Series/Parallel Panel to Charge Controller questions

basewindow

This may be a dumb question and a bit off topic, but can you have a 48v array feeding 12v batteries?

BB.

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

basewindow

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

Ok. The reason I ask is this. I currently have two 120w panels (12v) vmp 18.5 in paralell and was thinking of adding another two also in paralell. Problem was I only have a 6.9mm2 cable from the panels to the Reg (6meters) and that was going to put too many amps through the cable. So could I put two together in series and then those two in parallel to get 240w at 24v. I assume the MPPT would then down convert that to my 12v battery bank at higher amps (480w)? Is that right? Would it also convert the DC Load side down to 12v or would I need to get a step down converter for that? All my lights etc run off the 12v load side.

BB.

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

basewindow

Re: Series/Parallel Panel to Charge Controller questions

Yes that is my current controller, but I was going to get a new one if I was going to add the extra panels.

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

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

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

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.

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.

BB.

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

basewindow

Re: Series/Parallel Panel to Charge Controller questions

Thanks for all that.

I initally thought if I was going to increase my array voltage to 24v then I'd also have to icrease the battery to the same. If that was the case a 48v array with large AH 2v batteries in series would be very expensive indeed. I was going to replace my 2x12v agm with 6x2v 500Ah agm, increasing them to 24v was going to double the price! Maybe I might now still do it and leave it at 12v with a MPPT controller.

Would a voltage step down device of some sort or voltage regulator inserted off the 12v load side help? Is there such a thing?

BB.

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

inetdog

Re: Series/Parallel Panel to Charge Controller questions

BB. wrote: »

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

As an alternative to manual operation as you describe (not friend or mother-in-law proof) or the high price of a DC regulator, it might be worth considering a simple voltage sensor and relay circuit which switches one or more forward-biased diodes into the circuit to the sensitive loads when the supply voltage gets too high.

basewindow

Re: Series/Parallel Panel to Charge Controller questions

I'm only using AGM's because I'm a bit lazy with maintenance and I can be away for a few months at a time.
As it's only a small system the cost wasn't too much, I don't think it will get too much bigger......but who knows.
I've wired the system for 12v already so I'll probably stick with it. The onlt thing I'm stuck for is a fridge, just using an icebox at the moment.
Considering a 12v/Gas, as the hot water and stove are lpg already.

I've got an 600/1200 (bit of over kill really) inverter to run my Tv and other bits, but it's a cheap one and I will be replacing it soon as the fan seems to be playing up. I might have a look at that Morningstar if it comes recommended.

I'll have a look at DC to DC converters, but the relay sounds like a good idea.

Thanks for the help. If I'd found this site before I started things I might have done it a bit different, but for what it is, it all works well so far.

basewindow

Re: Series/Parallel Panel to Charge Controller questions

Is that Moringstar the suresine 300??

BB.

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