100 Watts Solar with Deep Cell 31s or Trojan 6 Volts

[Mike3]

I'm looking at a new truck camper that comes with 100 watts solar panel and control. I use minimal lights, water pump, etc when dry camping solo. Is that sufficient to maintain two batteries while dry camping?

I've had The same Trojan 105 golf cart batteries in my Fiver for 9 years and they are still in good shape. So I'm leaning towards them instead of traditional deep cycle. I know 6 volts have more amp hours but do they charge as quickly?

Thanks

[Almot]

BFL13 wrote:

So with a low charging rate like solar does, your "window" to be in Absorption is quite narrow between 90 something when you get to Vabs and 97% when you trigger Float.

However some controllers have no Float to trigger, so they just stay at Vabs until dark once they reach Vabs. Others have a timed Absorption Stage like two hours so they could go past 97% before dropping to Float. Others have adjustable Float and Absorption voltages. If you want a longer Absorption stage, you can make your Float voltage the same as your Vabs, so it will stay at your Vabs until dark.

BFL - it's a good explanation, thanks. I had a feeling that somehow my system was responsible for what I see, now I know why. Hopefully OP will get a decent controller that allows some tweaking of setpoints, to reach "true 99.999% SOC".

[BFL13]

Almot wrote:
I meant - to get to Bulk/Absorption transition, or Absoprtion voltage, whatever.

Yes, it's better if it not just gets to Abs point, but also completes the prescribed stay at this voltage, timer-based or current-based. In my system it goes to Float very soon after it has reached Abs voltage, timer is seldom triggered, so to me "getting to Abs" and "getting to Float" is almost the same. OP will probably get some PWM, so it will be a little different.

Generally, the State of Charge (SOC) of the battery when you get it to Vabs depends on the charging rate and that voltage. For a fixed voltage, and the same battery size, say 14.4v, the higher the charging current during Bulk, the sooner you will get the battery to that voltage and at a lower SOC.

Lower charging current to get to the same Vabs means you spend more time in Bulk and get to a higher SOC before reaching Vabs. ( That will be slower and longer generator time than if you used a higher charging rate--your tapering amps in Absorption will still be more amps than the lower charging rate amps for a time there, so you are still faster until amps are the same at some SOC up there nearer the end)

So on solar you have low amps and usually a decent sized battery bank, so you will not get to 14.x until your SOC is quite high, probably in the 90s percentage. Meanwhile, your Absorption Stage will usually end at about 97% SOC regardless, and go to Float.

So with a low charging rate like solar does, your "window" to be in Absorption is quite narrow between 90 something when you get to Vabs and 97% when you trigger Float.

However some controllers have no Float to trigger, so they just stay at Vabs until dark once they reach Vabs. Others have a timed Absorption Stage like two hours so they could go past 97% before dropping to Float. Others have adjustable Float and Absorption voltages. If you want a longer Absorption stage, you can make your
Float voltage the same as your Vabs, so it will stay at your Vabs until dark.

[Almot]

I meant - to get to Bulk/Absorption transition, or Absoprtion voltage, whatever.

Yes, it's better if it not just gets to Abs point, but also completes the prescribed stay at this voltage, timer-based or current-based. In my system it goes to Float very soon after it has reached Abs voltage, timer is seldom triggered, so to me "getting to Abs" and "getting to Float" is almost the same. OP will probably get some PWM, so it will be a little different.

[EsoxLucius]

Almot wrote:

So, we may sleep safely with our solar panels, and not worry about current being below "recommended minimum". As long as it gets to Bulk/Absorption every day or most of the days.

Do you mean get to Float? A system will be in Bulk charge mode as soon is there is enough current available from the panels, even when cloudy.

[Almot]

landyacht318 wrote:
Trojan's PDF lists a 10 to 13% bulk rate, but does not say this is a recommended minimum.

Found it: Page 13, diagram 4.

And I "think" that this is a recommended optimal charging current. Not a minimum current, and not a maximum either.

Which makes sense, because the next diagram #5 for Trojan AGM (didn't know Trojan had any AGM), shows 20%C bulk rate, also without explanations, and this surely can't be a minimum current. Other AGM brands have maximum charging current 30-35%C, and none have a minimum current except for Lifeline Concord.

So, we may sleep safely with our solar panels, and not worry about current being below "recommended minimum". As long as it gets to Bulk/Absorption every day or most of the days.

[Almot]

Mike@Asheville wrote:
... there are a number of quality providers. The manufacture's price was around $800 for a single 100 watt panel and controller. Locally, I can have 300 watts, a much better controller and installation for about 1K from a very reputable provider.

So, thanks for suggesting I learn more and go bigger!

Bigger? yes and no. Go bigger in solar watts. Don't go bigger in consumed watts or amp-hours if you want to live mostly generator-free.

