Community Forums

PeaceOwl · 04-24-2015, 06:50 PM

Yikes! I am hoping there is a warranty on the batteries., six months old. The rv never shows signs of battery problems otherwise. I was kind of wondering if the solar set up has disguised abnormal battery discharge. And maybe the long trips have charged it well enough to not show a problem....hmm...it's been sitting around for the last few weeks...no battery problems to note. Thnx guys!

Ok, read that often, now I know to get the MPPT controller. Always money!

wa8yxm · 04-25-2015, 02:06 AM

First you said by morning it is 50%... One of the big advantages of the six volt GC-2 Golf Car battery is that it is a TRUE DEEP CYCLE and 50 percent does not bother it as much as it would other battery types.

page 2:
You said "Fully charged by noon"

I would add more batteries,, You said you have 2 pair now.. I would add at least one more pair.. Possibly 2 more pair.

Bumps · 04-25-2015, 02:23 AM

More batteries rather than more solar panels?

Start by calculating your anticipated load.

Then I apply HandyBob's rule of thumb: you should balance batteries to solar panels. IOW, the numbers would be [close to being] equal. 400 watts of panels complements 400ah of [GC-2] batteries. 800 watts of panels complements 800ah of batteries. Etc.

I prefer mono- over poly-crystalline panels matched to a properly sized MPPT Charge Controller.

/ken

Mustang65 · 04-25-2015, 03:48 PM

I totally agree with HandyBob on a lot of his points, but here is where HandyBob and myself do not see eye to eye regarding the MPPT controller verses PWM controller on smaller sized RV solar setups. I am sure that I will get an ear full regarding this post. ….but since we live in America, we have that FREEDOM of SPEECH, so here we go.

I will use the Renogy 100 watt panel stats for this example. Let’s take 2 matched systems of 100 watts each. One is PWM and the other is MPPT. The 100 watt Panel voltage is 18.9 VDC (Vmp) and the panel current is 5.29 (IMP) Amps. The battery is at 12VDC and in need of a charge. It is a BRIGHT SUNNY DAY! No shade! I am not taking into consideration controller inefficiencies.

PWM:
(Amps IN equals Amps OUT)
(5.29 Amps IN equals 5.29 Amps OUT)
Battery voltage level is 12VDC
100 Watt Solar panel
Solar panel Output 5.29 Amps @ 18.9VDC
The PWM controller will charge the battery with 5.29 Amps at 12VDC (5.29Amps * 12VDC = 63 watts (From the 100 watt panel)
For the PWM controller the output is 63 Watts

MPPT:
(Watts IN equals Watts OUT)
(100 Watts IN equals 100 Watts OUT)
Battery voltage level is 12VDC
100 Watt Solar Panel
SOLAR panel output 100 watts
100 watts / 12VDC = 8.3 Amps (MPPT uses Panel output watts and battery voltage)
The MPPT controller will charge the battery with 8.3 Amps at 12VDC (8.3Amps * 12VDC = 100 watts (From the 100 watt Solar panel)
For the MPPT controller the output is 100 Watts

If you do the math that is about 37 Watts or 3 Amps lost using the PWM controller. Now multiply that times the 4 panels and you have 148 watts or 12 Amps lost.

This is why I believe that using an MPPT controller is the way to go, even for RV's, where you are limited by how much SOLAR your RV's roof can handle. EVERY LITTLE BIT COUNTS.... Especially when you go from September through March, when the sun is lower in the sky. Do you think that HandyBob will respond, probably.. I just hope my math is right...

Just my thoughts,

Don

twinboat · 04-25-2015, 05:15 PM

Hey Don, no argument here, but you should do your math with at least 13 volts. 12 is not charging.

I talked with a guy a few years back, he said, take the watts of the panels, times 13.5 volts, times 5.5 hours of sun a day and that will be close, to how many AH you can produce a day. This was with a MPPT controller.

PeaceOwl · 04-25-2015, 08:10 PM

Don, thnx, that sure is a substantial difference in output, and you are right, enough to make it through the night with normalcy. Maybe we wouldn't need the two more batteries. (If they are dead, and we have to get 4 new ones, that might be a problem solved too.

Wa8yxm, thanks, important note on the golfcart
batteries. Phew! We will have our batteries tested soon as well.
We have 4 now, was hoping for six, making it 480w solar and 660ah of battery.
I'm thinking summertime will be fine, more sun hours. Glad I asked tho...a lot to realize here on the charging ability.

