concern

cizzi

I've had my first 2 panels up on my roof for about 6 months now.. they are cheap 15W amorphous panels I got for 100$ each.. I put both in parallel, now I noticed I never get more than 1.2A on my ProStar 15M solar reading.. theoretically they should give me 2.4A when in parallel cause as we all know the amps add up in parallel. I'm sure they are connected in this manner, but in the whole time they've been up there I never saw more than 1.2A.. is this of because where I live? (canada), or the cheap material of the panels? or some other factor? I tested the voltage from the panels together and its about 24V (i think they call that open circuit) so it seems allright, for a second I thought I had put them in series but that wouldnt make sense, I put all the negatives together in the junction box and all the positive together.. anyways i was just curious why I dont get more amps..

BB.

Re: concern

Try just one connected at a time--see if one is producing 90% of the current and the other is only producing 10%... This would be the ultimate test (of course, your battery has to be discharged/load present so that the charge controller will output maximum current.

You could also try bypassing the controller (solar panel+10 amp meter) and see what current each panel/pair can produce into your battery bank.

Another test is to place a current meter set to 10 amp maximum scale and put it across each panel... The short circuit should be near--or a bit greater--than Imp rated current.

Amorphous panels can lose upwards of 20% of their output current in the first 6 months--they are supposed to degrade much less than that after six months--at least that is what the manufacturers claim.

On my GT array--with "good BP" panels with a Grid Tied Inverter system, I typically see about 70% or so of the STC rated wattage (2,500 watts out of 3,500 "panel" rated watts).

I only see 3,000 Watts (~85%) on a very clear and cool day with clean panels--and then only a few times per year.

Panels on a GT Inverter (properly running) is going to be about the maximum power one can get from solar panels. Off-Grid / Battery Charging type are going to get less than maximum unless the controller thinks the battery needs more current (controller settings, battery conditions, and load conditions are going to all affect the "max" current). With a calibrated/accurate DVM, you can measure the battery voltage and the controller output voltage (on its output terminals) and make sure that everything is working to specifications (proper voltage, not much voltage drop, bulk/absorb/float stages, etc.).

-Bill

cizzi

Re: concern

you made me think of something, since my battery is only a 31AH (Deka 8GU1) and I rarely deplete it more than 10% at any given time since I only have some DC lights on it and not on very much could it be that it never *needed* to output maximum current? and I dont have easy access to the panels at the moment so can I do a simple test by depleting it lets say 40% just this one time to see if the next sunny day it pulls more amps in my battery?

System2

Re: concern

What angle of tilt do you have on the panels, and have you changed it yet for the low position of the sun this time of year? For best results they should face the sun full on (perpendicular) at 12 noon standard time. I shift mine to vertical this time of year for a couple of reasons that work well for me. 1) snow either doesn't collect, or slides off quickly, so don't have to be chasing after them to keep them clean. 2) Being vertical this time of year here in northern Nova Scotia, they aren't that far off being perpendicular to the sun at noon, but it's excellent for when the sun pops up off the horizon in the morning, plus, I get full use of sunlight reflected off snow covered ground, which for me is better that having the panels exactly perpendicular to the sun.
If you haven't yet shifted the tilt of your panels, I suspect that's the problem. Otherwise, it could be that one of the panels has failed, or has developed a bad connection somewhere between it and the controller, so only one panel is actually delivering it's power.
Good luck
Wayne
PS Not stepping on your toes BB, you posted while I was making mine

cizzi

Re: concern

panels are set on a 45degree angle since thats my lattitude here in montreal, canada.. getting sunshine has not been a problem over the past 6 months.. im just wondering why i dont get 2.4A and only 1.2A..

System2

Re: concern

cizzi wrote: »

can I do a simple test by depleting it lets say 40% just this one time to see if the next sunny day it pulls more amps in my battery?

=================================
Personally I wouldn't go that route, I'd use an amp merer on the panels like BB said. Will show you what they are producing, without draining down the battery.

System2

Re: concern

If partial shading due to sun being low in the sky this time of year isn't a problem, then on the surface it looks like one panel is out of the circuit, or defective, or their outputs have degraded badly. You say you can't easily access the panels, any chance of them being dirty or having falling leaves stuck to them? Would only take one leaf to kill the output of one panel that size.

cizzi

Re: concern

whats an easy way to test the amperage ? if i disconnect the + and - wires comming from the parallel panels.. can i just use my fluke and put it around the wires? or does it need a circuit with a load pulling?

cizzi

Re: concern

or how about instead of dicharging 40% of my battery just put a load of > 2.4A on a very sunny day at noon time or something? to see if the panels really can generate over 1.2A of current.. would that work like BB suggested?

BB.

Re: concern

Yes, just disconnect the panels from the controller (or at least one lead), and put your Fluke set to 10 amp scale (and leads in appropriate holes in meter) and measure the current in full sun (panels pointing within 10 degrees of sun).

Solar panels will not be damaged by the "short" of the current meter... The current will be Isc (Current, short circuit) rating of panels...

