Charge voltage needed for 24 V system

[GeorgeF]

Thanks for the reply.
If the open circuit voltage is max 92v but the charge is limited to 40A @ 24v one can wire the panel to 48v max 20amp or not?

[sdold]

Thanks for the reply.
If the open circuit voltage is max 92v but the charge is limited to 40A @ 24v one can wire the panel to 48v max 20amp or not?

What's the Voc on your panels? That MPPT charger can handle over-wattage but not over-voltage. Are you in a cold climate?

[Helplease1]

Hello, I am hoping to find some help! I am building my first system and have been researching like crazy and just can't find the answers I am looking for. I have 8 195w 12v mono panels and 4 12v 100ah lead acid batteries along with a 24v 3500w pure sine inverter. I'm looking into the Victron SmartSolar mppt charge controller and am so confused as to which controller will suit me best. I will eventually add 2 to 4 more panels and switch over to Battle Born lithium batteries for my 24v system. Can anyone shed some light on which controller would suit me best? My panels are 195w 21.6 open circuit voltage short circuit current 10.83a working current 9.02a output tolerance +3% temperature range -40c to +80c. Also how should I wire my panels to get the most efficiency? I would like to put my panels 220' away if possible?

[chrisski]

You can expect a max of about 44 amps to charge the batteries for 24 volt batteries. Each of those panels, at max production, will send 5.5 charging amps at 24 volts, and with 8 of those panels they need to be set up at least 2 in series and 4 of these sets in parallel (2S4P).

So now, looks as if the Victron 100/50 will handle this.

There's a bit more work to be done. For example can your batteries handle this possible 44 amps? If these were my Trojan FLA batteries, they take 13% or 26 amps max, so all 8 panels would overcharge the battery. The Victron can limit production to something less than its max, so by setting it to 26, you'd be safe there.

How likely are you to see this max production? On panels that tilt, and I move into the sun, I get really close, but on my flat roof panels, perhaps I've seen 2/3 max output, but as winter turns into summer, I expect higher production from the flat panels.

For wiring the panels 2S4P will work with the 100/50, but the only other way to set the panels up at 4S2P, at first is less than the 100 volt rating, but you need to plan for the record low temperature in the month you operate off. Renogy lists a tempertaure cooefficient for panels and they push more volts as it gets cold, so at the starting the four panels in series pushes 86.4, but as it gets colder more math needs to be done to see how much it goes up.

You mention upgrading. I'm not sure you will need to add more panels when you swap to Battleborn Batteries. You will probably have enough panels, but if you do put more panels for battleborns, if you want to take advantage of the extra output, than you may need another charger controller. I have three Victron Charge controllers working together to charge my three different arrays I use. Once you have the first set installed, you will see.

Probably the most important thing is to take a look at your power requirements and do an audit so you can see if 400 ah of battery is enough for your needs. 200 AH usable with FLA. If you use that big inverter, you will burn through that very quickly. Wiring from the inverter to the battery becomes a lot on those large draws.

[Helplease1]

chrisski!! Thanks for responding so quickly! I wish I could join in on the intelligent conversation with you. I have to tell you that I'm a complete novice! I'm in the process of building a cabin and was decided on solar. I ordered a 1570w kit from eco-worthy thinking that it would be turn key lol. Now I realize that was a mistake! I was going to build a system but with everything I have going on I thought I'll just get a kit and save myself some research. Now I'm in 3k with eco-worthy and am also a proud owner of a $2500 solar refrigerator from ecosolarcool that you have to have a separate charge controller to run properly and validate the warranty. I'm not turning back now!! After pondering on your response it seems that I will have to increase my battery bank to do what I am trying to do? From what I understand I really don't want lead acid. I'm not sure if I can do 16 Battleborn right now. I recently seen a video on building lithium batteries. Maybe I should go that route if I need 1600ah I think. So basically I have the 8 panels that are good out of the kit. From there I will have to get a real charge controller, and some good batteries I suppose. I will take any advice and or suggestions!