Thnx Ken right now we have 480w solar and 440ah batteries. Was hoping adding two more batteries would be ok, but we need to be more diligent about measuring the charging and usage first. Mono Solars.
We will have to change out controller soon also.

Imurphy907 · 04-25-2015, 09:10 PM

Quote:

Originally Posted by Mustang65

I totally agree with HandyBob on a lot of his points, but here is where HandyBob and myself do not see eye to eye regarding the MPPT controller verses PWM controller on smaller sized RV solar setups. I am sure that I will get an ear full regarding this post. ….but since we live in America, we have that FREEDOM of SPEECH, so here we go.

I will use the Renogy 100 watt panel stats for this example. Let’s take 2 matched systems of 100 watts each. One is PWM and the other is MPPT. The 100 watt Panel voltage is 18.9 VDC (Vmp) and the panel current is 5.29 (IMP) Amps. The battery is at 12VDC and in need of a charge. It is a BRIGHT SUNNY DAY! No shade! I am not taking into consideration controller inefficiencies.

PWM:
(Amps IN equals Amps OUT)
(5.29 Amps IN equals 5.29 Amps OUT)
Battery voltage level is 12VDC
100 Watt Solar panel
Solar panel Output 5.29 Amps @ 18.9VDC
The PWM controller will charge the battery with 5.29 Amps at 12VDC (5.29Amps * 12VDC = 63 watts (From the 100 watt panel)
For the PWM controller the output is 63 Watts

MPPT:
(Watts IN equals Watts OUT)
(100 Watts IN equals 100 Watts OUT)
Battery voltage level is 12VDC
100 Watt Solar Panel
SOLAR panel output 100 watts
100 watts / 12VDC = 8.3 Amps (MPPT uses Panel output watts and battery voltage)
The MPPT controller will charge the battery with 8.3 Amps at 12VDC (8.3Amps * 12VDC = 100 watts (From the 100 watt Solar panel)
For the MPPT controller the output is 100 Watts

If you do the math that is about 37 Watts or 3 Amps lost using the PWM controller. Now multiply that times the 4 panels and you have 148 watts or 12 Amps lost.

This is why I believe that using an MPPT controller is the way to go, even for RV's, where you are limited by how much SOLAR your RV's roof can handle. EVERY LITTLE BIT COUNTS.... Especially when you go from September through March, when the sun is lower in the sky. Do you think that HandyBob will respond, probably.. I just hope my math is right...

Just my thoughts,

Don

Good info here. But on the MPPT controller you are running thru a transformer. Transformers are very lossy. Some Controllers are advertised at 93-95% eff. But if you measure them with a clamp on you will not find one in normal use better then 90%. So you need to take your 100 watts and make that 90. still more then the PWM but is the increase worth paying $300+ more for the controller? I would rather buy the $200 controller over the $700 controller and buy an extra panel and a few cases of beer with the savings.

Smitty77 · 04-26-2015, 09:28 AM

Good thread, with good info. And as mentioned, in America we still can have our own opinions and voice them

!

I like reading HandyBob's solar writings. Never met the man, but he was an early believer, and user of Solar in RV's. I also like AM Solars website, as a good source of easy to understand data for most of us who are layman. Jack Mayer's also has good easy to read data too... And BatteryPro Larry, shares his knowledge on this board frequently.

Lots of variables in Solar Panels, wiring, controllers, batteries, and all of the other assorted pieces of a total Solar Panel install. So, efficiencies in the actual solar to battery delivery can be as high as 25-35% different between systems. Other factors, include where you may RV. Say in the deserts of the Southwest vs the forrest of Montana - the solar available to you will be very different in those examples. Toss in some shading, or some clouds, and the Montana example can be dramatic in lower overall solar to battery delivery. I also mentioned 'batteries' as a key variable in systems. A wet cell golf cart 6V will charge differently then a Lifeline AGM.

When we set up our system, I went with 800AH of X's 4 L16's Lifeline AGM's. I did not want to tilt panels. I expect a usage of between 25-35% of the time having partial shade due to the locations we like to camp. So, for Solar Panels, I went with X's 5 240W 48V High Efficiency Sharp/Panasonic for 1200W of panels.