Yeah, you can run microwave when there is plenty of sun and batteries are full by noon. This would require a substantial inverter and proper wiring, I doubt that your 1K quote included this. And when it gets cloudy and stays dark for 2-3 days, you'll have to run a propane stove, so might as well make a habit of it.

Quality installers? This trade is not regulated. People that know just a little more than average retired snowbird (which isn't much), would call themselves solar installers, and if location is right, they would have enough orders and therefore "reputation". Because customers can't comprehend what and how is being done. There was an example few months ago with installer in Quartzite AZ, whose installation was downright dangerous, both electrically and mechanically - a disaster waiting to happen. Still, the guy had customers lined up, and was charging good money.

It's like with diner or coffee-shop - when location is right, the joint is full, no matter how terrible is coffee. Not to say that there are no good coffee shops.

"Much better controller"? Controller for 300w system may cost $15. A "better controller" may cost $40 or $140, or even $200 with display and other options. Both $40 and $200 could be of good brands, and both would work. But the difference between $40 and $200 will be tremendous. Needless to explain which one of 2 the installer would buy, being on a fixed $1K budget 🙂

One thing you got right: RV manufacturers are not competitive (to put it mildly), when it comes to solar installs.

[Mike3]

Thanks for all the great info folks. I learned a lot from your posts. I decided to have the solar done locally; being in Asheville there are a number of quality providers. The manufacture's price was around $800 for a single 100 watt panel and controller. Locally, I can have 300 watts, a much better controller and installation for about 1K from a very reputable provider.

So, thanks for suggesting I learn more and go bigger!

[wintersun]

Lance sells their campers with a 95 Watt solar panel and this is good enough. I have two 100 Watt panels on my camper and it is overkill.
Unless you are in Alaska during the winter months you will have more than enough sunlight to recharge the battery. Solar cells have been designed for decades to work with much less than a 90 degree angle to the sun and still put out power.

A 100 AH battery is not going to be discharged more than 50% so 5 amps over 10 hours is the most you will need from the panel. I have never been able to use anything close to 50 AH overnight and that is in 100 degree and 24 degree weather and the use of the lights, the fridge, the furnace fan, water pump, and a 17" LCD TV.

We stay at a spot for 2-3 days and then travel to the next location. While driving the truck alternator is recharging the battery as well as the solar panels. The solar panels are starting to recharge the battey long before we hit the road and they continue to charge after we have stopped at our new location.

What none of the camper or other RV manufacturers provide is a good digital charge metering device like the ones from Trimetric. Spend the $200 to add one to the camper and then you can monitor usage and charge level accurately. Without this information you are guessing as to what is going out and back in and how effective the charging setups are for your pattern of use with your camper.

Lots of opinions but I have actually installed a digital meter and a solar panel charging system and have been using it for the past two years.

I put about the same amount of money into the solar setup as I would have put into adding a generator. Difference is that the solar is charging my batteries and keeping them at 100% every day of the year and I need do nothing. It is 100% automatic with nothing to start or refuel or shut off and nothing to get stolen or have breakdown on a trip, and no gas cans to carry around. It is also dead silent and the idea of traveling hundreds of miles to a pristine area and listening to the noise of a generator is not something that I find rational in the least.

[BFL13]

Almot wrote,"To 3 tons - yes, absolutely. 300W array can support you without a generator. You only need to be reasonable and avoid high-current devices. Doable. "

You can use high current but the key is how long you do it. You don't need to be one of those self-denial is a virtue people. Enjoy your RV!

20 minutes of microwave, kettle, and toaster in a day is about 35AH. A 130w panel lying flat can do 56AH in May at 49N. So 300w is huge.

Besides that, in the afternoon, once the batts are near charged you can use your "free" solar to run lots of things. Eg, when it is hot in the afternoon I run the monster 120v ceiling fan our trailer has (Komfort must have got them off the noses of old P-51 fighters) from the inverter at no discharge of the battery at all. Also get some laptop time in, anything you want.

So in summer now we get essentially all the kettle, toaster, and microwave time we want, plus other goodies and use under 50AH /day that the battery ever sees. That's with one 230w panel. You do need a generator ready to go if it gets overcast for a couple days though.

Catching up on just solar once you get behind in some bad weather is not so good an idea. The surplus once the sun comes back would let you catch up eventually, but by then you will have gone several days without a full recharge, so now you get sulfation setting in and have to do an equalize session.

Instead I run the gen to catch up and then go right back to hitting full daily on solar. That way seldom need to equalize in summer.

[EsoxLucius]

I would add a panel or two no matter how you think you will use those batteries.

[Almot]

landyacht318 wrote:
...just because the charge controller indicates a full charge, does not mean the batteries are 100%.

If the goal is to get the solar controler to indicate a full charge, I could get there a half hour after sunrise every day, and replace batteries several times each year.