[chrisski]

If you take some time, look at the stickies, you’ll learn quite a bit on how to build a system. Then, start a post about your own design and ask for critiques. I’m about a year into this since I first started my design.

An energy audit is key to determining your needs.

I have a rather small system with 1350 watts of panels and 12 volts 440 ah batteries on my RV. I still use propane for cooking and heating, and don’t even think of using Air Conditioning. On a sunny day, I can be charged in 2 hours on moderate usage, and four hours on some heavier usage.

I opted for lead acid acid batteries for my first build with the intent to upgrade to lithium in about a year with a 24 VDC upgrade. With the times I’ve used my RV, I am happy with my energy production and charge times, I see no reason to drop the money for Lithium’s.

Assembling lithium cells into a battery is still foreign, but from what I’ve seen. If you decide to build your own battery pack, something slightly larger than my 12 volt 440 ah system people say cost them the same I paid for my Trojan FLA batteries, and about the same price as a single Battleborn.

[Picky17]

Hi, just wondering; I have 2 strings of 3 panels that are running at 125-136 volts but amps are running at 2.5-5.6 amps...Could I instead run them at 3 strings of 2 panels to get better amperage and fasten up the charging time?

[chrisski]

Hi, just wondering; I have 2 strings of 3 panels that are running at 125-136 volts but amps are running at 2.5-5.6 amps...Could I instead run them at 3 strings of 2 panels to get better amperage and fasten up the charging time?

My systems top out at 60 volts. If you're operating within specs of the SCC and panels, you would not see enough of a difference to justify rewiring it. The panels will produce the same watts and the SCC will convert those watts to the proper charging amps.

There could be a 10% better efficiency at a certain voltage level in your SCC, but before I rewired on that, I would need to see some data of efficiency levels in the SCC.

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One exception would be shading. Paralleling panels is better for shading, but the cost is thicker wires. After a certain point, like 30 amps, you can't use 10 gauge wire and MC4 connectors anymore so that becomes harder.

I have 3S2P on my roof. When I shade 2 cells on my one out of three of my 33 cell panels, String output is reduced by one third. That is only my hand shading a couple cells out of three. If I shade a hole panel, the output is reduced by 80%.

So, if where you have your panels has shade like a roof vent or AC that goes across a single panel through the day, then you could benefit by redoing the panels.

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Part of this for me also would be when my batteries are done charging. On a typical day, I can be done by 10 am for my RV, so not much motivation to rewire panels to be done at 9:50 instead. If I'm running out of daylight and the batteries are just charging, than I'd consider.

[Picky17]

my problem ist that if I don't turn the load off, the solar panels can't seem to charge enough to get the Battery to float. Also, the battery does not reach the boost charge volts, it remaches it is not maintained at it goes all day through the absorption cycle. If I turn off the loads, at 12 the Battery will go into float and keep there even when applying loads to it. I am still seeing what I can ron with the System. I have an Epever 200v/100amp SCC, 6 405w panels, a 6k Jupiter Inverter and 4 12v 228 ah deka batteries, everything running @ 24v

[sdold]

Hi, just wondering; I have 2 strings of 3 panels that are running at 125-136 volts but amps are running at 2.5-5.6 amps...Could I instead run them at 3 strings of 2 panels to get better amperage and fasten up the charging time?

I don't see any benefit other than the shade tolerance Chrisski mentioned, and you'd need to add a fuse to each panel with three parallel strings. Are there any obvious problems like shading, damage, etc? In good direct sun I would think you'd see 80-90 amps or more out of the charger. The amp numbers you gave are I assume between the panel and the charge controller, which should translate to 30-40A to the battery, which is about half of what it needs. If all else is good I'd look for a problem with one string.

[Picky17]

Fron controller to battery I've never seen that much amps. The problem I'm seeing is that if I don't turn off the inverter until 10am aproximatelly, batteries won't go from absorption to float.

[Picky17]

I can see the 28.9 volts that batteries need on the absorption cycle but If inverter is on, with any load it won't complete the absorption cycle