Why is this a bad idea?

[Majkhands]

I have 4-6volt deep cycle gold cart batteries(GC2-6v 105 min @ 75 amps) wired in series for 24vdc to match the input of my 3-270w 24v panels.
I have a GIANDEL 4kw 12v inverter. I see that picking up the postive and negative of each 2 pack of batteries is 12vdc. If I run leads from both 2 packs to the inverter will it short or evenly draw power off of each set?
I know the correct solution is to buy a 24vdc inverter but I don't have the cash at the moment and I want to use what I have temporarily.
I wonder about using a 24-12 converter off the EP Ever SCC it is 30amps, the converter is 40amps and the inverter is??? I am running a few small pond pumps, under 15 amps total. I want to avoid drawing the batteries down too far.
Thank you for all of your insights.

 

[time2roll]

Wire the batteries for 12 volts. Get a 12v MPPT controller. I assume the inverter does not have solar input connection.

 

[Majkhands]

I did not see a wire direct option in the manual. The panels are 24vdc so that would not work with a 12vdc inverter.
I had the battery bank wired as a 12 volt bank. It charged quickly and I assumed the excess Solar was being clipped. Now as a 24 volt battery system it does not reach full charge in the same time period.
I suppose back to 12vdc makes the most sense.

 

[Browneye]

I have 4-6volt deep cycle gold cart batteries(GC2-6v 105 min @ 75 amps) wired in series for 24vdc to match the input of my 3-270w 24v panels.
>snip

A solar charge controller takes care of voltages - panels don’t “match” battery voltage.

 

[Majkhands]

I was looking for maximum efficiency. The 12 volt system charged the batteries in short order. The 24v system has yet to charge the batteries.
I did discover the panels were covered in pollen and cleaned them. Still the 12v out preformed 24vas far as battery charge capacity.

 

[time2roll]

The EPEVER controller looks like it is compatible with 12v or 24v battery and up to 100 volt solar input.
Are the settings correct? Not sure why the effort to go 24v battery when everything is compatible with 12 volt.
Save your money.

 

[sunshine]

3-270w 24v panels

The confusion may be because of this. Can you post more data? There should be a sticker on the back. Just the Voc will do.
Also the Epever CC model number to ensure it can handle this Voc.

Like the others have said -wire as a 12v system.
The only problem I see is that the Voc may be in the range of 38-40v which is too close to the 48v of a Epever 30amp pwm for my liking.

 

[Majkhands]

270w panels
Rated Power: 270W
Open circuit voltage (VOC): 44.4 V
Max power voltage (VMP): 35.5 V
Short circuit current (ISC): 8.25 A
Max power current: 7.60 A
Power Tolerance 0/+3%
Maximum system voltage: 600V (UL)
Fuse Rating: 15 A
IP65 Junction Box w/MC4 Compatible Connectors
Frame: Anodized aluminum alloy
Weight: 61.7 lbs
Dimensions: 77 x 39.05 x 1.81 inch

EP Ever Tracer4215BN

 

[Browneye]

The BN is a mppt charge controller - specs below.

Yeah, those are 'grid-tie' type panels, not '24V'. You should be able to get by with panels in series, the BN is rated for up to 150V. Others will chime in about temperature adjustment for PV output. Would be rather over-panelled - but good for up to 40A battery charging at 12V. Still a little over for 24V but do-able.

Are these panels wired in series or parallel?
I would have to check the installation manual, but some EPEver controllers don't self-select for 24V - you have to hard-set them in the parameters. The spec does say 'auto selecting', but you do have to power it up on 24V first, then connect panels. It could well be powering up in 12V mode, which would not charge your 24V-wired battery pack.

Do you have the cable and software to program it? If so you can read the parameters and it will tell you. Also does some good charging data logging, and displays all of the current PV and battery readings, and control parameters.

Tracer 4215BN spec:

https://www.epever.com/upload/cert/file/1811/EPEVER-Datasheet-Tracer-BN.pdf

 

[rmaddy]

You should be able to get by with panels in series, the BN is rated for up to 150V.

Depending on the exact temperature coefficient for those panels, 3 in series will exceed 150V if the temperature gets below about -17ºC/2ºF. So if the OP may ever encounter such temperatures, 3 in series will be a problem.

 

[rmaddy]

Wire the batteries for 12 volts. Get a 12v MPPT controller.

This is by far the simpler solution. But it does require a 60A or 65A SCC to make full use of the 810W of solar on a 12V system.

 

[Browneye]

4000W inverter??

I'm still not understanding the 24V thing....why not 12V?

 

[rmaddy]

4000W inverter??

I didn't notice the 4kW inverter. That's nuts at 12V. Why would a company make such a thing? 4000W / 12V / 85% efficiency means it can pull up to 400A from the batteries. You need a 500A fuse. The wiring will be ridiculous to handle that. Can the batteries even handle having 400A of current pulled from them at once?

I'm still not understanding the 24V thing....why not 12V?

Because 4kW at 12V is nuts. 4kW at 24V is better but still a lot.

A 4kW inverter with 6V batteries is even crazier but I admit I know nothing about golf cart batteries.

 

[Browneye]

I didn't notice the 4kW inverter. That's nuts at 12V. Why would a company make such a thing? 4000W / 12V / 85% efficiency means it can pull up to 400A from the batteries. You need a 500A fuse. The wiring will be ridiculous to handle that. Can the batteries even handle having 400A of current pulled from them at once?


