Why 12.7v turn on point for solar charge controllers?

[FlyFishinRVr]

Maybe this should go in a general forum, but since I don't know if all Airstreams have solar and/or the Atkinson solar charge controller, I'll post it here.

I've been thinking about this for a while now, and can't figure it out. My question for the solar-knowledgeable crowd is why do all of the solar charge controllers, including the Atkinson that comes with the Interstate, have a turn-on voltage of 12.7v vs. just charging the batts when the sun is shining? At first I thought is was to avoid overcharging, but even the lowly Atkinson claims to monitor battery voltage and turn off to avoid this (according to their spec sheet, this happens at 14.2v, but I've never seen the solar panel get my batteries to that point.....).

Anyway, what am I missing? All of the charge controllers I've looked at seem to have this same behavior, regardless if they are PWM, MPPT, 3 stage, 5 stage, etc. I've searched the web, and nobody seems to talk about this. It's just some odd "given" and never explained (at least not that I've been able to find). It seems to me that if they all have electronics built in to sense battery voltage and go into the appropriate charge mode based on that (bulk, float, etc.), why not always do SOMETHING if the panel is getting sunlight?

If I had a controller that provided charge any time the panel was getting enough light to generate sufficient voltage vs. waiting until the batteries lost 20% of their SOC, I think I could get away with a single 100W panel on my roof while in storage with no problems. As-is, the single factory-supplied panel can't make up the loss that is allowed to take place so I'm stuck around 12.8v on my house batts and anywhere from 12.5v-12.8v on the chassis. My understanding is this will eventually degrade the battery performance, and that doesn't give me a happy face......

[Lotus54]

The ASC charge controllers I've used for decades do not do that.
Certainly some hysteresis is needed, but not that much.

Turn off. 14.3
Resumption. 13.5

[lsbrodsky]

Getting rid of that Atkinson was one of my early actions since it is either on or off, just like the stock charger. There are other options that get you multi-stage charging with a float capability.
Larry

[FlyFishinRVr]

Originally Posted by lsbrodsky

Getting rid of that Atkinson was one of my early actions since it is either on or off, just like the stock charger. There are other options that get you multi-stage charging with a float capability.
Larry

All of the multi-stage chargers I've found don't turn on until the batts are at 12.7v (at nominal temps). I've looked at the specs for Morningstar, Zamp, and Renogy and they all seem to have this limitation.

I'll look into the ASC controllers that Lotus54 mentions. Maybe I'm just not finding that "magic" controller that does what I'm looking for.....

EDIT: Looks like the ASC would do what I want, but it doesn't have any remote monitoring, just a LED on the charge controller. That's not ideal, so I'll keep looking, but it's encouraging to know at least ONE company makes something that has a more reasonable "on" voltage......

[73shark]

I'll bet the Lewster can answer your question.

[lsbrodsky]

With my Victron you can set what you want and a BT dongle would allow you to monitor it on your phone. I have a USB dongle to mine to plug in to my laptop.
Larry

[FlyFishinRVr]

Originally Posted by 73shark

I'll bet the Lewster can answer your question.

I'm hoping he can. What I'm finding is this is a somewhat arbitrary number and there really isn't any magic to it, yet most of the manufacturers that I've looked at seem to have settled on it as their standard. Bizarre......

I just looked at the specs for the ASC controller and it gives me hope there is one out there that has everything I'm looking for. As Lotus states, the ASC "turns on" at 13.5v, which is WAY better than the 12.7v of most other controllers I've found. The only downside is it doesn't have a remote monitor and doesn't seem to have the capacity to add one, so I'll keep looking. But, at least ONE company gets it.....

[73shark]

It's been over 50 years but I seem to remember learning in my mis-spent engineering education that the quiescent voltage of a fully charged wet cell battery was 12.7 V.

This seems to support that.

[FlyFishinRVr]

Originally Posted by lsbrodsky

With my Victron you can set what you want and a BT dongle would allow you to monitor it on your phone. I have a USB dongle to mine to plug in to my laptop.
Larry

Which Victron do you have? The ones I'm seeing on their website indicate a "resume" voltage of 12.6v and it's fixed.....

[SSquared]

Originally Posted by FlyFishinRVr

All of the multi-stage chargers I've found don't turn on until the batts are at 12.7v (at nominal temps). I've looked at the specs for Morningstar, Zamp, and Renogy and they all seem to have this limitation.

I'll look into the ASC controllers that Lotus54 mentions. Maybe I'm just not finding that "magic" controller that does what I'm looking for.....

EDIT: Looks like the ASC would do what I want, but it doesn't have any remote monitoring, just a LED on the charge controller. That's not ideal, so I'll keep looking, but it's encouraging to know at least ONE company makes something that has a more reasonable "on" voltage......

I have a Blue Sky unit in my trailer. (It was installed by Lewster). It has a remote display and control panel that can show things like amps being produced by the panels, amps being output from the controller, amps being fed to or removed from the battery, battery amp-hours from full, etc. It has programmable settings for the voltage target for the three stages of charging. When it gets to the third ("float" charging) stage, it will hold the voltage of the system at that point (until the sun goes away or the 12 volt loads exceed what the solar panels can provide).

While in float mode, it always puts out a little trickle of power to run the minor loads (propane detector, fridge, radio even when turned off, etc). This normally includes a fraction of an amp going to the battery as a float charge. On rare occasions I have seen the battery being discharged by one or two tenths of an amp in float mode, but that doesn't result in any significant consumption of the battery's charge.

