Ok to charge batteries with 2 different controllers?

Wxboy

I currently have a Midnite Classic 150 and one 255 watt panel at home and now I want to purchase a portable system for camping. I am thinking of getting a 50 watt 12v nominal panel and a Morningstar Sunsaver 6 pwm controller. Since I only camp a couple of weeks a year I'd like to utilize the panel at home to charge the same batteries that the Midnite is charging. No matter how I set up the charge controllers they won't be doing exactly the same thing at the same time so will this cause problems? For example if the Classic is charging at 14.7 and the Morningstar is charging at 14.2 is that bad? Also, I'm sure they won't go into float at the same time so that would probably be the biggest problem I would imagine. Looks like the Morningstar absorbs for 3 hours and I have the Classic programmed for 4 hours or a minimum current but it usually goes the full 4 hours.

Batteries are two 12 volt agm batteries in parallel, 68ah each. Current charge settings on the Classic are 14.5v absorb with a limit of 14.7v, 13.6v float per the manufacturer's recommendations. The batteries have no charging current limit.

The Morningstar has 2 settings, 14.1v(sealed) or 14.4v(fla) absorb and 13.7 float and it is temperature compensated.

It looks like if I choose the fla setting it would automatically equalize every 28 days so I would probably have to select the sealed 14.1 volt setting.

BB.

Re: Ok to charge batteries with 2 different controllers?

Using two or more charge controllers on one battery bank is fine.

I suggest that you use separate wires from the battery bank/bus common run to Each Controller (i.e., "star" configuration instead of "daisy chain" from battery to controller1 to controller2). That way, the two controllers will have less change of "confusing each other" and only seeing battery bank voltage instead.

With two or more controllers, they will each supply the current they think the battery bank needs, based on charging voltage and time. Eventually, one will go to absorb/float, while the other is in bulk (and changes state a few tenths of a volt later).

Basically, the one with the highest voltage setting will win. Which can be a bit of an issue... The small charge controller does not have a "float" setting, and will tend to hold the battery bank to a higher voltage during the day (when no power is being used). If this was a small battery bank, could be a bit of an issue (AGM do not usually like to sit at absorb voltage for long periods of time).

In any case, with AGM, I would select AGM/Sealed battery with no Equalization (or set equalization voltage equal to absorb voltage--depending on controller). AGM/Sealed batteries really do not need (and usually do not like) elevated equalization voltages.

-Bill

Wxboy

Re: Ok to charge batteries with 2 different controllers?

Thanks for the information Bill.

Next questions I have are...

This first one isn't really a question but I'm trying to decide whether or not to buy the Morningstar Sunsaver with the LVD. I guess if I don't plan to use 12 volt items like a light or a fan I don't need it right?

Next question is, for a 50 watt panel do I need a fuse between the panel and the controller and battery and controller? If so what fuse type and sizes would I need? I have breakers set up for my home system and I guess at first I wasn't thinking I needed anything for the small system but maybe I do? I do have a fuse between the inverter and the battery.

This is the panel I'm planning to buy...

http://www.amazon.com/Instapark%C2%AE-Black-Mono-crystalline-Solar-Panel/dp/B004OZDI7O/ref=sr_1_2?ie=UTF8&qid=1339425556&sr=8-2

BB.

Re: Ok to charge batteries with 2 different controllers?

Wxboy wrote: »

This first one isn't really a question but I'm trying to decide whether or not to buy the Morningstar Sunsaver with the LVD. I guess if I don't plan to use 12 volt items like a light or a fan I don't need it right?

The LVD output on some controllers does not usually handle more than 8-10 amps of load. So, that is useful only for smaller loads/systems.

I would not bother with LVD if your system is monitored by you. If you have a remote/automated system, you might want to look at some sort of LVD (possibly controlled by a Xantrex or Vectron Battery Monitor with alarm contact) to save you battery bank (discharging below ~20% state of charge can permanently damage one or more cells in your battery bank).

Next question is, for a 50 watt panel do I need a fuse between the panel and the controller and battery and controller? If so what fuse type and sizes would I need? I have breakers set up for my home system and I guess at first I wasn't thinking I needed anything for the small system but maybe I do? I do have a fuse between the inverter and the battery.

Fuses are there to protect wiring from high current sources... So, for safety with any moderate to larger battery/battery bank, a fuse for each wire that leaves the battery bank is recommended.

At a minimum, the wire (and fuse/breaker) should be rated to carry 1.25 times the maximum sustained current you expect... For example, if you have a 600 watt 12 VDC inverter with 10.5 volt cutoff and ~85% efficiency:

This is the panel I'm planning to buy...

Looks OK (and has free shipping).

What size battery bank/loads are you planning on connecting... 50 watts will not supply a lot of power.

-Bill

BB.

Re: Ok to charge batteries with 2 different controllers?

