mppt vs regular cheap 7A solar charger and battery problems

[terramir]

Hello,

I'm gonna list some factors first:

A. The Battery I have is a marine battery from everystart (johnson controls) 115Ah reserve capacity

B. Cheap cut-off controller (cuts off at 14.2 V cuts back on at 13V)

C. My old RCA 25" TV can't be powered more than two hours at night, but during the daytime even when it's cloudy (only getting 2A right now from two panels with 3.5A(open) cells max I've seen is like almost 4.5A charging at full sunlight) I can get several hours more than the math would support if I just factor the power from the panels vs. the battery (think high drain inefficency as well as the voltage stablizing effect of the solar input are factors)

D. My inverter has the nasty design of cutting off below 11V instead of 10.5V which is the calculation bases for the AH on marine batteries.

E. Also after I "drain" it at night time which should give me like at least three days to charge it it is done charging after like a day maybe a day and a half. If I figure an average of 3A over 12hrs that still just adds up to 36 Ah a day ( and even if I figure it's a good day and I get 48Ah if the battery was really empty at 115 Ah it should take 3 to 4 days.

My thoughts

#1 these panels should deliver each about 3A-3.5A at 15-20V depending on the time of year so 45 to 60W for a total of 90 to 120W right now with that charger I'm getting about 13-14.1V 1.5 A -4.5 A for a energy output of 18W - 63W depending on weather and time of day.

#2 The battery I have seems to only half discharge thanks to the inverter I have So adding a second battery might allow me to:

     A. Stay over the 11V border for longer hence allowing me to more fully discharge the batteries

     B. The lower drain on each battery may also significantly increase the efficency of the batteries, because then they won't get discharged with such a high drain rate. (half the drain rate might give me a 10 to 20% efficency increase)

#3 I don't know if someone makes a good mppt for 12V systems but I do know this right now I am getting far less power out of these cells than could theoretically.

So do you guys agree that a second battery would help tremendoulsly and would a mppt charger give me a significant boost? And before you bring it up a 24V system would cost me more than it's worth since one panel outputs 0.5A less than the other due to more chipped cells they are home-brew panels from ebay cells.

terramir

 

[SamoaPower]

Yes, it looks like you have a number of problems.

A. Batteries of this type are not well suited to this type of service, particularly in the way you seem to be using them. They're not meant to be discharged very far.

B. This type of controller has a number of problems. My guess is that your battery is chronically under charged. Don't think that just because it switches off at the higher voltage that the battery is fully charged. More likely, 80-90%. It takes a lot of cycles like this to bring them fully up.

This type of controller also wastes a lot of energy in that the power your panels could be generating during the off time is being lost.

C. It seems you actually have more like a total panel power of 75W using the convential rating system. I doubt you will ever see 120W.

D. Actually, I think your inverter is doing you a favor by cutting off at 11V. Bringing the battery down even this far routinely will significantly shorten the life, particularly for this type of battery.

E. I think you're pretty optimistic about how much energy you're going to get from those panels unless you live in Arizona during the summer.

I did a three-year study of my panels when they were new and found that I only had a 20% (of rated power) utilization factor, mostly due to always having some clouds around and the fact that panel ratings lie.

#1. I suspect you may see an average of 20Ah/day for those panels. If your daily usage is more than 18Ah (because of battery charge efficiency), you will end up in the hole leaving the battery under charged which will kill it.

#2. Adding a second battery will just compound the problem. Your self-discharge will double. Now you will have two more-under charged batteries.

Your basic problem is not having enough charge capability for your usage. This coupled with an inefficient controller is shooting you down.

#3. MPPT will help somewhat if you live in a cool climate. Here, in the tropics, it's not worth the trouble or expense.

[Opera House]

Anyone that uses 12V panels and a MPPT controller to charge a 12V battery is just wasting their time and money. There just isn't enough headroom to be effective. Panels should be connected as 24V going into the MPPT controller to gain benefits.  You can build a simple fixed power point switcher for not much on this size system.   Your battery may also have problems that you are not aware of even if you just bought it.  I used some more conservative estimates when I first bought panels and I never even came close to reaching those.

[terramir]

I live in los angeles, but getting another battery should that not enable me

A. Let it charge for more days

B. When I do have to drain it let me say have 4 hours of TV for example and then let it charge from there? I just drian it with the tv right now to not waste my free energy, Free TV is just a bonus

That way I don't have to fully discharge the batteries hence meaning longer life of the batteries and less high drain.

BTW This is basically right now a hobby system, I am connected to the grid and this is just a learning project I have enough cells to make like three more panels, but 24V is out of the question because these panels vary to much in quality it will get even worse when I have two more panels. Although if I do match those panels I might be able to make it a 24V system, I will see in time. But this problem is more immediate.

terramir

[ghurd]

I would not recommend this to anyone. You have a special situation.

Let the battery charge direct through only a diode, if the load is daily.

The battery is drained every night.

I feel the PV can not keep up with the drain, and has no chance.

A controller would usually hurt, given the unusual situation.  

The charging current is ~8% of capacity (C/12), for ~10% of the time.

(Bubbling batteries will help)

Get more battery. And add more PVs.

And use the TV less (Monday, Wednesday and Friday for battery powered TV?).

The system seems to be operating on 'surface charge'.

I have seen it before and have no explaination.  

The best I can guess is the top 1/3 of the battery is over charged/discharged, and the lower 1/3 of the battery is always over discharged.  Thats not good for the battery.

G-

[terramir]

ehhh yeah actually I bought another battery today and yeah if I get off my butt I got another panel in the closet that just needs a four cell add panel, at first I built my panels to be 32 instead of 36 cells I didn't know what I was doing LOL.

I already got one full 36 cell panel and a 32 + 4 = 36 on the roof. Well understand right now I just want to hook this second battery in parallel but I need to equalize the voltages first, I will be multimetering and assuming this one (new) is fully charged I might have too use the inverter on this one for a few minutes to get equal voltages. as for surface charging is there a way like charging it occasionally from the plug to break that up?

Anyways thanks for the comments and I do think I should get a different charging circuitry, maybe build my own

and yeah I did diode charging once (when I had these suckers in my windows instead of on the roof far less current then) and with the second battery in parallel I dunno let me see 115 Ah *2 = 230 Ah max current of 5A-6A Maybe 9 when you get that cloud edge effect(unlikely)it would be like 2% to 4% when I add that third panel maybe  2%-6% of C under 10% of C people say you dun need a charge controller.

[terramir]

ehhh forgot to ask one thing should I put a fuse between the two parallel batteries like a 30A fuse or something it's way above the drain and BTW I dun really need to drain the system I just do it every day or two to not waste the power that is being produced. as for bubbling the batteries, considering that this is in a apartment building if I do that should I build some sort of vent to the window? right now the battery is right under the window in the closet if I start producing hydrogen I might want to make sure that it goes strait outside, instead of being naturally ventilated.

terramir

[tecker]

As far as fuses go codes and logic support protecting your investments . If a short happens at the panel that wire from the panel to the battery will heatup fast and ignite until somthing opens up so a fuse at the battery is prudent .The  panel will take a direct short for awhile but somthing will let go so afuse at the panel set at the panels max + 1 amp is also prudent . I say a breaker at the batteries to cover the wire drop max ampeage and a fuse at the panel . Batteries areas have to be vented and of coarse the acid gets all over everything .