In your case, it should be Isc of the two panels in parallel--roughly equal to or slightly greater than Imp.

Yes, you could put a 2.4+ amp load on the battery--but now you have more "parts" to figure out what is happening... Is the controller limiting current, or are the panels? Is the controller limiting current because it is working properly or broken. It is even possible that the amp meter on your controller is not accurate.

One quick and dirty test to see what the controller is doing--in full sun, measure the solar panel voltage at the controller, and the battery voltage at the controller with your DVM... Assuming it is a PWM (not MPPT) controller, if the controller is trying to pass full panel current, the voltage at the controller input should be roughly equal too, or +1 volt higher than the battery bus voltage... If the solar panel voltage is more than +2 volts higher than the battery bus voltage, it is probably trying to throttle back the charging current to the battery (controller "switch" is not 100% closed).

By the way, check the Deka battery specs... It appears to be a Gel Cell type battery... And you should not be charging it much more than C/20 (5%) of the 31AH--or ~1.55 amps... (sorry, I have to go right now--so I cannot hunt up the mfg. specs. at the moment).

-Bill

cizzi

Re: concern

hey that last comment makes alot of sense.. yes its a gel battery.. and 5% of 31AH is about 1.55A.. I've set my MorningStar Pro-Star controller to gel type mode from day 1 so in this case its normal that it would not charge it more than 5% of the battery capacity?

found this quote on windsun website :

"Gelled cells should be charged at no more than the C/20 rate, or 5% of their amp-hour capacity."

I had no idea of this concept.. would the morningstar controller enforce this charge limit on my small 31AH battery?

BB.

Re: concern

The charger is probably controlling charging current by operating at a specific voltage set point... Basically, if you set your charging point at xx.x volts, the battery chemistry will probably limit the current to an "acceptable" value...

From the MK Battery website, PDF Spec. sheet:

Charge Voltage @ 68F (20C): Cycle 2.30 to 2.35; Float 2.25 to 2.30 v.p.c (Volts per cell?)

Important Charging instructions: Warranty void if opened or improperly charged. Constant under or overcharging will damage any battery and shorten its life! Use a good constant potential, voltage-regulated charger. For 12-volt batteries, charge to at least 13.8 volts but no more than 14.1 volts at 68F (20C)...

And found another PDF document on charging:

Max. [Bulk Charge State] Current (Monoblock Battery Design) Gel: 30% of 20hr Rate

I assume that this is for a multi-cell battery (12 volt) and the Bulk charge rate of 30% of 20hr rate (hmm, this is not clear to me--but it appears that this would be):

(31 AH / 20 Hours) * 0.30 = 0.465 amps

But that would mean that it would take 20/0.3=67 hours to charge from "dead"... Is that what they really mean? Or 1/67=1.5% charge rate...

Or, do they intend:

31 AH * 0.3 = 9.3 amps...

But that is way to much for what Wind-Sun's FAQ says for a Gel Cell battery.

Then we have another GEL Charging FAQ (read whole thing--not everything has been excerpted here):

Bulk Stage I1
Maintain Current <= 30 A per 100 Ah C20
Typically, Constant Current, but Constant
Power, or Taper Charge Permitted
End when voltage = 2.30 to 2.35 V/cell (20°C)

Absorption Stage V1
Maintain Constant Terminal Voltage
(Adjusting only for changing battery
temperature)
Voltage = 2.30 to 2.35 V/cell (20°C)

Optional Accelerated Finishing Stage I2
Maintain Constant Current:
1 to 1.5 A per 100 Ah C20
Charge for 1 to 4 hours based on Ah accumulated
in first two stages:
<25% of C20 – 1 hour
25% to 50% of C20 – 2 hours
>50% of C20 – 4 hours

There is a bunch of technical information (including the above links) here.

It appears that MK Batteries has similar charging profiles between their AGM and GEL batteries (other than exact voltage settings)... And that a charge rate of 25-30% of the 20Hr capacity of the battery is correct (~9 amps in your case)... The low 1-1.5% charge rates is the "trickle charge" limit for long term storage (if the battery is stored more than 3 months without load/charging).

-Bill

cizzi

Re: concern

Today I made a few calls.. first I called East Penn, makers of my 31AH 8GU1 gel battery and asked for some information on the charge rate. Although they told me it charges slower than other batteries they did not help me isolate my problem.

Then I called Wind&Sun in AZ and spoke to someone in the technical support dept. who asked me questions about my solar panels. He told me even in ideal conditions they would only output 2A together in parallel. They are thin film amorphous panels I got for 100$ at canadian tire.

He thinks thats most likely the source of the problem, although the slower charge rate of the gel type battery could be a factor too (not helping).

Also, if the c/20 rate is 1.55A/Hour (31AH / 20 ) then 31AH x 1.55 = 48 hours to charge the battery from a 0% charge state.. how do you firgure 67 hours?

I'm still new at all this so I'm learning!

BB.

Re: concern

Because, the wording in the first battery spec. was unclear--they talked about 30% of the C@20Hr rate... Which would have been 0.3*C/20 (and given a 67 hour charge time)...