The Blue Sky unit also has a battery temperature sensor, which it uses to adjust the charging voltage values.

[lsbrodsky]

Originally Posted by FlyFishinRVr

Which Victron do you have? The ones I'm seeing on their website indicate a "resume" voltage of 12.6v and it's fixed.....

I have the MPPT 100/15. Fully adjustable with the BT or USB to PC.

Larry

[FlyFishinRVr]

Originally Posted by 73shark

It's been over 50 years but I seem to remember learning in my mis-spent engineering education that the quiescent voltage of a fully charged wet cell battery was 12.7 V.



This seems to support that.

That could be it, although I've seen numbers ranging from 12.7v up to 13.0v as 100% SOC for these beasts. I think I'll take a look at the Lifeline website and see if they have any nuggets of info that will help. Thanks!

EDIT: According to the Lifeline site their fully charged AGM deep cycle battery will read 13.0v or higher. So....you may be onto something with your reasoning, but if you're right that's unfortunate because it doesn't fit the profile of our Interstate OEM batteries......[emoji53]

[Lotus54]

ASC

[FlyFishinRVr]

Originally Posted by lsbrodsky

I have the MPPT 100/15. Fully adjustable with the BT or USB to PC.

Larry

Thanks!

I was looking at the PWM controllers.....

So, it looks like their MPPT controllers are user programmable for many things including low voltage enable point, or you can use their built-in "Battery Life" algorithm which appears to be exactly what I want the system to do. It will determine if there was sufficient charge from the previous day to fully charge the batteries, and if not, it will turn on sooner the next day. It will keep doing this until the battery is fully charged. Cool!!! There also appears to be a number of remote monitoring panels available along with the Bluetooth solution, so the system looks to be really flexible. Huzzah!!!

Onto Santa's list it goes.

[FlyFishinRVr]

Originally Posted by SSquared

I have a Blue Sky unit in my trailer. (It was installed by Lewster).

Thanks S2. I'll take a look at that one along with the Victron that Larry has. Options are good!

[FlyFishinRVr]

Follow up:

So, it looks like both the Victron and Blue Sky MPPT controllers are able to adjust the "turn on" voltage to something that will basically ensure they are doing "something" any time there's sunlight hitting the panels (just set the "on" voltage to something above 100% SOC for the battery).

Of the two, the Victron is more flexible with it's settings as pretty much EVERYTHING can be adjusted, from on/off points to voltage levels for the different charging phases (bulk, float, etc). This is great because it means it can accommodate requirements for many battery manufacturers, which is good because it seems each manufacturer wants something a little different. The Victron also has a host of different remote panels to set it up and monitor how it's doing, or no panel at all and a Bluetooth adapter that you can connect to via your smart phone.

So....while I still don't have a definitive answer as to "why" most controllers have a 12.7v turn on voltage (although I think 73shark is likely right and for most batteries, and likely the older non-sealed, must-add-water flooded cells, this voltage likely represents 100% SOC, and for those older batteries, setting the "on" voltage any higher may result in boiling off the water), there are some good replacement charge controllers available (specifically the MPPT variety) that will do what I want, which is to maintain my batteries while my rig is on the storage lot using just the single, OEM-supplied 100W solar panel.

Thanks everyone!

[VAtom]

Originally Posted by FlyFishinRVr

Maybe this should go in a general forum, but since I don't know if all Airstreams have solar and/or the Atkinson solar charge controller, I'll post it here.

I've been thinking about this for a while now, and can't figure it out. My question for the solar-knowledgeable crowd is why do all of the solar charge controllers, including the Atkinson that comes with the Interstate, have a turn-on voltage of 12.7v vs. just charging the batts when the sun is shining? At first I thought is was to avoid overcharging, but even the lowly Atkinson claims to monitor battery voltage and turn off to avoid this (according to their spec sheet, this happens at 14.2v, but I've never seen the solar panel get my batteries to that point.....).

I have been paranoid about the SunExplorer and am trying to make sense of the issues.

I noticed that your Atkinson had the blue jumper clipped.

According to the Atkinson datasheet:

FLOODED BATTERY THRESHOLDS: @ Room Temperature 20-258C On @ 12.7VDC, Off @ 14.2VDC On @ 25.4VDC, Off @ 28.4VDC Accuracy 6 0.1V

DC SEALED BATTERY *Blue Jumper Clipped * THRESHOLDS: @ Room Temperature 20-258C On @ 12.4VDC, Off @ 13.9VDC On @ 24.8VDC, Off @ 27.8VDC Accuracy 6 0.1V DC

So it turns off at 13.9V.

Is this really the proper way to set up the SunExplorer?

I would like to replace the jumper if it makes sense.

[AtomicNo13]

I use Morningstar mppt tristar, you can program the charger every which way to Sunday! There are no limitations!

[uncle_bob]

Hi

The key issue is indeed "why?" in terms of the cut out process.

Simple answer is that, long term, batteries last longer if you cut out after they are fully charged and nothing at all is going on. Yes this very much depends on the exact definition of "nothing at all". As a general solution, you are better off hitting them with 8 amps every so often than dribbling 1/4A into them all the time. ( better = they last longer). The *idea* solution would be to separate any parasitic loads from the battery and be able to just handle charging. We don't live in an ideal world ....

Bob

[Boxster1971]

Originally Posted by AtomicNo13

I use Morningstar mppt tristar, you can program the charger every which way to Sunday! There are no limitations!

This is good advice. Dump that cheap Atkinson controller - it is junk! Get a good Morningstar or Blue Sky controller.