Because 4kW at 12V is nuts. 4kW at 24V is better but still a lot.

A 4kW inverter with 6V batteries is even crazier but I admit I know nothing about golf cart batteries.

Agreed. I was alluding to the OP decision to wire the bank 24V. Perhaps it was to support the giant inverter. [shrug]

Two GC2's wired in series is a large 200A +/- 12V battery. 2S 2P would be a 400A bank. These are very popular in larger motorhomes and trailers, house bank on a yacht. 6V FLA's only have 3 cells, so in wiring them in series, you have the 6 cells, same as a RV/marine type deep cycle battery. Only the plates are way thicker. They do quite well if you take care of them. But you do need to keep them watered and fully charged, and never discharge below 50%. Well, you can, but it greatly diminishes their already short life.

A good set of Crown, Trojan, or Rolls batteries will go up to ten years with light use, much less for heavy use. Another con is that heavy loads you see a lot of voltage sag, and their discharge voltage curve is a constant down-slope - not flat like lifepo4.

 

[Majkhands]

Thank you for all the information.
The panels are rated at 24vdc but open they measure 39-40 vdc. I thought 24 volt batteries setup would be the most efficient use of power. I was concerned wired 12vdv was clipping and wasting power.
It is back to 12vdc, cleaned panels, fixed something...now I am seeing 400 watts during peak hours. 1 panel does not appear to be adding to the system. I tested it at the connections and it measured 40volts. Maybe one leg of my Y connector is bad. Yes, wired in parallel. I need more amps not volts, 12 appears to be the right number.
I have a hard time imaging pulling 100s of amps at anyone time. My set up is fairly minimal. I am not running any large appliances, just a few pond pumps, lights and phone chargers.
The serious work is done on propane, soon to be green hydrogen.

 

[rmaddy]

The panels are rated at 24vdc but open they measure 39-40 vdc. I thought 24 volt batteries setup would be the most efficient use of power. I was concerned wired 12vdv was clipping and wasting power.

810W of panels on a 12V system is far too much for the Tracer4215BN solar charge controller. That controller can put out 40A of charge current. On 12V that is only 480W supported. The rest of your panel wattage can't be used. If you had a 24V setup then your charge controller can support 960W of solar.

Yes, wired in parallel. I need more amps not volts, 12 appears to be the right number.

Why do you need more amps? What do you mean exactly? With an MPPT charge controller the controller will take the input watts from the panels (regardless of their volts and amps) and converter that power into the appropriate charge voltage and corresponding amperage. Again, your solar charge controller is too small on a 12V system for the amount of solar panels that you have.

I have a hard time imaging pulling 100s of amps at anyone time. My set up is fairly minimal. I am not running any large appliances, just a few pond pumps, lights and phone chargers.

Then why do you have a 4000W inverter?

 

[Majkhands]

Hello rmaddy.
I have not figured out the cut and paste thing here. Please bear with me.

On 12V that is only 480W supported. The rest of your panel wattage can't be used. If you had a 24V setup then your charge controller can support 960W of solar.

Sort of my understanding. The reality to my batteries is 12v fills my battery bank in short order, an hour or two. As a 24v system it almost filled it one day. That is not the whole story for both scenarios, I have pond pumps to run for aeration for the fish. The system was initially setup as 12 volts because that was what my inverters were. When I saw the battery bank was filling faster than I was using it, I was concerned I was missing power produced. I switched to 24 volts and was sorely surprised, so back to 12 until I have a better understanding of the system.
I did note the SCC could handle more panel production at 24 vs 12.
Now I am considering shunting the excess power to a secondary SCC to a second smaller battery bank.
Sectioning the system is not conventional but it will allow for separated applications in separate areas. The second one will become the primary lighting for my home.
I originally had 20 -270w panels and purchased the components to Wills 2kw system and knew I would expand to 20kw just because the components are realitively cheap and available. Well life changes and the bulk of that system is in storage. I brought a small collection to power the other house. It is now completely off grid in the city.
I own an over sized inverter because the opportunity appeared. I thought it was 24vdc when I bought it, then realized I was wrong. Now that I am back to 12vdc I can run a little larger equipment like a vacuum, occasionally.
To say I am fascinated with solar and independent power production would be an understatement.
This is my education phase before dipping my toes into industrial solar. No, I won't be hands on with a real system, the stakes are too high for my skills.
For now and the rest of my days, I want to know more and understand all I can about these systems. Someday maybe I will have something to return to the community.
Thank you.

 

[rmaddy]

Something is wrong if you were able to charge your 12V battery setup but not your 24V battery setup. This assumes you were using the same 4 6V batteries in both cases (2S2P for 12V and 4S for 24V). It's the same total number of watt hours of battery capacity in either case. Charging either setup with a given amount of solar would result in the same charge duration. In fact, due to the 24V setup allowing the charge controller to make more use of your 810W of solar panels, your 24V setup should have charged much faster than the 12V setup did.

But that's all moot if you want to keep the 12V inverter and setup the batteries for 12V. You have two choices:

1 - Get a bigger charge controller that can make full use of your 810W at 12V. That requires a 65A controller.

2 - Keep the current controller but use it with just 2 of the 270W panels. Then get a second charge controller and use it with 1 or more panels as needed. No need to split up the battery bank. It's fine and normal to have more than one solar charge controller hooked up to a single system, each with its own solar panels.

 

[Browneye]

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