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]

OK not all, probably over 99% of multi-stage converters in use operate that way.

I believe Xantrex only has 2 stages. The others you listed are battery chargers. Not what we're talking about.

If you think lowering the absorption mode (or normal mode) voltage is crazy, then you must know more than the engineers of WFCO, PD and Iota combined. You're getting quite wacko.

Sal

BFL13 wrote:

Salvo wrote:
That's a fair question. All modern multi-stage converters have an algorithm to prevent boiling. They are designed to reach the max boost voltage and then go into absorption mode (at a lower voltage level).

Never say "all." Vector , Xantrex and Deltran don't. The whole idea is to get to the threshold voltage and switch to constant voltage at that threshold while amps taper doing the absorption stage. In fact Deltran has now added a new stage after the absorption stage where they *increase* the voltage to 16v for a time before dropping into Float.

Lowering the voltage for the absorption stage would be crazy. That would make the battery acceptance rate less in amps and prolong the recharge time a bunch, defeating the whole objective of achieving the fastest (but safe) recharge time for that size battery bank.

[pianotuna]

Hi Salvo,

That was my point--it isn't boiling it is electrolysis. If my battery bank is at 102 C I don't want to be anywhere near by.

Since you say current doesn't matter, I'd love to see an 875 amp-hour battery gas at 14.6 volts and 1 amp.

It is currently -3.7 C here and the blue sky is in absorption mode at 14.0 volts and 2.5 amps into 500 amp-hours. The other 375 amp-hours were at 14.2 and 1 amp. Of course I have the usual parasitic loads and no shore power, so those numbers may be 0.5 of an amp high.

[BFL13]

Salvo wrote:
That's a fair question. All modern multi-stage converters have an algorithm to prevent boiling. They are designed to reach the max boost voltage and then go into absorption mode (at a lower voltage level).

Never say "all." Vector , Xantrex and Deltran don't. The whole idea is to get to the threshold voltage and switch to constant voltage at that threshold while amps taper doing the absorption stage. In fact Deltran has now added a new stage after the absorption stage where they *increase* the voltage to 16v for a time before dropping into Float.

Lowering the voltage for the absorption stage would be crazy. That would make the battery acceptance rate less in amps and prolong the recharge time a bunch, defeating the whole objective of achieving the fastest (but safe) recharge time for that size battery bank.

They do limit the absorption stage though , because that could run for infinite time. They stop it around 97% SOC and THEN let the voltage drop to Float from Vabs.

Some limit Vabs to four hours. This does not matter if the battery bank will be recharged in that time anyway and go into Float, but IMO it is unsat for a larger bank and a low amp smart charger which might take longer than four hours to complete the absorption stage. (such as what Mr Wiz has with his bank and solar controller)

So with a four hour limit, just when you need the higher Vabs the most, near the end at the higher SOC with lower amps being accepted, the silly thing would get to four hours and drop the voltage on you! Ridiculous. Better not to have the time limit and just use the 97% SOC as the marker.

[Salvo]

That's already been said.

On the other hand, a setpoint of 14.6V is like pounding sand. You've not getting any advantage as opposed to 14.2V. You are running the risk of overcharging the batteries though.

greenrvgreen wrote:
Wouldn't checking the batteries for water loss tell you if you have a problem?

[mena661]

Salvo wrote:
That's a fair question. All modern multi-stage converters have an algorithm to prevent boiling. They are designed to reach the max boost voltage and then go into absorption mode (at a lower voltage level).

Iota has the most aggressive boost routine. If the converter's output voltage reaches 14.6V is will go into absorption mode after an additional 15 min in boost. The goal is to get a fast charge, but minimize time spent above the gassing voltage.

The solar charge controller is a different animal. While a converter has the capability of charging at 50 A, charge controllers charge at a much slower rate. They'll remain in boost a lot longer time period.

That's why Blue Sky adjusted the setpoint to 14.0V. They want to avoid boiling batteries for prolonged periods of time. I get the feeling when Wiz raised the setpoint to 14.6V the controller never gets out of boost mode. The battery may be above the boiling voltage all day long, every day.

Here's what Blue Sky says about their constant voltage charge mode when set at 14.0V:

"The precision PWM voltage control method provided by Solar Boost 2000E prevents over charge while maintaining a more fully charged battery."

Thanks Salvo. That explains some of it. Some (if not all) of the solar controller manufacturers tell you to put your charging regulation setpoints at the battery manufacturers recommendations (Outback Power for example). Most of them are above 14.0V. Do we ignore the battery manufacturers recommendations?

[greenrvgreen]

Wouldn't checking the batteries for water loss tell you if you have a problem? Just asking here. Would 30 days at 14.6 kill the batteries for certain? Because by that time you'd know if they were boiling.

I agree with Wiz, no sense saving your batteries for your Grandchildren. If you can get 3-4 years out of them that's plenty; past that why drag around the weight of additional batteries?

[Salvo]

That's a fair question. All modern multi-stage converters have an algorithm to prevent boiling. They are designed to reach the max boost voltage and then go into absorption mode (at a lower voltage level).

Iota has the most aggressive boost routine. If the converter's output voltage reaches 14.6V is will go into absorption mode after an additional 15 min in boost. The goal is to get a fast charge, but minimize time spent above the gassing voltage.

