Expanding my system

[ucl1966]

Hi
i'm expanding my shed system and looking for some advice with fitting extra panels.
At the moment I use 2 x 20 watt panels with a charge controller feeding 3 x 100ah gel filled batteries, I only use them to run some led lamps and some rechargeable power tools, but have just got 2 x 50 watt panels, the question is
1) If I use a second charge controller can I just add the panels to the system via the same connection on the batteries as the first.
Any real info would be helpful

Tony

[Shockah]

Hi
i'm expanding my shed system and looking for some advice with fitting extra panels.
At the moment I use 2 x 20 watt panels with a charge controller feeding 3 x 100ah gel filled batteries, I only use them to run some led lamps and some rechargeable power tools, but have just got 2 x 50 watt panels, the question is
1) If I use a second charge controller can I just add the panels to the system via the same connection on the batteries as the first.
Any real info would be helpful

Tony

Yes.
Both charge-controllers can connect directly to the battery.

Just to clarify, you are not "adding the panels to the system" ... you are building a 2nd system and adding it to the battery pack.

Gel?! In Parallel?! ... research the best way to charge Gel.

[ucl1966]

Hi
Thanks for the helpful info. As for the gel batteries I mean "deep cycle gel filled batteries" I use a charge controller that has a setting for that type of batteries,
but to ask another question,
2) I know I need to use another charge controller but dose it have to be the same make as the first one
3) Is it ok as long as both are pwm or both are mppt or can I mix them

Thanks
Tony

[PNjunction]

Don't feel bad - this is a common beginner mistake of applying the "too small a panel to too large of a battery" syndrome. Most of us have been there.

The bad news is that you are using gel in the first place (C/20 max charge current). They are the slowest to charge properly, and hence nobody recommends them for solar. Not to mention it is very easy to damage them. Few controllers get this right, UNLESS you specifically verify that the "setting" is truly at 14.0 to 14.1v MAX. If it only says "sealed" and you do not verify the voltage, you may actually be at AGM charging voltages, which damages gel. The poorest quality ones will say "gel", and not really mean it. You MUST verify the voltage.

Right now, you are running a "deficit-charge" scenario, where you just plainly don't have enough current to recharge them properly. This was popular in the 70's, where one just added capacity to make up for lack of solar-insolation hours, and ran the batteries into the ground. Costly.

One might say that if you are only running powertools and led lighting, that with your 300ah of capacity, you'll come out fine. Not so. You are micro-cycling them, and unless you reach a minimum of 5-10% DOD, the naturally occuring sulfate clumps, leading to hotspots later when you do put a real load on them.

First thing - use only ONE of your existing batteries. Verify the actual voltage of the controller, and not the silk-screen title.

The good news is that these will degrade under your conditions fast enough, that you'll want to use an AGM, much smaller in capacity than you have now. In winter, you only have maybe 2 hours of solar-insolation, so if you are only running powertools briefly and some led lighting, then I'd suggest starting with 35ah agm.

[ucl1966]

Hi
Thanks for that but you didn't answer the question at all, first and only thing is I need to know if and how to use the panels and batteries I have. I am not a high flying cash cow that can just discard what I have for some new top rated bit of bling that works out costing me more, I have used them for the last 6-8 months and managed to use them no problem, the batterie full light even comes on now and then so I think I,m doing ok but as the summer comes to an end I want to keep this going so please I need help with the panels and batteries I have. (only want answers that will help not advice on replacing my system)
Thanks

[inetdog]

You can add more panels and connect them to a second charge controller. But if you are not careful the result will be too high a charging current when the batteries are drained far enough that they are in the Bulk stage of the charging profile.
Your 3X100AH batteries IF they are still delivering full capacity, make up a 300AH bank at 12 volts. The highest recommended current, maximum, to avoid damaging GEL batteries will be 15A. If the batteries have lost capacity (say to 150AH) then the maximum charge current will also be reduced, to 7.5A. The voltage based charge indicator is just going to tell you that the batteries are as charged as they are going to get, not how much total capacity they are currently good for. Only a controlled discharge test can tell you that.

The good news: your 40W of panel is only going to give you at most 3A in good conditions. So you could add up to another 200W of panels on a second controller if that controller is also really set up properly for GEL. The alternative would be to just replace the existing controller, get 250 W of panel and retire the original panel and charger or use it for a separate system somewhere.

Can you tell use the manufacturer and model number of the batteries, since there is at least one manufacturer that claims to tolerate a much higher charge rate on their special design GEL models?

[mapmaker]

You are micro-cycling them, and unless you reach a minimum of 5-10% DOD, the naturally occuring sulfate clumps, leading to hotspots later when you do put a real load on them.

You are certainly correct that repeated very shallow discharges are not good for the battery. Lead dioxide clumps will form on the positive plates under those conditions.

--mapmaker

[ucl1966]

Hi
Great help INETDOG that info help me so so much will post all the info from my setup with a pic or two as well in the next day or so. Keep in mind it's only a shed setup, but my shed . Will give the batteries a good look over as well to see of anything look out of place but don't think what Mapmaker & NPjunction are telling me will be something I would be able to see from the outside of the batteries as they are sealed. Is there a way to check for this? And as for the charge controllers any info about needing to use the same type would be of great help too.
Thanks again.

[inetdog]

Hi
Great help INETDOG that info help me so so much will post all the info from my setup with a pic or two as well in the next day or so. Keep in mind it's only a shed setup, but my shed . Will give the batteries a good look over as well to see of anything look out of place but don't think what Mapmaker & NPjunction are telling me will be something I would be able to see from the outside of the batteries as they are sealed. Is there a way to check for this? And as for the charge controllers any info about needing to use the same type would be of great help too.
Thanks again.

As long as both CCs can be set to voltages which are compatible with your batteries and together they cannot produce too much current there is no need for them to communicate with each other or be the same type.
Just about the only test you can perform on the batteries (one at a time, removing it from the rest of the system) would be to do an informal capacity test. To do this you would have to have a known load (12V light bulbs, including auto headlamps would work) that you can use to draw a current of roughly 5A and record how long it takes to get the voltage down to ~11 volts. Then recharge the battery immediately. If the batteries are still 100AH, that should take close to 20 hours. If it takes a substantially shorter time, then you have managed to damage the batteries and you can get a rough approximation of the capacity left by multiplying the current times the time of discharge to reach the low voltage cutoff.