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

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.

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.

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

BLINKING LIGHT IN MEXICO = Floorboard it and pray

God only knows what it means in China.

landyacht318 wrote:
If only the charge controllers blinking green light did indicate a full charge.

Guess it does not really matter much if you get to go home and plug in.

100 watts on a pair of t105s cycled more than 20% every night is not going to work well after 2 weeks.

Negating overnight usage and proper full recharge are not the same thing

Landyyacht, I have some doubts.

1) Blinking light on cheap controllers is usually a bulk stage, and steady light is full or float :), but I guess they in China can make it the other way around too.

2) It's not clear how bulk at 30-50A on 110V charger at home is better than bulk at 10-15A on solar. My batteries don't have any "minimum" charging current, only "maximum". Do Trojan 6V have a recommended minimum current?

3) 20% depth of discharge (80% remaining charge) would be a VERY good cycle for any battery. Most users cycle them down to 60-50% (remaining charge) every night.

4) Yes, full recharge has not only to be full, but also at proper Absorption and Float voltages. Cheap controllers don't have means to adjust these voltages, so getting a better controller makes sense. But panel wattage has no bearing on this, as long as it's sufficient to get the battery bank to 14.4V or whatever is recommended Bulk/Absorption voltage.

Physically impractical to try and manufacture cyclable group 31 batteries with more than 110 ampere hours capacity. Plates jammed to the max in each cell.

90 would be better for cyclable usage. We are talking about a heavy battery.

The acid to active plate area ratio is all wrong for higher ampere hours.

Why do you think truly cyclable batteries contain all that electrolyte? It isn't because it offers a better chance of not running the acid level to expose the plates.

When my contractor was selling batteries, the same jar but lighter weight battery had half as many warranties. BTW we are talking about Trojan, and Ramcar. You couldn't give a T-125 away to golf courses even though they cost more. Yes, this was also for Trojans. Too many warranties. Other GC220's suffered the same fate.

Sorry about the bad news. I can't contribute smileys all the time :(

Since you said you have a generator, if you can, run the generator for an hour or so first thing in the morning. The bulk charge it will allow your convertor to put into your batteries quite a bit of watts. Then, let the solar "top off" the batteries the rest of the day.

If only the charge controllers blinking green light did indicate a full charge.

Guess it does not really matter much if you get to go home and plug in.

100 watts on a pair of t105s cycled more than 20% every night is not going to work well after 2 weeks.

Negating overnight usage and proper full recharge are not the same thing

I put 120 w on my previous 5 er with 2 - 6 v equal to T 105 s and it did good. We used minimal lights but I use a bipap every night and the batteries fully charged every day. Craig

Thanks for the great info folks.