some help with expanding a 24V RV solar system

[shgoren]

Hi, everywone, I live in and RV with off-grid solar system as my power source, i built it myself and i think ive done some things wrong on the way as my batteries often drain and would like to fix it so it works better and more correct.

this is the specs:

- 2X310W 24v pv (chinese made)
- 3 trojan T875 8V 170ah lead-acid battery
- 30A epsolar tracer 3210A controller
- meanwell ts1500 inverter

the setup is so that the solar panels are wired in parallel to the cotroller, the controller feeds the batteries and the inverter is connected directly to the batteries.

1. i would like your opinion about the setup as i built it myself and i didnt take alot of advice on it.

2. now its winter where i live and with the current setup usually the batteries dont get charged fully and often im running out of power (im running a fridge constantly and the rest is small amount of power like light and chargers for phone or laptop)
so looking into possibly increasing my battery size too i bought another 4 panels like the ones i have (2 are 340W and 2 310W) which means i need to upgrade my controller too and i have a few questions about it:
1) i thought about buying this controller: https://www.ebay.com/itm/161615675225
here is review where he opens it up: https://www.youtube.com/watch?v=vsUVY0JbitY

2) i want to set the input so its 48v because the limit on the controller is 1600W for 24V, can that be a problem?
3) if it is a problem can i use 2 charge controllers together on the same set of batteries?
4) this one is more general: if i have 1000w of consumption and 1100w of power coming in is it going through the battery somehow or straight to the inverter?

i hope its not too many questions!
any help or good reading material will be appreciated as im a real newbie

thanks

[MichaelK!]

Your batteries are small for your application. If you multiply the amphours times the system voltage you get 170AH X 24V =4080 watthour maximum. Assuming you should never consume more than 50% of your battery capacity, that limit is ~ 2040watthours. Since a standard refrigerator uses somewhere in the range of 1000-1400 watthours per day, it's easy to see why the batteries are getting depleted. As a general rule of thumb, you shouldn't be consuming more than 15-20% of capacity, so you can make it through a cloudy day or two.

This could be remedied by switching to a larger battery, such as Trojan's L-16. Assuming it has a capacity of 370AH, you can wire four of them in series to get 24VDC. That would give you 4440 watthours of capacity. 370AH X 24V X 0.5capacity = 4440watthours. Limit your consumption to about 1400watthours per day and that will get you through two cloudy days of weather.

All you panels combined might be adequate for charging the L16s. Can you post the Voc, Vmp, Imp, Ioc for each panel type? With those numbers we can determine whether or not they can be wired together.

I would skip the budget chinese controller and buy a name brand like Midnight, Outback, or Morningstar. I'm not sure what you mean by "setting the input so it's 48V". Do you mean wiring the panels in series? You first need to be aware that your 24V panels are NOT putting out 24V. More likely the Vmp is ~37.5 to 38.0V. Wired in series, they would be putting out about ~75VDC, which is fine for a MPPT controller. Voltage will also go up in very cold weather, and your controller now can handle a max voltage of 100; if you're in Montana or Minnesota, it might have an overvoltage problem. In warms climes, not likely, but we need to know those Voc.

Yes, you can have more than one controller feeding into you batteries. As a general rule of thumb, there are losses every step of the way from your panels all the way to the AC plugs. Your total loss from heat might add up to 50% of the total. So, if you have 1000 watthours of consumption, that needs to be filled by about 2000 watthours of production.

Getting back to monitoring your system, do you have a voltmeter? You really can't manage a solar system without one. You can pick something off Ebay for 6-10$ that will do an adequate job. The other essential monitoring tool is a battery hydrometer. That's the single best way to determine your state of charge. Get one that has temperature compensation.

[shgoren]

thank you sooo much for your response
i think i will add an extra set of 3 8v trojan battries to get my capacity to 340ah.
about the "setting the input so it's 48V". you understood me correctly
i live in Israel so the voltage going up because of cold is not very likely.

im attaching the data sheet of both types of pvs with all the info
i just bought 2 of each kind because they didnt have 4 of 340W (the q-cells) and i thought of maximizing wattage but i can still exchange them so their 4 of the same kind

[QUOTE=MichaelK!;n367051. As a general rule of thumb, there are losses every step of the way from your panels all the way to the AC plugs. Your total loss from heat might add up to 50% of the total. So, if you have 1000 watthours of consumption, that needs to be filled by about 2000 watthours of production.[/QUOTE]
are you talking about 50% loss only in the case i use 2 charge controllers or in general?
and another question regarding this topic:
my options are:
A. buying another 30A controller identical to what i have now and combine them so each one is taking in 3 panels
B. buying a 60A controller and replacing the one i have, but then i need to connect them in pairs as i described in my post
do you have any opinion on which option is better for me?

