What type of charge controll system would I use when adding 12 new panels

beth · August 2010

Hi I have just started living in a home with a ten year old system : 12 unisolar 64 watt 12 v panels, trace sw 24 v inverter and c40 charge controller, 12 trojan L16s (5 years old), honda generator. I am going to replace the batteries and I have room on the roof for 12 more panels. I want to get as much power as I can and buy 12 new panels. I thought I would go with something in the area of panels of 200 watts and 24 v. I would like to keep the old panels (and am willing to rewire them).

My question is what is the best charge controller set up to get to use these two sets of panels. I would have liked to go with the new MPPT controllers but from what I have read this may not be a good idea with two different types of panels and I am a little worried about their complicated electronics going haywire, I wouldn't mind going with two PWM controller if that makes sense. If I did use two PWM controllers how do you wire them. Thanks in advance for all replies!

BB. · August 2010

Re: What type of charge controll system would I use when adding 12 new panels

For batteries--There are some new offerings of 2 and 4 volt cells that are the same size/weight as the old 6 volt cells--Allows you to have a high Amp*Hour capacity cells that you can still move with one or two people (no crane/forklift access needed).

For me, I like to design battery banks with one string of batteries--and in any case, try to limit parallel strings to 2 or 3 maximum (paralleling batteries makes it more expensive for fuses/breakers per string, more cells to check/water, and it can be difficult to make each string share its part of the loads/current).

Before you throw new hardware at your system--review your average daily power usage (over the season) and make sure that your battery bank and system is designed to support your needed loads.

Typically, larger/higher power systems are easier and less expensive to build with higher voltage battery banks (48 volts). 12 volt systems typically work OK up to 1,200-1,500 watts maximum. 24 volt systems upwards of 2,400 watts, and above that--Look at 48 volts.

At this point--Look at the Morningstar 60 Amp MPPT charge controller... It is efficient and has several features that are very nice (remote battery voltage sense leads and even a web server for direct connection to the Internet).

Another tool I like is a Battery Monitor. Does a fairly good job of indicating the state of charge of your battery bank without using voltage to estimate the bank charge--and you don't have to use a Hydrometer nearly as often.

For AC household equipment--a Kill-a-Watt meter is very helpful (and relatively cheap) to measure your loads and help you with conservation efforts in general.

-Bill

Photowhit · August 2010

Re: What type of charge controll system would I use when adding 12 new panels

Beth, welcome!

Others here have suggested that you can use your old charge controller be it PWM or MPPT with a new charge controller of either 'gender'. I'll likely do this when I add in my new panels in the fall. It's not uncommon to have multiple charge controllers on the same battery bank.

I would check to see if the batteries are really at the end of their life cycle L16's can often go 8 years or more. For me, if your just starting out, learning maintanance and care for batteries would be best on an old set rather than taking chances with a new set of batteries.

FWIW - you do have a large battery bank for the size of your Array (panels) My guess is 3 strings of 4 batteries for a 24volt bank of about 1000 Amp hours with about a 750 watt array. To maintain the batteries you'd need to run the generator at least once a month to fully charge the battery bank, and at 5 years equalize the cells. I hope you have a way of charging the 24 volt bank from the generator?

niel · August 2010

Re: What type of charge controll system would I use when adding 12 new panels

to continue with what photowhit was saying the l16s would minimally be 360ah at 6v. it takes 4 in series to make 24v so you have 3 strings of them so it will be 360ah x 3 = 1080ah and if you have the 410ah l16s then it's 3 x 410ah = 1230ah. for the minimum of a 5% charge rate we recommend you would need 54a and 61.5a, but trojan recommends a 10% rate for their batteries and that doubles those requirements.
your system of unisolar 64s will deliver 23.28a if you are lucky for each pv is rated 3.88a at 12v. so you need 2 of them to make 24v at 3.88a and you can do this 6 times with a total of 12 pvs. 23.28a/1080ah=2.16% charge rate.
in keeping the old pv system in tact and just paralleling a new one with it to bring it up to snuff it would need 108a-23 (rounded down)=85a for the 360ah l16s and 123a-23=100a for the 410ah l16s. i have a strong suspicion those l16s you have may be sulfated even if they were charged with the generator and using a large utility charger too. btw, 100a at 24v for pvs is a very large array. for example using a suntech 175 which is rated at 35.2v vmp and 4.95a imp you would need for the smaller l16s about 17 of those pvs and that comes up just shy on the 85a required, but you get gains using the mppt that would overcome this loss and hopefully the other system losses too which can be appreciable if not done right.
as bb said work out your loads per day to see what is really needed to decide upon a battery bank that may be more appropriate for you seeing as how you will be buying new batteries anyway. if you have any refrigerators, air conditioners, fans, microwaves, etc. you may want to consider upgrading to a sine wave inverter as the modsine inverter will use more power and shorten the life of the appliances involved.

beth · August 2010

Re: What type of charge controll system would I use when adding 12 new panels

How basically do you hook up two charge controllers? Do they both just get wired to the battery bank in parallel. For example if you had two trace C40 controllers would they each just monitor whats going on in the batteries and work with the panels that are connected to them and they would not interfere with each other. Would they both be doing the same thing simultaneously but independently?

What if you mix different types or brands of controllers, does each just act as independent system that feeds the batteries when they are low? Do you have to worry about them interfering with each other or the inverter in son way?

I see that some of the new MPPT controllers have an interface connection, so I would assume you could have two different arrays each one made up containing the same type of panels, but the two could be made of different panels from on another and and each controller would work with and maximize the array hooked up to it and the I guess since they are interfaced you get one readout as to performance is this correct?

Thanks for all the advice!

mike95490 · August 2010

Re: What type of charge controll system would I use when adding 12 new panels

How basically do you hook up two charge controllers? Do they both just get wired to the battery bank in parallel.

Yep. One will "finish" before the other one, but quality units will / should be very close, or at least, adjustable.

niel · August 2010

Re: What type of charge controll system would I use when adding 12 new panels

yes, you can parallel the controllers, but do not share the pvs between the controllers. what this means is no pv will be connected to more than 1 controller and your analogy is correct in that it will just be 2 independent systems feeding a common battery bank.

monoloco · August 2010

Re: What type of charge controll system would I use when adding 12 new panels

Can a PWM controller be used with a MPPT controller without any problems?

niel · August 2010

Re: What type of charge controll system would I use when adding 12 new panels

sure, go for it.:D

What type of charge controll system would I use when adding 12 new panels

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