Yes, when LED indicator on controller says "full", it doesn't always tell the truth. But it - usually - tells something close to the truth. Normally, it tells that battery has hit the Bulk/Absorption setpoint and/or is now in Float mode.

Yes, Abs setpoint needs to be where battery specs require, which usually means - it needs to be adjustable. And Float setpoint needs to be adjustable too, because after some observations you might decide that for better charging you want Float different from what specs say.

Now, about controllers indicating full charge half hour after sunset :)... Maybe those were wrong controllers. Cheaper controllers keep it at Abs voltage for 60 minutes (usually), and then go to Float. Until controller indicates Float, it's not "full". Even if it doesn't show Float and only shows the beginning of Abs, getting batts to Abs half hour after sunrise would be no small feat. Only if you didn't use the battery at all after previous day charging, i.e. it was already 99% full by sunrise, then it could go into Abs shortly after sunrise. I saw this on my MPPT after had been floating new batts for a few days without loads - it went into Abs very early.

To 3 tons - yes, absolutely. 300W array can support you without a generator. You only need to be reasonable and avoid high-current devices. Doable.

[landyacht318]

Good points Almot. I am not aware of the lighting characteristics of cheap controllers. Mine (BS 2512i)is solid for bulk, slow blink absorb, fast blink float.
My wording should have been... just because the charge controller indicates a full charge, does not mean the batteries are 100%.

If the goal is to get the solar controler to indicate a full charge, I could get there a half hour after sunrise every day, and replace batteries several times each year. I could brag about the 1/2 hour and not mention the necessary replacement, and do a serious disservice to anybody less than informed and reading about such results. An Extreme example for illustrative purposes, but one must be wary of all internet claims.

Cheap controllers might not allow absorption voltage adjustments. If said controller only allows 14.4v on a battery that needs 14.8v, the full charge indicator means very little, and the observer should be made aware of this, rather than place blind trust in any given and perhaps very well marketed product, and claim excellent performance, when all they can realistically claim is they experienced no failures, yet, and the system Seems, to be perfect.


Trojan's PDF lists a 10 to 13% bulk rate, but does not say this is a recommended minimum. Besides, Solar ramps up slowly and does not conform to any of the usual charging profiles which apparently assume a flick of the switch charging source delivers instant bulk amps to a battery resting somewhere below 80% SOC.

Regarding my own apparently Acid starved Screwy 31, well I wont be replacing it, when necessary, with another 31. However my previous house bank, 2 27's which were cycled shallower hardly gave me an excellent lifespan either. Their location made hydrometer dipping a serious inconvenience, and I remained ignorant of how my Solar was actually doing replenishing them daily. I trusted my soothing blinking green light on my charge controller way more than I should have, and want to make others aware that they can be making this same mistake.

If I get a year of daily cycles from this 31, I'll have a better return on investment than I did with 2 different sets of 2-27's.
I believe, in my situation/usage that higher wattage to capacity ratios, and having figured out the voltage setpoints and durations on this screwy 31, will yield better return on investment.
But I can't say for sure until December. Lately I've been taking the poor thing to 40% or below nightly, making it work for me, and I have not been having enough Solar wattage or time to see much of my blinking green light, not that I believe it anyway.

I do believe that higher solar wattage to capacity ratios will always make the batteries happier for longer, but the person who sizes a system to replace only the capacity removed, +10%, and only cycles them for a week or 2, and then goes home and plugs in, will likely never notice the difference another hundred + watts will make.

Perhaps the timespan of the outing requiring daily replacement of overnight usage should be factored into recommendations. Each battery user is going to use/cycle their batteries differently and this difference requires different recommendations. There are few absolutes in life, yet many make well worded statements in absolute terms which can easily do a disservice to the Novice who takes them as gospel, and perhaps worse, repeats them as gospel, convincing others to follow the same path.

To the OP, in your case I'd go with GC batteries over the 31, and if 100 watts of solar is all you have to recharge during your outing, then look it is as negating some of your usage, but that when you get back home, you should have a good method of insuring you can return those batteries back to maximum Specific gravity before storing them.

[3_tons]

The information in these responses will all be helpful, but I'll add my own 0.02 cents...

I have two 6v GC's and started out with 200w which mostly worked out well, but found that in inclement weather, shorter days, and higher latitudes even another 100w was of great assist (300w total)...My system has now grown to 440w, whatever system you choose be sure and size it for future growth...As far as genny goes (Honda 2000), I really never need it except for very occasional Air Cond use...BTW, Retrofitting to a far more efficient two speed furnace saves regularly about 6 amps.

Best Regards,

3 tons

[MEXICOWANDERER]

BLINKING LIGHT IN MEXICO = Floorboard it and pray

God only knows what it means in China.