Solar vs Inverter

[Kingbiscuit]

I'm not a battery guru, but it looks to me like the 15.3 absorb voltage is listed on their 12 volt batteries. I am aware that you are running 2 x 6 v in series to get 12 volts. How does this affect the charging voltage shown on the chart?

[AKCamper]

I could not find the link on Interstates website although the link still goes to a PDF. The date on the PDF is 2012 so maybe it might be outdated. This is the PDF that was linked in older posts. I would assume that the tech support team of Interstate knows what they are talking about.

[padlin]

Kingbiscuit
If you're talking the chart I just posted, I double the 6v's 7.65 to get 15.3.

These are golf cart batteries, many are 36v or 48v systems, they'd multiply the rates by 6 or 8.

[padlin]

Originally Posted by AKCamper

I could not find the link on Interstates website although the link still goes to a PDF. The date on the PDF is 2012 so maybe it might be outdated. This is the PDF that was linked in older posts. I would assume that the tech support team of Interstate knows what they are talking about.

The point is that we are not all talking about the same batteries, mine are XHD's, yours are ECL's.

I won't delve into the knowledge level of phone support folks.

[AKCamper]

Originally Posted by sclifrickson

They are the standard batteries that Escape installs in the dual 6V setup: Interstate flooded lead acid GC2-ECL-UTL.

I was talking about the batteries that the post was talking about.

[Vermilye]

Check the battery nomenclature - the 15.3 absorption charging voltage is for the 6V GC2-XHD, HD, and RD. The 6V versions are rated at 232 amp hours. This battery is no longer made by Interstate, but was supplied with Escape trailers in 2011.

The absorption charging voltage of 14.8 is for the newer GCL-ECL line of batteries, which was a 225 amp hour battery. While the information is still on Interstate's web site (which is a Zoo!) still show the specifications for this series, a search for it states it has been replaced by the SRM series.

The 6V batteries in my 7 week old Escape 21 are Interstate GC2-ECL-UTL's (And someone owes my a steak dinner for digging into the battery box - it sure was easier to check them in the 17B & I'm seriously thinking about switching to AGM's).

In any case, I suspect that this line of batteries uses the lower charging voltages (14.8 Bulk, 14.8 Absorption, and 13.2 float) that are listed for the other GC2-ECL series - I can't find any specifics for the UTL series on Interstate's web site).

The discussion I had with Interstate a few years back was that the GC2-XHD, 232 amp hour battery used some different additives from their other batteries that allowed for a higher absorption voltage.

I have to admit, when I set my Blue Sky solar controller for 15.3, the batteries did store more, but outgassed more than I was happy with. I had to add water every couple of weeks. I went back to 15 volts, and had no problems, although I estimate that I lost 10 - 15 amp hours of storage.

On Edit - Sorry for repeating padlin's information - it took me awhile to type all this!

[sclifrickson]

Originally Posted by AKCamper

I know there has been a lot of discussion about Interstate charge rates through the years and how they differ from all the other manufactures specs. I sent an e-mail to Interstate and received this response from Lisa Simonini who works at Interstate. Lisa.Simonini@ibsa.com
Lisa's response was: Here is information from our tech support team. If this information does not answer your questions then please email them and they will get back to you with the correct answer. Their emailed Information is attached.

Thank you for posting this, Eric. I apologize for my oversight on the ECL vs XHD versions of the GC2 batteries. All of my info was on the XHD’s and I assumed (what they say about assumptions is sadly too often true) that the charge profiles would be the same.

As a side note, I find it quite remarkable to discover that humble pie goes nicely with licorice ice cream!

Apologies for my earlier snappiness.

Best regards to all,
Scott

[AKCamper]

Hey, no problem. I don't mean to sound so argumentative. As long as we choose to back our discussions up with facts we all win in the end. Brian B-P has corrected me a time or two when I made some un-factual statements. Not sure if that's even a word. By the way, have you read "The Battery Charging Puzzle"? Now "Robert" is kind of opinionated, but he sure knows his stuff. It's a good read.

[sclifrickson]

Okay, so setting Absorption to 14.8 does not solve my issue, as I have the temperature sensor on my BlueSky, which boosts the charging voltage in lower temps, so this morning at 40F/7C it’s charging at well over the 15V cutoff of the inverter.

I had read The Battery Charging Puzzle a couple of years ago, but went back and reread it a couple of days hence, and Handy Bob addresses all of my points of concern in his thorough breakdown of the matter, including the importance of compensating for temperature of batteries by adjusting voltage. I’m happy with our setup overall, although Bob (and I) would prefer larger gauge wiring. Nevertheless, we have nice short runs, and my Trimetric sees the same voltage at the batteries as the BlueSky reports putting out, so I’m happy with the system overall.

I just want the inverter to work all the time as well. I’m back to liking the diode on a switch option.

Any other thoughts out there?