My view is that with a well designed, and good quality components system, having more Solar Panel capacity then actually needed in 'ideal conditions' - would mean we'd have a much higher number of days of 100% SOC by the end of the day of sunshine. With a good well programmed controller (we are using the MidNite Classic 150, temp sensor adjusted, set per Lifeline's AGM recommendations), you are not going to hurt the battery bank by overcharging. So if fully charged by noon, and we are frequently in float by 10:00-11:00AM, no harm no foul to the battery bank. For those days when we have clouds, or partial shading, we may not ever reach float. But, we're typically much further along then if we had gone with 800 watts of Solar Panels.

Costs were not that much more for the extra panels. I could have stopped with X's 3 720W, and probably been in decent shape. But he group selling me the panels, offered me a higher discount for each extra panel I bought, so for less then $475 - I went ahead and added the extra two panels, bringing us to 1200W. And yes, another 1 1/2 of labor, and a few more mounting parts too. But in the overall costs of things, that extra say 480W (1200-720) - means many times never having to run the generator. We plan on using our current rig for a 10-15 years ahead, so I usually amortize the costs of mods out over the years of planned usage. And admit that sometimes I can go a bit overboard

!

Many angles to how we all approach solar, including the use of portable to augment fixed panels. And that is OK...

I have seen many systems installed with what I considered poor quality components, and in some cases terrible workmanship. So for those that are not going to do it themselves, or participate in the design, go to a reputable shop. Paying for quality parts, and craftsmanship installation - can really be a discount over the years of usage ahead.

Best to all,
Smitty

**CountryFit** · 04-26-2015, 07:18 PM

Smitty,

nothermark · 04-26-2015, 08:01 PM

1. Transformers are seldom less than 95% efficient and usually better than that. I do not know where the "lossy" line comes from.

2. The power supplied by the charger combined with the generator run time set the total charging time of the battery bank. The simple truth is that you do not know what you have going on because your metering is not accurate. Track it with a voltmeter and you can find out. A $20 meter and a table of charge level voltages might be all you need to sort out your problem. Understand the charge/discharge cycle of your setup and see what is really happening. With the generator to provide bulk charging as well as off load heavy consumption a few more minutes each cycle may do what you want. If you are fully charging what you have and then they do not have enough capacity add to the capacity and see what it takes to charge the new bank. Once you understand that then you can decide to add solar or change controllers with the confidence that you are doing what you need not just throwing money down the hole based on what somebody else did according to their best guess.

A secondary benefit of getting the system working is that you can run a dataset once a month to monitor capacity drop with age and use. That will give you better answers than the average battery tester. It is a lot better for the batteries and more informative. That is housekeeping just like an occasional dusting or oil change.

PeaceOwl · 04-26-2015, 10:58 PM

Excellent advice, thnx everyone. Agree, hard to be accurate without the voltage meter. A cheap addition to what could be an expensive mistake. You are right, the sun has control of this in any or all circumstances,

we are pretty new to this. My common sense tells me we do not have quite enough solar set up to work well at all times.

OLYLEN · 04-27-2015, 08:57 AM

Seems most newer HM' s that have regular refers HAVE either six batteries or bigger capacity. Some owners have wired in smaller inverter just for the refer to minimize the inverter overhead. HAVE several owners I know running 400-500 watts with 6 batteries and doing OK boondocking. Most if not all are very usage conservative or run the gen for a while in the morning and in the evening during the higher demand times.

LEN

PeaceOwl · 04-28-2015, 02:48 PM

We do that too, Len. Run the gen one hour in morn and one hour in evening, to give it a boost.

My husband just tested the specific gravity this morn and it was 1.30. 13.4v after sitting for two weeks. Solar on, chassis power off. More later.
Thnx everyone for your help.

Will do some more tests tonight now that we have it home. Hoping they hold the power normally.
I think after checking it, we might get two more batteries and a portable panel to stock up some more power.

Blackhat6mike · 04-29-2015, 04:25 PM

Renogy Solar has their stuff on Amazon.com and their equipment is first class. If you are going solar, don't make the mistake of buying too small of a controller that you can't add more panels to later, as you probably will once you see how well it works. Also, only get a MPPT controller and NOT a PWM controller. The difference is night and day. Sure they cost more, but you get what you pay for with the MPPT unit.
If you just want to keep your batteries topped off, one 100w panel will be fine. Three or more 100w panels and you can leave your gen at home except for AC or microwave. I have 6 x 100w panels and 5,000w inverter that will run my AC for several hours or microwave when ever. Boondocking is no big deal anymore or parking lot overnights while traveling. 115 vac when ever I want it.