i have a voltmeter, and ill get a a hydrometer even though i cant seem to find one on ebay with temperature compensation for less than 40$ including shipping whereas the cheaper ones are like 5-10$ including shipping, is it worth the difference?

do you think there is permanent damage to the batteries from being depleted to 22.5V (fully depleted)? if so, is there anything i can do to fix it or know the extent of the damage?

thanks again for you amazing help

[MichaelK!]

OK, now that were are numbers to work with, I can make some suggestions. First, most importantly, do NOT buy a second set of new 8V trojans. That is a sure way to get 6 ruined batteries! Your old batteries are most likely already seriously sulfunated because of the chronic lack of charging. Yes, they are damaged. You'll be able to tell easily if you use a hydrometer. If they are wired in parallel with new ones, the new ones will quickly deteriorate to the same charge level of the old batteries. Even if you had 6 brand new 8V batteries, slight resistance differiences between each string will result in different charging rates. You want to avoid parallel strings of batteries whenever you can. The simplest thing to do right now is get rid of the old damaged batteries and replace them with higher capacity L-16s (or something similar) in one single string.

It looks like the panels you have are close to each other. The 310s have a Vmp of 37.5 at 8.3amps while the 340s are 38.2Vmp at 9.4 amps. If you wired panels in series you'd get 3 pairs (2S3P) Set one and two of the 310s will produce 8.3amps at 75 VDC each, while set three will produce 9.4amps at 76.4 VDC. That's less than 2% difference in voltage. You can string each set into a combiner box containing DC breakers. If you physically position set three the furthest from the combiner box, the extra distance might eat a volt due to voltage drop. You can calculate this using a voltage drop calculator like this one. http://www.calculator.net/voltage-dr...wiresize=8.286 &voltage=76.4&phase=dc&noofconducto r=2 &distance=50&distanceunit=feet&ampe res =9&x=67&y=21. One plus and minus wire each comes out of the combiner to go to the charge controller (and a ground wire).

So, on paper, your three 2-panel strings will produce about ~25amps at ~75VDC. Expect no more than ~20 amps in the real world. The controller will transform this into ~65amps at 28.8VDC at the battery terminal. If you want to use all three sets, the power may on occasion excede what L16s should be charged at. In the real world though, you're not likely to ever see a max amperage higher than 50amps, but that is something you will need to watch. If you look at the NOCT ratings of your panels, those 340s will only be putting out 250 watts when they're at 45 degrees C. Personally, I wouldn't trust that cheap Chinese controller, even though the 60amp model might work for you. Stick with a name brand. I have a Midnight 200, and I'm satisfied with its performance. It has a settable limit on how many amps it can charge the battery.

In regards to the hydrometer, though temperature correcting is best, have a non-correcting one is better than none at all. The proper temperature to make readings is 25C, so if you are watching the temperature when you make your readings, you'll be close. If your batteries are as damaged as I think they are, even temperature correction isn't likely to make much difference.

[shgoren]

about the hydrometer, thank you! i think ill skip ordering from ebay due to the urgency of my problems and just buy one locally and ill post my findings here so maybe you can help in deciding what do with my battery bank.
now the first thing im doing now is adding more panels so my batteries will finally have some decent rest and charge
on this topic, how can i know how bad my batteries are? they might not be as bad as you think cause during the summer they did reach maximum every day and didnt discharge as often as in the past month and half of winter.
if they are, is there anything i can do to undo or minimize the potential damage they suffered?
the thing is that buying a totally new set of batteries is super expensive and i dont think i cant afford it now.

what problems might be with the chinese controller that arent in the reviews? i mean by that, that im interested in what are the risks im taking in going for this one because unfortunatly money is and issue and the difference in price is more than double.

how is it possible to avoid linking my batteries in parallel? my system is built on 24V so i guess i wouldnt find 24v batteries

can you tell me a bit more (or add a link) about whats is the combiner box? right now i have two panels in parallel and i dont have anything in between them and the controller.

another new question i had in mind is:
now i never see as much as 12-13a of current coming from the solar panel and my controller is 30A, can i attach 4 to it just now for winter until i get my new controller or is too risky?

thanks again
you are amazing and your help is priceless for me

[MichaelK!]