But, they appeared to really mean that you can charge at 0.3*C ("C"apacity measured at the 20Hr rate)--which appears to be the correct interpreation because the mfg. estimates a 4 hour charging cycle for a battery taken down to <25% state of charge (I think that is what they are saying)... Which is really quite good--AGM's are the only other "typical" lead acid battery that can charge at those higher rates.

The 1.55 Amp rate appears to be the maximum "trickle" charge rate.

At least, according to MK Batteries, they do not have the low charge rate restriction that Wind-Sun found/saw that Gel Batteries typically needed for long life...

In fact, if you go through the online specs. for MK Batteries, you find that the AGM and Gel batteries have the same charging profile--only slightly differing voltage steps (because of slightly differing construction/chemistry?).

-Bill

cizzi

Re: concern

You stated c/20 actually means "C"apacity/20 so for example 31AH/x which gives you the number of amps per hour the battery can deliver over the number of hours x, correct?

Also, in trickle charge mode I would not see current beyond 1.55A and it seems my battery is almost always in trickle charge mode, one of the LED blinks on my charge controller which means its pulsing to a near full charge state, keeping it as charged as possible?

BB.

Re: concern

Yes, when "we" talk about charge and discharge rates, it is usually C=xxAH (when measured at the 20Hr rate--X amps such that 20 hours will discharge 100% of the battery's energy)--that C/10 or C/20 is XXAH/10 or XXAH/20...

1.55 amps would be the maximum long term charge rate (it appears)... But, there is really no reason to charge at that high of current for a battery that is in storage (there are charts of storage time vs temperature where it can be several months or longer before a Gel battery needs to be recharged in storage).

Remember that the company is talking about 1.55 amps 24 hours per day--you are able charge at that rate for 3-5 hours per day... So it is much less overall.

If the battery where in storage (no load), the amount of trickle charge needed is probably on the order of a few 0.1'ths of amps (low self discharge).

But, the recommendation of "...at least 13.8 volts but no more than 14.1 volts at 68F (20C)..." for "charging" and 0.30 volts less for float charging will probably take care of your needs. If your charger does not have a "float" mode--you can probably just crank the charging voltage towards 13.8 volts (if you don't draw much power from the batteries) or towards 14.1 volts if you take significant amounts of power every day (~10%+ or so).

In the end, you need to make sure your "loads" are less than the ability of your solar panels to put energy into the system (allow to recharge batteries plus losses)... And given the variations in seasons, weather, etc... You either end up with a system that is way over-sized, can only be used 6-9 months of the year, and/or you have a backup power source (generator, wind turbine, AC mains, etc.).

I don't think there is anything "wrong" that you can fix... It is the limitations of the panels (and probably controller) you have (and the system overall).

-Bill

crewzer

Re: concern

Hey Guys,

A couple of things to consider:

1) The 45 degree tilt angle was optimal or ~Mar 21 and ~ Sep 21, but it’s a bit low for this time of year. Try something closer to 60 degree tilt (= lat + 15 degrees) for a “winter” setting in Montreal.

2) The East Penn / Deka / MK voltage targets are typically referenced for 68 F (20 C) battery temperature. The Morningstar temp comp ref is 77 F (25 C), so the targets will have to be normalized for 77 F (25 C). For a 12 V battery, just subtract 0.15 V from the 68 F (20 C) targets to determine the 77 F (25 C) targets.

3) Additional technical info on the East Penn / Deka / MK VRLA batteries (AGM and gel) is available from their very good technical manual: http://www.eastpenn-deka.com/assets/base/0139.pdf

4) The ProStar 15’s regulation (absorb) and float target voltages for the “gel” setting are 14.0 V and 13.7 V respectively, ref 77 F (25 C). These values are at the high end of East Penn’s recommendations. See: http://www.morningstarcorp.com/en/support/library/PS2.DAT.Datasheet.01.EN3.pdf

5) The ProStar charge controller contains a temp sensor (check the center of the front panel). If a remote BTS is not used, the controller uses its ambient temperature (and not the battery temperature) to make temperature compensation adjustments to the target voltages.

6) The charge controller does not know how big the battery is. Accordingly, it does not control charge current based on battery capacity.

7) The controller will limit charge current when operating in absorb- or float modes. This may be why the controller indicates low charge current. The controller usually emits an audible “buzz” when operating in these modes.

HTH,
Jim / crewzer

cizzi

Re: concern

Thank you for your time guys.

cizzi

Re: concern

Allright today I went on the roof to look at my panels, wipped them off a bit before the winter kicks in. I tested the voltage on both panels and got between 25-26 volts on each one seperately. I wasnt able to test the amperage individually because I don't have a DC amp probe yet (went to a store yesterday called Lumen and they had one by the company Ideal for 280$, I'm like no thanks). And I was alone so its was hard with the ladder and such to do proper tests back and forth to the charge controller room. I still get a good 1A steady with sun but thats only half of the promised amps from the panels since I have 2 in paralell. Anyways, I will be replacing both of them with something like a 200W next spring and getting a bigger battery. This was my first experience with solar panels.