More Solar for "Us"

[MrWizard]

Ok, I went off.the deep end?
Bought 3 used 37watt uni-solar panels and a blue sky 2000e controller for the hefty price of $400,
They were being listed as 75w panels, they are not

The tested open circuit voltage was 21+, short circuit amps 2.9
I tested each panel multiple times tilted into the sun and laying flat on the ground , got the same readings each way, that was the deciding factor, they appear to put out full power while laying flat, I will try to mount them tomorrow before it gets hot, right now 104°F
I will use the existing wiring until I buy & install the new wire

[Salvo]

This indeed is no lab situation. I'm only commenting on what you said. A 14.6V setpoint will boil batteries. Have at it. 😉

MrWizard wrote:

you seem to be superimposing "constants" that don't exist , on a static unused bank, setting in the middle of nowhere exposed to constant sun,
this is not a lab setting doing a controlled durability test,

[MrWizard]

were talking about a solar controller in the storage bay, I'm not opening the box to get to the terminal strip every time I make voltage reading

I have test points inserted in the 8ga for the panel voltage,.the output voltage comes from the controller display & the turnigy power meter that's wired into the charge circuit 4ga wires

I used my fluke meter to read the panel voltage and the voltage at the batteries

yes I raised the set point, to compensate for voltage drop, besides it was wrong to begin with, this equipment is ALL USED, not new and was not at factory spec

my converters can easily do FOUR hours at 14v+ , and get to do several hours of this everyday , with more amp capability and at a more even pace held for those hours
the solar voltage is not as high at the battery as the converters voltage and the solar charge is not as constant and level, as it is constantly changing with the clouds the dust the sun angle

you seem to be superimposing "constants" that don't exist , on a static unused bank, setting in the middle of nowhere exposed to constant sun,
this is not a lab setting doing a controlled durability test,

this is real world daily use attempting to do a fuel expense reduction while maximizing battery charge, yes with out premature death of these batteries, but they are an expendable item as long as that expense does.not occur more than every.four years
I'm not looking for ten year battery life

and I agreed Pianotuna the biggest problem is most of us do not have and maintain a large enough battery bank for all the power we use therefore we stress our batteries

on another.note I'm happy to report that 12:30am my voltmeter read 12.60v and at 6:30am (before sunrise) it read 12:35v
not to shabby with fridge cycling on&off all night maintaining cold food and frozen ice cream & ice

I seem to have struck upon a proper balance ( at least during cooler weather )

[BFL13]

Salvo wrote:
.... Gassing begins above 13.9V. It's important to note, gassing is a function of battery voltage, not current. If the battery voltage rises to 14.6V, then there's enough current to make it happen.

I suspect you might be onto something, but also suspect you are confusing yourself, which is why am seeking clarification.

eg, above you say it is the voltage not the current but then say it needs current to make it happen. ?

Also we have the switch from constant current to constant voltage for the Stage 2 absorption phase. At this constant voltage of 14.7 (say) the current tapers specifically to prevent the battery from overheating and gassing "too much" --we want some gassing.

The whole point there is to reduce the current as SOC rises while voltage remains at 14.7. So why worry about reducing the current if it is the voltage that causes the gassing? I don't get it.

I agree that holding the battery at high voltage after it has been charged -no current- will keep it gassing and it will lose water. but here Mr Wizard's batteries are not charged yet, and the controller will prevent "too much" gassing, while allowing the desired "some" gassing.

So is this just all about how much gassing is "too much" for "too long?" The time factor (too long) is taken care of every day around sunset isn't it? Doesn't that also take care of "too much?" whether it is voltage or current?

[pianotuna]

Hi Salvo,

Is not gassing temperature related too?

Salvo wrote:
I can only surmise you're not comprehending what's taking place. The factory voltage setting is 14.1V. MrWiz cranked this setpoint voltage up to 14.7V. Gassing begins above 13.9V. It's important to note, gassing is a function of battery voltage, not current. If the battery voltage rises to 14.6V, then there's enough current to make it happen.

As a homework assignment, do your own research & analysis to the rest of your questions.

[Salvo]

You got a measurement error as the previous data results in a different line resistance. Are you using the same meter for both measurements?

The best way to measure line resistance (or line voltage drop) is to use just one meter. Connect one meter probe to + output of converter and the other meter probe to + battery. Measure voltage (less than 1 V) and current. Now place probe to neg. output of converter and battery ground. Measure voltage and current again. The total line resistance is the sum of the two.

MrWizard wrote:

just measured
15.67v panel voltage into controller
14.44v at controller output
13.55v at batteries

12.20amps controller output

that 14ft run 4ga has 0.89v drop at 12.20 amps

[Salvo]

I can only surmise you're not comprehending what's taking place. The factory voltage setting is 14.1V. MrWiz cranked this setpoint voltage up to 14.7V. Gassing begins above 13.9V. It's important to note, gassing is a function of battery voltage, not current. If the battery voltage rises to 14.6V, then there's enough current to make it happen.

As a homework assignment, do your own research & analysis to the rest of your questions.

BFL13 wrote:

How can the controller crank out so much more than the battery will accept and create this gassing problem when it is designed to not do that?