Forgot to add, a Fuse near battery to wire going to solar charge controller (keep wire short and heavy for low voltage drop). You do not usually need any fuses on the solar panels until you combine 3 or more strings in parallel--then you need a series protection fuse per parallel string protection.

-Bill

Wxboy

Re: Ok to charge batteries with 2 different controllers?

I'm going to pull the agm batteries from my home system for camping since I won't be running anything at home while I'm gone. So that's 2 68ah agm batteries.

I know a 50 watt panel won't do much but it's just for charging cell phones, running a portable dvd player, charging batteries for fluorescent lanterns and then running camper lights and a small 12v fan at night. I'm guessing I'll pull in about 100 watt hours per day(assuming 25 watts x 4 hours). I'm just trying to be able to extend the # of days I can run on battery power and prevent the battery voltage from getting too low. I don't like to be camping and watching the battery voltage drop each day without being able to put something back in. The 50 watt panel will at least give me something to put back in. I once saw a guy using only one 15 watt panel so I'll be better off than him. If I had more money I would surely be going for a larger panel.

I have a fuse between the Inverter(Xantrex SW2000) and batteries(250 amp fuse).

It sounds like I don't need a fuse between the panel and the charge controller and I do need one between the battery and the charge controller? What type of fuse and what size should be used between the batteries and the controller?

BB.

Re: Ok to charge batteries with 2 different controllers?

Do you have the manual for your solar charge controller?

Anyway, as a rough starting point:

• 50 watts / 17.5 volts Vmp = 2.86 amps Imp

So, at the very least, use:

• 2.86 amps * 1.25 NEC derating for solar * 1.25 NEC derating for wiring = 4.5 amp branch circuit (round up to next standard fuse/breaker size)

For wiring, I would suggest a maximum of 0.05 to 0.10 volt drop on wiring while charging (charge controller "sees" accurate battery bank voltage). Using a generic voltage drop calculator, assuming 4 foot one way wire run:

• 2.86 amps @ 4 feet => 16 awg with Vdrop~0.11 volts
• 2.86 amps @ 4 feet => 12 awg with Vdrop~0.04 volts

Obviously, a 12 awg wire can manage upward of 25 amp fuse/breaker--So you can use a larger fuse/breaker than 5 amps (note that fuses and breakers are a significant source of voltage drop--So a larger fuse/breaker will have less drop too).

Cutting the wire length in 1/2 (4 to 2 feet), you can "drop" 3 awg (rounding to 14 awg @ 2 feet or so for 0.3 volt drop).

Anyway, plug in the numbers that make sense for your system and review the installation manual.

-Bill

Wxboy

Re: Ok to charge batteries with 2 different controllers?

I downloaded the manual and it doesn't specify what to use for a fuse. Would a 25 amp anl fuse like the one in the attached link work between the battery and controller or is there a better type of fuse to use?

http://www.amazon.com/Install-Bay-MANL25-Mini-Fuses/dp/B004WK4SPW/ref=sr_1_1?s=electronics&ie=UTF8&qid=1339437702&sr=1-1

Link to manual as well...
http://www.morningstarcorp.com/en/support/library/SS3.IOM.Operators_Manual.01.EN.pdf

BB.

Re: Ok to charge batteries with 2 different controllers?

What size controller (amperage)? 6.5/10/20 amps?

From the manual:

Fuse Chart
Wire Gauge (AWG) Max. Fuse Size (standard NEC ratings)
14awg = 15Amps
12awg = 20Amps
10awg = 30Amps

-Bill

Wxboy

Re: Ok to charge batteries with 2 different controllers?

I'm going to go with the 10 amp controller.

BB.

Re: Ok to charge batteries with 2 different controllers?

Ideally, then go with the "20 amp branch circuit" wiring and fuse/breaker.

-Bill

Wxboy

Re: Ok to charge batteries with 2 different controllers?

Bill, I'm not sure what you mean by "20 amp branch circuit" but I think I'm changing directions anyway. I've been thinking out how little output I would be getting from the 50 watt panel so now I'm considering the 90 watt panel in the attached link. If I buy this I won't have money to buy a controller so I will have to bring my Classic 150 on the road with me. By doing that I'll also have the battery breaker with me since I have everything mounted on a 2 x 10 so I'll be fine from the fuse/breaker perspective now. Then I'll have to buy a pwm controller in a few months to put the panel to work at home. Once I do that I'll buy another breaker for the box for the new charger.

http://www.amazon.com/HQRP-Mono-crystalline-Anodized-Aluminum-Radiation/dp/B004KSGPJ8/ref=sr_1_6?s=lawn-garden&ie=UTF8&qid=1339543117&sr=1-6

BB.

Re: Ok to charge batteries with 2 different controllers?

20 amp circuit (branching from the main source of power--the battery bank--Like trunk of tree and branching limbs)---Meaning 12 AWG wiring and 20 amp fuse (14 AWG and 15 amp fuse would probably have been close enough for a 10 amp controller--but I was looking to leave you some room to grow).