......please help me with my confusion

[j.steele]

Kia ora and greetings from New Zealand. New to the forum, so please let me know if I am in the right place(or not!). I am just getting into the solar vibe and although enjoying the learning process immensely, there are a few things I'm currently struggling to get my head around with my new system and am looking for some advice please.

System Specs. 4x 260 watt 24v panels wired in series. Max150v in, 40Amp out Tracer MPPT controller, 4 x 12v 150 ah wired series parallel ( 24v 300Ah), 2000 watt nomad inverter. It will be powering a cabin with LED lights, a small fridge (on timer) and a 24v dc water pump with 8 litre pressure tank.

I went live with the system today for the first time. I am needing to "exercise" the batteries before they go live as they have been sitting unused for 12 months and am waiting on a pulse charger so I can do this. So today, I just messed around trying each of the batteries set up as single 12v's just to get a feel for things. ( the batteries are approx 3 years old and were bought by the previous owner who used them to power a light bulb and radio, so I would guess they have had a very easy life). There was no load on the system whilst I was doing this today.

My confusion stems from two things:
1. When I put the battery on initially it showed a SOC of 77% 12.7V. Switched on the array and the battery was "boost charged" (14.7v) up to 90% withn 10 minutes. At this point the SOC slowed down and setled on 90%. I turned off the panels to swap to another of the batteries and noticed as the voltage dropped, the SOC increased, eventually reaching 100% . But, within a minute or so the SOC started to drop approx 1% with every 2 or so minutes passing. When I left it it had dropped to 87% SOC . Why did it reach 100% SOC only when I disconnected the array and why the subsequent slow drop in SOC. Does this indicate that the batteries have been damaged by not being used and not maintained at 100%.

2. According to the display on the MT50, the panels were producing 130(ish) volts, but only 0.1a and around 10 watts! I would have thought this would have been up around 6-8amp going to the CC ( based on the specs of 1x24v 260w panel). What woud account for such a low AMP reading. In saying this though it seemed to be charging the batteries OK.

Sorry for the long winded explanation. Hope it makes sense and look forward to your help in me getting my head around it. Cheers

[Bala]

At 3 years old and having sat unused for 12 months it is most likely that those batteries are no good.

Basically for the system to work properly the batteries need to be good.

Before you rush out and buy new batteries decide what you want to achieve with the system so you get it set up the best long term.

[j.steele]

Thanks Bala. Ummm.. my better half is of the opinion that the batteries are actually 5 or 6 years old..... they measured at 12.7v when I multimetred them. Would this indicate they were still ok?

What about my second confusion? Any ideas? Cheers.

[Bala]

Im not totally clear on your questions,

I think SOC readings on controllers are based on a battery being fully charged then calculating how much has gone out, but I am guessing there quite a bit.

You need a hydrometer to get a real idea of what is going on with SOC.

As for amps from the panels, they will only deliver what the charger settings and battery demand.

I have had batteries that read good volts but have no capacity and will not take amps, they appear charged but are no good.

Batteries will die from not being used, if not kept on charge.

Your best option is to charge them as best you can and use a hydrometer to check them.

Again its not likely that will be any good, nut charge them and test them and see what happens.

[j.steele]

Thanks Bala... I am getting the batteries load tested tomorrow.... but I suspect you might be right - toast!!! The current batteries are gel, and I simply cannot afford to replace with more gels, so I will likely go with flooded. In order to build a 24v bank, am I correct in thinking I am better off going with 6v (x4) in series over 12v in series.(x2) to give me more available Watts?

As for my confusion over the current coming off the panels, I now get it that the CC display is showing me how much is being transferred to the batteries rather than what is being produced by the array- when i put a load across the battery the reading jumped from 0.1A to 0.9A.

Thanks for taking the time..Cheers.

[Bala]

Thanks Bala... I am getting the batteries load tested tomorrow.... but I suspect you might be right - toast!!! The current batteries are gel, and I simply cannot afford to replace with more gels, so I will likely go with flooded. In order to build a 24v bank, am I correct in thinking I am better off going with 6v (x4) in series over 12v in series.(x2) to give me more available Watts?

