Help, trouble shooting solar/battery system

[Traveling 2gether Journal]

Ok, I didn't want to wait for shipping and processing, so I drove the 3 hours to Renogy office yesterday. After an in person conversation with another tech guy who gave me yet another explanation and conclusion to my issue I got him to test my charge controller. Turns out it was working how it was designed to, but he finally just admitted that it probably isn't sufficient for my battery and the person that sold it to me may not have been correct. Bla, bla, eventually he agreed to give me credit for the charge controller if I got a different one that better suited my needs.

I ended up coming home with their Commander 40a mppt charge controller and mt-50 meter. I hooked it up this morning and am waiting to see what I get out of it, but it does have adjustable charging parameters, so hopefully I can get a more complete charge into my battery.

 

[dwh]

I haven't seen a charge controller (or a battery charging recommendation) having a lower absorptive charging voltage than the voltage at which the Bulk stage terminates, all the ones I've seen have always been the same voltage. Odyssey's recommendation seems very much the norm to me.

Iota:

http://www.iotaengineering.com/iq.htm

14.8/14.2/13.6


But yea, since solar and AGMs have become common and people have discovered the joys of higher voltages, it's become more common for solar charge controllers to absorb at the same voltage that they bulk to, which is a good thing IMO. Or it would be, if they used higher voltages rather than lower voltages.

Unfortunately most of those that do that, set a time limit on the absorb stage, which is a bad thing IMHO. I'd rather have the higher bulk, lower absorb with no time limit on solar controllers, since the sun sets a time limit anyway, and they can always end the absorb stage when the amp flow drops below a certain level. But they pretty much have to set a short time limit - at least on non-programmable non-RBTS charge controllers, so they can stay in the "totally safe" zone and avoid liability suits if something goes wrong (like a load on the battery during charging fooling the charger into never dropping to float).

(Of course, on shore power chargers it's always best to have a time limit on absorb IMO. For instance, the Iota IQ/4 sets an 8 hour time limit on absorb.)



Lifeline recommends the same voltage for both bulk and absorb (pretty sure they didn't used to) for their AGMs, but at a lower voltage, 14.2v - 14.4v.



Odyssey's recommended 14.8v bulk and 14.8v absorb is actually such an usually high voltage (compared to other batteries recommended specs) that you can pretty much just call it a one-off.


Optima Yellow Top also has a strange one-off recommended profile:

Cyclic Applications:

• 14.7 volts, no current limit as long as battery temperature remains below 125°F (51.7°C). When current falls below 1 amp, finish with 2 amp constant current for 1 hour.

http://www.optimabatteries.com/en-us/support/battery-care/charging/


Good luck finding any non-programmable charger that does what either of those batteries wants. (Except of course, the chargers from those companies specifically designed for those batteries.)

 

[dwh]

(AFAIK all residential installs are series.)

Not with micro-inverters.

 

[dwh]

I had similar problems with a 145 ah agm battery. Which would be floating at noon, but at night time it didnt take long to get down to 12.3 volts or lower. Eventually I replaced it with a kinitek khc2000 102ah agm, this battery after all night use reads 12.6 volts. The battery might have been 145 ah but had lost most its capacity. It was a giant telecom backup battery, and I suspect that was why it was giving problems.

Theres ways to test your battery but it requires special tools, but you done a somewhat decent load test, and a fully charge battery wouldnt drop below 12.1 volts with just a 5 amp load. I myself put a 11 amp load on my fully charge agm and run it for 30 minutes and it dont drop below 12.4 volts and goes right back up to 12.6 as soon as I unplug the load.

VMAX is suppose to be a decent agm battery comparable to the kinetiks. So I'm surprise its not holding a charge. At 155ah it should run your fridge at least 2 days before you need to recharge it.

If you can set the float on your controller to 14.4 volts, no need to replace it. The solar charge controller as long as the voltage never goes over 15 volts wont overcharge your battery, but if it keeps undercharging your battery it will kill it.
By setting the float to 14.4 volts you will never undercharge the battery. AGM batteries can float at 14.4 volts all the time its on solar without damage. My kinitek has been floating at 14.3 volts (the highest setting my controller allows) for the past 2 years, the battery still reads 12.9 volts after a day of charging. I bought the battery use 3 years ago and still running great. Once the battery gets full, it just comsumes 1 or 2 amps, even if your panel produces 15 amps a fully charge battery wont take more than it needs.

solarpaneltalk forum has good info on everything solar, thats where I learned about setting my float to 14.4 volts to keep from undercharging my battery. And undercharging your batteries is the primary cause of premature battery failure. A fully charge battery is a happy battery.

His charge controller is not programmable.

Yours is, and since it almost certainly also has an RBTS, it's adjusting the voltage based on temperature anyway, so even though it's programmed to 14.4v float, it's going to back that down so as to not overheat the battery.

That plus the fact that the float stage ends when the sun goes down, is probably the only reason you haven't cooked your battery with such an insanely high float voltage.