[Vermilye]

Another possibility is to set the Maximum Set Point Value to 15V, or as high as the inverter will let you (see page 5 of the manual). Of course this will limit charging at low temperatures, but, as I mentioned in an earlier post, you are going to do a lot of outgassing at 15.3V, plus you are getting pretty close to the maximum voltage for some appliances - I'm not sure it is worth it for the extra 10 - 15 amp hours.

[rbryan4]

Originally Posted by Vermilye

Another possibility is to set the Maximum Set Point Value to 15V, or as high as the inverter will let you (see page 5 of the manual). Of course this will limit charging at low temperatures, but, as I mentioned in an earlier post, you are going to do a lot of outgassing at 15.3V, plus you are getting pretty close to the maximum voltage for some appliances - I'm not sure it is worth it for the extra 10 - 15 amp hours.

This is very true, and the other thing I keep thinking is, how important is it to charge at .3V higher in terms of battery life and number of charging cycles? My guess is, probably not much.

[gbaglo]

If you are only supposed to discharge the battery to 50%, would that mean you only have an extra 5-7 amp hrs. ?

[sclifrickson]

Maybe the battery engineers that make these things don’t know what they’re talking about. And yet the convergence of evidence between the engineers that design the batteries lines up with the engineers that make the chargers, and even with Handy Bob on the matter.

I’m not really interested in debating whether they’re right or not, nor am I interested in undercharging my batteries, even 10%, or in reducing they’re usability or their service life - all real consequences of undercharging. I am happy with my solar charge setup, and do not intend to compromise it.

I am not happy with my inverter’s input limitation.

[sclifrickson]

Originally Posted by gbaglo

If you are only supposed to discharge the battery to 50%, would that mean you only have an extra 5-7 amp hrs. ?

Yes. If the 10-15 A figure is correct, and not a guess.

Edited to add:
Handy Bob addresses the math of this a bit:

“It is so important to get your batteries full because a 95% charged battery has 10% less usable power in it than a 100% charged one, since you are trying to keep it in the top 50% of its operating range (5% of full = 10% of 50%.)”

And,
“...amps pushed at 10% higher volts give you 10% more watts. Therefore, the power stored in the upper range of a battery’s charge is greater, so it is very important to get a full charge.”

[sclifrickson]

So I came up with a different solution for the solar vs inverter problem: I installed a disconnect switch between the roof panels and the solar controller, basically a more convenient version of throwing a blanket or jacket on the roof panel to keep the charger voltage under the inverter’s cutoff for the usually brief periods we use the inverter during the daytime. The cutoff is not often needed, but in the occasional situation when charger both can and wants to put out high volts, and we want to simultaneously use the inverter, this works.



Disconnect is the round one under the solar charge controller.

[sclifrickson]

Two other side benefits of our new “solar disconnect” switch that I thought I’d throw out for consideration:

1. As disconnect is wired between the roof panels and the solar controller, I can now easily prevent possible damage to solar controller if batteries need to be disconnected for some reason (solar input to controller without an attached battery for it to go to is a no no).
2. Disconnect switch is only for roof panels, *not* solar port (portable auxiliary panel). I haven’t done so yet, but this will allow me to see how much juice is coming from each source if so desired. Read the combined input, switch off the roof, do the math to calculate the roof part!

But most importantly, I can now use the inverter any time, night or day!

[paulk]

Originally Posted by sclifrickson

am not really interested in good enough. I want my trailer to work the best that it can, and I want my batteries fully charged, not 90%. Otherwise I would have stuck with the GoPower controller.

If your goal is to have the trailer work the best that it can, without regard to cost, you would want to consider replacing the flooded cells with AGMs, or perhaps Lithium Iron Phosphate batteries depending on your usage patterns. In the case of AGMs, the ideal bulk charging voltage would be below 15 volts since AGMs don't have much internal resistance. You'd also get a longer lasting battery that can be drawn down to a lower percentage without as much damage. Wet cell lead acid batteries lose some of the precious energy that your solar cells have collected due to their internal resistance generating heat, so there is another benefit to AGM/lithium. You also pay the price for internal resistance when you discharge the battery, especially when done quickly.

I'm not a fan of adding a diode before the inverter. If the inverter is the primary energy draw in the trailer, then it would effectively make the batteries 5% smaller since 0.7/12 % of the energy would be converted to heat in the diode. The switch method is better in that regard.

Supposedly, one of the reasons that the WFCO charger is hard to get into bulk mode is that the higher charging voltage can reduce the lifespan of other trailer components [fans, fridges, pumps, lights, etc] and OEMs don't like this. A high charging voltage, although good for the batteries, may not be the best for other components. I have no direct experience with this however, and I note that the Progressive Dynamics charger, which is easier to get into bulk mode, is now included by other OEMs.

My guess is that there is no "perfect" charging voltage and that it's more a question of tradeoffs between multiple competing factors, which leads different manufactures to reach different voltage conclusions using different base assumptions. Do you want to maximize total holding capacity, or battery lifespan, or maintenance considerations in the case of flooed cells, or the lifespan of other components in the trailer, etc..