As for my confusion over the current coming off the panels, I now get it that the CC display is showing me how much is being transferred to the batteries rather than what is being produced by the array- when i put a load across the battery the reading jumped from 0.1A to 0.9A.

Thanks for taking the time..Cheers.

You need to stay in series rather than any parallel configuration.

perhaps someone else can chime in with what size batteries/configuration best fit your current system items.

When you get them tested see what options for new you have and come back to see if you can get some guidance on the best option, before you buy.

[SunEagle]

Thanks Bala... I am getting the batteries load tested tomorrow.... but I suspect you might be right - toast!!! The current batteries are gel, and I simply cannot afford to replace with more gels, so I will likely go with flooded. In order to build a 24v bank, am I correct in thinking I am better off going with 6v (x4) in series over 12v in series.(x2) to give me more available Watts?

As for my confusion over the current coming off the panels, I now get it that the CC display is showing me how much is being transferred to the batteries rather than what is being produced by the array- when i put a load across the battery the reading jumped from 0.1A to 0.9A.

Thanks for taking the time..Cheers.

Depending on how many watt hours you want your battery system to be it will be better to go with more lower voltage (2V, 4V, 6V) type with higher AH rating then the 12V batteries. When you use a higher voltage the battery starts to get real heavy as you increase it's AH rating.

With that 40 amp charger your battery system should be between 320 and 500Ah. So look for some 4V 480Ah batteries and get 6 of them for your 24volt system.

[Mike90250]

Thanks Bala... I am getting the batteries load tested tomorrow.... but I suspect you might be right - toast!!! The current batteries are gel, and I simply cannot afford to replace with more gels, so I will likely go with flooded.

GEL batteries are NOT good for solar at all. AGM batteries are OK, but cost 2x as much as flooded, and last half as long.

In order to build a 24v bank, am I correct in thinking I am better off going with 6v (x4) in series over 12v in series.(x2) to give me more available Watts?

Correct, 4 ea, 6V batteries (like a golf cart battery 6v, 200ah) wired in series, make a great set of learning batteries

As for my confusion over the current coming off the panels, I now get it that the CC display is showing me how much is being transferred to the batteries rather than what is being produced by the array- when i put a load across the battery the reading jumped from 0.1A to 0.9A.

Thanks for taking the time..Cheers.

[Sunking]

System Specs. 4x 260 watt 24v panels wired in series. Max150v in, 40Amp out Tracer MPPT controller,

Asside from your batteries being shot to hell, I don't think anyone caught this part. What is the Voc of those panels? (Bet you it is above 30 Voc) You are applying too much voltage to the controller. So far you are getting away with it, but one cool morning you risk letting the smoke out of your controller.

Rewire those panels in 2 x 2.

[j.steele]

Thanks for the replies....... I wasn't aware that Gels were not considered good for PV. Why is this?

I am looking at Crown 4x 6v 430aH batteries. Although a little overkill for what I am running, I am keen to future proof my setup now whilst I have available $$. Also, given the cabin will be open to paying guests, I want to make sure the sytem gives me several days of autonomy,

Asside from your batteries being shot to hell, I don't think anyone caught this part. What is the Voc of those panels? (Bet you it is above 30 Voc) You are applying too much voltage to the controller. So far you are getting away with it, but one cool morning you risk letting the smoke out of your controller.

Rewire those panels in 2 x 2.

This is interesting as I had this very converstion with the fella that supplied the equipment. For the record the panels are Trina 260watt 24v, Voc 30.8, the specs on the CC rate a maximum input of 150v or 1040 Watts. So yes, the CC is definitely on the max of what it can handle with 4 panels in series. My supplier explained it to me that it is better to have a high voltage, low current setup, especially with MPPT. Hmmmm... you've got me wondering now whether I am better off with 2x2 which would yield 620 watts 16amps (correct??) Anyone else running a similar seup of 4 in series? How does th CC handle it? Thanks again.

[Mike90250]

Thanks for the replies....... I wasn't aware that Gels were not considered good for PV. Why is this? ......

Gel batteries are electrolyte & some additive to .... make it gel. AGM batteries have liquid and fiberglass mat and can flow as it heats. Gel electrolyte cannot "flow" and while fast charging, will get air bubbles and lose capacity.