 

[dwh]

Ok, I didn't want to wait for shipping and processing, so I drove the 3 hours to Renogy office yesterday. After an in person conversation with another tech guy who gave me yet another explanation and conclusion to my issue I got him to test my charge controller. Turns out it was working how it was designed to, but he finally just admitted that it probably isn't sufficient for my battery and the person that sold it to me may not have been correct. Bla, bla, eventually he agreed to give me credit for the charge controller if I got a different one that better suited my needs.

I ended up coming home with their Commander 40a mppt charge controller and mt-50 meter. I hooked it up this morning and am waiting to see what I get out of it, but it does have adjustable charging parameters, so hopefully I can get a more complete charge into my battery.

Sweet. Did you get the remote temp sensor too? If not, you should.

The manual for the charge controller says it needs the meter for programming. The manual for the meter shows min/max programmable voltage for each stage of the charging profile, but doesn't appear to allow changing the absorb timer. So you can adjust the bulk/absorb together, but not separately (what they call the boost voltage) to match what is recommended for your battery. Same with float voltage and charging limit voltage.

I'd set that every 28 days wannabe EQ to the same voltage as bulk/absorb and just forget about it. I believe you said your battery wants 14.7v and the default for that so-called EQ is 14.6v when set to "sealed"...so...meh...useless.

 

[dwh]

The trimetric is a good choice. If you get one, and decide you want a more cohesive charger/monitor combo you can get the sc2030 charge controller which interfaces with the trimetric and makes a very powerful and configurable solar charging system

Note: That's a PWM charge controller. (Fine with me, I like PWM, but people should be advised.)

 

[Traveling 2gether Journal]

I did not get the remote temp sensor, but I did get the meter and set the parameters to better fit the battery and got a much better result.
The battery reached the voltages specified by Vmax before switching to float and I unplugged the panels at 3:30pm today and turned on my fridge/freezer. It was 77 degrees Fahrenheit in the fridge when I started it. 6.5 hours later when I checked it both compartments were at the programmed temps, I had made some ice and I was still getting a 12.4V reading at the battery with the fridge still plugged in.

I feel like we figured out my problem and solved it. Thanks a lot to everyone who contributed!

The "boost" phase is still time based with my new charge controller and set for 120 minutes from the factory, but the charge controller does have the ability to adjust this time. I'm not sure what to set it to yet. I would be happy to hear any thoughts on the matter, but for now my plan is to monitor how well charged the battery gets during real world use before switching into float mode and trying to adjust the boost time based on this.

Thanks again! this was the only major issue I was having on my trial run. Now that this is solved I get to pack up and start my trip! Leaving Friday for Joshua Tree, then down Baja and with some luck and determination we plan to get to Panama in about two years. So excited!

 

[DiploStrat]

Some thoughts/comments:

I did not get the remote temp sensor, but I did get the meter and set the parameters to better fit the battery and got a much better result.

Do get the temperature sensor unless you are sure you will remain at sea level in the summer. This is especially important in your case as your Toyota's voltage is a bit marginal for your batteries. You really need that final jolt of higher voltage from your solar charger to compete the accept/absorb stage of charge.

The battery reached the voltages specified by Vmax before switching to float and I unplugged the panels at 3:30pm today and turned on my fridge/freezer. It was 77 degrees Fahrenheit in the fridge when I started it. 6.5 hours later when I checked it both compartments were at the programmed temps, I had made some ice and I was still getting a 12.4V reading at the battery with the fridge still plugged in.

WHY DID YOU UNPLUG THE PANELS??? Don't do that! Keep them plugged in at all times. (Unless they are not mounted to your vehicle.) Lead acid batteries want to be under charge all the time; don't charge and then take them off charge, especially if you have the refrigerator running.

N.B. If you can, let your refrigerator get cold while the engine is running, rather than dumping that huge load on the batteries. You don't have a lot of battery to begin with, baby them!

The "boost" phase is still time based with my new charge controller and set for 120 minutes from the factory, but the charge controller does have the ability to adjust this time. I'm not sure what to set it to yet. I would be happy to hear any thoughts on the matter, but for now my plan is to monitor how well charged the battery gets during real world use before switching into float mode and trying to adjust the boost time based on this.

120 minutes seems way too short to me. Part of the tapering off of the amp rate is simply a reaction to the battery's rising voltage, but, as noted, Lifeline, at least, calls for the absorb stage to be at full voltage. (In fact, they don't specify a bulk voltage, only the absorb voltage.) The L O N G absorb stage (Lifeline even specifies two or more hours AFTER the battery reaches "full" charge.) is important to the longevity of your batteries. Any battery will do well in its first year or so, the test comes in the third through fifth years.

Finally, enjoy the trip to Panama. Lived there for a few years and my daughter was born there. If you can, go visit Porto Bello and Nombre de Dios on the Atlantic side. (And, of course, Panama Vieja on the Pacific side.)