Acid density is the gold standard for evaluating battery health. Max voltage after charging is a far behind second choice. The density of a fully charged battery should be greater than 1.275 at 25^oC. The voltage should be ~ 25.5. You can only accurately measure the voltage after the battery has rested with no load for several hours after sunset. Switch off all loads, fully charge, then measure the voltage at about 9-10pm. Use this chart to determine how well the batteries charged. For my own bank I routinely see 1.280.



This is an example of a combiner box. I myself am using Midnight's MNPV6

http://www.midnightsolar.com/

Each of the negative leads from each solar array are attached at the negative busbar on the left. Each of the positive leads from each solar array are connected at the bottom of each of the DC breakers you see. The box on the left has 6 breakers for 6 different arrays. The box on the right has 4. One heavy negative wire off the negative busbar, and one positive wire off the top of the breaker bar lead straight to the charge controller. When you are working with more than one string of panels you need to fuse/breaker them to mitigate the threat of short-circuits.

In your case, you would have three arrays with two panels wired in series per array, wiring into breakers 1, 2, and 3. The "combined amperage" at 75VDC gets directed straight to the charge controller, unless you have a power center that incorporates a main array breaker. A power center is the electrical box that contains all the AC/DC wiring and breakers that all the AC/ battery terminal/ charge controller wires lead in and out of. I have this one. You need something in between the panels and the controller/battery, if only a fuse. The electricity could spark a fire if short-circuited. The white things in the upper left are the AC breakers. The big black things in the top center are the battery -+ terminals. The little red/black busbars in the lower right are the DC terminals from the charge controller. You punch out the round/rectangular knockouts to run wires in or connect breakers.


https://www.solarpanelstore.com/sola...XWPSINGLE.html
That Chinese controller may be OK because it's from Taiwan. I would trust them to make a higher quality product than the mainland Chinese. The mainlanders have a history for making fake MPPT controllers that are basicly a PWM controller with a MPPT label painted on it. You only find this out after your money has disappeared overseas.

You avoid paralleling batteries by selecting the right size battery in first place. You will not find a 24V battery. The way you create a 24V battery bank is to wire several 4, 6, or 8V batteries in series. You were on the right track wiring three 8V batteries in series, it's just that you selected the wrong size for your application. It's sort of like selecting a Honda Civic engine to drop into the cab of a 18 wheel lorry. Good engine, but wrong size for the purpose. You really need larger batteries, and mixing new small batteries with degraded small batteries is a really bad idea. I'm sorry, but you just have to suck it up and realize you made a mistake and now have to pay for it.

In regards to the amperage you are already producing, that mirrors what the NOCT (look at your PDF file#2) values of you panels actually are. In desert heat, your 310W panels are most likely producing only 230-240W, about 6-7 amps at ~35VDC. If they are really hot, the voltage goes even lower. That may be one explanation as to why they never get fully charged, because the voltage is not high enough to perform an equilization charge. Wiring the panels in series for 75V will correct this (if your controller really is MPPT). I can't say what will happen to your controller. A good controller, like my Midnight, has a max amperage set point, so I can tell the controller at what amperage to turn off if it gets too high. You'll have to carefully read your manual to find out if there's a high amperage cut-off, or if the controller just gets fried. You can mitigate the max amperage by directing each array away from due south. Point one array SE, and the other SW. That way the max noon amperage will be somewhat lower.

[littleharbor]

While on the lower end of the spectrum of MPPT charge controllers the controller shgoren has is a true MPPT controller with a 100 Voc. max input. The one he is contemplating seems to be a bit more sophisticated besides being double the amperage rating.

[sensij]

The EPEver charge controller is fine. It can be safely overpaneled within the voltage and current ratings, and will limit its output to its rating (30 A, in this case). The output limit is not user settable like it is in higher end models.

Putting two 72 cell panels in series on a 100 V input limit could trip the over voltage protection if the system is installed someplace that experiences a cold winter. Even in hot weather, parallel panels should have no trouble delivering the voltage for equalize.

The costs of adding panels in parallel include heavier wire to handle to combined amperage. A combiner box is not needed as long as current is within the rating of MC4 branch connectors. In line fuses are an inexpensive way to get the protection you need when going to more than two panels in parallel.

To some extent, increasing the PV size takes some load off the battery, so you can get away with a smaller battery for the application than conventional design rules suggest. It would be a good idea to have a secondary source of charging (generator, or isolator on the alternator) to deal with cloudy periods in that approach.

Before spending any more money on *anything*, get a hydrometer and learn how to use it.