[j.steele]

Gel batteries are electrolyte & some additive to .... make it gel. AGM batteries have liquid and fiberglass mat and can flow as it heats. Gel electrolyte cannot "flow" and while fast charging, will get air bubbles and lose capacity.

Ok. Thanks for the clarification.... Personally, weight alone is reason enough to stay away from them! Mine weigh 50kg each!

[Sunking]

Thanks for the replies....... I wasn't aware that Gels were not considered good for PV. Why is this?

I am looking at Crown 4x 6v 430aH batteries. Although a little overkill for what I am running, I am keen to future proof my setup now whilst I have available $$. Also, given the cabin will be open to paying guests, I want to make sure the sytem gives me several days of autonomy,





This is interesting as I had this very converstion with the fella that supplied the equipment. For the record the panels are Trina 260watt 24v, Voc 30.8, the specs on the CC rate a maximum input of 150v or 1040 Watts. So yes, the CC is definitely on the max of what it can handle with 4 panels in series. My supplier explained it to me that it is better to have a high voltage, low current setup, especially with MPPT. Hmmmm... you've got me wondering now whether I am better off with 2x2 which would yield 620 watts 16amps (correct??) Anyone else running a similar seup of 4 in series? How does th CC handle it? Thanks again.

You are good on Crown Batteries, top of the line. You are pushing the limit on panel Voc voltage you do not want to flirt with.

Your guy is right you do want to run as high of a voltage as you safely can to reduce current on the wiring between panels and controller. But 260 watt panels Voc running between 30 and 40 volts, and 4 in series is 120 to 160 volts in hot weather. Panel Voc goes up as temps drop. that low limit of 30 Voc in 25 Ce weather jumps to over 150 volts on a cold morning just as the sun hits you panels and lets the magic smoke out.

Eliminate that risk and run 2 x 2. You still get fairly high voltage efficiency, but no risk of damage. Either that or look at higher wattage panels to use 3 in series like 300 watt panels.

What you are looking for is a 25 C temp at 120 volts or less on a 150 Voc controller input. With 4 panels of that size you are exceeding 120 Voc when wired in series. One work around is to use something like a Midnite Classic 200 or 250 where Voc input is 200 or 250 plus battery voltage.

[j.steele]

You are good on Crown Batteries, top of the line. You are pushing the limit on panel Voc voltage you do not want to flirt with.

Your guy is right you do want to run as high of a voltage as you safely can to reduce current on the wiring between panels and controller. But 260 watt panels Voc running between 30 and 40 volts, and 4 in series is 120 to 160 volts in hot weather. Panel Voc goes up as temps drop. that low limit of 30 Voc in 25 Ce weather jumps to over 150 volts on a cold morning just as the sun hits you panels and lets the magic smoke out.

Eliminate that risk and run 2 x 2. You still get fairly high voltage efficiency, but no risk of damage. Either that or look at higher wattage panels to use 3 in series like 300 watt panels.

What you are looking for is a 25 C temp at 120 volts or less on a 150 Voc controller input. With 4 panels of that size you are exceeding 120 Voc when wired in series. One work around is to use something like a Midnite Classic 200 or 250 where Voc input is 200 or 250 plus battery voltage.

Thanks again... I see where you are coming from. I've just got off the phone with the supplier, and raised this concern with him. Hi reply was that allowing for inefficiencies, the panels will never put out the spec'd output.

I wasn't aware that colder panels put out more Voc, that's good to know. It is not an option for me to upsize panels or controller as everything is brand new and I am running out of $$. Ok,right now, I think I am leaning towards 2x2.

[mschulz]

Thanks again... I see where you are coming from. I've just got off the phone with the supplier, and raised this concern with him. Hi reply was that allowing for inefficiencies, the panels will never put out the spec'd output.

I wasn't aware that colder panels put out more Voc, that's good to know. It is not an option for me to upsize panels or controller as everything is brand new and I am running out of $$. Ok,right now, I think I am leaning towards 2x2.

I think you are smart to move to 2x2 and think of it as insurance. The last thing you want is to get a call from a paying guest telling you there is no power and your batteries got killed because your charge controller died on you with out your knowledge. Like SunKing said, you will still have plenty of Juice coming from those panels 2x2.