Basic battery charging and solar question

:R

If you don't understand how proper quoting works, your problem, not mine.

mike-s wrote:

Almot wrote:

And a lot of misquoted lines too :)...

For future reference, a quote is what's inside the quotation marks. I started with your comment because it was simply wrong, then expanded because other were, too.

You used my quote and added what wasn't there, i.e. 50W and no controller, - all in the same line. And went on commenting and interpreting from there.

As to what exactly was "wrong", i.e. why 15W panel is capable of much more than maintaining 2*6V flooded bank in storage - I'm lost here. If you read the linked article again, it doesn't really tell whether 225 AH wet bank would need max 6W or 12W array to float (if used on a sunny day without controller).

Half the article is talking about some other articles written by big box stores that most people here on Tech forum rarely read anyway, as they don't consider it a valuable source of info. This is why it is messy.

webrx wrote:
if you have 300 ma parasitic draw you need to replace 7.2 amps a day (.3 x 24)

Amp-hours, not amps. 300 mA would seem to be an unrealistically large parasitic draw. What device(s) do you have which add up to that much?

webrx wrote:
if you get 6 hours of good sunlight to charge you battery with, you theoretically (panel efficiency comes in here) need 1.2 amps charging an hour.
a 15 watt panel will put out 1.25 amps (15 / 2) again - theoretically

??? Not sure how you make 15/2=1.25, or where any of those numbers come from. A 15 W "12 volt" panel would typically put out something less than 1 A at charging voltage (say, 13 V).

webrx wrote:
Reality, is a 40 to 50 watt is in my opinion the bare minimum you need to make up for parasitic loads and running the water pump for a couple showers, etc.

Ah, you're talking about constant usage loads (like a refrigerator, or the switch which lights red when the water pump is turned on), not parasitic loads. That's completely different.

Almot wrote:

And a lot of misquoted lines too :)...

For future reference, a quote is what's inside the quotation marks. I started with your comment because it was simply wrong, then expanded because other were, too.

Almot wrote:
As to the parasitic draws, half the time people include the fridge draw in this - though I don't think this is correct.

It's not. If it can be turned off and draw no current (as one might do during storage), it's not a parasitic load. A parasitic load is caused by a device which draws power even when off (like a car radio using power to keep station memory), or a device which simply can't be turned off (like a LPCO detector).

Almot wrote:
PS: The linked article is a bit messy. He was charging 2 different banks, 220 AH and 125 AH, with a nominal 12V/12W panel, and measured overcharging on 220 AH AGM. This battery is AGM, very low self-discharge.

Messy? it's quite simple - he saw both banks go above 15V when using an unregulated 12W panel. He then goes on to show just how little current is needed to maintain the charge on a battery, e.g. 0.2 A (~3 W) to maintain a 400 Ah flooded lead acid bank.

if you have 300 ma parasitic draw you need to replace 7.2 amps a day (.3 x 24)
if you get 6 hours of good sunlight to charge you battery with, you theoretically (panel efficiency comes in here) need 1.2 amps charging an hour.
a 15 watt panel will put out 1.25 amps (15 / 2) again - theoretically

Reality, is a 40 to 50 watt is in my opinion the bare minimum you need to make up for parasitic loads and running the water pump for a couple showers, etc. A 40w will (depending on sun conditions) top off your battery if you don't waste a lot of power and use less than say 20 amps a day. At a minimum it will allow you to replace some of what you use each day.

100 watts / 12v = 8.3 amps an hour theoretically (multiple by .6 to get closer to actual which will be around 5 amps) 5 amps x 6 hours will get your 30 amps to charge your battery with. (you will get more than this as you will have a couple less than perfect sun hours on either side of your 6 hours but this is conservative so a good value to use)

to sum up, if you are going to buy portable solar, I would recommend that you go a minimum of 100 watts, and if you are a heavier user of 12v or are in cloudy conditions or surrounded by trees, etc, then you will need more.

Again, this is what my experience has shown, I am not a solar expert, nor electrical engineer, and I dont play one on TV - so YMMV.

Have just re-read the article again. Or - tried to. Maybe somebody with better detective skills will decipher it better than me :)

160 AH bank in an excellent shape needs 0.02-0.08A in Float (not measured in these experiments, but he says it does, so let it be). Take a middle, 0.05A*24H/5.5 hours of sun = 0.22A panel. This is for 160 AH.

For 2 GC, 225 AH total, it would be 0.31A panel or 5.6W. This is - in excellent shape. If less than excellent? 8W,10W - who knows...

Another pointer from the article: keep controller-less current under 0.3% C. For 2 GC, 225 AH, this is 0.68A or 12W panel. A bit different from previous 5.6W, isn't it? Did he mean 3% for panel in good or bad shape? Who knows...

The gist of the story - the only that I could deduct from all this - know your batteries. If it needs 1A panel to float them, then it needs 1A.

mike-s wrote:
A 12 W panel can ruin even a sizable battery bank by overcharging if used without a controller, so ignore those who claim 15 (or 50!) watts "is barely enough to provide the charge that your 2*6V lose in 24 hours due to" self-discharge/parasitic draw.

There's a lot of misinformation out there

And a lot of misquoted lines too :)...

It was said that "15W is barely enough to provide the charge that your 2*6V lose in 24 hours due to self-discharge". Not 50W. Neither did I suggest using 15W without a controller.

As to the parasitic draws, half the time people include the fridge draw in this - though I don't think this is correct.

PS: The linked article is a bit messy. He was charging 2 different banks, 220 AH and 125 AH, with a nominal 12V/12W panel, and measured overcharging on 220 AH AGM. This battery is AGM, very low self-discharge.

Parasitic draws are minimal, at least as actually measured in my rig. That would be the LPCO detector, which draws about 50 mA, and nothing else. A 10 W panel is much, much more than enough to take care of that in storage. I wouldn't use more than a 2-3 W panel without a controller. A 12 W panel can ruin even a sizable battery bank by overcharging if used without a controller, so ignore those who claim 15 (or 50!) watts "is barely enough to provide the charge that your 2*6V lose in 24 hours due to" self-discharge/parasitic draw.

There's a lot of misinformation out there, most based on someone reading something somewhere on the Internet, and not fully understanding it. Place more trust in those who've actually _measured_ and _tested_ and provide documentation for what they're claiming.

I have a Battery Tender 15 wt Solar Panel and I can tell you that it will not really charge your batteries. It is a TENDER. That is what I use it for and it keeps GOOD batteries that are FULLY CHAGED and that have little or no parasitic drain topped off, NO MORE. That is what it should do and what it was designed to do.

I'm going for a bit more than that for the roof.