The solar charge controller is a different animal. While a converter has the capability of charging at 50 A, charge controllers charge at a much slower rate. They'll remain in boost a lot longer time period.

That's why Blue Sky adjusted the setpoint to 14.0V. They want to avoid boiling batteries for prolonged periods of time. I get the feeling when Wiz raised the setpoint to 14.6V the controller never gets out of boost mode. The battery may be above the boiling voltage all day long, every day.

Here's what Blue Sky says about their constant voltage charge mode when set at 14.0V:

"The precision PWM voltage control method provided by Solar Boost 2000E prevents over charge while maintaining a more fully charged battery."

Sal

mena661 wrote:
Salvo says that 14.6V "boils" batteries. I understand some bubbling is wanted but how can 14.6V "boil" a battery when it's the recommended charging voltage by well respected, prominent manufacturers? Sure, if you have manual charger and you left it running for a few days but that's not happening on a multistage charger which Mr.Wiz has. What am I missing?

[Salvo]

We're talking California conditions: 25 to 30 C. According to your link, boiling voltage is 14.2V at 30C. That's not to say gassing starts at a lower voltage.

You're showing some fundamental errors while discussing gassing.

1. There is no defined gassing current. It's all about voltage. Forget current. If the battery reaches 14.4V it will boil, regardless of current.

2. There is little heat associated with boiling. It's a chemical reaction.

Sal

pianotuna wrote:
Hi Salvo,

Gassing may happen as low as 13.8 or as high as 17.8 volts. It is temperature, voltage and current dependent. That is why I want a temperature probe on the battery post. It is unlikely to happen if the current is below the c/20 rate.

Mr Wiz. has 450 amp-hours of battery bank. His gassing current needs to be 22.5 amps. That is more than his panels are likely to produce.

Let's say we have 20 amps @ 14.6 volts going into 200 pounds of lead. That's about 300 watts. That works out to about 1000 BTU's, if 100% of the energy going in is waste heat. That may raise the temperature 5 F internal to the battery. But of course, even worst case that doesn't happen--as Mr. Wiz's current is too low.

Gassing voltages. Scroll down

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

[pianotuna]

Hi Mena,

Boiling comes from bubbles on the plates. The bubbles are a "non conductor" and prevent that area of the plate from charging, that is until they become large enough to "break free" and float to the surface.

Really it is electrolysis (i.e. hydrogen at one plate and oxygen at the other). We just call it boiling because if you do it long enough the bubbles are pretty violent. The true boiling point of 100% sulpheric acid is 337 C (but of course we are dealing with a much weaker solution, so the boiling point is a bit over 100 C {212 F}).

Take a glass of water and put two "electrodes" in it. Connect it to a DC voltage source (a battery perchance?) with sufficient amperage. Watch what happens as the voltage is increased.

[mena661]

pianotuna wrote:
Hi Mena,

Different chemistries offer different charging voltages. Clearly Rv'ers live to split hares *grin* (misspelling intentional).

Salvo says that 14.6V "boils" batteries. I understand some bubbling is wanted but how can 14.6V "boil" a battery when it's the recommended charging voltage by well respected, prominent manufacturers? Sure, if you have manual charger and you left it running for a few days but that's not happening on a multistage charger which Mr.Wiz has. What am I missing?

[MaxThrust]

pianotuna wrote:
Hi Mena,

Different chemistries offer different charging voltages. Clearly Rv'ers live to split hares *grin* (misspelling intentional).

sic

[pianotuna]

Hi Mena,

Different chemistries offer different charging voltages. Clearly Rv'ers live to split hares *grin* (misspelling intentional).

[mena661]

MrWizard wrote:
constant 14.6 "at the batteries" will indeed boil batteries

I just don't see how your controller is going to let your batteries get messed up. Universal Battery recommends a charge voltage between 14.5 to 14.9V for their AGM's. Trojan recommends 14.8V for their flooded batteries. Are these people just stupid or are we talking two totally different things here?

[MrWizard]

constant 14.6 "at the batteries" will indeed boil batteries

I'm not on shore power, there is no applied charge voltage from dark to dawn unless I run the generator, the solar has NOT YET gotten the batteries up to gassing voltage,
IF & WHEN that point is reached I can assess the situation and reset the controller output If necessary

at the last posted reading "Solar Applied" voltage was 13.55 at the battery and the system accepting 12.20a minus the 2.5a the fans were using, less than 10amps actual charge, the batteries were still thirsty and were not at gassing voltage,
your concern is that I am going to be holding the batteries at gassing voltage for unduly long times via the solar charging, that has not happen,maybe next summer, winter is only going to get less sun and more wet and less charging.not more

[pianotuna]

Hi Salvo,

Gassing may happen as low as 13.8 or as high as 17.8 volts. It is temperature, voltage and current dependent. That is why I want a temperature probe on the battery post. It is unlikely to happen if the current is below the c/20 rate.

Mr Wiz. has 450 amp-hours of battery bank. His gassing current needs to be 22.5 amps. That is more than his panels are likely to produce.

Let's say we have 20 amps @ 14.6 volts going into 200 pounds of lead. That's about 300 watts. That works out to about 1000 BTU's, if 100% of the energy going in is waste heat. That may raise the temperature 5 F internal to the battery. But of course, even worst case that doesn't happen--as Mr. Wiz's current is too low.

Gassing voltages. Scroll down

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