 

[dwh]

Look at the Vmax charts:

https://www.vmaxtanks.com/assets/images/technical info folder/charge_discharge_charts.pdf

Look at the one on the upper right.

Now, it says it's for a constant voltage charge, but they screwed up - that's a multi-stage charge profile. It starts out at a constant current of 0.25C (or C/4 which would be battery capacity in amp*hours (C) times 0.25 or 155 / 4 = 38.75 amps).

So 4 hours at constant current of 40a (for a 155ah battery) and then switch to constant voltage and let is absorb. Unfortunately, they are showing a drop to float at 13.8v after 4 hours, so it takes 20 hours (16 hours at 13.8v) for the battery "charge volume" (state of charge) to actually reach 100%.

If the absorb voltage is where they spec it (14.7 v - 14.9v), then the absorb won't take 16 hours...but it won't be done in 2 hours either.

Also note that at 4 hours, the SoC is only at 60%. Of course, they started with a battery at 0% SoC.


Personally, I would probably set the absorb stage timer to something like 12 hours and just let it absorb until the sun goes down. But that would depend on a couple things - A) having the remote temp sensor, and B) how long does it take to bulk. You can figure out the bulk stage time by just subtracting 2 hours from when it switched to float. For instance, if it switched to float at 3:30, then it was done bulking at 1:30.

If it was dropping to float at like 10am, then I'd probably set the absorb timer to like 4 hours because the SoC was still pretty high when the sun came up. But if it's taking until late in the afternoon to hit float, then I'd just open up the absorb timer and let it absorb until the PV is no longer producing.

That battery is a monster. You are going to have a difficult time hurting it by overcharging with only 300w of PV, especially if you get the temp sensor and you certainly should do that. It's cheap and will make a significant difference by allowing the charge controller to fine-tune the actual working voltages based on the battery's actual working temperature.

Your biggest worry is chronic undercharging, which seems more and more to be a very common problem on the newer AGMs which like high voltages and lots of charge current.

 

[DiploStrat]

...
Your biggest worry is chronic undercharging, which seems more and more to be a very common problem on the newer AGMs which like high voltages and lots of charge current.

Supporting fire from a contact at Lifeline:

"Most damage is caused simply from not charging enough. For example I have a lot of customers that tell me the batteries were low and the let their engine idle for 15 minutes and they’re still not charged. It is not how the voltage that damages them, it’s the lack of charging. What most people don’t know is undercharging (amperage) is often just as harmful as overcharging with voltage."

 

[dwh]

Also note that at 4 hours, the SoC is only at 60%. Of course, they started with a battery at 0% SoC.

[Whoops. Just noticed that I didn't finish that train of thought...here's the rest of it.]

So...if you started at 50% SoC, then you could roughly guesstimate 2 hours of 40a constant current bulk and then 8 hours at 13.8v to reach 100%.

But of course, with 300w of solar / 14.7v = 20a so figure with your setup you'd need 4 hours to reach the end of bulk and start absorb, and at a volt higher you might cut your absorb time in half. So 4 hours bulk and 4 hours absorb would be a fair back of napkin guesstimate.


Or in other words...if you take it down 50%, then just run the solar rig wide open until the sun goes down.


(And this ignores the fact that you've also got loads running sucking away power that could be going into the battery.)

 

[Traveling 2gether Journal]

Wow. Thanks again guys. blown away by all the truly helpful input.

WHY DID YOU UNPLUG THE PANELS??? Don't do that! Keep them plugged in at all times. (Unless they are not mounted to your vehicle.) Lead acid batteries want to be under charge all the time; don't charge and then take them off charge, especially if you have the refrigerator running

I just did this as a way of testing to see how long i could run the fridge with out the panels hooked up. Simulating night in a way.

I am going to increase the absorb cycle to 4 hours for now and just monitor things and try to dial it in. Wish I would have gotten that temp sensor. maybe we will stop by Renogy tomorrow on our way south, but we are planning on camping around joshua tree in southern california tomorrow night and crossing the border into Mex Saturday, so no time to order one.

 

[DiploStrat]

Beating the Dead Horse

I just did this as a way of testing to see how long i could run the fridge with out the panels hooked up. Simulating night in a way.

… Wish I would have gotten that temp sensor. maybe we will stop by Renogy tomorrow on our way south, but we are planning on camping around joshua tree in southern california tomorrow night and crossing the border into Mex Saturday, so no time to order one.

Batteries don't like being "tested." Baby 'em! Especially prior to a two year trip.

Elsewhere in the news, get what you need before you leave the US as the availability of goodies goes down and the cost goes up. This is a mildly sobering read: http://www.expeditionportal.com/forum/threads/158482-Simple-Dual-Battery-Set-up-Gone-Wrong

If all else fails, get the temp sensor before you leave and get it installed in Central America - it is not hard to install.

Have a great trip!