[pianotuna]

Hi,

Now, just add a temperature compensation probe into that mix....

[MrWizard]

this bank has 4 new matched 6v GC'S
this means even spread among the two pairs, 10a from the controller is 5a into each pair, with a drop of 0.89v from controller to batteries and the batteries applied voltage is approx 13.91

just measured
15.67v panel voltage into controller
14.44v at controller output
13.55v at batteries

12.20amps controller output

that 14ft run 4ga has 0.89v drop at 12.20 amps

[BFL13]

The Blue Sky solar controller has the "true multi-stage" smart charger profile. How can it "force" the battery to take higher amps? Amps taper as required to prevent overheating etc. Amps still taper wrt to the battery's "natural acceptance rate" (defined as the max amps without overheating at an SOC--so max amps keeps dropping as SOC rises) as SOC rises whether that rate is for 14.7v or 14.0v.

How can the controller crank out so much more than the battery will accept and create this gassing problem when it is designed to not do that?

Also just what amps are we talking about for the SOC involved? It seems that in the 14v range the acceptance rate at 80% is about 15amps per battery and at 90% it is down to about 5 amps per battery.

After that it continues to taper. Some define "fully charged" as both 97% SOC and when acceptance rate has fallen to 2% of ah capacity. That would be 2 amps on a 100ah battery.

This suggests that on a pair of batteries, at 10 amps from solar, the controller will deliver constant 10amps till the bank is at about 90% SOC when amps will then taper properly to about 4 amps at 97% SOC.

Where is this overcharging /gassing threat?

At that 97% SOC point some chargers will just stop or else shift down to their Float voltages.

[Salvo]

Here's the situation. If the battery is over 80% SOC it can't accept a high charging current. You can force it to accept more current by increasing the charging voltage. But you're only increasing the batteries surface charge. The higher the surface charge, the greater the gassing and the lower the efficiency. Coulomb efficiency will drop below 50%. That means less than half the current is charging the battery and the greater proportion is boiling the battery (as well as heating it up).

It's foolhardy to think 14.7V and 10A does a better job than 14.0V and 6A. At 14V, the efficiency is greatly improved.

[Salvo]

You got 0.1V line drop at 8.52A. Line resistance is:

R = delta V / I = 0.1V/8.52A = 11.7 mohm.

That's not bad.

When the controller is pegged at 14.7V, the battery voltage is:

Vbat = Vconv - I * Rline = 14.7V - 10A * 11.7 mohm
Vbat = 14.58V (not much of a drop)

I would monitor battery gassing the next time controller is sitting at 14.7V.

Are you going to do a comparison between the old and new controller? Difference in AH per day would be interesting.

MrWizard wrote:

current voltage readings: from panels 14.53 into the controller with an 8.52 amp output from controller, output voltage measures 13.52 @ controller & 13.02 @ batteries

[BFL13]

Salvo, I don't know if solar is different somehow, but what happened to the preference for higher absorption voltages in the 14.8 area?

I know some converters drop voltage after absorption or four hours whichever is sooner, but this should more like at 97% SOC? At over 80% till 97% you still want the 14.8 AFAIK.

Also whatever amps is produced is shared among all the batteries so the threat of overcharging is much diluted anyway?

We had a link to a paper not long ago ISTR on how charging efficiency drops right off after battery passes 80% so that is just a normal part of doing business AFAIK.

If you lowered the absorption voltage so soon at 80% instead of at 97% IMO all you would do is take too long to get the recharge done and run out of sunlight. How would you ever get them fully charged?

[MrWizard]

at 2 in the.afternoon on a sunny there.should be.little load,. ( at least that's the.situation I hope for, the instructions for adjustment are quite explicit about adjusting the controller when near full and to adjust for voltage at the batteries, I adjusted high enough to allow for drop with the intent of having 14.2v on the batteries , after all this point will not be maintained for more that a couple hours at best during winter, as an example trojan recommends holding this voltage for two hours after the batteries reach 14.2 this allows the SG to catch up with the applied voltage to reach full charge
yes I will keep an eye on the batteries, But far more batteries die from under charge than over charge when used in RV'S
current voltage readings: from panels 14.53 into the controller with an 8.52 amp output from controller, output voltage measures 13.52 @ controller & 13.02 @ batteries

[Salvo]

The fact that the controller outputs 14.6V indicates there is little load and battery is already above 80% SOC.

When fridge is cycling on or SOC is less than 80%, it doesn't matter if setpoint is 14.0V or 14.6V. Controller output voltage will be less than 14.0V. You don't have the solar wattage to keep the voltage higher.

I see no benefit at 14.6V. Keep an eye on battery water!

[MrWizard]

@ Salvo,
possibly
but remember we full time and there is always some drain on the system, there is never a "no load" situation, and when the fridge.cycles it will use that 10 amps resulting in a "no charge" during the fridge compressor run period approx 20 minutes per hour
also this voltage was measured at the controller, Not at the batteries , there is some drop on the wires going to the batteries
and in my case I want the solar to do the top off bringing them to as near full SOC as possible