inverter minimum. Fridges are about the large loads (outside of a full sized AC well pump) that most people run on off grid systems.

A MorningStar 300 watt inverter is too small.

If the fridge is not used >9 months of the year (and the off grid system generates less than ~2-3 kWH per day), an LPG unit is usually the more cost effective choice. Although, with the price of fuel lately, perhaps an electric fridge makes more sense.

There is the option of using a converted chest freezer as fridge which can reduce power needs a lot (by 1/2 to 3/4 less power).... But the top access to food/moving stuff around to get a things underneath, is usually not a lot of fun for a spouse/kids.

Chest freezer as a chest refrigerator

-Bill